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Unit Operation Models

S T E A D Y S T A T E S I M U L A T I O N

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Unit Operation Models iiiVersion 10

ContentsAbout the Unit Operation Models Reference Manual

For More Information..............................................................................................................xTechnical Support ..................................................................................................................xi

1 Mixers and Splitters

Mixer .....................................................................................................................................1-2Flowsheet Connectivity for Mixer....................................................................................1-2Specifying Mixer...............................................................................................................1-3

FSplit.....................................................................................................................................1-5Flowsheet Connectivity for FSplit...................................................................................1-5Specifying FSplit ...............................................................................................................1-6

SSplit.....................................................................................................................................1-8Flowsheet Connectivity for SSplit ....................................................................................1-8Specifying SSplit ...............................................................................................................1-8

2 Separators

Flash2....................................................................................................................................2-2Flowsheet Connectivity for Flash2..................................................................................2-2Specifying Flash2 .............................................................................................................2-3

Flash3....................................................................................................................................2-5Flowsheet Connectivity for Flash3..................................................................................2-5Specifying Flash3 .............................................................................................................2-6

Decanter................................................................................................................................2-8Flowsheet Connectivity for Decanter..............................................................................2-8Specifying Decanter .........................................................................................................2-9

Sep.......................................................................................................................................2-12Flowsheet Connectivity for Sep ......................................................................................2-12Specifying Sep .................................................................................................................2-13

Sep2.....................................................................................................................................2-14Flowsheet Connectivity for Sep2 ....................................................................................2-14Specifying Sep2...............................................................................................................2-15

3 Heat Exchangers

Heater ...................................................................................................................................3-2Flowsheet Connectivity for Heater..................................................................................3-2Specifying Heater .............................................................................................................3-3

HeatX ....................................................................................................................................3-5Flowsheet Connectivity for HeatX...................................................................................3-5Specifying HeatX..............................................................................................................3-6

References...........................................................................................................................3-18

iv Unit Operation ModelsVersion 10

MHeatX.............................................................................................................................. 3-19Flowsheet Connectivity for MHeatX ............................................................................ 3-19Specifying MHeatX........................................................................................................ 3-20

Hetran ................................................................................................................................ 3-23Flowsheet Connectivity for Hetran .............................................................................. 3-23Specifying Hetran.......................................................................................................... 3-24

Aerotran ............................................................................................................................. 3-26Flowsheet Connectivity for Aerotran ........................................................................... 3-26Specifying Aerotran....................................................................................................... 3-27

4 Columns

DSTWU ................................................................................................................................ 4-3Flowsheet Connectivity for DSTWU................................................................................ 4-3Specifying DSTWU........................................................................................................... 4-4

Distl ...................................................................................................................................... 4-6Flowsheet Connectivity for Distl...................................................................................... 4-6Specifying Distl ................................................................................................................ 4-7

SCFrac.................................................................................................................................. 4-8Flowsheet Connectivity for SCFrac ................................................................................. 4-8Specifying SCFrac ............................................................................................................ 4-9

RadFrac.............................................................................................................................. 4-11Flowsheet Connectivity for RadFrac ............................................................................ 4-12Specifying RadFrac........................................................................................................ 4-13Free-Water and Rigorous Three-Phase Calculations .................................................. 4-20Efficiencies ..................................................................................................................... 4-20Algorithms...................................................................................................................... 4-22Rating Mode................................................................................................................... 4-23Design Mode................................................................................................................... 4-24Reactive Distillation...................................................................................................... 4-25Solution Strategies ........................................................................................................ 4-25Physical Properties........................................................................................................ 4-28Solids Handling ............................................................................................................. 4-28

MultiFrac ........................................................................................................................... 4-30Flowsheet Connectivity for MultiFrac .......................................................................... 4-31Specifying MultiFrac ..................................................................................................... 4-33Efficiencies ..................................................................................................................... 4-41Algorithms...................................................................................................................... 4-42Rating Mode................................................................................................................... 4-42Design Mode................................................................................................................... 4-42Column Convergence..................................................................................................... 4-43Physical Properties........................................................................................................ 4-46Free Water Handling..................................................................................................... 4-46Solids Handling ............................................................................................................. 4-46Sizing and Rating of Trays and Packings .................................................................... 4-47

PetroFrac............................................................................................................................ 4-48Flowsheet Connectivity for PetroFrac.......................................................................... 4-49Specifying PetroFrac...................................................................................................... 4-51Efficiencies ..................................................................................................................... 4-57

Unit Operation Models vVersion 10

Convergence....................................................................................................................4-58Rating Mode....................................................................................................................4-59Design Mode ...................................................................................................................4-59Physical Properties.........................................................................................................4-60Free Water Handling .....................................................................................................4-60Solids Handling ..............................................................................................................4-61Sizing and Rating of Trays and Packings .....................................................................4-61

RateFrac..............................................................................................................................4-62Flowsheet Connectivity for RateFrac............................................................................4-63The Rate-Based Modeling Concept................................................................................4-65Specifying RateFrac .......................................................................................................4-66Mass and Heat Transfer Correlations...........................................................................4-77

References...........................................................................................................................4-85Extract ................................................................................................................................4-87

Flowsheet Connectivity for Extract...............................................................................4-87Specifying Extract ..........................................................................................................4-88

5 Reactors

RStoic ....................................................................................................................................5-2Flowsheet Connectivity for RStoic ..................................................................................5-2Specifying RStoic..............................................................................................................5-3

RYield....................................................................................................................................5-6Flowsheet Connectivity for RYield..................................................................................5-6Specifying RYield .............................................................................................................5-7

REquil ...................................................................................................................................5-8Flowsheet Connectivity for REquil..................................................................................5-8Specifying REquil .............................................................................................................5-9

RGibbs.................................................................................................................................5-10Flowsheet Connectivity for RGibbs...............................................................................5-10Specifying RGibbs ..........................................................................................................5-11

References...........................................................................................................................5-15RCSTR ................................................................................................................................5-16

Flowsheet Connectivity for RCSTR...............................................................................5-16Specifying RCSTR ..........................................................................................................5-17

RPlug...................................................................................................................................5-21Flowsheet Connectivity for RPlug.................................................................................5-21Specifying RPlug ............................................................................................................5-22

RBatch ................................................................................................................................5-25Flowsheet Connectivity for RBatch...............................................................................5-25Specifying RBatch ..........................................................................................................5-26

6 Pressure Changers

Pump .....................................................................................................................................6-2Flowsheet Connectivity for Pump ...................................................................................6-2Specifying Pump ...............................................................................................................6-3

Compr....................................................................................................................................6-9Flowsheet Connectivity for Compr..................................................................................6-9Specifying Compr ............................................................................................................6-10

vi Unit Operation ModelsVersion 10

MCompr.............................................................................................................................. 6-13Flowsheet Connectivity for MCompr ............................................................................. 6-13Specifying MCompr........................................................................................................ 6-15

References .......................................................................................................................... 6-19Valve................................................................................................................................... 6-20

Flowsheet Connectivity for Valve................................................................................. 6-20Specifying Valve ............................................................................................................ 6-20

References .......................................................................................................................... 6-29Pipe..................................................................................................................................... 6-30

Flowsheet Connectivity for Pipe ................................................................................... 6-30Specifying Pipe .............................................................................................................. 6-31Two-Phase Correlations ................................................................................................ 6-35Closed-Form Methods.................................................................................................... 6-39

References .......................................................................................................................... 6-40Pipeline .............................................................................................................................. 6-42

Flowsheet Connectivity for Pipeline............................................................................. 6-42Specifying Pipeline ......................................................................................................... 6-43Two-Phase Correlations ................................................................................................ 6-47Closed-Form Methods.................................................................................................... 6-50

References .......................................................................................................................... 6-52

7 Manipulators

Mult ...................................................................................................................................... 7-2Flowsheet Connectivity for Mult...................................................................................... 7-2Specifying Mult................................................................................................................ 7-3

Dupl ...................................................................................................................................... 7-4Flowsheet Connectivity for Dupl...................................................................................... 7-4Specifying Dupl................................................................................................................ 7-5

ClChng ................................................................................................................................. 7-6Flowsheet Connectivity for ClChng................................................................................ 7-6Specifying ClChng............................................................................................................ 7-6

8 Solids

Crystallizer .......................................................................................................................... 8-3Flowsheet Connectivity for Crystallizer .......................................................................... 8-3Specifying Crystallizer ..................................................................................................... 8-4

References .......................................................................................................................... 8-11Crusher............................................................................................................................... 8-13

Flowsheet Connectivity for Crusher............................................................................. 8-13Specifying Crusher ........................................................................................................ 8-14

References .......................................................................................................................... 8-18Screen ................................................................................................................................. 8-19

Flowsheet Connectivity for Screen ............................................................................... 8-19Specifying Screen........................................................................................................... 8-19

References .......................................................................................................................... 8-22FabFl .................................................................................................................................. 8-23

Flowsheet Connectivity for FabFl................................................................................. 8-23Specifying FabFl............................................................................................................. 8-23

Unit Operation Models viiVersion 10

References...........................................................................................................................8-26Cyclone ................................................................................................................................8-27

Flowsheet Connectivity for Cyclone................................................................................8-27Specifying Cyclone ..........................................................................................................8-28

References...........................................................................................................................8-35VScrub.................................................................................................................................8-36

Flowsheet Connectivity for VScrub ................................................................................8-36Specifying VScrub ...........................................................................................................8-37

References...........................................................................................................................8-39ESP......................................................................................................................................8-40

Flowsheet Connectivity for ESP .....................................................................................8-40Specifying ESP................................................................................................................8-41

References...........................................................................................................................8-44HyCyc ..................................................................................................................................8-45

Flowsheet Connectivity for HyCyc..................................................................................8-45Specifying HyCyc ............................................................................................................8-46

References...........................................................................................................................8-51CFuge..................................................................................................................................8-52

Flowsheet Connectivity for CFuge ................................................................................8-52Specifying CFuge............................................................................................................8-53

References...........................................................................................................................8-55Filter ...................................................................................................................................8-56

Flowsheet Configuration for Filter................................................................................8-56Specifying Filter .............................................................................................................8-56

References...........................................................................................................................8-59SWash .................................................................................................................................8-61

Flowsheet Connectivity for SWash................................................................................8-61Specifying SWash ...........................................................................................................8-62

CCD.....................................................................................................................................8-64Flowsheet Connectivity for CCD ...................................................................................8-64Specifying CCD...............................................................................................................8-65

9 User Models

User.......................................................................................................................................9-2Flowsheet Connectivity for User .....................................................................................9-2Specifying User.................................................................................................................9-3

User2.....................................................................................................................................9-4Flowsheet Connectivity for User2 ...................................................................................9-4Specifying User2...............................................................................................................9-5

10 Pressure Relief

Pres-Relief...........................................................................................................................10-2Specifying Pres-Relief ....................................................................................................10-2Scenarios.........................................................................................................................10-3Compliance with Codes..................................................................................................10-6Stream and Vessel Compositions and Conditions........................................................10-6Rules to Size the Relief Valve Piping............................................................................10-7Reactions.........................................................................................................................10-9

viii Unit Operation ModelsVersion 10

Relief System ............................................................................................................... 10-10Data Tables for Pipes and Relief Devices................................................................... 10-12Valve Cycling ............................................................................................................... 10-16Vessel Types................................................................................................................. 10-16Disengagement Models ............................................................................................... 10-18Stop Criteria ................................................................................................................ 10-18Solution Procedure for Dynamic Scenarios................................................................ 10-19Flow Equations ............................................................................................................ 10-20Calculation and Convergence Methods ...................................................................... 10-23Vessel Insulation Credit Factor.................................................................................. 10-24

References ........................................................................................................................ 10-25

A Sizing and Rating for Trays and Packings

Single-Pass and Multi-Pass Trays..................................................................................A-2Modes of Operation for Trays .........................................................................................A-8Flooding Calculations for Trays......................................................................................A-8Bubble Cap Tray Layout .................................................................................................A-9Pressure Drop Calculations for Trays ..........................................................................A-10Foaming Calculations for Trays ...................................................................................A-11Packed Columns ............................................................................................................A-12Packing Types and Packing Factors.............................................................................A-12Modes of Operation for Packing....................................................................................A-12Maximum Capacity Calculations for Packing .............................................................A-13Pressure Drop Calculations for Packing ......................................................................A-15Liquid Holdup Calculations for Packing ......................................................................A-16Pressure Profile Update ................................................................................................A-17Physical Property Data Requirements.........................................................................A-17

References ..........................................................................................................................A-18

Index

Unit Operation Models ixVersion 10

About the Unit OperationModels Reference Manual

Volume 1 of the ASPEN PLUS Reference Manuals, Unit Operation Models,includes detailed technical reference information for all ASPEN PLUS unitoperation models and the Pres-Relief model. The information in this manual isalso available in online help and prompts.

Models are grouped in chapters according to unit operation type. The referenceinformation for each model includes a description of the model and its typicalusage, a diagram of its flowsheet connectivity, a discussion of the specificationsyou must provide for the model, important equations and correlations, and otherrelevant information.

An overview of all ASPEN PLUS unit operation models, and general informationabout the steps and procedures in using them is in the ASPEN PLUS User Guideas well as in the online help and prompts in ASPEN PLUS.

x Unit Operation ModelsVersion 10

For More Information

Online Help ASPEN PLUS has a complete system of online help andcontext-sensitive prompts. The help system contains both context-sensitive helpand reference information. For more information about using ASPEN PLUS help,see the ASPEN PLUS User Guide, Chapter 3.

ASPEN PLUS Getting Started Building and Running a Process Model This tutorial includes several hands-on sessions to familiarize you withASPEN PLUS. The guide takes you step-by-step to learn the full power and scopeof ASPEN PLUS.

ASPEN PLUS User Guide The three-volume ASPEN PLUS User Guideprovides step-by-step procedures for developing and using an ASPEN PLUSprocess simulation model. The guide is task-oriented to help you accomplish theengineering work you need to do, using the powerful capabilities ofASPEN PLUS.

ASPEN PLUS reference manual series ASPEN PLUS reference manualsprovide detailed technical reference information. These manuals includebackground information about the unit operation models and the physicalproperties methods and models available in ASPEN PLUS, tables ofASPEN PLUS databank parameters, group contribution method functionalgroups, and a wide range of other reference information. The set comprises:• Unit Operation Models• Physical Property Methods and Models• Physical Property Data• User Models• System Management• Summary File Toolkit

ASPEN PLUS application examples A suite of sample online ASPEN PLUSsimulations illustrating specific processes is delivered with ASPEN PLUS.

ASPEN PLUS Installation Guides These guides provide instructions onplatform and network installation of ASPEN PLUS. The set comprises:• ASPEN PLUS Installation Guide for Windows• ASPEN PLUS Installation Guide for OpenVMS• ASPEN PLUS Installation Guide for UNIX

The ASPEN PLUS manuals are delivered in Adobe portable document format(PDF) on the ASPEN PLUS Documentation CD. You can also order printedmanuals from AspenTech.

Unit Operation Models xiVersion 10

Technical SupportWorld Wide Web For additional information about AspenTech products andservices, check the AspenTech World Wide Web home page on the Internet at:

http://www.aspentech.com/

Technical resources To obtain in-depth technical support information on theInternet, visit the Technical Support homepage. Register at:

http://www.aspentech.com/ts/

Approximately three days after registering, you will receive a confirmation e-mailand you will then be able to access this information.

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AspenTech Hotline If you need help from an AspenTech Customer Supportengineer, contact our Hotline for any of the following locations:

If you are located in: Phone Number Fax Number E-Mail Address

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xii Unit Operation ModelsVersion 10

Unit Operation Models 1-1Version 10

Chapter 1

1 Mixers and Splitters

This chapter describes the unit operation models for mixing and splittingstreams. The models are:

Model Description Purpose Use For

Mixer Stream mixer Combines multiple streamsinto one stream

Mixing tees. Stream mixing operations.Adding heat streams. Adding work streams

FSplit Stream splitter Divides feed based on splitsspecified for outlet streams

Stream splitters. Bleed valves

SSplit Substream splitter Divides feed based on splitsspecified for eachsubstream

Stream splitters. Perfect fluid-solidseparators

1-2 Unit Operation ModelsVersion 10

Mixers andSplitters

MixerStream Mixer

Use Mixer to combine streams into one stream. Mixer models mixing tees or othertypes of mixing operations.

Mixer combines material streams (or heat streams or work streams) into onestream. Select the Heat (Q) and Work (W) Mixer icons from the Model Library forheat and work streams respectively. A single Mixer block cannot mix streams ofdifferent types (material, heat, work).

Flowsheet Connectivity for Mixer

Material

Water (optional)

Material(2 or more)

Flowsheet for Mixing Material Streams

Material StreamsInlet At least two material streams

Outlet One material streamOne water decant stream (optional)


Chapter 1

HeatHeat

(2 or more)

Flowsheet for Adding Heat Streams

Heat StreamsInlet At least two heat streams

Outlet One heat stream

WorkWork

(2 or more)

Flowsheet for Adding Work Streams

Work StreamsInlet At least two work streams

Outlet One work stream

Specifying MixerUse the Mixer Input Flash Options sheet to specify operating conditions.

When mixing heat or work streams, Mixer does not require any specifications.


Mixers andSplitters

When mixing material streams, you can specify either the outlet pressure orpressure drop. If you specify pressure drop, Mixer determines the minimum ofthe inlet stream pressures, and applies the pressure drop to the minimum inletstream pressure to compute the outlet pressure. If you do not specify the outletpressure or pressure drop, Mixer uses the minimum pressure from the inletstreams for the outlet pressure.

You can select the following valid phases:

Valid Phase Solids? Number of phases? Free Water? Phase?

Vapor-Only Yes or no 1 No V

Liquid-Only Yes or no 1 No L

Vapor-Liquid Yes or no 2 No

Vapor-Liquid-Liquid Yes or no 3 No

Liquid Free-Water † Yes or no 1 Yes

Vapor-Liquid Free-Water † Yes or no 2 Yes

Solid-Only Yes 1 No S

†Check Use Free Water Calculations checkbox on the Setup Specifications Global sheet.

An optional water decant stream can be used when free-water calculations areperformed.

Mixer performs an adiabatic calculation on the product to determine the outlettemperature, unless Mass Balance Only Calculations is specified on the MixerBlockOptions SimulationOptions sheet or the Setup SimulationOptionsCalculations sheet.

Use the following forms to enter specifications and view results for Mixer:

Use this form To do this

Input Enter operating conditions and flash convergence parameters

BlockOptions Override global values for physical properties, simulation options, diagnostic message levels,and report options for this block

Results View Mixer simulation results

Dynamic Specify parameters for dynamic simulations


Chapter 1

FSplitStream Splitter

FSplit combines streams of the same type (material, heat, or work streams) anddivides the resulting stream into two or more streams of the same type. All outletstreams have the same composition and conditions as the mixed inlet. Select theHeat (Q) and Work (W) FSplit icons from the Model Library for heat and workstreams respectively. Use FSplit to model flow splitters, such as bleed valves.

FSplit cannot split a stream into different types. For example, FSplit cannot splita material stream into a heat stream and a material stream.

To model a splitter where the amount of each substream sent to each outlet candiffer, use an SSplit block. To model a splitter where the composition andproperties of the output streams can differ, use a Sep block or a Sep2 block.

Flowsheet Connectivity for FSplit

Material(2 or more)Material

(any number)

Flowsheet for Splitting Material Streams

Material StreamsInlet At least one material stream

Outlet At least two material streams


Mixers andSplitters

Heat(2 or more)Heat

(any number)

Flowsheet for Splitting Heat Streams

Heat StreamsInlet At least one heat stream

Outlet At least two heat streams

Work(2 or more)Work

(any number)

Flowsheet for Splitting Work Streams

Work StreamsInlet At least one work stream

Outlet At least two work streams

Specifying FSplitTo split material streams Give one of the following specifications for eachoutlet stream except one:• Fraction of the combined inlet flow• Mole flow rate• Mass flow rate• Standard liquid volume flow rate• Actual volume flow rate• Fraction of the residue remaining after all other specifications are satisfied

FSplit puts any remaining flow in the unspecified outlet stream to satisfy materialbalance. You can specify mole, mass, or standard liquid volume flow rate for one ofthe following:• The entire stream• A subset of key components in the stream


Chapter 1

To specify the flow rate of a component or group of components in an outlet stream,specify a group of key components and the total flow rate for the group (the sum ofthe component flow rates) on the Input Specifications sheet, and define the keycomponents in the group on the Input KeyComponents sheet.

Outlet streams have the same composition as the mixed inlet stream. For thisreason, when you specify the flow rate of a key component, the total flow rate ofthe outlet stream is greater than the flow rate you specify.

When FSplit has more than one inlet, you can do one of the following:• Enter the outlet pressure on the FSplit Input FlashOptions sheet• Let the outlet pressure default to the minimum pressure of the inlet streams

To split heat streams or work streams Specify the fraction of the combinedinlet heat or work for each outlet stream except one. FSplit puts any remainingheat or work in the unspecified outlet stream to satisfy energy balance.

Use the following forms to enter specifications and view results for FSplit:


Input Enter split specifications, flash conditions and calculation options, and keycomponents associated with split specifications

BlockOptions Override global values for physical properties, simulation options,diagnostic message levels, and report options for this block

Results View split fractions for outlet streams, and material and energy balanceresults


Mixers andSplitters

SSplitSubstream Splitter

SSplit combines material streams and divides the resulting stream into two ormore streams. Use SSplit to model a splitter where the split of each substreamamong the outlet streams can differ.

Substreams in the outlet streams have the same composition, temperature, andpressure as the corresponding substreams in the mixed inlet stream. Only thesubstream flow rates differ. To model a splitter in which the composition andproperties of the substreams in the output streams can differ, use a Sep block ora Sep2 block.

Flowsheet Connectivity for SSplit

Material(2 or more)Material

(any number)



Specifying SSplitFor each substream, specify one of the following for all but one outlet stream:• Fraction of the inlet substream• Mole flow rate• Mass flow rate• Standard liquid volume flow rate

SSplit puts any remaining flow for each substream in the unspecified stream.You cannot specify standard liquid volume flow rate when the substream is oftype CISOLID, and mole and standard liquid volume flow rates when thesubstream is of type NC.


Chapter 1

You can specify mole or mass flow rate for one of the following:• The entire substream• A subset of components in the substream

You can specify the flow rate of a component in a substream of an outlet stream. Todo this, define a key component and specify the flow rate for the key component.Similarly, you can specify the flow rate for a group of components in a substream ofan outlet stream. To do this, define a key group of components and specify the totalflow rate for the group (the sum of the component flow rates).

Substreams in outlet streams have the same composition as the correspondingsubstream in the mixed inlet stream. For this reason, when you specify the flowrate of a key, the total flow rate of the substream in the outlet stream is greaterthan the flow rate you specify.

When SSplit has more than one inlet, you can do one of the following:• Enter the outlet pressure on the Input FlashOptions sheet.• Let the outlet pressure default to the minimum pressure of the inlet streams.

The composition, temperature, pressure, and other substream variables for alloutlet streams have the same values as the mixed inlet. Only the substream flowrates differ.

Use the following forms to enter specifications and view results for SSplit:


Input Enter split specifications, flash conditions, calculation options, and key componentsassociated with split specifications

BlockOptions Override global values for physical properties, simulation options, diagnostic messagelevels, and report options for this block

Results View split fractions of each substream in each outlet stream, and material and energybalance results

❖ ❖ ❖ ❖


Mixers andSplitters


Chapter 2

2 Separators

This chapter describes the unit operation models for component separators, flashdrums, and liquid-liquid separators. The models are:


Flash2 Two-outlet flash Separates feed into two outletstreams, using rigorous vapor-liquid or vapor-liquid-liquidequilibrium

Flash drums, evaporators, knock-outdrums, single stage separators

Flash3 Three-outlet flash Separates feed into threeoutlet streams, using rigorousvapor-liquid-liquid equilibrium

Decanters, single-stage separators withtwo liquid phases

Decanter Liquid-liquid decanter Separates feed into two liquidoutlet streams

Decanters, single-stage separators withtwo liquid phases and no vapor phase

Sep Component separator Separates inlet streamcomponents into multiple outletstreams, based on specifiedflows or split frractions

Component separation operations, suchas distillation and absorption, when thedetails of the separation are unknown orunimportant

Sep2 Two-outlet componentseparator

Separates inlet streamcomponents into two outletstreams, based on specifiedflows, split fractions, or purities

Component separation operations, suchas distillation and absorption, when thedetails of the separation are unknown orunimportant

You can generate heating or cooling curve tables for Flash2, Flash3, andDecanter models.


Separators

Flash2Two-Outlet Flash

Use Flash2 to model flashes, evaporators, knock-out drums, and other single-stage separators. Flash2 performs vapor-liquid or vapor-liquid-liquid equilibriumcalculations. When you specify the outlet conditions, Flash2 determines thethermal and phase conditions of a mixture of one or more inlet streams.

Flowsheet Connectivity for Flash2

Vapor

Liquid

Water (optional)

Heat (optional)

Heat(optional)

Material(any number)


Outlet One material stream for the vapor phaseOne material stream for the liquid phase. (If three phases exist, the liquidoutlet contains both liquid phases.)One water decant stream (optional)

You can specify liquid and/or solid entrainment in the vapor stream.


Chapter 2

Heat StreamsInlet Any number of heat streams (optional)

Outlet One heat stream (optional)

If you give only one specification (temperature or pressure) on the InputSpecifications Sheet, Flash2 uses the sum of the inlet heat streams as a dutyspecification. Otherwise, Flash2 uses the inlet heat stream only to calculate thenet heat duty. The net heat duty is the sum of the inlet heat streams minus theactual (calculated) heat duty.

You can use an optional outlet heat stream for the net heat duty.

Specifying Flash2Use the Input Specifications sheet for all required specifications and validphases. For valid phases you can choose the following options:

You can choose the followingoptions Solids? Number of phases? Free Water?

Vapor-Liquid Yes or no 2 No

Vapor-Liquid-Liquid Yes or no 3 No

Vapor-Liquid-FreeWater Yes or no 2 Yes

Use the Input FlashOptions sheet to specify temperature and pressure estimatesand flash convergence parameters.

Use the Input Entrainment sheet to specify liquid and solid entrainment in thevapor phase.

Use the Hcurves form to specify optional heating or cooling curves.

Use the following forms to enter specifications and view results for Flash2:


Input Enter flash specifications, flash convergence parameters, and entrainment specifications

Hcurves Specify heating or cooling curve tables and view tabular results

Block Options Override global values for physical properties, simulation options, diagnostic messagelevels, and report options for this block

Results View Flash2 simulation results



Separators

Solids

All phases are in thermal equilibrium. Solids leave at the same temperature asthe fluid phases.

Flash2 can simulate fluid phases with solids when the stream contains solidsubstreams or when you request electrolytes chemistry calculations.

Solid Substreams Materials in solid substreams do not participate in phaseequilibrium calculations.

Electrolyte Chemistry Calculations You can request these on the PropertiesSpecifications Global sheet or the BlockOptions Properties sheet. Solid saltsparticipate in liquid-solid phase equilibrium and thermal equilibriumcalculations. The salts are in the MIXED substream.


Chapter 2

Flash3Three-Outlet Flash

Use Flash3 to model flashes, evaporators, knock-out drums, decanters, and othersingle-stage separators in which two liquid outlet streams are produced. Flash3performs vapor-liquid-liquid equilibrium calculations. When you specify outletconditions, Flash3 determines the thermal and phase conditions of a mixture ofone or more inlet streams.

Flowsheet Connectivity for Flash3

Vapor

2nd Liquid

1st Liquid

Heat (optional)

Heat(optional)



Outlet One material stream for the vapor phaseOne material stream for the first liquid phaseOne material stream for the second liquid phase

You can specify liquid entrainment of each liquid phase in the vapor stream. Youcan also specify entrainment for each solid substream in the vapor and firstliquid phase.


Separators



If you give only one specification on the Input Specifications Sheet (temperatureor pressure), Flash3 uses the sum of the inlet heat streams as a dutyspecification. Otherwise, Flash3 uses the inlet heat stream only to calculate thenet heat duty. The net heat duty is the sum of the inlet heat streams minus theactual (calculated) heat duty.


Specifying Flash3Use the Input Specifications sheet for all required specifications.

Use the Input Entrainment sheet to specify solid entrainment.

To specify optional heating or cooling curves, use the Hcurves form.

Use the following forms to enter specifications and view results for Flash3:


Input Enter flash specifications, key components, flash convergence parameters, andentrainment specifications


Block Options Override global values for physical properties, simulation options, diagnosticmessage levels, and report options for this block

Results View Flash3 simulation results


Solids


Flash3 can simulate fluid phases with solids when the stream contains solidsubstreams, or when you request electrolyte chemistry calculations.



Chapter 2

Electrolyte Chemistry Calculations You can request these on the PropertiesSpecifications Global sheet or on the Input BlockOptions Properties sheet. Solidsalts do participate in liquid-solid phase equilibrium and thermal equilibriumcalculations. You can only specify apparent component calculations (SelectSimulation Approach=Apparent Components on the BlockOptions Propertiessheet). The salts will not appear in the MIXED substream.


Separators

DecanterLiquid-Liquid Decanter

Decanter simulates decanters and other single stage separators without a vaporphase. Decanter can perform:• Liquid-liquid equilibrium calculations• Liquid-free-water calculations

Use Decanter to model knock-out drums, decanters, and other single-stageseparators without a vapor phase. When you specify outlet conditions, Decanterdetermines the thermal and phase conditions of a mixture of one or more inletstreams.

Decanter can calculate liquid-liquid distribution coefficients using:• An activity coefficient model• An equation of state capable of representing two liquid phases• A user-specified Fortran subroutine• A built-in correlation with user-specified coefficients

You can enter component separation efficiencies, assuming equilibrium stage ispresent.

Use Flash3 if you suspect any vapor phase formation.

Flowsheet Connectivity for Decanter

Heat(optional)

Heat(optional)

1st Liquid

2nd Liquid



Outlet One material stream for the first liquid phaseOne material stream for the second liquid phase

You can specify entrainment for each solid substream in the first liquid phase.


Chapter 2



If you specify only pressure on the Input Specifications sheet, Decanter uses thesum of the inlet heat streams as a duty specification. Otherwise, Decanter usesthe inlet heat stream only to calculate the net heat duty. The net heat duty is thesum of the inlet heat streams minus the actual (calculated) heat duty.


Specifying DecanterYou can operate Decanter in one of the following ways:• Adiabatically• With specified duty• At a specified temperature

Use the Input Specifications sheet to enter:• Pressure• Temperature or duty

Use the following forms to enter specifications and view results for Decanter:


Input Specify operating conditions, key components, calculation options, valid phases,efficiency, and entrainment

Properties Specify and/or override property methods, KLL equation parameters, and/or usersubroutine for phase split calculations



Results Display simulation results



Separators

Defining the Second Liquid Phase

If two liquid phases are present at the decanter operating condition, Decantertreats the phase with higher density as the second phase, by default.

When only one liquid phase exists and you want to avoid ambiguities, you canoverride the default by:• Specifying key components for identifying the second liquid phase on the

Input Specifications sheet• Optionally specifying the threshold key component mole fraction on the Input

Specifications sheet

When Decanter treats the

Two liquid phases are present Phase with the higher mole fraction of key components as the second liquid phase

One liquid phase is present Liquid phase as the first liquid phase, unless the mole fraction of key components exceedsthe threshold value

Methods for Calculating the Liquid-Liquid DistributionCoefficients (KLL)

When calculating liquid-liquid distribution coefficients (KLL), by defaultDecanter uses the physical property method specified for the block on theProperties PhaseProperty sheet or BlockOptions Properties sheet.

On the Input CalculationOptions sheet, you can override the default by doing oneof the following:• Specify separate property methods for the two liquid phases using the

Properties PhaseProperty sheet• Use a built-in KLL correlation. Enter correlation coefficients on the

Properties KLLCorrelation sheet.• Use a Fortran subroutine that you specify on the Properties KLLSubroutine

sheet

See ASPEN PLUS User Models for more information about writing Fortransubroutines.

Phase Splitting

Decanter has two methods for solving liquid-liquid phase split calculations:• Equating fugacities of two liquid phases• Minimizing Gibbs free energy of the system

You can select a method on the Input CalculationOptions sheet.


Chapter 2

If you select Minimizing Gibbs free energy of the system, the following must bethermodynamically consistent:• Physical property models• Block property method

You cannot use the Minimizing Gibbs free energy of the system method when:

You specify On this sheet

Separate property methods for the two liquidphases

Properties PhaseProperty

The built-in correlation for liquid-liquiddistribution coefficient ( KLL) calculations

Input CalculationOptions

A user subroutine for liquid-liquid distributioncoefficient (KLL) calculations

Input Calculation Options

Equating fugacities of two liquid phases is not restricted by physical propertyspecifications. However, Decanter can calculate solutions that do not minimizeGibbs free energy.

Efficiency

Decanter outlet streams are normally at equilibrium. However, you can specifyseparation efficiencies on the Input Efficiency sheet to account for departure fromequilibrium. If you select Liquid-FreeWater for Valid Phases on the InputCalculationOptions sheet, you cannot specify separation efficiencies.

Solids Entrainment

If solids substreams are present, they do not participate in phase equilibriumcalculations, but they do participate in enthalpy balance. You can use the InputEntrainment sheet to specify solids entrainment in the first liquid outlet stream.Decanter places any remaining solids in the second liquid outlet stream.


Separators

SepComponent Separator

Sep combines streams and separates the result into two or more streamsaccording to splits specified for each component. When the details of theseparation are unknown or unimportant, but the splits for each component areknown, you can use Sep in place of a rigorous separation model to savecomputation time .

If the composition and conditions of all outlet streams of the block you aremodeling are identical, you can use an FSplit block instead of Sep.

Flowsheet Connectivity for Sep

Heat(optional)

Material(2 or more)




Heat StreamsInlet No inlet heat streams

Outlet One stream for the enthalpy difference between inlet and outlet materialstreams (optional)


Chapter 2

Specifying SepFor each substream of each outlet stream except one, use the Sep InputSpecifications sheet to specify one of the following for each component present:• Fraction of the component in the corresponding inlet substream• Mole flow rate of the component• Mass flow rate of the component• Standard liquid volume flow rate of the component

Sep puts any remaining flow in the corresponding substream of the unspecifiedoutlet stream.

Use the following forms to enter specifications and view results for Sep:


Input Enter split specifications, flash specifications, and convergence parameters for the mixed inletand each outlet stream


Results View Sep simulation results

Inlet Pressure

Use the Sep Input Feed Flash sheet to specify either the pressure drop or thepressure at the inlet. This is useful when Sep has more than one inlet stream. Theinlet pressure defaults to the minimum inlet stream pressure.

Outlet Stream Conditions

Use the Sep Input Outlet Flash sheet to specify the conditions of the outletstreams. If you do not specify the conditions for a stream, Sep uses the inlettemperature and pressure.


Separators

Sep2Two-Outlet Component Separator

Sep2 separates inlet stream components into two outlet streams. Sep2 is similar toSep, but offers a wider variety of specifications. Sep2 allows purity (mole-fraction)specifications for components.

You can use Sep2 in place of a rigorous separation model, such as distillation orabsorption. Sep2 saves computation time when details of the separation areunknown or unimportant.

If the composition and conditions of all outlet streams of the block you aremodeling are identical, you can use FSplit instead of Sep2.

Flowsheet Connectivity for Sep2

Material

Material

Heat(optional)



Outlet Two material streams


Outlet One stream for the enthalpy difference between inlet and outlet materialstreams (optional)


Chapter 2

Specifying Sep2Use the Input Specifications sheet to specify stream and/or component fractionsand flows. The number of specifications for each substream must equal thenumber of components in that substream.

You can enter these stream specifications:• Fraction of the total inlet stream going to either outlet stream• Total mass flow rate of an outlet stream• Total molar flow rate of an outlet stream (for substreams of type MIXED or

CISOLID)• Total standard liquid volume flow rate of an outlet stream (for substreams of

type MIXED)

You can enter these component specifications:• Fraction of a component in the feed going to either outlet stream• Mass flow rate of a component in an outlet stream• Molar flow rate of a component in an outlet stream (for substreams of type

MIXED or CISOLID)• Standard liquid volume flow rate of a component in an outlet stream (for

substreams of type MIXED)• Mass fraction of a component in an outlet stream• Mole fraction of a component in an outlet stream (for substreams of type

MIXED or CISOLID)

Sep2 treats each substream separately. Do not:• Specify the total flow of both outlet streams• Enter more than one flow or frac specification for each component• Enter both a mole-frac and a mass-frac specification for a component in a

stream

Use the following forms to enter specifications and view results for Sep2:


Input Enter split specifications, flash specifications, and convergence parameters for the mixed inletand each outlet stream

Block Options Override global values for physical properties, simulation options, diagnostic message levels,and report options for this block

Results View Sep2 simulation results


Separators

Inlet Pressure

Use the Input Feed Flash sheet to specify either the pressure drop or pressure atthe inlet. This information is useful when Sep2 has more than one inlet stream.The inlet pressure defaults to the minimum of the inlet stream pressures.

Outlet Stream Conditions

Use the Input Outlet Flash sheet to specify the conditions of the outlet streams.If you do not specify the conditions for a stream, Sep2 uses the inlet temperatureand pressure.

❖ ❖ ❖ ❖


Chapter 3

3 Heat Exchangers

This chapter describes the unit operation models for heat exchangers and heaters(and coolers), and for interfacing to the B-JAC heat exchanger programs. Themodels are:


Heater Heater or cooler Determines thermal and phaseconditions of outlet stream

Heaters, coolers, condensers, and so on

HeatX Two-stream heat exchanger Exchanges heat between twostreams

Two-stream heat exchangers. Ratingshell and tube heat exchangers whengeometry is known.

MHeatX Multistream heat exchanger Exchanges heat between anynumber of streams

Multiple hot and cold stream heatexchangers. Two-stream heatexchangers. LNG exchangers.

Hetran Shell and tube heatexchanger

Provides interface to theB-JAC Hetran shell and tubeheat exchanger program

Shell and tube heat exchangers,including kettle reboilers

Aerotran Air-cooled heat exchanger Provides interface to theB-JAC Aerotran air-cooled heatexchanger program

Crossflow heat exchangers, including aircoolers


HeatExchangers

HeaterHeater/Cooler

You can use Heater to represent:• Heaters• Coolers• Valves• Pumps (whenever work-related results are not needed)• Compressors (whenever work-related results are not needed)

You also can use Heater to set the thermodynamic condition of a stream.

When you specify the outlet conditions, Heater determines the thermal andphase conditions of a mixture with one or more inlet streams.

Flowsheet Connectivity for Heater

Heat (optional)

MaterialMaterial(any number)

Heat(optional)

Water (optional)






Chapter 3

If you give only one specification (temperature or pressure) on the Specificationssheet, Heater uses the sum of the inlet heat streams as a duty specification.Otherwise, Heater uses the inlet heat stream only to calculate the net heat duty.The net heat duty is the sum of the inlet heat streams minus the actual(calculated) heat duty.


Specifying HeaterUse the Heater Input Specifications sheet for all required specifications and validphases.

Dew point calculations are two- or three-phase flashes with a vapor fraction ofunity.

Bubble point calculations are two- or three-phase flashes with a vapor fraction ofzero.

Use the Heater Input FlashOptions sheet to specify temperature and pressureestimates and flash convergence parameters.

Use the Hcurves form to specify optional heating or cooling curves.

This model has no dynamic features. The pressure drop is fixed at the steadystate value. The outlet flow is determined by the mass balance.

Use the following forms to enter specifications and view results for Heater.


Input Enter operating conditions and flash convergence parameters



Results View Heater results


HeatExchangers

Solids

Heater can simulate fluid phases with solids when the stream contains solidsubstreams or when you request electrolyte chemistry calculations.

All phases are in thermal equilibrium. Solids leave at the same temperature asfluid phases.


Electrolyte Chemistry Calculations You can request these on the PropertiesSpecifications Global sheet or the Heater BlockOptions Properties sheet. Solidsalts participate in liquid-solid phase equilibrium and thermal equilibriumcalculations. The salts are in the MIXED substream.


Chapter 3

HeatXTwo-Stream Heat Exchanger

HeatX can model a wide variety of shell and tube heat exchanger types including:• Countercurrent and cocurrent• Segmental baffle TEMA E, F, G, H, J, and X shells• Rod baffle TEMA E and F shells• Bare and low-finned tubes

HeatX can perform a full zone analysis with heat transfer coefficient andpressure drop estimation for single- and two-phase streams. For rigorous heattransfer and pressure drop calculations, you must supply the exchangergeometry.

If exchanger geometry is unknown or unimportant, HeatX can perform simplifiedshortcut rating calculations. For example, you may want to perform only heatand material balance calculations.

HeatX has correlations to estimate sensible heat, nucleate boiling, andcondensation film coefficients.

HeatX cannot:• Perform design calculations• Perform mechanical vibration analysis• Estimate fouling factors

Flowsheet Connectivity for HeatX

Cold Outlet

Water (optional)

Hot Outlet

Water(optional)

HotInlet

Cold Inlet


HeatExchangers

Material StreamsInlet One hot inlet

One cold inlet

Outlet One hot outletOne cold outletOne water decant stream on the hot side (optional)One water decant stream on the cold side (optional)

Specifying HeatXConsider these questions when specifying HeatX:• Should rating calculations be simple (shortcut) or rigorous?• What specification should the block have?• How should the log-mean temperature difference correction factor be

calculated?• How should the heat transfer coefficient be calculated?• How should the pressure drops be calculated?• What equipment specifications and geometry information are available?

The answers to these questions determine the amount of information required tocomplete the block input. You must provide one of the following specifications:• Heat exchanger area or geometry• Exchanger heat duty• Outlet temperature of the hot or cold stream• Temperature approach at either end of the exchanger• Degrees of superheating/subcooling for the hot or cold stream• Vapor fraction of the hot or cold stream• Temperature change of the hot or cold stream

Use the following forms to enter specifications and view results for HeatX:


Setup Specify shortcut or detailed calculations, flow direction, exchanger pressure drops, heat transfercoefficient calculation methods, and film coefficients

Options Specify different flash convergence parameters and valid phases for the hot and cold sides, HeatXconvergence parameters, and block-specific report option

Geometry Specify the shell and tube configuration and indicate any tube fins, baffles, or nozzles

UserSubroutines Specify parameters for user-defined Fortran subroutines to calculate overall heat transfer coefficient,LMTD correction factor, tube-side liquid holdup, or tube-side pressure drop

Hot-Hcurves Specify hot stream heating or cooling curve tables and view tabular results

continued


Chapter 3


Cold-Hcurves Specify cold stream heating or cooling curve tables and view tabular results


Results View a summary of results, mass and energy balances, pressure drops, velocities, andzone analysis

Detailed Results View detailed shell and tube results, and information about tube fins, baffles, andnozzles


Shortcut Versus Rigorous Rating Calculations

HeatX has two rating modes: shortcut and rigorous. Use the Calculation Typefield on the Setup Specifications sheet to specify shortcut or rigorous ratingcalculations.

In shortcut rating mode you can simulate a heat exchanger block with theminimum amount of required input. The shortcut calculation does not requireexchanger configuration or geometry data.

For rigorous rating mode, you can use exchanger geometry to estimate:• Film coefficients• Pressure drops• Log-mean temperature difference correction factor

Rigorous rating mode provides more specification options for HeatX, but it alsorequires more input.

Rigorous rating mode provides defaults for many options. You can change thedefaults to gain complete control over the calculations. The following table liststhese options with valid values. The values are described in the followingsections.


HeatExchangers

Variable Calculation MethodAvailable inShortcut Mode

Available inRigorous Mode

LMTD CorrectionFactor

ConstantGeometryUser subroutine

DefaultNoNo

YesDefaultYes

Heat TransferCoefficient

Constant valuePhase-specific valuesPower law expressionFilm coefficientsExchanger geometryUser subroutine

YesDefaultYesNoNoNo

YesYesYesYesDefaultYes

Film Coefficient Constant valuePhase-specific valuesPower law expressionCalculate from geometry

NoNoNoNo

YesYesYesDefault

Pressure Drop Outlet pressureCalculate from geometry

DefaultNo

YesDefault

Calculating the Log-Mean Temperature DifferenceCorrection Factor

The standard equation for a heat exchanger is:

Q U A LMTD= ⋅ ⋅

where LMTD is the log-mean temperature difference. This equation applies forexchangers with pure countercurrent flow.

The more general equation is:

Q U A F LMTD= ⋅ ⋅ ⋅

where the LMTD correction factor, F, accounts for deviation from countercurrentflow.

Use the LMTD Correction Factor field on the Setup Specifications sheet to enterthe LMTD correction factor.


Chapter 3

In shortcut rating mode, the LMTD correction factor is constant. In rigorousrating mode, use the LMTD Correction Method field on the Setup Specificationssheet to specify how HeatX calculates the LMTD correction factor. You canchoose from the following calculation options:

If LMTD Correction Method is Then

Constant The LMTD correction factor you enter is constant.

Geometry HeatX calculates the LMTD correction factor using the exchanger specificationand stream properties

User subroutine You supply a user subroutine to calculate the LMTD correction factor.

Calculating the Heat Transfer Coefficient

To determine how the heat transfer coefficient is calculated, set the CalculationMethod on the Setup U Methods sheet. You can use these options in shortcut orrigorous rating mode:

If Calculation Method is HeatX uses And you specify

Constant value A constant value for the heat transfer coefficient The constant value

Phase-specific values A different heat transfer coefficient for each heat transferzone of the exchanger, indexed by the phase for the hotand cold streams

A constant value foreach zone

Power law expression A power law expression for the heat transfer coefficient asa function of one of the stream flow rates

Constants for the powerlaw expression

In rigorous rating mode, three additional values are allowed:

If Calculation Method is Then

Exchanger geometry HeatX calculates the heat transfer coefficient using exchanger geometry and streamproperties to estimate film coefficients.

Film coefficients HeatX calculates the heat transfer coefficients using the film coefficients. You can useany option on the Setup Film Coefficients sheet to calculate the film coefficients.

User subroutine You supply a user subroutine to calculate the heat transfer coefficient.


HeatExchangers

Film Coefficients

HeatX does not calculate film coefficients in shortcut rating mode. In rigorousrating mode, if you use film coefficients or exchanger geometry for the heattransfer coefficient calculation method, HeatX calculates the heat transfercoefficient using:

1 1 1

U h hc h

= +

Where:

hc = Cold stream film coefficient

hh = Hot stream film coefficient

To choose an option for calculating film coefficients, set the Calculation Methodon the Setup Film Coefficients sheet. The following are available:

If Calculation Method is HeatX uses And you specify

Constant value A constant value for the film coefficient A constant value to beused throughout theexchanger

Phase-specific values A different film coefficient for each heattransfer zone (phase) of the exchanger,indexed by the phase of the stream

A constant value foreach phase

Power law expression A power law expression for the film coefficientas a function of the stream flow rate

Constants for the powerlaw expression

Calculate from geometry The exchanger geometry and streamproperties to calculate the film coefficient

The hot stream and cold stream film coefficient calculation methods areindependent of each other. You can use any combination that is appropriate foryour exchanger.

Pressure Drop Calculations

To enter exchanger pressure or pressure drop for the hot and cold sides, use theOutlet Pressure fields on the Setup Pressure Drop sheet. In shortcut rating modethe pressure drop is constant.


Chapter 3

In rigorous rating mode, you can choose how pressure drops are calculated bysetting the pressure options on the Setup PressureDrop sheet. The followingpressure drop options are available:

If Pressure Option is Then

Outlet Pressure You must enter the outlet pressure or pressure drop for the stream.

Calculate from geometry HeatX calculates the pressure drop using the exchanger geometry and streamproperties

HeatX calls the Pipeline model to calculate tube-side pressure drop. You can setthe correlations for pressure drop and liquid holdup that the Pipeline model useson the Setup PressureDrop sheet.

Exchanger Configuration

Exchanger configuration refers to the overall patterns of flow in the heatexchanger. If you choose Calculate From Geometry for any of the heat transfercoefficients, film coefficients, or pressure drop calculation methods, you may berequired to enter some information about the exchanger configuration on theGeometry Shell sheet. This sheet includes fields for:• TEMA shell type (see the next figure, TEMA Shell Types)• Number of tube passes• Exchanger orientation• Tubes in baffle window• Number of sealing strips• Tube flow for vertical exchangers


HeatExchangers

Two Pass Shellwith Longitudinal Baffle

One Pass Shell

E Shell

F Shell

G Shell

H Shell

J Shell

X Shell

Split Flow

Double Split Flow

Divided Flow

Cross Flow

TEMA Shell Types


Chapter 3

The Geometry Shell sheet also contains two important dimensions for the shell:• Inside shell diameter• Shell to bundle clearance

The next figure shows the shell dimensions.

Outer TubeLimit

Shell to BundleClearance

Shell Diameter

Shell Dimensions

Baffle Geometry

Calculation of shell-side film coefficient and pressure drop require informationabout the baffle geometry within the shell. Enter baffle geometry on theGeometry Baffles sheet.

HeatX can calculate shell-side values for both segmental baffle shells and rodbaffle shells. Other required information depends on the baffle type. Forsegmental baffles, required information includes:• Baffle cut• Baffle spacing• Baffle clearances

For rod baffles, required information includes:• Ring dimensions• Support rod geometry


HeatExchangers

The next two figures show the baffle dimensions. The Baffle Cut in theDimensions for Segmental Baffles figure is a fraction of the shell diameter. Allclearances are diametric.

Baffle Cut

Tube Hole Shell to BaffleClearance

Dimensions for Segmental Baffles

Ring OutsideDiameter

Ring InsideDiameter

Rod Diameter

Dimensions for Rod Baffles

Tube Geometry

Calculation of the tube-side film coefficient and pressure drop requireinformation about the geometry of the tubebank. HeatX also uses thisinformation to calculate the heat transfer coefficient from the film coefficients.Enter tube geometry on the Geometry Tubes sheet.


Chapter 3

You can select a heat exchanger with either bare or low-finned tubes. The sheetalso includes fields for:• Total number of tubes• Tube length• Tube diameters• Tube layout• Tube material of construction

The next two figures show tube layout patterns and fin dimensions.

TubePitch

30o

Triangle

45o

TubePitch

RotatedSquare

60o

TubePitch

RotatedTriangle

90o

TubePitch

Square

Direction of Flow

Tube Layout Patterns

OutsideDiameter

Fin Thickness

Root MeanDiameter

Fin Height

Fin Dimensions

Nozzle Geometry

Calculations for pressure drop include the calculation of pressure drop in theexchanger nozzles. Enter nozzle geometry on the Geometry Nozzles sheet.

Model Correlations

HeatX uses open literature correlations for calculating film coefficients andpressure drops. The next four tables list the model correlations.


HeatExchangers

Tube-side Heat Transfer Coefficient Correlations

Mechanism Flow Regime Correlation References

Single-phase LaminarTurbulent

SchlunderGnielinski

[1][1]

Boiling - vertical tubes Steiner/Taborek [2]

Boiling - horizontal tubes Shah [3, 4]

Condensation - vertical tubes LaminarLaminar wavyTurbulentShear-dominated

NusseltKutateladzeLabuntsovRohsenow

[5][6][7][8]

Condensation - horizontal tubes AnnularStratifying

RohsenowJaster/Kosky method

[8][9]

Shell-side Heat Transfer Coefficient Correlations

Mechanism Flow Regime Correlation References

Single-phase segmental Bell-Delaware [10, 11]

Single-phase ROD Gentry [12]

Boiling Jensen [13]

Condensation - vertical LaminarLaminar wavyTurbulentShear-dominated

NusseltKutateladzeLabuntsovRohsenow

[5][6][7][8]

Condensation - horizontal Kern [9]

Tube-side Pressure Drop Correlations

Mechanism Correlation

Single-phase Darcy’s Law

Two-phase See Chapter 6†

†See Pipeline, Two-Phase Correlations, for the correlations available for two-phase pressure drop in apipe.

Shell-side Pressure Drop Correlations

Mechanism Correlation References

Single-phase segmental Bell-Delaware [10, 11]

Single-phase ROD Gentry [12]

Two-phase segmental Bell-Delaware method with Grant’s correction for two-phase flow

[10, 11], [14]

Two-phase ROD Gentry [12]


Chapter 3

Flash Specifications

Use the Options Flash Options sheet to enter flash specifications.

If you want to performthese calculations Solids? Set Valid Phases to

Vapor phase Yes or no Vapor-only

Liquid phase Yes or no Liquid-only

2-fluid flash phase Yes or no Vapor-Liquid

3-fluid flash phase Yes or no Vapor-Liquid-Liquid

3-fluid phase free-water flash Yes or no Vapor-Liquid-FreeWater

Solids only Yes Solid-only

Physical Properties

To override global or flowsheet section property specifications, use theBlockOptions Properties sheet. You can use different physical property optionsfor the hot side and cold side of the heat exchanger. If you supply only one set ofproperty specifications, HeatX uses that set for both hot and cold sidecalculations.

Solids


HeatX can simulate fluid phases with solids when the stream contains solidsubstreams, or when you request electrolyte chemistry calculations.


Electrolyte Chemistry Calculations You can request these on the PropertiesSpecifications Global sheet or HeatX BlockOptions Properties sheet. Solid saltsparticipate in liquid-solid phase equilibrium and thermal equilibriumcalculations. The salts are in the MIXED substream.


HeatExchangers

References

1. Gnielinski, V., "Forced Convection in Ducts." In: Heat Exchanger DesignHandbook. New York: Hemisphere Publishing Corporation, 1983.

2. Steiner, D. and Taborek, J., "Flow Boiling Heat Transfer in Vertical TubesCorrelated by an Asymptotic Model." In: Heat Transfer Engineering, 13(2):43-69, 1992.

3. Shah, M.M., "A New Correlation for Heat Transfer During Boiling FlowThrough Pipes." In: ASHRAE Transactions, 82(2):66-86, 1976.

4. Shah, M.M., "Chart Correlation for Saturated Boiling Heat Transfer:Equations and Further Study." In: ASHRAE Transactions, 87(1):185-196,1981.

5. Nusselt, W., "Surface Condensation of Water Vapor." Z. Ver. Dtsch, Ing.,60(27):541-546, 1916.

6. Kutateladze, S.S., Fundamentals of Heat Transfer. New York: AcademicPress, 1963.

7. Labuntsov, D.A., "Heat Transfer in Film Condensation of Pure Steam onVertical Surfaces and Horizontal Tubes." In: Teploenergetika, 4(7):72-80,1957.

8. Rohsenow, W.M., Webber, J.H., and Ling, A.T., "Effect of Vapor Velocity onLaminar and Turbulent Film Condensation." In: Transactions of the ASME,78:1637-1643, 1956.

9. Jaster, H. and Kosky, P.G., "Condensation Heat Transfer in a Mixed FlowRegime." In: International Journal of Heat and Mass Transfer, 19:95-99,1976.

10. Taborek, J., "Shell-and-Tube Heat Exchangers: Single Phase Flow." In: HeatExchanger Design Handbook. New York: Hemisphere PublishingCorporation, 1983.

11. Bell, K.J., "Delaware Method for Shell Side Design." In: Kakac, S., Bergles,A.E., and Mayinger, F., editors, Heat Exchangers: Thermal-HydraulicFundamentals and Design. New York: Hemisphere Publishing Corp., 1981.

12. Gentry, C.C., "RODBaffle Heat Exchanger Technology." In: ChemicalEngineering Progress 86(7):48-57, July 1990.

13. Jensen, M.K. and Hsu, J.T., "A Parametric Study of Boiling Heat Transfer ina Tube Bundle." In: 1987 ASME-JSME Thermal Engineering JointConference, pages 133-140, Honolulu, Hawaii, 1987.

14. Grant, I.D.R. and Chisholm, D., "Two-Phase Flow on the Shell Side of aSegmentally Baffled Shell-and-Tube Heat Exchanger." In: Journal of HeatTransfer, 101(1):38-42, 1979.


Chapter 3

MHeatXMultistream Heat Exchanger

Use MHeatX to represent heat transfer between multiple hot and cold streams,such as in an LNG exchanger. You can also use MHeatX for two-stream heatexchangers. Free water can be decanted from any outlet stream. MHeatX ensuresan overall energy balance but does not account for the exchanger geometry.

MHeatX can perform a detailed, rigorous internal zone analysis to determine theinternal pinch points and heating and cooling curves for all streams in the heatexchanger. MHeatX can also calculate the overall UA for the exchanger andmodel heat leak to or from an exchanger.

MHeatX uses multiple Heater blocks and heat streams to enhance flowsheetconvergence. ASPEN PLUS automatically sequences block and streamconvergence unless you specify a sequence or tear stream.

Flowsheet Connectivity for MHeatX

Hot Inlets(any number)

Hot Outlets

Water (optional)

Hot OutletsWater (optional)

Water(optional)

ColdOutlets

Cold Inlets(any number)

Material StreamsInlet At least one material stream on the hot side. At least one material stream

on the cold side

Outlet One outlet stream for each inlet streamOne water decant stream for each outlet stream (optional)

The inlet stream sides are non-contacting.


HeatExchangers

Specifying MHeatXYou must give outlet specifications for each stream on one side of the heatexchanger. On the other side you can specify any of the outlet streams, but youmust leave at least one unspecified stream.

Different streams can have different types of specifications. MHeatX assumesthat all unspecified streams have the same outlet temperature. An overall energybalance determines the temperature of any unspecified stream(s).

You can use a different property method for each stream in MHeatX. Specify theproperty methods on the BlockOptions Properties sheet.

Use the following forms to enter specifications and view results for MHeatX:


Input Specify operating conditions, flash convergence parameters, parameters forzone analysis, flash table, MHeatX convergence parameters, and block-specificreport options


BlockOptions Override global values for physical properties, simulation options, diagnosticmessage levels and report options for this block

Results View stream results, exchanger results, zone profiles, stream profiles, flashprofiles, and material and energy balance results

Zone Analysis

MHeatX can perform a detailed, rigorous internal zone analysis to determine:• Internal pinch points• UA and LMTD of each zone• Total UA of the exchanger• Overall average LMTD

To obtain a zone analysis, specify Number of zones greater than 0 on the MHeatXInput Zone Analysis sheet. During zone analysis MHeatX can add:• Stream entry points (if all feed streams are not at the same temperature)• Stream exit points (if all product streams are not at the same temperature)• Phase change points (if a phase change occurs internally)

MHeatX can also account for the nonlinearities of zone profiles by adding zonesadaptively. MHeatX can perform zone analysis for both countercurrent and co-current heat exchangers.


Chapter 3

Using Flash Tables in Zone Analysis

Use Flash Tables to estimate zone profiles and pinch points quickly. These tablesare most useful for heat exchangers that have many streams, for which zoneanalysis calculations can take a long time.

To use a Flash Table for a stream, specify the number of flash points for thestream on the MHeatX Input Flash Table sheet. When you specify a flash tablefor a stream, MHeatX generates a temperature-enthalpy profile of that streambefore zone analysis, and interpolates that profile during zone analysis, ratherthan flashing the stream.

You can also specify the fraction of total pressure drop in each phase region of astream on the MHeatX Input Flash Table sheet. ASPEN PLUS uses thesefractions to determine the pressure profile during Flash Table generation.

Computational Structure for MHeatX

The computational structure of MHeatX may affect your specifications.

Unlike other unit operation blocks, MHeatX is not simulated by a singlecomputation module. Instead, ASPEN PLUS generates heaters and heat streamsto represent the multistream heat exchanger. A Heater block represents streamswith outlet specifications. A multistream heater block represents streams withno outlet specifications. The next figure shows the computational structuregenerated for a sample exchanger.

S3 S4 S5 S6 S7 S8

S1 S2

LNGIN LNGOUT

$LNGH03

$LNGQ03

$LNGQ02

HEATER HEATER

$LNGH02

$LNGQ04

HEATER

$LNGH04

$LNGHTR

MHEATER

Example of MHeatX Computational Structure

This computational sequence converges much more rapidly than simulation ofMHeatX as a single block. Block results are given for the entire MHeatXsequence. In most cases, you do not need to know about the individual blocksgenerated in the sequence. The following paragraphs describe the exceptions.


HeatExchangers

Simulation history and control panel messages are given for the generatedHeater blocks and heat streams.

You can provide an estimate for duty of the internally generated heat stream. Ifthe heat stream is a tear stream in the flowsheet, ASPEN PLUS uses thisestimate as an initial value.

You can give convergence specifications for the flowsheet resulting when MHeatXblocks are replaced by their generated networks. The generated Heater block andheat stream IDs must be used on the Convergence SequenceSpecifications andConvergence TearSpecifications sheets.

Automatic flowsheet analysis is based on the flowsheet resulting when MHeatXblocks are replaced by generated Heater blocks. The generated Heater blocks,instead of the MHeatX block, appear in the calculation sequence. You can selectgenerated heat streams as tear streams.

Solids

MHeatX can simulate fluid phases with solids when the stream contains solidsubstreams, or when you request electrolyte chemistry calculations.



Electrolyte Chemistry Calculations You can request these on the PropertiesSpecifications Global sheet or the MHeatX BlockOptions Properties sheet. Solidsalts participate in liquid-solid phase equilibrium and thermal equilibriumcalculations. The salts are in the MIXED substream.


Chapter 3

HetranInterface to the B-JAC Hetran Program for Shell and Tube HeatExchangers

Hetran is the interface to the B-JAC Hetran program for designing andsimulating shell and tube heat exchangers. Hetran can be used to simulate shelland tube heat exchangers with a wide variety of configurations. To use Hetran,place the block in the flowsheet, connect inlet and outlet streams, and specify asmall number of block inputs, including the name of the B-JAC input file for thatexchanger.

You enter information related to the heat exchanger configuration and geometrythrough the Hetran standalone program interface. The exchanger specification issaved as a B-JAC input file. You do not have to enter information about theexchanger’s physical characteristics through the ASPEN PLUS user interface orthrough input language.

Flowsheet Connectivity for Hetran

Cold InletHot Inlet

Hot Water (optional)

Hot OutletCold Outlet

Cold Water (optional)


One cold inlet

Outlet One hot outletOne cold outletOne water decant stream on the hot side (optional)One water decant stream on the cold side (optional)


HeatExchangers

Specifying HetranEnter the input for the shell and tube heat exchanger through the Hetranprogram’s graphical user interface. The input for Hetran in ASPEN PLUS islimited to:• The B-JAC input file name that contains the heat exchanger specification• A set of parameters to control how property curves are generated• A set of Hetran program inputs that you can change from within

ASPEN PLUS (for example, fouling factors and film coefficients)

Use the following forms to enter specifications and view results for Hetran:


Input Specify the name of the B-JAC input file, parameters for calculating the property curves,optional Hetran program inputs, flash convergence parameters, and valid phases

BlockOptions

Override global values for physical properties, simulation options, diagnostic messagelevels, and report options for this block

Results View inlet and outlet stream conditions and material and energy balance results

DetailedResults

View overall results and detailed results for the shell side and tube side


Use the FlashOptions sheet to enter flash specifications.

If you want to perform these calculations Solids? Set Valid Phases to








Chapter 3

Physical Properties

To override global or flowsheet section property specifications, use theFlashOptions sheet. You can use different physical property methods for the hotside and cold side of the heat exchanger. If you supply only one set of propertyspecifications, Hetran uses that set for both hot- and cold-side calculations.

Solids

Hetran cannot currently handle streams with solids substreams.


HeatExchangers

AerotranInterface to the B-JAC Aerotran Program for Air-cooled Heat Exchangers

Aerotran is the interface to the B-JAC Aerotran program for designing andsimulating air-cooled heat exchangers. Aerotran can be used to simulate air-cooled heat exchangers with a wide variety of configurations. It can also be usedto model economizers and the convection section of fired heaters. To useAerotran, place the block in the flowsheet, connect inlet and outlet streams, andspecify a small number of block inputs, including the name of the B-JAC inputfile for that exchanger.

You enter information related to the air cooler configuration and geometrythrough the Aerotran standalone program interface. The air cooler specificationis saved as a B-JAC input file. You do not have to enter information about the aircooler’s physical characteristics through the ASPEN PLUS user interface orthrough input language.

Flowsheet Connectivity for Aerotran

Cold (Air) Inlet

Cold (Air) Outlet

Hot Outlet

Hot Inlet

Hot Water (optional)

Cold Water (optional)


One cold (air) inlet

Outlet One hot outletOne cold (air) outletOne water decant stream on the hot side (optional)One water decant stream on the cold side (optional)


Chapter 3

Specifying AerotranEnter the input for the air-cooled heat exchanger through the Aerotran program’sgraphical user interface. The input for Aerotran in ASPEN PLUS is limited to:• The B-JAC input file name that contains the heat exchanger specification• A set of parameters to control how property curves are generated• A set of Aerotran program inputs that you can change from within ASPEN

PLUS (for example, fouling factors and film coefficients)

Use the following forms to enter specifications and view results for Aerotran:


Input Specify the name of the B-JAC input file, parameters for calculating the propertycurves, optional Aerotran program inputs, flash convergence parameters, and validphases

BlockOptions Override global values for physical properties, simulation options, diagnosticmessage levels, and report options for this block

Results View inlet and outlet stream conditions and material and energy balance results

Detailed Results View overall results, detailed results for the outside and tube side, and fan results


Use the FlashOptions sheet to enter flash specifications.

If you want to perform these calculations Solids? Set Valid Phases to








HeatExchangers

Physical Properties

To override global or flowsheet section property specifications, use theFlashOptions sheet. You can use different physical property methods for the hotside and cold side of the air cooler. If you supply only one set of propertyspecifications, Aerotran uses that set for both hot- and cold-side calculations.

Solids

Aerotran blocks cannot currently handle streams with solids substreams.

❖ ❖ ❖ ❖


Chapter 4

4 Columns

This chapter describes the unit operation models for distillation columns usingshortcut and rigorous calculations, and for liquid-liquid extraction. The modelsare:


DSTWU Shortcut distillation designusing the Winn-Underwood-Gillilandmethod

Determines minimum reflux ratio,minimum number of stages, and eitheractual reflux ratio or actual number ofstages

Columns with one feedand two product streams

Distl Shortcut distillation ratingusing the Edmister method

Determines separation based on refluxratio, number of stages, and distillate-to-feed ratio

Columns with one feedand two product streams

SCFrac Shortcut distillation forcomplex petroleumfractionation units

Determines product composition and flow,number of stages per section, and heatduty using fractionation indices

Complex columns, such ascrude units and vacuumtowers

RadFrac Rigorous fractionation Performs rigorous rating and designcalculations for single columns

Ordinary distillation,absorbers, strippers,extractive and azeotropicdistillation, three-phasedistillation, reactivedistillation

MultiFrac Rigorous fractionation forcomplex columns

Performs rigorous rating and designcalculations for multiple columns of anycomplexity

Heat integrated columns,air separation columns,absorber/strippercombinations ethyleneplant primary fractionatorquench towercombinations, petroleumrefining applications

continued


Columns


PetroFrac Petroleum refiningfractionation

Performs rigorous rating and designcalculations for complex columns inpetroleum refining applications

Preflash tower,atmospheric crude unit,vacuum unit, catalyticcracker main fractionator,delayed coker mainfractionator, vacuum lubefractionator, ethylene plantprimary fractionator andquench towercombinations

RateFrac† Rate-based distillation Performs rigorous rating and design forsingle and multiple columns. Based onnonequilibrium calculations. Does notrequire efficiencies and HETPs.

Distillation columns,absorbers, strippers,reactive systems, heatintegrated units, petroleumapplications, such ascrude and vacuum units,absorber-strippercombination

Extract Rigorous liquid-liquidextraction

Models countercurrent extraction of aliquid stream using a solvent

Liquid-liquid extractors

†RateFrac requires a separate license and can be used only by customers who have purchased it througha specific license agreement with Aspen Technology, Inc.

This chapter is organized into the following sections:

Section Models

Shortcut Distillation DSTWU, Distl, SCFrac

Rigorous Distillation RadFrac, MultiFrac, PetroFrac, RateFrac

Liquid-Liquid Extraction Extract


Chapter 4

DSTWUShortcut Distillation Design

DSTWU performs shortcut design calculations for single-feed, two-productdistillation columns with a partial or total condenser.

DSTWU assumes constant molal overflow and constant relative volatilities.

DSTWU uses this method/correlation To estimate

Winn Minimum number of stages

Underwood Minimum reflux ratio

Gilliland Required reflux ratio for a specified number of stages or the requirednumber of stages for a specified reflux ratio

For the specified recovery of light and heavy key components, DSTWU estimates:• Minimum reflux ratio• Minimum number of theoretical stages

DSTWU then estimates one of the following:• Required reflux ratio for the specified number of theoretical stages• Required number of theoretical stages for the specified reflux ratio

DSTWU also estimates the optimum feed stage location and the condenser andreboiler duties. DSTWU can produce tables and plots of reflux ratio versusnumber of stages.

Flowsheet Connectivity for DSTWU

Heat(optional)

Heat(optional)

Heat(optional)

Heat(optional)

Water(optional)

Distillate

Feed

Bottoms

1

2

N-1

N


Columns

Material StreamsInlet One material feed stream

Outlet One distillate streamOne bottoms streamOne water decant stream from condenser (optional)

Heat StreamsInlet One stream for condenser cooling (optional)

One stream for reboiler heating (optional)

Outlet One stream for condenser cooling (optional)One stream for reboiler heating (optional)

Each outlet heat stream contains the net heat duty for either the condenser or thereboiler. The net heat duty is the inlet heat stream minus the actual (calculated)heat duty.

If you use heat streams for the reboiler, you must also use them for thecondenser.

Specifying DSTWUUse the Input Specifications sheet to enter column specifications. The followingtable shows the specifications and what is calculated based on them:

Specification Result

Recovery of light and heavy key components Minimum reflux ratio and minimum number of theoretical stages

Number of theoretical stages Required reflux ratio

Reflux ratio Required number of theoretical stages

DSTWU also estimates the optimum feed stage location, and the condenser andreboiler duties.

DSTWU can generate an optional table of reflux ratio versus number of stages.Use the Input CalculationOptions sheet to enter specifications for the table.


Chapter 4

Use the following forms to enter specifications and view results for DSTWU:


Input Specify configuration and calculation options, block-specific report options, flashconvergence parameters, valid phases, and DSTWU convergence parameters


Results View summary results, material and energy balance results, and reflux ratio profile


Columns

DistlShortcut Distillation Rating

Distl simulates multistage multicomponent columns with a feed stream and twoproduct streams.

Distl performs shortcut distillation rating calculations for a single-feed, two-product distillation column. The column can have either a partial or totalcondenser. Distl calculates product composition using the Edmister approach. Distlassumes constant mole overflow and constant relative volatilities.

Flowsheet Connectivity for Distl

Heat(optional)

Heat(optional)

Heat(optional)

Heat(optional)

Water(optional)

Distillate

Feed

Bottoms

1

2

N-1

N


Outlet One distillate streamOne bottoms streamOne water decant stream from condenser (optional)

Heat StreamsInlet One stream for condenser cooling (optional)

One stream for reboiler heating (optional)

Outlet One stream for condenser cooling (optional)One stream for reboiler heating (optional)


Chapter 4

Each outlet heat stream contains the net heat duty for either the condenser or thereboiler. The net heat duty is the inlet heat stream minus the actual (calculated)heat duty.

If you use heat streams for the reboiler, you must also use them for thecondenser.

Specifying DistlUse the Input Specifications sheet to enter the number of stages, reflux ratio,distillate to feed ratio, and other column specifications.

Use the Input Convergence sheet to override default valid phases for condenser,convergence parameters for flash calculations, and model convergence parameters.

Use the following forms to enter specifications and view results for Distl:


Input Specify basic column configuration, operating conditions, Distl convergence parameters, and flashconvergence parameters

BlockOptions Override global values for physical properties, simulation options, diagnostic message levels, andreport options for this block

Results View summary of column results and material and energy balance results

Dynamic Specify parameters for dynamic simulation


Columns

SCFracShortcut Distillation for Complex Columns

Use SCFrac to simulate complex distillation columns with a single feed, optionalstripping steam, and any number of products. SCFrac also estimates the numberof theoretical stages and the heating/cooling duty for each section.

SCFrac can model complex columns, such as crude units and vacuum towers.SCFrac performs shortcut distillation calculations for columns with a single feed,one optional stripping steam stream, and any number of products. SCFracdivides a column with n products into n – 1 sections. These sections arenumbered from the top down. SCFrac assumes:• Relative volatilities are constant for each section• The flow of liquid from section to section is negligible

SCFrac does not handle solids. SCFrac can perform free-water calculations in thecondenser.

Flowsheet Connectivity for SCFrac

Steam(optional)

Distillate

Bottoms

Side Products(any number)

Feed


One optional stripping steam stream (used for all sections)

Outlet One distillate streamOne bottoms streamAt least one side product stream


Chapter 4

Specifying SCFracSCFrac divides an n–product column into n – 1 sections (see the next figure,SCFrac Multidraw Column). SCFrac numbers the column sections from the topdown. For each section, you must specify:• Product pressure• Estimate of product flow or flow fraction based on feed flow

You must specify the ratio of steam to product flow rate for all product streamsexcept the distillate. You must also enter 2(n – 1) specifications from the following:• Fractionation index (number of theoretical stages at total reflux) of a section• Total flow, flow rate, or recovery of any group of components for a product

stream• Value of a property set property for a product stream (see ASPEN PLUS User

Guide, Chapter 28)• Difference of any pair of property set properties for one or a pair of product

stream(s)• Ratio of any pair of property set properties for one or a pair of product

stream(s)

Because SCFrac performs steam calculations, water must always be present. Allwater flow leaves with the top product stream.

A MultidrawColumn P1

P2

P3

P4

P5

Stream-1

P1

P2Stream-1

P3Stream-2

P4

P5

Stream-3

Stream-4

Stream-2

Stream-3

Stream-4

FeedFeed

SCFrac Multidraw Column


Columns

Use the following forms to enter specifications and view results for SCFrac:


Input Specify operating parameters, valid phases, SCFrac convergence parameters, andflash convergence parameters


Results View condenser results, material and energy balance results, design specificationresults, section profiles, and product summary


Chapter 4

RadFracRigorous Fractionation

RadFrac is a rigorous model for simulating all types of multistage vapor-liquidfractionation operations. These operations include:• Ordinary distillation• Absorption• Reboiled absorption• Stripping• Reboiled stripping• Extractive and azeotropic distillation

RadFrac is suitable for:• Two-phase systems• Three-phase systems• Narrow and wide-boiling systems• Systems exhibiting strong liquid phase nonideality

RadFrac can detect and handle a free-water phase or other second liquid phaseanywhere in the column. RadFrac can handle solids on every stage.

RadFrac can handle pumparounds leaving any stage and returning to the samestage or to a different stage.

RadFrac can model columns in which chemical reactions are occurring. Reactionscan have fixed conversions, or they can be:• Equilibrium• Rate-controlled• Electrolytic

RadFrac can also model columns in which two liquid phases and chemicalreactions occur simultaneously, using different reaction kinetics for the twoliquid phases. In addition, RadFrac can model salt precipitation.

Although RadFrac assumes equilibrium stages, you can specify either Murphreeor vaporization efficiencies. You can manipulate Murphree efficiencies to matchplant performance.

You can use RadFrac to size and rate columns consisting of trays and/orpackings. RadFrac can model both random and structured packings.


Columns

Flowsheet Connectivity for RadFrac

Bottoms

Product

Products (optional)

Decanters

ReturnBoil-Up

Feeds

1

Reflux

Heat (optional)

Heat (optional)Liquid Distillate

Vapor Distillate

Water Distillate(optional)

Heat (optional)

Heat(optional)

Heat(optional)

NstageBottom Stage

or ReboilerHeat Duty

Top Stageor Condenser

Heat Duty

RadFrac can have any number of:• Stages• Interstage heaters/coolers• Decanters• Pumparounds

Material StreamsInlet At least one inlet material stream

Outlet One vapor or liquid distillate product stream, or bothOne water distillate product stream (optional)One bottoms liquid product streamUp to three side product streams per stage (optional)Any number of pseudo-product streams (optional)

Each stage can have:• Any number of inlet streams• Up to three outlet streams (one vapor and two liquid)

Outlet streams can be partial or total drawoffs of the stage flows.

Decanter outlet streams can return to the stage immediately below. Or they canbe split into any number of streams, each returning to a different user-specifiedstage. Pumparounds can go between any two stages, or to the same stage.

Any number of pseudoproduct streams can represent column internal flows,pumparound flows, and thermosyphon reboiler flows. A pseudoproduct streamdoes not affect column results.


Chapter 4

Heat StreamsInlet One inlet heat stream per stage (optional)

One heat stream per pumparound (optional)

Outlet One outlet heat stream per stage (optional)One heat stream per pumparound (optional)

RadFrac uses an inlet heat stream as a duty specification for all stages except thecondenser, reboiler, and pumparounds. If you do not give two column operatingspecifications on the Setup Configuration sheet, RadFrac uses a heat stream as aspecification for the condenser and reboiler. If you do not give two specifications onthe Pumparounds Specifications sheet, RadFrac uses a heat stream as aspecification for pumparounds.

If you give two specifications on the Setup Configuration sheet or PumparoundsSpecifications sheet, RadFrac does not use the inlet heat stream as aspecification. The inlet heat stream supplies the required heating or cooling.

Use optional outlet streams for the net heat duty of the condenser, reboiler, andpumparounds. The value of the outlet heat stream equals the value of the inletheat stream (if any) minus the actual (calculated) heat duty.

Specifying RadFracThis section describes the following topics on RadFrac column configuration:• Stage Numbering• Feed Stream Conventions• Columns Without Condensers or Reboilers• Reboiler Handling• Heater and Cooler Specifications• Decanters• Pumparounds

Use the following forms to enter specifications and view results for RadFrac:


Setup Specify basic column configuration and operating conditions

DesignSpecs Specify design specifications and view convergence results

Vary Specify manipulated variables to satisfy design specifications and view final values

HeatersCoolers Specify stage heating or cooling

Pumparounds Specify pumparounds and view pumparound results

continued


Columns


Pumparounds Hcurves Specify pumparound heating or cooling curve tables and view tabularresults

Decanters Specify decanters and view decanter results

Efficiencies Specify stage, component or sectional efficiencies

Reactions Specify equilibrium, kinetic, and conversion reaction parameters

CondenserHcurves Specify condenser heating or cooling curve tables and view tabularresults

ReboilerHcurves Specify reboiler heating or cooling curve tables and view tabular results

TraySizing Specify sizing parameters for tray column sections and view results

TrayRating Specify rating parameters for tray column sections and view results

PackSizing Specify sizing parameters for packed column sections and view results

PackRating Specify rating parameters for packed column sections and view results

Properties Specify physical property parameters for column sections

Estimates Specify initial estimates for stage temperatures, vapor and liquid flows,and compositions

Convergence Specify convergence parameters for the column and feed flashcalculations, and block-specific diagnostic message levels

Report Specify block-specific report options and pseudostreams


UserSubroutines Specify user subroutines for reaction kinetics, KLL calculations, traysizing and rating, and packing sizing and rating

ResultsSummary View key column results for the overall RadFrac column

Profiles View and specify column profiles


Stage Numbering

RadFrac numbers stages from the top down, starting with the condenser (orstarting with the top stage if there is no condenser).

Feed Stream Conventions

Use the Setup Streams sheet to specify the feed and product stages.

RadFrac provides three conventions for handling feed streams:• Above-Stage• On-Stage• Decanter (for three phase calculations only)


Chapter 4

(See the following figures, RadFrac Feed Convention Above-Stage and RadFracFeed Convention On-Stage.)

When the feed convention is Above-Stage, RadFrac introduces a material streambetween adjacent stages. The liquid portion flows to the stage you specify. Thevapor portion flows to the stage above. You can introduce a liquid feed to the topstage (or condenser) by specifying Stage=1. You can introduce a vapor feed to thebottom stage (or reboiler) by specifying Stage= the number of equilibrium stages+ 1. Feed convention Decanter is used only in three-phase calculations (ValidPhases=Vapor-Liquid-Liquid on the Setup Configuration sheet) involvingdecanters. You can introduce a feed directly to a decanter attached to a stageusing this convention.

n - 1

n

Mixed feedto stage n

Vapor

Liquid

RadFrac Feed Convention Above-Stage

n - 1

n

n + 1

Mixed feed tostage n

RadFrac Feed Convention On-Stage

When the Feed Convention is On-Stage, both the liquid and vapor portions of afeed flow to the stage you specify.


Columns

Columns Without Condensers or Reboilers

You can specify the column configuration on the Setup Configuration sheet.

If the column has no Then specify On sheet

Condenser None forCondenser

Setup Configuration

Reboiler None for Reboiler Setup Configuration

Reboiler Handling

RadFrac can model two reboiler types:• Kettle• Thermosyphon

A kettle reboiler is modeled as the last stage in the column on the SetupConfiguration sheet. Select Kettle for reboiler. By default, RadFrac uses a kettlereboiler. To specify the reboiler duty, enter Reboiler Duty as one of the operatingspecifications on the Setup Configuration sheet or leave it as a calculated value.

A thermosyphon reboiler is modeled as a pumparound with a heater, from and tothe bottom stage. Select Thermosyphon for Reboiler on the Setup Configurationsheet. Enter all other thermosyphon reboiler specifications on the Setup Reboilersheet.

The next figure shows the thermosyphon reboiler configuration. By default,RadFrac returns the reboiler outlet to the last stage using the On-Stage feedconvention. You can also use the Reboiler Return Feed Convention on theReboiler sheet to specify Above-Stage. This directs the vapor portion of thereboiler outlet to Stage= the number of equilibrium stages - 1.

Reboiler

Bottoms (B)

Nstage - 1

Nstage

Thermosyphon Reboiler


Chapter 4

The thermosyphon reboiler model has five related variables:• Pressure• Flow rate• Temperature• Temperature change• Vapor fraction

You must specify one of the following:• Temperature• Temperature change• Vapor fraction• Flow rate• Flow rate and temperature• Flow rate and temperature change• Flow rate and vapor fraction

If you choose an option consisting of two variables, you must specify the reboilerheat duty on the Setup Configuration sheet. RadFrac treats the value you enterfor the reboiler heat duty as an initial estimate.

The reboiler pressure is optional. If you do not enter a value, RadFrac uses thebottom stage pressure.

Heater and Cooler Specifications

You can specify interstage heaters and coolers in one of two ways:• Specifying the duty directly on the HeatersCoolers SideDuties sheet• Requesting UA calculations on the HeatersCoolers UtilityExchangers sheet

If you specify the duty directly on the HeatersCoolers SideDuties sheet, enter apositive duty for heating and a negative duty for cooling.

If you request UA calculations on the HeatersCoolers UtilityExchangers sheet,RadFrac calculates the duty and outlet temperature of the heating/cooling fluidsimultaneously with the column. The UA calculations:• Assume the stage temperature is constant• Use an arithmetic average temperature difference• Assume the heating or cooling fluid does not experience any phase change

To request UA calculations, specify the:• UA• Heating or cooling fluid component• Flow and inlet temperature of the fluid


Columns

You can specify the heat capacity of the fluid directly on the HeatersCoolersUtilityExchangers sheet or RadFrac can compute it from a property method. IfRadFrac computes the heat capacity, you must also enter the pressure and phaseof the heating or cooling fluid. By default, RadFrac calculates the heat capacityusing the block property method. But you can also use a different propertymethod.

You can also specify the heat loss for sections of the column on theHeatersCoolers HeatLoss sheet.

Decanters

For three-phase calculations (Valid Phases=Vapor-Liquid-Liquid on the SetupConfiguration sheet), you can define any number of decanters. Enter decanterspecifications on the Decanters form.

For the decanter on the top stage, you must enter the return fraction of at leastone of the two liquid phases (Fraction of 1st Liquid Returned, Fraction of 2ndLiquid Returned on the Decanters Specifications sheet). For decanters on otherstages, you must always specify both Fraction of 1st Liquid Returned andFraction of 2nd Liquid Returned.

You can enter Temperature and Degrees Subcooling on the Decanters Optionssheet to model subcooled decanters. If you do not specify Temperature andDegrees Subcooling, the decanter is operated at the temperature of the stage towhich the decanter is attached. If side product streams are decanter products,you cannot specify their flow rates. RadFrac calculates their flow rates from theFraction of 1st Liquid Returned and Fraction of 2nd Liquid Returned.

By default RadFrac returns decanter streams to the stage immediately below.You can return the decanter streams to any other stage by entering a differentReturn Stage number on the Decanters Specifications sheet. You can split areturn stream into any number of streams by giving a split fraction (SplitFraction of Total Return for the 1st Liquid and 2nd Liquid). Each resultingstream may go to a different return stage.

When return streams do not go to the next stage, a feed or pumparound must goto the next stage. This prevents dry stages.

Pumparounds

RadFrac can handle pumparounds from any stage to the same or any other stage.Use the Pumparounds form to enter all pumparound specifications.

You must enter the source and destination stage locations for pumparounds. Apumparound can be either a partial or total drawoff of the:• Stage liquid• First liquid phase


Chapter 4

• Second liquid phase• Vapor phase

You can associate a heater or cooler with a pumparound. If the pumparound is apartial drawoff of the stage flow, you must enter two of the followingspecifications:• Flow rate• Temperature• Temperature change• Vapor fraction• Heat Duty

If the pumparound is a total drawoff, you must enter one of the followingspecifications:• Temperature• Temperature change• Vapor fraction• Heat Duty

Vapor fraction is allowed only when Valid Phases=Vapor-Liquid orVapor-Liquid-Liquid.

Use the Pumparounds Specifications sheet to enter these operatingspecifications.

Pressure specification is optional. The default pumparound pressure is the sameas the source stage pressure. RadFrac assumes that the pumparound at theheater/cooler outlet has the same phase condition as the pumparound at theinlet. You can override the phase condition using the Valid phases field onPumparound Specifications sheet.

RadFrac can return the pumparound to a stage using either the:• On-stage option• Above-stage option (returns the pumparound to the column between two

stages)

In three-phase columns, RadFrac can also return the pumparound to a decanterassociated with a stage. You can select above-stage using the Return option field.

RadFrac assumes the pumparound at the heater/cooler outlet has the samephase condition as the inlet.

You can use Return-Phase on the Pumparounds Specifications sheet to assign adifferent phase at the heater/cooler outlet. Or you can specify ValidPhases=VaporLiquid or Vapor-Liquid-Liquid and let RadFrac determine thereturn phase condition from the heater/cooler specifications.


Columns

Free-Water and Rigorous Three-Phase CalculationsRadFrac can perform both free-water and rigorous three-phase calculations. (SeeASPEN PLUS Physical Property Methods and Models, Chapter 6.) Thesecalculations are controlled by options you specify on the Setup Configuration sheet.

You can select from three types of calculations:• Free water in the condenser only• Free water on any or all stages• Rigorous three-phase calculations

When you choose free-water calculations in the condenser, only free water can bedecanted from the condenser. You cannot use nonideal for the Overall Loopconvergence method.

Specify one of the following on the Setup Configuration sheet:

Valid Phases= On Sheet For

Vapor-Liquid-FreeWaterCondenser SetupConfiguration

Free water in the condenser only

Vapor-Liquid-FreeWaterAnyStage SetupConfiguration

Free water on all stages

Vapor-Liquid-Liquid SetupConfiguration

Rigorous three-phase calculations

For RadFrac calculations, you must also specify which stages to test for twoliquid phases on the Setup 3-Phase sheet.

When you choose completely rigorous three-phase calculations on all stagesselected, RadFrac makes no assumptions about the nature of the two liquidphases. You can associate a decanter with any stage. You cannot use Sum-Ratesfor the Overall Loop convergence method.

EfficienciesYou can specify one of two types of efficiencies:• Vaporization• Murphree

Vaporization efficiency is defined as:

Effy

K xiv i j

i j i j

= ,

, ,


Chapter 4

Murphree efficiency is defined as:

Effy y

K x yi jM i j i j

k j i j i j,

, ,

, , ,

=− +

− +

1

1

Where:

K = Equilibrium K value

x = Liquid mole fraction

y = Vapor mole fraction

Eff v = Vaporization efficiency

Eff M = Murphree efficiency

i = Component index

j = Stage index

To specify vaporization or Murphree efficiencies, enter the number of actualstages on the Setup Configuration sheet. Then use the Efficiencies form to enterthe efficiencies.

For three-phase calculations, the vaporization and Murphree efficiencies youenter apply equally to the following equilibrium by default:• Vapor-liquid1 (VL1E)• Vapor-liquid2 (VL2E)

You can use the Efficiencies form to enter separate efficiencies for VL1E andVL2E. You cannot enter separate efficiencies for VL1E and VL2E when youspecify equilibrium reactions or when using Murphree efficiencies.

You can use any of these efficiencies to account for departure from equilibrium.But you cannot convert from one efficiency to the other. Magnitudes of theefficiencies can be quite different. You should manipulate the Murphreeefficiency to match the operating data when:• Efficiency is unknown• Actual column operating data are available

When manipulating the Murphree efficiency, use design specifications on theDesignSpecs and Vary forms. Details on using and estimating efficiencies aredescribed by Holland, Fundamentals of Multi-Component Distillation, McGraw-Hill Book Company, 1981.


Columns

AlgorithmsYou can select an algorithm and/or initialization option for column simulation onthe Convergence Basic sheet. The default standard algorithm and standardinitialization option are appropriate for most applications. You can improveconvergence behavior for the following applications using the guidelines describedin this section:• Petroleum and Petrochemical Applications• Highly Nonideal Systems• Azeotropic Distillation• Absorbers and Strippers• Cryogenic Applications

To change the algorithm and initialization option on the Convergence Basicsheet, you must first choose Custom as the option in the Convergence field on theSetup Configuration sheet.

Petroleum and Petrochemical Applications

In petroleum and petrochemical applications involving extremely wide-boilingmixtures and/or many components and design specifications, you can improve theconvergence efficiency and reliability by choosing Sum-Rates in the Algorithm fieldon the Convergence Basic sheet.

Highly Nonideal Systems

When liquid phase nonidealities are exceptionally strong, choose Nonideal in theAlgorithm field on the Convergence Basic sheet to improve the convergencebehavior. Use this algorithm only when the number of outside loop iterations(using the standard algorithm) exceeds 25.

You can also use the Newton algorithm for highly nonideal systems. Newton isbetter for columns with highly sensitive specifications. But it is usually slower,especially for columns with many stages and components.

Azeotropic Distillation

For azeotropic distillation applications where an entraining agent separates anazeotropic mixture, specify the following on the Convergence Basic sheet:• Algorithm, Newton• Initialization method, Azeotropic

A classic example of azeotropic distillation is ethanol dehydration using benzene.


Chapter 4

Absorbers and Strippers

To model absorbers and strippers, specify Condenser=None and Reboiler=None onthe Setup Configuration sheet. The heat duty is zero for adiabatic operation. Forextremely wide-boiling mixtures, specify one of the following:• Algorithm=Sum-Rates on the Convergence Basic sheet• Convergence=Standard on the Setup Configuration sheet and choose

Absorber=Yes on the Convergence Basic sheet

Cryogenic Applications

For cryogenic applications such as air separation, the standard algorithm isrecommended. To invoke a special initialization procedure designed for cryogenicsystems, specify Cryogenic for Initialization on the Convergence Basic sheet.

Rating ModeRadFrac allows the column to be operated in a rating mode or a design mode.Rating mode requires different column specifications for two- and three-phasecalculations.

For two-phase calculations, you must enter the following on the Setup Form:• Valid Phases=Vapor-Liquid or Vapor-Liquid-FreeWaterCondenser for

handling free water in condenser• A Total, Subcooled, or Partial-Vapor condenser• Two additional column operating variables

If the condenser or reflux is subcooled, you can also specify the degreessubcooling or the subcooled temperature.

For three-phase calculations, you must specify Valid Phases= Vapor-Liquid-Liquid or Vapor-Liquid-FreeWaterAnyStage (for free water calculations) on theSetup Configuration sheet. The required specifications depend on what youspecify for the return fractions of the two liquid phases (Fraction of 1st LiquidReturned and Fraction of 2nd Liquid Returned) in the top stage decanter. Thefollowing table lists the three specification options:

If you specified this onDecanters Specifications Enter on Setup Configuration

Fraction of 1st Liquid Returned or Fractionof 2nd Liquid Returned, or no top decanter

A Total, Subcooled, or Partial-Vapor condenser and two operatingspecifications

Fraction of 1st Liquid Returned andFraction of 2nd Liquid Returned

A Total, Subcooled, or Partial-Vapor condenser and one operatingspecification

Fraction of 1st Liquid Returned andFraction of 2nd Liquid Returned

Two operating specifications, and an estimate for the amount of vapor in thedistillate on the Estimates Vapor Composition sheet. RadFrac assumes apartial condenser with both vapor and liquid distillates.


Columns

Design ModeRadFrac allows the column to be operated in rating mode or design mode. In designmode, use the DesignSpecs form to specify column performance parameters (suchas purity or recovery). You must indicate which variables to manipulate to achievethese specifications. You can manipulate any variables that are allowed in ratingmode, except:• Number of stages• Pressure profile• Vaporization efficiency• Subcooled reflux temperature• Degrees of subcooling• Decanter temperature and pressure• Locations of feeds, products, heaters, pumparounds, and decanters• Pressures of thermosyphon reboiler and pumparounds• UA specifications for heaters

The flow rates of inlet material streams and the duties of inlet heat streams canalso be manipulated variables.

These are the design specifications:

You can specify For any

Purity Stream including internal streams†

Recovery of any components groups Set of product streams, including sidestreams ††

Flow rate of any components groups Internal stream or set of product streams

Temperature Stage

Value of any Prop-Set property Internal or product stream †††

Ratio or difference of any pair ofProp-Set properties

Single or paired internal or product streams

Flow ratio of any components groups to anyother component groups

Internal streams to any other internal streams, or to any set of feed or productstreams

†Express the purity as the sum of mole, mass, or standard liquid volume fractions of any group ofcomponents relative to any other group of components .

††Express recovery as a fraction of the same components in any set of feed streams.

†††See ASPEN PLUS User Guide.


Chapter 4

Reactive DistillationRadFrac can handle chemical reactions. These reactions can occur in the liquidand/or vapor phase. The details about the reactions are entered on a genericReactions form outside RadFrac. RadFrac allows two different reaction modeltypes: REAC-DIST or USER. RadFrac can model the following types of reactions:• Equilibrium-controlled• Rate-controlled• Conversion• Electrolytic

RadFrac can also model salt precipitation, especially in the case of electrolyticsystems. You can request reaction calculations for the entire column, or you canrestrict reactions to a certain column segment (for example, to model thepresence of catalyst). For three-phase calculations, you can restrict reactions toone of the two liquid phases, or use separate reaction kinetics for the two liquidphases.

To include reactions in RadFrac you must enter the following information on theReactions Specifications sheet:• Reaction type and Reaction/Chemistry ID• Column section in which the reactions occur

Depending on the reaction type, you must enter equilibrium constant, kinetic, orconversion parameters on the generic Reactions form outside RadFrac. Forelectrolytic reactions, you can also enter the reaction data on the ReactionsChemistry form outside RadFrac. To consider salt precipitation, enter the saltprecipitation parameters on the Reactions Salt sheet or the Reactions Chemistryform outside RadFrac.

To associate reactions and salt precipitation with a column segment, enter thecorresponding Reactions ID (or Chemistry ID) on the Reactions Specificationssheet.

For rate-controlled reactions, you must enter holdup or residence time data inthe phase where the reactions occur. Use the Reactions Holdups or ResidenceTimes sheets. For conversion reactions, use the Reactions Conversion sheet tooverride the conversion parameters specified on the Reactions Conversion form.RadFrac also supports User Reaction Subroutine. The name and other details ofthe reaction subroutine are entered on the UserSubroutines form.

Solution StrategiesRadFrac uses two general approaches for column convergence:• Inside-out• Napthali-Sandholm


Columns

The standard, sum-rates, and nonideal algorithms are variants of the inside-outapproach. The MultiFrac, PetroFrac, and Extract models also use this approach.The Newton algorithm uses the classical Napthali-Sandholm approach. Use theConvergence form to select the algorithm and specify the associated parameters.

Inside-Out Algorithms

The inside-out algorithms consist of two nested iteration loops.

The K-value and enthalpy models you specify are evaluated only in the outsideloop to determine parameters of simplified local models. When using nonideal,algorithm RadFrac introduces a composition dependence into the local models.The local model parameters are the outside loop iteration variables. The outsideloop is converged when the changes of the outside loop iteration variables aresufficiently small from one iteration to the next. Convergence uses a combinationof the bounded Wegstein method and the Broyden quasi-Newton method forselected variables.

In the inside loop, the basic describing equations (component mass balances,total mass balance, enthalpy balance, and phase equilibrium) are expressed interms of the local physical property models. RadFrac solves these equations toobtain updated temperature and composition profiles. Convergence uses one ofthe following methods:• Bounded Wegstein• Broyden quasi-Newton• Schubert quasi-Newton• Newton

RadFrac adjusts the inside loop convergence tolerance with each outside loopiteration. The tolerance becomes tighter as the outside loop converges.

Newton Algorithm

The Newton algorithm solves column-describing equations simultaneously, usingNewton’s method. The convergence is stabilized using the dogleg strategy ofPowell. Design specifications may be solved either simultaneously with the column-describing equations or in an outer loop.

Design Mode Convergence

RadFrac provides two methods for handling design specification convergence:• Nested convergence• Simultaneous convergence


Chapter 4

Nested Design Spec Convergence (for all algorithmsexcept SUM-RATES)

The Nested Middle Loop convergence method attempts to satisfy the designspecifications by determining the values of the manipulated variables (withintheir bounds) that minimize the weighted sum of squares function:

Φ = −

∑∧

WmG m GM

Gm m*

2

Where:

m = Design specification number

G∧

= Calculated value

G = Desired value

G* = Scaling factor

w = Weighting factor

The algorithm that manipulates the variables to minimize Φ does not depend onmatching particular variables with corresponding design specifications. Youshould carefully select the manipulated variables and design specifications. Makesure that each manipulated variable has a significant effect on at least onedesign specification.

The number of design specifications must be equal to or greater than the numberof manipulated variables. If there are more design specifications thanmanipulated variables, assign weighting factors to reflect the relative importanceof the specifications. The larger the weighting factor, the more nearly aspecification will be satisfied. Scale factors normalize the errors, so that differentspecification types are compared on a consistent basis.

When a value of a manipulated variable reaches a bound, that bound is active. Ifa problem has no active bounds and the same number of manipulated variablesas design specifications, then Φ will approach zero (within some tolerance) whenall specifications are satisfied.

If there are active bounds or more design specifications than manipulatedvariables, RadFrac minimizes Φ . The weighting factors determine the relativedegree to which the design specifications are satisfied.


Columns

Simultaneous Design Spec Convergence (forAlgorithm=SUM-RATES, NEWTON)

The Simultaneous Middle Loop convergence method algorithm solves the designspecification functions simultaneously with the column-describing equations:

FmG m GM

Gm

=−

=∧

* 0

Because the Simultaneous Middle Loop convergence method uses an equation-solving approach, there must be an equal number of design specifications andmanipulated variables. In the nested method, no coupling is assumed betweendesign specifications and manipulated variables. However, each designspecification must be significantly affected by at least one manipulated variable.Bounds and weighting factors are not used. In general, the Simultaneous methodgives better performance if all the specifications are feasible.

Physical PropertiesTo override the global physical property method, use the PropertiesPropertySections sheet. You can specify different physical properties for differentparts of the column.

For three-phase calculations, you can specify separate calculation methods forVapor-Liquid1 Equilibrium (VL1E) and Liquid1-Liquid2 Equilibrium (LLE). Useone of the following methods:• Associate separate property methods with VL1E and LLE using the Phase

Equilibrium list box• Calculate VL1E using a property method. Specify LLE using liquid-liquid

distribution (KLL) coefficients

You can use the Properties KLLSections sheet to enter the KLL coefficients usinga built-in temperature polynomial, and associate the coefficients with one ormore column segments. Or you can use the Properties KLLCorrelations sheet toassociate a user-KLL subroutine with one or more column segments.

Solids HandlingRadFrac has two methods for handling inert solids:• Overall-balance• Stage-by-stage


Chapter 4

Use the Solids handling option on the Convergence Basic sheet to select either anoverall balance or stage-by-stage. The two methods differ in how they treat solidsin the mass and energy balances. Neither method considers inert solids in thephase equilibrium calculations. However, salts formed by salt precipitationreactions (see Reactive Distillation) are considered in phase equilibriumcalculations.

The overall-balance method:• Temporarily removes all solids from inlet streams• Performs column calculations without solids• Adiabatically mixes solids removed from inlet streams with liquid product

from the bottom stage

The overall-balance method maintains an overall mass and energy balancearound the column. But it does not satisfy individual stage balances. This is thedefault method.

The stage-by-stage method treats solids rigorously in all stage mass and energybalances. The ratio of liquids to solids on a stage is maintained in the productstreams withdrawn from that stage. The specified product flow is the total flowrate of the stream, including the solids. If a nonconventional (NC) solidssubstream is present in the column feeds, you must give all column flow and flowratio specifications on a mass basis.

When you specify a decanter, RadFrac can decant the solids partially or totally.By default, RadFrac decants the solids partially along with the second liquidphase. RadFrac uses the return fraction you specify for the second liquid phase(Fraction of 2nd Liquid Returned on the Decanters Specifications sheet) to decantthe solids. If there is no second liquid phase in the decanter, RadFrac decants thesolids partially along with the first liquid phase. RadFrac uses the returnfraction you specify for the first liquid phase (Fraction of 2nd Liquid Returned onthe Decanters Specifications sheet) in this case. You can request completedecanting of the solids by selecting Decant Solids Totally on the DecantersOptions sheet.


Columns

MultiFracRigorous Fractionation

MultiFrac is a rigorous model for simulating general systems of interlinkedmultistage fractionation units. MultiFrac models can handle a complexconfiguration consisting of:• Any number of columns, each with any number of stages• Any number of connections between columns or within each column• Arbitrary flow splitting and mixing of connecting streams

MultiFrac can handle operations with:• Side strippers• Pumparounds• External heat exchangers• Single-stage flashes• Feed furnace

Typical MultiFrac applications include:• Heat-interstaged columns, such as Petlyuk towers• Air separation column systems• Absorber/stripper combinations• Ethylene plant primary fractionator/quench tower combinations

You can also use MultiFrac for petroleum refining fractionation units such asatmospheric crude units and vacuum units. But for these applications, PetroFracis more convenient to use. Use MultiFrac only when the configuration is beyondthe capabilities of PetroFrac.

MultiFrac can detect a free-water phase in the condenser or anywhere in thecolumn. It can decant the free-water phase on any stage.

Although MultiFrac assumes equilibrium stage calculations, you can specifyeither Murphree or vaporization efficiencies.

You can use MultiFrac for both sizing and rating trays and packings. MultiFraccan model both random and structured packings.


Chapter 4

Flowsheet Connectivity for MultiFrac

Nstage

Top Stage or Condenser

Heat Duty (optional)

Feeds

Heat

Heat

Heat (optional)

Vapor Distillate

Side Products (optional)

Interconnecting Streams (Heater Optional)

Bottoms (or InterconnectingStream)

Liquid Distillate (optional)

Water Distillate (optional)

Pumparoundsand Bypasses

(Heater Optional)

Bottom Stage or Reboiler Heat Duty

(optional)


Heat (optional)

Top Stage or Condenser

Heat Duty (optional)

Feeds

Heat

Heat

Heat (optional)

Vapor Distilate

Side Products (optional)


Bottoms (or InterconnectingStream)

Liquid Distillate (optional)

Water Distillate (optional)


(Heater Optional)

Bottom Stage or Reboiler Heat Duty

(optional)


Heat (optional)

Reflux

1

1

Nstage

Nstage


Columns


Outlet Any number of optional pseudo-product streamsUp to three optional outlet material streams per stage (one vapor, oneliquid, and one free water)

You can connect any number of columns by any number of connecting streams. Foreach column, any number of connecting streams can represent pumparounds andbypasses. These streams can flow between any two stages, or to the same stage.Each connecting stream can have an associated heater.

Each column must have one liquid product or connecting stream leaving thebottom stage. The top stage of the main column (column 1) must have a productstream, which cannot be a connecting stream. The top stage of the other columns(column 2, 3, ...) must have a vapor product or a vapor connecting stream.

The pseudoproduct streams represent column internal flows and connectingstream flows.

Heat StreamsInlet One inlet heat stream per stage (optional)

One inlet heat stream per connecting stream (optional)

Outlet One outlet heat stream per connecting stream (optional)

MultiFrac uses an inlet heat stream as a duty specification for all stages except thecondenser, reboiler, and connecting streams. If you do not provide two columnoperating specifications on the Columns Setup Configuration sheet, MultiFrac usesa heat stream as a specification for the condenser and reboiler.

If you do not provide two specifications on the ConnectStreams form, MultiFracuses a heat stream as a specification for connecting streams.

If you provide two specifications on the Columns Setup Configuration sheet orConnectStreams form, MultiFrac does not use the inlet heat stream as aspecification. The inlet heat stream supplies the required heating or cooling.

You can use optional outlet heat streams for the net heat duty of the condenser,reboiler, and connecting streams. The value of the outlet heat stream equals thevalue of the inlet heat stream (if any), minus the actual (calculated) heat duty.


Chapter 4

Specifying MultiFracIndividual columns are identified by column numbers. The numbering order doesnot affect algorithm performance. Column 1 has different specifications from theother columns. Within each column, the stages are numbered from the top down,starting with the condenser.

Use the following forms to enter specifications and view results for MultiFrac:


Columns Setup Specify basic column configuration and operating conditions

Columns HeatersCoolers Specify interstage heaters/coolers

Columns FlowSpecs Specify liquid and vapor flow specifications

Columns Efficiencies Specify stage or component efficiencies

Columns Properties Specify physical property parameters for column sections

Columns Estimates Specify initial estimates for stage temperatures, and vapor and liquid flows andcompositions

Columns Results View column summary

Columns Profiles View column profiles

InletsOutlets Specify inlet and outlet material and heat stream locations

ConnectStreams Specify sources and destinations of connecting material and heat streams, view connectingstream results

FlowRatios Specify stream flow ratios

DesignSpecs Specify design specifications, and view convergence results


CondenserHcurves Specify condenser heating or cooling curve tables and view tabular results

ReboilerHCurves Specify reboiler heating or cooling curve tables and view tabular results

ConnectStreamHCurves Specify connecting stream heating or cooling curve tables and view tabular results

TraySizing Specify sizing parameters for tray column sections, and view results

TrayRating Specify rating parameters for tray column sections, and view results

PackSizing Specify sizing parameters for packed column sections, and view results

PackRating Specify rating parameters for packed column sections, and view results

Convergence Specify convergence parameters for column calculations, and block-specific diagnosticmessage levels

Report Specify block-specific report options and pseudostream information


UserSubroutines Specify user subroutine parameters for tray sizing and rating, and packing sizing and rating

ResultsSummary View results of balances and splits


Columns

Stream Definitions

MultiFrac uses four types of streams:• External streams• Connecting streams• Internal streams• Pseudostreams

External streams are standard MultiFrac inlet and outlet streams. They areidentified by stream IDs.

Connecting streams are within MultiFrac but external to individual columns.They can connect two columns, or stages of the same column (bypasses andpumparounds). You can associate a heater with any connecting stream.Connecting stream heaters are identified by connecting stream numbers.

Internal streams are liquid or vapor flows between adjacent stages of the samecolumn. An internal stream is identified by a source stage number and a columnnumber.

Pseudostreams store the results of internal and connecting streams. They are asubset of external outlet streams. Unlike normal outlet streams, pseudostreamsdo not participate in block mass balance calculations.

Required Specifications

Follow these guidelines when entering specifications for column 1:• The number of stages must be greater than 1• Two additional operating specifications are required• The distillate flow may not be a connecting stream

You must specify:• Bottoms rate or distillate rate. The distillate rate includes both the vapor and

liquid distillate flows• Either condenser duty, reboiler duty, reflux ratio or reflux rate• Distillate vapor fraction or condenser temperature

If you specify the condenser stage temperature:• Both liquid and vapor distillate products must be present (distillate vapor

fraction is greater than 0 or less than 1)• You must also specify an estimate for the distillate vapor fraction


Chapter 4

Follow these guidelines when entering specifications for other columns:• The number of stages can be 1 (for example, to model a single-stage flash or

feed furnace)• The distillate can be a connecting stream• MultiFrac calculates the distillate vapor fraction• The distillate rate includes only the vapor distillate flow and must be greater

than zero. If a liquid distillate is present, specify flow on the InletsOutletsform.

For columns with more than one stage, you may specify condenser duty, reboilerduty, bottoms rate, distillate rate, and reflux rate.

For columns with one stage, you must specify either:• Bottoms rate• Distillate rate (includes only the vapor distillate)• Condenser duty

Feed Stream Conventions

MultiFrac provides two conventions for handling feed streams (see MultiFrac FeedConvention Above-Stage and MultiFrac Feed Convention On-Stage in the followingfigures):• Above-Stage• On-Stage

When Feed-Convention is Above-Stage, MultiFrac introduces a material streambetween adjacent stages. The liquid portion flows to the stage (n) you specify. Thevapor portion flows to the stage above (n – 1). You can introduce a liquid feed tothe top stage (or condenser) by specifying Stage=1. You can introduce a vaporfeed to the bottom stage (or reboiler) by specifying Stage=Number of stages + 1.

Vapor

Liquid

n - 1


MultiFrac Feed Convention Above-Stage


Columns

n - 1

n + 1

nMixed feed to stage n

MultiFrac Feed Convention On-Stage

When Feed-Convention is On-Stage, both the liquid and vapor portions of a feedflow to the stage (n) you specify.

Connecting Streams

MultiFrac allows any number of connecting streams. Any number of these streamscan have the same:• Source column, stage, and phase• Destination column and stage

MultiFrac introduces connecting streams on the destination stage regardless oftheir phase (that is, Feed Convention=On-Stage). All connecting streams canhave a heater with heat duty, temperature, or temperature change specified. Usethe ConnectStreams form to enter all specifications for connecting streams.

Each terminal stream can be the source of a product stream and any number ofconnecting streams. If there is no product stream, at least one connecting streammust have an unspecified flow.

For a connecting stream, required specifications depend on whether the stream:• Has a flow rate that is fixed indirectly on the FlowRatios or Columns

FlowSpecs form• Is a terminal stream• Is a pumparound to the top stage of column 1


Chapter 4

For this type of connectingstream You must specify

One that does not satisfy theabove conditions

Two of the following: flow, temperature (or temperature change), and duty†

One whose flow is fixedindirectly on the FlowRatios orColumns FlowSpecs form

Either temperature (or temperature change), or duty†

A terminal stream (vapordistillate or liquid bottoms)

Either temperature (or temperature change) or duty†

†Duty can default to 0 if necessary.

You can enter a second specification. If this specification is missing, MultiFracuses the net flow from the stage excluding any other connecting stream with flowspecifications.

For a connecting stream that is the liquid pumparound to the top stage of column1, enter two of the following:• Flow• Temperature (or temperature change)• Duty (specify 0 if there is no associated heater or cooler)

If you enter only one of flow, temperature, or temperature change, MultiFracuses the top stage duty for the missing requirement.

When a stage is the destination of a connecting stream, MultiFrac uses the heatduty associated with the stage to determine the temperature of the connectingstream. When you enter the duty, temperature, or temperature change of theconnecting stream, the stage duty does not affect the connecting streamtemperature. Stage duty is properly accounted for in the stage enthalpycalculations.

When a pumparound, bypass, or other connecting stream has a specifiedtemperature change or outlet temperature, MultiFrac assumes that the specificvalue does not result in a phase change of any fraction of the stream. When youspecify heat duty, a phase change may occur.

Connecting streams can be either a total or partial drawoff of the stage flow.MultiFrac determines the drawoff type based on the number of specifications yougive.

If the drawoff type is You enter

Partial Two of the following: flow, temperature, temperature change, and heat duty†

Total One of the following: temperature, temperature change, and heat duty††

†Enter zero for heat duty if heater is absent.

††Flow rate is taken as the net flow of the stage, excluding any product flow and any other connectingstream flow.


Columns

MultiFrac allows total drawoff only for the top vapor stream and bottom liquidstream. For partial drawoffs you can specify the flow rate. Or MultiFrac candetermine the flow rate based on one of the following:• Another flow specification (Columns FlowSpecs form)• A flow ratio specification (FlowRatios form)

If you enter only one specification for pumparounds to the top stage of the maincolumn, MultiFrac uses the top stage heat duty as the second specification.

When a connecting stream has a specified temperature or temperature change,MultiFrac assumes the specified value does not result in a phase change of anyfraction of the stream. When you specify the heat duty, a phase change can occur.

Heaters

Use the Columns HeatersCoolers form to enter heater stage locations and duties.You can specify heaters indirectly by choosing a heater duty as the adjustedvariable in one of the following forms:

Form Used to specify

Columns FlowSpecs Stage liquid or vapor flow rate

FlowRatios Vapor-to-liquid flow ratio

Flow Rate Specifications

You can use the Columns FlowSpecs form to specify any stage liquid and vaporflow rates. The value you specify refers to the net flow of the stage liquid or vaporflow. This value excludes any portions withdrawn by side products and otherconnecting streams with flow specifications. This feature is typically used forspecifying:• Internal reflux rate or total internal drawoff• Overflash in refining applications• Boilup rate

For a terminal stream, flow specifications refer to the net flow of the streamexcluding any portion withdrawn by connecting streams with flow specifications.Flow specifications include:• Specifications provided on the ConnectStreams form• Specifications fixed by the associated heater specifications• Another FlowSpecs or FlowRatios specification

For an internal stream, flow specifications refer to the net flow of the streamexcluding any portions withdrawn as products or connecting streams.


Chapter 4

When you enter a flow specification, MultiFrac adjusts the flow rate of aconnecting stream or the duty of a heater.

If the adjusted variable is You enter the

A connecting stream flow Connecting stream number in the IC-Stream field

A heater duty Heater column and stage numbers

You can place the calculated heat duty in an outlet heat stream using theInletsOutlets form. Initial estimates for adjusted variables are not required.

If a product or connecting stream of the same phase is leaving the stage, aspecified value may be zero to model a total drawoff .

MultiFrac will vary the heat duty associated with the heater of the same stage oranother stage or the flow rate of an associated connecting stream to satisfyenthalpy and mass balances.

If this will be varied You must specify

Heat duty Q-Column and Stage

Flow rate of a connectingstream

Stream number (IC-Stream)

Be cautious when selecting the:• Associated stage with varied heat duty• Connecting stream with varied flow rate

An initial guess for the associated heat duty is not required.


Columns

Flow Ratio Specifications

Use the FlowRatios form to specify the ratio of two flow rates. The flows can be ofdifferent phases, and come from any stage of any column. This feature is typicallyused for specifying the:• Internal reflux ratio• Overflash in refining applications• Boilup ratio

For a terminal stream, the flows refer to the net flow of a stream, excluding anyportion withdrawn by connecting streams with flow specifications. Flowspecifications include those:• Specified on the ConnectStreams form• Fixed by either the associated heater specification, another Columns

FlowSpecs sheet, or a FlowRatios Specifications sheet)

For an internal stream, the flows refer to the net flow of the stream, excludingany portion withdrawn as products or connecting streams. When you specify aflow ratio, these will be varied to satisfy enthalpy and mass balances:• Heat duty of the same stage or another stage• Flow rate of an associated connecting stream

When you enter a flow ratio specification, MultiFrac adjusts the flow rate of aconnecting stream or the duty of a heater.

If the adjusted variable is You enter the

A connecting stream flow Connecting stream number in the IC-Stream field

A heater duty Heater column and stage numbers

You can place the calculated heat duty in an outlet heat stream using theInletsOutlets form. Initial estimates for these adjusted variables are notrequired.

Be cautious when selecting the:• Associated stage with varied heat duty• Connecting stream with varied flow rate


Chapter 4



Effy

K xiv i j

i j i j

= ,

, ,


Effy y

K x yi jM i j i j

i j i j i j,

, ,

, , ,

=−

−+

+

1

1

Where:






i = Component index

j = Stage index

To specify vaporization or Murphree efficiencies, enter the number of actualstages on the Columns Setup Configuration sheet. Then use the ColumnsEfficiencies form to enter the efficiencies.

You can use any of these efficiencies to account for departure from equilibrium.But you cannot convert from one efficiency to the other. Magnitudes of theefficiencies can be quite different. Details on using and estimating theseefficiencies are described by Holland, Fundamentals of Multi-ComponentDistillation, McGraw-Hill Book Company, 1981.


Columns

AlgorithmsMultiFrac has three convergence algorithms. Use the Overall field on theConvergence Methods sheet to select the algorithm. The default standardalgorithm is appropriate for most applications. Your choice of algorithm dependson the types of systems you are modeling:

Application Algorithm

Air separation Standard

Close-boiling, e.g., C3 splitter Standard

Wide-boiling, e.g., absorbers Sum-Rates

Petroleum refining, e.g., crude unit Sum-Rates

Ethylene plant primary fractionator Sum-Rates

Highly-nonideal, e.g., azeotropic Newton

Highly-coupled design specifications Sum-rates or Newton

Rating ModeIn rating mode, MultiFrac calculates column profiles and product compositionsbased on specified values of column parameters. Examples of column parametersare reflux ratio, reboiler duties, and feed flow rates.

Design ModeIn design mode, use the DesignSpecs form to specify column performanceparameters (such as purity or recovery). You must indicate which variables tomanipulate to achieve these specifications using the Vary form. You can specifyany variables that are allowed in rating mode, except:• Number of stages• Pressure profile• Efficiencies• Subcooled reflux temperature• Degrees of subcooling• Locations of feeds, products, heaters, and connecting streams


Chapter 4

The flow rates of inlet material streams and the duties of inlet heat streams canalso be manipulated variables.


Purity Stream, including an internal stream†

Recovery of any component groups Set of product streams††

Flow rate of any component groups Internal stream or set of product streams

Temperature Stage

Heat duty Stage or connecting stream

Heat duty ratio Stage or connecting stream to any other stage or connecting stream

Value of any Prop-Set property Internal or product stream†††

Ratio or difference of any pair of properties ina Prop-Set

Single or paired internal or product stream

Flow ratio of any component groups to anyother component groups

First group can be in any internal streams††††

†Express the purity as the sum of mole, mass, or standard liquid volume fractions of any group ofcomponents, relative to any other group of components.

††You can express recovery as a fraction of the same components in a subset of the feed stream.

†††See ASPEN PLUS User Guide.

††††The second group can be in any other internal streams, or set of feed or product streams.

Column ConvergenceMultiFrac uses the inside-out approach for column convergence. You can choosefrom two algorithm variants of this approach:• Standard• Sum-rates

To select an algorithm, use the Overall field on the Convergence Methods sheet.

The standard algorithm uses the standard inside-out formulation for the insideloop. It uses either the nested or simultaneous approach (specified as the Middleloop method on the Convergence Methods sheet) to converge the designspecifications. This algorithm is appropriate for most systems.

The sum-rates algorithm uses:• A sum-rates variant formulation for the inside loop• The simultaneous approach to converge the design specifications


Columns

Sum-rates is well suited for:• Wide-boiling systems• Columns with steep flow gradients

MultiFrac also has the Newton algorithm, which uses a Napthali-Sandholmformulation. It solves the column-describing equations and design specificationssimultaneously, using Newton’s method. This method can enhance convergencefor highly-nonideal systems, such as azeotropic distillation. The Newtonalgorithm is generally slower than the other algorithms.

Design Specification Convergence

MultiFrac provides two methods for handling design specification convergence:• Nested middle loop• Simult middle loop

When you use the nested middle loop method, the algorithm attempts to satisfythe design specifications by determining the values of the manipulated variables(within their bounds) that minimize the weighted sum of squares function:

Φ = −

∑

mmw

G G

G

^

**

2

Where:


$G = Calculated value

G = Desired value

G** = Scaling factor


For purity and recovery, $G and G are transformed by taking the logarithm, andG** is taken as unity.

When you use the simult middle loop method, the following algorithm solves thedesign specification functions simultaneously with the column describingequations:

( )F G G Gm m m m= − =$ / ** 0


Chapter 4

The weighting factor is not available for this method.

You can handle design specification convergence by using either scaling factors orweighting factors. The following algorithm attempts to satisfy designspecifications by determining the values of the manipulated variables (withintheir bounds) that minimize the weighted sum of squares function:

Φ = −

∑

mmw

G G

G

$**

2

Where:


$G = Calculated value

G = Desired value

G** = Scaling factor


Initialization

Use Initialization Method on the Convergence Methods sheet to choose theinitialization method.

MultiFrac has two initialization procedures:• Standard• Crude

Standard is appropriate for most systems. You must enter at least the top andbottom temperature estimates for each column.

Crude invokes a special initialization procedure designed for petroleum refiningand ethylene plant primary fractionator/quench tower applications. Thisprocedure is designed for systems consisting of a main column connected to anynumber of sidestrippers. If you specify the following information on the ColumnsSetup and/or Columns FlowSpecs forms, you do not need to provide estimates:• All stripper bottoms flow rates• Either the distillate or bottoms flow rate of the main column

Otherwise, you must enter at least the top and bottom temperature estimates foreach column. You may enter profile estimates on the Columns Estimates form toenhance convergence. Temperature estimates are usually adequate. Highlynonideal systems may require composition estimates.


Columns

Physical PropertiesUse the BlockOptions form to override the global physical property method. Youcan specify a single property method on the BlockOptions form. MultiFrac uses thisproperty method for all stages in all columns.

Use the Columns Properties form to specify physical property methods when youuse a separate property method for an individual column. You can also split acolumn into any number of segments, each using a different property methods.

Free Water HandlingMultiFrac can perform free-water calculations. By default, MultiFrac performsfree-water calculations for the main column condenser. The free-water phase, ifpresent, is decanted.

Use the Columns Properties form to request free-water calculations foradditional stages in any column. You can define additional water decant productstreams on the InletsOutlets form. You can use this capability to simulate theprimary fractionator/quench tower combination of an ethylene plant.

Solids HandlingMultiFrac handles solids by:• Temporarily removing all solids from inlet streams• Performing calculations without solids• Adiabatically mixing solids removed from inlet streams with main column

liquid bottoms

This calculation approach maintains an overall mass and energy balance aroundthe MultiFrac block. But the bottom stage liquid product will not be in exactthermal or phase equilibrium with other bottom stage flows (for example, thebottom stage vapor flow).


Chapter 4

Sizing and Rating of Trays and PackingsMultiFrac has extensive capability to size, rate, and perform pressure dropcalculations for trayed and packed columns. Use the following forms to enterspecifications:• TraySizing• TrayRating• PackSizing• PackRating

See Appendix A for details on tray and packing types and correlations.


Columns

PetroFracRigorous Fractionation

PetroFrac is a rigorous model designed for simulating all types of complex vapor-liquid fractionation operations in the petroleum refining industry. Typicaloperations include:• Preflash tower• Atmospheric crude unit• Vacuum unit• Catalytic cracker main fractionator• Delayed coker main fractionator• Vacuum lube fractionator

You also can use PetroFrac to model the primary fractionator/quench towercombination in the quench section of an ethylene plant. PetroFrac can detect afree-water phase in the condenser or anywhere in the column. It can decant thefree-water phase on any stage. Although PetroFrac assumes equilibrium stagecalculations, you can specify either Murphree or vaporization efficiencies. Youcan use PetroFrac to size and rate columns consisting of trays and/or packings.PetroFrac can model both random and structured packings.


Chapter 4

Flowsheet Connectivity for PetroFrac

PetroFrac models column configurations consisting of a main column with anynumber of pumparounds and side strippers. You can specify a feed furnace. Forsingle columns without pumparounds and side strippers, use RadFrac. For othermulticolumn systems such as air separation systems, Petlyuk towers, andcomplex primary fractionators, use MultiFrac.


One steam feed per stripper (optional)

Outlet One vapor or liquid distillate, or bothOne free water distillate stream (optional)One bottoms product from the main columnAny number of side products from main column (optional)Any number of water decant products from main column (optional)One bottoms product per side stripperAny number of pseudoproduct streams (optional)


Columns

You can use any number of pseudoproduct streams to represent:• Column internal streams• Pumparound streams• Column connecting streams

A pseudoproduct stream does not affect column results.

Heat StreamsInlet One heat stream per stage for the main column (optional)

One heat stream per pumparound heater/cooler (optional)One heat stream per stripper reboiler (optional)One heat stream per stripper bottom liquid return (optional)

Outlet One heat stream per stage for the main column (optional)One heat stream per pumparound heaters/cooler (optional)One heat stream per stripper reboiler (optional)One heat stream per stripper bottom liquid return (optional)

PetroFrac uses an inlet heat stream as a duty specification for all stages exceptthe condenser, reboiler, pumparounds, and stripper bottom liquid return.

If you do not give sufficient operating column specifications on the SetupConfiguration sheet, PetroFrac uses a heat stream as a specification for thecondenser and reboiler.

If you do not give two specifications on the Pumparounds Specifications sheet,PetroFrac uses a heat stream as a specification for pumparounds.

If you do not give two specifications for the bottom liquid return on the StrippersSetup LiquidReturn sheet, PetroFrac uses a heat stream as a specification.

If you give two specifications on the Setup Configuration sheet or PumparoundsSpecifications sheet, PetroFrac does not use the inlet heat stream as aspecification. The heat stream supplies the required heating or cooling.

Use optional outlet streams for the net heat duty of the condenser, reboiler, andpumparounds. The value of the outlet heat stream equals the value of the inletheat stream (if any) minus the actual (calculated) heat duty.

Main Column

The main column can have any number of inlet streams. It can also have up tothree product streams per stage (one vapor, one hydrocarbon liquid, and one freewater).


Chapter 4

Side Strippers

The side strippers can have a steam feed. They must have a liquid bottomsproduct. You can use a heat stream as the heat source for the reboiler. If you do notspecify the reboiler duty, bottoms flow rate, and steam feed, PetroFrac uses theheat stream as a duty specification.

Optionally, the stripper liquid bottoms may be partially returned to the maincolumn. To specify a bottom liquid return, you must enter two specifications onthe Strippers Setup LiquidReturn sheet.

Feed Furnace

You can specify a feed furnace. A feed furnace can have any number of feeds. Thevapor and liquid streams from the furnace are fed to the stage where the furnace isattached.

Specifying PetroFracWithin each column or stripper, stages are numbered from the top down. Ifpresent, the main column condenser is stage 1.

Use the following forms to enter specifications and view results of PetroFrac:



Pumparounds Specify pumparound specifications and view results

Pumparounds Hcurves Specify pumparound heating or cooling curve tables and view tabular results

Strippers Setup Specify stripper operating specifications

Strippers Efficiencies Specify stripper column or stage efficiencies

Strippers ReboilerHcurves Specify stripper reboiler heating or cooling curve tables and view tabular results

Strippers TraySizing Specify sizing calculation parameters for tray stripper sections, and view results

Strippers TrayRating Specify rating calculation parameters for tray stripper sections, and view results

Strippers PackSizing Specify sizing calculation parameters for packed stripper sections, and view results

Strippers PackRating Specify rating calculation parameters for packed stripper sections, and view results

Strippers Properties Specify physical property parameters for stripper sections

continued


Columns


Strippers Estimates Specify estimates for stripper temperatures and flows

Strippers Results View stripper product stream and connecting stream results

Strippers Profiles View stripper profiles

HeatersCoolers Specify stage heating or cooling specifications

RunbackSpecs Specify runback specification parameters

Efficiencies Specify stage or component efficiencies

DesignSpecs Specify design specifications, manipulated variables, and view results



TraySizing Specify sizing calculation parameters for tray column sections, and view results

TrayRating Specify rating calculation parameters for tray column sections, and view results

PackSizing Specify sizing calculation parameters for packed column sections, and view results

PackRating Specify rating calculation parameters for packed column sections, and view results

Properties Specify physical property parameters for column sections

Estimates Specify estimates for column temperatures and flows

Convergence Specify convergence parameters

Report Specify block-specific report options and pseudostreams


UserSubroutines Specify user subroutines for tray and packing rating and sizing

Connectivity View stream connectivity for the PetroFrac block

ResultsSummary View key column results for the overall PetroFrac column

Profiles View column profiles


Chapter 4

Main Column

You define the main column configuration using Condenser and Reboiler on theSetup Configuration sheet. PetroFrac allows six condenser types:• Subcooled• Total• Partial with vapor distillate product only• Partial with both vapor and liquid distillate products• No condenser, with pumparound to top stage• No condenser, with external feed to top stage

You can specify one of three reboiler types:• Kettle reboiler• No reboiler, with pumparound to bottom stage• No reboiler, with external feed to bottom stage

The types and number of required operating specifications depend on the columnconfiguration. Normally, you must enter two column operating specifications. Ifeither a condenser or a reboiler is absent, you must enter one specification. Ifboth the condenser and reboiler are absent, do not enter any specification.

Feed Stream Handling

Use the Setup Streams sheet to specify the feed and product stage locations. Youmay also identify a feed as the stripping steam, and override its flow by specifyinga steam-to-product ratio.

PetroFrac provides three conventions for handling feed streams (see PetroFracFeed Convention Above-Stage and PetroFrac Feed Convention On-Stage in thefollowing figures):• Above-Stage• On-Stage• Furnace

When Feed-Convention is Above-Stage, PetroFrac introduces a material streambetween adjacent stages. The liquid portion flows to the stage (n) you specify. Thevapor portion flows to the stage above (n – 1). You can introduce a liquid feed tothe top stage (or condenser) by specifying Stage=1. You can introduce a vaporfeed to the bottom stage (or reboiler) by specifying Stage=Number of stages+1.

When Feed-Convention is On-Stage, both the liquid and vapor portions of a feedflow to the stage (n) you specify.


Columns

Vapor

Liquid

n - 1


PetroFrac Feed Convention Above-Stage

n - 1

n + 1

nMixed feed to stage n

PetroFrac Feed Convention On-Stage

When Feed-Convention is Furnace, a furnace is attached to the stage (n) youspecify. The feed enters the furnace before being introduced to the specifiedstage.

Feed Furnace

PetroFrac can simulate a feed furnace simultaneously with the column/strippers.You can simulate the feed furnace as a simple heater or as a single stage flash withor without feed overflash bypass to the furnace. You can specify one of thefollowing:• Heat Duty• Temperature• Fractional overflash


Chapter 4

To do this Use this sheet

Define a feed to the feed furnace Setup Streams (Feed Convention)

Enter a furnace model type and associated specifications Setup Furnace

You can select from three furnace model types, as shown in the next threefigures.

Heat

Feed

Main Column

Furnace Modeled as a Stage Heat Duty

Feed Furnace

Main Column

Furnace Modeled as a Single Stage Flash


Columns

FeedFurnace

Main Column

Furnace Modeled as a Single Stage Flash with Overflash Bypass

If Model= PetroFrac models the furnace as And calculates

Heater Stage heat duty on the feed stage —

Flash Single-stage flash Furnace temperature, degree of vaporization,vapor/liquid compositions

Flash-Bypass Single-stage flash with the overflash bypassedback to the furnace

Furnace temperature, degree of vaporization,vapor/liquid compositions

Liquid Runbacks

Use the RunbackSpecs form to specify the flow rate of liquid runback from anystage. When you enter a liquid runback specification, you must allow PetroFrac toadjust one of the following:• Flow rate of a pumparound• Duty of an interstage heater/cooler

Pumparounds

Use the following sheets to enter specifications for pumparounds.

Use this sheet To enter

PumparoundsSpecifications

Pumparound connectivity and cooler/heater specifications

Report PseudoStreams Pseudostream assignment for the pumparound

Hcurves Specifications Heating/cooling curve specifications


Chapter 4

Pumparounds are associated with the maincolumn. They can be total or partialdrawoffs of the stage liquid flow. You must specify the draw and return stagelocations for each pumparound. For partial drawoffs, you must specify two of thefollowing:• Flow rate• Temperature• Temperature change• Heat Duty

For total drawoffs, you must specify one of the following:• Temperature• Temperature change• Heat Duty

Side Strippers

Use the Stripper forms and sheets to enter specifications for side strippers.

Side strippers may be either steam-stripped or reboiled. For steam strippers, youmust enter a steam stream. You can override its flow rate by specifying a steam-to-product ratio. For reboiled strippers, you must specify a reboiler duty.

PetroFrac assumes:• A liquid draw goes from the main column to the top of the stripper.• The stripper overhead is returned to the main column.

You must specify the draw and return stage locations. You can also:• Return a fraction of the stripper bottoms to the main column• Specify additional liquid draws from other stages of the main column as feeds

to the strippers



Effy

K xiv i j

i j i j

= ,

, ,


Effy y

k x yi jM i j i j

i j i j i j,

, ,

, , ,

=−

−+

+

1

1


Columns

Where:






i = Component index

j = Stage index

To specify vaporization or Murphree efficiencies, enter the number of actualstages on the Setup Configuration sheet and Strippers Setup Configuration sheetas Number of stages. Then use the Efficiencies and Strippers Efficiencies formsto enter the efficiencies.

You can use any of these efficiencies to account for departure from equilibrium.But you cannot convert from one efficiency to the other. Magnitudes of theefficiencies can be quite different. Details on using and estimating theseefficiencies are described by Holland, Fundamentals of Multi-ComponentDistillation, McGraw-Hill Book Company, 1981.

ConvergenceFor convergence PetroFrac uses:• The sum-rates variant of the inside-out algorithm• A special initialization procedure designed for petroleum refining applications

PetroFrac generally does not need initial estimates. For ethylene plant primaryfractionator/quench tower combinations, you should provide temperatureestimates.

To enhance convergence, you may enter profile estimates on the followingPetroFrac forms:• Estimates• Strippers Estimates

Temperature estimates are usually adequate. You can increase convergencestability by selecting varying degrees of damping on the Convergence Basic sheet.


Chapter 4

Rating ModeIn rating mode, PetroFrac calculates the column profiles and product compositionsbased on specified values of column parameters. Examples of column parametersare:• Reflux ratio• Reboiler duties• Feed flow rates• Furnace temperature• Pumparound loads

Design ModeIn design mode you can manipulate subsets of the column parameters to achievecertain specifications on column performance.


Purity Stream, including internal streams†

Recovery of any components group Set of product streams††

Flow rate of any components group Internal stream or set of product streams

Flow rates of any components groups to anyother component groups

Internal streams to any other internal streams, or set of feed or productstreams

Temperature Stage

Heat duty Stage

Fractional overflash Stage

TBP and D86 temperature gaps Pair of product streams

TBP temperature Product stream

D86 temperature Product stream

D1160 temperature Product stream

Vacuum distillation temperature Product stream

API gravity Product stream

Standard liquid density Product stream

Specific gravity Product stream

Flash point Product stream

Pour point Product stream

Refractive index Product stream

continued


Columns


Reid vapor pressure Product stream


Difference of any pair of Prop-Set properties Pair of product streams

Watson UOP K factor Product stream

†Express the purity as the sum of mole, mass, or standard liquid volume fraction of any group ofcomponents relative to any other group of components.

††Express recovery as a fraction of the same components in a subset of feed streams.

†††See ASPEN PLUS User Guide, Chapter 28.

You can also specify overflash for a furnace feed stream.

Physical PropertiesUse the BlockOptions form to override the global physical property method. Youcan specify one method on this form, which PetroFrac uses for all stages in themain column and strippers.

You can also split the main column or a stripper into any number of segments,each using a different property method.

Use this sheet When you use different properties for

Properties Property Sections The main column

Strippers Properties Property Sections A stripper

Free Water HandlingPetroFrac can perform free-water calculations in the main column and sidestrippers. By default, PetroFrac performs free-water calculations for the maincolumn condenser. The free-water phase, if present, is decanted.

To do this Use these sheets

Request free-water calculations for additional stages in themain columns and strippers

Properties Freewater StagesStrippers Properties Freewater Stages

Define additional water decant product streams for the maincolumn

Setup Streams


Chapter 4

Solids HandlingPetroFrac handles solids by:• Temporarily removing all solids from inlet streams• Performing calculations without solids• Adiabatically mixing solids removed from inlet streams with main column

liquid bottoms

This calculation approach maintains an overall mass and energy balance aroundthe PetroFrac block. But the bottom stage liquid product will not be in exactthermal or phase equilibrium with other bottom stage flows (for example, thebottom stage vapor flow).

Sizing and Rating of Trays and PackingsPetroFrac has extensive capabilities to size, rate, and perform pressure dropcalculations for trayed and packed columns. Use the following PetroFrac forms toenter specifications:• TraySizing, TrayRating, PackSizing, PackRating• Strippers TraySizing, Strippers TrayRating, Strippers PackSizing, Strippers

PackRating

See Appendix A for details on tray and packing types and correlations.


Columns

RateFracRate-Based Distillation

RateFrac is a rate-based nonequilibrium model for simulating all types ofmultistage vapor-liquid fractionation operations. RateFrac simulates actual trayand packed columns, rather than the idealized representation of equilibriumstages. RateFrac explicitly accounts for the underlying interphase mass and heattransfer processes to determine the degree of separation. RateFrac does not useempirical factors such as efficiencies and the Height Equivalent to a TheoreticalPlate (HETP).

RateFrac is applicable for:• Ordinary distillation• Absorption• Reboiled absorption• Stripping• Reboiled stripping• Extractive and azeotropic distillation

RateFrac is suitable for:• Two-phase systems• Narrow and wide-boiling systems• Systems exhibiting strong liquid phase nonideality

RateFrac can also detect and handle a free water phase in the condenser.

RateFrac can model columns with chemical reactions. Reactions include:• Equilibrium• Rate-controlled• Electrolytic

RateFrac models a complex configuration consisting of a single column orinterlinked columns. The configuration may have:• Any number of columns, each with any number of RateFrac Segments• Any number of connections between columns or within each column• Arbitrary flow splitting and mixing of connecting streams

RateFrac can handle operations with:• Side strippers• Pumparounds• Bypasses• External heat exchangers

RateFrac can be used to• Rate existing columns• Design new columns


Chapter 4

You can define pseudoproduct streams to represent column internal flows orconnecting streams in RateFrac.

You can use Fortran Blocks, Sensitivity Analysis, and Case Study blocks to varyconfiguration parameters, such as feed location or number of segments.

RateFrac can produce segmentwise column profile plots.

RateFrac can be used with other ASPEN PLUS features and capabilities much inthe same way as the equilibrium-based models, RadFrac, PetroFrac, andMultiFrac.

Flowsheet Connectivity for RateFrac

1

Vapor Distillate orInterconnecting Stream

Heat (optional)

Heat (optional)

Heat (optional)

Heat (optional)

Liquid Distillate (optional)Water Distillate (optional)

Side Products

Interconnecting Streams (Heater optional)

Bottoms orInterconnecting Streams

Interconnecting Streams (Heater optional)

Reflux

NBottom Segment or Reboiler Heat

Duty (optional)

Top Segment or Condenser Heat

Duty (optional)

Feeds


(Heater optional)

RateFrac models single and interlinked columns. Any number of columns can beconnected by any number of connecting streams. Each connecting stream canhave an associated heater.

Each column may have:• Any combination of packed and tray segments• Any number of connecting streams• Any number of side product streams


Columns


Outlet Up to two product streams (one vapor, one liquid) per segmentOne water distillate product stream (optional)Any number of pseudoproduct streams (optional)

Each column must have:• At least one vapor or liquid stream leaving the top segment• One liquid stream leaving the bottom segment

When you model interlinked columns, the top and bottom streams can beconnecting streams. However, the free-water stream from the condenser cannotbe a connecting stream.

Heat StreamsInlet One heat stream per segment (optional)

One heat stream per connecting stream (optional)

Outlet One heat stream per connecting stream (optional)

RateFrac uses an inlet heat stream as a duty specification for all segments exceptthe condenser, reboiler, and connecting streams. If you do not provide two columnoperating specifications on the Columns Setup Configuration sheet, RateFrac usesa heat stream as a specification for the condenser and reboiler.

If you do not provide two specifications on the ConnectStreams Input sheet,RateFrac uses a heat stream as a specification for connecting streams.

If you provide two specifications on the Columns Setup Configuration sheet orConnectStreams Input sheet, RateFrac does not use the inlet heat stream as aspecification. The inlet heat stream supplies the required heating or cooling.

You can use optional outlet heat streams for the net heat duty of the condenser,reboiler, and connecting streams. The value of the outlet heat stream equals thevalue of the inlet heat stream (if any), minus the actual (calculated) heat duty.


Chapter 4

The Rate-Based Modeling ConceptMost models available for simulating and designing multicomponent, multistageseparation processes are based on the idealized concept of equilibrium ortheoretical stages. This approach assumes that the liquid and vapor phasesleaving any stage are in thermodynamic equilibrium with each other. The phasecompositions, temperature, and vapor and liquid flow profiles are calculated bysolving the governing material balances, energy balances, and equilibriumrelations for each stage.

In practice, columns rarely operate under thermodynamic equilibrium conditions.Vapor-liquid equilibrium prevails only at the interface separating vapor andliquid phases. The separation achieved in a multistage column depends on theinterphase mass and heat transfer rate processes. Multicomponent mass transferinteractions can also have pronounced effects on the separation.

When the equilibrium approach is used to model a tray column, a correctionfactor (referred to as an efficiency) attempts to account for the departure fromequilibrium. Many definitions for efficiency exist, with wide variations incomplexity and accuracy. In general, efficiencies depend on:• Physical characteristics of the equipment, such as column configuration• Hydrodynamics of the column• Fluid properties of the system

Murphree vapor efficiencies are the most widely used. These efficienciesgenerally vary from stage to stage within a column, and from component tocomponent. For multicomponent systems, there are no theoretical limitations onMurphree efficiencies. Experimental evidence shows that component efficiencies:• May vary strongly from component to component• Can take any value including negative values

Methods used to calculate component efficiencies generally do not include theeffect of the departure from thermal equilibrium.

Packed columns are also designed using the equilibrium stage concept. However,HETP is commonly used in place of efficiencies. HETP varies with:• Type and size of the packing• Hydrodynamics of the column• Fluid properties of the system

Like efficiencies, HETPs may vary strongly from point to point within a columnand from system to system.


Columns

RateFrac is based on a fundamental and rigorous approach. This approach avoidsuncertainties that result when the equilibrium approach is used with estimatedefficiencies or HETP. RateFrac directly includes mass and heat transfer rateprocesses in the system of equations representing the operation of separationprocess units. RateFrac:• Describes the simultaneous mass and heat transfer rate phenomena• Accounts for the multicomponent interactions between simultaneously

diffusing species

For nonreactive systems, RateFrac comprises:• Mass and heat balances around vapor and liquid phases• Mass and heat transfer rate models to determine interphase transfer rates• Vapor-liquid equilibrium relations applied at interfacial conditions• Correlations to estimate mass and heat transfer coefficients and interfacial

areas

For chemically reactive systems, RateFrac includes equations to account for theinfluence of chemical reactions on heat and mass transfer rate processes. Forsystems involving equilibrium reactions, RateFrac includes equations torepresent the chemical equilibrium conditions.

RateFrac completely avoids the need for efficiencies in tray columns or HETPs inpacked columns. RateFrac has far greater predictive capabilities than theconventional equilibrium model.

Specifying RateFracRateFrac numbers segments from the top down, starting with the condenser (orstarting with the top segment if there is no condenser).

Use the following forms to enter specifications and view results for RateFrac:


BlockParameters Specify overall block parameters, convergence and initialization parameters, block-specific diagnostic message levels, and feed flash convergence parameters

Columns Setup Specify basic column configuration and operating conditions

Columns TraySpecs Specify tray column section parameters

Columns PackSpecs Specify packed column section parameters

Columns Reactions Assign reactions to column sections, and specify vapor and liquid holdup data

continued


Chapter 4


Columns Estimates Specify initial estimates for segment temperatures, and vapor and liquid flows andcompositions

ColumnsEquilibriumSegments

Specify optional equilibrium segments and column efficiencies

Columns HeatersCoolers Specify segment heating or cooling and utility exchangers

Columns FlowTempSpecs Specify liquid, vapor, and temperature specifications

Columns Results View column performance summary

Columns Profiles View column profiles

Columns InterfaceProfiles View column interface profiles

Columns EfficienciesFlooding View tray and component efficiencies, packing HETPs, and flooding summary

Columns TransferCoefficients View binary diffusion, binary mass, and heat transfer coefficients

InletsOutlets Specify feed and product stream locations and conventions, inlet and outlet heatstreams

ConnectStreams Specify connecting stream sources and destinations and view results

DesignSpecs Specify design specifications and view convergence results


FlowRatios Specify the flow ratio and view results



ConnectStreamHcurves Specify connecting stream heating or cooling curve tables and view tabular results

Reports Specify block-specific report options, and pseudostream information


UserSubroutines Specify user subroutine parameters for mass and heat transfer coefficients, interfacialarea, pressure drop, and kinetics

ResultsSummary View material and energy balance results and overall split fractions

Column Numbering

Individual columns are identified by a column number. The numbering order doesnot affect algorithm performance. Within each column, segments are numberedfrom top to bottom, starting with the condenser (when present).


Columns

Stream Definition

RateFrac uses four types of streams:• External streams• Connecting streams• Internal streams• Pseudostreams

External streams are the standard RateFrac inlet and outlet streams. They areidentified by stream IDs.

Connecting streams are streams within RateFrac but external to individualcolumns. These streams are identified by connecting stream numbers.Connecting streams may connect two columns or segments of the same column(such as bypasses and pumparounds). You can associate a heater with anyconnecting stream. Heaters are identified by the connecting stream number.

Internal streams are the liquid or vapor flows between adjacent segments of thesame column. These streams are identified by a segment number and a columnnumber.

Pseudostreams store the results of internal and connecting streams. They are asubset of external outlet streams. Unlike normal outlet streams, pseudostreamsdo not participate in the block material balance calculations.

Material Feed Streams

RateFrac uses two conventions for handling material feed streams (see RateFracFeed Conventions in the following figures):• Above segment• On segment

Segment n-1

Mixed Feed to

Segment n

Segment n

Vapor

Liquid

RateFrac Feed Convention Above Segment


Chapter 4

Segment n-1

Mixed Feed to

Segment nSegment n

Segment n + 1

Vapor

Liquid

RateFrac Feed Convention On Segment

When the feed convention is defined as Above segment, RateFrac introduces amaterial stream between adjacent segments. The liquid portion flows to segmentn, specified as the feed segment. The vapor portion flows to the segment above(segment n-1 in the figure RateFrac Feed Convention Above segment). You canintroduce a liquid to the top segment (or condenser) by specifying Segment=1.You can introduce a vapor feed to the bottom segment (or reboiler), by specifyingthe segment equal to the last segment in the column +1. When a two-phase feedstream is fed to segment 1, the vapor phase is combined directly with the vapordistillate. Similarly, when a two-phase feed stream is fed to the last segment ofthat column + 1, the liquid phase is combined directly with the liquid bottomsproduct.

When the feed convention is defined as On segment, both the liquid and vaporportions of the feed flow to segment specified (segment n in the previous figureRateFrac Feed Convention On segment).

RateFrac assumes that a vapor feed (or the vapor portion of a mixed feed)combines with the vapor phase in the segment it enters. RateFrac also assumesthat a liquid feed (or the liquid portion of a mixed feed) combines with the liquidphase in the segment it enters.


Columns

Column Configuration

Specify the column configuration by indicating the following on the ColumnsConfiguration sheet:• Number of segments• Presence or absence of condensers and reboilers• Equilibrium and nonequilibrium segments

Connecting Streams

RateFrac allows any number of connecting streams. Any number of these streamscan have the same:• Source column, segment, and phase• Destination column and segment

RateFrac introduces connecting streams on the destination segment regardless oftheir phase (Convention = On Segment). All connecting streams can have aheater. Enter all specifications for connecting streams on the ConnectStreamsInput sheet. RateFrac does not allow phase change for connecting streams.

Connecting streams can be either a total or a partial drawoff of the segment flow.Enter the required specifications as follows:

If the drawoff type is You enter

Partial Two of the following: flow, temperature or temperature change and heat duty†

Total One of the following: temperature or temperature change and heat duty††

†Enter zero for heat duty if heater is absent.

††Flow is taken as the net flow of the segment, excluding any product flow and any other connectingstream flow.

Required Specifications

You must specify the total number of columns and connecting streams.

Use this form To enter Such as

Columns TraySpecs Tray specifications Number of trays orNumber of trays per segmentTray typeTray characteristics

Columns PackSpecs Packing specifications Total height of packing orHeight of packing per segmentPacking typePacking characteristics


Chapter 4

You must also specify:• Inlet stream locations• Heat stream locations, heat duty, and phase• Pressure profile for each column• Condenser type• Two operating specifications for multisegment columns and one for single-

segment columns• Source and destination of any connecting stream and associated heater

specifications• Outlet stream locations and phases. If the outlet stream is a side drawoff

stream from a segment, you must specify its flow.

A segment refers to one of the following:• A slice (or portion) of packing in a packed column (see the preceding figure,

Nonequilibrium Segment in a Packed Column)• One (or more) tray(s) in a tray column (see the preceding figure,

Nonequilibrium Segment in a Tray Column)

A column consists of segments. To evaluate mass and heat transfer ratesbetween contacting phases, RateFrac uses one of the following:• Height of packing in a packed segment• Number of trays in a tray segment

Nonequilibrium Segment in a Packed Column


Columns

Nonequilibrium Segment in a Tray Column

Equilibrium Stages

RateFrac can model both equilibrium stages and nonequilibrium segments in thesame column. Use the Columns EquilibriumSegments form to specify the locationof equilibrium stages. When all stages are equilibrium, you can obtain the sameresults using RateFrac as you can using RadFrac, MultiFrac, or PetroFrac withideal stages.

Reactive Systems

RateFrac can handle kinetically controlled reactions and equilibrium reactions inboth liquid and vapor phases. Chemical reactions can be of any type, including:• Simultaneous• Consecutive• Parallel• Forward• Reverse

For kinetically controlled reactions, the kinetics can be defined by one of thefollowing:• Built-in power law expressions• User-supplied Fortran subroutines


Chapter 4

For equilibrium reactions, the chemical reaction equilibrium constant can bedefined either in terms of user-supplied coefficients for a temperature-dependentpolynomial, or can be computed from the reference state free energies ofparticipating components.

RateFrac can model electrolyte systems using both the apparent and the truecomponent approaches.

Enter the following information on the Reactions form:• Reaction stoichiometry• Reaction type• Phase in which reactions occur

Depending on the reaction type, you must enter either the equilibrium constantor kinetic parameters. For electrolytic reactions, you can also enter the reactiondata on the Chemistry form.

To associate reactions with a column segment, enter the corresponding ReactionsID (or Chemistry ID or User Reactions ID) on the Columns ReactionsSpecifications sheet.

For rate-controlled reactions, you must enter holdup data for the phase wherereactions occur.

For these segments Use this form to enter holdup information

Equilibrium Columns Reactions

Tray Columns TraySpecs

Packed Columns PackSpecs

Heaters and Coolers

Use the Columns HeatersCoolers Side Duties sheet to specify:• Heat duty for a segment• Heater segment location (column and segment)• Phase

Use the Columns HeatersCoolers Utility Exchangers sheet to specify cooling (orheating) of any segment using a coolant (or heating fluid).

You can use a heat stream to provide heat integration. Heat integration occurswhen the duty recovered from another block is used as the heat source of heatersand coolers. Enter heat stream data on the InletsOutlets Heat Streams sheet.


Columns

Physical Property Specifications

Use the RateFrac BlockOptions form to override the global physical propertyproperty method. You can specify only one property method on the BlockOptionsform. RateFrac uses this property method for the whole column. RateFrac does notallow multiple physical property methods.

Handling Free Water

RateFrac can perform free-water calculations only in condensers.

Rating Mode

In rating mode, RateFrac calculates temperatures, flows, and mole fraction profilesbased on specified values of column parameters such as:• Reflux ratio• Product flows• Heat duties

Design Mode

In design mode, use the DesignSpecs form to specify column performanceparameters (such as purity or recovery). You must indicate which variables tomanipulate to achieve these specifications using the Vary form. You can specifyany variables that are allowed in rating mode, except:• Number of columns, segments, and connecting streams• Pressure profile• Locations of feeds, products, heaters, and connecting streams• Column configurations, including the number of trays, tray characteristics,

height of packing, packing specifications


Chapter 4

The flows of inlet material streams and the duties of inlet heat streams can alsobe manipulated variables.


Purity Stream, including an internal stream†

Recovery of any component groups Set of product streams††

Flow of any component groups Internal stream or set of product streams

Component ratio Internal stream and a second internal stream or feed streams and product streams

Temperature of vapor stream Segment

Temperature of liquid stream Segment

Heat duty Condenser, reboiler, or a connecting stream


Ratio or difference of any pair ofproperties in a Prop-Set

Single or paired internal or product stream

†Express the purity as the sum of mole, mass, or standard liquid volume fractions of any group ofcomponents, relative to any other group of components.

††You can express recovery as a fraction of the same components in a subset of the feed stream.

†††See ASPEN PLUS User Guide, Chapter 28.

Calculating Efficiency and HETP

From converged vapor and liquid composition profiles, RateFrac back-calculatesthe component Murphree vapor efficiencies. These efficiencies are defined for eachcomponent as the fractional approach to equilibrium of the vapor stream leavingany segment, with the liquid stream leaving the same segment.

Effy y

K x Yijij ij

ij ij ij

=−

−+

+

1

1

Where:

Eff = Murphree vapor efficiencyK = Vapor-liquid equilibrium K valuex = Liquid mole fractiony = Vapor mole fractioni = Component indexj = Segment index


Columns

For each segment of packed columns, RateFrac calculates the fractional approachto equilibrium using the same definition as used for Murphree vapor efficiency.RateFrac reports the height of packing required to achieve equilibrium as theHETP for that segment.

Convergence and Computing Time

RateFrac must solve many more equations for a given column than an equilibriummodel. Computing times for RateFrac are greater than they are for equilibriummodels, particularly for problems containing many components. The solutionalgorithm RateFrac uses is an efficient, Newton-based simultaneous correctionapproach. RateFrac solution times increase with the square of the number ofcomponents. Solution times can be an order of magnitude greater than RadFrac,MultiFrac, or PetroFrac solution times for the same problems.

References for Built-In Correlations

RateFrac uses well-known and accepted correlations to calculate:• Binary mass transfer coefficients for the vapor and liquid phase• Interfacial areas

In general, these quantities depend on column diameter and operatingparameters such as:• Vapor and liquid flow• Densities• Viscosities• Surface tension of liquid• Vapor and liquid phase binary diffusion coefficients

Mass transfer coefficients and interfacial areas depend on:

Packing characteristics Tray characteristics

Type (random or structured) Type (sieve, valve, or bubble-cap)

Size Weir and flow path length

Specific surface area Downcomer area

Material of construction Weir height

The correlations involve well-defined dimensionless groups, such as theReynolds, Froude, Weber, Schmidt, and Sherwood numbers. The correlationshave been fitted to experimental measurements from laboratory and pilot plantabsorption and distillation columns.


Chapter 4

The correlations RateFrac uses for mass transfer coefficients and interfacialareas are:

Column type Correlation used

Packed Columns (random packing) Onda et al. (1968)

Packed Columns (structured) Bravo et al. (1985, 1992)

Sieve Trays† Chan and Fair (1984)

Valve Trays Scheffe and Weiland (1987)

Bubble-Cap Trays† Grester et al. (1958)

†These correlations do not provide the mass transfer coefficients and interfacial areas separately.

RateFrac allows you to write Fortran subroutines to calculate:• Binary mass transfer coefficients• Heat transfer coefficients• Interfacial areas

The subroutines are described in the ASPEN PLUS User Models referencemanual.

By applying a rigorous multicomponent mass transfer theory (Krishna andStandart, 1976), RateFrac uses binary mass transfer coefficients to evaluate:• Multicomponent binary mass transfer coefficients• Component mass transfer rates between vapor and liquid phases

RateFrac calculates the vapor phase and liquid phase heat transfer coefficientsusing the Chilton-Colburn analogy (King, 1980). This analogy relates:• Mass transfer coefficients• Heat transfer coefficients• Schmidt number• Prandtl number

Mass and Heat Transfer CorrelationsRateFrac uses several mass and heat transfer correlations for:• Packed columns.• Valve Tray columns• Bubble-Cap Tray columns• Sieve Tray columns

Packed Column

RateFrac calculates the mass transfer coefficients and the interfacial areaavailable for mass transfer using the correlations developed by Onda et al., 1968.


Columns

The correlation for the liquid phase binary mass transfer coefficients is:

( ) ( )kg

L

aSc a dL

in

L

L LinL

p p

ρµ µω

=

−1 3 2 3

1 2 0 4

0 0051

/ // .

.

The correlation for the gas phase binary mass transfer coefficient is:

( ) ( )kRT

a D

G

a uSc a dg

in

g

p in p ging

p p

=

−5 23

0 7

1 3 2

.

.

/

The interfacial area available for mass transfer is given by the correlation:

( )[ ]{ }a a Re Fr Wep L L L cω σ σ= − − − −1 145

0 1 0 05 0 2 0 75exp .

. . . .

Where:

ReL

aLp L

=µ

, Fra L

gLL

= ρ

ρ

2

2 , WeL

aLp L

=2

σρ

and:

k L

in

= Binary mass transfer coefficient for the binary pair i and nin the liquid phase (m/sec)

ρL = Density of liquid (kg/m 3 )

g = Acceleration due to gravity (m/sec 2 )

µ L = Viscosity of liquid (Newton-sec/m 2 )

L = Liquid superficial mass velocity (kg/m 2 /sec)

aw = Wetted interfacial area (m 2 interfacial area/m 3 packingvolume)

Sc L

in

= Schmidt number for the binary pair i and n in the liquidphase =

( )µ ρL L inLD

D L

in

= Binary Maxwell-Stefan diffusion coefficient for the binarypair i and n(m 2 /sec)

ap = Specific surface area of the packing

continued


Chapter 4

dp = Nominal diameter of packing or packing size (m)

k g

in

= Binary mass transfer coefficient for the binary pair i and nin the vapor phase (kg mole/atm/m 2 /sec)

R = Universal gas constant (m 3 atm/kg mole/K)

Tg = Gas phase temperature (K)

G = Gas superficial mass velocity (kg/m 2 /sec)

µ g = Viscosity of gas mixture (Newton-sec/m 2 )

Sc g

in

= Gas phase Schmidt number for the binary pair i and n =

( )µ ρg g ingD

ρg = Density of gas mixture (kg/m 3 )

D g

in

= Gas-phase binary Maxwell-Stefan diffusion coefficient forthe binary pair i and n (m 2 /sec)

σ = Surface tension (Newton/m)

σ c = Critical surface tension of the packing material (Newton/m)

Valve Tray Column

RateFrac calculates the mass transfer coefficients and the interfacial areaavailable for mass transfer using the correlations developed by Scheffe andWeiland, 1987.

The correlation for the liquid phase binary mass transfer coefficient is:

( ) ( ) ( ) ( )Sh Re Re v ScinL

g L inL= 1254

0 68 0 09 0 05 0 5.

. . . .

The correlation for the gas phase binary mass transfer coefficients is:

( ) ( ) ( ) ( )Sh Re Re Scing

g L ing= 9 93

0 87 0 13 0 39 0 5.

. . . .ϖ

The interfacial area available for mass transfer is given by the correlation:

( ) ( ) ( )a Reg L= 0 270 37 0 25 0 52.

. . .Re ϖ


Columns

Where:

Shk ad

DinL

L

in

L

L

in

=ρ

, Shk ad

Ding

g

in

g

g

in

=ρ

, ScD

inL L

LL

in

=µ

ρ, Sc

Ding g

gg

in

=µ

ρ,

ReLd

LL

=µ

, ReGd

gg

=µ

, ϖ =W

d

and:

L = Liquid mass velocity (kg/m 2 /sec) (Velocity is based on toweractive area.)

d = Geometric parameter of unit length (m)

µ L = Viscosity of liquid mixture (Newton-sec/m 2 )

G = Gas mass velocity (kg/m 2 /sec) (Velocity is based on toweractive area.)


k L

in

= Binary mass transfer coefficient for the binary pair i and nin the liquid phase (kg mole/m 2 /sec)

a = Interfacial area (m 2 interfacial area/m 2 tower active area)

ρL

= Molar density of liquid (kg mole/m 3 )

D L

in


k g

in

= Binary mass transfer coefficient for the binary pair i and nin the vapor phase (kg mole/m 2 /sec)

ρg

= Molar density of gas mixture (kg mole/m 3 )

D g

in


ρL = Density of liquid mixture (kg/m 3 )


W = Weir height (m)


Chapter 4

Bubble-Cap Tray Column

RateFrac calculates the product of the binary mass transfer coefficients andinterfacial areas using the correlations developed by Grester et al., 1958.

The product of liquid phase binary mass transfer coefficients and interfacial areais given by the correlation:

( ) )k a D F LtL

in inL

L= × +4127 10 0 21313 0158 0 5. ( . .

.

The product of gas phase binary mass transfer coefficient and interfacial area isgiven by the correlation:

( )( )k a

h F Q

ScGg

in

w L

ing

=+ − +0 776 4 567 0 2377 104 85

0 5

. . . ..

Where:

k L

in



D L

in


F = F-Factor =µ ρg g

1 2/ kg / sec / m1/2 1/2

µ g = Gas volumetric flow per unit active area (m 3 /sec/m 2 )


L = Liquid molar velocity (kg mole/m 2 /sec) (Velocity is based onactive area.)

tL = Liquid residence time =0 9998. / (sec)h Z QL L L

hL = Liquid holdup =0 04191 0 19 2 0 0135. . .4545 . ( )+ + −h Q F mw L

ZL = Liquid flow path length (m)

continued


Columns

QL = Liquid flow per average path width (m 3 /sec/m)

hw = Outlet weir height (m)

k g

in

= Binary mass transfer coefficient for the binary pair i and nin the vapor phase (kg mole/m 2 /sec)

G = Gas molar velocity (kg mole/m 2 /sec) (Velocity is based onactive area.)

Sc g

in

= Gas-phase Schmidt number for the binary pair i and n =

( )µ ρg g ingD


D g

in


Sieve Tray Column

RateFrac calculates the product of mass transfer coefficients and interfacialareas using the correlations developed by Chan and Fair, 1984.

The product of liquid phase binary mass transfer coefficient and interfacial areais given by the correlation:

( ) ( )k a x D F LtL

in inL

L= +4127 10 0 21313 0158 0 5. . .

.

The product of the gas phase binary mass transfer coefficient and interfacial areais given by the correlation:

( ) ( )k a

D F F

hg

in

ing

L

=−

0 5 2

0 5

1030 867.

.

Where:

k L

in



D L

in


continued


Chapter 4

F = F-Factor =( )µ ρg g

1 2 1 2 1 2/ / // /kg sec m

µ g = Gas volumetric flow per unit active area (m 3 /sec/m 2 )


L = Liquid molar velocity (kg mole/m 2 /sec) (Velocity is based onactive area.)

t L = Liquid residence time =0 9998. / (sec)h Z QL L L

hL = Liquid holdup =0 04191 0 19 2 0 0135. . .4545 . ( )+ + −h Q F mw L

ZL = Liquid flow path length (m)

QL = Liquid flow per average path width (m 3 /sec/m)

hw = Outlet weir height (m)

k g

in

= Binary mass transfer coefficient for the binary pair i and nin the vapor phase (m/sec)

D g

in


F = Fractional approach to flooding gas velocity =µ µg g F/

µ g F = Gas velocity through active area at flooding (m/sec)

h L = Liquid height =

( ) ( )Γ Γ Γe w e L eh B Q+ 15332 3

//

m

Γe = ( )exp . .− 12 55 0 91Ks

B = ( )0 0327 0 0286 137 8. . exp .+ − hω

Ks = ( ) ( )µ ρ ρ ρg g L g( ) / sec.

−0 5

m

ρL = Density of liquid mixture (kg/m 3 )


Columns

Heat Transfer Coefficients

RateFrac calculates the heat transfer coefficients, using the Chilton-Colburnanalogy (King, 1980).

The heat transfer coefficient is given by:

( )k Sch

Cpavtc

mix

2 3/ =

Where:

k av = Average binary mass transfer coefficients (kgmole/sec)

Sc = Schmidt number

htc = Heat transfer coefficient (Watts/K)

Cpmix = Molar heat capacity (Joules/kg mole/K)

Pr = Prandtl number


Chapter 4

References

Bravo, J.L., Rocha, J.A., and Fair, J.R., "Mass Transfer in Gauze Packings,"Hydrocarbon Processing, January, 91 (1985).

Bravo, J.L., Rocha, J.A., and Fair, J.R., "A Comprehensive Model for thePerformance of Columns Containing Structured Packings," ICHEME SymposiumSeries, 128, A439 (1992).

Chan, H. and Fair, J.R., "Prediction of Point Efficiencies in Sieve Trays: 1. BinarySystems, 2. Multicomponent Systems," Ind. Eng. Chem. Process Des. Dev., 23,(1984) p. 814.

Grester, J.A., Hill, A.B., Hochgraf, N.N., and Robinson, D.G., "Tray Efficienciesin Distillation Columns," AIChE Report, (1958).

King, C.J., Separation Processes, Second Edition, McGraw-Hill Company, (1980).

Krishna, R. and Standart, G.L., "A Multicomponent Film Model Incorporating aGeneral Matrix Method of Solution to the Maxwell-Stefan Equations," AIChE J.,22, (1976) p. 383.

Onda, K., Takeuchi, H., and Okumoto, Y., "Mass Transfer Coefficients betweenGas and Liquid Phases in Packed Columns," J. Chem. Eng., Japan, 1, (1968) p.56.

Perry, R.H. and Chilton, C.H., "Chemical Engineers’ Handbook," Fifth Edition,McGraw-Hill Book Company, Section 18 (1973).

Scheffe, R.D. and Weiland, R.H., "Mass Transfer Characteristics of Valve Trays,"Ind. Eng. Chem. Res., 26, (1987) p. 228.


Columns


Chapter 4

ExtractRigorous Extraction

Extract is a rigorous model for simulating liquid-liquid extractors. It can havemultiple feeds, heater/coolers, and side streams. Extract can calculatedistribution coefficients using:• An activity coefficient model or equation of state capable of representing two

liquid phases• A built-in temperature-dependent correlation (KLL Correlation sheet)• A Fortran subroutine (KLL Subroutine sheet)

Although equilibrium stages are assumed, you can specify component or stageseparation efficiencies. Extract can be used only for rating calculations.

You can define pseudoproduct streams (Report PseudoStreams sheet) torepresent extractor internal flows. You can use Fortran and sensitivity blocks tovary configuration parameters, such as feed location or number of stages.

Flowsheet Connectivity for Extract

L1 Phase

L1 Phase

L2 Phase

Side products(any number)(any number)

Side feeds

L2 Phase

Nstage

1

Material StreamsInlet One material stream to the first (top) stage, rich in the first liquid phase

(L1)One material stream to the last (bottom) stage, rich in the second liquidphase (L2)One material stream per intermediate stage (optional)

Outlet One material stream for L1 from the last stageOne material stream for L2 from the first stageUp to two side product streams per stage, one for L1 and one for L2(optional)


Columns

Specifying ExtractExtract can operate in one of the following ways:• Adiabatically (default)• At a specified temperature• With specified stage heater or cooler duties

You must specify:• Number of stages• Feed and product stream stage locations• Side product stream phase and mole flow rate• Pressure profile

The first liquid phase (L1) flows from the first stage to the last stage. The second(L2) flows in the opposite direction. You must identify the key components in eachphase using L1-Comps and L2-Comps on the Setup form. Extract can treat phaseL1 as the solvent/extract phase or the feed/raffinate phase.

Liquid-liquid distribution coefficients are required to represent the liquid-liquidequilibrium. Extract calculates these coefficients using one of the followingmethods:

You can use You enter On sheet

Any physical property method that canrepresent two liquid phases

A global property method or an Opsetname to override the global physicalproperty method

BlockOptions Properties

A built-in temperature-dependentpolynomial

Polynomial coefficients Properties KLL Correlation

A Fortran subroutine Subroutine name Properties KLL Subroutine

Use the following forms to enter specifications and view results for Extract:



Efficiencies Specify stage or component efficiencies

Properties Specify parameters for KLL correlations and KLL subroutines

Estimates Specify initial estimates for stage temperatures and compositions

Convergence Specify convergence parameters and block-specific diagnostic message levels

Report Specify block-specific report options and pseudostream information

continued


Chapter 4



Results View column performance summary, material and energy balance results, and splitfractions

Profiles View extractor profiles


See ASPEN PLUS User Models for more information about Fortran subroutines.

❖ ❖ ❖ ❖


Columns


Chapter 5

5 Reactors

This chapter describes the unit operation models for reactors. The models are:


RStoic Stoichiometric reactor Models stoichiometricreactor with specifiedreaction extent orconversion

Reactors where reaction kinetics are unknownor unimportant but stoichiometry and extent ofreaction are known

RYield Yield reactor Models reactor withspecified yield

Reactors where stoichiometry and kinetics areunknown or unimportant but a yield distributionis known

REquil Equilibrium reactor Performs chemical andphase equilibrium bystoichiometric calculations

Reactors with simultaneous chemicalequilibrium and phase equilibrium

RGibbs Equilibrium reactor withGibbs energy minimization

Performs chemical andphase equilibrium by Gibbsenergy minimization

Reactors with phase equilibrium orsimultaneous phase and chemical equilibrium.Calculating phase equilibrium for solidsolutions and vapor-liquid-solid systems.

RCSTR Continuous stirred tankreactor

Models continuous stirredtank reactor

One-, two, or three-phase stirred tank reactorswith rate-controlled and equilibrium reactions inany phase based on known stoichiometry andkinetics

RPlug Plug flow reactor Models plug flow reactor One-, two-, or three-phase plug flow reactorswith rate-controlled reactions in any phasebased on known stoichiometry and kinetics

RBatch Batch reactor Models batch or semi-batchreactor

One-, two-, or three-phase batch and semi-batch reactors with rate-controlled reactions inany phase based on known stoichiometry andkinetics

RCSTR, RPlug, and RBatch are kinetic reactor models. Use the ReactionsReactions form to define the reaction stoichiometry and data for these models.


Reactors

You do not need to specify heats of reaction, because ASPEN PLUS uses theelemental enthalpy reference state for the definition of the component heat offormation. Therefore, heats of reaction are accounted for in the mixture enthalpycalculations for the reactants versus the products.

RStoicStoichiometric Reactor

Use RStoic to model a reactor when:• Reaction kinetics are unknown or unimportant and• Stoichiometry and the molar extent or conversion is known for each reaction

RStoic can model reactions occurring simultaneously or sequentially. In addition,RStoic can perform product selectivity and heat of reaction calculations.

Flowsheet Connectivity for RStoic

Material

Water (optional)

Heat (optional)


Heat(optional)


Outlet One product streamOne water decant stream (optional)


Chapter 5

Heat StreamInlet Any number of heat streams (optional)

RStoic uses the sum of the inlet heat streams as the heat duty specification, ifyou do not specify an outlet heat stream.


The value of the outlet heat stream is the net heat duty (sum of the inlet heatstreams minus the calculated heat duty) for the reactor.

Specifying RStoicUse the Setup Specifications sheet to specify the reactor operating conditions andto select the phases to consider in flash calculations in the reactor.

Use the Setup Reactions sheet to define the reactions occurring in the reactor.You must specify the stoichiometry for each reaction. In addition, you mustspecify either the molar extent or the fractional conversion for all reactions.

When solids are created or changed by the reactions, you may specify thecomponent attributes and the particle size distribution in the outlet stream usingthe Setup Component Attr. sheet and the Setup PSD sheet respectively.

If you wish to calculate the heats of reaction, use the Setup Heat of Reactionsheet to specify the reference component for each reaction defined in the SetupReactions sheet. You may also choose to specify the heats of reaction, and RStoicadjusts the calculated reactor duty, if needed.

If you wish to calculate product selectivities use the Setup Selectivity sheet tospecify the selected product component and the reference reactant component.

Use the following forms to enter specifications and view results for RStoic:


Setup Specify operating conditions, reactions, reference conditions for heat of reactioncalculations, product and reactant components for selectivity calculations, particle sizedistribution, and component attributes

Convergence Specify estimates and convergence parameters for flash calculations


Results View summary of operating results, mass and energy balances, heats of reaction,product selectivities, reaction extents, and phase equilibrium results for the outletstream



Reactors

Heat of Reaction

RStoic calculates the heat of reaction from the heats of formation in thedatabanks when you select the Calculate Heat of Reaction option on the SetupHeat of Reaction sheet. The heats of reaction are calculated at the specifiedreference conditions based on consumption of a unit mole or mass of the referencereactant selected for each reaction. The following reference conditions are usedby default:

Specification Default

Reference temperature 25 °C

Reference pressure 1 atm

Reference fluid phase Vapor phase

You can also use the Setup Heat of Reaction sheet to specify the heats ofreaction. The specified heat of reaction may differ from the heat of reaction thatASPEN PLUS computes from the heats of formation at reference conditions. Ifthis occurs, RStoic adjusts the calculated reactor heat duty to reflect thedifferences. Under these circumstances, the calculated reactor heat duty will notbe consistent with the inlet and outlet stream enthalpies.

Selectivity

The selectivity of the selected component P to the reference component A isdefined as:

S

P

AP

A

P A, =

∆∆∆∆

Real

Ideal

Where:

∆P = Change in number of moles of component P due to reaction

∆A = Change in number of moles of component A due to reaction

In the numerator, real represents changes that actually occur in the reactor.ASPEN PLUS obtains this value from the mass balance between the inlet andoutlet.


Chapter 5

In the denominator, ideal represents changes according to an idealized reactionscheme. This scheme assumes that no reactions are present, except for thereaction that produces the selected component from the reference component.Therefore, the denominator indicates how many moles of P are produced permole of A consumed in an ideal stoichiometric equation, or:

∆∆

P

A Ideal

P

A

= υυ

where υ A and υ P are stoichiometric coefficients.

This example shows how RStoic calculates selectivity:

a1 A + b1 B → c1 C + d1 D

c2 C + e2 E → p2 P

a3 A + f3 F → q3 Q

The selectivity of P to A is:

SMoles of P produced

Moles of A consumed

c p

a cP A, /=

∗∗

1 2

1 2

In most cases, selectivity ranges between 0 and 1. However, if the selectedcomponent is also produced from components other than the referencecomponent, selectivity may be greater than 1. If the selected component isconsumed in other reactions, selectivity may be less than 0.


Reactors

RYieldYield Reactor

Use RYield to model a reactor when:• Reaction stoichiometry is unknown or unimportant• Reaction kinetics are unknown or unimportant• Yield distribution is known

You must specify the yields (per mass of total feed, excluding any inertcomponents) for the products or calculate them in a user-supplied Fortransubroutine. RYield normalizes the yields to maintain a mass balance. RYield canmodel one-, two-, and three-phase reactors.

Flowsheet Connectivity for RYield

Material

Water (optional)

Heat (optional)


Heat(optional)


Outlet One product streamOne water decant stream (optional)




Chapter 5

If you give only one specification on the Setup Specifications sheet (temperatureor pressure), RYield uses the sum of the inlet heat streams as a dutyspecification. Otherwise, RYield uses the inlet heat stream(s) only to calculatethe net heat duty. The net heat duty is the sum of the inlet heat streams minusthe actual (calculated) heat duty.

You can use an outlet heat stream for the net heat duty.

Specifying RYieldUse the Setup Specifications and Setup Yield sheets to specify the reactorconditions and the component yields. For each reaction product, specify the yieldas either moles or mass of a component per unit mass of feed. If you specify inertcomponents on the Setup Yield sheet, the yields will be based on unit mass ofnon-inert feed.

Calculated yields are normalized to maintain an overall material balance. Forthis reason, yield specifications establish a yield distribution, rather thanabsolute yields. RYield does not maintain atom balances because you enter thefixed yield distribution.

You can request one-, two-, or three-phase calculation.

When solids are created or changed by the reactions, you can specify theircomponent attributes and/or particle size distribution in the outlet stream usingthe Setup Component Attr. and Setup PSD sheets, respectively.

Use the following forms to enter specifications and view results for RYield:


Setup Specify reactor operating conditions, component yields, inert components, flashconvergence parameters, and PSD and component attributes for the outlet stream

UserSubroutine Specify subroutine name and parameters for the user-supplied yield subroutine


Results View summary of operating results, mass and energy balances for the reactor andphase equilibrium results for the outlet stream



Reactors

REquilEquilibrium Reactor

Use REquil to model a reactor when:• Reaction stoichiometry is known and• Some or all reactions reach chemical equilibrium

REquil calculates simultaneous phase and chemical equilibrium. REquil allowsrestricted chemical equilibrium specifications for reactions that do not reachequilibrium. REquil can model one- and two-phase reactors.

Flowsheet Connectivity for REquil

Heat (optional)

Material (vapor phase)

Material (liquid phase)


Heat(optional)


Outlet One material stream for the vapor phaseOne material stream for the liquid phase



If you give only one specification on the REquil Input Specifications sheet(temperature or pressure), REquil uses the sum of the inlet heat streams as aduty specification. Otherwise, REquil uses the inlet heat stream(s) only tocalculate the net heat duty. The net heat duty is the sum of the inlet heatstreams minus the actual (calculated) heat duty.



Chapter 5

Specifying REquilYou must specify the reaction stoichiometry and the reactor conditions. If noadditional specifications are given, REquil assumes that the reactions will reachequilibrium.

REquil calculates equilibrium constants from the Gibbs energy. You can restrictthe equilibrium by specifying one of the following:• The molar extent for any reaction• A temperature approach to chemical equilibrium (for any reaction)

If you specify temperature approach, ∆T, REquil evaluates the chemicalequilibrium constant at T + ∆T, where T is the reactor temperature (specified orcalculated).

REquil performs single-phase property calculations or two-phase flashcalculations nested inside a chemical equilibrium loop. REquil cannot performthree-phase calculations.

Use the following forms to enter specifications and view results for REquil:


Input Specify reactor operating conditions, valid phases, reactions, convergenceparameters, and solid and liquid entrainment in the vapor stream


Results View summary of operating results, mass and energy balances, and calculatedchemical equilibrium constants

Solids

Reactions can include conventional solids. REquil treats each participating solidcomponent as a separate pure solid phase, not as a component in a solid solution.Any participating solids must have a free energy formation (DGSFRM) andenthalpy of formation (DHSFRM), or heat capacity parameters (CPSXP1).

Solids not participating in reactions, including any nonconventional components,are treated as inert. These solids have no effect on the equilibrium calculationsexcept on the energy balance.


Reactors

RGibbsEquilibrium Reactor (Gibbs Free Energy Minimization)

RGibbs uses Gibbs free energy minimization with phase splitting to calculateequilibrium. RGibbs does not require that you specify the reaction stoichiometry.Use RGibbs to model reactors with:• Single phase (vapor or liquid) chemical equilibrium• Phase equilibrium (an optional vapor and any number of liquid phases) with

no chemical reactions• Phase and/or chemical equilibrium with solid solution phases• Simultaneous phase and chemical equilibrium

RGibbs can also calculate the chemical equilibria between any number ofconventional solid components and the fluid phases. RGibbs also allowsrestricted equilibrium specifications for systems that do not reach completeequilibrium.

Flowsheet Connectivity for RGibbs



Heat(optional)

Heat(optional)


Outlet At least one material stream

If you specify as many outlet streams as the number of phases that RGibbscalculates, RGibbs assigns each phase to an outlet stream. If you specify feweroutlet streams, RGibbs assigns the additional phases to the last outlet stream.


Chapter 5



If you specify only pressure on the Setup Specifications sheet, RGibbs uses thesum of the inlet heat streams as a duty specification. Otherwise, RGibbs uses theinlet heat stream(s) only to calculate the net heat duty. The net heat duty is thesum of the inlet heat streams minus the actual (calculated) heat duty.


Specifying RGibbsThis section describes how to specify:• Phase equilibrium only• Phase and chemical equilibrium• Restricted chemical equilibrium• Reactions• Solids

Use the following forms to enter specifications and view results for RGibbs:


Setup Specify reactor operating conditions and phases to consider in equilibriumcalculations, identify possible products, assign phases to outlet streams, specifyinert components and specify equilibrium restrictions.

Advanced Specify atomic formula of components, estimates for temperature and componentflows, and convergence parameters.

Block Options Override global values for physical properties, simulation options, diagnosticmessage levels and report options for this block.

Results View summary of operating results, mass and energy balances, molarcompositions of fluid and solid phases present, the atomic formula ofcomponents, and calculated reaction equilibrium constants.



Reactors

Phase Equilibrium Only

To specify Use this option On

Phase equilibriumcalculations only

Phase Equilibrium Only Setup Specifications sheet

Maximum number of fluidphases that RGibbs shouldconsider

Maximum Number of FluidPhases

Setup Specifications sheet

Maximum number of solidsolution phases

Maximum Number of SolidSolution Phases

Solid Phases dialog box from the SetupSpecifications sheet

RGibbs distributes all species among all solution phases by default. You can usethe Setup Products sheet to assign different sets of species to each solutionphase. You can also assign different thermodynamic property methods to eachphase.

If there is a possibility that a solid solution phase may exist, use the SetupProducts sheet to identify the species that will exist in that phase.

Phase Equilibrium and Chemical Equilibrium

To specify Use this option On

Chemical equilibriumcalculations (with or withoutphase equilibrium)

Phase Equilibrium andChemical Equilibrium


Maximum number of fluidphases that RGibbs shouldconsider

Maximum Number of FluidPhases


Maximum number of solidsolution phases

Maximum Number of SolidSolution Phases

Solid Phases dialog box from the SetupSpecifications sheet

By default, RGibbs considers all components entered on the ComponentsSpecifications Selection sheet as possible fluid phase or solid products. You canspecify an alternate list of products on the Setup Products sheet.

RGibbs distributes all solution species among all solution phases by default. Youcan use the Setup Products sheet to assign different sets of species to eachsolution phase. You can also assign different thermodynamic property methods toeach phase.


Chapter 5

RGibbs needs the molecular formula for each component that is present in a feedor product stream. RGibbs retrieves this information from the componentdatabanks. For non-databank components, use the Properties Molec-StructFormula sheet to enter:• Atom (the atom type)• Number of occurrences (the number of atoms of each type)

Alternatively, you can enter the atom matrix on the Advanced Atom Matrixsheet. The atom matrix defines the number of each atom in each component. Ifyou enter the atom matrix, you must enter it for all components and atoms,including databank components.

If there is a possibility that a solid solution phase may exist, use the SetupProducts sheet to identify the species which will exist in that phase.

Restricted Chemical Equilibrium

To restrict chemical equilibrium:

Specify On

The molar extent of the reaction Edit Reactions dialog box (from the SetupRestrictedEquilibrium sheet)

A temperature approach to equilibrium for individual reactions Edit Reactions dialog box (from the SetupRestrictedEquilibrium sheet)

A temperature approach to chemical equilibrium for the entire system Edit Reactions dialog box (from the SetupRestrictedEquilibrium sheet)

The outlet amount of any component as total mole flow or as a fraction ofthe feed of that component

Setup Inerts sheet†

†You can specify inert components by setting the fraction to 1.

For temperature approach specifications, RGibbs evaluates the chemicalequilibrium constant at T T+ ∆ , where T is the actual reactor temperature(specified or calculated) and ∆T is the desired temperature approach.

You can enter one of the following restricted equilibrium specifications forindividual reactions:• The molar extent of a reaction• The temperature approach for an individual reaction

Use the Setup RestrictedEquilibrium sheet to supply the reaction stoichiometry.

If you enter one of the preceding specifications, you must also supply thestoichiometry for a set of linearly independent reactions involving all componentsin the system.


Reactors

Reactions

You can have RGibbs consider only a specific set of reactions. You can restrict thechemical equilibrium by specifying temperature approach or molar extent for thereactions. You must specify the stoichiometric coefficients for a complete set oflinearly independent chemical reactions, even if only one reaction is restricted.

The number of linearly independent reactions required equals the total numberof products in the product list, including solids (see the Setup Products sheet),minus the number of atoms present in the system. The reactions must involve allparticipating components. A component is participating if it satisfies thesecriteria:• It is in the product list.• It is not inert. A component is inert if it consists entirely of atoms not present

in any other product components.• It has not been dropped. A component listed on the Setup Products sheet is

dropped if it contains an atom not present in the feed.

Solids

RGibbs can calculate the chemical equilibria between any number ofconventional solid components and the fluid phases. RGibbs detects whether thesolid is present at equilibrium, and if so, calculates the amount. RGibbs treatseach solid component as a pure solid phase, unless it is specified as a componentin a solid solution. Any solid that RGibbs considers a product must have both:• Free energy of formation (DGSFRM or CPSXP1)• Heat of formation (DHSFRM or CPSXP1)

Nonconventional solids are treated as inert and have no effect on equilibriumcalculations. If chemical equilibrium is not considered, RGibbs treats all solids asinert. RGibbs cannot perform solids-phase-only calculations.

RGibbs places all pure solids in the last outlet stream unless you specifyotherwise on the Setup AssignStreams sheet. RGibbs can handle only a singleCISOLID substream, which contains all conventional solids products defined aspure solid phases. RGibbs places the solid solution phases in the MIXEDsubstream of the outlet stream(s).

RGibbs cannot directly handle phase equilibrium between solids and fluid phases(for example, water-ice equilibrium). To work around this, you can list the samecomponent twice on the Components Specifications Selection sheet, withdifferent component IDs. If you want RGibbs to calculate the chemicalequilibrium between these components:• Specify both component IDs on the Setup Products sheet.• Designate one ID as a solids phase component, the other as a fluid phase

component.


Chapter 5

References

Gautam, R. and Seider, W.D., "Computation of Phase and ChemicalEquilibrium," Parts I, II, and III, AIChE J. 25, 6, November, 1979, pp. 991-1015.

White, C.W. and Seider, W.D., "Computation of Phase and ChemicalEquilibrium: Approach to Chemical Equilibrium," AIChE J., 27, 3, May, 1981,pp. 446-471.

Schott, G. L., "Computation of Restricted Equilibria by General Methods," J.Chem. Phys., 40, 1964.


Reactors

RCSTRContinuous Stirred Tank Reactor

RCSTR rigorously models continuous stirred tank reactors. RCSTR can modelone-, two-, or three-phase reactors. RCSTR assumes perfect mixing in thereactor, that is, the reactor contents have the same properties and composition asthe outlet stream.

RCSTR handles kinetic and equilibrium reactions as well as reactions involvingsolids. You can provide the reaction kinetics through the built-in Reactionsmodels or through a user-defined Fortran subroutine.

Flowsheet Connectivity for RCSTR

Material

Heat (optional)


Heat(optional)


Outlet One material stream



If you specify only pressure on the Setup Specifications sheet, RCSTR uses thesum of the inlet heat streams as a duty specification. Otherwise, RCSTR uses theinlet heat stream only to calculate the net heat duty. The net heat duty is thesum of the inlet heat streams minus the actual (calculated) heat duty.



Chapter 5

Specifying RCSTRYou must specify the reactor operating conditions, which are pressure and eithertemperature or heat duty. You must also enter the reactor volume or residencetime (overall or phase).

Use the following forms to enter specifications and view results for RCSTR:


Setup Specify reactor operating conditions and holdup, select the reaction sets to be included,and specify PSD and component attributes in the outlet stream

Convergence Provide estimates for component flow rates, reactor temperature and volume, and specifyflash convergence parameters, RCSTR convergence methods and parameters, andinitialization options

UserSubroutine Specify parameters for the user-supplied kinetics subroutine and block-specific reportoption for the kinetics subroutine


Results View summary of operating results and mass and energy balances for the block


Reactions

You must specify reaction kinetics on the Reactions Reactions forms and selectthe Reaction Set ID on the Setup Reactions sheet.

You can specify one-, two-, or three-phase calculations. You can specify the phasefor each reaction on the Reactions Reactions forms. RCSTR can handle kineticand equilibrium type reactions.

Phase Volume

In a multi-phase reactor, by default, ASPEN PLUS calculates the volume of eachphase, using phase equilibrium results, as:

V VV f

V fPi Ri i

j j

=Σ

Where:

VPi = Volume of phase i

VR = Reactor volume

Vi = Molar volume of phase i

f i = Molar fraction of phase i


Reactors

You can override the default calculation by specifying the volume of a phasedirectly (Phase Volume) or as a fraction of the reactor volume (Phase VolumeFrac) on the Setup Specifications sheet.

Alternatively, when you specify the residence time of a phase in the reactor,ASPEN PLUS calculates the phase volume iteratively.

Residence Time

ASPEN PLUS calculates the residence time (overall and phase) in the CSTR as:

RTV

F f VR

i i=

* Σ

RTV

F f ViPi

i i

=*

Where:

RT = Overall residence time

RTi = Residence time of phase i

VR = Reactor volume

F = Total molar flow rate (outlet)

Vi = Molar volume of phase i

fi = Molar fraction of phase i

VPi = Volume of phase i

When the default calculation for phase volume, based on phase equilibriumresults, is used, the phase residence time is equal for all phases. If you specifyPhase Volume or Phase Volume Frac on the Setup Specifications sheet, theresidence time for the phase specified in the Holdup Phase is calculated with thespecified phase volume rather than the default phase volume.

Solids

RCSTR can handle reactions involving solids. RCSTR assumes that solids are atthe same temperature as the fluid phase. RCSTR cannot perform solids-phase-only calculations.


Chapter 5

Scaling of Variables

Four types of variables are predicted by RCSTR: component flow rates, streamenthalpy, component attributes and PSD (if present). RCSTR normalizes thesevariables, for faster convergence, by dividing each one by a scale factor.

Two types of scaling are available in RCSTR: component-based scaling andsubstream-based scaling. Component-based scaling weighs each variable againstits previous or estimated value. Substream-based scaling weighs each variable ina substream against the substream flow rate. For component-based scaling,minimum scale values are set by the Trace Scaling Factor in the AdvancedParameters dialog box (from the Convergence Parameters sheet). You mayreduce the trace scaling threshold to increase the prediction accuracy of tracecomponents.

Component-based scaling generally provides more accuracy than substream-based scaling, especially for trace components. Use component-based scalingwhen:• The reaction network involves trace intermediates• The reaction rates are very sensitive to trace reactants (such as catalysts and

initiators which participate in degradation reactions)

The following tables summarize the scale factors used by each method.

Substream-based Scaling Method

Variable Type Variable Initial Scale Factor

Component Flows Component mole flow inoutlet stream

Estimated outlet substream mole flow rate

Stream Enthalpy Net enthalpy flow of outletstream

Net enthalpy flow of inlet stream

Component Attributes(attr/kg)

Product of component massflow (with attributes) andattribute value in outletstream

Default attribute scale factor

PSD Product of substream massflow rate (with PSD) andPSD value in outlet stream

Default attribute scale factor

Note If any substream-based scaling factor is equal to zero, the defaultscaling factor is used instead (the default factor is 1.0 forcomponent flow rates and 1.0E5 for stream enthalpy).


Reactors

Component-based Scaling Method

Variable Type Variable Initial Scale Factor

Component Flows Component mole flow inoutlet stream

Larger of:

- Estimated component mole flow in outlet stream

- Product of Trace threshold and estimated outletsubstream mole flow

Stream Enthalpy Net enthalpy flow of outletstream

Net enthalpy flow of inlet stream

Component Attributes(attr/kg)

Product of component massflow with attributes andattribute value in outletstream

Larger of:

- Product of estimated attributed component mass flowand estimated attribute value in outlet stream

- Product of Trace threshold and estimated outletsubstream mole flow

PSD Product of substream massflow rate and PSD value inoutlet stream

Larger of:

- Product of estimated substream mass flow with PSDsand estimated PSD value in outlet stream

- Product of Trace threshold and default attribute scalefactor


Chapter 5

RPlugPlug Flow Reactor

RPlug is a rigorous model for plug flow reactors. RPlug assumes that perfectmixing occurs in the radial direction and that no mixing occurs in the axialdirection. RPlug can model one-, two-, or three-phase reactors. You can also useRPlug to model reactors with coolant streams (co-current or counter-current).

RPlug handles kinetic reactions, including reactions involving solids. You mustknow the reaction kinetics when you use RPlug to model a reactor. You canprovide the reaction kinetics through the built-in Reactions models or through auser-defined Fortran subroutine.

Flowsheet Connectivity for RPlug

Material Material

Heat (optional)

Flowsheet Reactor without Coolant Stream

Material Material

Material Coolant(optional)

Material Coolant(optional)

Flowsheet Reactor with Coolant Stream


Reactors


One coolant stream (optional)

Outlet One material product streamOne coolant stream (optional)


Outlet One heat stream (optional) for the reactor heat duty. Use the heat outletstream only for reactors without a coolant stream.

Specifying RPlugUse the Setup Configuration sheet to specify reactor tube length and diameter. Ifthe reactor consists of multiple tubes, you can also specify the number of tubes.You can specify the pressure drop across the reactor on the Setup Pressure sheet.Additional required input for RPlug depends on the reactor type.

When you use thisReactor Type And solid phase is

And fluid and solid phasetemperatures are Specify

Reactor with specifiedtemperature

— — Reactor temperature, ortemperature profile

Adiabatic reactor Not present — No required specifications

Present Same No required specifications

Present Different U (fluid phase - solids phase)

Reactor with constant coolanttemperature

Not present — Coolant temperature, andU (coolant - process stream)

Present Same Coolant temperature, andU (coolant - process stream)

Present Different Coolant temperature,U (coolant - fluid phase),U (coolant - solids phase),andU (fluid phase - solids phase)

Reactor with co-currentcoolant

Not present — U (coolant - process stream)

Present Same U (coolant - process stream)

continued


Chapter 5

When you use thisReactor Type And solid phase is

And fluid and solid phasetemperatures are Specify

Reactor with co-currentcoolant

Not present — U (coolant - process stream)

Present Same U (coolant - process stream)

Present Different U (coolant - fluid phase),U (coolant - solids phase),andU (fluid phase - solids phase)

Reactor with counter-currentcoolant

Not present — Coolant outlet temperature ormolar vapor fraction, andU (coolant - process stream)

Present Same Coolant outlet temperature ormolar vapor fraction, andU (coolant - process stream)

Present Different Coolant outlet temperature ormolar vapor fraction,U (coolant - fluid phase),U (coolant - solids phase),andU (fluid phase - solids phase)

For reactors with countercurrent external coolant, RPlug calculates the coolantinlet temperature. The result overrides your specified inlet coolant temperature.You can use a design specification that manipulates the coolant exit temperatureor vapor fraction to achieve a specified coolant inlet temperature.

For reactors with an external coolant stream, you can use different physicalproperty methods and options (BlockOptions Properties sheet) for the processstream and the coolant stream.

Use the following forms to enter specifications and view results for RPlug:


Setup Specify operating conditions and reactor configuration, select reaction sets to be included,and specify pressure drops

Convergence Specify flash convergence parameters, calculation options and parameters for theintegrator

Report Specify block-specific report options

UserSubroutine Specify user subroutine parameters for kinetics, heat transfer, pressure drop, and list uservariables to be included in the profile report

BlockOptions Override global values for property methods, simulation options, diagnostic levels, andreport options for this block

continued


Reactors


Results View summary of operating results and mass and energy balances for the block

Profiles View profiles versus reactor length for process stream conditions, coolant streamconditions, properties, component and substream attributes, and user variables


Reactions

You must specify reaction kinetics on the Setup Reactions sheet, by referring toReaction IDs that you select. You can specify one-, two-, or three-phasecalculations. Specify the reaction phases on the Reactions Reactions forms. RPlugcan handle only kinetic type reactions.

Solids

Reactions can involve solids. Solids can be:• At the same temperature as the fluid phases• At a different temperature from the fluid phases (only for Reactor Types other

than the reactor with specified temperature)

In the latter case, you must specify the heat transfer coefficients on the SetupSpecifications sheet.


Chapter 5

RBatchBatch Reactor

RBatch is a rigorous model for batch or semi-batch reactors. Use RBatch whenyou know the kinetics of the reactions taking place. You can specify any numberof continuous feed streams. A continuous vent is optional. The reaction runs untilit reaches a stop criterion that you specify.

Batch operations are unsteady-state processes. RBatch uses holding tanks andyour specified cycle times to provide an interface between the discrete operationsof the batch reactor and the continuous streams used by other models.

RBatch can model one-, two-, or three-phase reactors.

Flowsheet Connectivity for RBatch

Vent(optional)

Heat (optional)

Continuous feed(any number)

Product

Batch charge

Material StreamsInlet One batch charge stream (required)

One or more continuous feed streams for semi-batch reactors (optional)

Outlet One product stream (required)One vent stream for semi-batch reactors (optional)




Reactors

Specifying RBatchUse the Setup Specifications sheet to specify the reactor conditions.

Use the Setup Operations sheet to specify:• One or more stop criteria• Either a feed time or a batch cycle time

Other required input for RBatch depends on reactor type.

To establish the pressure of the vessel, enter one of the following specificationson the Setup Specifications sheet:• Constant pressure• Pressure profile• Reactor volume

Use the Setup ContinuousFeeds sheet to enter mass flow rates for the continuousfeeds at any number of points in time. You can thus simulate delayed feeds andstep changes in feeds.

For specified duty reactors, you can specify either a constant heat duty or a heatduty profile. For a reactor with constant duty, RBatch assumes adiabaticoperation if you do not specify a heat duty.

For reactors with specified coolant temperature, you must specify:• Coolant temperature• An over-all heat transfer coefficient• Total heat transfer area

For constant temperature and specified temperature reactors, RBatch handlesthe temperature specification in one of the following ways:• By assuming perfect control• By interpreting the specified temperature(s) as the setpoint(s) of a PID

controller

Use the following forms to enter specifications and view results for RBatch:


Setup Specify operating conditions, select reaction sets to be included, specify operation stopcriteria, operation times, continuous feeds, and controller parameters

Convergence Specify convergence parameters for flash calculations, integration, and pressurecalculations

Report Specify block-specific report options for profiles and reactor, vent, and vent accumulatorproperty profiles

UserSubroutine Specify parameters for the user kinetics subroutine, name and parameters for the user heattransfer subroutine, and user variables for the profile report.

continued


Chapter 5



Results View summary of block operating results and mass and energy balances

Profiles View time profiles of reactor conditions, compositions, continuous feed stream flows,properties, component attributes, and user variables

Controller

RBatch assumes perfect control when one of these conditions exists:• Pressure in the reactor is converged upon (that is, reactor volume is specified)• A single-phase batch reactor is used with no continuous feed streams

If RBatch cannot assume perfect control, it interprets the specifiedtemperature(s) as the setpoint(s) of a PID controller. This interpretation occurswhen:• A two-phase reactor is used• RBatch performs pressure convergence calculations (that is, reactor volume is

specified)• Continuous feeds are present during semi-batch operation

Use the Setup Controllers sheet to specify the controller tuning parameters.

The controller equation is:

Q M K T T K I T T dt KDd T T

dtcs s

st

= − + − +−

∫( ) ( / ) ( )

( )

0

Where:

Q = Reactor heat duty (J/sec)

Mc = Reactor charge (kg)

K = Proportional gain (J/kg/K)

T = Reactor temperature (K)

T s = Temperature set point (K)

I = Integral time (sec)

D = Derivative time (sec)

t = Time (sec)

The gain factor is a specific gain per unit mass.


Reactors

Reactions

Reactions may or may not be present in RBatch. If they are, you must include theReaction Set IDs on the Setup Reactions sheet. You can specify one-, two-, orthree-phase calculations. You specify the reaction phases on the ReactionsReactions forms. RBatch can only handle kinetic type reactions.

Specifying Stop Criteria

A reaction runs until one of your specified stop criteria reached. A stop criterioncan be one of the following:• Reaction time• Reactor composition• Vent accumulator or continuous vent composition• Conversion of a component• Amount of material in the reactor or vent accumulator• Vent flow rate• Temperature in the reactor• Vapor fraction in the reactor• Any property specified on the Properties Prop-Sets Properties sheet

As the stop criterion variable approaches its cut-off from above or below, you canspecify whether or not RBatch should halt the reaction. If you specify more thanone stop criterion, RBatch halts the reaction as soon as one of the criteria isreached. In addition, you must specify a halt time for the reaction. If the reactiondoes not reach the specified stop criteria by this time, RBatch halts the reaction.

Cycle Time

You can specify a reactor cycle time. Or, you can let RBatch calculate it from yourspecified reaction and down times for draining, cleaning, and charging thereactor. If you do not specify reactor cycle time, then specify a feed cycle time.RBatch uses this time to determine the batch charge, because the reaction timeis not known at the beginning of block execution.

Note If the reactor batch charge stream is in a recycle loop, you mustspecify the reactor cycle time.

Mass Balances

Because RBatch uses different cycle times to calculate time-averaged flows,RBatch may not maintain a mass balance around the block. For example,suppose you specify a feed time of 30 minutes, but the down time plus thecalculated value reaction time equals 45 minutes. The resulting net mass flowfrom the reactor is less than the charge flow by a factor of 45/30=1.5.


Chapter 5

Remember that the mass balance pertains to the time-averaged inlet and outletcontinuous streams. RBatch always satisfies a mass balance for its own internalbatch computations. If there is no continuous feed stream, the mass balancearound RBatch closes only if the cycle time is specified. This ensures that thesame time is used for averaging the batch change and product streams. If there isa continuous feed stream, and it is not time-varying, the mass balance closes onlyif the cycle time is specified, and the specified value is equal to the calculatedreaction time. In all other cases, the mass balance around RBatch does not close,although the compositions, temperature, and so on are correct.

Batch Operation

RBatch can operate in a batch or in semi-batch mode. The reactor mode isdetermined by the streams you enter on the flowsheet. A semi-batch reactor canhave a vent product stream, one or more continuous feed streams, or both. Thevent product stream exits a vent accumulator. It does not exit the reactor itself.The vent accumulator is for the continuous (but time-varying) vapor vent leavingthe reactor. The composition and temperature of each continuous feed streamremain constant throughout the reaction. The flow rate also remains constant,unless you specify a time profile for the flow rate of a continuous stream.

Batch operations are unsteady-state processes. Variables like temperature,composition, and flow rate change with time, in contrast to steady-stateprocesses. To interface RBatch with a steady-state flowsheet, it is necessary touse time-averaged streams.

Four types of streams are associated with RBatch, as follows:

Batch Charge The material transferred to the reactor at the start of thereactor cycle. The mass of the batch charge equals the flow rate of the batchcharge stream, multiplied by the feed cycle time. The mass of the batch charge isequivalent to accumulating the batch charge stream in a holding tank during areactor cycle. The contents of the holding tank are transferred to the reactor atthe beginning of the next cycle . (See figure RBatch Reactor Configuration - NoVent Case.)

To compute the amount of the batch charge, RBatch multiplies the flowsheetstream representing the batch charge by a cycle time you enter (either CycleTime or Batch Feed Time). Batch Feed Time is not the time required to chargethe reactor; it is a total cycle time used only to compute the amount of the charge.Batch Feed Time is required when Cycle Time is unknown.

If Batch Feed Time differs from the actual computed cycle time, the RBatchflowsheet inlet and outlet streams are not in mass balance. However, all internalRBatch calculations and reports will be correct for the computed batch charge.


Reactors

Continuous Feed A steady-state flowsheet stream fed continuously to thereactor during reaction. Its composition and temperature remain constantthroughout the reaction. Its flow rate either remains constant or follows aspecified time profile.

Reactor Product The material left in the reactor at the end of the reactorcycle. The flow rate of the reactor product stream equals the total mass in thereactor, divided by the reactor cycle time. You can think of this process asanalogous to transferring the reactor product to a product holding tank. Thistank is drawn down during the next reactor cycle to feed the continuous blocksdownstream (see figure RBatch Reactor Configuration - No Vent Case ).

Vent Product The contents of the vent accumulator at the end of the reactorcycle. During the reactor cycle, the time-varying vent stream accumulates in thevent accumulator (see figure RBatch Reactor Configuration - Vent Case). Theflow rate of the vent product stream is the total mass in the vent accumulator,divided by the reactor cycle time.

FeedHolding

Tank

FlowsheetStream for

BatchCharge

Batch chargetransferredonce each

cycle

ProductHolding

Tank

Reactorproduct

transferredonce each

cycle

FlowsheetStream for

ReactorProduct

Reactor

RBatch Reactor Configuration—No Vent Case


Chapter 5

FeedHolding

Tank

FlowsheetStream for

BatchCharge

Batch chargetransferredonce each

cycleProductHolding

Tank

Reactorproduct

transferredonce each

cycle

FlowsheetStream for

ReactorProduct

VentHolding

Tank

VentAccumulator

VentProduct

transferredonce per

cycle

FlowsheetStream for

VentProduct

Reactor

Optional FlowsheetStream for

Continuous Feed

RBatch Reactor Configuration—Vent Case

❖ ❖ ❖ ❖


Reactors


Chapter 6

6 Pressure Changers

This chapter describes the unit operation models for pumps and compressors,and models for calculating pressure change through pipes and valves. The modelsare:


Pump Pump or hydraulic turbine Changes stream pressurewhen the power requirementis needed or known

Pumps and hydraulic turbines

Compr Compressor or turbine Changes stream pressurewhen power requirement isneeded or known

Polytropic compressors, polytropic positivedisplacement compressors, isentropiccompressors, isentropic turbines

MCompr Multistage compressor orturbine

Changes stream pressureacross multiple stages withintercoolers. Allows for liquidknockout streams fromintercoolers

Multistage polytropic compressors, polytropicpositive displacement compressors, isentropiccompressors, isentropic turbines

Valve Valve pressure drop Models pressure dropthrough a valve

Control valves and pressure changers

Pipe Single segment pipe Models pressure dropthrough a single segment ofpipe

Pipe with constant diameter (may includefittings)

Pipeline Multiple segment pipeline Models pressure dropthrough a pipe or annularspace

Pipeline with multiple lengths of differentdiameter or elevation

Use Pump, Compr, and MCompr models when energy-related information such aspower requirement is needed or known.


PressureChangers

PumpPump/Hydraulic Turbine

Use Pump to model a pump or a hydraulic turbine.

Pump is designed to handle a single liquid phase. For special cases, you canspecify two- or three-phase calculations to determine the outlet stream conditionsand to compute the fluid density used in the pump equations. The accuracy of theresults depends on a number of factors, such as the relative amounts of thephases present, the compressibility of the fluid, and the efficiency specified.

Use Pump to change pressure when the power requirement is needed or known.For pressure change only, you can use other models such as Heater.

Pump can model pumps and hydraulic turbines.

Use the Pump block to rate a pump or a turbine by specifying scalar parametersor by specifying the related performance curves. To use the performance curves,you can specify either:• Dimensional curves such as head versus flow or power versus flow• Dimensionless curves such as head coefficient versus flow coefficient

Flowsheet Connectivity for Pump

Work(optional)

Material

Work (optional)

Water (optional)





Chapter 6

Work StreamsInlet Any number of work streams (optional)

Outlet One work stream for the net work load (optional)

If you do not specify either power or pressure on the Setup Specifications sheet,Pump uses the sum of the inlet work streams as a power specification.Otherwise, Pump uses the inlet work stream(s) only to calculate the net workload. The net work load is the sum of the inlet work streams minus the actual(calculated) work load.

You can use an optional outlet work stream for the net work load.

Specifying PumpUse the Setup Specifications sheet for Pump specifications.

If you specify Pump calculates

Discharge pressure Power required or produced

Pressure increase (for a pump) or decrease (for a turbine) Power required or produced

Pressure ratio (outlet pressure to inlet pressure) Power required or produced

Power required (for a pump) or produced (for a turbine) Discharge pressure

Curves of head, discharge pressure, pressure ratio,pressure change, or head coefficient

Power required or produced

Power curve Discharge pressure

You can supply a Fortran subroutine to calculate performance curves in Pump.See ASPEN PLUS User Models for more information.

Use the following forms to enter specifications and view results for Pump:


Setup Specify operating conditions, efficiencies, net positive suction head parameters,specific speed parameters, valid phases, and flash convergence parameters

PerformanceCurves Specify parameters and enter data for the performance curves

UserSubroutines Specify name and parameters for the user performance curve subroutine


Results View summary of Pump results, material and energy balance results, andperformance curve summary


PressureChangers

NPSH Available

The Net Positive Suction Head (NPSH) available for a pump is defined as:

NPSHA P P H Hin vapor v s= − + +

Where:

NPSHA = Net Positive Suction Head Available

Pin = Inlet pressure

Pvapor = Vapor pressure of the liquid at inlet conditions

Hv = Velocity head(= u g2 2/ , u is the velocity and g is gravitation constant)

H s = Hydraulic static head corrected to the pump centerline

The NPSH available has to be greater than the NPSH required (NPSHR) to avoidcavitation. NPSH required is a function of pump design.

NPSH Required

The Net Positive Suction Head (NPSH) required can be considered the suctionpressure required by the pump for safe, reliable operation. The NPSHR can bespecified using the performance curves on the PerformanceCurves NPSHR sheet,or calculated from the following empirical equation by specifying suction specificspeed ( N ss ) on the Setup CalculationOptions sheet.

NPSHRN Q

N ss

=

0 54

3.

Where:

NPSHR = Net Positive Suction Head Required

N = Pump shaft speed (rpm)

Q = Volumetric flow rate at the suction conditions

N ss = Suction specific speed


Chapter 6

The units for Q and NPSHR are:

US: Q in gal/min and NPSHR in feet

Metric: Q in cum/hr and NPSHR in meters

Specific Speed

Specific speed and suction specific speed are two important parameters thatdefine the suitability of a pump design for its intended conditions. The pumpspecific speed is defined as:

NN Q

Heads =0 5

0 75

.

.

Where:

Head = Head developed across the pump

N s = Specific speed



The units for Q and Head are:

US: Head in feet

Metric: Head in meters


PressureChangers

In general, pumps with a low specific speed are termed low capacity and thosewith a high specific speed are termed high capacity. For a turbine, the specificspeed is defined as follows:

NN BHP

Heads =0 5

1 25

.

.

Where:

N s = Specific speed

BHP = Developed horsepower

Head = Total dynamic head across turbine

Suction Specific Speed

Suction specific speed ( N ss ) is an index number for a centrifugal pump and isused to define its suction characteristic. It is defined as follows:

NN Q

NPSHRss =0 5

0 75

.

.

Where:

NPSHR = Net positive suction head required for a pump or netpositive discharge head required for a turbine

N ss = Suction specific speed



The units for Q and NPSHR are:

US: Q in gal/min and NPSHR in feet

Metric: Q in cum/hr and NPSHR in meters


Chapter 6

Suction specific speed is a criterion of a pump’s performance with regard tocavitation. For a pump of normal design, values of N ss vary from 6,000 to 12,000in US units. A typical value is 8,500.

Head Coefficient

Head coefficient is defined as follows:

HeadcHead g

u=

2

Where:

Headc = Head coefficient

Head = Head developed across the pump

g = Gravitational constant

u = Impeller tip speed

Flow Coefficient

Flow coefficient is the ratio of discharge throat velocity to impeller tip speed. It isdefined as:

FlowcQ

A u=

1

A d1 12 4= ×π /

Where:

Flowc = Flow coefficient

Q = Volumetric flow rate

A1 = Cross-sectional area of discharge throat

d1 = Diameter of discharge throat

u = Impeller tip speed


PressureChangers

The diameter of throat and diameter of impeller are related by the followingempirical equation:

Nd

Diams = 5500 1

Where:

N s = Specific speed at the best efficiency point

Diam = Diameter of impeller

You can specify Specific Speed ( N s ) on the Setup CalculationOptions sheet.


Chapter 6

ComprCompressor/Turbine

Use Compr to model:• A polytropic centrifugal compressor• A polytropic positive displacement compressor• An isentropic compressor• An isentropic turbine

Use Compr to change stream pressure when energy-related information, such aspower requirement, is needed or known.

Compr can handle single-phase as well as two- and three-phase calculations.

You can use Compr to rate a single stage of a compressor or a single wheel of acompressor, by specifying the related performance curves. Compr allows you tospecify either:• Dimensional curves, such as head versus flow or power versus flow• Dimensionless curves, such as head coefficient versus flow coefficient

Compr can also calculate compressor shaft speed.

Compr cannot handle performance curves for a turbine.

Flowsheet Connectivity for Compr


Material

Water (optional)

Work(optional)

Work (optional)




PressureChangers


Outlet One work stream for net work load (optional)

If you do not specify either power or pressure on the Compr Setup Specificationssheet, Compr uses the sum of the inlet work streams as a power specification.Otherwise, Compr uses the inlet work stream(s) only to calculate the net workload. The net work load is the sum of the inlet work streams minus the actual(calculated) work load.

You can use an optional outlet work stream for the net work load.

Specifying Compr

If you specify Compr calculates


Power required (for a compressor) or produced (for a turbine) Discharge pressure

Curves of head, power, discharge pressure, pressure ratio, pressurechange, or head coefficient

Power required and discharge pressure

Discharge pressure and curves of head or power or head coefficient Power required, discharge pressure, and shaftspeed

Power required and curves of discharge pressure, pressure ratio, orpressure change

Discharge pressure, and shaft speed

When you use performance curves, you can specify either a scalar value ofefficiency or efficiency curves.

You can supply a Fortran subroutine to calculate performance curves in Compr.See ASPEN PLUS User Models for more information.

Some required specifications depend on the compressor type. Specify thecompressor type on the Setup Specifications sheet.

You can model a polytropic compressor using either the GPSA or ASME method.You can model an isentropic compressor/turbine using either the GPSA, ASME,or Mollier-based methods.

The GPSA method can be based on either:• Suction conditions• Average of suction and discharge conditions


Chapter 6

The ASME method is more rigorous than the GPSA method for polytropic orisentropic compressor calculations. The Mollier method is the most rigorous forisentropic calculations.

Use the following forms to enter specifications and view results for Compr:


Setup Identify compressor specifications, calculation options, convergence parameters,and valid phases

Performance Curves Specify parameters and enter data for the performance curves

User Subroutine Enter performance curve subroutine parameters and name


Results View summary of Compr results, material and energy balance results, andperformance curve summary


Polytropic Efficiency

The polytropic efficiency ηp is used in the equation for the polytropic

compression ratio:

n

n

k

k p

− = −

1 1 η

The basic compressor relation is:

∆hP V

n

n

P

Pin in

p

out

in

n

n

= −

−

−

η 11

1

Where:

n = Polytropic coefficientk = Heat capacity ratio Cp/Cvηp = Polytropic efficiency

∆h = Enthalpy change per mole

P = PressureV = Molar volume


PressureChangers

Isentropic Efficiency

There are two equations for the isentropic efficiency ηs

For compression:

ηsouts

in

out in

h h

h h= −

−

For expansion:

ηsout in

outs

in

h h

h h= −

−

Where :

h = Molar enthalpy

houts = Outlet molar enthalpy assuming isentropic compression or

expansion to the specified outlet pressure

Mechanical Efficiency

Mechanical efficiency ηm is used to calculate the brake horsepower:

IHP F h= ∆

BHP IHP m= / η

Where:

IHP = Indicated horsepowerF = Mole flow rate∆h = Enthalpy change per mole

BHP = Brake horsepowerηm = Mechanical efficiency


Chapter 6

MComprMultistage Compressor/Turbine

Use MCompr to model:• A multi-stage polytropic compressor• A multi-stage polytropic positive displacement compressor• A multi-stage isentropic compressor• A multi-stage isentropic turbine

For polytropic compressors, MCompr can handle a single, compressible phase.For special cases you can specify two- or three-phase calculations. Thesecalculations determine the outlet stream conditions and the properties used inthe compressor equations. The accuracy of results depends primarily on therelative amounts of the phases present and the efficiency specified. The rigorouspolytropic compressor uses real fluid properties calculated from the propertymethod you specify. It does not assume ideal gas behavior.

MCompr handles single-phase isentropic compressors and turbines. MCompr canalso handle two- and three-phase mixtures.

You can use MCompr to rate a multi-stage compressor, by using either:• Stage-by-stage dimensional performance curves, such as head versus flow or

power versus flow• Wheel-by-wheel dimensionless performance curves, such as head coefficient

versus flow coefficient

MCompr can also calculate shaft speed.

MCompr cannot handle performance curves for a turbine.

Flowsheet Connectivity for MCompr

Heat(optional)

Work(optional)

Work(any number)

ToStageK + 1

FromStageK - 1

Feed toStageK + 1(any number)

Heat(any number)

Water(optional)

KnockoutStage K

Cooler

Stage KCompressor

Stage K


PressureChangers

Material StreamsInlet At least one material stream for the first compressor stage

One or more material streams for stages after the first (optional). Thesestreams enter the intercooler before the stages you specify.

Outlet One material stream leaving the last compressor stageEither one optional knockout material stream for each intercooler for theliquid formed, or one optional global knockout for the liquid formed in allintercoolersEither one optional water decant stream for each intercooler, or oneoptional global water decant stream

If you use liquid knockout outlet streams from one stage, you must use them forall stages. The last stage cannot have a liquid knockout material stream or awater decant stream.

Heat StreamsInlet Any number of heat streams to each intercooler (optional)

Outlet Either one optional heat stream for the net heat load of each intercooler,or one global heat outlet stream for the net heat duty for all intercoolers

If you do not specify cooler conditions on the Setup Cooler sheet, MCompr addsthe heat streams together and uses the total as a duty specification for the cooler.

The net heat load equals the heat in the inlet heat streams minus the actual(calculated) heat duty.

If you use a heat outlet from one stage, you must use one for all stages.

Work StreamsInlet Any number of work streams to each compressor stage (optional)

Outlet Either one optional work stream for net work load, or one global workstream for the net power for all compressor stages

MCompr adds all work inlet streams together to provide the power requirement.If you do not specify power or pressure on the Setup Specs sheet, MCompr usesthe total power as a power specification for the stage.

The power in the outlet work stream equals the power in the inlet work streamsminus the actual (calculated) power required.

If you use a work outlet from one stage, you must use one for all stages.


Chapter 6

Specifying MCompr

If you specify MCompr calculates


Power required (for a compressor) or produced (for a turbine) Discharge pressure

Curves of head, power, discharge pressure, pressure ratio,pressure change, or head coefficient

Power required and discharge pressure

Discharge pressure and curves of head or power or headcoefficient

Power required and shaft speed

When you use performance curves, you can specify either a scalar value forefficiency or efficiency curves.

You can supply a Fortran subroutine to calculate performance curves inMCompr. See ASPEN PLUS User Models for more information.

MCompr can have an intercooler between each compression (or expansion) stage,and an aftercooler after the last stage. You can perform one-, two-, or three-phaseflash calculations in the intercoolers. Each cooler can have a liquid knockoutstream, except the cooler after the last stage.

You can model a polytropic compressor using either the GPSA1 or ASME2

method. You can model an isentropic compressor/turbine using either the GPSA,ASME, or Mollier-based methods.

The GPSA method can be based on either:• Suction conditions• Average of suction and discharge conditions

The ASME method is more rigorous than the GPSA method for polytropic orisentropic compressor calculations. The Mollier method is the most rigorous forisentropic calculations.

Use the following forms to enter specifications and view results for MCompr:


Setup Identify multi-stage compressor specifications, stage specifications, cooler specifications,convergence parameters, and valid phases

Performance Curves Specify parameters and enter data for the performance curves

User Subroutine Specify performance curve user subroutine parameters and name


continued


PressureChangers


BlockOptions Override global values for physical properties, simulation options, diagnostic message levels, and reportoptions for this block

Results View summary of operating results, material and energy balance results, compressor and cooler profiles,and performance profiles


Polytropic Efficiency

The polytropic efficiency ηp is used in the equation for the polytropic compression

ratio:

n

n

k

k p

− = −

1 1 η

The basic compressor relation is:

∆hP V

n

n

P

Pin in

p

out

in

n

n

= −

−

−

η 11

1

Where:

n = Polytropic coefficient

k = Heat capacity ratio Cp/Cv

ηp = Polytropic efficiency


P = Pressure

V = Molar volume

Isentropic Efficiency

There are two equations for the isentropic efficiency η s

For compression:

ηsouts

in

out in

h h

h h= −

−


Chapter 6

For expansion:

ηsout in

outs

in

h h

h h= −

−

Where :

h = Molar enthalpy

houts = Outlet molar enthalpy assuming isentropic compression or

expansion to the specified outlet pressure

Mechanical Efficiency

Mechanical efficiency ηm is used to calculate the brake horsepower:

IHP F h= ∆

BHP IHP m= / η

Where:

IHP = Indicated horsepower

F = Mole flow rate


BHP = Brake horsepower

ηm = Mechanical efficiency

Parasitic Pressure Loss

The parasitic pressure loss at the suction of a stage is calculated using theequation:

∆P KV

= ρ2

2

Where:

∆ P = Parasitic pressure loss

K = Velocity head multiplier

ρ = Density

V = Linear velocity of process gas at suction conditions


PressureChangers

Specific Speed

The specific speed is defined as:

SpSpd = ShSpd (VflIn)

(Head)

0.5

0.75

Where:

ShSpd = Shaft speed

VflIn = Suction volumetric flow rate

Head = Head developed

Specific Diameter

The specific diameter is defined as:

SpDiam = ImpDiam (Head)

(VflIn)

0.25

0.5

Where:

ImpDiam = Impeller diameter of compressor wheel


VflIn = Volumetric flow rate at suction conditions

Head Coefficient

The head coefficient is defined as:

Hc = Head g

( ShSpd ImpDiam) 2π

Where:


g = Gravitational constant

π = 3.1416

ShSpd = Shaft speed



Chapter 6

Flow Coefficient

The flow coefficient is defined as:

FcVflIn

ShSpd (ImpDiam=

)3

Where:

VflIn = Volumetric flow rate at suction conditions

ShSpd = Shaft speed


References

1. GPSA Engineering Data Book, 1979, Chapter 4, pp. 5-6 to 5-10.

2. ASME Power Test Code 10, 1965, pp. 31-32.


PressureChangers

ValveValve Pressure Drop

Valve models control valves and pressure changers. Valve relates the pressuredrop across a valve to the valve flow coefficient. Valve assumes the flow isadiabatic, and determines the thermal and phase condition of the stream at thevalve outlet. Valve can perform one-, two-, or three-phase calculations.

Flowsheet Connectivity for Valve

Material Material

Material StreamsInlet One material stream


Specifying ValveUse the Input Operation sheet to select the calculation type.

If you select the Pressure changer option or the Design option for the calculationtype, you must specify, on the same sheet, one of the following:• Outlet pressure• Pressure drop

If you select the Pressure changer option, the specification is complete and Valveperforms an adiabatic flash to calculate the thermal and phase condition of theoutlet stream.

If you select the Rating option for the calculation type, you must specify, on thesame sheet, one of the following:• Flow coefficient at operating valve position• Valve operating position (% Opening)


Chapter 6

If you specify the valve operating position, you must also specify one of thefollowing on the Input ValveParameters sheet:• Characteristic equation type and flow coefficient at maximum valve opening• Data for flow coefficient (Cv) versus valve opening in the Valve Parameters

Table• A valve from the built-in library based on valve type, manufacturer,

series/style, and size

On the Input CalculationOptions sheet, you can specify that Valve:• Check for choked flow• Calculate cavitation index

For vapor-containing streams, you must specify the pressure drop ratio factor(Xt) for the valve. For liquid-containing streams, if you specify that Valve checkfor choked flow, you must also specify the pressure recovery factor (Fl) for thevalve. You can specify the pressure drop ratio factor and the pressure recoveryfactor for the valve in one of the following ways on the Input ValveParameterssheet:

Specify

Value at the operating valve position (Pres Drop Ratio Factor, Pres Recovery Factor)

Data for pressure drop ratio factor (Xt) and for pressure recovery factor (Fl) versus valve opening (% Opening) in the ValveParameters Table

A valve from the built-in library based on Valve Type, Manufacturer, Series/Style, and Size

If you want to include the effect of head loss from pipe fittings on the valve flowcapacity, you must specify the diameters of the valve and pipe fittings on theInput PipeFittings sheet. Valve uses the valve and pipe diameters, and estimatesthe piping geometry factor to account for the reduction in flow capacity.

Use the following forms to enter specifications and view results for Valve:


Input Specify valve operating conditions, flash convergence parameters, valid phases, valveparameters, sizes for pipe fittings, calculation options, and Valve convergence parameters

Block Options Override global values for physical properties, simulation options, diagnostic message levels,and report options for this block

Results View summary of operating results and mass and energy balances


PressureChangers

Pressure Drop Ratio Factor

The pressure drop ratio factor ( Xt ) accounts for the effect of the internalgeometry of the valve on the change in fluid density as it passes through thevalve.

The pressure drop ratio factor is the limiting value (under choked conditions) ofthe pressure drop ratio and is given by:

XF

dP

Ptk

ch

in

=

1(1)

Where:

dPch = Pressure drop for choked vapor flow

Fk = Ratio of specific heats factor


You can specify the pressure drop ratio factor on the Input ValveParameterssheet in one of the following ways:• Choose a Library Valve• Enter data for Xt and % Opening in the Valve Parameters Table• Specify the value at the operating valve position in Valve Factors

If you know the ratio of the gas sizing coefficient ( )Cg to the liquid sizing

coefficient ( )Cv , as defined in Fisher Controls Company Control Valve Handbook,you can calculate the pressure drop ratio factor (with the assumption Fk = 1) byeither:

• Using valve manufacturer’s data for dP

Pch

in

versus

C

Cg

v

in equation (1)

• Using the expression

XF

C

Ctk

g

v

=×

−6 31 10 4 2.

This relationship is based on equating the choked flow calculated (in US units ofmeasure) with:

Universal Gas Sizing Equation W C rPch g in= 106.

ISA Standard Valve Sizing Equation W N C Y F X rPch v k t in= 6


Chapter 6

Where:

Wch = Mass flow rate (choked flow)

r = Mass density of inlet stream

Y = Expansion factor (= 0.667 for choked flow)

N 6 = Numerical constant (= 63.3 for US units of measure)

If you specify the pressure drop ratio factor by choosing a valve from the built-inlibrary or by entering data in the Valve Parameters Table on the InputValveParameters sheet, Valve uses cubic splines to interpolate the value of thepressure drop ratio factor at the operating valve position.

Valve uses the pressure drop ratio factor only when both of the following aretrue:• Vapor is present in the inlet stream• The Design or Rating option is selected for Calculation Type on the Input

Operation sheet

Pressure Recovery Factor

The pressure recovery factor ( )Fl accounts for the effect of the internal geometry

of the valve on its liquid flow capacity under choked conditions.

The pressure recovery factor is defined as:

FdP

P Plch

in vc

=−

1 2/

Where:

dPch = Pressure drop for choked liquid flow


Pvc = Pressure at the vena contracta in the valve

and

Pvc = F Pf v

with

Pv = Vapor pressure of inlet liquid stream

Ff = Liquid critical pressure ratio factor


PressureChangers

You can specify the pressure recovery factor on the Input ValveParameters sheetin one of the following ways:• Choose a Library Valve• Enter data for Fl and % Opening in the Valve Parameters Table• Specify the value at the operating valve position in Valve Factors

The pressure recovery factor is equivalent to the valve recovery coefficient Km , asdefined in Fisher Controls Company Control Valve Handbook.

You can use the valve recovery coefficient to calculate the pressure recoveryfactor as:

F Kl m=

If you specify the pressure recovery factor by choosing a valve from the built-inlibrary or by entering tabular data in the Valve Parameters Table on the InputValveParameters sheet, Valve uses cubic splines to interpolate the value of thepressure recovery factor at the operating valve position.

The pressure recovery factor is used in the Valve model calculations only whenall of the following are true:• Liquid is present in the inlet stream• The Check for Choked Flow box is checked or the Set Equal to Choked Outlet

Pressure option is selected on the Input CalculationOptions sheet• The Design or Rating option is selected for Calculation Type on the Input

Operation sheet.

Valve Flow Coefficient

The valve flow coefficient ( )Cv measures the flow capacity of the valve. The flowcoefficient is defined as the number of US gallons per minute of water (at 60°F)that will pass through the valve with a pressure drop of 1 psi.

The valve flow coefficient relates the pressure drop across the valve to the flowrate as (Instrument Society of America, 1985)1:

Liquid W N F C r P Pp v in out= −6 ( )

Gas/Vapor W N F Y r P Pp in out= −6 ( )

withY

P P

F X Pin out

k t in

= −−

13


Chapter 6

Where:

W = Mass flow rate

N 6 = Numerical constant (based on the units of measure)

Fp = Piping geometry factor

Cv = Valve flow coefficient

Y = Expansion factor


Pout = Outlet pressure

r = Mass density of inlet stream


X t = Pressure drop ratio factor

You can specify the flow coefficient in one of the following ways:• Use Flow Coef on the Input Operation sheet to specify the value at the

operating valve position• Choose a Library Valve on the Input ValveParameters sheet• Enter data for Cv and % Opening in the Valve Parameters Table on the Input

ValveParameters sheet• Specify Valve Characteristics in the Input ValveParameters sheet

If you specify the flow coefficient by choosing a valve from the built-in library orby entering data in the Valve Parameters Table, Valve uses cubic splines tointerpolate the value of the flow coefficient at the operating valve position.


PressureChangers

Characteristic Equation Type

The characteristic equation for the valve relates the flow coefficient to the valveopening. Use the Input ValveParameters sheet to specify the characteristicequation type. The six built-in characteristic equations are:

Type Equation †

Linear V P=

ParabolicV P= 0 01 2.

Square RootV P= 10 0.

Quick Opening

( )V

P

P=

+ × −

10 0

10 9 9 10 3 2

.

. .

Equal Percentage

VP

P=

− × −

0 01

2 0 10 10

2

8 4

.

. .

Hyperbolic

( )V

P

P=

− × −

01

10 9 9 10 5 2

.

. .

† Where:P = Valve opening as a percentage of maximum openingV = Flow coefficient as a percentage of flow coefficient at maximum opening

Piping Geometry Factor

The piping geometry factor is defined as:

FC

Cpp= υ

υ

Where:

C pυ = Flow coefficient of the valve with attached fittings

Cυ = Flow coefficient of the valve installed in a straight pipe of thesame size

The piping geometry factor accounts for the reduction in the flow capacity of avalve due to the head loss from the pipe fittings. The piping geometry factor hasa default value of 1.0 if the valve and pipe fittings have the same diameter.


Chapter 6

ASPEN PLUS calculates the piping geometry factor as (Instrument Society ofAmerica, 1985)1:

FKC

N dp = +

−

Σ 2

24

0 5

1υ

.

with ΣK K K K KB B= + + −1 2 1 2

Where:

Kd

D1

2

12

2

05 1= −

. , K

d

D2

2

22

2

10 1= −

. , K

d

DB11

4

1= −

, K

d

DB22

4

1= −

and:

Fp = Piping geometry factor

Cυ = Valve flow coefficient

N2 = Numerical constant (based on the units of measure)

d = Valve diameter

K K1 2, = Resistance coefficients of the inlet and outlet fittings

K KB B1 2, = Bernoulli coefficients for the inlet and outlet fittings

D1 = Inlet pipe diameter

D2 = Outlet pipe diameter

If the valve and pipe fittings diameters are different and you wish to include theeffect of the additional head loss on the valve flow capacity, you must specify thevalve and pipe diameters on the Input PipeFittings sheet.


PressureChangers

Choked Flow

ASPEN PLUS calculates the limiting pressure drop for choked flow conditionsusing (Instrument Society of America, 1985)1:

Liquid ( )dP F P F Plc L in f= −2υ

Vapor dP F X Pc k T inυ =

withF

P

Pfv

c

= −

0 96 0 28

0 5

. .

.

Where:

FL = Pressure recovery factor

Ff = Liquid critical pressure ratio factor


XT = Pressure drop ratio factor


Pυ = Vapor pressure at inlet

Pc = Critical pressure at inlet

dPlc = Limiting pressure drop, liquid phase

dPvc = Limiting pressure drop, vapor phase

For multi-phase streams, Valve takes the limiting pressure drop for choked flowto be the smaller of dPlc and dPvc . Flow in the valve is choked when the pressuredrop exceeds this limiting pressure drop. Valve displays the choking status of thevalve if you check the Check for Choking box on the Input CalculationOptionssheet.


Chapter 6

Cavitation Index

The likelihood of cavitation in a valve is measured by the cavitation index.ASPEN PLUS calculates the cavitation index as (Instrument Society of America,1985)1:

KP P

P Pcin out

in v

=−−

Where:

Kc = Cavitation index


Pout = Outlet pressure

Pv = Vapor pressure at inlet

The cavitation index definition is valid only for all-liquid streams. Valvecalculates the cavitation index if you check the Calculate Cavitation Index box onthe Input CalculationOptions sheet.

References

1. Flow Equations for Sizing Control Valves, ISA-S75.01-1985, InstrumentSociety of America, 1985.


PressureChangers

PipePipe Pressure Drop

Pipe calculates the pressure drop and heat transfer in a single segment pipe. Youcan also use Pipe to model the pressure drop due to fittings.

Pipe handles a single inlet and outlet material stream. Pipe assumes the flow isone-dimensional, steady-state, and fully developed (that is, no entrance effectsare modeled). Pipe can perform one-, two-, or three-phase calculations. Flowdirection and elevation angle are arbitrary.

To model multiple pipe segments of different diameters or elevations, usePipeline instead of Pipe.

If the inlet pressure is known, Pipe calculates the outlet pressure. If the outletpressure is known, Pipe calculates the inlet pressure and updates the statevariables of the inlet stream.

Use Pipe to:• Calculate inlet or discharge conditions• Calculate pressure drops for one-, two-, or three-phase vapor and liquid flows

Flowsheet Connectivity for Pipe

Material

Material




Chapter 6

Specifying PipeYou must specify the following for Pipe:• Pipe length, diameter, roughness, and angle on the Setup PipeParameters

sheet• Thermal specification type on the Setup ThermalSpecification sheet to

determine whether Pipe operates with a temperature profile or temperatureis calculated

• Whether to integrate, assume constant dP/dL, or use a closed form equationon the Advanced Methods sheet

• Frictional and holdup correlation when a closed form equation is not used onthe Advanced Methods sheet

• Pressure and temperature grid for fluid property calculations on theAdvanced PropertyGrid sheet, if you request a pressure-temperature grid onthe AdvancedCalculation Options sheet

• Integration direction in which calculations proceed with respect to flow on theAdvanced CalculationOptions sheet

If the option selected is Pipe needs the And the integration direction is

Calculate pipe outletpressure (default)

Inlet pressure Downstream

Calculate pipe inlet pressure Outlet pressure Upstream

Pipe uses the inlet or outlet stream pressure to start the calculations. If thestream is an external feed to your flowsheet, or the outlet of a block that willexecute after Pipe, use the Stream Specifications sheet to specify the streampressure. If the integration direction is upstream, you can also specify the initialpressure for Pipe on the Advanced CalculationOptions sheet, by entering theoutlet pressure. This pressure value will override the stream pressure entered onthe Stream Specifications sheet.

Select the flow calculation option on the Advanced CalculationOptions sheet tospecify whether Pipe is to calculate the outlet or inlet stream flow andcomposition.

If the option selected is Pipe needs the

Reference inlet stream(default)

Inlet flow and composition

Use outlet stream flow Outlet flow and composition


PressureChangers

Use the following forms to enter specifications and view results for Pipe:


Setup Specify pipe parameters, thermal specifications, fittings, flash convergenceparameters and property profiles to be reported

Advanced Specify calculation options, solution methods, property grid, integrationparameters and Beggs and Brill coefficients

UserSubroutine Specify pressure drop and/or holdup user subroutine name and parameters


Results View summary of Pipe results, inlet and outlet stream results, material andenergy balance results, and profiles

Stream Specification

You must initialize the inlet stream to Pipe whenever the option to referenceinlet stream is selected, even if the inlet pressure is being calculated. Similarly,you must initialize the outlet stream whenever the option to use the outletstream flow is selected. The initialized stream must be one of the following:• Entered on a Stream Specifications sheet• An outlet stream from part of the flowsheet executed (if option to use outlet

stream flow is selected)• Transferred from another part of a flowsheet using a Transfer block

Physical Property Calculations

You can specify that a rigorous flash is to be performed each time properties arecalculated, by selecting the option to do Flash at Each Integration Step on theAdvanced CalculationOptions sheet. If you select the option to Interpolate fromProperty Grid, Pipe will determine properties by interpolating in a table ofproperty values at various temperatures and pressures. Specify one of thefollowing if you use the Property Grid:• A range of temperatures and pressures on the Advanced Property Grid sheet.

Pipe will calculate properties at these conditions and interpolate• The block ID of a Pipe block for which the option to interpolate from property

grid was also selected, and which will be executed before the current block inthe flowsheet


Chapter 6


Pipe can calculate pressure drop for either one-, two-, or three-phase vapor andliquid flows. If vapor-liquid flow exists, Pipe also calculates liquid holdup andflow regime (pattern). You may specify a flowing fluid temperature profile, orPipe can determine it from heat transfer calculations. Pipe treats multiple liquidphases (for example, oil and water) as a single homogeneous liquid phase forpressure-drop and holdup calculations. Pipe automatically detects the specialcase of a single component fluid (for example, steam) and treats it appropriately.

Downstream and Upstream Integration

For downstream and upstream integration, the combination of options selectedfor pressure and flow calculation on the Advanced CalculationOptions sheetdetermine which stream Pipe will update. The following table describes theavailable combinations. The next figure, Downstream and Upstream Integration,defines the inlet and outlet stream and pressure variables:

If the pressure calculation option is And the flow calculation option is Then Pipe updates the

Calculate pipe outlet pressure Reference inlet stream Outlet stream only

Calculate pipe outlet pressure Use outlet stream flow Outlet stream thermodynamic conditions

Inlet stream composition and flow

Calculate pipe inlet pressure Use outlet stream flow Inlet stream only

Calculate pipe inlet pressure Reference inlet stream Inlet stream thermodynamic conditions

Outlet stream composition and flow

Inlet Stream

Inlet Pressure Outlet Pressure

Outlet Stream



PressureChangers

Design-Spec Convergence Loop

Use caution when using Pipe inside a Design-Spec convergence loop. Forexample, you can manipulate the flow rate to a pipe to achieve a desired pipeoutlet pressure. During the design specification convergence, the flow ratevariables may become unreasonable in an intermediate iteration, causing Pipe topredict a negative pressure. Convergence difficulties occur as a result. You canavoid this situation by doing one of the following:• Keep the upper limit of the flow rate sufficiently low in Design-Spec• Perform an upstream integration from the known outlet pressure. Select

option to calculate pipe inlet pressure on the Advanced CalculationOptionssheet for this purpose. Define a Design-Spec to manipulate the flow rate toachieve the specified inlet pressure.

Erosional Velocity

Erosional velocity is the velocity of the fluid in the pipe, above which the pipematerial will start to break off. The fluid is traveling so fast that it starts to stripmaterial from the walls of the pipe. In general use, the flow rate should be belowthis value.

You can specify the erosional velocity coefficient on the Setup Pipe Parameterssheet.

The erosional velocity is related to the erosional velocity coefficient by thefollowing equation:

υρc

c=

Where:

υc = Erosional velocity in ft/second

c = Erosional velocity coefficient (default=100)

ρ = Density in lbs/cubic ft

Methane Gas Systems

Gas systems consisting mostly of methane occur frequently in the dense-phaseregion of wellbores and flowlines. In the dense-phase region, definable vapor andliquid phases do not exist. Equation-of-state methods classify the dense-phasematerial as either all vapor or all liquid. Significant differences in the predictedfluid transport properties may occur, depending on whether you choose the vaporor liquid state.


Chapter 6

Experience has shown that gas system flow in the dense-phase region is bestmodeled by using vapor-phase properties. For systems consisting of mostlymethane, where the pipe conditions lie above the cricondenbar of the phaseenvelope, specify vapor-only valid phase on the Setup FlashOptions sheet.

Modeling Valves and Fittings

Pipe assumes that the pressure drop due to valves and fittings is distributedevenly along the specified length of the pipe. The total length Pipe uses incalculations corresponds to the specified pipe length, plus any equivalent pipelength due to valves, fittings, and miscellaneous L/D.

If the pipe is not horizontal, Pipe adjusts the angle from the horizontal to achievethe same vertical rise or fall for the total length used in the calculations. Thisadjustment ensures the correct pressure drop due to elevation.

If the order and position of the valves and fittings are important, you need tomodel each valve and fitting separately with a Pipe model, specifying zero lengthof pipe.

Two-Phase CorrelationsThe following tables list the two-phase frictional pressure drop and holdupcorrelations available.

Two-Phase Friction Factor Correlations

Pipe orientation Inclination Friction factor correlations

Horizontal -2 deg to +2 deg Beggs and Brill (BEGGS-BRILL)Dukler (DUKLER)Lockhart-Martinelli (LOCK-MART)User subroutine (USER-SUBR)

Vertical +45 deg to +90 deg Beggs and Brill (BEGGS-BRILL)Orkiszewski (ORK)Angel-Welchon-Ros (AWR)Hagedorn-Brown (H-BROWN)User subroutine† (USER-SUBR)

Downhill -2 deg to -90 deg Beggs and Brill (BEGGS-BRILL)Slack (SLACK)Darcy (DARCY)User subroutine† (USER-SUBR)

†See ASPEN PLUS User Models.

continued


PressureChangers


Inclined +2 deg to +45 deg Beggs and Brill (BEGGS-BRILL)Dukler (DUKLER)Orkiszewski (ORKI)Angel-Welchon-Ros (AWR)Hagedorn-Brown (H-BROWN)Darcy (DARCY)User subroutine† (USER-SUBR)


Two-Phase Liquid Holdup Correlations

Pipe orientation Inclination Liquid holdup correlations

Horizontal -2 deg to +2 deg Beggs and Brill (BEGGS-BRILL)Eaton (EATON)Lockhart-Martinelli (LOCK-MART)Hoogendorn (HOOG)Hughmark (HUGH)User subroutine† (USER-SUBR)

Vertical +45 deg to +90 deg Beggs and Brill (BEGGS-BRILL)Orkiszewski(ORKI)Angel-Welchon-Ros (AWR)Hagedorn-Brown (H-BROWN)User subroutine† (USER-SUBR)

Downhill -2 deg to -90 deg Beggs and Brill (BEGGS-BRILL)Slack (SLACK)User subroutine† (USER-SUBR)

Inclined +2 deg to +45 deg Beggs and Brill (BEGGS-BRILL)Flanigan (FLANIGAN)Orkiszewski (ORKI)Angel-Welchon-Ros (AWR)Hagedorn-Brown (H-BROWN)User subroutine† (USER-SUBR)


Note Some of the related information for the two-phase friction factorand liquid holdup correlations was taken from "Two-Phase Flowin Pipes" by James P. Brill and H. Dale Beggs, Sixth Edition,Third Printing, January, 1991.


Chapter 6

Beggs and Brill Correlation

The Beggs and Brill correlation1 considers slip and flow regimes are consideredwith this method. Friction factor and holdup correlations depend on flow regimeand pipe inclination. It is suitable for all inclinations, including vertical flowdownward.

Dukler Correlation

The Hughmark holdup method should be used with this pressure drop method.The Dukler method2 was developed from field data using air-water mixtures in1-inch pipes. It tends to overpredict frictional pressure drop. It is recommendedin a design manual published jointly by the AGA and API.

Hagedorn-Brown Correlation

The Hagedorn-Brown correlation3 considers slip between phases, but flow regimeis not considered. It uses the same correlations for liquid holdup and frictionfactor for all flow regimes. It is an old method which works well for conventionaloil wells. It is suitable for vertical upward flow, but not downward. It is generallyrecommended for gas wells, and is based on data obtained from U.S. Gulf Coastoil wells with 2-3/8 inch and 2-7/8 inch tubing.

Lockhart-Martinelli Correlation

The Lockhart-Martinelli correlation4 is one of the oldest pressure dropcorrelations. It does not consider pressure drop due to acceleration. The methodtreats the vapor and liquid phases separately and uses a correction factor to findthe 2-phase pressure gradient. Our implementation assumes turbulent gas andliquid phase flow.

Orkiszewski Correlation

Slip and flow regimes are considered in the Orkiszewski correlation5. The frictionfactor and holdup correlation depend on the flow regime. It is suitable for verticalflow upward, but not downward. It is generally reliable for oil wells. It mayexhibit problems for oil wells with high water cuts or high total gas to liquidratios. It can significantly underpredict pressure drop for higher rate and higherpressure wells (Beggs and Brill/1984) 3.


PressureChangers

Angel-Welchon-Ros Correlation

The Angel-Welchon-Ros correlation method6, 7 was developed for low gas-to-liquidratio water wells. It assumes no slip between the vapor and liquid phases whencalculating liquid holdup.

Slack Correlation

The Slack correlation method assumes a stratified flow regime, and should beused only for downhill flow.

Eaton Correlation

The Eaton correlation8 holdup method was developed from data on 2- and 4-inchpipes with a gas-water-crude mixture, and a 17-inch pipe with a gas-oil mixture.It is often used with the Dukler frictional pressure drop correlation.

Flanigan Correlation

The Flanigan correlation9 holdup methodwas developed from data taken in a16-inch pipe. It calculates liquid holdup as a function of superficial gas velocity.It is suitable for inclined flow.

Beggs and Brill Correlation Parameters

The following table lists the Beggs and Brill liquid holdup correlationparameters.

Flow Regime Name Description

Segregated BB1BB2BB3

Leading coefficient, A (default = 0.98)Liquid volume fraction exponent, alpha (default = 0.4846)Froude no. exp., beta (default = 0.0868)

Intermittent BB4BB5BB6


Distributed BB7BB8BB9


In addition, you can change the Beggs and Brill two-phase Friction Factor modifier,BB10 (default = 1.0).


Chapter 6

Closed-Form MethodsThe following are closed-form methods:• Smith• Weymouth• AGA• Oliphant• Panhandle A• Panhandle B• Hazen-Williams

Smith

The Smith method10 may be used for vertical dry gas flow. It should be consideredfor gas wells with condensate-gas ratios less than 50 bbls/mcf, water-gas ratiosless than 3.5 bbls/mcf, and flow rates above the Turner predicted critical rate.Smith does not model gas well loadup, and will significantly under predictwellbore pressure drop if loadup is actually occurring. Smith results must becross-checked against the Turner predicted critical rates to verify that the well isunloaded. Smith also does not model condensation of water vapor in the wellbore.

Weymouth

The Weymouth horizontal gas flow equation11 was first published in 1912. It isbased on data taken on pipes with diameters from 0.8 inches to 11.8 inches. As aresult, it is most accurate for smaller pipes having a diameter less than 12inches.

AGA

The AGA method12 may be used for horizontal gas applications.

Oliphant

The Oliphant method13 may be used for horizontal gas applications withpressures between vacuum and 100 PSI.


PressureChangers

Panhandle A

The Panhandle A method14 was developed by Panhandle Eastern for horizontalgas flow in large diameter cross country gas transmission lines. As a result, it isbest used on lines having diameters larger than 12 inches. However, it does notaccount for gas compressibility (Z-factor), and assumes completely turbulentflow.

Panhandle B

The Panhandle B method14 is a revised version of the Panhandle A method forhorizontal gas flow and was developed by Panhandle Eastern. It is also called the"Panhandle Eastern Revised Equation". It accounts for the gas compressibilityfactor, and has revised exponents. This equation is not quite so Reynolds-Numberdependent as the Panhandle A equation, although it, too, is best for pipediameters of 12 inches or more.

Hazen-Williams

The Hazen-Williams method14 was developed for the horizontal flow of water.When this method is used, the Hazen-Williams Coefficient must be specified inplace of the Segment Efficiency on the Connectivity Edit dialog box.

References

1. Beggs, H.D. and Brill, J.P., "A Study of Two-Phase Flow in Inclined Pipes,"Journal of Petroleum Technology, May 1973, pp. 607-617.

2. Dukler, A.E., Wicks, M., and Cleveland, R.G, "Frictional Pressure Drop inTwo-Phase Flow: An Approach Through Similarity Analysis," AIChE Journal,Vol. 10, No. 1, January 1964, pp. 44-51.

3. Beggs, H.D. and Brill, J.P., "Two-Phase Flow in Pipes," University of TulsaShort Course Notes, Third Printing, February 1984.

4. Lockhart, R.W. and Martinelli, R.C., "Proposed Correlation of Data forIsothermal Two-Phase, Two-Component Flow in Pipes," ChemicalEngineering Progress, Vol. 45, 1949, pp. 39-48.

5. Orkiszewski, J., "Predicting Two-Phase Pressure Drops in Vertical Pipe,"Journal of Petroleum Technology, June 1967, pp. 829-838.


Chapter 6

6. Angel, R.R., and Welchon, J.K., "Low-Ratio Gas-Lift Correlation for Casing-Tubing Annuli and Large Diameter Tubing," API Drilling and ProductionPractice, 1964, pp. 100-114.

7. Ros, N.C.J., "Simultaneous Flow of Gas and Liquid as Encountered in WellTubing," Journal of Petroleum Technology, October 1961, pp. 1037-1049.

8. Eaton, B.A. et al., "The Prediction of Flow Patterns, Liquid Holdup, andPressure Losses Occurring During Continuous Two-Phase Flow in HorizontalPipelines," Trans. AIME, June 1967, pp. 815-828.

9. Flanigan, Orin, "Effect of Uphill Flow on Pressure Drop in Design of Two-Phase Gathering Systems," Oil and Gas Journal, March 10, 1958, pp. 132-141.

10. Smith, R. V., "Determining Friction Factors for Measuring Productivity ofGas Wells," AIME Petroleum Transactions, Volume 189, 1950, pp. 73-82.

11. Weymouth, T.R., Transactions of the American Society of MechanicalEngineers, Vol. 34, 1912.

12. "Steady Flow in Gas Pipes," American Gas Association, IGT Technical Report10, Chicago, 1965.

13. Oliphant, F.N., "Production of Natural Gas," Report of USGS, 1902.

14. Engineering Data Book, Volume II, Gas Processors Suppliers Association,Tulsa, Oklahoma, Revised Tenth Edition, 1994.


PressureChangers

PipelinePipe Pressure Drop

Use Pipeline to calculate the pressure drop in a straight pipe or annular space.Pipeline can:• Simulate a piping network with successive blocks, including wellbores and

flowlines• Contain any number of segments within each block to describe pipe geometry• Calculate inlet or discharge conditions• Calculate pressure drops for one-, two-, or three-phase vapor and liquid flows.

Pipeline treats multiple liquid phases (for example, oil and water) as a singlehomogeneous liquid phase for pressure-drop and holdup calculations. Ifvapor-liquid flow exists, Pipeline calculates liquid holdup and flow regime(pattern).

You may specify a flowing fluid temperature profile, or Pipeline can calculate itfrom heat transfer calculations. Flow is assumed to be one-dimensional, steady-state, and fully developed (no entrance effects are modeled). Flow direction andelevation angle are arbitrary. To model a single pipe segment with constantdiameter and elevation, you can also use Pipe.

Flowsheet Connectivity for Pipeline

Material

Material

Pipeline Streams




Chapter 6

Specifying PipelineUse the Calculation Direction option on the Setup Configuration sheet to specifywhether Pipeline is to calculate the outlet or inlet pressure.

If Calculation Direction = Pipeline will need the And the integration direction is

Calculate outlet pressure(default)

Inlet pressure Downstream

Calculate inlet pressure Outlet pressure Upstream

Pipeline uses the inlet or outlet stream pressure to start the calculations. If thestream is an external feed to your flowsheet, or the outlet of a block that willexecute after Pipeline, use the Streams Specifications sheet to specify the streampressure. You can also specify the initial pressure for Pipeline on the SetupConfiguration sheet by entering the pressure value at the inlet or outlet. Thispressure value overrides the stream pressure.

Use the Pipeline flow basis option on the Setup Configuration sheet to specifywhether Pipeline is to calculate the outlet or inlet stream flow and composition.

If Pipeline flow basis= Pipeline will need the

Use inlet stream flow(default)

Inlet flow and composition

Reference outlet streamflow

Outlet flow and composition

Use Thermal Options on the Setup Configuration sheet to specify whether or notthe node temperatures are to be calculated by Pipeline using an energy balance.When you select the Specify Temperature Profile option, the temperature at eachnode can be specified. When you choose the Constant Temperature option, thetemperature will be same at every node. You can define this temperature byspecifying the inlet temperature (for downstream integrations) or the outlettemperature (for upstream integrations). If neither the inlet nor the outlettemperatures are specified, the temperature of the referenced stream will beused. When you choose the linear temperature profile option, you can specify thetemperature at one or more nodes. Pipeline will do a linear interpolation betweenthe temperatures specified to calculate the fluid temperature in each segment.


PressureChangers

Use the following forms to enter specifications and view results for Pipeline:


Setup Specify pipeline configuration, segment connectivity and characteristics, calculation methods,property grid parameters, flash convergence parameters, valid phases, and block-specificdiagnostic message level

Convergence Override default values for integration parameters, downhill flow options, correlationparameters and Beggs and Brill coefficients (optional input)


UserSubroutines Specify name and parameters for pressure drop and liquid holdup user subroutines

Results View summary of Pipeline results, inlet and outlet stream results, profiles, and material andenergy balance results

Stream Specification

You must initialize the inlet stream to Pipeline whenever the Use Inlet Flow optionis selected for Pipeline Flow Basis, even if the inlet pressure is being calculated.Similarly, you must initialize the outlet stream whenever you select the ReferenceOutlet Stream Flow option. The initialized stream must be one of the following:• On a stream form• An outlet stream from part of the flowsheet executed previously• Transferred from another part of a flowsheet using a Transfer block

Nodes and Segments

Create at least one segment using the New button on the Pipeline SetupConnectivity sheet.

Enter specifications for each segment on the Setup Connectivity Segment Datadialog box . For each segment, enter the inlet and outlet node names (maximum 4characters). The required data depends on the options selected on the SetupConfiguration sheet. If you select Do Energy Balance with Surroundings, youmust specify a heat transfer coefficient (U-Value) and the ambient temperature.If you select the Linear Temperature Profile option, Pipeline uses thetemperatures specified for the nodes to override the stream values. If specificationsare not made for the nodes, then Pipeline uses the stream values.

If you select Enter Node Coordinate, you must enter node coordinates (X, Y, andElevation) for each segment node. You must enter Length and Angle for eachsegment if you select Enter Segment Length and Angle.


Chapter 6

Physical Property Calculations

You can specify a rigorous flash each time properties are calculated by selecting DoFlash at Each Step on the Setup Configuration sheet. If Interpolate from PropertyGrid is selected, Pipeline will determine properties by interpolating in a table ofproperty values at various temperatures and pressures. Specify one of the followingif you use the Property Grid:• A range of temperatures and pressures grid on the Setup PropertyGrid sheet.

Pipeline calculates properties under these conditions and interpolates them.• The block ID of a Pipeline block for which you selected Interpolate from the

Property Grid, and which will be executed before the current block in theflowsheet.


Pipeline can calculate pressure drop for either one-, two-, or three-phase vapor andliquid flows. If vapor-liquid flow exists, Pipeline also calculates liquid holdup andflow regime (pattern). You may specify a flowing fluid temperature profile, orPipeline can calculate it from heat transfer calculations. Pipeline treats multipleliquid phases (for example, oil and water) as a single homogeneous liquid phase forpressure-drop and holdup calculations. Pipeline automatically detects the specialcase of a single component fluid (for example, steam) and treats it appropriately.


For downstream and upstream integration, the combination of the selectionsmade for Calculation Direction and Pipeline Flow Basis on the SetupConfiguration sheet determine which stream Pipeline will update. The followingtable describes the available combinations. The next figure, Downstream andUpstream Integration, defines the inlet and outlet stream and pressurevariables.

If you specify CalculationDirection= And Pipeline Flow Basis= Then Pipeline updates the

Calculate Outlet Pressure Reference inlet stream flow Outlet stream only

Calculate Outlet Pressure Use outlet stream flow Outlet stream thermodynamic conditions

Inlet stream composition and flow

Calculate Inlet Pressure Reference Outlet Stream Flow Inlet stream only

Calculate Inlet Pressure Use Inlet Stream Flow Inlet stream thermodynamic conditions

Outlet stream composition and flow


PressureChangers

Inlet Stream

Inlet Pressure Outlet Pressure

Outlet Stream


Design Spec Convergence Loop

Use caution when using Pipeline inside a Design-Spec convergence loop. Forexample, suppose you achieve a desired pipeline outlet pressure by varying theflow rate to the pipeline. In this case, the flow rate variable might cause Pipeline topredict negative pressures, resulting in convergence problems. You can avoid thissituation by doing one of the following:• Keep the upper limit of the flow rate sufficiently low in the Design-Spec• Perform an upstream integration from the known outlet pressure. Use

Calculate Inlet Pressure on the Setup Configuration sheet for this purpose.Your Design-Spec will then need to manipulate the flow rate to achieve thespecified inlet pressure.

Erosional Velocity

Erosional velocity is the velocity of the fluid in the pipe over which the pipematerial will start to break off. The fluid is traveling so fast that it starts to stripmaterial from the walls of the pipe. In general usage, the flow rate should be belowthis value.

You can specify the erosional velocity coefficient in the C-Erosion field on theSegment Data dialog box on the Setup Connectivity sheet.

The erosional velocity is related to the erosional velocity coefficient by thefollowing equation:

vc

c =ρ

Where:

vc = Erosional velocity in ft/sec

c = Erosional velocity coefficient (default=100)ρ = Density in lb/cubic ft


Chapter 6

Methane Gas Systems

Gas systems consisting mostly of methane occur frequently in the dense-phaseregion of wellbores and flowlines. In the dense-phase region, definable vapor andliquid phases do not exist. Equation-of-state methods classify the dense-phasematerial as either all vapor or all liquid. Significant differences in the predictedfluid transport properties may occur, depending on whether you choose the vaporor liquid state.

Experience has shown that gas system flow in the dense-phase region is bestmodeled by using vapor-phase properties. For systems consisting of mostlymethane, where the pipeline conditions lie above the cricondenbar of the phaseenvelope, specify Valid Phases = Vapor only on the Setup FlashOptions sheet.

Two-Phase CorrelationsThe following tables list the two-phase frictional pressure drop and holdupcorrelations available.

Two-Phase Friction Factor Correlations


Horizontal -2 deg to +2 deg Beggs and Brill (BEGGS-BRILL)Dukler (DUKLER)Lockhart-Martinelli (LOCK-MART)Darcy (DARCY)User subroutine†(USER-SUBR)

Vertical +45 deg to +90 deg Beggs and Brill (BEGGS-BRILL)Orkiszewski (ORKI)Angel-Welchon-Ros (AWR)Hagedorn-Brown (H-BROWN)Darcy (DARCY)User subroutine† (USER-SUBR)

Downhill -2 deg to -90 deg Beggs and Brill (BEGGS-BRILL)Slack (SLACK)Darcy (DARCY)User subroutine† (USER-SUBR)

Inclined +2 deg to +45 deg Beggs and Brill (BEGGS-BRILL)Dukler (DUKLER)Orkiszewski (ORKI)Angel-Welchon-Ros (AWR)Hagedorn-Brown (H-BROWN)Darcy (DARCY)User subroutine† (USER-SUBR)



PressureChangers

Two-Phase Liquid Holdup Correlations

Pipe orientation Inclination Liquid holdup correlations

Horizontal -2 deg to +2 deg Beggs and Brill (BEGGS-BRILL)Eaton (EATON)Lockhart-Martinelli (LOCK-MART)Hoogendorn (HOOG)Hughmark (HUGH)User subroutine† (USER-SUBR)

Vertical +45 deg to +90 deg Beggs and Brill (BEGGS-BRILL)Orkiszewski (ORKI)Angel-Welchon-Ros (AWR)Hagedorn-Brown (H-BROWN)User subroutine† (USER-SUBR)

Downhill -2 deg to -90 deg Beggs and Brill (BEGGS-BRILL)Slack (SLACK)User subroutine† (USER-SUBR)

Inclined +2 deg to +45 deg Beggs and Brill (BEGGS-BRILL)Flanigan (FLANIGAN)Orkiszewski (ORKI)Angel-Welchon-Ros (AWR)Hagedorn-Brown (H-BROWN)User subroutine† (USER-SUBR)


Note Some of the related information for the two-phase friction factorand liquid holdup correlations was taken from "Two-Phase Flowin Pipes" by James P. Brill and H. Dale Beggs, Sixth Edition,Third Printing, January, 1991.

Beggs and Brill Correlation

Slip and flow regimes are considered with this method. Friction factor andholdup correlations depend upon flow regime and pipe inclination. It is suitablefor all inclinations, including vertical flow downward.1

Dukler Correlation

The Hughmark holdup method should be used with this pressure drop method.The Dukler method was developed from field data using air-water mixtures in1-inch pipes.2 It tends to over-predict frictional pressure drop. It is recommendedin a design manual published jointly by the AGA and API.


Chapter 6

Hagedorn-Brown Correlation

The Hagedorn-Brown correlation3 considers slip between phases, but flow regimeis not considered. It uses the same correlations for liquid holdup and frictionfactor for all flow regimes. It is an old method that works well for conventional oilwells. It is suitable for vertical upward flow, but not downward. It is generallyrecommended for gas wells, and is based on data obtained from U.S. Gulf Coastoil wells with 2-3/8 inch and 2-7/8 inch tubing.

Lockhart-Martinelli Correlation

The Lockhart-Martinelli correlation4 is one of the oldest pressure dropcorrelations. It does not consider pressure drop due to acceleration. The methodtreats the vapor and liquid phases separately and uses a correction factor to findthe 2-phase pressure gradient. Our implementation assumes turbulent gas andliquid phase flow.

Orkiszewski Correlation

The Orkiszewsi correlation considers slip and flow regimes5. The friction factorand holdup correlation depend on the flow regime. It is suitable for vertical flowupward, but not downward. It is generally reliable for oil wells. It may exhibitproblems for oil wells with high water cuts or high total gas to liquid ratios. Itcan significantly underpredict pressure drop for higher rate and higher pressurewells (Beggs and Brill/1984)3.

Angel-Welchon-Ros Correlation

This Angel-Welchon-Ros method6,7 was developed for low gas-to-liquid ratio waterwells. It assumes no slip between the vapor and liquid phases when calculatingliquid holdup.

Slack Correlation

This method assumes a stratified flow regime, and should be used only fordownhill flow.

Eaton Correlation

The Eaton correlation8 holdup method was developed from data on 2- and 4-inchpipes with a gas-water-crude mixture, and a 17-inch pipe with a gas-oil mixture.It is often used with the Dukler frictional pressure drop correlation.


PressureChangers

Flanigan Correlation

The Flanigan correlation9 holdup method was developed from data taken in a16-inch pipe. It calculates liquid holdup as a function of superficial gas velocity.It is suitable for inclined flow.

Beggs and Brill Correlation Parameters

The following table lists the Beggs and Brill liquid holdup correlationparameters.

Flow Regime Name Description

Segregated BB1BB2BB3


Intermittent BB4BB5BB6


Distributed BB7BB8BB9


In addition, you can change the Beggs and Brill two-phase Friction Factor modifier,BB10 (default = 1.0).

Closed-Form MethodsThe following are closed-form methods:• Smith• Weymouth• AGA• Oliphant• Panhandle A• Panhandle B• Hazen-Williams


Chapter 6

Smith

The Smith method10 may be used for vertical dry gas flow. It should be consideredfor gas wells with condensate-gas ratios less than 50 bbls/mcf, water-gas ratiosless than 3.5 bbls/mcf, and flow rates above the Turner predicted critical rate.Smith does not model gas well loadup, and will significantly underpredictwellbore pressure drop if loadup is actually occurring. Smith results must becross-checked against the Turner predicted critical rates to verify that the well isunloaded. Smith also does not model condensation of water vapor in the wellbore.

Weymouth

The Weymouth11 horizontal gas flow equation was first published in 1912. It isbased on data taken on pipes with diameters from 0.8 inches to 11.8 inches. As aresult, it is most accurate for smaller pipes having a diameter less than 12inches.

AGA

The AGA method12 may be used for horizontal gas applications.

Oliphant

The Oliphant method13 may be used for horizontal gas applications withpressures between vacuum and 100 PSI.

Panhandle A

The Panhandle A method14 was developed by Panhandle Eastern for horizontalgas flow in large diameter cross country gas transmission lines. As a result, it isbest used on lines having diameters larger than 12 inches. However, it does notaccount for gas compressibility (Z-factor), and assumes completely turbulentflow.

Panhandle B

The Panhandle B method14 is a revised version of the Panhandle A method forhorizontal gas flow and was developed by Panhandle Eastern. It is also called the"Panhandle Eastern Revised Equation". It accounts for the gas compressibilityfactor, and has revised exponents. This equation is not quite so Reynolds-Numberdependent as the Panhandle A equation, although it, too, is best for pipediameters of 12 inches or more.


PressureChangers

Hazen-Williams

The Hazen-Williams method14 was developed for the horizontal flow of waterWhen this method is used, the Hazen-Williams Coefficient must be specified inplace of the Segment Efficiency on the Connectivity Edit Dialog Box.

References

1. Beggs, H.D. and Brill, J.P., "A Study of Two-Phase Flow in Inclined Pipes,"Journal of Petroleum Technology, May 1973, pp. 607-617.

2. Dukler, A.E., Wicks, M., and Cleveland, R.G, "Frictional Pressure Drop inTwo-Phase Flow: An Approach Through Similarity Analysis," AIChE Journal,Vol. 10, No. 1, January 1964, pp. 44-51.

3. Beggs, H.D. and Brill, J.P., "Two-Phase Flow in Pipes," University of TulsaShort Course Notes, Third Printing, February 1984.

4. Lockhart, R.W. and Martinelli, R.C., "Proposed Correlation of Data forIsothermal Two-Phase, Two-Component Flow in Pipes," ChemicalEngineering Progress, Vol. 45, 1949, pp. 39-48.

5. Orkiszewski, J., "Predicting Two-Phase Pressure Drops in Vertical Pipe,"Journal of Petroleum Technology, June 1967, pp. 829-838.

6. Angel, R.R. and Welchon, J.K., "Low-Ratio Gas-Lift Correlation for Casing-Tubing Annuli and Large Diameter Tubing," API Drilling and ProductionPractice, 1964, pp. 100-114.

7. Ros, N.C.J., "Simultaneous Flow of Gas and Liquid as Encountered in WellTubing," Journal of Petroleum Technology, October 1961, pp. 1037-1049.

8. Eaton, B.A. et al., "The Prediction of Flow Patterns, Liquid Holdup, andPressure Losses Occurring During Continuous Two-Phase Flow in HorizontalPipelines," Trans. AIME, June 1967, pp. 815-828.

9. Flanigan, Orin, "Effect of Uphill Flow on Pressure Drop in Design of Two-Phase Gathering Systems," Oil and Gas Journal, March 10, 1958, pp. 132-141.

10. Smith, R. V., "Determining Friction Factors for Measuring Productivity ofGas Wells," AIME Petroleum Transactions, Volume 189, 1950, pp. 73-82.

11. Weymouth, T.R., Transactions of the American Society of MechanicalEngineers, Vol. 34, 1912.

12. "Steady Flow in Gas Pipes," American Gas Association, IGT Technical Report10, Chicago, 1965.


Chapter 6

13. Oliphant, F.N., "Production of Natural Gas," Report of USGS, 1902.

14. Engineering Data Book, Volume II, Gas Processors Suppliers Association,Tulsa, Oklahoma, Revised Tenth Edition, 1994.

❖ ❖ ❖ ❖


PressureChangers


Chapter 7

7 Manipulators

This chapter describes the models for stream manipulators. The models are:


Mult Stream multiplier Multiplies component and total flow rates bya factor

Scaling streams by a factor

Dupl Stream duplicator Copies inlet stream into any number ofduplicate outlet streams

Duplicating feed or internalstreams

ClChng Stream class changer Changes stream class between blocks andflowsheet sections

Adding or deleting emptysolid substreams betweenflowsheet sections

Use stream manipulators to modify stream variables for your convenience. They donot represent real unit operations.


Manipulators

MultStream Multiplier

Mult multiplies the component flow rates and the total flow rate of a materialstream by a factor you supply on the Mult Input Specifications sheet. For heat orwork streams, Mult multiplies the heat or work flow. Select the Heat (Q) and Work(W) Mult icons from the Model Library for heat and work streams respectively.

Mult is useful when other conditions during the simulation determine the flow rateof the stream. Mult does not maintain heat or material balances. For materialstreams, the outlet stream has the same composition and intensive properties asthe inlet stream.

Flowsheet Connectivity for Mult

Material

or

Heat

or

Work

Material

or

Heat

or

Work



Heat StreamsInlet One heat stream

Outlet One heat stream

Work StreamsInlet One work stream

Outlet One work stream


Chapter 7

The outlet stream must be the same type (material, heat, or work) as the inletstream.

Specifying MultThe stream multiplication factor, specified on the Input Specifications sheet, isthe only input required for Mult. This factor has to be positive for materialstreams. You can specify either a positive or negative factor for heat or workstreams, thus allowing a change in direction for the heat or work flow.

Use the Input Diagnostics sheet to override global values for the stream andsimulation message levels specified on the Setup Specifications Diagnosticssheet.

This model has no dynamic features. For material stream multipliers thepressure of each outlet stream is equal to the pressure of the inlet stream. Theflow rate of each outlet stream is equal to the flow rate of the inlet streammultiplied by the factor as specified in the steady-state simulation.


Manipulators

DuplStream Duplicator

Dupl copies an inlet stream (material, heat, or work) to any number of duplicateoutlet streams. It is useful for simultaneously processing a stream in differenttypes of units. Select the Heat (Q) and Work (W) Dupl icons from the ModelLibrary for heat and work streams respectively. Dupl does not maintain heat ormaterial balances.

Flowsheet Connectivity for Dupl

Material Material(any number)

Flowsheet for Duplicating Material Streams


Outlet At least one material stream, which is a copy of the inlet stream

Heat Heat(any number)

Flowsheet for Duplicating Heat Streams

Heat StreamsInlet One heat stream

Outlet At least one heat stream, which is a copy of the inlet stream


Chapter 7

Work Work(any number)

Flowsheet for Duplicating Work Streams

Work StreamsInlet One work stream

Outlet At least one work stream, which is a copy of the inlet stream

Specifying DuplDupl requires no input parameters. Use the Input Diagnostics sheet to overrideglobal values for the stream and simulation message levels specified on the SetupSpecifications Diagnostics sheet.

This model has no dynamic features. For material stream duplicators thepressure of each outlet stream is equal to the pressure of the inlet stream. Theflow rate of each outlet stream is equal to the flow rate of the inlet stream.


Manipulators

ClChngStream Class Changer

ClChng changes the stream class between blocks and flowsheet sections. You canuse ClChng to add or delete empty solid substreams between flowsheet sections.ClChng does not represent a real unit operation.

Flowsheet Connectivity for ClChng

Feed Product


Outlet One material product stream

Specifying ClChngClChng does not require input. It copies substreams from the inlet stream to thecorresponding substreams of the outlet stream.

If a substream is Then ClChng

In the outlet but not in the inlet Initializes the substream to zero flow

In the inlet but not in the outlet Drops the substream

ClChng does not maintain mass and energy balances if any dropped substreamcontains material flow or heat/work information.

❖ ❖ ❖ ❖


Chapter 8

8 Solids

This chapter describes the unit operation models for solids processing such ascrystallizers, solid crushers and separators, gas-solid separators, liquid-solidseparators, and solids washers. The models are:


Crystallizer Crystallizer Produces crystals from solution based onsolubility

Mixed suspension, mixed product removal(MSMPR) crystallizer

Crusher Solids crusher Breaks solid particles to reduce particlesize

Wet and dry crushers, primary andsecondary crushers

Screen Solids separator Separates solid particles based on particlesize

Upper and lowerdry and wet screens

FabFl Fabric filter Separates solids from gas using fabricfilter baghouses

Rating and sizing baghouses

Cyclone Cycloneseparator

Separates solids from gas using gasvortex in a cyclone

Rating and sizing cyclones

VScrub Venturi scrubber Separates solids from gas by directcontact with an atomized liquid

Rating and sizingventuri scrubbers

ESP Electrostaticprecipitator

Separates solids from gas using anelectric charge between two plates

Rating and sizing dry electrostaticprecipitators

HyCyc Hydrocyclone Separates solids from liquid using liquidvortex in a hydrocyclone

Rating or sizing hydrocyclones

CFuge Centrifuge filter Separates solids from liquid using arotating basket

Rating or sizing centrifuges

Filter Rotary vacuumfilter

Separates solids from liquid using acontinuous rotary vacuum filter

Rating or sizing rotary vacuum filters

SWash Single-stagesolids washer

Models recovery of dissolved componentsfrom an entrained liquid of a solids streamusing a washing liquid

Single -stage solids washer

CCD Counter-currentdecanter

Models multi-stage recovery of dissolvedcomponents from an entrained liquid of asolids stream using a washing liquid

Multi-stage solids washers


Solids

This chapter is organized into the following sections:

Section Models

Crystallizer Crystallizer

Crushers and Screens Crusher, Screen

Gas-Solid Separators FabFl, Cyclone, VScrub, ESP

Liquid-Solid Separators HyCyc, CFuge, Filter

Solids Washers SWash, CCD


Chapter 8

CrystallizerMixed Suspension Mixed Product Removal Crystallizer

Crystallizer models a mixed suspension, mixed product removal (MSMPR)crystallizer. It performs mass and energy balance calculations and optionallydetermines the crystal size distribution.

Crystallizer assumes that the product magma leaves the crystallizer inequilibrium, so the mother liquor in the product magma is saturated.

The feed to Crystallizer mixes with recirculated magma and passes through aheat exchanger before it enters the crystallizer.

The product stream from Crystallizer contains liquids and solids. You can passthis stream through a hydrocyclone, filter, or other fluid-solid separator toseparate the phases. Crystallizer can have an outlet vapor stream.

Flowsheet Connectivity for Crystallizer


Heat(optional)

Vapor(optional)

Heat(optional)

Liquidand Solid


Outlet One material stream for liquid and solidOne optional vapor stream

The outlet material stream should normally have at least one solid substream forthe crystals formed. If you select Calculate PSD from Growth Kinetics or User-Specified Values on the PSD PSD sheet, each substream must have a particlesize distribution (PSD) attribute.


Solids

If electrolyte salts are formed based on electrolyte chemistry calculations, a solidsubstream is not required when you select Copy from Inlet Stream on the PSDPSD sheet.

If you do not use the vapor outlet stream, vapor products will be placed in theliquid/solid product stream.

Heat StreamsInlet Any number of optional inlet heat streams

Outlet One optional outlet heat stream

If you give only one specification on the Setup Specifications sheet (temperatureor pressure), Crystallizer uses the sum of the inlet heat streams as a dutyspecification. Otherwise, Crystallizer uses the inlet heat streams only tocalculate the net heat duty. The net heat duty is the sum of the inlet heatstreams minus the actual (calculated) heat duty.


Specifying CrystallizerCrystallizer calculates crystal product flow rate and/or vapor flow, based onsolubility data you supply. Or you can specify the chemistry for electrolyte systemsinstead of specifying solubility data.

You must specify two of the following:• Crystallizer temperature• Pressure or pressure drop• Heat duty for the heat exchanger• Crystal product flow rate• Vapor flow

If you specify Crystallizer calculates

Temperature and Pressure Heat duty, crystal product flow rate, vapor flow rate

Pressure and Heat Duty Temperature, crystal product flow rate, vapor flow rate

Temperature and Heat Duty Pressure, crystal product flow rate, vapor flow rate

Pressure and Crystal Product Flow Rate Temperature, heat duty, vapor flow rate

Temperature and Crystal Product Flow Rate Pressure, heat duty, vapor flow rate

Pressure and Vapor Flow Rate Temperature, heat duty, crystal product flow rate

Temperature and Vapor Flow Rate Pressure, heat duty, crystal product flow rate


Chapter 8

Use the following forms to enter specifications and view results for Crystallizer:


Setup Specify operating parameters, crystal product and solubility parameters,recirculation options, and flash convergence parameters

PSD Specify PSD and crystal growth calculation parameters

Advanced Specify component attributes, convergence parameters, and name and parametersfor user solubility subroutine


Results View summary of Crystallizer results, material and energy balance results, andcrystal size distribution results

Recirculation Specifications

You can model crystallizer with or without magma recirculation. To activaterecirculation, specify one of the following on the Setup Recirculation sheet:• Recirculation fraction• Recirculation flow rate• Temperature change across heat exchanger

If you want to model a different crystallization process flowsheet, you can useCrystallizer without recirculation, and use other blocks in the flowsheet to modelthe recirculation.

Solubility

Crystallizer calculates the amount of crystal produced at its saturation (class IIcrystallization). You can provide solubility data in one of these ways:• Enter solubility data on the Setup Solubility sheet• Reference an electrolyte chemistry (defined in the Reactions Chemistry

forms) in which the crystallizing component has been declared as a "salt"• Supply a subroutine to provide the saturation concentration or to calculate

crystal product flow rate directly


Solids

Saturation Calculation Method

Choose the saturation calculation method from these options:• Solubility method: Identify the crystallizing component as solid product on

the Setup Crystallization sheet. Enter solubility data on the Setup Solubilitysheet. This data applies to the reactant species in the mixed substream.

• Chemistry method: Create a new Chemistry on the Reactions Chemistryobject manager. Enter the crystallization as a salt reaction on the ReactionsStoichiometry sheet. On the BlockOptions Properties sheet of the crystallizer,enter the Chemistry ID and select True Species for Simulation Approach. Youmust specify the crystallizing component as a Salt Component ID on theSetup Specifications sheet.

• User Subroutine method: Identify the crystallizing component on the SetupCrystallization sheet and the solubility data basis and solvent ID on theSetup Solubility sheet. Specify a user subroutine to calculate saturationconcentration or crystallizer yield on the Advanced UserSubroutine sheet.

In general, when using the Solubility method, you should blank out theChemistry ID field on the BlockOptions Properties sheet. If you specify chemistrywhen using the Solubility method, the chemistry must not contain thecrystallizing component.

Supersaturation

The degree of supersaturation is the driving force for crystallization processes.Supersaturation is defined as:

S C Cs= −

Where:

S = Supersaturation (kg of solute/m3 of solution)

C = Solute concentration

Cs = Solute saturation concentration

Because the crystallizer model assumes that the product magma is in phaseequilibrium, this equation is not used. It is provided only for reference.


Chapter 8

Crystal Growth Rate

The crystal growth rate can be expressed as a function of the degree ofsupersaturation (S):

G k Sog

n=

Where:

Go = Growth rate dependence on supersaturation (m/s)

kg = Growth rate expression coefficient

n = Exponent

This expression is provided as background information only.

In ASPEN PLUS, Go is calculated implicitly from the third moment of thepopulation density.

For a size-dependent growth rate, the growth rate is a function of crystallength (L):

G G Lo= +( )1 γ α For 0 1≤ ≤α

Where:

γ = Constant

α = Exponent

If the growth rate is independent of crystal size, then the values for γ and α areset to zero.


Solids

Crystal Nucleation Rate

The overall nucleation rate can be expressed as the sum of specific contributingfactors (Bennett, 1984)1:

B k G M Rob

iTj k=

Where:

Bo = Overall nucleation rate

i, j, k = Exponents

kb = Overall nucleation rate expression coefficient

MT = Magma density = P/q (kg/m3)

G = Crystal growth rate

R = Impeller rotation rate (revs/s)

P = Crystal mass flow rate (kg/s)

q = Volumetric flow rate of slurry in the discharge (m3/s)

Population Balance

If the feed stream contains no crystals, the population balance for a well-mixedcontinuous crystallizer can be written as (Randolph and Larson, 1988)2:

d nG

dL

qn

V

( )+ = 0

Where:

G = Crystal growth rate

n = Population density (no. /m3/m)

L = Crystal length (m)

V = Crystallizer volume (m3)

q = Volumetric flow rate of slurry in the discharge (m3/s)


Chapter 8

The boundary condition is n no= at L = 0, where n B Go o= / is the populationdensity of nuclei. For a constant crystal growth rate, the population density is:

n L nL

Go( ) = −

expτ

where τ = V / q is the crystal residence time.

PSD Statistics

ASPEN PLUS calculates the crystal size distribution statistics once you selectthe Calculate PSD from Growth Kinetics option on the PSD PSD sheet.

Properties of the distribution may be evaluated from the moment equations. Thej-th moment of the particle size distribution is defined as:

m L n L dLjj=

∞

∫0( )

The system reports several crystal size distribution statistics, measured on avolume or mass basis, including:• Mean size• Standard deviation• Skewness• The coefficient of variation (expressed as a percentage)

The mean size is the mass-weighted average crystal size, as determined by theratio of the fourth moment to the third moment, as follows:

Lm

m= 4

3

The skewness of a symmetric size distribution about the mean is zero. Negativevalues of skewness indicate the distribution is skewed toward the presence ofsmall crystals. Positive values of skewness indicate the crystal distributioncontains an excess of large crystals.

Skewness is defined as ∑ −f ( )

( )

x mean

standard deviation

3

3


Solids

The system uses the coefficient of variation to calculate variation related to thecumulative volume (or mass) distribution.

Coeff Var(%)− =−

10084 16

2 50

pd pd

pd

@(. ) @(. )

@(. )

where pd@ (x) is the particle diameter corresponding to fraction x of thecumulative volume (or mass) distribution. The fraction can be entered as theFractional Coefficient on the PSD CrystalGrowth sheet; otherwise, it defaults to.16.

Calculating PSD

The magma density, defined as total mass of crystals per unit volume of slurry,can be obtained from the third moment:

M k L n L dLT c v=∞

∫ρ0

3 ( )

Where:

ρc = Density of crystal (kg/m3)

kv = Volume shape factor of the crystal

Since:

n L nL

Go( ) = −

expτ

,

nB

Go

o

o= ,

and B k G M Rob

iTj k=

these equations can be substituted into the third moment of population density,yielding:

M k L kG

GM R

L

GdLT c v b

i

o Tj k=

−

∞

∫ρτ

3

0exp

where G G Lo= +( )1 γ α .

Because L is made discrete by the increments of the particle size distribution, theequations can be solved for Go .


Chapter 8

References

1. Bennett, R.C. "Crystallization from Solution," Perry’s Chemical Engineers’Handbook, 6th Ed., pp. 19.24-19.40, McGraw-Hill, 1984.

2. Randolph, A.D. and Larson, M.A., Theory of Particulate Processes, 2nd Ed.,Academic Press, 1988.


Solids


Chapter 8

CrusherSolids Crusher

Use Crusher to simulate the breaking of solid particles.

Crusher can model the wet or dry continuous operation of:• Gyratory/jaw crushers• Single-roll crushers• Multiple-roll crushers• Cage mill impact breakers

Crusher assumes the feed is homogeneous. The breaking process createsfragments with the same composition as the feed. Crusher calculates the powerrequired for crushing, and the particle size distribution of the outlet solidsstream.

Crusher does not account for the heat produced by the breaking process.

Flowsheet Connectivity for Crusher

Feed

Crushed Solids

Work (optional)

Material StreamsInlet One material stream with at least one solids substream


Each solids substream must have a particle size distribution (PSD) attribute.


Solids

Work StreamsInlet No inlet work streams

Outlet One work stream containing the calculated power requirement(optional)

Specifying CrusherUse the Input Specifications and Grindability sheets to specify operatingconditions. You must enter the type of crusher and maximum particle diameter onthe Input Specifications sheet. You must also specify the Bond work index or theHardgrove grindability index for each solids substream on the Grindability sheet.

The outlet flow rate of crushed product in the k-th size interval is:

[ ]P F S B S Fkj i

ij i ikj

k kj( ) ( ( ) ( )β β β β= + −∑ ∑ ∑) 1

Where:

Bik = Breakage function. Fraction of particles originally in sizeinterval i that end up in size interval k

Fij = Flow rate of feed in the size interval i and particle sizedistribution j

Pk = Flow rate of solid in size interval k

Si = Selection function. Fraction of feed particles in size interval ito be crushed at the outlet diameter β

Sk = Selection function. Fraction of feed particles in size intervalk to be crushed at the outlet diameter β

β = Crusher outlet diameter (Maximum Particle Diameter field)

i = Size interval counter within a PSD

j = PSD counter for multiple size distribution

If the inlet stream contains no liquid, then Crusher assumes dry crushing, andpower requirements increase by 34%.


Chapter 8

You can enter tabular values for the breakage ( )Bik function on the InputBreakageFunction sheet and for the selection ( )Si function on the InputSelectionFunction sheet, or let Crusher use the built-in tables (U.S. Bureau ofMines, 1977) (see the following two tables).

Breakage Function Correlations Bik ( )β

Feed size/solids outlet diameter >1.7Feed size/solidsoutlet diameter <1.7

Ratio of product size tofeed size

Multiple rollcrusher

Gyratory/jawcrusher

Single rollcrusher

Cage millcrusher All crushers

1.0 1.0 1.0 1.0 1.0 1.0

0.8308 0.95 0.95 0.96 0.84 0.8972

0.5882 0.85 0.85 0.79 0.50 0.7035

0.4176 0.65 0.70 0.45 0.32 0.54

0.2065 0.35 0.35 0.20 0.15 0.2952

0.1041 0.22 0.20 0.10 0.052 0.1564

0.0522 0.14 0.19 0.05 0.019 0.0805

0.0368 0.11 0.17 0.03 0.011 0.0572

0.026 0.09 0.12 0.02 0.0066 0.0406

0.0131 0.03 0.08 0.0 0.002 0.0206

0.0 0.0 0.0 0.0 0.0 0.0

Selection Function Correlations, Si ( )β

Ratio of feed size tooutlet diameter Primary crusher Secondary crusher

0.95 0.5695 0.7693

0.9 0.3817 0.6962

0.8 0.1716 0.5695

0.7 0.0771 0.4667

0.6 0.0347 0.3817

0.5 0.0156 0.3128

0.4 0.007 0.256

0.3 0.00315 0.2096

0.2 0.00145 0.1716

continued


Solids

Ratio of feed size tooutlet diameter Primary crusher Secondary crusher

0.1 0.0006 0.1405

0.05 0.00043 0.1271

0.001 0.00026 0.1153

0.0001 0.00026 0.1148

If the ratio of feed size to outlet diameter is greater than 1.0, then Si ( ) .β = 0 85 .

Use the following forms to enter specifications and view results for Crusher:


Input Enter crusher operating parameters, the Bond work index or the Hardgrovegrindability index, and user-specified selection and breakage functions


Results View summary of Crusher results and material and energy balances

Primary and Secondary Crushers

Crushing operations are usually performed in stages. The reduction ratio is theratio of the maximum diameter of feed particles to product particles. Thereduction ratio in crushers ranges from 3 to 6 per stage. Feed particles are fed tothe primary crushers. Outlet particles from the primary crushers are reducedfurther by the secondary crushers.

Crusher uses different correlations for primary and secondary crushers. Use theOperating Mode field on the Input Specifications sheet to enter the type ofcrusher.

To improve the efficiency of multistage crushers, use screens between stages.

Power Requirement

The following equation determines the power requirement for Crusher:

( )POWER

X X BWI FLOWT

X X

F p

F p

=− × ×

×

0 01.


Chapter 8

Where:

POWER = Required power (Watt)

XF = Diameter larger than 80% of feed particle mass (m)

XP = Diameter larger than 80% of product particle mass (m)

BWI = Bond work index

FLOWT = Total solids mass flow rate (kg/s)

For dry crushing, power requirement increases by 34%.

If Xp is less than 70 micrometers, then the power required is further adjusted

by:

POWER POWERX

Xp

p

=× +

−10 6 10

1145

6.

.

Bond Work Index

The Bond equation defines the work consumed in size reduction:

E EX X

X Xi

F P

F P

=− 100

Where:

E = Work required to reduce a unit weight of feed with 80%passing a diameter X F microns to a product with 80%passing a diameter Xp microns

Ei = Bond work index, that is, the work required to reduce a unitweight from a theoretical infinite size to 80% passing adiameter of 100 micrometers

The Bond work index is a semi-empirical parameter that depends on the propertiesof the material processed. The Bond work indices have been measuredexperimentally for a wide range of materials, and are available in Perry’s ChemicalEngineers’ Handbook. Use experimental values with caution. The Bond work indexis also a function of the:• Particle size for non-homogeneous materials• Efficiency of the size-reduction equipment


Solids

Hardgrove Grindability Index

The Hardgrove grindability index indicates the difficulty of grinding coal based onphysical properties such as hardness, fracture, and tensile strength. TheHardgrove grindability index can be approximated by:

BWIHGI

= 4350 91.

Where:

BWI = Bond work index

HGI = Hardgrove grindability index

The HGI for some United States coals are available in Perry’s ChemicalEngineers’ Handbook.

References

1. Computer Simulation of Coal Preparation Plants, U.S. Bureau of Mines,Grant No. GO-155030, Final Report August (1977).

2. Perry’s Chemical Engineers’ Handbook, 6th Ed., McGraw Hill, 1984.


Chapter 8

ScreenSolids Separator

Screen simulates the separation by screens of a mixture containing various sizes ofsolid particles into particles that have more uniform sizes than the originalmixture. You can use Screen to model wet or dry operations and upper or lowerlevel screens.

Screen calculates the separation efficiency of the screen from the size of screenopenings you specify.

Flowsheet Connectivity for Screen

Feed

Overflow

Underflow


Outlet One material stream for particles that do not pass through thescreen (overflow)One material stream for particles that pass through the screen(underflow)

Each solids substream must have a particle size distribution attribute.

Specifying ScreenUse the Input Specifications sheet to enter:• Screen size opening• Operating level (Upper or Lower)• Operating mode (Wet or Dry)• Entrainments


Solids

You can also use the Input SelectionFunction sheet to enter the followingfunctions:• Selection function ( Si ) (optional)• Separation strength (optional)

Use the following forms to enter specifications and view results for Screen:


Input Specify screen parameters, operating conditions, and user-specified screenseparation strength and selection functions


Results View summary of Screen results and material and energy balances

Upper and Lower Level Screens

You can specify the operating level as Upper or Lower. The most efficientconfiguration is a multiple-deck screen with a series of Screen blocks. The inletstream is fed over the upper level screen. The underflow from the upper levelscreens is fed over the lower level screens. Screen uses different correlations forupper and lower level screens.

Screen calculates the flow rate of the screen overflow stream as:

F S Fo ii

ijj

= ∑ ∑

Where:

Si = Selection function. The fraction of feed particles in size rangei that passes over the screen into the overflow product

Fij = Flow rate of feed in size range i and particle size distributionattribute j

Selection Function and Separation Strength

Screen calculates the selection function for a certain size interval as:

( )[ ]SA d S

for d Si

p o

p o=−

<1

1exp

S for d Si p o= ≥1


Chapter 8

Where:

d p = Particle diameter

So = Size of screen opening

A = Separation strength

The default value of the screen separation strength, A, is a function of the size ofthe screen opening. Screen has four built-in functions (U.S. Bureau of Mines,1977)1 for all possible combinations of screen types (see the table, Screen SeparationStrength/Screen Size Correlation):• Upper level dry• Lower level dry• Upper level wet• Lower level wet

You can enter your own separation strength value, separation strength correlationor selection function correlation on the Input SelectionFunction sheet. Screen thenuses these selection function values for its mass balance calculation.

Screen Separation Strength/Screen Size Correlation

Size of screenopening (m) Dry, upper level Dry, lower level Wet, upper level Wet, lower level

0.457 60 60 60 60

0.152 20 20 20 20

0.038 8 8 9 9

0.0095 8 6 8.5 6.6

0.00635 5 4 5.5 4.5

0.00236 3 2 3.5 2.3

0.00059 0.7 0.7 0.8 0.8

0.00042 0.6 0.6 0.7 0.7

0.000295 0.5 0.5 0.55 0.55

Separation Efficiency

The separation efficiency of the screen is calculated as the ratio of the mass flowrate of the underflow to the fraction of the feed flow rate containing particlessmaller than the screen openings.


Solids

References

Computer Simulation of Coal Preparation Plants, U.S. Bureau of Mines, GrantNo. GO-155030, Final Report August (1977).


Chapter 8

FabFlFabric Filter

FabFl is a gas-solids separator model used to separate an inlet gas streamcontaining solids into a solids stream and a gas stream carrying the residualsolids. Use FabFl to simulate or design baghouse units in which solid particlesare separated from the inlet gas stream. A baghouse consists of a number of cellsin which vertically-mounted cylindrical fabric filter bags operate in parallel.

You can use FabFl to rate or size baghouses.

Flowsheet Connectivity for FabFl

Feed

Gas (overflow)

Solids (underflow)


Outlet One overflow stream for the cleaned gasOne underflow stream for the solids particles

Each solids substream must have a particle size distribution (PSD) attribute.Solids may be entrained in the overflow, based on the separation efficiency.

Specifying FabFlUse the Input Specifications sheet to specify operating conditions and baghousecharacteristics.

For these calculations Set Mode= And number of cells is

Rating Simulation Specified

Sizing Design Calculated


Solids

For sizing or rating calculations:

If you enter FabFl calculates

Maximum allowable pressure drop Filtration time

Filtration time Pressure drop

Use the following forms to enter specifications and view results for FabFl:


Input Enter operating conditions, baghouse characteristics, and separationefficiency


Results View summary of FabFl results and material and energy balances

Operating Ranges

FabFl uses empirical models because no theoretical models exist. Expect unreliableresults when operating conditions exceed the ranges of the experimental data onwhich the models are based. Your data should fall within these ranges:

• Diameter of solid particles between 10 7− to 10 4− m (0.1 to 100 micrometers)• Maximum gas velocity through the cloth between 0.1 and 0.2 m/s (20 to 40

ft/min)

Filtering Time

When rating fabric filters, FabFl calculates the filtering time t as:

tP P

CKVf i

o

=−∆ ∆

2

Where:

fP∆ = Final pressure drop across collected dust and filter cloth

iP∆ = Pressure drop of the clean bag

C = Dust concentration

K = Dust resistance coefficient

oV = Air to cloth ratio (gas velocity through the cloth)


Chapter 8

The air to cloth ratio Vo is:

VQ

N N A Nocell shake bag bag

=−( )

Where:

Q = Volumetric flow rate of the gas

Ncell = Number of cells

Nshake = Number of cells being cleaned

Abag = Total filter surface of all bags

Nbag = Number of bags per cell

Resistance Coefficient

The resistance coefficient K depends on the particle size and nature of solidparticles. In an industrial-scale baghouse, the resistance coefficient also varieswith time and bag position. If specific resistance coefficients are not available,the following values can be used as rough estimates1:

Dust particle diameter

( 10 6− m)

Resistance coefficients

[Pa/(kg/m 2 ) (m/s)]

Less than 20 300,000

20 to 90 60,000

Greater than 90 15,000

These coefficients were determined from a small fabric filter. The filter has an airflow of 2 ft 3 / min through 0.2 ft 2 of cloth area (a filtering gas velocity of 10ft/min). The pressure drop across the bag and dust was 8 inches of H O2 .

An approximation for the resistance coefficient2 is:

Kdp

= 10002

Where:

dp = The average particle size in microns

The units for K are (inches of water)/(lbs dust/ft 2 of area)(ft/min velocity).


Solids


The overall separation efficiency of the baghouse is:

ηη

oj i

ij ijS

Total inlet flow rate of solids

flow rate of solids removed from the inlet

total inlet flow rate of solids= =

∑ ∑

Where:

Sij = Flow rate of solid j in size increment i

In FabFl, the separation efficiency is a function of the particle diameter of thesolids. For large particles (greater than 10 micrometers in diameter), fractionalcollection efficiency ( )ηi is 1.0. For particles smaller than 10 micrometers,efficiency decreases rapidly.

η i When

1.0 ( )d mp av > 10 µ

0.0011 ( )dp av + 0.989 1 10µ µm (dp< <)av m

0.495 ( )dp av + 0.495 ( )dp av < 1µm

You also can enter efficiency as a function of particle sizes on the Input Efficiencysheet to override the built-in correlations.

References

1. Air Pollution Engineering Manual, Public Health Service Publication No. 999-AP-40, pp. 106-135, Washington D.C., DHEW (1967).

2. Billings, C.E. and Wilder, J., Handbook of Fabric Filter Technology, Vol. I,NIIS PB 200648.


Chapter 8

CycloneCyclone Separator

Cyclone separates an inlet gas stream containing solids into a solids stream and agas stream carrying the residual solids.

Use Cyclone to simulate cyclone separators in which solid particles are removed bythe centrifugal force of a gas vortex. You can use Cyclone to size or rate cycloneseparators. In simulation mode, Cyclone calculates the separation efficiency andpressure drop from a user-specified cyclone diameter.

In design mode, the cyclone geometry is calculated to meet the user-specifiedseparation efficiencies and maximum pressure drop. In both calculation modes,the particle size distributions of the outlet solids streams are determined.

Flowsheet Connectivity for Cyclone

Feed

Gas

Solids


Outlet One stream for the cleaned gasOne stream for the solids



Solids

Specifying CycloneUse the Input Specifications sheet to specify the type of cyclone and operatingconditions.

Use the Input Dimensions sheet to enter cyclone dimensions, or use the InputRatios sheet to enter ratios of cyclone dimensions.

To performthese calculations Specify Cyclone calculates

Rating Simulation modeCyclone DiameterNumber of Cyclones

Separation efficiencyPressure drop

Sizing Design modeSeparation EfficiencyMaximum PressureDrop (optional)Maximum Number ofCyclones (optional)

Cyclone diameterNumber of cyclones

For rating calculations, if you specify Type=User-Specified or User-SpecifiedRatios, you can specify cyclone dimensions on the Input Dimensions or InputRatios sheets.

For design calculations, you must also enter the Maximum Number of Cyclonesin parallel. If either of the following occurs, Cyclone calculates the number ofcyclones in parallel:• The efficiency of a single cyclone is less than the required separation efficiency.• The calculated pressure drop exceeds the maximum pressure drop specified.

Use the following forms to enter specifications and view results for Cyclone:


Input Enter cyclone specifications, dimensions, dimension ratios, separation efficiencies,and solids loading


Results View summary of Cyclone results and material and energy balances


Chapter 8


The overall separation efficiency is:

ηm

flow rate of solids removed from the inlet

total inlet flow rate of solids=

ηmo i

o

o o

o o o o

C C

C

Q C E

Q C

E

Q C=

−=

−= −1

Where:

Co = Concentration of solids in inlet gas

Ci = Concentration of solids in outlet cleaned gas

Qo = Inlet gas flow rate

E = Outlet emission rate of solids in the cleaned gas

Cyclone attains higher separation efficiencies with particles that are 5 to 10microns or greater in diameter. For particles smaller than 5 microns, Cycloneefficiency decreases. Even with large particles, it is difficult to obtain a collectionefficiency greater than 95%.

If you enter a design efficiency higher than 95%, use either:• Multi-stage cyclones• Cyclone as a precleaner, followed by other collectors

You can specify the Efficiency Correlation field on the Input Specifications sheet. IfEfficiency Correlation=User-Specified, you can enter efficiency as a function ofparticle sizes on the Input Efficiency sheet.

Operating Ranges

Cyclone uses correlations that are semi-empirical models. Do not expectsatisfactory accuracy when the specified conditions exceed the ranges ofexperimental data from which the models were developed. In general, the pressuredrop should be less than 2500 N / m2 (10 inches of H O2 ). The operating pressureshould not exceed atmospheric pressure. The inlet gas velocity should be in therange of 15 to 27 m/s (50 to 90 ft/s).

The Leith and Licht efficiency correlation is accurate for inlet velocitiesapproximately 25 m/s (80 ft/s). The correlation overestimates the separationefficiency at high velocities.


Solids

The Shepherd and Lapple correlation is accurate for particle sizes of 5 to 200microns. This correlation tends to overestimate the efficiency of large particles(greater than 200 microns). The Shepherd and Lapple correlation alsounderestimates the efficiency of fine particles (smaller than 5 microns).

Pressure Drop

Cyclone calculates the pressure drop (Shepherd and Lapple, 1939)1 as:

∆P U Nf t h= 0.0030 ρ 2

Where:

ρ f = Density of the fluid

Ut = Inlet gas velocity

Nh = Inlet velocity speeds

Use the Input SolidsLoading sheet to enter values to correct for solids loading.

The inlet velocity speed, Nh , is:

N Kab

Dke

= 2

Where:

K = Dimensionless ratio

a = Inlet height of the cyclone

b = Inlet width of the cyclone

De = Outlet diameter of the cyclone

The dimensionless ratio K is:

c

nls

abD

VVK

)2/(8 +=

Where:

Vs = Annular shaped volume above the exit duct to midlevel ofthe entrance duct

Vnl = Effective volume of the cyclone calculated by natural length l

Dc = Body diameter of the cyclone


Chapter 8

The annular shaped volumeVs above the exit duct to midlevel of the entrance duct is:

Vs a D D

sc e=

− −π( / ) ( )2

4

2 2

Cyclone Diameter

Cyclone calculates the diameter of the body of the cyclone Dc as:

Db D

a D b Dcf

p f

c

c c

=−

×−

0.0502Q

(

2ρµ ρ ρ )

( / )

( / ) ( / ) .

.1

2 2

0 454

Where:

Q = Overflow gas flow rate

ρ f = Density of the fluid

µ = Viscosity of gas fluid

ρp = Density of the particles

In this empirical equation, units are:

Unit type Unit

Length Feet

Mass Pounds

Time Seconds

Dimension Ratios

Use the Input Dimensions sheet to enter the dimensions of a cyclone whenMode=Simulation and Type=User-Specified. If you specify Type=User-SpecifiedRatios, you can use the Input Ratios sheet to enter dimension ratios (dimension /cyclone diameter) for a cyclone.


Solids

The dimension ratios and some default values of the two built-in configurationsare:

Dimension ratio (dimension/cyclone diameter) Type = High efficiency Type = Medium efficiency

Cyclone diameter 1.0 1.0

Inlet height 0.5 0.75

Inlet width 0.2 0.375

Length of overflow 0.5 0.875

Diameter of overflow 0.5 0.75

Length of cone section 1.5 1.50

Overall length 4.0 4.0

Diameter of underflow 0.375 0.375

Number of gas turn in cyclone 7.0 4.0

Maximum diameter (m) 1.5 5.0

Minimum diameter (m) 0.1 0.1

Cyclone calculates the dimensions of the built-in cyclones using these ratios andthe cyclone diameter you specify. The built-in configurations (Type=High orMedium) may not be the best designs. It is recommended that you enterdimensions or dimension ratios, if available.

Vane Constant

Use the Vane Constant field on the Input Specifications sheet to specify the vaneconstant. The vane constant varies with the configuration of the inlet duct. In thecommon configuration, the inlet duct terminates at the wall of the cyclone. Thevane constant is 16. To reduce friction loss, extend the duct into the interior of thecyclone. When the duct is in the middle of the cyclone separator, the vane constantis 7.5.

Cyclone Dimensions

The next figure shows the Cyclone geometry. The table following the figure showsthe Cyclone dimensions.


Chapter 8

a

De

Dc

b

s

h

H

B

Cyclone Geometry

The Cyclone design configurations are:

Term Description High efficiency High throughput

Dc Body diameter 1.0 1.0

a Inlet height 0.5 0.75

b Inlet width 0.2 0.375

s Outlet length 0.5 0.875

De Outlet diameter 0.5 0.75

h Cylinder height 1.5 1.50

H Overall height 4.0 4.0

B Dust outlet diameter 0.375 0.375


Solids

Solids Loading Correction

The feed concentration of solids affects the separation efficiency. Concentrationhigher than 1 0 3. gm m usually leads to higher efficiency. Smolik (1975)2, 3

presented the following relationship between the efficiency and solidsconcentration:

1

1

−−

=

E

E

c

cT

T

a* *

Where:

c* = "Low loading" solids concentration, 1.0 gm / m3

c = Solids concentration

E T* = Total efficiency

ET = "Low loading" total efficiency

α = Exponent

Smolik gives values of α = 0.182. This form can only serve as a guide, because theeffect of dust concentration depends on the nature of the solids, the humidity of thegas, and many other factors that do not figure in the existing correlations.

The actual pressure drops with dust-laden gases are normally lower than thoseobtained with clean gas. Smolik gives an empirical correlation for the effect offeed concentration on pressure in the form:

∆∆p

pc

* = −1 β γ

Where:

c = Solids concentration in the feed, g / m3

∆p * = Pressure drop

∆p = Pressure drop with clean gas

β γ, = Constants depending on the material

Smolik gives values of β γ= 0.02 and 0.6.


Chapter 8

References

1. Shepherd, G.B. and Lapple, C.E., "Flow Pattern and Pressure Drop inCyclone Dust Collectors," Industrial and Engineering Chemistry, 31, pp. 972-984 (1939).

2. Smolik, J. et al., Air Pollution Abatement, Part I. Scriptum No. 401-2099 (inCzech). Technical University of Prague (1975). Quoted by Svarovsky, L.,"Solid-Gas Separation," Handbook of Powder Technology, Williams, J.C. andAllen, T. (Eds.), Amsterdam: Elsevier, 1981.

3. Svarovsky, L., Solid-Gas Separation, Chapter 3, New York: Elsevier, 1981.


Solids

VScrubVenturi Scrubber

Use VScrub to simulate venturi scrubbers.

Venturi scrubbers remove solid particles from a gas stream by direct contact withan atomized liquid stream.

You can use VScrub to rate or size venturi scrubbers.

Flowsheet Connectivity for VScrub

Gas

Liquid

Feed Gaswith Solids Liquid and

Solids

Material StreamsInlet One stream for solids with at least one solids substream

One stream for the atomized liquid

Outlet One stream for the cleaned gasOne stream for the liquid with solid particles


Chapter 8

Specifying VScrubUse the VScrub Input Specifications sheet to specify operating conditions andparameters for sizing or rating calculations.

To perform thesecalculations Set Mode = Enter scrubber VScrub calculates

Rating Simulation Throat DiameterThroat Length

Separation efficiencyPressure drop

Sizing† Design Separation efficiency Liquid flow rateThroat diameterThroat lengthPressure drop

†Because the required liquid flow rate is varied to meet the efficiency, the material balance isnot satisfied if the calculated liquid flow rate is different from the rate you enter.

In both modes, VScrub also calculates the particle size distributions of the solids inthe outlet streams.

VScrub assumes that the liquid stream is introduced before or at the beginning ofthe scrubber throat. It also assumes the separation of the solid particles from thegas stream occurs only at the scrubber throat.

Use the following forms to enter specifications and view results for VScrub:


Input Specify operating parameters and throat operating conditions


Results View summary of VScrub results and material and energy balances


Solids

Pressure Drop

VScrub calculates the pressure drop (Yung, S. et al., 1977)1 ∆ p across the throat ofthe scrubber as:

( )∆pV

g

Q

Qx x xl t

c

l

g

=

− + −

21

22 4 2ρ

Where:

ρl = Density of the liquid

Vt = Relative velocity of gas to liquid at the throat

gc = Conversion factor in Newton’s law of motion

Q

Ql

g

= Liquid to gas volume flow rate

x = Dimensionless throat length defined by:

xl C

Dt D g

d l

= +3

161

ρρ

Where:

lt = Throat length

CD = Drag coefficient, as a function of the Reynolds number(Dickinson and Marshall, 1968)2 N Re .

CN

ND = + +. ( . ).2224

1 015 0 6

ReRe

ρg = Density of the gas

ρl = Density of the liquid

Dd = Drop diameter (Sauter mean), defined by (Nukiyama, S.,Tanasawa, Y. 1939)3:

585597

10000 5 0 45 1 5

V

Q

Qt

l

l

l

l l

l

g

σρ

µσ ρ

+

. . .

Where:

σ l = Surface tension

µ l = Viscosity of liquid


Chapter 8


The separation efficiency (Yung, S., et al., 1978)4 ηo is defined as:

ηo

Mass flow rate of particles in outlet liquid stream

Mass flow rate of particles in inlet gas stream=

= ∑ S

Total inlet flow rate of solidsi iη

Where:

ηi= Efficiency for size increment i

Si = Mass flow rate of size increment i

References

1. Yung, S. et al., Journal of the Air Pollution Control Association, 27, 348(1977).

2. Dickinson, D.R. and Marshall, W.R., AIChE Journal, 14, 541, (1968).

3. Nukiyama, S. and Tanasawa, Y., Transcripts of the Society of MechanicalEngineers (Japan), 5, 63 (1939).

4. Yung, S. et al., Environmental Science and Technology, 12, 456 (1978).


Solids

ESPElectrostatic Precipitator

Use ESP to simulate dry electrostatic precipitators.

Dry electrostatic precipitators separate solids from a gaseous stream.Electrostatic precipitators have vertically mounted collecting plates withdischarge wires. The wires are parallel and positioned midway between theplates.

The corona discharge of the high-voltage wire electrodes first charges the solidparticles in the inlet gas stream. Then the electrostatic field of the collectingplate electrodes removes the solids from the gas stream.

You can use ESP to size or rate electrostatic precipitators.

Flowsheet Connectivity for ESP

Feed

Gas

Solids


Outlet One material stream for the cleaned gasOne material stream for the solids



Chapter 8

Specifying ESPUse the Input Specifications sheet to specify parameters for sizing or ratingcalculations.

To perform thesecalculations Set Mode= Enter ESP calculates

Rating Simulation Number of platesPlate heightPlate length

Separation efficiencyPower requiredCorona voltagePressure dropPrecipitator width

Sizing Design Separation efficiency Number of platesPrecipitator dimensionsPower requiredPressure drop

You can specify maximum dimensions for sizing calculations on the InputSpecifications sheet.

Use the following forms to enter specifications and view results for ESP:


Input Specify operating parameters and dielectric constants and precipitatordimensions


Results View summary of ESP results and material and energy balances

Operating Ranges

The velocity of gas should be between 1 and 2.5 m/sec (for plate spacing 200 and300 mm). If the gas velocity is larger than 3 m/s or less than 0.5 m/s, then themodels for efficiency and pressure drop are not valid. This is because the transportof fine particles by turbulent diffusion may become more significant than transportby electrostatic force.

ESP models wire-and-plate precipitators with relatively high dust concentration( ).≥ 1011 particles / m or 0.1 kg / m3 3 If the particle concentration is too low, ESPmay overestimate the results. ESP is not suitable for a cylindrical electrostaticprecipitator.


Solids


The separation efficiency is defined as (Crawford, M. 1976)1:

ηov

Mass outlet flow rate of solids

Total mass flow rate of the inlet solids substream=

ηπµov

nvs

nvo

s ps cC

C

X L q E C

dWV= −

−

1

3exp

( )

Where:

Cnvs = Particle concentration at Xs

Cnvo = Particle concentration at inlet

Xs = Point at which all particles have acquired a saturation charge

L = Plate length

qps = Particle saturation charge

Ec = Collecting field strength ( . ( ))= 0 25 Eo

C = Conningham correction factorµ = Viscosity of the gas

d = Particle diameter

W = Distance between wires and plates

V = Actual gas velocity through the precipitator

The point at which all particles have acquired a saturation charge Xs , is definedas:

XdW s V C C

E C E Ws E rsw nvo nvs

o c c w

=−

−µε

2

0 00 332 0 8

( )

. ( . )

Where:

sw = Distance between two wires

εo = Electric permissivity constant = −8 85 10 12. x c / vm

Eo = Corona field strength 2

ro = Corona radius


Chapter 8

The collecting field strength Ec , is defined as:

E V fT P

TP

T P

TP rc Bo

o

o

o o

= +

−0 25 0 03. .

Where:

VB = Breakdown voltage

f = Roughness factor of wire

To = Atmospheric temperature

Po = Atmospheric pressure

T = Temperature

P = Pressure

The particle concentration at the point where the particles first have saturationcharge, Cnvs is:

Ck

kd

E Ws E r

Ws E E r Ws rnvs

c w o o

w c o o w o

=+ −

+ −0 212 2 08

0 427 2 05332

. ( ) .

. ( . )

Where:

k = Dielectric constant ( / )= ε εo

The particle saturation charge, qps is:

qk d

kE

E r

Ws

r

Wspso

co o

w

o

w

=+

+ −

3

2

2

3

2 5 2

3

1 252πε . .

Pressure Drop

ESP calculates the pressure drop across the precipitator as:

∆p Vg g= 45 5 2. ρ

Where:

ρg = Gas density

Vg = Gas velocity


Solids

Required Power

The power required2 Pw to meet a specified separation efficiency is:

P Qw ov= −52 75 1. ln( )η

Where:

Q = Volumetric gas flow rate

Gas Velocity

The models used in ESP are valid for inlet gas velocities ranging from 0.5 to 3m/s. Outside this range, transport by turbulent diffusion becomes moresignificant than by electrostatic force and large errors should be expected.

Particle Diameter

You can use ESP to model the separation of fine particles with diameters rangingfrom 0.01 to 10 microns. ESP is accurate when the inlet particle concentration ishigh ( ).≥ 1011 particles / m or 0.1 kg / m3 3 If the concentration is too low, the modeltends to overestimate the separation efficiency.

References

1. Crawford, M., Air Pollution Control Theory, Chapter 8: ElectrostaticPrecipitation, pp. 298-358. New York: McGraw-Hill, 1976.

2. White, H.J., Industrial Electrostatic Precipitation, 204, pp. 91-92 (1963).


Chapter 8

HyCycHydrocyclone Solids Separator

Use HyCyc to simulate hydrocyclones. Hydrocyclones separate solids from the inletliquid stream by the centrifugal force of a liquid vortex.

You can use HyCyc to rate or size hydrocyclones. In simulation mode (rating),HyCyc calculates the particle diameter with 50% separation efficiency from theuser-specified hydrocyclone diameter. In design mode (sizing), HyCyc determinesthe hydrocyclone diameter required to achieve the user-specified separationefficiency of the solids with the desired particle size.

In both calculation modes, pressure drop and the particle size distribution of theoutlet solids streams are determined.

Flowsheet Connectivity for HyCyc

Feed

Liquid

Solids

Material StreamsInlet One liquid stream with at least one solids substream

Outlet One stream for the cleaned liquid with residual solidsOne stream for solids

Each inlet solids substream must have a particle size distribution (PSD)attribute.


Solids

Specifying HyCycUse the Input Specifications sheet to specify hydrocyclone operating conditions.

To perform these calculations Enter HyCyc calculates

Rating Simulation ModeHydrocyclone Diameter

Separation efficiencyParticle diameter with 50% separationefficiencyPressure drop, particle size distribution ofoutlet solids stream

Sizing Design ModeSeparation Efficiency

Hydrocyclone diameterPressure drop, particle sizedistribution of outlet solids stream

To obtain practical dimensions when sizing hydrocyclones, enter the:• Maximum diameter of the hydrocyclone• Maximum pressure drop allowed across the hydrocyclone

HyCyc designs multiple hydrocyclones in parallel if one of the following conditionsexists:• The calculated diameter is greater than the maximum specified diameter.• The calculated pressure drop is greater than the maximum specified pressure

drop.

Use the following forms to enter specifications and view results for HyCyc:


Input Specify simulation parameters, dimensions, tangential velocity correlationparameters, and separation efficiency


Results View summary of HyCyc results and material and energy balances

Operating Ranges

HyCyc uses empirical and semi-empirical correlations. Expect unreliable resultswhen operating conditions (Bradley, D., 1965)1 are outside the ranges ofexperimental data on which the models are based. In general, your data should fallwithin these ranges:• Particle diameter between and (5 to 200 micrometers)• Hydrocyclone diameter between 0.01 and 0.6 m• Pressure drop between 35 and 345 kPa• Separation efficiency between 2% and 98%


Chapter 8

The solids concentration should be less than 11% of the volume fraction, or lessthan 25% of the weight fraction.


Separation efficiency E is defined as:

Emass underflow rate of solids

mass feedflow rate of solids=

Reduced efficiency E′ is defined as the fraction of feed solids that go to theunderflow minus the fraction of the feed liquid that also goes to the underflow.

′ =−−

EE R

Rf

f1

Where Rf is the volumetric ratio of underflow to feed flow (see Material Split ,

this chapter).

The reduced efficiency is obtained from the following equation2:

′ = − − −

E

d

d100 1 0 115

50

3

exp .

Where:

d = Diameter of the solid particles to be separated

d50 = Particle diameter for which 50% of feed passes through underflow

In turn, 50d is obtained from the following equation which includes operational

and geometric parameters (Bradley, D., 1965)1:

d D

D

D R

Qc

i

nc f50

2

0 53 0 38 1

2=

−−

( . ) ( )

( )tan

.

αµ

σ ρθ


Solids

Where:

Q = Volumetric flow rate at inlet

Dc = Chamber diameter

Di = Inlet diameter

n = Power of R in the tangential velocity distribution function

α = Inlet velocity loss coefficient

σ = Density of solid

Rf = Underflow rate/feed rate

θ = Cone angle

ρ = Density of liquid

µ = Viscosity of liquid

Material Split

HyCyc splits the feed according to the following empirical correlation (Moder, J.M.and Dahlstrom, D.A., 1952)3:

SD

DQu

o

= −β ( ) . .4 4 44

Where:

S = Volume split = underflow rate/overflow rate

β = A constant, 6.13

Du = Diameter for underflow

Do = Diameter for overflow

Q = Inlet volumetric flow rate (gal/min)


Chapter 8

The flow ratio fR (underflow rate/feed rate) is then obtained by:

11

1− =

+R

Sf

Tangential Velocity

The following empirical correlation gives the tangential velocity V (Dahlstrom,D.A., 1954)4 in a hydrocyclone at a radius R:

VR constant VDn

ic

n

= =

α

2

Where:

α = Inlet velocity loss coefficient

Vi = Inlet velocity

Dc = Diameter of the hydrocyclone

n = Exponent of radial dependence

R = Radius

For most cases, α and n are determined experimentally to be 0.45 and 0.8. Thesetwo variables are then used to determine d50 .

Dimension Ratios

Common hydrocyclones have the following ranges of dimension ratios(dimension/chamber diameter):

Inlet diameter: 1/7 to 1/3

Length: 4 to 12

Overflow diameter: 1/8 to 1/2.3

Underflow diameter: 1/10 to 1/5

Cone angle: 9 deg. to 20 deg.


Solids

Pressure Drop

For the pressure drop correlation to be valid (overflow diameter/underflowdiameter) should be 0.6 to 2.0. HyCyc uses the empirical pressure dropcorrelation (Dahlstrom, D.A., 1954)4:

Q

HD Do i0 5

0 96 38... ( )= ×

Where:

Q = Volumetric flow rate (US gallons/minute) at the inlet

H = Height of fluid (feet) or length of vortex finder

Do = Overflow diameter

Di = Inlet diameter

Hydrocyclone Dimensions

The next figure shows the HyCyc geometry.

Inlet Di

L

θ

Do

Dc

Du

Hydrocyclone Dimensions


Chapter 8

The following table describes the HyCyc dimensions.

Term Description

Dc Chamber diameter

Di Inlet diameter

DoOverflow diameter

Du Underflow diameter

L Length of hydrocyclone

θ Cone angle

References

1. Bradley, D., The Hydrocyclone, 1st edition., Pergamon Press, London (1965).

2. Yoshioka, H. and Hatta, Y., Kagaku Kagolar, Chemical Engineering, Japan,19, 633 (1955).

3. Moder, J.M. and Dahlstrom, D.A., Chemical Engineering Progress, 48,75(1952).

4. Dahlstrom, D.A., “Mineral Engineering Techniques,” Chemical EngineeringProgress Symposium Series 50, No. 15, 41 (1954).


Solids

CFugeCentrifuge Filter

Use CFuge to simulate centrifuge filters. The centrifuge filters separate liquidsand solids by the centrifugal force of a rotating basket.

Use CFuge to rate or size centrifuge filters.

CFuge assumes that the separation efficiency of the solids equals 1, so that theoutlet filtrate stream contains no residual solids.

Flowsheet Connectivity for CFuge

Feed

Liquid

Solids


Outlet One material stream for the liquidOne material stream for the solids

If you specify the particle size distribution (PSD), CFuge calculates the averageparticle size.


Chapter 8

Specifying CFugeUse the Input Specifications sheet to specify operating conditions and the InputFilterCake sheet to specify filter cake properties.

To perform thesecalculations Enter CFuge calculates

Rating DiameterRate of revolutionFilter cake properties

Filtrate flow rateFilter cake moisture contentHeight of centrifuge basket

Sizing List of centrifuge diameters and ratesof revolutionFilter cake moisture content (CFugeestimates if not entered)

Filtrate flow rateFilter cake moisture contentHeight of centrifuge basket

For sizing calculations, CFuge also calculates the liquid-handling capacities of allof the centrifuges you specify. CFuge selects the centrifuge with a liquid-handlingcapacity greater than or equal to the required filtrate flow rate. If more than onecentrifuge satisfies this criterion, CFuge selects the one with the smallestcapacity. If none of the centrifuges satisfies this criterion, CFuge selects the onewith the highest filtrate flow rate.

In both rating and sizing calculations, CFuge calculates the content and height ofthe centrifuge basket.

Use the following forms to enter specifications and view results for CFuge:


Input Specify centrifuge and filter cake parameters and centrifuge dimensions


Results View summary of CFuge results and material and energy balances

Filter Cake Characteristics

Use the Input FilterCake sheet to specify:• Cake resistance• Moisture Content• Sphericity• Medium resistance• Porosity• The average diameter of the solid particles in the cake


Solids

The filter cake moisture content is the ratio of the mass flow rate of liquid to thatof the solid in the outlet solids stream. The filter cake moisture content is animportant design parameter. You should provide it if possible. If you do not enterit, CFuge calculates an estimate from the average particle diameter and cakeparameters (Dombrowski, H.S., and Brownell, L.E., 1954)1.

If you enter the particle size distribution (PSD) of the inlet solid stream, CFugecalculates the average particle diameter, so you do not need to enter averagediameter on the Input FilterCake sheet.

Filtrate Flow Rate

CFuge calculates the filtrate volumetric flow rate from:

Q F WMl

= −1

ρ( )

Where:

F = Feed liquid volumetric flow rate

M = Moisture content, mass of liquid/mass of dried solid(specified as Moisture Content on the FilterCake sheet orcalculated by the model)

W = Dry solids feed rate

ρl = Liquid density

Pressure Drop

CFuge calculates the pressure drop (Grace, H.P., 1953)2 across the filter cake as:

∆pr rl=

−ρ ω 222

12

2

( )

Where:

ω = Rotational speed

r1 = Radius of liquid surface

r2 = Radius of inner wall of bowl

ρl = Liquid density


Chapter 8


Separation efficiency, E, is defined as:

Eunderflow rate of solids

feedflow rate of solids=

CFuge assumes that the separation efficiency of the solids equals 1, so that theoutlet filtrate stream contains no residual solids.

References

1. Dombrowski, H.S., and Brownell, L.E., Industrial and EngineeringChemistry, 46, 6, 1207 (1954).

2. Grace, H.P., Chemical Engineering Progress, 49, 8, 427 (1953).


Solids

FilterRotary Vacuum Filter

Use Filter to simulate continuous rotary vacuum filters. You can use Filter torate or size rotary vacuum filters.

Filter assumes the separation efficiency of the solids equals 1, so that the outletfiltrate stream contains no residual solids.

Flowsheet Configuration for Filter

Feed

Filtrate

Solids


Outlet One material stream for the liquid filtrateOne material stream for the solids

Specifying FilterUse the Input Specifications sheet to specify operating conditions andparameters.


Chapter 8

To perform thesecalculations Enter Filter calculates

Rating SimulationDiameterWidthRate of revolutionFilter cake characteristics (optional)

Pressure dropacross filter

Sizing DesignMaximum allowable pressure drop across the filter cake andmediumRate of revolutionFilter cake characteristics (optional)Width to diameter ratio (optional)

DiameterWidth

In both calculation modes, ASPEN PLUS determines the following:• Filtrate volumetric flow rate• Cake thickness• Mass fraction of solids in the solids filter cake

Use the following forms to enter specifications and view results for Filter:


Input Specify filter and filter cake parameters


Results View summary of Filter results and material and energy balances

Filter Cake Characteristics

Filter assumes:• The cake thickness is greater than 0.00635 m.• The capillary number is greater than 1.• The filter cake is incompressible or compacted uniformly throughout its

thickness2

When the specific cake resistance α at the required pressure drop ∆P is notavailable, Filter can estimate it using the following empirical correlation:

( )α α= OkP∆

Where:

αO = Specific cake resistance at unit pressure drop

k = Cake compressibility


Solids

You can use this equation for interpolation and short-range extrapolation whensome experimental data of αO and ∆P are available. αO is the intercept of thelog-log plot of α versus ∆P. α and αO both have the units determined by thespecified units set, and ∆P is always in Pascals.

Use the Average Diameter field on the FilterCake sheet to specify the averagediameter of solid particles in the filter cake. If you enter the particle sizedistribution (PSD) of the inlet solid stream, Filter calculates the average particlesize.

Pressure Drop

Filter calculates the pressure drop1 across the filter cake with:

Q RHV RHp V

W= =

ω

ωθµα

21 2

∆/

Where:

Q = Filtrate volume flow rate

ω = Angular velocity

R = Radius

H = Width

V = Filtrate volume per unit area

∆p = Pressure drop

θ = Wetting angle

µ = Viscosity

α = Filtration resistance

W = Solid mass per unit area


Separation efficiency, E, is defined as:

Eunderflow rate of solids

feedflow rate of solids=


Chapter 8

Filter assumes the separation efficiency of the solids equals 1, so that the outletfiltrate stream contains no residual solids.

References

1. Brownell, L.E. and Katz, D. I., Chemical Engineering Progress, 43, 11, 601(1947).

2. Dombrowski, H.S. and Brownell, L.E., Industrial and Engineering Chemistry,46, 6, 1207 (1954).

Additional Reading:

Brownell, L.E. and Katz, D. I., Chemical Engineering Progress, 43, 10, 537(1947).

Dahlstrom, D.A. and Silverblatt, C.E., Solid/Liquid Separation Equipment ScaleUp, Chapter 2, Purchas, D.B., Ed., Uplands Press Ltd. (1977).

Silverblatt, C.E., Risbud, H., and Tiller, F.M., Chemical Engineering, 127 (April27, 1974).


Solids


Chapter 8

SWashSingle-Stage Solids Washer

Use SWash to simulate solids washers in which dissolved components in theentrained liquid of a solids stream are recovered by a washing liquid. SWashsimulates a single-stage solids washer; it does not consider the presence of avapor phase.

SWash calculates the flow rates and compositions of the outlet solids and liquidstreams from a user-specified liquid-to-solid mass ratio of the outlet solidsstream and the mixing efficiency of the washer. For non-adiabatic operations,SWash determines the outlet temperature when outlet pressure and heat dutyare given. Alternatively, SWash calculates the required heat duty when outlettemperature and pressure are specified.

Flowsheet Connectivity for SWash

Liquid

Solids

Liquid

Solids

Heat (optional) Heat (optional)

Material StreamsInlet One stream for the solids particles with an entrained liquid

One stream for the washing liquid

Outlet One stream for the washed solids particlesOne stream for the washing liquid and entrained liquid from the inletsolids stream

Heat StreamsInlet One stream for heat duty (optional)

Outlet One stream for net heat duty (optional)


Solids

If you specify only pressure on the Input OutletFlash sheet, SWash uses the inletheat stream as a duty specification. Otherwise, SWash only uses the inlet heatstream to calculate the net heat duty. The net heat duty is the inlet heat streamminus the actual (calculated) heat duty.


Specifying SWashYou must specify the mixing efficiency of the washer and the liquid-to-solid massratio of the outlet solids stream. For non-adiabatic operations, you must specifythe pressure of the washer and one of the following:• The temperature of the washer• Heat duty (or an inlet heat stream without an outlet heat stream)

Alternatively, SWash calculates the required heat duty when outlet temperatureand pressure are specified.

SWash assumes adiabatic operations if neither temperature nor heat duty isspecified.

Use the following forms to enter specifications and view results for SWash:


Input Specify operating parameters, flash specifications, and convergence parameters


Results View summary of SWash results and material and energy balances

Mixing Efficiency

The mixing efficiency of the washer, E, is defined as:

Ex x

x xINS

OUTS

INS

OUTL=

−−

Where:

xINS = Mass fraction of dissolved components in the entrained

liquid of the inlet solids stream

xOUTS = Mass fraction of dissolved components in the entrained

liquid of the outlet solids stream

xOUTL = Mass fraction of dissolved components in the outlet liquid

stream


Chapter 8

Bypass Fraction

The bypass fraction is the fraction of liquid in the feed that bypasses the mixing,when mixing efficiency is less than 1. It is calculated as:

Bypass fraction mixing efficiencyliquid to solid ratio specified for SWashliquid to solid ratio in inlet solids stream

= − × − −− −

( )1


Solids

CCDCounter-Current Decanter

CCD simulates a counter-current decanter or a multistage washer. CCDcalculates the outlet flow rates and compositions from:• Mixing efficiency• Liquid-to-solid mass ratio of each stage

CCD can calculate:• The heat duty profile from a specified temperature profile• The temperature profile from a specified heat duty profile

CCD does not consider a vapor phase.

Flowsheet Connectivity for CCD

OverflowSolids(Top feed)

Product FromOverflow (optional)

Feed ToOverflow(optional)

WashingLiquid(Bottom feed)

Underflow

Product FromUnderflow (optional)

Feed ToUnderflow (optional)

Nstage

1

Material StreamsInlet One solids inlet material stream (top feed)

One liquid inlet material stream (bottom feed)Any number of optional inlet material side streams per stage

Outlet One top product stream (overflow)One bottom product stream (underflow)One optional stream per stage for the solids (underflow)One optional stream per stage for the liquid (overflow)Any number of pseudoproduct streams (optional)


Chapter 8

Any number of pseudoproduct streams can represent internal underflows oroverflows. A pseudoproduct stream does not affect the results of the simulation.

Specifying CCDUse the CCD Input Specifications sheet to enter the number of stages, pressure,mixing efficiency, and liquid-to-solid mass ratio.

Use the CCD Input Streams to enter feed, product, and optional heat streamlocations.

On the CCD Input Temp-DutyProfiles sheet, note the following:

If you enter CCD calculates

Stage temperature Stage heat duty

Stage heat duty Stage temperature

Stage overall heat transfercoefficient

Stage temperature

You cannot enter both temperature profiles and heat duties or overall heattransfer coefficients. If you enter stage heat duty and/or an overall heat transfercoefficient, and you do not enter values for all stages, the system assumesunspecified values to be zero. Enter the medium temperature of each stage whenyou enter overall heat transfer coefficients. Use the Estimated Temperature fieldto enter estimated stage temperatures.

Note CCD interpolates unspecified values and, by default, assumesthem to be the same as the ambient temperature.

Use the CCD Input PseudoStream sheet to transfer the internal overflow orunderflow of a stage to a pseudostream.

Use the following forms to enter specifications and view results for CCD:


Input Specify operating parameters, temperature profile parameters,pseudostream information, and convergence parameters


Results View summary of CCD results, material and energy balances, and stageprofiles


Solids

Component Attributes

CCD does not consider the mixing of component attributes and PSDs. CCDassumes all outlet solids streams have the same attributes and PSD as the solidsfeed stream to stage one. CCD also assumes all outlet liquid streams have thesame attributes and PSD as the liquid feed stream throughout the final stages.

Multistage Washer Profiles

For any CCD profile, such as mixing efficiency, liquid-to-solid-ratio, temperature,duty, enter a value for every stage, as information becomes available. If you enteronly some of the values for some stages, CCD generates the complete profile bylinear interpolation of the given values. If you enter only one value, CCDassumes a constant profile of that value throughout the washer.

Mixing Efficiency

The mixing efficiency of stage n is defined as:

Ex x

x xINS

OUTS

INS

OUTL=

−−

Where:

xINS = Mass fraction of dissolved components in the entrained liquid of the

total inlet solids stream to stage n.

xOUTS = Mass fraction of dissolved components in the entrained liquid of the

total outlet solids stream from stage n.

xOUTL = Mass fraction of dissolved components in the outlet liquid stream

from stage n.


Chapter 8

Medium Temperature

The duty for each stage is calculated according to the following equations:

Q UA Tcalc Tmedi i i i= −( )

Where:

Qi = Heat duty for stage i

UAi = Product of heat transfer coefficient and area for stage i

Tcalci = Calculated outlet temperature of stage i

Tmedi = Temperature of the heat transfer medium at stage i

❖ ❖ ❖ ❖


Solids


Chapter 9

9 User Models

This chapter describes the models that allow you to write your own unitoperation models as Fortran subroutines. These subroutines must follow theguidelines described in the ASPEN PLUS User Models reference manual. Themodels are:


User User-defined unit operationmodel

Model a unit operation using a user-suppliedFortran subroutine

Unit operations with four (orfewer) inlet and outletstreams

User2 User-defined unit operationmodel

Model a unit operation using a user-suppliedFortran subroutine.

Unit operations with no limiton number of streams


User Models

UserUser-Supplied Unit Operation Model

User can model any unit operation model. You must write a Fortran subroutineto calculate the values of the outlet streams based on the inlet streams andparameters you specify.

User and User2 differ only in the number of inlet and outlet streams allowed andthe argument lists to the model subroutine. User is limited to a maximum of fourmaterial and one heat or work inlet stream and a maximum of four material andone heat or work outlet stream. User2 has no limits on the number of inlet andoutlet streams.

Flowsheet Connectivity for User

Heat (optional)Work (optional)

Heat (optional)

Material

Work (optional)

Material StreamsInlet One to four inlet material streams

Outlet One to four outlet material streams

Heat StreamsInlet One heat stream (optional)


Work StreamsInlet One work stream (optional)

Outlet One work stream (optional)


Chapter 9

Specifying UserYou must specify the name of the subroutine model on the Input Specificationssheet. You have the option of specifying:• A report subroutine name• Size of the integer and real arrays (INT and REAL) passed to the user model

subroutine• Values of the integer and real arrays passed to the user model subroutine• Length of integer and real workspace vectors• Thermodynamic conditions of each outlet stream• Type of flash calculations (vapor, liquid, two-phase, three-phase)

For information on writing Fortran subroutines for user models, see theASPEN PLUS User Models reference manual.

Use the following forms to enter specifications and view results for User:


Input Specify name and parameters for user subroutine, calculation options, andoutlet stream conditions and flash convergence parameters


Results View summary of User results and material and energy balances


User Models

User2User-Supplied Unit Operation Model

User2 can model any unit operation model. You must write a Fortran subroutineto calculate the values of the outlet streams based on the inlet streams andparameters you specify.

User and User2 differ only in the number of inlet and outlet streams allowed andthe argument lists to the model subroutine. User2 has no limits on the number ofinlet and outlet streams. User is limited to a maximum of four material and oneheat or work inlet stream, and a maximum of four material and one heat or workoutlet stream.

Flowsheet Connectivity for User2

Heat (optional)Work (optional)

Heat (optional)

Material

Work (optional)


Outlet At least one outlet material stream


Outlet Any number of heat streams (optional)


Outlet Any number of work streams (optional)


Chapter 9

Specifying User2You must specify the name of the subroutine model on the User2 InputSpecifications sheet. You have the option of specifying:• A report subroutine name• Size of the integer and real arrays (INT and REAL) passed to the user model

subroutine• Values of the integer and real arrays passed to the user model subroutine• Length of integer and real workspace vectors• Thermodynamic conditions of each outlet stream• Type of flash calculations (vapor, liquid, two-phase, three-phase)

For information on writing Fortran subroutines for user models, see ASPENPLUS User Models reference manual.

Use the following forms to enter specifications and view results for User2:


Input Specify name and parameters for user subroutine, calculation options, and outletstream conditions and flash convergence parameters


Results View summary of User2 results and material and energy balances

❖ ❖ ❖ ❖


User Models


Chapter 10

10 Pressure Relief

This chapter contains detailed reference information on the ASPEN PLUSPres-Relief model for pressure relief calculations. For information on usingPres-Relief, see the ASPEN PLUS User Guide, Chapter 33.

This chapter describes the following topics:• Specifying Pres-Relief• Scenarios• Rules to size the relief valve piping• Compliance with codes• Stream and vessel compositions and conditions• Reactions• Relief system• Data tables for pipes and relief devices• Valve cycling• Vessel types• Disengagement models• Stop criteria• Solution procedure for dynamic scenarios• Flow equations• Calculation and convergence methods• Vessel insulation credit factor


PressureRelief

Pres-ReliefPressure Relief Model

Use Pres-Relief to do either of the following:• Determine the steady-state flow rating of pressure relief systems• Dynamically model vessels undergoing pressure relief due to a fire or heat

input specified by the user. You may specify that reactions occur in the vessel.

Specifying Pres-ReliefUse Pres-Relief to do either of the following:• Determine the steady-state flow rating of pressure relief systems• Dynamically model vessels undergoing pressure relief due to a fire or heat

input specified by the user. You may specify that reactions occur in the vessel

Use the Setup form to specify the pressure relief scenario, general specificationssuch as the discharge pressure and the estimated flow rate, inlet streamconditions, initial vessel conditions, design rules, and any reactions (dynamicscenarios only) that occur.

Use the Relief Device form to specify the relief system. You must select a reliefdevice and specify its characteristics. You must also specify the vessel neck andthe number of inlet and tail pipe sections to be used.

Use the Dynamic Input form to specify the required parameters for dynamicscenarios. These include vessel specifications, disengagement models and detailsspecific to the chosen scenario. For the fire scenario, you must specify the firestandard and the credits to be used. When the scenario is Dynamic run withspecified heat flux, you must specify the heat input parameters.

When the number of inlet and tail pipe sections exceeds 0, you must specify thedetails for each section in the Inlet Pipes and Tail Pipes forms.

For dynamic scenarios, use the Operations form to specify one or more variablesto be used as stop criteria. The simulation will stop when the value of any ofthese variables exceeds the user-specified limit.


Chapter 10

Use the following forms to enter specifications and view results for Pres-Relief:


Setup Specify pressure relief scenario, general specifications, initial stream conditions, designrules, and any reactions that occur (required input)

Relief Device Specify the type of relief device and the characteristics of the device (required input)

Inlet Pipes Specify piping, fittings, and valves immediately upstream of the relief device (optionalinput)

Tail Pipes Specify piping, fittings, and valves immediately downstream of the relief device (optionalinput)

Dynamic Input Specify parameters describing the dynamic event (required for dynamic scenarios)

Operations Specify criteria that will terminate the dynamic simulation (required for dynamicscenarios)

Convergence Override default methods and convergence parameters for the algorithms involved in thepressure relief simulation (optional input)

Block Options Override default methods and options for property calculation, simulation, diagnostics,and reporting (optional input)

Results Review calculated results and profiles for the steady-state scenarios

Dynamic Results Review calculated results and profiles for the dynamic scenarios

ScenariosScenarios are situations that cause venting through the pressure relief system tooccur. Pres-Relief supports the following scenarios:• Dynamic run with vessel engulfed by fire• Dynamic run with specified heat flux into vessel• Steady state flow rating of relief system• Steady state flow rating of relief valve

Dynamic Run with Vessel Engulfed by Fire

Use this scenario to model a vessel engulfed by fire. You must specify the vesselgeometry and initial composition. ASPEN PLUS can compute the energy inputfor this scenario according to the following standards:• NFPA-30• API-520• API-2000


PressureRelief

ASPEN PLUS assumes the calculated energy input is constant during the entireventing transient. ASPEN PLUS uses credit factors for drainage, water-spray,fire-fighting equipment, and insulation to reduce energy input, if appropriate forthe chosen standard. You may specify a total credit factor instead of individualcredit factors. You must specify the fire duration time. This is a dynamicscenario. The vessel contents and relief rate change as a function of time.

The following tables describe how ASPEN PLUS calculates wetted area, energyinput, and credit factors for each of the three standards.

Calculation of Wetted Area

Vessel type NFPA-30 API-2000 API-520

Horizontal 75% of total exposedarea

75% of total area or area to a height of30 ft. above grade, whichever is greater

Wetted area up to 25 ft. above grade(based on specified liquid level)

Vertical Area up to 30 ft.above grade. Bottomplate is included ifexposed

Area up to 30 ft. above grade. If onground, bottom plate is not included.

Wetted area up to 25 ft above grade(based on specified liquid level).Bottom plate is included if exposed.

Sphere 55% of total exposedarea

55% of surface area, or surface area toa height 30 ft. above grade, whicheveris greater

Up to a maximum horizontal diameteror up to height of 25 ft. above grade,whichever is greater

Calculation of Q (Btu/hr), Based on Area (sq-ft)NFPA-30† and API-2000

Area range Heat input

20 < area < 200 Q=20,000Area

200 < area < 1000 Q=199,300(Area 0.566 )

1000 < area < 2800 Q=963,400(Area 0.338 )

2800 < area Q=21000(Area 0.82 )

†For NFPA-30 , QMAX=14,090,000 at 2800 square feet if operating pressure < 1 PSIG

API-520

Heat input

Q=34,500(Area 0.82 )


Chapter 10

Calculation of Credit Factors

Type NFPA-30 API-2000 API-520

Insulation only .3 F=K(1660-TF)/21,000t†

You must specify F

Same as API-2000

Drainage only .5

(Area > 200 sq. ft.)

1. Not defined

Water and drainage .3 1. Not defined

Water, insulation, anddrainage

.15


NSUL Not defined

Insulation and drainage .15


Not defined Not defined

Drainage and prompt firefighting effort

No credit Not defined 0.6*INSUL

Portable No credit factors allowed Not defined Not defined

†See Vessel Insulation Credit Factor, this chapter.

Dynamic Run with Specified Heat Flux into Vessel

This scenario is similar to the fire exposure scenario, except it can model anyenergy input. ASPEN PLUS can compute the energy input for this scenario inthree ways depending on whether you specify:• A constant duty• A duty profile• An area for heat transfer, a heat transfer coefficient, and a source fluid

temperature

This scenario is a dynamic scenario and is typically used for electrical heatersand other energy sources.

Steady State Flow Rating of Relief System

Use this scenario to find the flow rate through a specified relief system at thespecified composition. For this scenario, you must enter your own:• Relief rate• Piping description• Feed stream composition• Feed stream condition


PressureRelief

Steady State Flow Rating of Relief Valve

Use this scenario to find the flow rate through a valve, given the composition andcondition at the entrance to the valve. This is the simplest scenario. It is similarto the steady state flow rating of relief system scenario, except no piping isallowed.

Compliance with CodesPres-Relief allows two types of runs:• Code capacity• Actual capacity

The primary purpose of the code capacity run is to ensure that the capacity of therelief system, rated as required by code, exceeds the maximum capacity dictatedby the scenario. The maximum pressure reached during the relief event must beless than the code allowable accumulation. The Code Capacity run includes the:• ASME valve rating factor of .90• Valve flow coefficient• A combination coefficient

The combination coefficient is only included if a rupture disk/relief valvecombination is being designed. Typical combination coefficients for NBBIcertified combinations are close to 1.00. If the combination is not certified, theASME code requires a combination coefficient of .90. The primary purpose of theactual capacity run is to provide the best estimate of the actual flow through thesystem. Design of downstream equipment (other than the tail pipe) is oneexample why you might need this information. The actual capacity run containsthe valve flow coefficient, but not the ASME valve rating factor of .90 or thecombination coefficient.

Stream and Vessel Compositions and ConditionsFor the steady-state scenarios, you must specify the composition and conditions(two of temperature, pressure, and vapor fraction) of the feed stream. You can dothis on the Setup Streams sheet in two ways:• Reference an ASPEN PLUS stream• Give the composition and conditions of the stream as input to Pres-Relief


Chapter 10

For the dynamic scenarios, you must specify the composition and the conditionsin the vessel at the beginning of the pressure relief calculations. Do this byreferencing an ASPEN PLUS stream, or by specifying the composition and two oftemperature, pressure, and vapor fraction on the Setup Vessel Contents sheet.As with the steady-state scenarios, you may reference an ASPEN PLUS streamor give the composition and conditions as input to Pres-Relief. When vaporfraction is not specified, you may also specify:• Initial liquid fill fraction (fillage) of the vessel• Pad-gas pressure and Component ID

Only two of temperature, pressure, and vapor fraction can be specified orreferenced from a stream.

Rules to Size the Relief Valve PipingASPEN PLUS uses several rules (3% rule, X% rule, and 97% rule) to size theinlet and outlet piping with PSVs. The rules use the following terminology:

DSP = Differential set pressureCBP = Constant back pressurePsta = Static pressurePtot = Static pressure + velocity pressureIDP = Inlet pressure drop

Ptot (vessel) - Ptot (valve in)BBP = Built-up back pressure

Psta (valve out) - CBP

These rules are applied for both actual and code capacity runs and are applied atthe converged solution for the steady-state scenarios.

For dynamic scenarios, the 3% Rule and X% Rule are applied once, at 10%overpressure. If all pressures are above 10% overpressure, the test is notperformed and a warning is issued. If all pressures are below 10% overpressure,the highest pressure value is scaled up to 10% overpressure, and the scaledvalues are used in applying the rule. The 97% rule is applied when the pressureat the valve inlet is at or above 10% overpressure.

None of the required standards mentions any of these rules except for the X%rule with X=10. The X% rule is mentioned in the non-mandatory appendix of theASME code.


PressureRelief

3% Rule

According to the 3% rule, the total pressure loss in the inlet must be less than 3%of the differential set pressure when the flow rate is equal to the code capacity ofthe valve at 10% overpressure.

IDP DSP≤ 0 03.

For cases where the overpressure does not reach 10%, adjust the pressure droprule by multiplying by the ratio of the maximum flowing pressure to 10%overpressure (psig).

IDPRP

SP≤ 0 03

11.

.

X% Rule

According to the X% rule, the built-up back pressure must be less than X% of thedifferential set pressure when the flow rate is equal to the code capacity of thevalve at 10% overpressure.

BBPX

DSP≤100

For cases where the overpressure does not reach 10% adjust the pressure droprule by multiplying by the square of the ratio of the maximum flowing pressureto 10% overpressure (psig).

BBPX RP

PS≤

100 11

2

.

97% Rule

According to the 97% rule, 97% of the differential set pressure must be availableacross the valve anytime the over pressure is equal to or above 10% with a flowthrough the valve based on code capacity.

RP CBP IDP BBP DSP− − − ≥ 0 97.

For cases where the overpressure does not reach 10%, apply the rule at peakoverpressure.


Chapter 10

Recommendations for Specific Valve Types

For standard spring loaded valves or pop action pilot valves withunbalanced pilots vented to the discharge:

The differential set pressure is the set pressure minus the constant backpressure.

DSP SP CBP= −

Size the inlet piping using the 3% rule.

Size the outlet piping using the 97% rule.-Or-Size the outlet piping with the X% rule using X = 10.

For balanced bellows spring loaded valves:

The differential set pressure is the set pressure.

DSP SP=

Size the inlet piping using the 3% rule.

Size the outlet piping with the X% rule using X = 30.

For modulating pilot operated valves with balanced pilots or pilotsvented to atmosphere:

The differential set pressure is the set pressure.

DSP SP=

You can use the scenario required flow rather than the valve capacity forpressure drop calculations as an option. This can easily be simulated by changingthe input orifice area until the overpressure reaches 10%.

There is no inlet pressure drop rule.

Size the outlet piping with the X% rule using X = 50.

ReactionsIf the protected vessel is a vertical, horizontal, API, spherical , or user-specifiedtank, you may model it with or without reactions. Specify the reactions by givingthe Reactions ID on the Setup Reactions sheet.


PressureRelief

Relief SystemThe venting system consists of:• A vessel neck• One or two sections of inlet pipe• The relief device itself• One or two sections of tail pipe

In a simulation, the system being modeled may consist of an inlet pipe without arelief device, or a relief device connected to the vessel without an inlet pipe. Thetail pipe is optional.

Relief Devices

Pres-Relief can model the following types of relief devices:• Safety relief valves (PSVs; both liquid and gas/2-phase)• Rupture disks (PSDs)• Emergency relief valves (ERVs)• SRV/rupture disk combinations• Open vent pipes

Internal tables (accessed from the ReliefDevice SafetyValve sheet) containseveral standard commercially available valves, along with all the mechanicalspecifications and certified coefficients needed in the relief calculations. You maychoose one valve from the tables, or enter your own valve specifications andcoefficients.

For liquid service valves, you must also specify the full-lift overpressure. Thisallows ASPEN PLUS to simulate some of the older style valves which do notachieve full lift until 25% overpressure is reached.

For gas/2-phase service valves, you must also specify the average opening andclosing factors. The valve does not open until the pressure drop across the valvereaches (opening factor * Dif-Setp). The valve closes when the pressure dropacross it reaches (closing factor * Dif-Setp).

In an actual capacity run, the rupture disk is modeled as a bit of resistance usingthe pipe model. The default value of L/D is 8 for a rupture disk with a diameterof 2 inches or less and 15 if the diameter is greater than 2 inches. You canoverride the default by specifying a value on the Relief Device Rupture Disksheet.

In the code capacity run, the rupture disk is modeled as an ideal nozzle with acertified discharge coefficient. If no certified discharge coefficient is available, avalue of 0.62 is suggested.

In a code capacity run in combination with a safety relief valve, the resistance ofthe rupture disk is modeled by the combination coefficient in the valve model.


Chapter 10

The emergency relief vent is modeled as a nozzle. A de-rating factor of 0.9 is usedin a code capacity run.

Piping System

The inlet piping system can be made of one of the following:• One pipe section• Two sections of pipe plus a vessel neck, all with different diameters

The tail pipe can be made of one section of pipe or of two sections of pipe withdifferent diameters.

For each pipe section, specify:• Pipe diameter• Length• Elevation• Whether the pipes are screwed together or held together with flanges or

welds

If pipes of different diameters are used, reducer and expander resistancecoefficients ("K" factors) can be specified. ASPEN PLUS uses the equationK=4*fr*(L/D) to convert from resistance coefficients to equivalent L/D, where theterm "fr" is the friction factor. Optional information for each section consists ofthe number of 90 degree elbows, straight tees, branched tees, gate valves,butterfly valves, transflo valves, and control valves. You can add other fittingsnot listed by specifying the L/D value. ASPEN PLUS calculates a total equivalentL/D before modeling the pipe section.

You may also specify:• Ambient temperature at the inlet and outlet of the pipe• A heat transfer coefficient to exchange heat with the pipe contents

While modeling the pipe section, ASPEN PLUS detects the choked condition inthe pipe by keeping track of the Mach Number as integration down the pipeproceeds. If the Mach Number goes above 1.0, integration is stopped and a flag isreturned to indicate that the pipe choked.

Pipeline pressure drop modeling can work in two ways. You may specify one ofthe following:• Rigorous flashes are to be done at each step in the integration• A flash table is used during pipe integration


PressureRelief

If you request a table, specify the number of temperature and pressure points inthe table. At each temperature-pressure pair, ASPEN PLUS performs a flash andcalculates all necessary properties (density, viscosity, surface tension, and so on).As integration proceeds, ASPEN PLUS interpolates in this table to get thenecessary properties. If properties outside the table are needed, a rigorous flashis performed at that point. In general, the pipe integration proceeds faster if theflash table is used. Several correlations are available, depending on the pipeinclination. The default method for all inclinations (holdup and frictionalpressure loss) is Beggs and Brill. Other available options are:• Darcy• Lockhart-Martinelli• Dukler for frictional loss• Lockhart-Martinelli, Slack, and Flanigan for holdup

Data Tables for Pipes and Relief DevicesPres-Relief includes several customizable tables that list the available options forpipes, general purpose valves, safety relief valves, emergency relief vents, andrupture disks. You can modify the tables by changing data files. Then process thefiles through ModelManager Table Building System (MMTBS).

Pipes

Pres-Relief includes a table of actual diameters for several steel pipe schedules.Use this table when choosing the piping for the inlet and tail pipes. You can modifythis table by including more pipe materials and/or schedules. The following sectionshows the table organization.


Chapter 10

first material of construction# of typesfirst type# of diametersnominal diameter actual diameternominal diameter actual diameter..second type# of diametersnominal diameter actual diameternominal diameter actual diameter..second material of construction# of typesfirst type# of diametersnominal diameter actual diameternominal diameter actual diameter..second typenominal diameter actual diameternominal diameter actual diameter..

General-Purpose Valves

For general-purpose valves in the inlet or tail pipes, Pres-Relief includes a table ofvarious manufacturers’ valves from 1 inch to 10 inches. The valves include:• Durco Plug• Tufline Plug• Jamesbury Ball• AGCO Selector• KTM Ball (L-Port and T-Port)


PressureRelief

For each manufacturer, the table contains:• Valve type (for example., L-Port or T-Port)• Nominal diameter• Port area• Flow coefficient

The table is organized as follows:

first manufacturer# of typesfirst type# of diametersnominal diameter port area flow coeffnominal diameter port area flow coeff..second type# of diametersnominal diameter port area flow coeffnominal diameter port area flow coeff..

Safety Relief Valves

Pres-Relief includes a table of manufacturers’ safety relief valves. It containsvalves for liquid and gas/2-phase service. For each valve, the table contains:• Service• Type• Manufacturer• Series, size (for example, 3L4)• Throat diameter• Inlet diameter• Outlet diameter• Discharge coefficient• Overpressure factor (for liquid service valves)


Chapter 10


Service (Liquid, Gas, or 2-phase)# of typesfirst type# of manufacturersfirst manufacturer# of seriesfirst series# of sizesfirst size# of throat diametersthroat diam inlet diam outlet diam dischg coeff over pr factorthroat diam inlet diam outlet diam dischg coeff over pr factor..throat diam inlet diam outlet diam dischg coeff over pr factorthroat diam inlet diam outlet diam dischg coeff over pr factor

Emergency Relief Vents

This table contains:• Nominal diameter• Effective diameter• Allowed setpoint for several Protectoseal and Groth emergency relief vents

You must specify an over-pressure factor. The table is organized as follows:

first manufacturer# of typesfirst type# of nominal diametersnominal diameter effective diameter allowed setpointnominal diameter effective diameter allowed setpoint..

Rupture Disks

This table contains manufacturers’ information on rupture disks. Each entrycontains:• A manufacturer• Type• Nominal diameter• Actual diameter• Discharge coefficient


PressureRelief


first manufacturer# of typesfirst type# of nominal diametersfirst nominal diam actual diam discharge coeffsecond nominal diam actual diam discharge coeff..

Valve CyclingIf a relief valve is too large for a given application, valve cycling may occur. In thissituation, the pressure in the vessel builds up to a point where the valve opens, butthen closes almost immediately because enough material is released to lower thevessel pressure below the closing pressure. In some simulations, the valve mayopen and close several times per second. The simulation may run for a long time,just opening and closing the valve over and over.

To stop such a simulation, you can specify whether or not to stop cycling, andhow many openings and closings of the valve are allowed in a specified amount oftime.

Vessel TypesYou must enter vessel geometry for the dynamic scenarios. You can choose one ofthe following vessel types:• Vertical Vessel• Horizontal Vessel• API Tank• Sphere• Heat exchanger shell• Vessel jacket• User-specified

If you choose user-specified, you must specify surface area and volume. Surfacearea is also required for vessel jacket. Maximum Allowable Working Pressure(MAWP) with corresponding temperature is required for all vessel types. Somevessel types require diameter, length, and volume of internals.


Chapter 10

Vertical Vessel, Horizontal Vessel, and API Tank

If you choose vertical vessel, horizontal vessel, or API tank, choose one of thesehead types:• Flanged and dished• Ellipsoidal• User-specified

If you choose user-specified head type, you must specify the area and volume of ahead.

Sphere

If the protected vessel is a sphere, you must specify:• Diameter• MAWP with corresponding temperature• Volume of internals

Heat Exchanger Shell

If the protected vessel is a heat exchanger shell, in addition to the items specifiedfor a vertical vessel you must also specify whether the vessel is mountedvertically or horizontally.

Vessel Jacket

If the protected vessel is a vessel jacket, you must specify:• MAWP with corresponding temperature• Volume of internals• Jacket volume

User-Specified

If the protected vessel is user-specified, you must specify:• Volume• Area• MAWP with corresponding temperature• Volume of internals


PressureRelief

Disengagement ModelsThe following disengagement options are available:

Option Description

Homogeneous Vapor fraction leaving vessel is the same as vapor fraction in vessel

All-vapor All vapor leaving vessel

All-liquid All liquid leaving vessel

Bubbly DIERS bubbly model

Churn-turbulent DIERS churn-turbulent model

User-specified Homogeneous venting until vessel vapor fraction reaches the user-specified value,then all vapor venting

For the bubbly and churn-turbulent methods, ASPEN PLUS uses the DIERS“switch-point” calculations to compute the point at which total vapor-liquiddisengagement occurs. Use the bubbly and churn-turbulent models only forvertical or API tanks.

Stop CriteriaFor dynamic scenarios, stop criteria need to be specified which will terminate thesimulation. You must:• Select a specification type• Enter a value for the specification at which the simulation will stop• Select a component and substream for component-related specification types• Specify which approach direction (above or below) to use in stopping the

simulation

You may select from the following specification types:• Simulation time• Vapor fraction in the vessel• Mole fraction of a specified component• Mass fraction of a specified component• Conversion of a specified component• Total moles or moles of a specified component• Total mass or mass of a specified component• Vessel temperature• Vessel pressure• Vent mole flow rate or mole flow rate of a component• Vent mass flow rate or mass flow rate of a component


Chapter 10

You must also select the location of the stop criteria specification. You may selectfrom the following locations:• Vessel• Relief vent system• Accumulator

Certain restrictions apply depending on the location selected.

When location = vessel, mole and mass flow rate are not allowed.

When location = vent accumulator, only the following specifications are allowed:• Mass fraction of a specified component• Mole fraction of a specified component• Total moles of a specified component• Total mass of a specified component

When location = vent, only the flowing specifications are allowed:• Mass fraction of a specified component• Mole fraction of a specified component• Vent molar flow rate• Vent mass flow rate

Solution Procedure for Dynamic ScenariosThe problem to be solved is:

Given the initial conditions in the vessel, a description of the pressure reliefsystem, and the heat flow into the vessel, calculate the flow rate through thepressure relief system and determine if the pressure relief system meets coderequirements.

The problem is solved as outlined below. This algorithm is for the Heat-Input andFire Scenarios.1. Given the heat input to the vessel, solve the energy balance and flash

equations along with the reaction equations for the vessel at the present timestep. If any of the termination criteria are met, go to Step 6. The options forspecifying termination criteria include:

• Time for scenario exceeded• Specified vapor fraction reached• Vessel contents have reached specified value• Pressure in the vessel is greater than the maximum allowed

2. If the pressure in the vessel is less than the device opening pressure,increment time and go to Step 1.


PressureRelief

3. Calculate the maximum flow rate possible through the pressure relief system.This value is calculated by finding the smallest diameter of any pipe or valvein the system, and calculating the sonic velocity through that diameter.

4. Calculate the pressure at the end of the vessel neck, after each section of theinlet pipe, after the pressure relief device, and after each section of the tailpipe based on the current flow estimate. If the pressure at the end of anysection is less than the user-specified discharge pressure, it is not necessaryto do the calculations for the next section.

5. If the pressure at the end of the pressure relief system is within tolerance ofthe user-specified discharge pressure, increment time and go to Step 1.

Otherwise, calculate a new guess for the flow through the relief system andgo to Step 4.

6. Given the flow at any time, check where the choke point is. If the choke pointis not at the pressure relief valve, the system is unacceptable. Check if anyapplicable codes are violated. If so, the system is unacceptable.

Flow Equations

Pipe Flow

This is the general differential equation for flow through a constant diameter pipe:

υ υ υυ

dp G d fD

dL g dL+ +

+ =2

2

42

0sin Φ (1)

Where:

υ = Specific volume of stream

p = Static (flowing) pressure of streamG = Mass flow rate per unit areaf = Friction factorD = Inside diameter of pipeL = Equivalent pipe lengthg = Acceleration due to gravitysin Φ = Vertical rise/equivalent pipe length


Chapter 10

Φ represents the physical angle of the pipe with respect to the horizontal only ifthe equivalent pipe length is the same as the physical flow path length (that is,only pipe, no fittings or other resistances). The potential energy term in theequation assumes that the vertical elevation is distributed evenly along theentire equivalent length.

For example, you have only a single 20 meter length of pipe that rises a total ofsix meters, then

sin .Φ = =6

200 3

If the same system also includes a fitting resistance of 5 equivalent meters, then:

sin .Φ =+

=6

20 50 24

Equation (1) applies to any flow system (all vapor, non-flashing liquid, flashingtwo-phase, non-flashing two-phase, etc.). All that is needed to solve the equationis the proper relationship between the pressure (p) and the stream specificvolume (υ ). This relationship is determined by the type of constraint chosen.

For adiabatic flow, the defining equation is:

H KE PE CONSTANT+ + =

Where:

H = Stream enthalpyKE = Kinetic energy of streamPE = Potential energy of stream

Between points 1 and 2:

H KE PE H KE PE1 1 1 2 2 2+ + = + +

Thus:

H H KE PE2 1= − −∆ ∆

ASPEN PLUS flash routines can be used to calculate enthalpy at point 2.


PressureRelief

Nozzle Flow

ASPEN PLUS calculates nozzle flow by treating the flow as adiabatic through aperfect nozzle which has no friction losses and is short enough so that any potentialenergy effects can be neglected. The actual flow is then calculated by applying acorrection factor (the flow coefficient, Cd) to the flow calculated as if the nozzlebehaved as perfect. Frictionless flow is described by:

udu dp+ =υ 0 (2)

Where:

u = Stream linear velocityυ = Specific volume of stream

For adiabatic flow:

d U PVu

PE+ + +

=

2

20

Where:

U = Internal energyPV = Pressure-volume product

Neglecting PE, and combining the definition of enthalpy (H = U + PV) into thisequation gives:

dH udu+ = 0 (3)Combining (2) and (3) gives:

dH dp=υ (4)

By definition:

dH dp=υ (5)

(4) and (5) yield:

Tds = 0

or

ds = 0

Thus, adiabatic frictionless flow is isentropic.


Chapter 10

The flow equation (2) can be integrated to describe the flow through a perfectnozzle as follows:

Let p0 = The upstream stagnation pressure where the velocity is zero (u0 = 0).

Let p1 = The pressure in the nozzle throat at which the flow is accelerated tovelocity u.

Thus, the integrated form of (2) becomes:

1

22

01

1

u dpp

p

= − ∫υ

which can be re-written (noting that u = G υ ):

G dpp

p

212 2

0

1

υ υ= − ∫ (6)

Equation (6) provides the means to calculate the flow rate through a perfectnozzle given the upstream stagnation pressure and the proper p-v relationship(which is isentropic). As one integrates (6) from p0 to p1, a maximum G indicatesthat the flow has become choked at the current value of p. (6) also serves as amethod for converting between stagnation and static pressures at any point inthe flow system (pipe or nozzle).

Calculation and Convergence MethodsASPEN PLUS uses the same equations used to model the safety relief valve as tomodel the conversion from stagnation to flowing pressure and back again. To becompletely accurate, the valve should be modeled as in equation (6) in the NozzleFlow section, this chapter. This model requires that constant entropy flashes beperformed at each point in the integration of equation (6). This is a very timeconsuming calculation, so several options are provided to speed up the calculations.First, you can choose to do constant enthalpy flashes rather than constant entropyflashes through the nozzle. This speeds up the calculations by an order ofmagnitude, since the constant entropy flash is modeled by a series of constantenthalpy flashes converging on entropy.

ASPEN PLUS also provides a shortcut method to calculate molar volume as afunction of pressure during the nozzle integration. This method was developed byL. L. Simpson1 and gives very good results. Instead of doing a flash calculation tocalculate the molar volume at each point in the integration, two flashes are doneat the start and parameters are calculated which allow you to calculate the molarvolume at other pressures without doing flashes.


PressureRelief

Vessel Insulation Credit FactorWhen Fire Standard API-520 or API-2000 is used, you may claim an insulationcredit factor calculated from the formula:

( )F

k Tf

t=

−1660

21000

Where:

k = Thermal conductivity of insulation, in British thermal units perhour per square foot per degree Fahrenheit per inch at meantemperature.

Tf = Temperature of vessel contents at relieving conditions, in degreesFahrenheit.

t = Thickness of insulation, in inches.

Assuming a k value of 4.0, and Tf of 0.0, the following table, which was takenfrom API-2000, gives values of F for various values of insulation thickness:

Insulation thickness (t) F Factor

6 inches (152 millimeters) 0.05



12 inches (305 millimeters)or more

0.025


Chapter 10

References

Simpson, L.L., "Estimate Two-Phase Flow in Safety Devices," ChemicalEngineering, August, 1991, pp. 98-102.

Additional Reading

"Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries"Part I - Sizing and Selection, API Recommended Practice 520, AmericanPetroleum Institute, 1220 L Street Northwest, Washington, D.C. 20005.

"Venting Atmospheric and Low Pressure Storage Tanks," (Non-refrigerated andRefrigerated), API Standard 2000, American Petroleum Institute, 1220 L StreetNorthwest, Washington, D.C. 20005.

❖ ❖ ❖ ❖


PressureRelief

Unit Operation Models A-1Version 10

Appendix A

A Sizing and Rating forTrays and Packings

ASPEN PLUS has extensive capabilities to size, rate, and perform pressure dropcalculations for trayed and packed columns. Use the following Tray/Packing formsto enter specifications:• TraySizing• TrayRating• PackSizing• PackRating

These capabilities are available in the following column unit operation models:• RadFrac• MultiFrac• PetroFrac

You can choose from the following five commonly-used tray types:• Bubble caps• Sieve• Glitsch Ballast®

• Koch Flexitray®

• Nutter Float Valve

ASPEN PLUS can model a variety of random packings. You can also use any ofthe following types of structured packings:• Goodloe®

• Glitsch Grid®

• Norton Intalox Structured Packing• Sulzer BX, CY, Mellapak, and Kerapak• Koch Flexipac, Flexeramic, Flexigrid

A-2 Unit Operation ModelsVersion 10

Sizing andRating forTrays andPackings

For sizing and rating calculations, ASPEN PLUS divides a column into sections.Each section can have a different tray type, packing type, and diameter. The traydetails can vary from section to section. A column can have an unlimited numberof sections. In addition, you can size and rate the same section with differenttypes of trays and packings.

The calculations are based on vendor-recommended procedures whenever theseare available. When vendor procedures are not available, well-establishedliterature methods are used.

ASPEN PLUS calculates sizing and performance parameters such as:• Column diameter• Flooding approach or approach to maximum capacity• Downcomer backup• Pressure drop

These parameters are based on:• Column loadings• Transport properties• Tray geometry• Packing characteristics

You can use the computed pressure drop to update the column pressure profile.

Single-Pass and Multi-Pass TraysYou can use the column models in ASPEN PLUS to:• Size one- and two-pass trays• Rate trays with up to four passes

Schematics of one-, two-, three-, and four-pass trays are shown in the next fourfigures. ASPEN PLUS performs and reports rating calculations for all panels.

When specifying Weir heights, cap positioning, and number of valves:

For Specify

One-pass tray A single value

Two-pass tray Up to two values, one for each panels A and B

Three-pass tray Up to three values, one for each panel (A, B and C)

Four-pass tray Up to four values, one for each panel (A, B, C and D)


Appendix A

The values for the number of caps and number of valves applies for each panel.For example, two-pass trays have two A panels for tray AA, and two B panels fortray BB. Therefore, the number of caps per panel is the number of caps per traydivided by two. Similar consideration is necessary for three- and four-pass trays.

If you specify only one value for multi-pass trays, that value applies to all panels.

When specifying downcomer clearance and width:

For Specify

One-pass tray A single value for the side downcomer

Two-pass tray Up to two values, one for the side downcomer, one for the center downcomer

Three-pass tray Up to two values, one for the side downcomer, one for the off-center downcomer

Four-pass tray Up to three values: one for the side downcomer, one for the center downcomer, and one forthe off-center downcomer



DC-WTOPWEIR-HT

DC-HTDC-WBOT

Ou

tlet

Wei

r L

eng

th

Column Diameter

DC-CLEAR

A One-Pass Tray


Appendix A

DC-WTOP

DC-CLEAR

DC-CLEAR

Panel A

Panel B

WEIR-HT

DC-HT

DC-HTDC-WBOT

DC-WBOT

Tray AASideDowncomer

Tray BB

CenterDowncomer

Below

CTR. DC

CTR. DC

~

~

~

~

~ ~

DC-WTOP

Column Diameter

Ou

tlet W

eir

Len

gth

A Two-Pass Tray



DC-WTOPDC-WBOT

DCOFPanel A. B. C.

Panel A. B. C.

Panel C. B. A.

BA C

DC-WTOP DC-WTOP

B A

OFF-CTR.DC

OFF-CTR.DC

WEIR-HT

DC-HT

DC-CLEAR

Column Diameter

Ou

tlet

Wei

r L

eng

th

A Three-Pass Tray


Appendix A

OFF-CTR.DCOFF-CTR.DC

SIDE DC

CTR.DC

DC-WTOP DC-WTOP

WEIR-HTDC-HT

DC-WBOTDC-WBOT

Panel A. B.

Panel C. D.

Panel A. B.

DCOF

DC-CLEAR D D C

A AB B

Column Diameter

Ou

tlet

Wei

r L

eng

th

A Four-Pass Tray



Modes of Operation for TraysASPEN PLUS provides two modes of operation for trays:• Sizing• Rating

In either mode, you can divide a column into any number of sections. Eachsection can have a different column diameter, tray type, and tray geometry. Youcan re-rate or re-design the same section with different tray types and/orpackings.

ASPEN PLUS performs the calculations one section at a time. In sizing mode,the column model determines tray diameter to satisfy the flooding approach youspecified for each stage. The largest diameter is selected.

In rating mode, you specify the column section diameter and other tray details.For each stage, the column model calculates tray performance and hydraulicinformation such as flooding approach, downcomer backup, and pressure drop.

Flooding Calculations for TraysFor bubble caps and sieve trays, ASPEN PLUS provides two procedures forcalculating the approach to flooding. The first procedure is based on the Fair1

method. The second uses the Glitsch procedure2 for ballast trays. This procedurede-rates the calculated flooding approach by 15% for bubble caps and by 5% forsieve trays. All other hydraulic calculations are based on the Fair and Bolles1,3

methods. For sizing calculations, you can also supply your own calculationprocedure:

= Specify On form

Flooding calculation method = USER TraySizing or PackSizing

Subroutine name UserSubroutines

For valve trays (Glitsch Ballast, Koch Flexitray, and Nutter Float Valve trays),ASPEN PLUS uses procedures from vendor design bulletins.2,4,5


Appendix A

Bubble Cap Tray LayoutRadFrac uses cap diameter only for tray type CAPS. Valid entries are:

Cap Diameter Default Weir Height

Inches Millimeters Inches Millimeters

3 76.2 2.75 69.85

4 101.6 3.00 76.20

6 152.4 3.25 82.55

Use the cap diameter to retrieve cap characteristics based on standard capdesigns.

For columns with diameter The default is

Up to 48 in (1219.2 mm). 3 in (76.2 mm)

Greater than 48 in (1219.2mm)

4 in (101.6 mm)

The following table lists standard cap designs:

Materials Stainless Steel

Nominal Size, in 3 4 6

Cap

U.S. Standard gauge 16 16 16

OD, in 2.999 3.999 5.999

ID, in 2.875 3.875 5.875

Height overall, in 2.500 3.000 3.750

Number of slots 20 26 39

Type of slots Trapezoidal Trapezoidal Trapezoidal

Slot width, in

Bottom 0.333 0.333 0.333

Top 0.167 0.167 0.167

Slot height, in 1.000 1.250 1.500

Height shroud ring, in 0.250 0.250 0.250

continued



Materials Stainless Steel

Nominal size, in 3 4 6

Riser

U.S. Standard gauge 16 16 16

OD, in 1.999 2.624 3.999

ID, in 1.875 2.500 3.875

Standard heights, in

0.5-in skirt height 2.250 2.500 2.750

1.0-in skirt height 2.750 3.000 3.250

1.5-in skirt height 3.250 3.500 3.750

Riser-slot seal, in 0.500 0.500 0.500

Cap areas, in

Riser 2.65 4.80 11.68

Reversal 4.18 7.55 17.80

Annular 3.35 6.38 14.55

Slot 5.00 8.12 14.64

Cap 7.07 12.60 28.30

Area ratios

Reversal/riser 1.58 1.57 1.52

Annular/riser 1.26 1.33 1.25

Slot/riser 1.89 1.69 1.25

Slot/cap 0.71 0.65 0.52

Pressure Drop Calculations for TraysNormally, RadFrac, MultiFrac, and PetroFrac treat the stages you enter asequilibrium stages. You must enter overall efficiency to:• Convert the calculated pressure drop per tray to pressure drop per

equilibrium stage• Compute the column pressure drop

If you do not enter overall efficiency, these models assume 100% efficiency. If youspecify Murphree or vaporization efficiency, you should not enter overallefficiency. RadFrac, MultiFrac, and PetroFrac will treat the stages as actualtrays.


Appendix A

Foaming Calculations for TraysSuggested values for Ballast trays are:

Service System Foaming Factor

Non-foaming systems 1.00

Fluorine systems 0.90

Moderate foamers, such as oilabsorbers, amine, and glycolregenerators

0.85

Heavy foamers, such asamine and glycol absorbers

0.73

Severe foamers, such as MEKunits

0.60

Foam stable systems, such ascaustic regenerators

0.30

Suggested values for Flexitrays are:


Depropanizers 0.85-0.95

Absorbers 0.85

Vacuum towers 0.85

Amine regenerators 0.85

Amine contactors 0.70-0.80

High pressure deethanizers 0.75-0.80

Glycol contactors 0.70-0.75

Suggested values for Float valve trays are:


Non foaming 1.00

Low foaming 0.90

Moderate foaming 0.75

High foaming 0.60



Packed ColumnsThe calculations for packings are based on the height equivalent of a theoreticalplate (HETP). HETP=packed height/number of stages. The HETP is required.You can provide it using one of the following methods:• Enter it directly on the PackSizing or PackRating forms• Enter the packing height on the same form

Packing Types and Packing FactorsASPEN PLUS can handle a wide variety of packing types, including differentsizes and materials from various vendors.

For random packings, the calculations require packing factors. ASPEN PLUSstores packing factors for the various sizes, materials, and vendors allowed in adatabank. If you provide the following information, ASPEN PLUS retrieves thesepacking factors automatically for calculations:• Packing type• Size• Material

You may specify the vendor on the PackSizing or PackRating form.

Is the vendorspecified? ASPEN PLUS uses

Yes The packing factor published by the vendor

No A value compiled from various literature sources†,††

†Fair, J.R., et al., "Liquid-Gas Systems," Perry’s Chemical Engineers’ Handbook, R.H. Perry and D.Green, ed., 6th ed. (New York: McGraw Hill, 1984).

††Tower Packings, Bulletin No. 15 (Tokyo: Tokyo Special Wire Netting Company).

You can enter the packing factor directly to override the built-in values. ASPENPLUS uses the packing type to select the proper calculation procedure.

Modes of Operation for PackingThe column models have two modes of operation for packing:• Sizing• Rating


Appendix A

In either mode, you can divide a column into any number of sections. Eachsection can have different packings. You can re-rate or re-design the same sectionwith different packings and/or tray types. ASPEN PLUS performs thecalculations one section at a time.

In sizing mode, ASPEN PLUS determines the column section diameter from:• The approach to the maximum capacity• A design capacity factor you specify

You can impose a maximum pressure drop per unit height (of packing or persection) as an additional constraint. Once ASPEN PLUS has determined thecolumn section diameter, it re-rates the stages in the section with the calculateddiameter.

In rating mode, you specify the column diameter. ASPEN PLUS calculates theapproach to maximum capacity and pressure drop.

Maximum Capacity Calculations for PackingASPEN PLUS provides several methods for maximum capacity calculations. Forrandom packings you can use:

Method For this type of packings

Mass Transfer, Ltd. (MTL)† MTL

Norton†† Norton IMTP

Koch††† Koch

Eckert All other random packings

†Cascade Mini-Ring Design Manual (Tokyo: Dodwell & Company, Ltd., 1984).

††Intalox High-Performance Separation Systems, Bulletin IHP-1 (Akron: Norton Company, 1987).

†††McNulty, K.J., "Hydraulic Model for Packed Tower Design." Paper presented at the American Instituteof Chemical Engineers Spring Meeting in Houston, 1993.

For structured packings, ASPEN PLUS provides vendor procedures for each type.If you specify the maximum capacity factor, ASPEN PLUS bypasses themaximum capacity calculations.

The definition of approach to maximum capacity depends on the type of packings.



For Norton IMTP and Intalox structured packings, approach to maximumcapacity refers to the fractional approach to the maximum efficient capacity.Efficient capacity is the operating point at which efficiency of the packingdeteriorates due to liquid entrainment. The efficient capacity is approximately 10to 20% below the flood point.

For Sulzer structured packings (BX, CY, Kerapak, and Mellapak), approach tomaximum capacity refers to the fractional approach to maximum capacity.Maximum capacity is the operating point at which a pressure drop of 12 mbar/m(1.47 in-water/ft) of packing is obtained. At this condition, stable operation ispossible, but the gas load is higher than that at which maximum separationefficiency is achieved.

The gas load corresponding to the maximum capacity is 5 to 10% below the floodpoint. Sulzer recommends a usual design range between 0.5 and 0.8 for approachto flooding.

For all other packings, approach to maximum capacity refers to the fractionalapproach to the flood point.

Because there are different definitions for approach to maximum capacity, sizingresults are not on the same basis for packings from different vendors, even whenyou use the same value for approach to maximum capacity. Direct performancecomparison of packings from different vendors is not recommended.

The capacity factor is:

CS VS V

L V

=−ρ

ρ ρ

Where:

CS = Capacity factor

VS = Superficial velocity of vapor to packing

ρV = Density of vapor to packing

ρ L = Density of liquid from packing


Appendix A

Pressure Drop Calculations for PackingFor random packings, ASPEN PLUS provides several built-in methods tocompute the pressure drop.

Vendor Pressure drop method

MTL Vendor†

Norton Vendor procedure††, †††, ♦

Koch Vendor procedure♦♦

Not specified Eckert GPDC♦♦♦, Norton GPDC††, †††, ♦, Prahl GPDC§, Tsai GPDC§§

†Cascade Mini-Ring Design Manual (Tokyo: Dodwell & Company, Ltd., 1984).

††Dolan, M.J. and Strigle, R.F., "Advances in Distillation Column Design," CEP, Vol.76, No.11(November 1980), pp. 78-83.

†††Intalox High-Performance Separation Systems, Bulletin IHP-1 (Akron: Norton Company, 1987).

♦Intalox Metal Tower Packing, Bulletin IM82 (Akron: Norton Company, 1979).

♦♦McNulty, K.J., "Hydraulic Model for Packed Tower Design." Paper presented at the American Instituteof Chemical Engineers Spring Meeting in Houston, 1993.

♦♦♦Fair, J.R., et al., "Liquid-Gas Systems," Perry’s Chemical Engineers’ Handbook, R.H. Perry and D.Green, ed., 6th ed. (New York: McGraw Hill, 1984), pp. 18-22.

§McNulty, K.J. and Hsieh, C.L., "Hydraulic Performance and Efficiency of Koch Flexipac StructuredPackings." Paper presented at American Institute of Chemical Engineers Annual Meeting in LosAngeles, 1982.

§§Tsai, T.C. "Packed Tower Program Has Special Features," Oil and Gas Journal, Vol. 83 No. 35(September, 1985), p. 77.

If you specify the vendor, ASPEN PLUS uses the vendor procedure. If you do notspecify the vendor, you can choose one of four different pressure drop methods. Ifyou do not specify a method, ASPEN PLUS uses the Eckert generalized pressuredrop correlation (GPDC).



For structured packings, vendor pressure drop correlations are available for allpackings:

Packing type Pressure drop method

Goodloe Vendor procedure†

Glitsch Grid Vendor procedure††

Norton Intalox Structured Packings Vendor procedure†††

Sulzer BX, CY, Mellapak, and Kerapak Vendor procedure♦

Koch Flexipac, Flexeramic, and Flexigrid Vendor procedure♦♦

†Goodloe, Bulletin 520A (Dallas: Glitsch, Inc., 1981).

††Glitsch Grid-Grid/Ring Combination Bed, Bulletin No. 7070 (Dallas: Glitsch, Inc., 1978).

†††Norton Company, private communication, 1992.

♦Spiegel, L. and Meier, W., "Correlations of the Performance Characteristics of the Various MellapakTypes." Paper presented at the 4th International Symposium of Distillation and Absorption, Brighton,England, 1987.

♦♦McNulty, K.J., "Hydraulic Model for Packed Tower Design." Paper presented at the American Instituteof Chemical Engineers Spring Meeting in Houston, 1993.

Liquid Holdup Calculations for PackingASPEN PLUS performs liquid holdup calculations for both random andstructured packings. The calculations use the Stichlmair6 correlation. TheStichlmair correlation requires these parameters:• Packing void fraction and surface area• Three Stichlmair correlation constants

ASPEN PLUS provides these parameters for a variety of packings in the built-inpacking databank. If these parameters are missing for a particular packing,ASPEN PLUS will not perform liquid holdup calculations for that packing.

You can also enter these parameters to provide missing values, or to override thedatabank values.


Appendix A

Pressure Profile UpdateYou can update the pressure profile using:• Computed pressure drops for the rating mode of both trays and packings• The sizing mode of packings

If you choose to update the pressure profile, the column models solve the tray orpacking calculation procedures simultaneously with the column-describingequations. For updating the pressure profile during calculations check UpdateSection Pressure Profile on the following forms:• TrayRating• PackSizing• PackRating

Also, you can fix the pressure at the top or bottom of the column and you canspecify this option on the above forms. The stage pressures become additionalvariables. ASPEN PLUS uses the pressure specifications given on thePres-Profile form to:• Initialize the column pressure profile• Fix the pressure drop of stages for which the pressure profile is not updated

Physical Property Data RequirementsSeveral physical properties that are not normally used for heat and materialbalance calculations are required for column sizing and rating. These propertiesare:• Liquid and vapor densities• Liquid surface tension• Liquid and vapor viscosities

The physical property method that you specify for a unit operation model must beable to provide the required properties. In addition, the physical propertyparameters needed to calculate the required properties must be available for allcomponents in the column. See the descriptions of properties in the ASPENPLUS User Guide Volume 1, for details on specifying physical property methodsand determining property parameter requirements.



References

1. Fair, J.R., et al., “Liquid-Gas Systems,” Perry’s Chemical Engineers'Handbook, R.H. Perry and D. Green, ed. 6th ed., New York: McGraw Hill,1984.

2. Ballast Tray Design Manual, Glitsch, Inc., Bulletin No. 4900, 3rd ed.,Dallas:1980.

3. Smith, B.D., “Tray Hydraulics: Bubble Cap Trays” and “Tray Hydraulics:Perforated Trays,” Design of Equilibrium Stage Processes, New York:McGraw Hill, 1963, pp. 474-569.

4. Koch Flexitray Design Manual, Koch Engineering Co., Inc. Bulletin No. 90,Wichita.

5. Nutter Float Valve Design Manual, Tulsa: Nutter Engineering Co., 1976.

6. Stichlmair, J., et al., "General Model for Prediction of Pressure Drop andCapacity of Countercurrent Gas/Liquid Packed Columns," Gas Separationand Purification, Vol. 3 (1989), p. 22.

❖ ❖ ❖ ❖

Unit Operation Models Index-1Version 10

Index

A

AbsorbersMultiFrac 4-30RadFrac 4-23RateFrac 4-62

Aerotranflash specifications 3-27flowsheet connectivity 3-26overview 3-26physical properties 3-28solids 3-28specifying 3-27

AGA methodPipe model 6-39Pipeline 6-51

Air separationMultiFrac 4-30

Air-cooled heat exchangersAerotran 3-26

Algorithmsconvergence 4-22, 4-25, 4-27, 4-28, 4-42, 4-58inside-out 4-26, 4-43Newton 4-22, 4-26, 4-42, 4-44nonideal 4-22, 4-26standard 4-26, 4-42, 4-43sum-rates 4-22, 4-26, 4-42, 4-43

Angel-Welchon-Ros correlationPipe model 6-38Pipeline 6-49

ASME methodCompr 6-10MCompr 6-15

Azeotropic distillationRadFrac 4-22

B

Baffle geometryHeatX 3-13

BaghousesFabFl 8-23resistance coefficients 8-25separation efficiency 8-26

Ballast traysvalues A-11

Batch reactorsRBatch 5-25

Beggs and Brill correlationPipe model 6-37Pipeline 6-48

Beggs and Brill correlation parametersPipe model 6-38Pipeline 6-50

B-JACAerotran interface 3-26Hetran interface 3-23

Bolles methodtray flooding calculations A-8

Bond work index (BWI)Crusher 8-14, 8-17

Brake horsepowerCompr 6-12MCompr 6-17

Bubble cap trayscap diameter A-9

C

Cavitation indexValve model 6-29

CCDcomponent attributes 8-66flowsheet connectivity 8-64medium temperature 8-67mixing efficiency 8-66overview 8-64profiles 8-66pseudostreams 8-65specifying 8-65

Centrifuge filtersCFuge 8-52

CFugefilter cake 8-53filtrate flow rate 8-54flowsheet connectivity 8-52overview 8-52

Index-2 Unit Operation ModelsVersion 10

CFuge (continued)pressure drop 8-54rating 8-53separation efficiency 8-55sizing 8-53specifying 8-53

Chilton-Colburn analogyRateFrac 4-77, 4-84

ClChngflowsheet connectivity 7-6overview 7-6specifying 7-6stream class change 7-6

Coalgrinding 8-18

Column configurationRateFrac 4-70

ColumnsDistl 4-6DSTWU 4-3Extract 4-87MultiFrac 4-30packings A-12PetroFrac 4-48physical property requirements A-17pressure drop calculations A-1RadFrac 4-11, 4-16RateFrac 4-62rating A-1SCFrac 4-8sizing A-1

Component ratioRateFrac 4-75

Component separatorsSep 2-12Sep2 2-14

ComprASME method 6-10flowsheet connectivity 6-9GPSA method 6-10isentropic efficiency 6-12mechanical efficiency 6-12Mollier method 6-10net work load 6-10overview 6-9performance curves 6-10polytropic efficiency 6-11specifying 6-10steam pressure 6-9

CompressorsCompr 6-9Heater model 3-2

Compressors (continued)MCompr 6-13

CondensersPetroFrac 4-51RateFrac 4-71

Connecting streamsRateFrac 4-70

Continuous stirred tank reactorRCSTR 5-16

Convergencealgorithms 4-42, 4-43RateFrac 4-76

Convergence algorithmsPetroFrac 4-58RadFrac 4-25

CoolersHeater model 3-2RadFrac 4-17RateFrac 4-73

Crude unitsSCFrac 4-8

CrusherBond work index (BWI) 8-14, 8-17breakage functions 8-14flowsheet connectivity 8-13Hardgrove grindability index (HGI) 8-14, 8-18overview 8-13power requirement 8-16primary crusher 8-16reduction ratios 8-16secondary crusher 8-16selection functions 8-14specifying 8-14

Cryogenic applicationsRadFrac 4-23

Crystallizercrystal growth rate 8-7crystal nucleation rate 8-8flowsheet connectivity 8-3magma recirculation 8-5overview 8-3particle size distribution (PSD) 8-9, 8-10population balance 8-8recirculation 8-5saturation calculation 8-6solubility 8-5specifying 8-4supersaturation 8-6

Cyclonedesign calculations 8-28diameter calculation 8-31dimension ratios 8-31


Cyclone (continued)dimensions 8-28, 8-32efficiency correlations 8-29flowsheet connectivity 8-27geometry 8-32Leith and Licht correlation 8-29operating ranges 8-29overview 8-27pressure drop 8-30rating calculations 8-28separation efficiency 8-29Shepherd and Lapple correlation 8-29solids loading correction 8-34specifying 8-28vane constant 8-32

D

Darcy correlationPres-Relief 10-12

Decanter modelflowsheet connectivity 2-8Gibbs free energy 2-10KLL coefficients 2-10liquid phases 2-10liquid-liquid distribution coefficients 2-10overview 2-8phase-splitting methods 2-10separation efficiencies 2-11solids entrainment 2-11specifying 2-9

DecantersCCD 8-64Decanter model 2-8Flash3 2-5RadFrac 4-18, 4-29

Design modeRateFrac 4-74

Design mode convergenceRadFrac 4-26

Design specification convergenceMultiFrac 4-44

DIERS calculationsPres-Relief 10-18

DistillationDistl 4-6DSTWU 4-3MultiFrac 4-30RateFrac 4-62SCFrac 4-8

DistlEdmister approach 4-6flowsheet connectivity 4-6overview 4-6specifying 4-7

DSTWUflowsheet connectivity 4-4Gilliland’s method 4-3overview 4-3reflux ratio 4-3specifying 4-4Underwood’s method 4-3Winn’s method 4-3

Dukler correlationPipe model 6-37Pipeline 6-48Pres-Relief 10-12

Duplflowsheet connectivity 7-4overview 7-4specifying 7-5

Dynamic scenario algorithmPres-Relief 10-19

E

Eaton correlationPipe model 6-38Pipeline 6-49

Edmister approachDistl 4-6

EfficienciesCompr 6-12MCompr 6-16, 6-17RadFrac 4-20

Electrostatic precipitatorsESP 8-40

Emergency relief vents (ERV)Pres-Relief 10-15

Equilibrium constantsREquil 5-9RGibbs 5-13

Equilibrium reactorsREquil 5-8RGibbs 5-10

ESPflowsheet connectivity 8-40gas velocity 8-41, 8-44operating range 8-41overview 8-40particle separation 8-42, 8-44


ESP (continued)power requirement 8-44pressure drop 8-43separation efficiency 8-42specifying 8-41

Ethylene plant primary fractionatorsMultiFrac 4-30PetroFrac 4-48

EvaporatorsFlash2 2-2Flash3 2-5

Exchanger configurationHeatX 3-11

Exchanger geometryHeatX 3-5

Extractflowsheet connectivity 4-87overview 4-87specifying 4-88

F

FabFlcalculation options 8-23filtering time 8-24flowsheet connectivity 8-23operating ranges 8-24overview 8-23resistance coefficients 8-25separation efficiency 8-26specifying 8-23

Fabric filtersFabFl 8-23

Fair methodtray flooding calculations A-8

Feed furnacesPetroFrac 4-54

Feed stream conventionsRateFrac 4-68

Feed streamsPetroFrac 4-53

Film coefficientsHeatX 3-10, 3-15

Filter modelfilter cake characteristics 8-57flowsheet connectivity 8-56overview 8-56pressure drop 8-58separation efficiency 8-58specifying 8-56

FiltersCFuge 8-52FabFl 8-23Filter model 8-56

Flanigan correlationPipe model 6-38Pipeline 6-50Pres-Relief 10-12

Flash tableszone analysis 3-21

Flash2electrolytes 2-4flowsheet connectivity 2-2overview 2-2solids 2-4specifying 2-3

Flash3electrolytes 2-6flowsheet connectivity 2-5overview 2-5solids 2-6specifying 2-6streams 2-5

FlashesFlash2 2-2Flash3 2-5

Flexitraysvalues A-11

Float valve traysvalues A-11

FractionatorsPetroFrac 4-48

Free-water calculationsMultiFrac 4-46PetroFrac 4-60RadFrac 4-20RateFrac 4-74

FSplitflowsheet connectivity 1-5overview 1-5specifying 1-6

G

Gas-solid separatorsCyclone 8-27ESP 8-40FabFl 8-23VScrub 8-36

General purpose valvesPres-Relief 10-13


Gibbs free energyDecanter model 2-10REquil 5-9RGibbs 5-10

Gilliland’s correlationDSTWU 4-3

Glitsch Ballast methodtray flooding calculations A-8

GPSA methodCompr 6-10MCompr 6-15

H

Hagedorn-Brown correlationPipe model 6-37Pipeline 6-49

Hardgrove grindability index (HGI)Crusher 8-14, 8-18

Hazen-Williams methodPipe model 6-40Pipeline 6-52

Heat exchangersAerotran 3-26computational structure 3-21equations 3-8Heater model 3-2HeatX 3-5Hetran 3-23MHeatX 3-19multistream 3-19zone analysis 3-21

Heat transfer coefficientHeatX 3-9

Heater modelelectrolytes 3-4flowsheet connectivity 3-3overview 3-2solids 3-4specifying 3-3

HeatersHeater model 3-2MultiFrac 4-38RadFrac 4-17RateFrac 4-73

Heat-interstaged columnsMultiFrac 4-30

HeatXbaffle geometry 3-13electrolytes 3-17exchanger configuration 3-11

HeatX (continued)exchanger geometry 3-5film coefficients 3-10, 3-15flash specifications 3-17flowsheet connectivity 3-6heat transfer coefficient 3-9log-mean temperature difference 3-8model correlations 3-15nozzle geometry 3-15option sets 3-17overview 3-5physical properties 3-17pressure drop 3-13, 3-14, 3-15pressure drop calculations 3-10, 3-15rating calculations 3-5, 3-6, 3-7, 3-8, 3-9shell-side film coefficient 3-13solids 3-17specifying 3-6streams 3-6TEMA shells 3-11tube geometry 3-14tube-side film coefficient 3-14zone analysis 3-5

HETPpackings calculations A-12RateFrac 4-75

Hetranflash specifications 3-24flowsheet connectivity 3-23overview 3-23physical properties 3-25solids 3-25specifying 3-24

Hughmark methodPipe model 6-37Pipeline 6-48

HyCycdimension ratios 8-49dimensions 8-50, 8-51feed splitting 8-48flowsheet connectivity 8-45geometry 8-50operating ranges 8-46overview 8-45particle velocity 8-49pressure drop correlation 8-50rating 8-46separation efficiency 8-47sizing 8-46solids separation 8-45specifying 8-46velocity correlation 8-49


Hydraulic turbinesPump model 6-2

HydrocyclonesHyCyc 8-45

I

Inside-out algorithmsMultiFrac 4-43RadFrac 4-26

Isentropic compressorsCompr 6-9, 6-12MCompr 6-13

Isentropic turbinesCompr 6-9MCompr 6-13

K

Kettle reboilersRadFrac 4-16

Knock-out drumsDecanter model 2-8Flash2 2-2Flash3 2-5

L

Leith and Licht correlationCyclone 8-29

Liquid-liquid extractionExtract 4-87

Liquid-solid separatorsCFuge 8-52Filter model 8-56HyCyc 8-45

LNG exchangerMHeatX 3-19

Lockhart-Martinelli correlationPipe model 6-37Pipeline 6-49Pres-Relief 10-12

Log-mean temperatureHeatX 3-8

M

ManipulatorsClChng 7-6Dupl 7-4

Manipulators (continued)Mult 7-2

MComprASME method 6-15brake horsepower 6-17flow coefficient 6-19flowsheet connectivity 6-14GPSA method 6-15head coefficient 6-18isentropic efficiency 6-16mechanical efficiency 6-17Mollier method 6-15overview 6-13parasitic pressure loss 6-17polytropic efficiency 6-16specific diameter 6-18specific speed 6-18specifying 6-14, 6-15

MHeatXcomputational structure 3-21electrolytes 3-22flash tables 3-21flowsheet connectivity 3-19LNG exchanger 3-19overview 3-19solids 3-22specifying 3-20zone analysis 3-19, 3-20, 3-21

Mixer modelflowsheet connectivity 1-2overview 1-2specifying 1-3

MixersHeater model 3-2Mixer model 1-2

Model correlationsHeatX 3-15

Mollier methodCompr 6-10MCompr 6-15

Multflowsheet connectivity 7-2overview 7-2specifying 7-3

MultiFracalgorithms 4-43connecting streams 4-36convergence algorithms 4-42, 4-43design mode 4-42design specification convergence 4-44efficiencies 4-41ethylene plant primary fractionator 4-30


MultiFrac (continued)feed stream conventions 4-35flow rate 4-38, 4-42flow ratio 4-40flowsheet connectivity 4-32free-water calculations 4-46heaters 4-38initialization methods 4-45Murphree efficiency 4-41Newton algorithm 4-44overview 4-30packings 4-47physical properties 4-46property methods 4-46rating mode 4-42solids 4-46specifying 4-33, 4-34stream definitions 4-34streams 4-32, 4-33, 4-35, 4-36, 4-42sum-rates algorithm 4-43trays 4-47vaporization efficiency 4-41

Multistage fractionation unitsMultiFrac 4-30

Murphree efficiencyMultiFrac 4-41PetroFrac 4-57RadFrac 4-21RateFrac 4-65, 4-75

N

Napthali-Sandholm algorithmRadFrac 4-26

Nested convergenceRadFrac 4-27

Newton algorithmMultiFrac 4-44RadFrac 4-22, 4-26RateFrac 4-76

Nonequilibrium fractionationRateFrac 4-62

Nozzle geometryHeatX 3-15

O

Oliphant methodPipe model 6-39Pipeline 6-51

Orkiszewski correlationPipe model 6-37Pipeline 6-49

P

Packingscalculations A-12capacity calculations A-13liquid holdup calculations A-16MultiFrac 4-47PetroFrac 4-61pressure drop calculations A-15pressure profile A-17RateFrac 4-70rating A-12sizing A-12specifying A-1Stichlmair correlation A-16types A-1, A-12, A-13

Panhandle methodsPipe model 6-40Pipeline 6-51

Particle separationESP 8-42, 8-44

PetroFraccondensers 4-51convergence algorithms 4-58design mode 4-59efficiencies 4-57ethylene plant primary fractionator 4-48feed furnace 4-51, 4-54feed streams 4-53flowsheet connectivity 4-49free-water calculations 4-60liquid runback 4-56main column 4-50, 4-51Murphree efficiency 4-57overview 4-48packings 4-61physical properties 4-60property methods 4-60pumparounds 4-56rating mode 4-59reboilers 4-51side strippers 4-51, 4-57solids 4-61specifying 4-51streams 4-49trays 4-61vaporization efficiency 4-57


Petroleum refining fractionationMultiFrac 4-30PetroFrac 4-48

Petroleum/petrochemical applicationsRadFrac 4-22

Physical propertiescolumns A-17HeatX 3-17

Physical property methodsRateFrac 4-74

Pinch pointsestimating 3-21

Pipe modelAGA method 6-39Angel-Welchon-Ros correlation 6-38Beggs and Brill correlation 6-37Beggs and Brill correlation parameters 6-38closed-form methods 6-39Design-Spec convergence loop 6-34downstream and upstream integration 6-33Dukler correlation 6-37Eaton correlation 6-38erosional velocity 6-34fittings modeling 6-35Flanigan correlation 6-38flash options 6-32flowsheet connectivity 6-30fraction factor correlations 6-35Hagedorn-Brown correlation 6-37Hazen-Williams method 6-40holdup correlations 6-35Hughmark method 6-37integration direction 6-33liquid holdup correlations 6-35Lockhart-Martinelli correlation 6-37methane gas systems 6-34Oliphant method 6-39Orkiszewski correlation 6-37overview 6-30Panhandle methods 6-40physical property calculations 6-32pressure drop calculations 6-33pressure specification 6-31Slack correlation 6-38Smith method 6-39specifying 6-31stream specification 6-32two-phase correlations 6-35valve modeling 6-35Weymouth method 6-39

PipelineAGA method 6-51Angel-Welchon-Ros correlation 6-49Beggs and Brill correlation 6-48Beggs and Brill correlation parameters 6-50closed-form methods 6-50Design-Spec convergence loop 6-46downstream and upstream integration 6-45Dukler correlation 6-48Eaton correlation 6-49erosional velocity 6-46Flanigan correlation 6-50flowsheet connectivity 6-42fraction factor correlations 6-47Hagedorn-Brown correlation 6-49Hazen-Williams method 6-52holdup correlations 6-47Hughmark method 6-48integration direction 6-45liquid holdup correlations 6-47Lockhart-Martinelli correlation 6-49methane gas systems 6-47nodes and segments 6-44Oliphant method 6-51Orkiszewski correlation 6-49overview 6-42Panhandle methods 6-51physical property calculations 6-45pressure drop calculations 6-45Slack correlation 6-49Smith method 6-51specifying 6-43stream specification 6-44two-phase correlations 6-47Weymouth method 6-51

PipesPipe model 6-30Pipeline 6-42

Piping systemPres-Relief 10-11

Plug flow reactorsRPlug 5-21

Polytropic compressorsCompr 6-9, 6-11MCompr 6-13

Pres-Relief3% rule 10-897% rule 10-8Beggs and Brill correlation 10-12calculation methods 10-23


Pres-Relief (continued)capacity runs 10-6code compliance 10-6convergence methods 10-23credit factors 10-4Darcy correlation 10-12data tables 10-12–10-16DIERS calculations 10-18disengagement options 10-18Dukler correlation 10-12dynamic scenarios 10-2, 10-7, 10-16, 10-18, 10-19energy input calculations 10-4fire scenario 10-3flow equations 10-20heat exchanger shell 10-17heat flux scenario 10-5insulation credit factor 10-24Lockhart-Martinelli correlation 10-12manufacturers' tables 10-12–10-16nozzle flow equation 10-22overview 10-2pipe diameters 10-12pipe flow equation 10-20pipe specifications 10-11reactions 10-9relief system 10-10relief system flow rating scenario 10-5relief valve flow rating scenario 10-6rupture disks 10-15safety relief valves 10-14sample solution 10-19scenarios 10-3sizing rules 10-7, 10-9Slack correlation 10-12specifying 10-2, 10-10, 10-11spheres 10-17steady-state scenarios 10-6stop criteria 10-18streams 10-7user-specified vessel 10-17valve cycling 10-16valve types 10-10, 10-13vents 10-15vessel geometry 10-16vessel head types 10-17vessel jacket 10-17wetted area calculations 10-4X% rule 10-8

Pressure changersCompr 6-9MCompr 6-13Pipe model 6-30

Pressure changers (continued)Pipeline 6-42Pump model 6-2Valve model 6-20

Pressure dropHeatX 3-13, 3-14, 3-15

Pressure drop calculationsHeatX 3-10, 3-15

Pressure drop modelsPipe model 6-30Pipeline 6-42

Pressure relief systemsPres-Relief 10-2

Pump modelflow coefficient 6-7flowsheet connectivity 6-2head coefficient 6-7net positive suction head (NPSH) 6-4overview 6-2specific speed 6-5specifying 6-3suction specific speed 6-6

PumparoundsRadFrac 4-18

PumpsHeater model 3-2Pump model 6-2

R

RadFrac 4-23absorbers 4-23algorithms 4-22azeotropic distillation 4-22column configuration 4-13, 4-16convergence algorithms 4-22, 4-25convergence methods 4-26, 4-27, 4-28coolers 4-17decanters 4-18, 4-29design mode 4-24design mode convergence 4-26design specifications 4-27efficiencies 4-20feed streams 4-14flowsheet connectivity 4-12free-water calculations 4-20heaters 4-17inside-out algorithms 4-26kettle reboilers 4-16Murphree efficiency 4-21Napthali-Sandholm algorithm 4-26


RadFrac (continued)Newton algorithm 4-22, 4-26nonideal systems 4-22overview 4-11petroleum/petrochemical applications 4-22physical properties 4-28property methods 4-28pumparounds 4-18rating mode 4-23reactive distillation 4-25reboilers 4-16salt precipitation 4-25simultaneous convergence 4-28solids handling 4-28specifying 4-12stage numbering 4-14streams 4-12strippers 4-23thermosyphon reboilers 4-16three-phase calculations 4-20, 4-23two-phase calculations 4-23UA calculations 4-17vaporizaton efficiency 4-20

Rate-based modelingRateFrac 4-62, 4-65

RateFracbubble-cap tray column 4-81Chilton-Colburn analogy 4-77, 4-84column configuration 4-70column numbering 4-67component ratio 4-75connecting streams 4-70convergence 4-76coolers 4-73correlations 4-76, 4-77design mode 4-74efficiencies 4-65, 4-75equilibrium stages 4-72feed stream conventions 4-68flowsheet connectivity 4-63Fortran subroutines 4-77free-water calculations 4-74heat transfer coefficients 4-84heaters 4-73HETP 4-65, 4-75interfacial areas 4-76, 4-77, 4-79, 4-81, 4-82mass transfer coefficients 4-76, 4-77, 4-79, 4-81, 4-82Murphree efficiency 4-65Newton algorithm 4-76overview 4-62packing specifications 4-70

RateFrac (continued)physical property method 4-74rate-based modeling 4-65rating mode 4-74reactions 4-72reactive distillation 4-72segments 4-71, 4-75side duties 4-73sieve tray column correlations 4-82solution times 4-76specifying 4-64, 4-66, 4-70stream definitions 4-68streams 4-63tray column 4-79tray column correlations 4-81, 4-82tray specifications 4-70utility exchangers 4-73valve tray column 4-79

Rating modeRateFrac 4-74

RBatchbatch operation 5-29cycle time 5-28flowsheet connectivity 5-25mass balances 5-28overview 5-25reactions 5-28specifying 5-26stop criteria 5-28temperature controller 5-27

RCSTRflowsheet connectivity 5-16overview 5-16phase volume 5-17reaction kinetics 5-17residence time 5-18scaling methods 5-19solids reactions 5-18specifying 5-17variable scaling 5-19

ReactionsRateFrac 4-72

Reactive distillationRadFrac 4-25

ReactorsRBatch 5-25RCSTR 5-16REquil 5-8RGibbs 5-10RPlug 5-21RStoic 5-2RYield 5-6


ReboilersPetroFrac 4-51RadFrac 4-16

Relief devicesPres-Relief 10-10

REquilequilibrium constants 5-9flowsheet connectivity 5-8Gibbs free energy 5-9net heat duty 5-8overview 5-8solids 5-9specifying 5-9streams 5-8

RGibbschemical equilibrium 5-12flowsheet connectivity 5-11overview 5-10phase equilibrium 5-12, 5-13reactions 5-14restricted chemical equilibrium 5-13solids 5-14specifying 5-11

Rigorous distillationMultiFrac 4-30PetroFrac 4-48RadFrac 4-11RateFrac 4-62

Rigorous extractionExtract 4-87

RPlugcoolant 5-23flowsheet connectivity 5-22overview 5-21reactions 5-24solids 5-24specifying 5-22

RStoicflowsheet connectivity 5-3heat of reaction 5-3, 5-4overview 5-2product selectivity 5-3, 5-4specifying 5-3stream specifications 5-3

RYieldcalculation types 5-7flowsheet connectivity 5-6heat duty specification 5-7overview 5-6specifying 5-7yield distribution 5-7

S

Salt precipitationRadFrac 4-25

SCFraccrude units 4-8flowsheet connectivity 4-8overview 4-8specifying 4-9vacuum towers 4-8

Screenflowsheet connectivity 8-19operating levels 8-20overview 8-19screen size correlation 8-21selection function 8-20separation efficiency 8-21separation strength 8-20specifying 8-19

Sepflowsheet connectivity 2-12inlet pressure 2-13outlet stream conditions 2-13overview 2-12specifying 2-13

Sep2flowsheet connectivity 2-14inlet pressure 2-16outlet stream conditions 2-16overview 2-14specifying 2-15substreams 2-15

SeparatorsDecanter model 2-8Flash2 2-2Flash3 2-5Sep 2-12Sep2 2-14

Shell heat exchangersHetran 3-23

Shell-side film coefficientHeatX 3-13

Shepherd and Lapple correlationCyclone 8-29

Shortcut distillationDistl 4-6DSTWU 4-3SCFrac 4-8

Simultaneous convergenceRadFrac 4-28

Sizing recommendationsPres-Relief 10-9


Slack correlationPipe model 6-38Pipeline 6-49Pres-Relief 10-12

Smith methodPipe model 6-39Pipeline 6-51

SolidsCrystallizer 8-3Flash2 2-4Flash3 2-6Heater model 3-4MHeatX 3-22RGibbs 5-14

Solids crushersCrusher 8-13

Solids separatorsCFuge 8-52Crusher 8-13Cyclone 8-27ESP 8-40FabFl 8-23Filter model 8-56HyCyc 8-45Screen 8-19VScrub 8-36

Solids washersCCD 8-64SWash 8-61

SplittersFSplit 1-5Sep 2-12Sep2 2-14SSplit 1-8

SSplitflowsheet connectivity 1-8overview 1-8specifying 1-8

Stichlmair correlationpackings calculations A-16

Stoichiometric reactorsRStoic 5-2

Stream classeschanging 7-6

Stream definitionsRateFrac 4-68

Stream manipulatorsClChng 7-6Dupl 7-4Mult 7-2

Stream mixersMixer model 1-2

Stream multiplicationMult 7-2

Stream pressure changersPump model 6-2

Stream splittersFSplit 1-5SSplit 1-8

Streamscombining 1-8Flash3 2-5splitting 2-12, 2-14

StrippersMultiFrac 4-30RadFrac 4-23RateFrac 4-62

Substream splittersSSplit 1-8

Sum-rates algorithmMultiFrac 4-43

SWashbypass fraction 8-63flowsheet connectivity 8-61mixing efficiency 8-62overview 8-61specifying 8-62

T

TEMA shellsHeatX 3-11

Thermosyphon reboilersRadFrac 4-16

Three-phase calculationsRadFrac 4-20

TraysBolles method A-8bubble cap A-9downcomer specifications A-3Flexitrays A-11float valve A-11flooding calculations A-8foaming calculations A-11MultiFrac 4-47PetroFrac 4-61pressure drop calculations A-10pressure profile A-17RateFrac 4-70rating A-2, A-8sizing A-2, A-8specifying A-1types A-1


Tube geometryHeatX 3-14

Tube heat exchangersHetran 3-23

Tube-side film coefficientHeatX 3-14

TurbinesCompr 6-9MCompr 6-13Pump model 6-2

U

Underwood’s methodDSTWU 4-3

Unit operation modelsuser-supplied 9-2, 9-4

User modelflowsheet connectivity 9-2Fortran subroutines 9-3overview 9-2specifying 9-3

User2flowsheet connectivity 9-4Fortran subroutines 9-5overview 9-4specifying 9-5

V

Vacuum filtersFilter model 8-56

Vacuum towersSCFrac 4-8

Valve modelcalculation types 6-20cavitation index 6-29characteristic equation 6-26choked flow 6-28flow coefficient 6-24flowsheet connectivity 6-20overview 6-20piping geometry factor 6-26pressure drop calculation 6-20, 6-28pressure drop ratio factor 6-22pressure recovery factor 6-23specifying 6-20

Valvescycling 10-16Heater model 3-2Pipe model 6-35

Valves (continued)safety relief 10-14types used in Pres-Relief 10-10, 10-13–10-16Valve model 6-20

Vaporization efficiencyMultiFrac 4-41PetroFrac 4-57RadFrac 4-20

VentsPres-Relief 10-15

Venturi scrubbersVScrub 8-36

VScrubflowsheet connectivity 8-36overview 8-36pressure drop 8-38rating 8-37separation efficiency 8-39sizing 8-37specifying 8-37

W

Weymouth methodPipe model 6-39Pipeline 6-51

Winn's methodDSTWU 4-3

Y

Yield reactorsRYield 5-6

Z

Zone analysisHeatX 3-5MHeatX 3-19, 3-20, 3-21

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