Section 04 - Fractionation
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FractionationFractionation
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Task Checklist
X Introduction
TOWER SIMULATION
Z Basic Concepts
Z Specifications
DEVICE SELECTION
Z Contacting Devices
Z Tray Hardware Definitions
Z Tray Hydraulics
Z Packing Hydraulics
Z Other Process Considerations
Z Other Tower Internals
Z Tower Revamps
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Did You Know?
Oldest and most important petrochemical manufacturing process
Equipment accounts for 30% of all investments today
Consumes 70% of all energy at plant
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More on Fractionation
Separate feed into products
according to boiling point
Products sent to finished
product tank or further
processed by other units
Multiple products and feeds
common
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Objective Questions
How can you improve separation efficiency?
How do you decide on the optimum number of trays for a new
tower?
What sets a towers operating pressure?
What are my options to increase a towers vapor / liquid handlingcapacity?
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Designers Role
Perform HMB calculations to develop tower loadings
New Towers Select optimum tower size, contacting device, and internals to meet
process requirements
Existing Towers
Select optimum contacting device and internals to improve
performance or expand capacity
Screening - Apply Concepts to Troubleshoot Problems
Prepare Design Package (Consult with Specialist)
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Engineers Toolbox
XOM DP Section III
(Intranet)
Simulation Tool (PRO/II or
HYSIS)
Pegasys ExxonMobil TowerInternals Program - EMoTIP
Fractionation Specialists
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Task Checklist
X Introduction
TOWER SIMULATION
XBasic ConceptsZ Specifications
DEVICE SELECTION
Z Contacting Devices
Z Tray Hardware Definitions
Z Tray Hydraulics
Z Packing Hydraulics
Z Other Process Considerations
Z Other Tower Internals
Z Tower Revamps
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Conventional Tower
Reflux Ratio = R / D
R
D
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Rules of Thumb
More Reflux
More Trays More Separation
Lower Pressure
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BINARY DISTILLATION: MCCABE - THIELE DIAGRAM
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MINIMUM REFLUX
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TOTAL REFLUX - MINIMUM STAGES
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Stages Versus Reflux
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Optimum Reflux Ratio
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ESTIMATING ACTUAL REFLUX RATIO AND ACTUAL NUMBER OF STAGES
General Rule of Thumb--
RACTUAL = (1.1 TO 1.35) x R MIN
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Task Checklist
X Introduction
TOWER SIMULATION
X Basic ConceptsXSpecifications
DEVICE SELECTION
Z Contacting Devices
Z Tray Hardware Definitions
Z Tray Hydraulics
Z Packing Hydraulics
Z Other Process Considerations
Z Other Tower Internals
Z Tower Revamps
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Factors to consider:
Temperature of available condensing fluid (air, water, etc.)
Wheres the overhead product go?
Is the overhead totally condensed?
Possible Limitations:+ Bottoms temperature (cracking / color)
+ Reboiler
+ Critical Point (poor separation)
How much pressure drop is acceptable?
Operating Pressure
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Operating Temperature
Fixed once product specifications and
pressure are set
Dew Point Calculation
Overhead temp.
Bubble Point Calculations
Bottoms temp.
Flash Calculations
Reflux temp.
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Feed Condition
If not specified, start with bubble
point feed - Then optimize.
Adjust temp. to balance tower
loading
Other Considerations:
Reflux vs. Reboiler Duty / Costs
Quenching
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HIGH FEED TEMPERATURE
L
RECYCLE GAS
COMPRESSORPRODUCT
FUEL GAS CONTROL:
FEED RATE
PRODUCT VAPOR PRESSURE
PRODUCT SULFUR
OVERHEAD DRUM LEVEL
FEED
OVERRIDE
F
A VAPOR PRESSURE
SULFUR
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Simulation Inputs
Feed Rate and Composition
VLE Data Method
Specifications & Control
Variables
Operating Pressure
Initial Guess (If Required)
For Rating: Plant Test Data
Pressure, Temperature Profile
Lab Data (Complete Set of Samples)
Tray Efficiencies
See DP III-I Table 2; Estimates
from Past Designs
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Tower Specif ications
Specifications: usually on product quality or temperatures Can be mathematical
Avoid specifying rate. Better to specify % recovery or fraction.
Condenser temperature
Variables: usually condenser / reboiler duty
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ProII Condensers
Stage 1, if present
Different Types
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ProII Reboilers
Last Stage(s)
Kettle or Thermosiphon
Kettle
Thermosiphon specify if have baffle or not
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KETTLE REBOILER
Advantages:
+ Additional fractionation stage
Disadvantages:
- Low NPSH to downstream pump- Very low hold-up
- Tubes can dry out
- High temperature increase
- Large plot space
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VERTICAL THERMOSIPHON REBOILER
-Advantages:
+ Partial fractionation stage
+ Low plot space
+ Low temperature increase
Disadvantages:
- Partial fractionation stage- High circulation rate
- Pressure drop critical
- Limited duty
- Difficult to clean
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HORIZONTAL THERMOSIPHON REBOILER
-Advantages:+ Partial fractionation stage
+ Large duty
+ Low temperature increase
+ LowerP than vertical
Disadvantages:- Partial fractionation stage
- High circulation rate
- Pressure drop critical
- Large plot space
- Large piping
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Column Stage Summary
Number of Stages Condenser (1)
Theoretical Trays (#)
Can also use Actual Trays * Tray
Efficiency Efficiency will be different above and
below feed
Reboiler (1 or 2)
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Simulation Strategy
Optimize Reflux Ratio, Stages, Feed Condition, and Feed
Location
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Simulation Pitfalls
Save / Backup cases often.
Viscosity (high temperature), otherproperties may need to be verified.
Others?
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SIMULATION RESULTS
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Task Checklist
X Introduction
TOWER SIMULATION
X Basic Concepts
X Specifications
DEVICE SELECTION
XContacting DevicesZ Tray Hardware Definitions
Z Tray Hydraulics
Z Packing Hydraulics
Z Other Process ConsiderationsZ Other Tower Internals
Z Tower Revamps
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Device Categories
Conventional Trays
High Capacity Trays(Proprietary)
Random Packing
Structured Packing
Baffles, Sheds, and Grid
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Valve Up to 5:1 Turndown
5-10% higher capacity over sieve
Marginally higher cost
Not recommended for fouling
services
Jet hExxon Design for High Liquid
Loads
Efficiency ~20% less than sieve
Mainly used in pumparounds
Conventional Trays
Sieve Most Widely Used
2:1 Turndown
Low Cost (Nonproprietary)
Bubble Cap Standard until 1950s
High Cost
Maintenance / Inspection Difficult
Excellent Turndown
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Pumparound Definition
Method to provide towerreflux by cooling tower liquid
Draw-off intermediate liquid
Cool liquid by pumping itthrough heat exchanger
Return liquid to tower
Use trays/packing to return
Can provide high value heat
Reduces OH condenser
duty Reduces furnace duty
Reduces liquid traffic intower
Can reduce tower diameter
Increases tower heightsince pumparound traysare for heat transfer, notfractionation
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High Performance Fixed Valves (Increase vapor handling capacity)
Koch-Glitsch PROVALVE
Directional effect reduces fouling and vapor jetting/entrainment
10-15% jet flood capacity advantage to 1/2 (13mm) sieve trays
Sulzer MVG
High Capacity Trays
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High Capacity Trays (Cont.)
Enhanced Downcomer(Increase vapor handling capacity) Koch-Glitsch
Nye
MaxFrac
SuperFrac
Triton
Sulzer MVG-T
(not shown)
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High Capacity Trays (Cont.)
Multiple Downcomers UOP
MD and ECMD
~20% higher capacity, but lower efficiency
than conventional sieve tray
Limited access; not recommended for
fouling (Very difficult to clean / inspect)
Sulzer Shell HiFi
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MD and ECMD Tray Unit Cells
W t M Hi h C it T I f ti ?
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Want More High Capacity Tray Information?
Read recently released:EE48E2008, Application Guidelines For Debottlenecking Light EndsTowers With Enhanced Capacity Fractionation Trays
R d P ki
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Random Packing
1ST Generation Berl Saddle
Intalox Saddle
Rashig Ring
2ND Generation Pall Ring
Flexirings
Ballast Rings
Slotted Rings
3RD
Generation CMR IMTP
Nutter Ring
Rashig Super-Ring
R d P ki (C t )
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Random Packing (Cont.)
Packing can usually provide higher capacity and better efficiency than
trays.
As size increases, the capacity increases while the pressure drop, cost,and efficiency decrease.
Usually not first choice for new designs
Consider for:
Small tower diameter (
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Packing Warning
Fire Hazard: Some sites prevent hot work above a packed bed
DP III-G (Packing and Grid)
Structured Packing
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Structured Packing
Conventional Koch-Glitsch: Flexipac, Intalox Sulzer: Mellapak
Montz: Montz-Pak Type B1
High Capacity Koch-Glitsch: Flexipac HC, Intalox Sulzer: Mellapak Plus
Montz: Montz-Pak Type M
Structured Packing (Cont )
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Structured Packing (Cont.)
Why Structured Packing?
Lowest pressure drop per stage
Best capacity / efficiency combination device Less sensitive to liquid maldistribution than random packing
Recently, cost is much more competitive with random packing
Why Not Structured Packing?
Not recommended for high pressure towers - above 100 psia (7
kg/cm2) due to poor test results, or where liquid rate exceeds 20
gpm/ft2
(13.6 dm3
/s*m2
) unless application is high pressureaqueous system.
Grid
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Grid
Used for entrainment removal where fouling is too severe for acrinkle wire mesh screen (CWMS)
High Open Area
Prevents plugging
Low Surface Area
Low efficiency
Baffles
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Baffles
Large Open Area
Prevents plugging
Low Liquid Residence Time
Prevents coking
Practice Tower Internal Type
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Practice Tower Internal Type
What type of tower internal would you use for the following? Desuperheating reactor effluent in bottom of a fractionator?
Vacuum fractionator
High pressure light ends tower
24 (610mm) diameter absorber
Recycle gas absorber (remove H2S from H2)
Tail gas absorber (remove H2S from Sulfur Plant effluent)
Pumparound section of large fractionator
Device Selection Criteria
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Device Selection Criteria
Fouling Tendency
Good Liquid & Vapor Handling Capacity
Good Contacting efficiency
Acceptable Pressure Drop
Predictable Turndown Characteristics
Economical
See DP III-A Tables 3-5
Device Selection Procedure
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Device Selection Procedure
New Design
Start with trays, unless pressuredrop is critical. If need low dP,consider 2 (50mm) random packing.
Calculate optimum tray spacing,diameter, and layout (i.e. bubble areaand downcomer dimensions) by trial anderror to avoid downcomer and jet
flood limitations.(Use Pegasys / EMoTIP)
Then select best device type basedon Device Selection Criteria.
(See DP III-A Tables 3&5 Decision Trees)
Dont consider High Capacity Traysfor new towers - Instead IncreaseDiameter, etc.
Revamp
Rate existing contacting device to identify
potential limitations (i.e. downcomer, jet
flood, etc.)
(See Table 1 Design Principles in appropriate
DP III Section)
Identify new layout and device where all
design parameters are satisfied
(Use Pegasys / EMoTIP)
Consider:
Multi-pass Conventional Trays
High Performance Fixed Valves
Enhanced Downcomer Trays
Multiple Downcomer Trays
Packing
Trays vs. Packing
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Trays vs. Packing
XOM DP III-A Table 3D -- Fouling Tendencies
Task Checklist
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as C ec st
X Introduction
TOWER SIMULATION
X Basic Concepts
X Specifications
DEVICE SELECTION
X Contacting Devices
XTray Hardware Definitions
Z Tray Hydraulics
Z Packing Hydraulics
ZOther Process Considerations
Z Other Tower Internals
Z Tower Revamps
Common Pass Arrangements
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g
Downcomer Types
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yp
Stepped / Sloped: Provide sufficient DC inlet area for adequate vapor / froth
disengagement while maximizing bubble area
Downcomer Expansion
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Can expand downcomer without welding Commonly called Z-bar or downcomer adapter
Exiting Downcomer
Bolting Bar
Exiting Tray Support
Ring
Koch-Glitsch supplied
Downcomer Adapter
Weir Types
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Picketing: Can reduce spray
regime operation by increasing
effective liquid height; Also
used to balance multipass
designs by making their
effective weir lengths the
same.
Downcomer Seal Techniques
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Design should ensure vapor cannot bypass a tray by flowing upward
through the DC resulting in poor efficiency.
Process SealMechanical Seals
Area Definitions
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Also see DP III-A, Figures 12-13
Task Checklist
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X Introduction
TOWER SIMULATION
X Basic Concepts
X Specifications
DEVICE SELECTION
X Contacting Devices
X Tray Hardware Definitions
XTray Hydraulics
Z Packing Hydraulics
Z Other Process Considerations
Z Other Tower Internals
Z Tower Revamps
Hydraulic Limitations
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VAPOR
Jet Flooding
Ultimate Capacity
Flow Regimes
Entrainment
LIQUID
Downcomer Backup
Secondary Limitations:
Liquid Rate per Inch of Weir
Downcomer Choking
Velocity Under the Downcomer Downcomer Seal
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FRI VIDEO
Jet Flooding
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At high vapor rates, liquid is
jetted to tray above
Vapor handling limitation; sets
design in most cases
Expressed as Percent;
Rigorously Calculated(See DP III-B / Use Pegasys)
Related to vapor velocity
through the free area
Strong function of:
Tower Diameter
Tray Spacing
Jet Flooding and Efficiency
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XOM Jet Flood Limit
85
Late Breaking News: XOM Jet Flood
Limit now 80% for new designs
Problem Jet Flood
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What steps can we take to reduce jet flood, and what are the
drawback for each?
Ultimate Capacity
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Highest vapor rate tower can handle -- Stokes Law
Cannot be increased by hardware changes; only way to increase
it is by increasing the tower diameter
Flow Regimes
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To Eliminate Spray Regime:
Use Picket Fence Weirs
Increase Open Area
Use Smaller Sized Orifices
Use Valve Trays
Entrainment
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Liquid [drops] carried by the
vapor to the tray above
Design should limit entrainment
to 10% of the tray liquid rate
Function of:
Vapor Rate
Liquid Rate
Tray Spacing
Other Hardware Parameters
Downcomer Backup
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DC froth height expressed as
percent of tray spacing plus the
weir height
DC Filling Components:
hi = inlet head; f(inlet & outlet weir)
ht = total tray dP
hud = head loss under DC;
f(DC Clearance)
hdc = head loss due to two-phase
flow in DC
Percent Downcomer Flood
P f it i t h l t i t fl di lt f
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Performance criteria to see how close a tower is to flooding as a result of
excessive froth height in the downcomer
Represents actual vapor / liquid rates as a percent of the rates which cause 100%
DC Backup
Rigorously Calculated
(See DP III / Use Pegasys)
Flooding Symptoms
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Jet Flooding
Tower unstable
Liquid entrainment intooverhead system; sharp
increase in reflux rate with no
separation improvement
Pressure drop increases sharplywith a small incremental
increase in vapor rate
Separation efficiency gradually
decreases
Downcomer Flooding
Tower unstable, surging
High pressure drop with a smallincrease in either vapor or liquid
rate
Separation efficiency suddenly
decreases
Loss of tower bottoms liquid
level
Problem Downcomer Backup
Wh t t h 2 ff t d filli ?
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What parameter has a 2x affect on downcomer filling?
Name steps we can take to lower downcomer filling, and what
drawbacks for each.
Secondary Liquid Hydraulic Limitations
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Liquid Rate per Inch of Weir The accuracy of the Jet flood and DC Flood correlations can only be
ensured within the range of liquid rates used to develop them.
Downcomer Choking results when the DC inlet area is too small.
Velocity Under the Downcomer
If too high, can produce channeling effect leading to vapor / liquid
maldistribution on the tray.
Downcomer Seal
If not sealed, vapor can bypass the tray and flow upward through the
downcomer resulting in reduced efficiency.
Two types: Mechanical [Static]
Process [Dynamic]
Tray Hydraulics
DP III-B P.20-22
SIEVE TRAY DESIGN PARAMETERS
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DP III-B P.20-22
SIEVE TRAY DESIGN PARAMETERS
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Task Checklist
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X Introduction
TOWER SIMULATION
X Basic Concepts
X Specifications
DEVICE SELECTION
X Contacting Devices
X Tray Hardware Definitions
X Tray Hydraulics
XPacking Hydraulics
Z Other Process Considerations
Z Other Tower Internals
Z Tower Revamps
Packing Hydraulics
Packing Hydraulics
Flooding -- (Use Pegasys)
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Flooding (Use Pegasys)
Harder to define than tray hydraulics (i.e. no tray spacing or downcomerto fill with liquid)
As vapor rate increases, liquid accumulates and the pressure drop
begins to rise more sharply.
With further increases in vapor rate, the pressure drop rises almostvertically and liquid stacks up on top of the packing.
Ultimate Capacity -- (Use Pegasys)
Similar to tray hydraulics
Packing Hydraulics
Task Checklist
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X Introduction
TOWER SIMULATION
X Basic Concepts
X Specifications
DEVICE SELECTION
X Contacting Devices
X Tray Hardware Definitions
X Tray Hydraulics
X Packing Hydraulics
XOther Process Considerations
Z Other Tower Internals
Z Tower Revamps
Packing Hydraulics
Tray Efficiency
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Overall Efficiency, EO, is a measure of the effectiveness of an entire
tower or tower section.
Allows designer to determine the number of actual trays to provide and
sets the tower height.
Actual Trays = Theoretical Stages / EO
Calculated Rigorously - Use Pegasys
(See DP III-I)
Factors affecting EO:
Weir Height
Flow Path Length and Number of Passes (i.e. Residence Time) Weeping or Vapor Recycle
VLE Properties and Tower Loading
Other Process Considerations
Calculation of Tray And Packing Efficiency
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# of theoretical trays = # of actual trays x tray efficiency
Screening Estimates - See DPM III-I
Table 2 for historical efficiencies
Figure 8 for heavy hydrocarbons
Rigorous Methods - DPM III-G (Packing) & DPM III-I (Trays)
Plot y* vs x for light key and heavy key
y* = vapor mole fraction in equilibrium with liquid
x = liquid mole fraction
Input slope into PEGASYS tray program
Estimating Tray Efficiency
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Estimating Tray Efficiency, Heavy Hydrocarbons
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Packing Height
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To specify correct packing height, designer must calculate height
equivalent to a theoretical plate (HETP)
Packing Height = Theoretical Stages x HETP
HETP must be calculated rigorously - Use Pegasys
(See DP III-G)
Other methods for packing efficiency exist, but HETP applies to most
systems
Factors affecting HETP:
Distributor Design
Packing Size / Geometry
VLE Properties and Tower Loading
Other Process Considerations
Turndown
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Defines range of loadings for acceptable device performance
Excessive Weeping Decreases Efficiency
Other Process Considerations
Dry Tray Pressure Drop, hed
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Dry tray dP is important because:
If its too high --- Entrainment
If its too low --- weeping at turndown
Calculated based on vapor flow through device with no liquid
present
Function of:
Vapor Rate Open Area / Device
Other Process Considerations
( )2
VelocityVapor
edh
Foaming
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Foaming Mechanisms: Presence of surface active materials or solids
HC entrainment or condensation in aqueous systems
Compensate design by using: Lower percent of Jet and Downcomer Flood
Low dry tray dP
Low DC entrance velocity and filling
Radial tips (shaped lips) and large DC clearance
Provide antifoam injection facilities
(Since degree of foaminess varies and is generally unpredictable, experience in similar
towers may be used instead - Contact a Fractionation Specialist)
Known Foamers
Amine and Glycol Absorbers Caustic Towers
Ethylene Demethanizers
Sour Water Strippers
Other Process Considerations
EXISTING T-2851 RE-DISTRIBUTOR
509
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20" Manway
650
1830
20" Manway
100
480
25
Top of PackingBed Limiter
Top Bed, 5334 deep (17.5')
2" Pall rings
800
74
254
180 Redistributor
110
Bed Support
396
286
357
Bottom Bed, 5334 deep (17.5')
2" Pall rings
This FLEXSORB
absorber tower
foams. Whatchanges would
you make to
improve it? Units
are in mm
(25mm=1) unless
stated.
Design Contingency
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To insure 90% chance of successful operation, safety margins
should be adhered to and are built into EMoTIP.
Examples
Jet Flooding (Trays) 80-90% of predicted
Downcomer Filling 35-50%
Packing Flooding 80-85% of predicted
Tray efficiency Point efficiency debited 10%
Packing HETP Predicted divided by 0.85
Other Process Considerations
Trayed Tower Thoughts
Review all designs with Fractionation Specialist
U EM TIP t ti i t
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Use EMoTIP as starting point
Will not optimize open area or downcomer slope
Design for vacuum if can occur
Check vapor pressure of contents if reduced to ambient temperature
Try high capacity designs instead of packing for revamps
Prevent water from entering tower
#1 cause of refinery tray damage
Specify additional static pressure drop for design pressure
Use water filled basis if not high cost
Consider if can condense water on top tray
BEWARE of foaming
A well designed tower for non-foaming service will still flood if itfoams
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CONTACTING DEVICE
PROBLEM
Other Process Considerations
Task Checklist
X Introduction
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91
X Introduction
TOWER SIMULATION
X Basic Concepts
X Specifications
DEVICE SELECTION
X Contacting Devices
X Tray Hardware Definitions
X Tray Hydraulics
X Packing Hydraulics
X Other Process Considerations
XOther Tower Internals
Z Tower Revamps
Other Tower Internals
Tray Internals
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Perforated Pipe Distributors
Usually directed against a downcomer
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Usually directed against a downcomer
Use baffle to prevent downcomer boiling
Hole/Slot Area should give 0.25-0.5 psi (0.018-0.035 kg/cm2) pressure
drop
(See Fluid Flow Equations, DP III-H)
Four common types:
Other Tower Internals
Tower Internals Details (DP III-H)
Pay special attention to tower inlets and outlets
Follow directions in DP III-H
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Follow directions in DP III H
Leave extra tray spacing for distributors and manways
Figure out where the manways will be
Distributors will create high velocity areas where flooding
can start Insulate baffle to prevent vaporization in downcomer
0.25-0.5 psi (0.02-0.04 kg/cm2) for distributor hole/slots
Chimneys
Long rectangular lowest cost, then round, last square
Size CWMS for 100% Vc, unless foaming service
Useful fluid flow equations hidden in DP III-H
Some drawoffs require self venting flow (eq 13)
Chance that vapor can enter drawoff line
Low residence time
Lack of seal in drawoff pan (coking or fouling services)
See also Distillation Operations, p. 89-94 (Kister)
Packing Internals
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Packing Liquid Distributors
Gravity Type
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Most important packing internal
Trough type preferred, but high cost
Design details by vendor but must
meet DP III-G, Appendix A criteria
Must be installed level
Other Tower Internals
Packing Distributor
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Packing Spray Nozzles
Provide poor liquid distribution
Plug easily; strainers required
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Plug easily; strainers required
upstream
Low cost, but often require
demister above
Sprays in action: Water Test of
BTRF PS 8 VPS Wash Oil
Distributor at Turndown Rate - 2003
Other Tower Internals
Distribution Quality
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All packing distributors should be
tested at vendor shop
Distributor should be fully
assembled during test
Area samples and individual
random sample are compiled to
verify performance
Other Tower Internals
Packing Supports
Located at bottom of packed bed
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Open Area sized for at least 100% of tower cross section to prevent flooding
Design details by vendor
Bed Limiters
Restrain packing during upsets - keep out of draw nozzles, etc.
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Fastened to clips welded to shell or suspended from distributor
Packed Tower Details
First, dont use packed tower unless necessary
Low pressure drop (vacuum or atmospheric pressure tower)
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Very small diameter tower (3 ft or 915mm or less)
Possibly foaming, but still try trays first
Revamp where high capacity trays still cant provide necessary
capacity/efficiency Specify liquid distributor to meet criteria in DP-III-G Appendix A
3/8 (10mm) minimum orifice desired, but can reduce to (6mm)
Smaller holes may plug, resulting in poor fractionation
Be careful of high turndown requires small orifices Specify liquid distributor to meet flow test criteria in Appendix B
Copy both appendices and give to vendor
Provide dual strainers on liquid feed to prevent plugging
No bypass recommended SS piping downstream of strainers (especially if at grade)
Liquid Draws - Trays and Packing
Two types:
Downcomer (Sump)
Chi T
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Chimney Tray
Either type may be a partial or total draw
Reboiler Draws are unique (see DP III-H)
Other Tower Internals
Reboiler Draw and Return Design11"
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3'-10"
1' - 3"
11"
2"
4"
4"
4"
8"
2'-0"
1'-6"
9"
2"
6"
1' - 9" 3' - 3"
4"
2'-10"
1'-4"
71
8"
1' - 0"
4'-10
"
5' - 0"
1
1/2"
4"
15
1' - 12"
2"
Task Checklist
X Introduction
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TOWER SIMULATION
X Basic Concepts
X Specifications
DEVICE SELECTION
X Contacting Devices
X Tray Hardware Definitions
X Tray Hydraulics
X Packing Hydraulics
X Other Process Considerations
X Other Tower Internals
XTower Revamps
Tower Revamps
Tower Revamps
Always consider process alternatives first!!!(e g increase tower pressure etc )
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(e.g. increase tower pressure, etc.)
Revamp Strategy: Rate existing tower to identify limitations
Vapor Handling Limitation? Liquid Handling Limitation?
Poor Separation Efficiency?
Different Service?
Explore high capacity tray options discussed previously before
considering packing
Fundamental design concepts remain the same. However, sometimes
design criteria are too conservative - consult with a FractionationSpecialist.
Tower Revamps
Options Guide
Revamp Objective: Increased capacity at constant separation efficiency
(XOM DP III-A Table 4A)
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107 Tower Revamps
Debottleneck Examples
Cheap
Operational changes
Expensive
Install sloped or mod arc
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Operational changes
Reduce weir height, increase DC
clearance or add a shaped lip tolower DC filling
Change tray decks
Packed Towers:
Increase Packing Size
Install Structured Packing
Replace liquid distributor(s)
Install sloped or mod. arc
downcomers
Increase number of liquidpasses
Install high capacity trays
Changing tray spacing
Install packing
Change amine type or
concentration
Tower Revamps
Packing Selection
C il
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Can easily compare
different packing types
using this chart
(see DP III-G, Figure 3)
Tower Revamps
Expansion Example
What consider for expansion?
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Top Trays
160%95%45%Expansion
150%90%42%Base
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Verify bolts are tight
Make sure internals are put together correctly
Levelness of weirs
Tools Helmet mounted and hand held flashlights (explosion proof recommended)
Rechargeable spotlight for large vessels/furnaces
Knee pads, and maybe seating pad
Wrench (to check bolts)
Ruler, tape measure, and wooden blocks cut to measurement tolerances Water bottle
Level (consider laser type)
Hardhat, gloves, clear safety glasses, pool FRCs
Marker or paint pen
Shoulder bag Do not enter vessel without signing in through hole watch
Do not even put head inside vessel without permission
Gas test required to make sure safe
Sign out through hole watch when leaving
NEW T-2851 RE-DISTRIBUTOR
20" Manway
509
Replace packing with
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649
1830
20" Manway
Old Top of Packing
Old Bed Limiter
Top Bed, 5334 deep (17.5')
Cascade Minirings #3
825
396
Bottom Bed, 5182 deep (17.0')
Cascade Minirings #3
Bed Support
112
New Top of PackingNew Bed Limiter (supported by clips)
152
Old Redistributor (removed)
New Redistributor
633
one with higher
capacity . Newer
packings can give
similar performance
with higher capacity
(at lower % jet flood).
Velocity through
chimneys was 21.5
ft/sec (6.6 m/s), with
only 3 (76 mm) gap
between top ofchimney and bed
support. Chimneys
were missing hats.
Lower distributor
and install hats on
chimneys.