Chapter 1

Diagrams for Understanding chemical processes Chapter 1 121-Diagrams for Understanding chemical processes

1 Block Flow Diagram BFD 1.1.1.Block flow process diagram BFD 1.1.2 Block Flow Plant Diagram BFD2 Process Flow Diagram PFD 1.2.1 Process Topology 1.2.2 Stream Information 1. 2.3 Equipment Information 1.2.4 Topology & stream data & control strategy for PFD

31.3 Piping & Instrument Diagram P&ID1.4 Additional Diagrams1.5 3 Dimensions Representation of Process1.6 Detailed plant layout1.7 The 3-D Plant Model

4Diagrams for Chemical Engineers

Most effective way of communicating information about a process is through the use of flow diagramsDiagrams evolve from time a process is conceived in lab through design, construction & plant operation53 diagrams are important to chemical engineer : Block flow diagram BFDProcess flow diagram PFDPipe& Instrument diagram P&ID

PFD is the most useful to chemical engineers1.1 Block Flow Diagram BFD

BFD Convert problem from words to simple block Diagram It consists of Series of blocks representing unit operations connected by input/output streams Important information T , P , flow , composition includedNo details of equipment are given in this diagramBlock Flow Process Diagram: for one process only. Block Flow Plant Diagram: for complete plant. This contains many Block flow process diagram

61.1.1 Block Flow Process Diagram BFD Example :Toluene and hydrogen are converted in a reactor to produce benzene and methane. The reaction does not go to completion, and excess toluene is required. The non-condensable gases are separated and discharged. The benzene product and the unreacted toluene are then separated by distillation. The toluene is then recycled back to the reactor and the benzene removed in the product stream

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89Conventions & Format Recommended for BFD

Operations are represented by series of blocksFlows by arrows giving direction of flowFlow goes from left to right whenever possibleLight steam ( gases ) at top & heavy streams at bottomCritical information unique to process are givenHorizontal lines are continuous , vertical lines are brokenSimplified material balance is provided

1.1.2 Block Flow Plant Diagram BFD

Plant BFD gives complete picture of a whole plantProcess BFD gives picture of one process in the plant Only limited information for each process unit is given to keep diagram simpleBFD is used as starting point to create PFDBFD is useful to compare alternative processes

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111.2 Process Flow Diagram PFD

Contains bulk of engineering data for design of processIt differs between companies but all have same featuresData include : All major equipment with description( Name & Number )All streams are numbered Descriptions of streams are included directly or in tableUtility streams are also shownBasic control loops with control strategy are shown

1213PFD should remain uncluttered & easy to read It is often drawn on a large sheet of paper (24 in x 36 in)Flow summery & equipment summery tables are providedPFD provides main information on :TopologyStreams data Equipment data

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1.2.1 Process Topology

Location & interaction between equipment & streamsEquipment are represented by iconsStandard ASME icons are often used Each company has its own icons but they are similarDescriptive name & No are printed at top of equipmentGeneral format XX - YZZ A/B

H-101

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1617Example : P-101 A/B :

P identifies the equipment as a pump100 indicates equipment is located in area 100 of plant01 indicates that this specific pump is number 01 A/B indicates 2 pumps , pump A with pump B as backup Equipment replaced by similar ones take the same (name & No )

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1.2.2 Stream Information

Diamond box located on stream with No of stream in it Direction is shown by arrowhead Utilities include (electricity , air, water, steam, inert gas, sewer, waste treatment, flares.)Electricity is treated separately & not shown on PFD or Table 1.3

21122Stream properties ( T , P, composition, Flow) are shown directly on PFD for simple process or by No of stream & tables for complicated Two types of information : Required & optionalPossible to use PFD & table to check mass & energy balance

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27Example 1.2Check the overall material balance for the benzene process shown in Figure 1.3. From the figure, identify the input streams as Stream 1 (toluene feed) & Stream 3 (hydrogen feed) & output streams as Stream 15 (product benzene) & Stream 16 (fuel gas).

28From the flow summary table, these flows are listed as (units are in (103 kg)/h): Input: Output:Stream 3 0.82 Stream 15 8.21Stream 1 10.00 Stream 16 2.61Total 10.82 103 kg/h Total 10.82 103 kg/hBalance is achieved since Output = Input29Example 1.3

Determine the conversion per pass of toluene to benzene in R-101 in Figure 1.3. Conversion is defined as: = (benzene produced)/(total toluene introduced)30From PFD, the input streams to R-101 are shown as Stream 6 (reactor feed) & Stream 7 (recycle gas quench),output stream is Stream 9 (reactor effluent stream).From the information in Table 1.5 (units are kmol/h):C7H8 introduced = 144 (S 6) + 0.04 (S7) = 144.04 kmol/hC6H6 produced =116 (S9)7.6 (S6)0.37(S7)=108.03 kmol/h Conversion = 108.03/144.04 = 0.75Or Conversion = (Tin Tout) / Tin = (144 36) /144 =0.751.2.3 Equipment Information

Final element of PFD is the equipment summary It supplies data for detail design & cost estimateTable 1.6 presents basic information needed for equipment summary

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1.2.4 Topology & stream data & control strategy for PFD

Up to now information on PFD is kept to minimumIncludes information on major control loops Information Flags on streams with dataFlags are easy to remove & change Data are shown in tables as wellData important for operation & safety included in PFD diagram as flags

3435Flags reduce number of streams in tables ( pump , HE)Often T , P & flow rates for streams above normal Important to keep PFD uncluttered & easy to followPFD prepared by the operating companySubsequent diagrams are contracted to design companiesPFD are valuable for start up , operation & training

36Example 1.6In the benzene process, the feed to the reactor is substantially hotter than the rest of the process & is crucial to operation of process. In addition, the reaction is exothermic & reactor effluent temperature must be carefully monitored. For this reason S 6 (entering) and S 9 (leaving) have temperature flags

37Example 1.7The pressures of the streams to and from R-101 in benzene process are also important. The difference in pressure between the two streams gives the pressure drop across the reactor. This, in turn, gives an indication of any maldistribution of gas through the catalyst beds. For this reason, pressure flags are also included on Streams 6 and 9.38Example 1.8Follow S 13 leaving top of the benzene column in benzene PFD given in Figure 1.5 & in Table 1.5. This stream passes through the benzene condenser, E-104, into reflux drum,V-104. The majority of this stream then flows into the reflux pump, P-102, and leaves as S 14, while the remaining noncondensables leave the reflux drum in S 19. The mass flowrate & component flowrates of all these streams are given in Table 1.5. The stream leaving E-104 is not included in stream table. Instead, a flag giving T (112C) was provided on diagram (indicating condensation without subcooling). An additional flag, showing P following the pump, is also shown. In this case the entry for S14 could be omitted from stream table, because it is simply the sum of S 12 & S 15 & no information is lost.

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401.3 Pipe & Instrument Diagram P&ID

P&ID is called also Mechanical Flow Diagram MFDIt is Final diagram for installation of equipment All mechanical data of plant except data in table 1.8General conventions for P&ID are given in table 1.9

4142Pipes ( size, schedule, material, insulation )as in Fig1.7

Ps Internal pressure in the pipe s Ultimate tensile strength of the material of pipe

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4445Physical size of unit operations is reflected by size of its symbol in the diagramUtilities connections identified by numbered box in P&IDKeys of utility connections are shown in table in P&IDVariables that can be measured are shown by circular flag Control symbols are shown in table 1.10

4647All controls end with a control valve All controls are based on effect of change in flow on a variable Direction of valve depends on desired change in variable Response time & type ( differential, integral, proportional ) is left to instrumentation engineer.48P&ID is last stage of process design

Mechanical + Civil engineer construct & install equipmentInstrument engineer specify, install & check control systemPipe engineers develop plant layout & elevation drawing4. Project engineers develop plant & construction scheduleP& ID is used as a checklist for equipmentP& ID is used for training operators

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PFD BPDP&ID1.4 Additional Diagrams

1- Utilities flow-sheet: shows all utilities headers , inputs , outputs , connections and types of stream 2- Vessel sketches, logic ladder diagram , wiring diagram , site plans , structural support3- Plot plans & elevation diagrams: location & elevation of major equipment Provide space for repair, remove bundles, replace unitsAdd structural support and piping

51524- Piping isometrics: for every pipe in plant drawn in 3-D with elevation & orientation of each section of pipe 5- Scale model: 3 dimensions models used in the past Replaced by 3-dimensional computer aided design CAD6- Virtual reality: software to walk through plant , touch equipment, turn valves, climb ladders ..etc.

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1.5 3 Dimensional Representation of a Process

Major design is done in 2-dimensions, but for construction 3-D model is requiredTo build electronic 3-D model all information in previous diagrams must be accessed & synthesizedHeat exchangers located to (remove & clean)bundle easilyPumps located for easy repair, Cranes for turbines etc.Control valves at elevation to allow operator accessibilitySample ports & instruments are located conveniently

541.5 Detailed plant layout

Divide PFD into logical subsystem ( Feed & reactor , purification , separation & recycle) dotted lines in Fig 1.82. Create a preliminary plot plan for each sub-section Grade-level: horizontal , in-line arrangement Structure - mounted vertical arrangement

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57In Grade level equipment aligned on both sides of pipe rackPipe Rack carries all pipes & run in the middle of unit Vertical mounting is limited to a single level Grade level require larger foot print or lands Fig 1.9 Space is set according to standard code for safety Sizing of equipment is complete & location assigned Placement of equipment within plot plan Fig 1.10

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593. Elevation of all major equipment established :Ground is less costly & gives easy access but requires larger spaceElevation of columns for NPSH on suction of pump to avoid cavitation from liquid at bubble point. Thermo syphon re-boiler use difference in density & requires elevation Fig 1.12Digging is not good, heavy vapor accumulates & dangerous

604. Major process & utility pipes sketched inChoose most direct route of pipes to avoid clashing Pipe rack for pipes from one end to another of plant Samples ports & control valves should be placed on grade or steel access platform

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1.6 The 3-D Plant Model

Virtual Plant tour AV1 in file on CDFigures based DME using PDMS softwareFig 1.13 isometric view of equipment, processes, utility & steel structure Pipe rack runs through the center of unit

6566Steel platforms are shown for supportDistillation in rearReactor & feed in near side of pipe rackFig 1.14 shows elevation of equipmentCondenser vertical above for gravity flow to reflux drum Fig 1.15 piping & equipment for reactor

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701.7 Operator & 3-D immersive simulator1.7.1 Operator training simulators OTS

OTS helps operator in (start-up, shut-down, emergency, off-design conditions) OTS is a dynamic simulation model of process to which human machine interface HMI is connected

71HMI Human-Machine Interface is a pictorial representation of process that communicates with the dynamic model HMI displays all the controls of the process - Fig 1.16 Errors are made & corrected without risk Starting point is a steady state simulation, equipment information & the P&ID since it contains all instruments72

731.7.2 3-D Immersive Training Simulators ITSModel built in electronic environment from design data on( size , location , elevation & orientation of equipment)All Piping , instrument , valves , sample , drains are specified Access through 2-D viewer or 3-D virtual environment by (3-D goggles )Resulting images are static & low fidelity

741.7.3 Linking ITS with an OTS Link OTS & ITS so they communicate in real-time of process, both in control room & outside in plantCan be simulated in virtual environment. Virtual realityAvatars are used to represent plant operators in fieldUser can navigate , interact , immerse truly in virtual plant

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76Augmented Reality AR

Actual plant simulated in virtual environment Cases simulated in VR are not possible in actual plantShow internals of distillation or heat exchanger Fig 1.18Avatars walk in plant & strip wall to see inside equipment & Display of process data Fig 1.19It provides training for safety , emergency , routine maintenance 77

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79SUMMARY

Three principal types of diagrams BFD, PFD, P&ID, which describe a process in increasing details1. BFD is useful in conceptualizing process in large complex, it gives little stream information, but clear overview of process2. PFD contains all information to complete M&E balance, Stream properties , equipment size, major control loops3. P&ID has all information for construction of plant, Including pipe sizes, location of instruments for process & utility

80Other diagrams are used in construction & engineering phase of projectThey contain little additional information about processPlacement & layout within the process was presented.Reasons for elevating equipment & providing access PFD is the most important diagram for chemical engineer