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THE NATURE OF PROCESS DESIGN. A Creative Activity !. The most effective way of communicating information about a process is through the use of flow diagrams. Block Flow Diagram (BFD) Process Flow Diagram (PFD) Piping and Instrumentation Diagram (P&ID). Mixed Gas (2,610 kg/h). Toluene - PowerPoint PPT Presentation
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THE NATURE OF PROCESS DESIGN
A Creative Activity !
[ Example ]
CH3
+ H2 + CH4
Toluene Hydrogen Benzene Methane
The most effective way of communicating information about
a process is through the use of flow diagrams.
• Block Flow Diagram (BFD)
• Process Flow Diagram (PFD)
• Piping and Instrumentation Diagram (P&ID)
Mixed Gas(2,610 kg/h)
Benzene(8,210 kg/h)
GasSeparator
Mixed Liquids
ReactorToluene
(10,000 kg/h)
Hydrogen(820 kg/h) Conversion
75% Toluene
Toluene
Reaction : C7H8 + H2 = C6H6 + CH4
Figure 1.1 Block flow process diagram for the production of benzene
Toluene and hydrogen are converted in a reactor to produce benzene and methane.Thereaction does not go to completion, and excess toluene is required. The noncondensablegases are separated and discharged. The benzene product and the unreacted toluene arethen separated by distillation. The toluene is then recycled back to the reactor and thebenzene removed in the product stream.
Table 1.1 Conventions and Format Recommended for Laying out a Block Flow Process Diagram
1. Operations shown by blocks.2. Major flow lines shown with arrows giving direction of flow.3. Flow goes from left to right whenever possible.4. Light stream (gases) toward top with heavy stream (liquids and solids) toward bottom.5. Critical information unique to process supplied.6. If lines cross, then the horizontal line is continuous and the vertical line is broken.7. Simplified material balance provided.
Process Flow Diagram (PFD)
A PFD includes the following items:
1. major equipments;2. principal flow route and control involved from raw material feed to final product;3. key temperature and pressure corresponding to anticipated normal operation;4. material flow rates and compositions;5. design duties and sizes of major equipments.
Table 1.2 Conventions Used for Identifying Process Equipment
Process Equipment General Format XX-YZZ A/B
XX are the identification letters for the equipment classification C - Compressor or Turbine E - Heat Exchanger H - Fired Heater P - Pump R - Reactor T - Tower TK - Storage Tank V - Vessel Y designates an area within the plant ZZ are the number designation for each item in an equipment class A/B identifies parallel units or backup units not shown on a PFD Supplemental Information Additional description of equipment given on top of PFD
Table 1.3 Conventions for Identifying Process and Utility Streams
Process StreamsAll conventions shown in Table 1.1 apply.Diamond (square) symbol located in flow lines.Numerical identification (unique for that stream) inserted in diamond (square).Flow direction shown by arrows on flow lines.
Utility Streamslps Low Pressure Steam: 3-5 barg (sat)‡
mps Medium Pressure Steam: 10-15 barg (sat)‡
hps High Pressure Steam: 40-50 barg (sat)‡
htm Heat Transfer Media (Organic): to 400Ccw Cooling Water: From cooling tower 30C returned at less than 45C+
wr River Water: From river 25C returned at less than 35Crw Refrigerated Water: In at 5C returned at less than 15Crb Refrigerated Brine: In at -45C returned at less than 0Ccs Chemical Waste Water with high CODss Sanitary Waste Water with high BOD, etc.el Electric Heat (specify 220, 440, 660V service)ng Natural Gasfg Fuel Gasfo Fuel Oilfw Fuel Water‡These pressure are set during the preliminary design stages and typical values vary within the ranges shown. +Above 45C, significant scaling occurs.
Table 1.4 Information Provided in a Flow Summary Essential InformationStream NumberTemperature (C)Pressure (bar)Vapor FractionTotal Mass Flow Rate (kg/h)Total Mole Flow Rate (kmol/h)Individual Component Flow Rates (kmol/s)
Optional InformationComponent Mole FractionsComponent Mass FractionsIndividual Component Flow Rates (kg/h)Volumetric Flow Rates (m3/h)Significant Physical Properties Density Viscosity OtherThermodynamic Data Heat Capacity Stream Enthalpy K-valuesStream Name
Table 1.6 Equipment Descriptions for PFD and P&IDs
Equipment TypeDescription of Equipment
TowersSize (height and diameter), Pressure, Temperature
Number and Type of TraysHeight and Type of PackingMaterials of Constructions
Heat ExchangersType: Gas-Gas, Gas-Liquid, Liquid-Liquid, Condenser, VaporizerProcess: Duty, Area, Temperature, and Pressure for both streams.
No. of shell and Tube PassesMaterials of Construction: Tubes and Shell
TanksSee vessels
VesselsHight, Diameter, Orientation, Pressure, Temperature, Materials of Construction
PumpsFlow, Discharge Pressure, Temperature, P, Driver Type, Shaft Power, Materials of Construction
CompressorsActual Inlet Flow Rate, Temperature, Pressure, DrverType, Shaft Power,
Materials of ConstructionHeaters (fired)
Type, Tube Pressure, Tube Temperature, Duty, Fuel, Material of ConstructionOthers
Provide Critical Information
Piping and Instrumentation Diagram (P&ID)
1. All process equipments and pipings required for start-up, shut-down, emergency and
normal operation of the plant, including valves, blinds, etc.
2. An id number, an identifier of the material of construction, diameter and insulation
requirements for each line.
3. Direction of flow.
4. Identification of main process and start-up lines.
5. All instrumentation, control and interlock facilities with indication of action on
instrument air failure.
6. Key dimensions or duties of all equipments.
7. Operating and design pressures and temperatures for vessels and reactors.
8. Equipment elevations.
9. Set pressure for relief valves.
10.Drainage requirements.
11.Special notes on piping configuration as necessary, e.g. “gravity drainage.”
Table 1.8 Exclusions from Piping and Instrumentation Diagram
1. Operating conditions T,P2. Stream flows3. Equipment locations4. Pipe routing a. Pipe lengths b. Pipe fittings5. Supports, structures, and foundations
Table 1.9 Conventions in Constructing Piping and Instrumentation Diagrams
For Equipment - Shown Every Piece IncludingSpare units
Parallel unitsSummary details of each unit
For Piping - Include All Lines Including Drains, Sample Connections and SpecifySize (use standard sizes)
Schedule (thickness)Materials of construction
Insulation (thickness and type)For Instruments - Identify
IndicatorsRecordersControllers
Show instrument linesFor Utility - Indentify
Entrance utilitiesExit utilities
Exit to waste treatment facilities
Activities of Process Design(1)Synthesis The step where one conjectures the building blocks and their
interconnections to create a structure which can meet the stated design requirements.
(2)Analysis (Simulation) The activity of modeling and then solving the resulting equations to
predict how a selected structure should behave if it were constructed.(3)Evaluation The activity of placing a worth on the structure where the worth might
be its cost, its safety, or its net energy consumption.(4)Optimization The systematic searching over the allowed operating conditions to
improve the evaluation as much as possible.
Parameterstructure
Process Synthesis
A design task where one conjectures the building blocks and their interconnections to create a structure which can meet the stated design requirements.
IMPORTANCE OF PROCESS STRUCTURE
(1) Recycle? A→ P
A P A P
o rR R S
(2)separation Sequence ? A (propane) B (1-Butene) C(n-Butane)
A B
BC
ABC ABCo r
CC
AB
B
C
A
(3)Heat Recovery ?
H
o r
PROCESS ?
(a) Process design starts with the synthesis of a process to convert raw
materials into desired products.
FeedStreams
ProductStreams
PROCESS
(b) Simulation predicts how a process would behave if it was constructed.
FeedStreams
ProductStreams ?
Figure 1.1 Synthesis is the creation of a process to transform feed streams into product streams. Simulation predicts how it would behave if it was
constructed.
Reactor
Separation and Recycle System
Heat Exchanger Network
Utilities
Figure 1.6 The “onion model” of process design. A reactor design in needed before the separation and recycle system can be designed, and so on. (From Smith and Linnhoff, Trans. IChemE, ChERD, 66:195, 1988; reproduced by permission of the Institution of Chemical Engineers.)
Example Hydrodealkylation of Toluene
H2+
CH3
CH4+
Toluene Benzene
1
2 H2+
Benzene Diphenyl
A HIERARCHICAL APPROACH
Toluene + H2 Benzene + CH4
2 Benzene Diphenyl + H21150 F ~ 1300 F
500 psia
compressor
Flashhh
Reactorfurnace
Purge
Liquidrecycle
Gasrecycle
H2, feed
CW
Benzeneproduct
H2, CH4
Diphenyl
FIGURE 1.2-2Hydrodealkylation of toluene; maximum energy recovery.
ENERGY INTEGRATION
Toluene feed
Reactor
compressor
Vapor Recovery System
Purge
FlashDrum
Benzene
Toluene Col.
Benzene C
ol.
Stablizer
H2 Feed
Toluene Feed
TolueneRecycle
Diphenyl
Distillation Train
ALTERNATIVES OF DISTILLATION TRAIN
(1) Recycle Diphenyl
(2)Feed
H2, CH4 Benzene
Toluene(recycle)
Diphenyl
(3) H2 CH4 Benzene Toluene
(recycle)
Diphenyl
ALTERNATIVES OF VAPOR RECOVERY SYSTEM
(1) Condensation;
(2) Absorption;
(3) Adsorption;
(4) Membrane.
Vapor recoverysystem
Phasesplit
Reactorsystem
Liquid separationsystem
Purge
H2 , CH4
Benzene
Dipheny1
H2 , CH4
Toluene
Simplified Flowsheet for the Separation System
Reactorsystem
Separationsystem
Gas recycle PurgeH2 , CH4
Benzene
Dipheny1
H2 , CH4
Toluene
Toluene recycle
Recycle Structure of the Flowsheet
Purge
H2 , CH4
Benzene
Dipheny1
H2 , CH4
Toluene
Input-Output Structure of the Flowsheet
Hierarchy of decisions
1. Batch versus continuous
2. Input-output structure of the flowsheet
3. Recycle structure of the flowsheet
4. General structure of the separation system Ch.5
a. Vapor recovery system
b. Liquid recovery system
5. Heat-exchanger network Ch.6, Ch.7, Ch.16
Ch. 4