Hierarchy of Decisions
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Transcript of Hierarchy of Decisions
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
LEVEL 3 :
reactor separator products
purge
feeds
Liquid ?Liquid / Vapor ?
Vapor ?
LEVEL 4 :
1 ) Liquid
reactorliquid
separationsystem
Liquid recycle
productsliquidfeeds
LEVEL 3
LEVEL 4 :
2 ) Liquid / Vapor
reactorliquid
separationsystem
Liq. recycle
productsliquid
feeds
LEVEL 3
PhaseSplit
VaporRecovery
system35Cgas recycle
vapor liq.liq.
vapor
purge
LEVEL 4 :
3 ) Vapor
reactorliquid
separationsystem
Liquid recycle
productsfeeds
LEVEL 3
PhaseSplit
VaporRecovery
system35Cgas recycle
liquidliquid
vapor
purge
vapor
LOCATIONS OF VAPOR RECOVERY SYSTEM
2 1
3
Gas
Recycle
Purge
vapor from phase split
1 ) The purge stream
2 ) The gas-recycle stream
3) The flash vapor stream
4 ) None
RULES FOR PLACING THE VAPOR RECOVERY SYSTEM
1 ) Place the vapor recovery system on the purge stream if significant amounts
of valuable materials are being lost in the purge.
2 ) Place the vapor recovery system on the gas-recycle stream if materials that
are deleterious to the reactor operation (catalyst poisoning, etc.) are present
in this stream or if recycling of some components degrades the product
distribution.
3 ) Place the vapor recovery system on the flash vapor stream if both 1 ) and 2 )
are valid.
4 ) Do not use a vapor recovery system if neither 1 ) nor 2 ) are important.
TYPE OF VAPOR RECOVERY SYSTEM
1 ) Condensation - low. T and/or high P
2 ) Absorption
3 ) Adsorption
4 ) Membrane separation
5 ) Reaction
ADJUST MATERIAL BALANCE ?
DECISION IN SYNTHESIZING LIQUID SEPARATION SYSTEM
1. How should light ends be removed, if they might contaminate the product ?
2. What should be the destination of light end ?
3. Do we recycle components that from azeotropes with reactants, or do we split the azeotropes ?
4. What separations can be made by distillation ?
5. What sequence of columns do we use ?
6. How should we accomplish separations if distillation is not feasible ?
1 ) ALTERNATIVES FOR LIGHT-ENDS REMOVAL
Phase Splitter — T and/or P
Partial Condenser on Product Column
Pasteurization Section on Product Column
a Stabilizer Column before the Product Column
Lowercost
Higher cost
lights
product
lights
product
lights
product
2 ) DESTINATION OF LIGHT ENDS
a ) vent or flare stacks - if light ends have very little value.
b ) fuel - if light ends are flammable.
c ) vapor recovery system - if light ends are valuable.
3 ) AZEOTROPES WITH REACTANTS
4 ) APPLICABILITY OF DISTILLATION
5 ) SEQUENCING OF SIMPLE COLUMNS
6 ) COMPLEX COLUMNS
Reactor Flash
Recycle
Product
Stablizer
Diphenyl
Toluene
H2, CH4
Compressor
Benzene H2, CH4
Purge
Process Simulation
Run ChemCAD to obtain M&E balance data !
ECONOMIC POTENTIAL AT LEVEL 4
EP4 = EP3 - annual purge loss - annualized distillation costs - annualized vapor recovery costs
2106
1106
$/yr 0
-1106
-2106
-3106
0.1 0.3 0.5 0.7
0.20.40.6
PHy
x
2 ) DESTINATION OF LIGHT ENDS
a ) vent or flare stacks - if light ends have very little value.
b ) fuel - if light ends are flammable.
c ) vapor recovery system - if light ends are valuable.
3 ) AZEOTROPES WITH REACTANTS
4 ) APPLICABILITY OF DISTILLATION
5 ) SEQUENCING OF SIMPLE COLUMNS
6 ) COMPLEX COLUMNS
A B
C
Design 1 : Direct Sequence
A
B
Design 2 : Indirect Sequence
C
B
Design 3 : Side-stream rectifier
C
A
Design 4 : Side-stream Stripper
C
A
B
Design 5
Prefractionator arrangement
C
A
B
A , B
B , C
A A
C
Design 6 Design 7
side stream
B
C
B