Episode 55 : Conceptual Process Synthesis-Design Process Flowsheet Synthesis: Method to determine a process flowsheet that satisfies all product, operational and other requirements SAJJAD KHUDHUR ABBAS Ceo , Founder & Head of SHacademy Chemical Engineering , Al-Muthanna University, Iraq Oil & Gas Safety and Health Professional – OSHACADEMY Trainer of Trainers (TOT) - Canadian Center of Human Development

1. SAJJAD KHUDHUR ABBAS
Ceo , Founder & Head of SHacademy
Chemical Engineering , Al-Muthanna University, Iraq
Oil & Gas Safety and Health Professional – OSHACADEMY
Trainer of Trainers (TOT) - Canadian Center of Human
Development
Episode 55 : Conceptual
Process Synthesis-Design

2. Conceptual Process Synthesis-Design
Process Flowsheet
???Raw Materials Products
Process Flowsheet Synthesis: Method to determine a process
flowsheet that satisfies all product, operational and other
requirements

3. Product Oriented Process Synthesis
Chemical
Product
Process
Raw Material
What are
chemical
products?
What are the raw
materials?
What is a
chemical process?

4. Chemical Product-Process Relationship
Chemical
Process ??
Raw Material Chemical
Product
Chemical process synthesis-design is about finding a
sustainable process that can convert the raw materials to the
desired chemical products

5. Chemical Process Design & Green Engineering
Chemical
Process
??
Chemical
Product
Raw Material
Chemical process design is about finding a sustainable
process that can convert the raw materials to the desired
chemical products
Sustainable: Economic, low environmental impact, low
waste, efficient operation, correct raw material, …..

6. Example of a Chemical Process & Product
Oxychlori-
nation Separa-
tion
block 1
Pyrolysis
Separa-
tion
block 2
HCl (addition) Water HCl (product)
The production of VCM is usually done from ethylene. In this case the process is carried out in two steps,
first reaction with either chlorine or hydrogen chloride in order to produce ethylene dichloride (EDC) and
next pyrolysis (cracking) to form VCM. The compounds in the system are Ethylene, EDC, VCM, HCl, O2,
Cl2 and H2O. The reactions involved is the process are:
Direct chlorination: C2H4 + Cl2  C2H4Cl2
Oxychlorination: C2H4+2HCl+½O2  C2H4Cl2 +H2O
Pyrolysis (cracking): C2H4Cl2  C2H3Cl + HCl
The two step process also requires two separation blocks. In the first step (formation of EDC) two different
reactions are considered (Direct chlorination and oxychlorination). Oxychlorination produces water in
EDC
VCM
(product)
HCl
Oxygen
Ethylene
Chlorine
Recycle
addition to EDC and it aClsoomrepquutierresAaidreedcyPcrloe.cess Engineering - Lecture 7 (R. Gani)
Direct
chlorinatio
n
Purge

7. Process design starts with defining the needs of the product
that will be manufactured by the process!

8. The Product Tree
It is important to
choose the right
product and the
corresponding raw
material from
which the product
can be made. This
also defines the
path (process
route)

9. A Scenario for Chemical Process Design
1. Board of Directors’ Design Problem
2. Discovery of possible new projects
3. Feedback & customer reaction
4. Planning & organizational design
5. Preliminary process design
6. Layout & three dimensional modelling
7. Construction
8. Startup & commissioning
9. Plant Operation
10. Debottelnecking
11. Decommissioning
Stages in
the life of a
process !

10. Computer Aide
d Process Engineering - Le 9
Roles of different groups of people in the different stages of the life of a proces
BU definition of
1 obejctive
PE conceptual
2
process
design
Chemical
Research
rating
mpany
Process C
Engineering
Business Unit
CR preliminary
1 study
PE preliminary
1 study
BU decision on
2 process
information about
novel compound
proposal for
process
improvement
idea for new
compound/
market strategy
state of the
market
 objective
 idea of production
amount
schedule
 description of the process
 PFD and pre-P&ID
 mass and energy balances
 datasheets for major units
 site and installation plan
onstruction
Company
Ope
Co
 estimated costs
 estimated schedule
 patents
 description of synthesis
path
 first process description
 analysis methods for
product, product quality,
etc.
 first safety considerations
cture 7 (R.
Gani
)

11. Roles of different groups of people in the different stages of the life of a proces
II
Chemical
Research
Operating
Company
Construction
Company
Process
Engineering
Business Unit
PE
3
detailed
process
design
CC
engineering
1
design and
construction
CC
2
commis-
sioning
hand-over
OC
2
operation
and
maintenance
OC
1
commis-
sioning,
hand-over
OC decom-
3 missioning
 P&ID
 data sheets and
equipment drawings
 mass and energy
balances
 information about
process at steady state
 comments on startup
and shutdown
 plant
 plant documentation
 P&ID
 data sheets
 equipment
drawings
 piping
specification
 installation plan
 building plan
 plant modell
BU
decision on
4
project
continuation
 description of the process
 PFD and pre-P&ID
 mass and energy balances
 datasheets for major units
 site and installation plan

12. The Synthesis Step
Chemical
Process
??
Chemical
Product
Raw Material
Concept Generation
Generation of Alternatives
Analysis & Evaluation of Alternatives
Final Selection

13. The Synthesis Step
Chemical
Process
??
Chemical
Product
Raw Material
Problem specification
Approaches for design
Design alternatives
Performance
Cost, safety, …
Concept generation
Alternative generation
Analysis
Evaluation
Comparison &
optimization
Abstract
Description
Refined
Description

14. Basic Steps in Flowsheet Synthesis
* Gathering Information
* Representing Alternatives
* Criteria for Assessing Preliminary Designs
 Economic evaluation
 Environmental concerns
 Safety analysis
 Flexibility & controllability
* Generating & searching among alternatives

15. Generating & searching among alternatives: Methods
* Total enumeration
* Evolutionary methods
* Mathematical programming
* Hybrid
Establish targets for the design
Generate (feasible) alternatives that will match the
targets
Order all the feasible alternatives and select the most
appropriate

16. Generating & searching among alternatives: Methods
* Total enumeration
* Evolutionary methods
* Mathematical programming
* Hybrid
Concepts:
Superstructure & Alternatives
C[1]
C[2]
1
2
3
H[1]
T[in] T[out]
C[3]

17. Generating & searching among alternatives: Methods
* Total enumeration
* Evolutionary methods
* Mathematical programming
* Hybrid
A, E
Concepts:
Superstructure & Alternatives
A, B, C, D, E, F
A / B, C, D, E, F
B, F
A, E, F / C, D, B
Reactor
C
D A, F / F C / D, B
E
F

18. Decomposition Strategies for Process Synthesis
• Bounding Strategies for Process Synthesis
• Hierarchical Decomposition for Process
Synthesis
P1 = Cp Fp – Cr Fr = Original space = Profit bound
P2 = P1 – Constraints = Profit bound
P3 = P2 – Cop
P4 = P3 – Cop
P4 = P3 – Cop

19. Decomposition Strategies for Process Synthesis
• Bounding Strategies for Process Synthesis
• Hierarchical Decomposition for Process Synthesis
Level 1. Input Information
i problem definition Batch versus Continuous (1)
Level 2. Input-Output Structure
i material selection i reaction pathways
Input-output structure of
flowsheet (2)
Recycle structure of flowsheet (3)
Separation system synthesis (4)
Levels 3 & 4.
i recycle i separation system
Levels 5 - 8.
i energy integration i detailed evaluation
i control i safety
Heat/mass recovery network (5)
Design problem decomposed into a hierarchy of decisions

20. Hierarchical Decomposition for Process Synthesis
Level 1: Decisions on Batch versus Continuous
Consider,
• Technical Information
•Does any apparatus work in batch mode? Is
process sensitive to upsets & variations?
• Production Rate
•High or low production rate? Only few days
production needed? Few days operational notice!
• Product Lifetime
• One or two years or longer?
• Value of Product
• Product value >> manufacturing cost?
Note: Several batch units can be combined to give a
continuous production!

21. 20
Hierarchical Decomposition for Process Synthesis
Level 2: Decisions on Input-Output Structure
Consider,
• Raw materials – what to do with impurities ?
• How many product streams?
• Recycle streams? Purge streams?
• Reversible by-products? Recycle or recover?
• Selectivity versus cost
Three Types of Decisions (Assumptions)
1. Decision that fix parts of the flowsheet
2. Decisions that fix some of the design variables
3. Decisions that fix connections to the environment

22. Hierarchical Decomposition for Process Synthesis
Level 2: Decisions on Input-Output Structure
Raw Materials - Impurities?
• If the impurities are inert, remove
them after reaction, if they are
valuable
•If the impurities are inert, present in large amounts, and,
can be easily separated, remove them before the reactor
• If the impurities have boiling points lower than
reactants and products, and, they are also inert, recycle
them (note: purge unit will be needed!)
• If the impurities are also products from the reactor,
place the feed stream before the unit that will remove the
impurities

23. Hierarchical Decomposition for Process Synthesis
Level 2: Decisions on Input-Output Structure
Product streams?
Observe the following Rules
• Recycle unreacted reactants
• Recycle intermediate reactants (products)
• Recycle/remove azeotropes with reactants*
• Remove (recover) the main product
• Remove (recover) the valuable by-products
• Remove (as waste)/recycle by-
products that are not valuable

24. Hierarchical Decomposition for Process Synthesis
Level 2: Decisions on Input-Output Structure
Recycle? Purge Units? Consider the following:
• For < 100% conversion of reactants and reaction in
the gas phase,
Recycle of gases will be necessary
If impurities are present, purge units will be
necessary
• For < 100% conversion and reaction in the liquid
phase,
Recycle of liquids (reactants) will be necessary
If impurities are present, purge units will be
necessary

25. Hierarchical Decomposition for Process Synthesis
Level 2: Decisions on Input-Output Structure
Reversible by-products? Selectivity versus cost?
EP2 = Product value – Byproduct value – Raw material value
Function of conversion, selectivity, reaction T & P, ….

26. Hierarchical Decomposition for Process Synthesis
Level 3: Decisions on Recycle Structure & Reactor
Consider,
• Number of reactors?
• Number of recycle streams?
• Need for compressor/pump?
• Reactor type? Adiabatic or Isothermal?
• Reaction equilibrium or kinetics?
• Reactor cost (capital & operating)?

27. Hierarchical Decomposition for Process Synthesis
Level 3: Decisions on Recycle Structure & Reactor
• Number of reactors?
• If more than one reaction is needed to get the desired product,
more than one reactor will be needed if the conditions are very
different
• Number of recycle streams?
• Depends on the number of raw materials and conversion of all
reactants
• Need for compressor/pump?
• Compressor for gas recycle; pump for liquid recycle
• Reactor type? Adiabatic or Isothermal?
• If temperature change is too high or low, heating or cooling will be
needed
• Reaction equilibrium or kinetics?
• Kinetically controlled or equilibrium reached?
• Reactor cost (capital & operating)?
EP3 = EP2 – Compressor/pump cost – Reactor cost

28. Hierarchical Decomposition for Process Synthesis
Level 4: Decisions on Separation System
Vapour recovery and/or Liquid recovery? - Rules
• If reactor stream is in liquid phase, use liquid recovery
• If reactor stream has 2 phases (separate the 2 phases first)
• Use vapour recovery for vapour phase
• Use liquid recovery for liquid phase
• Reactor stream is gas (vapour) phase
• Perform phase split (if possible) by reducing temperature (ie.,
condenser) and then separate the 2-phase. Otherwise, use
vapour recovery
How to locate & perform the separation?
EP4 = EP3 – Vapour recovery cost – Liquid recovery cost

29. Hierarchical Decomposition for Process Synthesis
Level 4: Decisions on Separation System
Vapour Recovery System (VS) - Location
• If vapour stream contains significant amount of valuable material
(reactants, impurities, product), place VS after purge unit
• If vapour stream contains components that may slow down the
reaction or destroy or affect the catalyst, place VS on the recycle
stream
• If both the above criteria are satisfied, place VS after a “phase
split” unit
• If none of the above are satisfied, VS is most likely not necessary!
How to perform the separation?
Condensation (high pressure and/or low temperature)
Absorption (needs solvent and solvent recovery – try water!)
Adsorption (needs adsorbent and regeneration of adsorbent)
Membrane separation (suitable membrane, low flux, etc.)

30. 29
Hierarchical Decomposition for Process Synthesis
Level 4: Decisions on Separation System
Liquid Recovery System (LS) - Decisions on …
• Which separations can be made with distillation?
• Sequence of distillation columns
• Removal of light ends (send to VS if valuable, otherwise, waste disposal)
• Other types of separations possible?
Rule for selecting separation by distillation or phase split (V-L)
• If  > 1.1, between two key components, use distillation provided the key components d
not form azaotrope
• If  >>> 1.1, try phase split (condensation or vaporization)
Rules for sequencing of distillation columns
• Recover lightest component first
• Recover most plentiful component first
• Make the most difficult separation last
• Always try equimolar separations

31. 30
Method for Separation Process Synthesis
Separation Process Identification
Step 1: Mixture Analysis (number of components in mixture,
mixture type, mixture state, temperature, pressure, number of
binary pairs, azeotrope pairs, etc.)
Step 2: Generate binary ratio matrix
R = rij = piA / piB for property I, binary pair j
compounds A & B in pair j
Step 3: Identify separation technique
If, rmin < rij < rmax for separation technique k, select this
technique for separation of the compounds in the binary
pair j
Step 4: If more than one separation technique is feasible for binary
pair j, select the separation technique with the largest rij value
Principle for separation is a driving force created by a difference in
property; different separation techniques employ different properties!

32. Case Study: Maleic Anhydride (MA) Production
Level 1. Input / Output Information
Alternative 1
Benzene Process
V2O5-MoO3
Alternative 2
n-Butane Process
VPO
2C6H6  9O2  2C4H2O3  4CO2  4H2O
C4 H 2O3  O2  4CO  H2O
2C6 H6  9O2 12CO  6H2O
C4H2O3  3O2  4CO2  H2O
2C6 H6 15O2 12CO2  6H 2O
2C4H10  7O2  2C4H2O3 8H2O
C4 H2O3  O2  4CO  H2O
C4 H2O3  3O2  4CO2  H2O
2C4 H10  9O2  8CO 10H2O
2C4 H10 13O2  8CO2 10H2O
Benzene conversion, 95%
MA Yield, 70%
Air/Benzene, ~ 66 (moles)
Temperature, 375°C
Pressure, 150 kPa
n-butane conversion, 85%
MA Yield, 60%
Air/n-butane, ~ 62 (moles)
Temperature, 400°C
Pressure, 150 kPa

33. MA Production: IO Assumptions
Level 1. Input / Output Information
“Tier 1” Environmental Impact Analysis
CO2, H2O, air,
traces of CO, MA
??
Reactor
Benzene
or
n-butane
Product
Recovery
Pollution
Control
99% control
99% MA recovery
Design
DecisionsUnreacted
Benzene
or
n-butane
CO, CO2 , H2O, air, MA
Air MA, CO,
CO , H O2 2
air
MA
50x10
lb/yr
6
Production rate

34. Initial Flowsheet for MA from n-C4
Reactors
Air
n-Butane
Absorber
Distillation
column
Compressor
MA
Vaporizer
Off-gas
Off-gas
Pump
Solvent

35. Thanks for Watching
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