2. Conceptual Design of a chemical process
Q: What is a conceptual design?
A: Finding best flowsheet:
1- selecting appropriate equipment
2- best configuration of the equipment
3- determining optimum operating conditions
How do we categorize the above decisions?
1 & 2 are discrete while 3 is continuous decision
3. Design variables
Discrete ( no. & type of reactors,…)
1- variables
Continuous ( temperature, pressure,…)
with local effect (reflux ratio,…)
2- variables
with global effect (reactor conversion,…)
Conceptual design is an MINLP optimization problem
4. Hierarchical nature of process synthesis
Utility system
HEN
Separation
Reactor
Design steps
Outwards
5. A Typical Chemical Process
Hydrodealkylation of Toluene to produce Benzene (HDA)
Toluene + H2 Benzene + CH4
2 Benzene Diphenyl + H2
T = 1150 – 1300 °F
P = 500 psia
H2
2
2
2 / Toluene @ reactor inlet
/ Toluene @ reactor inlet
/ Toluene @ reactor inlet
/ Toluene @ reactor inlet ≃
≃
≃
≃ 5/1
5/1
5/1
5/1
7. How can we create this flowsheet ?
Let’s simplify the flowsheet first:
1- remove all heat exchangers, drums and storage
vessels
2- group all distillation columns
3- Simplify general structure of separation system
4- Lump complete separation system
5- Lump complete process
12. Hierarchy of decisions
1- Batch Vs. Continuous
2- Input – output structure
3- Recycle structure
4- General structure of separation system:
a) Vapor recovery system
b) Liquid recovery system
5- Heat exchanger network
13. Advantages:
1- If the project is not profitable at any level, seek
another alternative or terminate the project
2- At each level, there are few number of alternatives
and therefore less possibility of losing an
alternative. Thus, this is a systematic way to
generate alternatives
Disadvantages:
1- It cannot be applied for batch processes (a similar
approach has been presented for batch processes by
O. Irribarren and M.F. Malone, 1985 )
2- It cannot be applied for solid or heavy polymer
process with no vapor – liquid equilibrium
