Question bank for process synthesis With Correct Answers

Question bank for process synthesis



Exam 1A
The following flowsheet is for the production of methanol from synthesis gas (Syngas) which is a mixture
of different gases mainly hydrogen and carbon monoxide. Study the flowsheet carefully then answer the
associated questions.

2H2 + CO  CH3OH

,Q1. Choose the correct answer.
1. Heat integration is applied in:
a) HX1
b) HX4
c) FEHE (Feed-Effluent Heat Exchanger)

2. Eliminating difference in composition is done in:
a) C1
b) Reactor
c) All equipment

3. HX3 heats the process stream from 145°C to 155°C, the used utility is medium-pressure
steam (mps, 184°C & 11 bar); why?:
a) The heating requirement is up to 155 °C and a heating utility like mps is sufficient
b) The low pressure steam is not readily available
c) The only reason is that mps doesn’t cost much compared to hps

4. Knowing that the distillate (nearly pure CH3OH) boils at 64.7°C. The reason behind running
the distillation column (C1) at 1 bar is:
a) Inexpensive CW at 25C can be used to condense the distillate
b) To reduce the diameter of the column
c) For safety reasons

5. The manufacture of CH3OH is favoured by high pressure in the reaction operation (107.5 bar),
this can be explained as:
a) To enable product (methanol) removal
b) The reaction involves reduction in the number of molecules from three molecules reactant to
one molecule product and thus will increase yield
c) To reduce the costs

6. Reducing temperature of reaction would results in
a) Reduced energy costs but decreased rate
b) Increased rate
c) Increase energy costs and decreased conversion



Q2. Answer the following
(A) Which equipment in the process performs phase separation only ?
Answer: the flash drum F1

,(B) Which pieces of equipment in the process performs pressure-change operations? Indicate
the difference in pressure across these units (specify two at least).
Answer: 1) K1 --> a gas compressor, diff. in press. = 110-75 bar
2) Valve before distillation column C1, diff. in press. = 1-2 bar
3) K4 --> a compressor of vapor leaving the reflux drum, diff. in press. = 1-110 bar

(C) Specify the “Distribution of Chemicals Step” in the process attached.
Answer: the recycle stream that is mixed with the fresh feed to the process (Syngas).
(D) Specify from the given flowsheet one operation of “Eliminating Difference in Temperature”.
Answer: 1. Reduction of “T” from 175C to 38C in HX4.
2. Raising of “T” from 53C to 145C in FEHE.


(E) How many stream are recycled and mixed with the fresh feed?
Answer: three recycle streams
( vapor from “Sep” + vapor from Flash drum F1 + vapor from reflux drum of column)


Q3. The figure shown below is a basic block diagram for the production of methanol from
carbon monoxide and hydrogen. The available information is:
 Perfect separation between product and raw materials (CO & H2) and recycle of
unreacted raw materials.
 Conversion in reactor is 64%.
 The feed to reactor contains 28,000 kmol H2/h.
 Stoichiometric feed
Calculate the following
a) The fresh feed (FF) to the process in kmol/h
b) The flow rate of the recycle (R) in kmol/h
c) What is the price of methanol that can result in a gross profit of $5/kg methanol if the
prices of all raw material is $4/kg (atomic weight of C=12 , O=16 , H=2)

, Solution:
CO+ 2 H 2 →C H 3 OH
28000
RF , CO= =14000 kmol/h
2

kmol
RP ,CO=R , CO=( 1−0.64 ) × 14000=5,040
h

kmol
RP , H 2=R , H 2= (1−0.64 ) ×28000=10,080
h
kmol
Recycle R=5040+10080=15,120
h
FF , CO+ R , CO=RF , CO
FF , CO+5040=14000
FF , CO=8,960 kmol CO


FF , H 2+ R , H 2=RF , H 2

FF , H 2+ 10,800=28,000

FF , H 2=17,200 kmol H 2




FF=17200+8960=26160 kmol/h




Exam1 B