Process Plant Design –Assignment (10%)
Process Plant Design:
1. Assignment mark: 100 marks, Total Assessment = 10%
2. Submission method: e-file (compiled in pdf format) and UNISIM simulation file, via TIMeS
3. Submission due date: 19 June 2020 (Friday), latest by 5pm.
4. Reports addressing the case study should be typed and 1.5 spaced; font: Arial, size 12
5. Reports will be graded on organization, style, and grammar as well as content.
Mass and Energy Balance
A styrene (S) production plant is producing S by converting ethylenebenzene (EB) in the catalytic
dehydrogenation reactor. The simplified process flow diagram of the styrene production plant is given
in Figure 1.
H2
25°C
EB
25°C
560°C
QA
D
C
EB
25°C
25°C
E
A
B
G
600°C
F
EB
500°C
EB, S
25°C
H2O
25°C
H2O
700°C
S
25°C
QB
Figure 1. Simplified process flow diagram of styrene production
Process description
Fresh EB and recycled EB are combined and heated from 25°C to 500°C in the EB preheater (A). The
heated EB is then mixed adiabatically with steam at 700°C at point (B) to produce the feed to the reactor
(C) at 600°C. The steam is used to suppress the undesired side reactions and removes carbon
deposited on the catalyst surface. The single pass conversion at reactor (C) is 35%, and products leave
the reactor (C) at 560°C. Then, the product stream is cooled in a condenser (D), condensing essentially
all the water, EB and styrene, while allowing hydrogen to pass out as a recoverable by-product of the
process.
Process Plant Design –Assignment (10%)
The water and hydrocarbon liquid are immiscible and separated in the decanter (E). The water
is vaporized and heated in the steam generator (F) to produce steam that mixes with EB feed to the
reactor. The hydrocarbon stream that leave the decanter (E) is then sent to distillation column (series
of distillation columns) (G) to separate the mixture into pure S and EB at 25°C after cooling and
condensation of the streams. The EB is recycled back to the reactor (C), while S is withdrawn as the
product.
The reaction of converting EB to S is given in Eq. 1.
C8H10 (g)  C8H8 (g) + H2
i.
̂𝑟° (600°C) = + 124.5 kJ/mol
∆𝐻
(Eq. 1)
Analyze the process and calculate on the basis of 155 kg/h styrene produced the required fresh
ethylenebenzene feed rate, the flow rate of the recycled ethylenebenzene, and the circulation
rate of the water, all in mol/h and kg/h. (Assume P = 1 atm)
ii.
Calculated the required rates of heat input or withdrawal in kJ/h for EB preheater (A), steam
generator (F) and reactor (C). Physical property of EB and S are given in Table 1.
Component
Ethyelenebenzene
Styrene
iii.
Table 1. Physical property data of ethylenebenzene and styrene
̂𝑣 (kJ/mol)
Cp, liquid (J/mol °C)
Cp, vapor (J/mol °C)
∆𝐻
118 + 0.3T(°C)
182
36 @ 136°C
115 + 0.27T(°C)
209
37.1 @ 145°C
Simulate this case study in UNISIM, compare the simulation result with the manual calculation
in part i. and ii. Analysis the results and justify the percentage error for each of the answer.
Tabulate the result in the sample table shown in Table 2:
Table 2. Sample of results
Parameter (unit) Manual calculation
Fresh EB feed …….kg/h
(kg/h)
QA (kJ/h)
….kW
UNISIM simulation
…….kg/h
Percentage error (%)
…….%
….kW
….%