Page 152 - Chemical engineering design

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CHEMICAL ENGINEERING
3.9. Estimate the work required to compress ethylene from 32 MPa to 250 MPa in a
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two-stage reciprocating compressor where the gas is initially at 30 C and leaves
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the intercooler at 30 C. See Example 3.13.
3.10. Determine the pinch temperature and the minimum utility requirements for the
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process set out below. Take the minimum approach temperature as 15 C. Devise
a heat exchanger network to achieve maximum energy recovery.
Stream Type Heat capacity Source Target
Ž
Ž
Ž
number kW/ C Temp. C Temp. C
1 hot 13.5 180 80
2 hot 27.0 135 45
3 cold 53.5 60 100
4 cold 23.5 35 120
3.11. Determine the pinch temperature and the minimum utility requirements for the
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process set out below. Take the minimum approach temperature as 15 C. Devise
a heat exchanger network to achieve maximum energy recovery.
Stream Type Heat capacity Source Target
Ž
Ž
Ž
number kW/ C Temp. C Temp. C
1 hot 10.0 200 80
2 hot 20.0 155 50
3 hot 40.0 90 35
4 cold 30.0 60 100
5 cold 8.0 35 90
3.12. To produce a high purity product two distillation columns are operated in series.
The overhead stream from the first column is the feed to the second column.
The overhead from the second column is the purified product. Both columns are
conventional distillation columns fitted with reboilers and total condensers. The
bottom products are passed to other processing units, which do not form part of this
problem. The feed to the first column passes through a preheater. The condensate
from the second column is passed through a product cooler. The duty for each
stream is summarised below:
No. Stream Type Source Target Duty, kW
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temp. C. temp. C
1 Feed preheater cold 20 50 900
2 First condenser hot 70 60 1350
3 Second condenser hot 65 55 1100
4 First reboiler cold 85 87 1400
5 Second reboiler cold 75 77 900
6 Product cooler hot 55 25 30

Find the minimum utility requirements for this process, for a minimum approach
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temperature of 10 C.
Note: the stream heat capacity is given by dividing the exchanger duty by the
temperature change.