Page 147 - Chemical engineering design

Below pinch
9. CP hot ½ CP cold FUNDAMENTALS OF ENERGY BALANCES 127
10. Note that stream 4 starts at the pinch temperature so can not provide any cooling
below the pinch.
11. Cannot match stream 1 or 2 with stream 3 at the pinch.
12. So, split stream 3 to reduce CP. An even split will allow both streams 1 and 2 to
be matched with the split streams adjacent to the pinch, so try this:
13. Check the heat available from bringing the hot streams from the pinch temperature
to their target temperatures.
stream 1 H D 40.0 100 40 D 2400 kW
stream 2 H D 30.0 100 60 D 1200 kW
14. Check the heat required to bring the cold streams from their source temperatures
to the pinch temperature:
stream 3 H D 60.0 80 30 D 3000 kW
stream 4 is at the pinch temperature.
Ž
15. Note that stream 1 can not be brought to its target temperature of 40 Cbyfull
Ž
interchange with stream 3 as the source temperature of stream 3 is 30 C, so T min
would be violated. So transfer 1800 kW to one leg of the split stream 3.
16. Check temperature at exit of this exchanger:
1800
Ž
Temp out D 100 D 55 C, satisfactory
40
17. Provide cooler on stream 1 to bring it to its target temperature, cooling needed:
H cold D 2400 1800 D 600 kW
18. Transfer the full heat load from stream 2 to second leg of stream 3; this satisfies
both streams.

Note that the heating and cooling loads, 2900 kW and 600 kW, respectively, match
those predicted from the problem table.

3.18. REFERENCES

BARLOW, J. A. (1975) Inst. Mech. Eng. Conference on Energy Recovery in the Process Industries, London.
Energy recovery in a petro-chemical plant: advantages and disadvantages.
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BLOCH,H. P., CAMERON,J.A., DANOWSKY,F. M., JAMES,R., SWEARINGEN,J. S. and WEIGHTMAN,M. E.
(1982) Compressors and Expanders: Selection and Applications for the Process Industries (Dekker).
BOLAND,D. and LINNHOFF, B. (1979) Chem. Engr, London No. 343 (April) 222. The preliminary design of
networks for heat exchangers by systematic methods.
BUSE, F. (1981) Chem. Eng., NY 88 (Jan 26th) 113. Using centrifugal pumps as hydraulic turbines.
CHADA, N. (1984) Chem. Eng., NY 91 (July 23rd) 57. Use of hydraulic turbines to recover energy.
DOUGLAS, J. M. (1988) Conceptual Design of Chemical Processes (McGraw-Hill).
DRYDEN, I. (ed.) (1975) The Efficient Use of Energy (IPC Science and Technology Press).
DUNN,K.S. and TOMKINS, A. G. (1975) Inst. Mech. Eng. Conference on Energy Recovery in the Process Indus-
tries, London. Waste heat recovery from the incineration of process wastes.
DUNN,R. F.and EL-HALWAGI, M. M. (2003) J. Chem. Technol. Biotechol. 78, 1011. Process integration
technology review: background and applications in the chemical process industry.
EDMISTER, W. C. (1948) Pet. Ref. 27 (Nov.) 129 (609). Applications of thermodynamics to hydrocarbon
processing, part XIII heat capacities.