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Unformatted text preview: International Journal of Food Science and Technology (1987) 22, 209-218 Improved heat exchanger networks for energy conservation in palm oil refineries R. M . WOOD$ AND M . HASAN* Summary In designing a network of heat exchangers for the recovery of waste heat, there is usually a pinch at which the minimum approach temperature difference limits energy recovery. Pinch technology emphasizes the importance of utility targets, which are independent of the network design, and so allow a very useful comparison with the utility requirements of actual networks. The design of a heat recovery network of exchangers used in palm oil refining has been examined using such pinch technology targeting procedures. The network was found to be well designed for the situation where steam is a cheaper utility than hot oil. As this was not the case, improved networks were designed. These allowed a significant reduction in heat exchanger surface area for the same energy consumption, or a 25% reduction in energy consump- tion for a modest increase in network area of about 10%. Keywords Energy conservation, heat exchanger network design, palm oil refining, utility targets. Introduction In the last decade much attention has been focused on the need to reduce manufacturing costs by improvements in energy conservation. This is also urgent in the processing of natural products such as palm oil, and Wong (1985) outlines various means by which energy consumption may be reduced. Some of these measures are good house- keeping, in that process steam requirements (as stripping steam or supplied to ejectors to maintain vacuum) should be minimized. However, very significant energy savings have also been achieved by the development of systematic procedures for the design of heat exchanger networks, which recover waste heat from process streams. These advances (Hohman, 1971; Linnhoff & Flower, 1978; Umeda, Itoh & Shiroko, 1978; Boland & Linnhoff, 1979) emphasize the need to set targets for the minimum energy flows exchanged with utilities and the minimum number of exchangers in the network. Appreciation of such targets has undoubtedly led to the design of better networks. The minimum utilities target can be obtained from the composite curves in which temperature is plotted against enthalpy flow rate. As explained by Linnhoff et al. (1982), two curves are constructed: one for all streams that require cooling (the so-called hot streams such as reactor or distillation column products, flows to con- densers, etc.) and the other for all cold streams (reactor or distillation column feeds, Authors addresses: School of Chemical Engineering and Industrial Chemistry, University of New South Wales, Kensington, NSW 2033, Australia and *Department of Chemical Engineering, University of Malaya, 59100 Kuala Lumpur, Malaysia....
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This note was uploaded on 01/28/2011 for the course CHE 160 taught by Professor Blanche during the Spring '10 term at University of California, Berkeley.
- Spring '10