COST OPTIMUM HEAT EXCHANGER NETWORKS-l. MINIMUM ENERGY AND CAPITAL USING SIMPLE MODELS FOR CAPITAL COST

An important feature of heat exchanger network design is the energy-capital tradeoff. This tradeoff has been regarded as complex due to the number of structural network alternatives usually available, each being subject to continuous optimization. Current procedures tend to first identify minimum energy networks. The total cost (capital and energy) can then be improved by evolution and continuous optimization. The disadvantages of this approach is that optimality is local to the structures examined. Alternatively, mathematical programming can be used but user interaction with the solution is more complicated and generally performed at higher levels in the problem formulation rather than in the design. Until now no generalized techniques have been introduced for the prediction of global optimum cost networks which allow user interaction with the network structure. This paper presents a simple methodoIogy for the design of near-optimal heat exchanger networks which systematically takes account of the energy-capital tradeoff. The method is based on setting cost targets, and optimizing these targets prior to design. It is shown how networks can be developed which are typicalty within 5% of the optimized total cost target. This allows inappropriate design structures to be avoided in design. This part (Part 1) of the paper introduces methods based on simple models for capital cost.