(445b) A Simultaneous Optimization Approach for Synthesizing Integrated Water- Allocation and Heat-Exchange Networks

A systematic design methodology has been developed in this work for simultaneously optimizing integrated water-allocation and heat-exchange networks (WAHEN) in the chemical processes. The state-space superstructure (Bagajewicz et al., 1998) has been modified in the present study to formulate a holistic MINLP model for one-step optimization of WAHEN with multi-contaminant water streams. Notice that the state-space representation is adopted mainly to capture the structural characteristics of the integrated water and energy system. In particular, the added design options of mixing/splitting process flows can be easily incorporated in the distribution network of the proposed superstructure. Furthermore, the optimal water-reuse policy as well as wastewater-treatment strategy in a chemical plant can be generated within the same framework, and the benefits of installing indirect and/or direct heat exchangers, i.e., mixers, can also be evaluated by including proper cost models in the objective function of the MINLP program. A three-stage search strategy has been developed to solve the aforementioned mathematical programming model. The solution quality and efficiency are guaranteed with a combination of stochastic initialization, deterministic optimization, and artificial evolution procedures. Three examples are presented in this paper to demonstrate the validity and advantages of the proposed approach. In the application studies we have carried out so far, it can be clearly observed that the WAHEN designs obtained in this study are indeed superior to those produced with the conventional procedures.

Reference: Bagajewicz, M., Pham, R., Manousiouthakis, V., ?On the State Space Approach to Mass/Heat Exchanger Network Design,? Chem. Eng. Sci. 53, 2595 (1998).