Simultaneous design of heat integrated water allocation networks considering all possible splitters and mixers

Abstract Heat integrated water allocation networks (HIWAN) can be recognized as a nexus between water and energy within the process industry. Water and energy are so tightly related in this kind of networks that water saving options may cause more energy consumption or vice versa. Various mathematical programming methods have been proposed to simultaneous optimize HIWAN. However, this problem is believed to be difficult to solve. Compared to the traditional HEN, the direct heat transfer of stream mixing is more flexible in this problem and the actual number of heat exchangers can be much smaller than the traditional HEN. This paper takes advantage of these two features to build up a novel superstructure to simultaneously design HIWAN. Stream splitters and mixers are considered for every water-using operations and heat exchange units, so that possibilities of stream mixing can be fully explored and there are more series and parallel modes between heat exchangers than that of stage-wise superstructure. The proposed model is solved under given different number of heat exchange units. A small to large iteration strategy is introduced to find the best solutions. Applying this proposed approach, the better results are obtained in large-scale problems compared with the previous papers.