Efficient Solution Strategy for Stage-wise MINLP Model of Interplant Heat Integration using Heat Recovery Loop

Abstract

Interplant Heat Integration using Heat Recovery Loop (HRL) is very different from intra-plant Heat Integration. As the heat sources and sinks are always separated in different regions, some additional factors should be focused on, i.e. capital cost of heat exchangers, installation cost of pumps and pipelines for long distance, and operation cost of pumping power and heat loss during the transportation. Based on economic criteria, this paper presents a stage-wise MINLP model for HRL designs considering the factors aforementioned. Unlike traditional heat exchanger networks (HENS), the flow rate of intermediate-fluid is considered as an important variable which results in a large complex, non-convex model. An efficient strategy is proposed for the problem by sequentially solving an MILP, an MINLP and a NLP. The distance plays a significant role in the design of HRL and it significantly affects the investment of pipelines. The optimum results show that the influence of pumps is relatively less. An industry case study is demonstrated to illustrate the efficiency of the strategy.