Indirect heat integration across plants using hot water circles

Total site heat integration (TSHI) provides more opportunities for energy saving in industry clusters. Some design methods including direct integration using process streams and indirect integration using intermediate-fluid circuits, i.e., steam, dowtherms and hot water, have been proposed during last few decades. Indirect heat integration is preferred when the heat sources and sinks are separated in independent plants with rather long distance. This improves energy efficiency by adaption of intermediate fluid circle which acts as a utility provider for plants in a symbiotic network. However, there are some significant factors ignored in conventional TSHI, i.e. the investment of pipeline, cost of pumping and heat loss. These factors simultaneously determine the possibility and performance of heat integration. This work presents a new methodology for indirect heat integration in low temperature range using hot water circuit as intermediate-fluid medium. The new methodology enables the targeting of indirect heat integration across plants considering the factors mentioned earlier. An MINLP model with economic objective is established and solved. The optimization results give the mass flow rate of intermediate-fluid, diameter of pipeline, the temperature of the circuits and the matches of heat exchanger networks (HENS) automatically. Finally, the application of this proposed methodology is illustrated with a case study.

Graphical abstractThe superstructure in the figure includes alternatives for splitting, mixing and bypass of stream, where streams can be mixed non-isothermally to increase the amount of heat recovery with minimal heat transfer area. Heat integration between plants using intermediate-fluid circuits can be seen as heat exchange between cold water and many source streams or one hot water and many cold streams. This superstructure also includes options for series and parallel matching as well as splitting, mixing and bypassing between streams. The procedure is presented for automatic generation of optimal configurations for heat integration across plants.Figure optionsDownload full-size imageDownload as PowerPoint slide