Simultaneous optimization of multi-plant heat integration using intermediate fluid circles

Multi-plant heat integration can be carried out indirectly through intermediate fluids like steam, thermal oil and hot water. Current researches mainly focus on heat recovery aspect and some important factors are not holistically considered, for instance, the parameters of intermediate fluid, interconnectivity patterns between plants and the detailed configurations of multi-plant heat exchanger networks (HENs). To overcome the limitation mentioned above, this paper presents a simultaneous optimization methodology for multi-plant heat integration using intermediate fluid circles. Given an industrial zone and the data for all the hot and cold process streams in each individual plant, the better design with lower TAC including energy cost, heat exchanger cost, piping and pumping cost can be found by using this methodology. From the results of case study, in the industrial scale problem (5 plants), the cost of piping and pumping account for 12% of total cost, proving that these distance related factors cannot be ignored. Compared with literature results, this method can obtain same energy savings with lower number of heat exchangers and intermediate fluid circles. •A new MINLP model is established for multi-plant heat integration.•Both interplant integration and intra-plant integration are considered simultaneously.•The interconnectivity patterns between plants and the relative piping cost and pumping cost are considered.•Parameters of intermediate fluid are optimized.•More economic and practical design can be obtained through the proposed method.