Heat Exchanger Network Synthesis For Batch Processes Based On TAM And TSM

The significant flexibility of batch processes makes them more accommodating to the market requirement. As people’s demands for small-batch and high value-added chemicals are increasing, batch processes gain rapid development in recent years and accounts for almost half of the processes in chemical industry as result. However, there are still very limit studies about the synthesis of heat exchanger networks (HEN) for batch processes, compared with their continuous counterparts. Thus in this paper, the improved time average model (TAM) and improved time slice model (TSM) are proposed and investigated for batch processes, the major contents are as following:(1) Considering the low utility cost obtained by TAM is achieved at the expense of sacrificing equipment cost, the improved TAM is proposed to reduce the equipment cost in this paper. How to choose the number of heat storages is studied firstly, then the method used for structure optimization after adding heat storages is proposed and a mathematic model is built to determine the optimum temperature of heat storages. At last, two examples are illustrated to verify that the equipment cost can be reduced with the improved TAM.(2) Considering time interval division in TSM will limit the heat exchange between intervals, with generating a high utility cost as result, two improved TSMs are proposed to reduce the utility cost. The iterative approach and the graphical approach are proposed to decide the temperatures of heat storages in the first improved TSM. The two approaches are combined for the sake of simplifying the synthesis process. While in the second improved TSM, two rule used to determine the temperatures of heat storages above and below pinch are proposed firstly, then the time intervals, which can be matched based on the temperature of heat storages, are found out for the network synthesis. Results of two examples have shown the effectiveness of the two improved TSM.(3) At last, the two proposed models are compared and analyzed. It shows that the improved TAM is able to recovery more heat than the improved TSM as there is time limit in the latter model. However, the networks obtained by the improved TSM show better stability, because there are fewer storages involved. Then two examples are used to verify conclusions.