Heat Exchanger Network Synthesis Based On Nonlinear Relationship Between Enthalpy And Temperature

As an important subsystem and energy recovery system in chemical process plants, the result of heat exchanger networks synthesis(HENS) determines the energy consumption and economical efficiency. Therefore, heat exchanger networks synthesis gradually becomes an important research problem. Meanwhile, the existing methods of HENS have limitation and shortcoming which need to be solved further.Sequential and simultaneous are two approaches of HENS. Pinch design method(PDM) is the representative of sequential approaches while mathematical programming method is the representative of simultaneous approaches. By far, the most approaches assume the contact heat capacity flow rate. In fact, the heat capacity flow rate is a function of temperature which can be described by nonlinear relationship between enthalpy and temperature. Based on the nonlinear relationship between enthalpy and temperature, this paper use pinch design method and mathematical programming based on genetic algorithm(GA) to solve HENS, the main research work is listed as follows:1. Based on the nonlinear relationship between enthalpy and temperature, the nonlinear pinch design method is proposed which can calculate the energy target and pinch temperature, two other cases are taken into account which can describe the nonlinear relationship in PDM. This paper analysis the influence of nonlinear stream in heat exchanger network synthesis.2. Based on the stage-superstructure, the mix integer nonlinear programming formulation of HENS is established which consider the nonlinear relationship between enthalpy and temperature. The model removes the isothermal mixing assumption and considers the nonlinear relationship between enthalpy and temperature, these improvements make the model more general. To solve this non-convex and non-continuous model, the genetic algorithm is applied in the formulation.3. On the basis of the existing HENS software system HenDesign, the nonlinear PDM module and nonlinear GA module are developed which enrich the software and offer tools for further research. The detailed functions and operation steps of the software are introduced. The software tests the research results of this paper well.4. Two case studies are analyzed using GA based on the nonlinear relationship between enthalpy and temperature. The optimization result is better and the difference is discussed between the contact heat capacity flow rate and nonlinear relationship in streams. The conclusion is that the nonlinear relationship stream must be taken into account in HENS.