Research On Heat Exchanger Network Synthesis Strategy Based On Entransy Theory And Its Application

Heat exchanger network synthesis is an important part of the process system engineering.It is of great significance to save energy and improve energy efficiency in the process industry with high energy consumption.In order to solve the problem of heat exchanger network synthesis,the pinch analysis method can determine the energy saving target of the heat exchanger networks(HENs),and the HENs to achieve the maximum heat recovery goal,but it can not determine the thermal efficiency of the HENs.Entropy analysis method and exergy analysis method can calculate the thermal efficiency of the HENs,but can not get the matching relation.It is of great scientific significance to propose a heat exchanger network synthesis strategy,based on the thermal efficiency optimization goal,to guide the synthesis of heat exchanger network,and to maximize the energy recovery.The irreversibility of HENs results in the existence of entransy dissipation.Firstly,the heat transfer state diagram based on entransy theory is discussed,and the temperature-heat flow diagram is determined.Then,the relationship between the cold and hot utility entransy,entransy dissipation,entransy recovery,and the method of determining the energy target of the HENs based on entransy theory is proposed.Then the heat exchanger network synthesis problem based on entransy theory is analyzed.The four matching criterion of HENs based on entransy theory is proposed,including entransy conservation criterion,minimum entransy dissipation criterion,minimum heat transfer temperature differences criterion,and the thermal potential energy transfer irreversibility criterion.The HENs with the highest entransy transfer efficiency is obtained by the method of determining the energy target and the matching criterion.Thus,a complete heat exchanger network synthesis strategy based on entransy theory is formed.In order to verify the correctness of the heat exchanger network synthesis strategy based on entransy theory,the energy saving of the HENs is studied based on the diesel hydrogenation unit and the gasoline adsorption desulfurization unit.The diesel hydrogenation unit requires 8.543×106 kW·K of hot utility entransy and 7.428×106 kW·K of cold utility entransy.Using the heat exchange network synthesis strategy based on entransy theory,the highest entransy transfer efficiency of HEN is consistent with energy targets is obtained.Saving 47.72 % of hot utility and 41.19 % of cold utility,the entransy transfer efficiency increased from 69.77% to 92.29%,and the investment recovery period is 0.71 years.The gasoline adsorption desulfurization unit requires 8.196×105 kW·K of hot utility entransy and 5.506×105 kW·K of cold utility entransy.Based on the heat exchanger network synthesis strategy of entransy theory,the highest entransy transfer efficiency of HEN which is consistent with energy targets is obtained.Saving 75.75% of hot utility and 71.60 % of cold utility,the entransy transfer efficiency increased from 77.63 % to 91.07 %,and the investment recovery period is 0.38 years.The results verify the correctness of the heat exchanger network synthesis strategy based on entransy theory.Through the research of the two units,the HEN is consistent with energy target is obtained,and the universality of the strategy is proved.Therefore,this strategy can improve the actual industrial production of energy-saving effect,to achieve the effective use of energy.