Thermodynamic Analysis Of Absorption Refrigeration In CCHP

CCHP(Combined cooling heating and power)system integrated the cogeneration and absorption refrigeration technology,so that the thermal power plant can supply cold energy while supplying power and heating,which can significantly improve the comprehensive utilization rate of energy.There are three key issues involved in the application.First,which cooling method should be selected when the distance between the refrigeration station and the thermal power plant is different in CCHP system.Second is which absorption cooling type should be selected to match the waste heat at different temperatures in the thermal power plant.Third is what kind of thermodynamic mechanism exists between the heat transfer process and the mass transfer process in the absorption refrigeration cycle.Firstly,the heat transfer and conversion process in CHP(Combined heating and power)system were analyzed in thermodynamic,and the specific expressions and corresponding definitions of the energy saving effect of CHP system.Second,based on the actual situation of the difference between the cooling station and the thermal power plant in CCHP system,the absorption refrigeration and electric compression refrigeration in CCHP system were respectively carried out for efficiency,unit cooling capacity,economic cost and energy comprehensive utilization efficiency,the comparative study provides a basis for judging the selection of better cooling methods for CCHP system.Then according to the fact that there are high and low grade heat sources in the thermal power plant,some typical thermal matching problems about absorption refrigeration in CCHP syetems were investigated,the best type of absorption refrigeration cycle suitable for waste heat recovery of thermal power plant is determined simultaneously.Finally,based on the generalized Carnot's theorem,the coupling thermodynamic analysis has been done on the thermo-wet crossover phenomenon between heat transfer process and mass transfer processes in absorption refrigeration cycle,revealing the energy conversion mechanism contained in the refrigeration cycle.The results show that when the distance between the refrigeration station and the thermal power plant is less than 5km,the energy comprehensive utilization rate and the refrigeration efficiency of the absorption refrigeration system are higher.Whenthe distance is from 5km to 9.2km,the comprehensive utilization efficiency of energy in the system with absorption refrigeration is high but the refrigeration efficiency is low.The economic cost per unit cooling capacity of absorption refrigeration is higher than the maximum distance of voltage contraction refrigeration,which is affected by the steam heat price and electricity price.Single effect absorption refrigeration is suitable for low temperature hot water waste heat recovery,double effect absorption refrigeration is suitable for high temperature flue gas waste heat recovery,coupled absorption refrigeration is suitable for waste heat recovery with two kinds of heat sources.The series process is easy to produce positive pressure in the mixed effect absorption refrigeration system,which is not conducive to the normal operation of the system.The parallel process does not cause positive pressure operation,which is more suitable for the application in the CCHP system.The system of absorber,generator,condenser and evaporator in absorption refrigeration cycle can be regarded as an isolated system composed of heat transfer process and mass transfer process.The energy conversion between heat transfer process and mass transfer process conforms to the generalized Carnot theorem,the spontaneous process with positive dissipation rate drives the non spontaneous process with negative dissipation rate.In this paper,the thermal economy,thermal matching and thermal mass crossover of absorption refrigeration in CCHP system are analyzed,which are of theoretical guiding significance for the selection of better refrigeration mode,the determination of the best absorption refrigeration type and the improvement of absorption refrigeration performance in CCHP system,thereby improving the waste heat recovery efficiency of CCHP system.