Study On Mechanism Of Energy Level Upgrading In Absorption Heat Transformer And System Integration

In the field of distributed energy and industrial energy,the absorption heat transformer(AHT)is a useful tool to solve the problem that the low-temperature heat is difficult to be utilized,for its feature to upgrade the energy level of low-grade heat.Research in this dissertation has focused on the mechanism of temperature lift in the absorption heat transformer for energy recycle and reuse and the method of energy system integration.On the basis of the concept of energy level,the expressions of solution exergy and solution energy level have been established,which are related to the solution concentration and temperature.The energy level method has been adopted to analyze the changes of temperature and/or solution concentration during the key process in the AHT.By mutual conversion of heat exergy and solution exergy,the mechanism of energy level upgrading has been revealed,providing theoretical basis for the proposal of new absorption cycle and new efficient distributed energy system.Aiming at the inefficient use of recycled energy caused by the poor utilization of low-temperature heat in the AHT,a new combined heat pump transformer(CHPT)has been proposed by coupling the process of evaporation and generation,by combining the absorption heat pump and absorption heat transformer.It can use waste heat at medium temperature to generate useful heat at both levels simultaneously to meet the requirement of different levels of heat in the process,greatly improving the overall efficiency of the waste heat at medium temperature.On the established model of the CHPT,parametric analysis has been performed on the energy ratio,exergy destruction and system exergy efficiency of the CHPT,including the temperatures,the flow rate and the temperature lift.Optimal flow ratio or gross temperature lift exists,corresponding to highest system exergy efficiency.Higher gross temperature lift is at the expense of decreasing energy ratio.An experimental rig of vertical falling-film AHT with useful output heat of 20 kW has been developed.The influence of temperature or flowrate of the heating water,cooling water and heated water on the performance of the experimental AHT has been studied,respectively.To improve the temperature of heating water,to reduce the temperature of cooling water or to reduce the temperature of heated water,can improve system performance within certain range.It is possible to improve the performance of the system by increasing the flowrate of heating water,cooling water or heated water,but the influence of the erosion corrosion on the system life caused by the high-speed liquid flow should be taken into account.The experimental study has been also carried out under the condition of direct steam generation.Under the condition of same heating water temperature or heating water flowrate,AHT cam achieve the similar useful output heat as high-temperature water.A new adjustment method has been proposed and validated to improve the performance of the AHT under off-design condition.AHT has been integrated to three energy recovery systems to upgrade the level of low-temperature heat.Parametric analysis has been performed on the performance of seawater desalination system integrated with AHT using sensible heat from the coastal plant.Performance analysis has been carried out on the steam generation system with AHT using latent heat released from the sterilization process.Energy and exergy analyses have been conducted on the performance of solar assisted absorption heat transformer on seasonal typical days.A combined adjustment method has been proposed to improve the performance of the system under off-design condition.Economic analysis has been performed on the system integrated with the AHT,including the type of low-temperature heat,the fuel cost,the type of fuel and operation time,providing important reference for the wide use of the AHT.In general,AHT is useful to improve economically the energy efficiency.The research in this paper shows that the AHT has a good prospect in the field of distributed energy and industrial energy.