| Heat-driven refrigeration cycel or heat-driven heat pump cylcle is one kind of efficient and enegy saving thermal cycle using heat as the driving energy. Li-Br absorption cycle is a common realization among these heat-driven cycles. Waste heat from the sewage water can be utilized by applying Li-Br absorption refrigeration system to the sewage source heat pump system to improve the energy efficiency. However, constrained by the characteristics of the lithium bromide solution working pair, when temperature of the low-grade heat source is too low, the value of the system deflation ratio will be negative and the refrigeration cycle could not be realized. For the purpose to solve this problem, a kind of double-effect-double-absorption Li-Br sewage source heat pump(SSHP) system is proposed in this research. On the basis of the normal double-effect system, one absorption-evaporation champer is add to the addressed system to satisfy the heat supplying demand and efficiency with the low evaporating temperature.This research conducted the in-depth research on the double-effect-doubleabsorption SSHP(Sewage Source Heat Pump) system from the five aspects of system configuration analysis, mathematical model construction, applicable conditions, system optimizaion design, and the operation in variable conditions.This research starts from the system configuration, according to the solution loops inside this system, 16 kinds of double-effect-double-absorption SSHP system are constructed. By analyzing the feasibility and practicality, one type with the generator in series and absorber in parallel is screened as the focus of our study. The concepts of solution equivalnet latent heat of vaporizaiton is addressed, which is used to verify the empirical estimated thermal coefficient of our system.For the preliminary design and the parameters analysis of this system, the mathematical models of the double-effect-double-absorption SSHP system are built. By solving the mathematical model, further analysis is conducted on the low pressure generator and the absorption-evaporation champer, which are the self energy balance components of the system, the results shows that the low pressure generatir tube condensing tempeature and the absorption-evaporation champer tube evaporation tempearture have great influence on the other parameters in this system. Meanwhile, the comparision with double-effect system on operation heat source analysis shows that this system can reduce the evaporating temperature by 20℃, and enhance the condensing temperature by10℃,and the feasibility of this system under the demand heat source condition can be confirmed.With the confriming of the evaluation index, the optimization based on the genetic algorithm is conducted on the design of this system. During the process of the optimization, the selection method of the optimization variables and the constraints are provided. Meanwhile, the object function is determined taking the economic and technical characteristics into account combining the initial cost and the COPh, which is called heat supply unit cost. The local one-parameter optimization approach is also used to verify the results of global optimization.Finally, with analysis of operating characteristics under varying operating conditions of the double-effect-double-absorption SSHP system, the variation trend diagram of the system parameters are drawn. Results of the analysis shows that the sewage water temperature and solution flow distribution ratio within the system are important factors affecting the performance of the system.The research studys and discusses the binding mode of lithium bromide heat pump system and sewage source heat pump system, which is the theoretical guidance to engineering design or debugging for the practical system. |
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