Performance Simulation Study Of Combined Cooling And Freshwater System Driven By Waste Heat Of A Diesel Generator

Island construction is the basis for safeguarding national maritime rights and ensuring the development of marine resources.However,the lack of energy and the low energy efficiency have seriously restricted the construction and development of the island.The combined cooling freshwater and power system combines the advantages of multi-purpose,high efficiency,energy saving and environmental protection.It is one of the effective ways to alleviate the shortage of island energy.And it provides a powerful guarantee for improving China's national defense strength and developing marine resources.Aiming at the energy demand of a residential area in the island,the paper carries out the simulation integrated design of combined cooling and freshwater system driven by the waste heat of diesel generator.The paper also studies the modeling method of each component in the system and builds a system simulation model to calculation and analyze the performance of system.Finally,the control system is designed to ensure the cooling capacity meets the demand.The main research work is as follows:(1)According to the needs of the island users,the preliminary design of the overall scheme of combined cooling and freshwater system driven by the waste heat of diesel generator was completed.Specifically,it includes the selection and power matching of the diesel generator,the double-effect lithium bromide absorption chiller,and the distilled seawater desalination unit.The parameters of the design condition point are determined and the system integration is realized.(2)The establishment and debugging of the diesel generator simulation model was completed.The diesel generator is divided into turbocharger,intercooler,in-cylinder process,diesel engine dynamics,speed governor and generator by modular modeling method.The average model of diesel generator is established.The power generation and smoke exhaust performance of diesel generator can be accurately simulated by debugging.(3)The establishment of the simulation models of the lithium bromide absorption chiller and the distilled seawater desalination unit are completed.According to different heat exchange methods,the components are divided into single-phase heat exchange tube model,immersion boiling heat transfer model,spray heat transfer model,vertical falling film heat transfer model.The volume lumping method is used to establish its lumped parameter model,and the physical process of heat exchanger in the system is accurately simulated.Based on the empirical formulas,the calculation models of thermal properties of flue gas,lithium bromide solution,water and water vapor are established.Finally,the simulation models of the lithium bromide absorption chiller and the distilled seawater desalination unit are established and debugged respectively.(4)With the Matlab/Simulink simulation platform,the simulation model of the combined cooling and freshwater system driven by the waste heat of diesel generator is established.The steady-state simulation calculation shows that the relative error meets the design requirements,and the accuracy and correctness of the model are verified.The dynamic simulation calculation is carried out by adding the load disturbance of diesel generator,and the influence of load disturbance on each component in the system is analyzed.The accuracy of the dynamic model is verified by comparing the changes of system parameters under different diesel generator loads.According to the island environment,the system performance parameters are simulated at different cooling water temperatures.(5)The paper completes the design of control system for chilled water outlet temperature.Based on the principle of “determining freshwater by cooling”,control system uses the method of supplementary flue gas to control the chilled water outlet temperature.The paper presents a feedforward and feedback control strategy to solve the inertial delay problem of the system.Fuzzy control is used to modify the parameters of PID controller in real time.In the end,the simulation calculation and analysis of the control system are carried out,which realizes the temperature control of the chilled water outlet.The efficiency of the control strategy is verified by simulation comparison.