Study On System Integration Of Power/cooling Cogeneration Cycles Driven By Mid-and Low-temperature Waste Heat

With the increasing demand for energy consumption and the serious environmental pollution in our country,efficient recovery of industry and household waste heat has become an essentially important resort in energy saving and emission reduction.Based on the National Basic Research Program of China(973 Program),National Natural Science Foundation of China,National Science and Technology Support Program,the research of this dissertation mainly focuses on the power/cooling cogeneration cycles driven by mid-and low-temperature waste heat.This research was carried out from the aspects of energy conversion mechanism of key processes,system integration and experimental verification.In the power/cooling cogeneration cycles,the thermal compression process composed of absorption and generation sub-processes is a key process for the cascade utilization of waste heat,especially for the low-temperature portion.After making a comprehensive analysis of the thermal compression process,a model characterized by boost pressure ratio was proposed.As a dimensionless parameter,the boost pressure ratio represents the ratio of the practical pressure rise to the ultimate pressure rise in the thermal compression process.The energy conversion mechanism of low-temperature waste heat and thermodynamic principles of performance in the thermal compression process were studied,and results show that the boost pressure ratio can be used as a key parameter to simplify the design and optimization of the thermal compression process.Based on the model,the integration pattern of the thermal compression process in the power/cooling cogeneration cycles was presented.The thermodynamic performances and characteristics of the coupling between thermal and mechanical processes were elucidated to lay the foundation for the system integration of power/cooling cogeneration cycles.Both the heat and mechanical work can be coupled between the power and cooling generation cycles by combining the thermal compression process and the mechanical compressor.Then,a new power and refrigeration cogeneration system for hybrid utilization of mid-and low-temperature waste heat was proposed.The mid-temperature waste heat is converted into mechanical work through the power generation subcycle with non-azeotropic mixture working fluid,while the low-temperature waste heat is utilized to drive the thermal compression process,which is coupled with mechanical compressor for refrigeration.The power consumption of the mechanical compressor is satisfied by partial power output of the turbine.The system can not only recover the waste heat from the combustion engine flue gas efficiently and solve the problem of temperature fault in the heat utilization of engines'exhaust gas,but also recover the waste heat of the jacket water to produce cooling energy below 0?.The proposed system uses different recovery modes for different heat sources to reduce the irreversible loss effectively and reach a high thermodynamic performance.Economic analysis results show that the system has good economic benefits and promotional value.A new open-style power and refrigeration cogeneration system was studied,focusing on the recovery of the active ingredient in the turbine exhaust vapor,and the method to improve the recovery potential of the active ingredient was also explored.The higher-temperature condensation heat carried by the turbine exhaust vapor is used to provide heat load in the reboiler for distillation process,while the lower-temperature portion is to preheat the feed to the distillation column.In the gas-liquid mixture after partial condensation,the active ingredient(refrigerant)concentration in the gas component increases a lot and is suitable to be recovered in the refrigeration cycle.The cogeneration system validates the beneficial effects of chemical exergy coupling,and provides a new idea for the coupling of power and cooling generation cycles.Based on the cascade utilization mechanism of mid-and low-temperature waste heat,the high-grade heat is converted into mechanical work,while the low-grade heat is used to boost the pressure of the gaseous working fluid within a thermal compression process.Two low-temperature refrigeration systems driven by waste heat were proposed and investigated,in which the thermal compression process is integrated with a mechanical compressor powered by the mechanical work converted from the high-grade heat.The two systems adopted cascade and hybrid styles,respectively,for the coupling of the thermal and mechanical compression processes.It was found that the hybrid low-temperature refrigeration system has better thermal performance.The results of the energy-saving mechanism analysis show that the mechanical compression process in the refrigeration subcycle can ensure the high performance of the thermal compression process when the evaporation temperature is very low.At the same time,the power generation subcycle using mixture as working fluid decreases the temperature difference between the heat source and working fluid,which achieves the cascade utilization of the waste heat and reduces exergy destructions.In addition,sensitive analysis was conducted to provide guidance for the system design and optimization.An experimental platform for power and refrigeration cogeneration system driven by waste heat has been designed and built.The main body of the experimental platform consists of ammonia-water vapor generation subsystem,power generation subsystem and ammonia-water absorption refrigeration subsystem.Under the design condition,the expected power and cooling output of the system are 20 kW and 40 kW,respectively.The auxiliary experimental subsystems are the flue gas generation subsystem,the cooling output subsystem,the cooling water circulation subsystem,the data monitoring and acquisition subsystem and the safety protection subsystem.The experimental study on the performances of the power generation subsystem using ammonia water as working fluid and ammonia-water refrigeration subsystem were conducted.Results show that the subsystems can operate well and lay the foundation for further study on the cogeneration mode and operation under off-design conditions.