Study On Mechanism Of Energy Efficiency Upgrading And Methods Under Active Operating Strategies In CCHP Systems

The off-design conditions of the combined cooling,heating and power(CCHP)system accounts for a bulk of the operation periods.The appropriate operation strategy is an essential requirement to provide high-efficiency,economic feasibility as well as environmental-friendly performance,for its feature to improve the match between energy demand and supply.Based on the National Basic Research Program of China(973 Program)"Study on Mechanism of energy efficiency upgrading and Rules of Exergy Cost in Energy System",the research of this dissertation mainly focuses on the active operating strategy of the system.This study is carried out from the aspects of energy efficiency upgrading mechanism of key components,the match between energy demand and supply and experimental verification.Through the exergy analysis based on the analysis of the second law of thermodynamics,the irreversibility in each component is presented to show the feasible ways to improve system performance.An energy level difference graphic analysis method that describes the variation of the driving force for a thermodynamic process is proposed.This method is based on the average energy level difference,in which the irreversibility among energy transfer and conversion processes especially for off-design conditions is presented.The analysis is elucidated to lay the foundation for the selection of the system operating strategies.Based on the energy level difference graphic method,the common thermodynamic processes including heat transfer process,compression process and mixing process are analyzed in order to verify the feasibility of the new method.Moreover,the graphic analysis using this method is conducted on a CCHP system under the design conditions.Different from the traditional operating strategy,the more high-temperature flue gas is generated under the inlet air throttling(IAT)and flue gas reinj ecting(FGR+TIT)operating strategies in part-load conditions improving the performance of waste heat recovery.Energy level difference graphic analysis method is introduced to evaluate the off-design performance of the CCHP system with the different system operating strategies.The results show that the improved off-design performance of the gas turbine under the IAT operating strategy is presented.However,increasing the energy level difference are main driving forces to increase the exergy destruction result in poor thermodynamic performances of the main components contained in the absorption chiller.Maybe the energy level difference of the heat transfer can be reduced by applying a heat-driven cooling and power cogeneration in the CCHP system.Moreover,the adjustable range of output ratio of cooling energy and power is enlarged that is flexible to meet the customers’ variable requirements.An appropriate operation strategy is the requirement to obtain high-efficiency performance of a CCHP system.The off-design performance is evaluated with the IAT operating strategy combined with different operation strategies and the emphasis is placed on the analysis of the match between energy demand and supply based on typical reference building to reveal the energy saving mechanism.The results indicate that the following electric load operation strategy is found to have better off-design performance especial in hot summer and cold winter.Because too much electricity and heat from the electric grid and the boiler,respectively,the poor off-design performance is presented under the following hybrid load operation strategy although the excess electricity and heat are avoided.To maintain advantages of different operating strategies,the mix operating strategy(TIT+IAT)is proposed in this study.The operating strategy is readjusted continuously base to accommodate changing users load demands.Moreover,combined with the economic analysis,the thermodynamic analysis of the CCHP system is extended from the exergy to the exergoeconomic analysis.Compared with the TIT operating strategy,the cost of the energy products are decreased distinctly under IAT operating strategy,which increases the operation profit of the energy system.An experimental platform for system operating strategy has been designed and built.The main body of the experimental platform consists of a micro-gas turbine and a compressor inlet throttle device.The design output power and electric efficiency of the micro-gas turbine are 65 kW and 29%,respectively.The load level(100-50%)of the micro-gas turbine is controlled by the IAT operating strategy.The auxiliary experimental subsystem are the data collection and management subsystem,the cooling water circular subsystem,the hot-water exchanger,the natural gas boosting subsystem and the safety protection subsystem.The experimental studies on the off-design performance of the distributed energy system under different operating strategies are conducted.The experimental results verify the feasibility of the IAT operating strategy and lay the foundation for further work on the active operating strategy of the distributed energy system.