Thermodynamic Analysis And Optimization Of A CCHP System Based On PEMFC

The combined cooling,heating and power（CCHP）system base on PEMFC is a new energy supply system,which uses biomass gasification syngas as fuel,proton exchange membrane fuel cell as main body,and single-effect absorption refrigeration as auxiliary.The global biomass energy reserves are huge,with the characteristics of scattered resources and low energy conversion efficiency by power generation via direct combustion.Biomass gasification is one of the important technologies for efficient utilization of biomass energy,which greatly improves the energy density and fuel adaptability of solid biomass.Proton exchange membrane fuel cell（PEMFC）is a kind of clean and efficient power generation device whose efficiency is not sensitive to the power scale,which makes it more suitable for the biomass gasification technology with characteristics of small scale,scattered distribution and could potentially improve the efficiency of small and medium-sized biomass gasification technology.In addition,utilizing the waste heat generated by fuel cell operation for refrigeration can improve the economic performance of the system.Therefore,this new system has a great development prospect.The main purpose of this paper is to analyze the operation characteristics of the CCHP system base on PEMFC is a new energy supply system and optimize its operating conditions.The main contributions are:（1）Various modes and applications of cogeneration system based on fuel cell and biomass gasification were analyzed,and the advantages and disadvantages of their operation were compared.Based on the analysis of the existing cogeneration modes,a novel layout of CCHP systems based on PEMFC was proposed.（2）Based on the Engineering Equation Solver（EES）platform,the thermodynamic simulation model of the CCHP system base on PEMFC was established.Based on the principles of mass conservation,energy conservation and thermodynamic characteristic,the thermodynamic model of PEMFC was established considering the three major polarization losses.The thermodynamic model of biomass gasifier was established by thermodynamic equilibrium model.According to the working principle and the law of conservation of mass and energy,the thermodynamic model of other auxiliary parts was established,and finally the thermodynamic model of the whole system was obtained.（3）Using the established thermodynamic model,the energy efficiency,output power and cooling capacity under a given working condition were analyzed,the effects of key operating parameters on system performance were studied.The results show that CCHP is the best operating mode in terms of energy efficiency and CO₂ emission index of wood gasification,its energy efficiency is 57.41%and CO₂emission index is 0.516 t/MWh.（4）Based on exergy analysis theory and exergoeconomic theory,the exergy and exergoeconomic model of the system was established.Exergy destructions,exergy efficiency of major components and exergy efficiency of the system as a whole were obtained.It was found that exergy destructions of the system mainly occurred in the biomass gasifier and PEMFC stack,so it should be optimized and transformed first.In addition,the influences of key operating parameters of the system on exergy efficiency and economic performance were studied;Finally,based on the results of exergy and exergoeconomic analyses,genetic algorithm was used to optimize the system performance,and the optimal operating conditions of the system were found.