Performance Study Of A Sofc-clc Cogeneration System With Zero Co₂emissions

In recent years,more and more attention is paid to carbon emission reduction due to continuous rising global temperature.In order to deal with the global climate problem,the strategic goal of carbon peaking and carbon neutrality has been put forward by China.It is necessary to explore new ways to reduce carbon emission.Solid Oxide Fuel Cell（SOFC）has the advantages of high energy efficiency,low pollution,no noise and modularity,which is one of the most promising power generation methods in the future.Chemical Looping Combustion（CLC）is favored for its ability to separate CO₂without energy consumption.Based on the high energy efficiency of SOFC and the CO₂zero emission advantage of CLC,an efficient zero CO₂emission SOFC-CLC cogeneration system is constructed according to the energy utilization principle of“temperature matching,cascade utilization”in this thesis.The research on the new system is conducted from the perspectives of thermodynamic performance,economy and multi-objective optimization.The main research contents and conclusions are as follows:Firstly,six different configuration schemes of SOFC,chemical looping technology and gas turbine（GT）are proposed.On the basis of the verification of SOFC and chemical looping models,the simulations of the six schemes are carried out.Through comparative analysis,the SOFC-CLC-GT power generation system with the best comprehensive performance is selected.Simulation results show that the generation efficiency of SOFC-CLC-GT system is improved by 1.31%compared with SOFC-GT system with CO₂capture.Besides,SOFC-CLC-GT system has the highest generation efficiency among all systems with CO₂capture.Secondly,in view of the mismatch in energy utilization caused by the large temperature difference heat transfer between the compressed air stream and the air reactor in the SOFC-CLC-GT system,four flue gas cycle schemes are constructed.Taking power generation efficiency as the main evaluation index,the thermodynamic performances of the four schemes are compared and analyzed.The results indicate that the power generation efficiency of scheme d is the highest.Compared with the basic system,the generation efficiency and exergy efficiency of scheme d are increased by 1.57%and1.52%,respectively.Simultaneously,the impact of flue gas split ratio on the thermal performance of each scheme show the same trend.With increasing flue gas split ratio,the temperature of the air reactor is decreased,and the output voltage,output power and energy efficiency of SOFC is improved,and output power of gas turbines and consumed power of compressors are increased as well as the generation efficiency and exergy efficiency.Thirdly,the scheme d is selected as the top cycle to construct an efficient zero CO₂emission SOFC-CLC cogeneration system,and the heat recovery steam generator and absorption heat pump are used to realize the recovery and utilization of low-temperature heat energy.The thermal characteristics of the new cogeneration system are studied by energy and exergy analysis.The overall generation efficiency is 73.48%,exergy efficiency and thermal efficiency are 74.01%and 91.04%under design condition.In addition,the effects of fuel utilization rate,current density,SOFC operating pressure,SOFC operating temperature and extraction shitter ratio of low-pressure steam turbine on the system performance are studied.With increasing fuel utilization rate,SOFC operating pressure and SOFC operating temperature,the total power generation efficiency is increased.However,with increasing current density and extraction shitter ratio of low-pressure steam turbine,the total power generation efficiency is decreased.The top three exergy loss components are SOFC,CLC and DC-AC,accounting for 28.06%、27.16%and17.63%.Finally,the economic evaluation model of SOFC-CLC cogeneration system is established,and the fluencies of fuel utilization rate,current density,SOFC operating pressure,SOFC operating temperature on equipment cost,levelized cost of exergy（LCOE）and dynamic payback period（DPP）are studied.When the fuel utilization rate and current density is increased,the total equipment cost,LCOE and DPP are decreased.When the SOFC operating temperature is increased,the total equipment cost is increased,while the LCOE and DPP are decreased.When the SOFC operating pressure is increased,the total equipment cost is increased,while the LCOE and DPP are firstly decreased and then increased.The total investment cost is 717,962.05$,the total cost rate is 16.86$/h,and the dynamic payback and levelized cost of exergy are 6.97 years and 98.74$/MWh,respectively under the design condition.Simultaneously,in order to balance thermal performance and economy,a multi-objective intelligent optimization algorithm is developed by coupling response surface method and genetic algorithm to perform multi-objective optimization on SOFC-CLC cogeneration system,and a Pareto solution set is obtained.The optimal exergy efficiency and total cost rate are68.978%and 15.85$/h by technique for order preference by similarity to an ideal solution（TOPSIS）decision scheme.