| With the development of human society,environmental problems can't be ignored.Solid oxide fuel cell(SOFC)has become one of the hotspots of green power generation technology because of its solid structure,high efficiency,easy maintenance and no pollution.Nowadays,the research on SOFC power generation technology has transformed from SOFC stack to SOFC power generation system.SOFC system has characteristics of multivariable coupling and strong nonlinearity.The steady-state performance analysis of a system is a necessary condition for the subsequent control of the system and is the foundation of its stable,efficient and long-term operation.Besides,the SOFC power generation system has diversified configuration and different performance.So the comparison of different system's performance could provide theoretical support for its integration and application.In this dissertation,four 5kW panel SOFC power generation systems are studied: pure hydrogen SOFC power generation system,external steam reformer SR-SOFC power generation system,SOFC-GT(gas turbine)hybrid power generation system and SOFC-SOEC(solid oxide electrolysis cell,convert carbon dioxide into fuel gas through absorbing solar energy,wind energy and other intermittent power)power generation system.The system performance analysis and optimization are carried out,and then the parameters such as battery life,system efficiency,power generation cost are compared under the same conditions.The advantages and disadvantages of each system are analyzed and suggestions are put forward.The specific contents and arrangements of this paper are as follows:First of all,the mechanism model of each power generation system is established according to the law of conservation of physics and chemical kinetics.In order to balance the calculation and accuracy of the model,the finite element method is used to build the 1D distributed model for the stack and the heat exchanger.The other components in balance of plant such as the reformer,the combustion chamber,the blower,the GT unit adopt the lumped parameter mode.The model of each component of the system is integrated to form the system model,which lays the foundation for the later analysis of the system.Then,based on the complete system analysis and optimization method,the SR-SOFC power generation system is taken as an example to analyze the steady-state performance in the whole input space.The optimal operating point with the maximum system efficiency at different output power level of the system is found under the condition of satisfying the system temperature constraint.Finally,the performance analysis of four different types of SOFC power generation system is carried out.And the advantages of each system are given and the suggestion of its application areas are proposed.The results show that due to the endothermic reaction of the reforming reaction and the efficiency of methane conversion to hydrogen in the methane-fueled SR-SOFC system,it makes its efficiency lower than the pure hydrogen SOFC system.The introduction of the GT unit in the SR-SOFC power generation system decrease the parasitic power of the system.In addition,the generator in the GT unit can generate additional power,which can improve the efficiency of the system.Since the SOEC is endothermic,the overall temperature of the system decreases.Through the absorption of solar energy to generate new fuel gas,it makes the system efficiency improve.In addition,in the high-power level of SOFC power generation system,SOEC advantage is more obvious.For different applications,the following recommendations could be concluded: For household electricity,the SR-SOFC system is a very suitable option for natural gas as fuel and with low system quality.SOFC-GT system which has high system efficiency and energy density is suitable for remote mountainous areas,large mobile devices and large fixed power plants.SOFC-SOEC system can use solar energy to improve the system's battery life,so that it has advantageous in desert and other solar-rich areas.Pure hydrogen SOFC system with high energy density and system efficiency and low system quality is very suitable for small mobile devices. |
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