Integration And Analysis Of A Distributed Total Energy System Based On Solid Oxide Fuel Cells

In the modern world, the problems related to energy and environment become more and more serious. For this reason, people constantly pursue a kind of ideal energy with the characteristics of high efficiency and environmental-friendly. Under this background, distributed total energy system (DTES) was born. With the unremitting efforts of scholars in the world, many kinds of DTES have been developed, which mainly employ gas turbine, internal combustion engine or high-temperature fuel cells as the prime mover. Solid oxide fuel cell (SOFC) which is the third generation of fuel cells with the advantages of high efficiency, environmental-friendly and useful waste heat has arouse people's enthusiasm. So, the study on the SOFC-based total energy system is of significant importance.The main content of this thesis is divided into three parts. First, the concept, principles and characteristics of fuel cell were presented and the development of SOFC was introduced in detail. Then a model of SOFC was developed and it was proved to be effective through the comparison between model and experimental data of a 100kW SOFC stack from Siemens-Westinghouse. The influence of current density, temperature, pressure on the stack performance was investigated. The conclusion is:the increase of temperature has a positive influence on the output of SOFC stack but it makes the efficiency decrease. When the temperature is higher than 1000℃, the efficiency of SOFC has little advantages over the traditional engines. The performance of SOFC was improved with increase in pressure, but more requirements of seal become necessary. With the growth of current density, the output of SOFC stack first increased and then decreased. It is because the output of the stack is determined by the product of the current and voltage.The second part is mainly about the constitution of a new kind of DETS on the base of pioneers. At present, the SOFC is usually combined with a gas turbine to form a SOFC/GT system or with an absorption refrigeration chiller. In this thesis, on the base of two stage energy utilization system, the waste heat of SOFC/GT system is used to power a single-effect LiBr absorption chiller which requires less heat than the others, and then a three stage energy utilization system is proposed.In the third part, models of compressor, turbine and chiller were set up. Through the computation, the parameters on the design point were attained. Then at the off-design point, the influence of current density, pressure ratio, fuel utilization factor, excess air ratio on the performance of system was analyzed. The obtained results are:with the growth of current density, the electrical efficiency decreased, the temperature of waste heat increased and the cooling power also increased. When the pressure ratio increased, the power consumption of compressor increased while the efficiency of SOFC and cooling power of the chiller both decreased. When the fuel utilization ratio is 0.85, the SOFC is most efficiency, with the fuel utilization ratio increased, the efficiency of SOFC decreased and the cooling power increased slightly. When the excess air ratio increased, more heat will be blew out which is harmful to the performance of the whole system, but it has the capacity to control the temperature of the fuel stack and makes the system operate safely.