The Solid Oxide Fuel Cell Cogeneration System Performance Calculation And Optimization

Solid oxide fuel cell (SOFC) is a new energy conversion device. Because of its highly efficiency, fuel adaptability and long term stability, the research and development of SOFC have been emphasized in many countries.Energy balance model and exergy analysing model of SOFC are established in this thesis. A SOFC power system, which is fed by natural gas, is calculated. Results show that the electrical efficiency and exergy efficiency of this power system can all exceed 45%. There are several sources that contribute to the irreversible losses in an operating SOFC. The performance of SOFC can be improved by improving SOFC structure and using advanced material.Owing to its working features, SOFC cannot convert all fuel. At the same time, SOFC has highly exit gas temperature. So SOFC can be combined with other power systems. In this paper, energy analysis and exergy analysis of hybrid power systems are given. A combined cycle system with SOFC and steam turbine can achieve an electrical efficiency of 58.933% and an exergy efficiency of 56.98%. For hybrid SOFC and gas turbine power system, the capacity usage ratio and exergy efficiency are, respectively, more than 80% and 70%. It can be find that decreasing the current density and increasing the fuel utilization of SOFC will improve the performance of system. In addition, the increase in operating pressure and inlet temperature of SOFC will increase the electrical efficiency and exergy efficiency of whole power system.Using exergy analysing identification, weak links of SOFC-GT power system can be find. In this paper, main weak links are heat exchanger and SOFC. In order to increase the electrical efficiency and exergy efficiency, two optimization schemes are researched. The electrical efficiency of first scheme is increased by 8.61% and exergy efficiency by 4.79%. For the second scheme, the electrical efficiency and exergy efficiency are increased respectively by 11.11% and 6.63%.At last, a SOFC power system combined both with steam turbine and gas turbine is calculated. Its performance is better than SOFC-ST power system, but not as good as SOFC-GT power system. Considering the investment cost, this system is not suggested when capacity is small.