Solid oxide fuel cell (SOFC) triple combined cycle system, integrated with gas turbine (GT) and steam turbine (ST), is an ultimate fossil fuel electric power generation system with very high efficiency. In 2008, Mitsubishi Heavy Industries, Ltd. (MHI) operated the 200 kW-class SOFC micro gas turbine (MGT) hybrid system under commission of New Energy and Industrial Technology Development Organization (NEDO) and we could demonstrate 52.1%-LHV net power generation efficiency. Based on the successful achievement, MHI developed a more compact 250 kW-class SOFC-MGT hybrid system for the purpose of utilization of a hybrid system in the NEDO project scheduled from fiscal 2011 to 2012. Furthermore, we have started a development of fundamental technologies of SOFC-GT-ST triple combined cycle system that aims to achieve more than 70% of power generation efficiency. In this paper, latest results on the development of SOFC and the systems are described.

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Solid oxide fuel cell (SOFC) triple combined cycle system, integrated with gas turbine (GT) and steam turbine (ST), is an ultimate fossil fuel electric power generation system with very high efficiency. Mitsubishi Hitachi Power Systems, Ltd. (MHPS) has been developing for commercialization of an SOFC-micro gas turbine (MGT) system from several hundred kW to several MW class. Recently prototype of a 250 kW class SOFC-MGT hybrid system was operated at Tokyo Gas Senju Techno Station. This system was stable without voltage degradation under operating 4,100 hours. At the same time, we have started the development of fundamental technologies for realization of SOFC-Gas Turbine (GT)-Steam Turbine (ST) triple combined cycle system that aims to achieve more than 70% of power generation efficiency. In this paper, recent progress of the SOFC-micro gas turbine (MGT) hybrid system and development of triple combined cycle system are described.

SOFC-gas turbine combined cycle system is able to attain extremely high efficiency over 70% (LHV). Mitsubishi Heavy Industries (MHI) has been developing SOFCs since 1984. Now, MHI is integrating SOFC with a gas turbine for a combined cycle power generation system. MHI has improved the components and the control technology for the combined cycle system; this includes improvement of the cell stack, verification of pressurized operation and control of SOFC module, and the combustor for low-calorie fuel. In 2006, MHI operated a combined cycle system with a maximum power output of 75 kW, for the first time in Japan. Now, MHI is ready to manufacture a 200 kW class SOFC-MGT combined cycle system, which will be operated in 2007.

Mitsubishi Heavy Industries (MHI) has developed SOFC with tubular type cell stack since 1984. In this study, we report the current status toward commercialization of SOFC-GTCC power generation system at MHI. To Redox robustness of a cell stack, the sintering characteristics of interconnect was improved. To improve durability of cell stack, long-term change of the electrochemical characteristics had been measured, and analyzed the interface of cathode and electrolyte by SIMS. For compact module, the packing density of the cell stack was increased from 400 to 700 stack/m2, and confirmed I-V characteristics and the temperature distribution of improved module. The generation performance of improved module is roughly comparable to that of conventional type module, and the temperature distribution is also roughly agreement of simulation result.