Solid oxide fuel cells combined cycles

F. P. Bevc, W. L. Lundberg and D. M. Bachovchin, "Solid Oxide Fuel Cell Combined Cycles," ASME Paper 96-GT-447, presented at International Gas Turbine and Aeroengine Congress Exhibition, Birmingham, UK, June 1996. 

McDermott Technology, Inc., of Alliance, OH, developed a conceptual design of a high efficiency power plant system that joins planar solid oxide fuel cell technology with microturbine technology in a combined cycle. The system was operated at atmospheric conditions. 

Siemens-Westinghouse Power Corporation of Pittsburgh, PA developed and fabricated the first advanced power plant to combine a solid oxide fuel cell and a gas turbine. The microturbine generator was manufactured by Northern Research and Engineering Corporation of Woburn, Mass. The factory acceptance test was completed in April 2000. Southern California Edison will operate the new hybrid plant at The National Fuel Cell Research Center at the University of California-Irvine. A year of testing in a commercial setting will be performed at this site. The system cycle is expected to generate electric power at 55 % efficiency. 

Koyama, M., Komiyama, H., Tanaka, K., Yamada, K., Evaluation of a Solid Oxide Fuel Cell and gas turbine combined cycle with different cell component materials, in Proceedings 7th International Symposium on Solid Oxide Fuel Cells, Tsukuba, Japan, H. Yokogawa, S.C. Sing-hal (Eds.), Proceedings Volume 2001-16, The Electrochemical Society, Pennington, NJ, 2001, pp. 234-243. 

Winkler, W., Thermodynamic influences on the cost efficient design of combined SOFC cycles, in Proceedings 3rd European Solid Oxide Fuel Cell Forum, Nantes, P. Stevens (Ed.), Oral Presentations, 1998, pp. 525-534. 

Hannett L.N., Feltes J.W., 2001. Testing and model validation for combined-cycle power plants, in Power Engineering Society Winter Meeting, Columbus, OH, USA, pp. 664-670. Haynes C.L., 1999. Simulation of Tubular Solid Oxide Fuel Cell Behavior for Integration Into Gas Turbine Cycles, Ph.D. thesis, Georgia Institute of Technolog. 

Massardo A.F., Lubelli F., 2000. Internal reforming solid oxide fuel cell-gas turbine combined cycles (IRSOFC-GT) Part A-Cell model and cycle thermodynamic analysis, J. Eng. Gas Turbines and Power, Vol. 122, No. 27, pp. 27-35. 

Lobachyov K, Richter HJ (1996) Combined cycle gas turbine power plant with coal gasification and solid oxide fuel cell. J Energy Resour Technol 118 285-292... 

A signihcant problem in tire combination of solid electrolytes with oxide electrodes arises from the difference in thermal expansion coefficients of the materials, leading to rupture of tire electrode/electrolyte interface when the fuel cell is, inevitably, subject to temperature cycles. Insufficient experimental data are available for most of tire elecuolytes and the perovskites as a function of temperature and oxygen partial pressure, which determines the stoichiometty of the perovskites, to make a quantitative assessment at the present time, and mostly decisions must be made from direct experiment. However, Steele (loc. cit.) observes that tire electrode Lao.eSro.rCoo.aFeo.sOs-j functions well in combination widr a ceria-gadolinia electrolyte since botlr have closely similar thermal expansion coefficients. 

Advanced power generation cycles that combine high-temper-ature fuel cells and gas turbines, reciprocating engines, or another fuel cell are the hybrid power plants of the future. As noted, these conceptual systems have the potential to achieve efficiencies greater than 70% and projected to be commercially ready by the year 2010 or sooner. The hybrid fuel cell/turbine (FC/T) power plant will combine a high-temperature, conventional molten carbonate fuel cell or a solid oxide... 

Unlike molten carbonates, solid oxides use a hard ceramic electrolyte instead of a liquid. That means the fuel cell can be cast into a variety of useful shapes, such as tubes. With higher temperatures, sofcs may be able to cogenerate steam at temperatures as high as i,ooo°f. The Siemens Westinghouse Power Corporation has built the first advanced hybrid system, which combines a gas turbine with a tubular sofc. As of 2003, the 220 kW hybrid system has operated in California for more than 2,000 hours with a respectable 53 percent efficiency, comparable to current combined cycle gas turbines. The ultimate goal is an efficiency of 70 percent or more. 

The most common solid oxide, which is used as electrolyte in SOFC, is a mixture of zirconia and yttria. YSZ contains between 8 and 10 mol% yttrium. It is an oxide ion conductor with a sufficiently high conductivity at temperatures around 1000 °C. This is an advantage for the direct oxidation of fuels in the fuel cell, but is a very challenging temperature for any material. Thermodynamics predict an efficiency of 80%. A further advantage of the high operation temperature is the possibility to efficiently use the waste heat in a combined cycle power plant. 

---