Addition of Highly Efficient Bottoming Cycles for the Nth-Generation Molten Carbonate Fuel Cell Power Plant

Abstract

An intermediate scale (2.0 MW gross) molten carbonate fuel cell (MCFC) power plant recently began operating in Santa Clara, California. The goal of the project is to demonstrate the possibility of long-term operation of MCFC stacks. The fuel cell stacks are the only source of electricity, which means a simple power plant system, and relatively low capital costs. This, however, results in substantial work losses in the plant, most of which come from the hot exhaust gas discharge. The predicted efficiency is a respectable 50 percent. In this paper, an exergy analysis is performed in order to study if a future plant’s efficiency can be improved. It is shown that for the future plant of this type it would be worthwhile to consider the addition of a steam bottoming cycle as well as changing the configuration of the top cycle. This can lead to improving the efficiency to close to 70 percent. The modified power plant requires additional equipment, such as steam turbines, heat exchangers, condensers; thus, the capital cost of the plant changes substantially. A cost analysis of the modified plant was performed, and a comparison of the cost of electricity between the two cycles is made. Finally, a Kalina cycle as one option for a bottoming cycle is considered as well.