Fuel cells have many characteristics that make them favorable as energy conversion devices. Two that have been instrumental in driving the interest for terrestrial application of the technology are the combination of relatively high efficiency and very low environmental intrusion (virtually no acid gas or solid emissions). Efficiencies of present fuel cell plants are in the range of 40 to 55% based on the lower heating value (LHV) of the fuel. Hybrid fuel cell/reheat gas turbine cycles that offer efficiencies greater than 70% LHV, using demonstrated cell performance, have been proposed. Figure 1-6 illustrates demonstrated low emissions of installed PAFC units compared to the Los Angeles Basin (South Coast Air Quality Management District) requirements, the strictest requirements in the US. Measured emissions from the PAFC unit are < 1 ppm of NOx, 4 ppm of CO, and <1 ppm of reactive organic gases (non-methane) (5). In addition, fuel cells operate at a constant temperature, and the heat from the electrochemical reaction is available for cogeneration applications. Because fuel cells operate at nearly constant efficiency, independent of size, small fuel cell plants operate nearly as efficiently as large ones.1 Thus, fuel cell power plants can be configured in a wide range of electrical output, ranging from watts to megawatts. Fuel cells are quiet and even though fuel flexible, they are sensitive to certain fuel contaminants that must be minimized in the fuel gas. Table 1-2 summarizes the impact of the major constituents within fuel gases on the various fuel cells. The reader is referred to Sections 3 through 8 for detail on trace contaminants. The two major
1. The fuel processor efficiency is size dependent; therefore, small fuel cell power plants using externally reformed hydrocarbon fuels would have a lower overall system efficiency.
impediments to the widespread use of fuel cells are 1) high initial cost and 2) high-temperature cell endurance operation. These two aspects are the major focus of manufacturers' technological efforts.
L.A. Basin Stand
Reactive Organic Gases
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