Fuel Cell Description

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
gaseous 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 up to 70%, LHV, using demonstrated cell performance, have been proposed.
Figure 1-5 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.
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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.