APC 400kW1MW User Manual download pdf (Page 14)

Figure 2-2 Fuel Cell Diagram [A]

The result of a fuel cell’s chemical process is water, as stated in the above net reaction

equation, and heat. The water produced, as well as some of the heat, is used in the fuel

reforming process. Water may also be used for humidification of the oxidant. The remainder of

the thermal energy generated by the fuel cell process can be recovered for a CHP application

[13, p. 5]. The use of the waste heat for CHP applications will be discussed more in Chapter 4.

As mentioned above, the fuel is oxidized as it enters the fuel cell. This requires an

oxidant, which is typically air. Most fuel cell stack designs require operating pressures between

1 and 8 atmosphere. Air can be supplied at high pressure using an air compressor or at low

pressure using a blower. As the pressure of the air is increased, the kinetics of the

electrochemical reactions are improved. This results in a higher power density and higher stack

efficiency. The drawback of using a compressor to provide high pressurized air is that the

compressor itself decreases the net power from the fuel cell. Also, at low loads, the

performance of the compressor is usually poor [10, p. 1812].

Power conditioning is another necessary component in order for a fuel cell to supply

power to a building. Fuel cells produce a low, variable voltage and require a power converter in

order to boost and regulate the voltage. The power converter also converts direct current (DC)

power from the fuel cell to alternating current (AC) power to serve the building [14, p. 643].

All of the components that make up a fuel cell system are housed within one enclosure.

Figure 2-3 shows a view of the UTC Power’s PureCell Model 400 fuel cell module and its

components.

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APC 400kW1MW User Manual Page 14