MCFC-Steam SOFC-Steam

2173 PPH (Steam)

1514R X4851PPH = 766R

3498 PPH (Steam)

15.934 15.934 14.63

1258 MBTUH 1835 MBTUH 3961 MBTUH

105 Tons 117 Tons 251 Tons

56.6 GPM 83 GPM 179 GPM

1132 MBTUH 1652 MBTUH 3583 MBTUH

Design Issues

Relationships between bulk electrical and thermal capacities at steady state operation for the proposed system have been developed, but several important design issues are not treated in this analysis. Transient behavior and turn down ratio are two important performance problems. With relatively long start up times and low turndown ratios, the first generation of fuel cells may not be suited for the application for many types of building. The ratios of bulk capacities, as well, indicate that thermal capacities may be insufficient to match electrical capacities in many applications. Thermal design for the integrated system will significantly affect the amount of waste heat available for cooling. One factor would include internal vs. external reforming; an external reformer would augment the waste heat from the fuel cell. Another significant design issue would be accommodating respective thermal and power capacities vs. load requirements across the operational envelope. This will probably involve a low temperature cooling system with circulating pump and cooling tower to trim excess thermal capacity and to dissipate secondary heat, eg., from the absorber. Some systems might schedule tandem heating and cooling during milder weather as a method for utilizing excess thermal capacity. The major factor in performance, though, is preheat of fuel, feed water and oxidant. An optimized design would probably employ two stage cooling with cathode gas cooling incoming oxidant and then supplying the first stage of heating to the chiller. Oxidized anode gas would preheat fuel and feedwater and then supply second stage heat.

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