Calculated values for Q^ss in equation (3) resulted in theoretical combustion efficiencies in the low 70 percent range. Oxidized anode gas and cathode gas exhausting at stack temperature contain the available waste heat. Most systems will use these streams to preheat incoming fuel, feed water and oxidant. This analysis accounted for the preheat losses and then combined the two streams. Having arrived at a single stream of waste heat, the capacity and heating water flow rate for a hot water generated chiller per megawatt of electricity are:


Where Cg is the product of gas mass flow rate and specific heat;"xi" is heat exchanger effectiveness.

For steam generated chillers, the mass and heat balances are modified to account for latent heating of steam. The conventional heat balance between gas and steam as it is superheated requires:

Where Tx is the so-called pinch point. typically 50 - 70R above saturated steam temperatures. Values for hs and hF are enthalpies of steam vapor and saturated liquid, respectively at 28 PSIA. Therefore, steam rate and chiller capacity are:


The factor x is the quality of steam leaving the chiller generator. Table 4 is a performance schedule for the three configurations of fuel cell-absorption chiller system: MCFC with hot water generation; MCFC with steam generation, and SOFC with steam generation. Heating performance assumes a 90 % efficiency in hydronic heating generator.

Table 4

Bulk Coqeneration per MW Electrical Output at Füll Power

Anode gas oxidation eff., excess air

T, waste gas

Mass flow, waste gas

Waste heat recovery efficiency

Generator mass flow

C9 BTU/R-LB0 fuel Qo


Hydronic flow Heating_

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