APC 400kW1MW User Manual download pdf (Page 37)

From the heat exchangers, excess waste heat is delivered to the fuel cell system’s

cooling module, where the heat is rejected. For example, UTC Power’s PureCell Model 400 has

an accompanying dry cooler that rejects unused waste heat.

Table 4-1 shows the waste heat temperatures and available heat recovery from UTC

Power’s PureCell Model 400 and FuelCell Energy’s DFC Model 300.

Table 4-1 Fuel Cell Low and High Grade Heat Recovery [H]

(Btuh = British Thermal Units per hour)

4.2.1 Using Absorption Chillers in a Fuel Cell CHP System

In a fuel cell CHP system, an absorption chiller replaces the electric chiller in the

diagram shown in Figure 4-1. Opposed to the vapor compression cycle used by electric chillers,

energy from waste heat drives an absorption refrigeration cycle within the absorption chiller [20,

p. 2-9]. Thermal energy is transferred from the heat source to the heat sink through an

absorbent fluid and a refrigerant. A common refrigerant-absorbent combination used for

absorption chillers is water-lithium bromide. The chiller refrigerates by absorbing and releasing

water vapor into and out of the lithium bromide solution [49, p.1; 20, p. 7-4].

The cooling process of a single-effect absorption chiller is shown in Figure 4-4. Heat is

first supplied to the generator. Water vapor produced at the generator is driven off to the

condenser. Cooled water vapor is passed through an expansion valve, which reduces its

pressure. From there, the vapor is supplied to an evaporator. The actual cooling takes place in

the evaporator where ambient heat is added from the chilled water return. The heated, low

pressure vapor then travels to the absorber, where it combines with lithium bromide and

becomes a low pressure liquid. This solution is then pumped to a high pressure and into the

generator to repeat the process [49, p.1].

Heat Recovery

Low Grade High Grade

Fuel Cell

Fuel

Cell

Type

Power

Generation

(kW)

Temperature

(ºF)

Heat Available

(Btuh)

Temperature

(ºF)

Heat Available

(Btuh)

PureCell 400

PAFC

400 140 1,708,000 250 785,000

DFC300

MCFC

300 120 808,000 250 480,000

1 2 ... 32 33 34 35 36 37 38 39 40 41 42 ... 85 86

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