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Micro-Cogeneration System Components

Micro-Turbine Generators

Small gas turbine generators are relatively new to the market. Other companies besides Capstone are developing them, such as the Northern Research and Engineering Corporation11, but Capstone was chosen because this company already has small turbine generators in production and available for use.

According to the relationship between the power rating of the cogenerator and the amount of hot water it can produce, seen in equation (2.15), one turbine, with a power rating of 28 kW, a load factor of 1.0, an gas-to-electric conversion efficiency 0.26 (see Table 4-1)3 and a heat recovery efficiency 0.70, can heat 13,700 gallons per day by 40 °F. The cost of a 28-kW micro-turbine generator3 is $36,000.

Exhaust Heat Recovery Heat Exchangers

The heat exchangers that are compatible with the 28-kW micro-turbine generators are relatively inexpensive. They can be custom-built according to the specifications of the equipment they are to be connected with. The main driver of their price is the size the heat exchanger needs to be. The temperature of the micro-turbine’s exhaust is relatively high, which reduces the required size of the heat exchanger. The quoted cost of a heat exchanger14 that is compatible with the 28-kW micro-turbine generator is about $400.

Table 4-1: Capstone Micro-Turbine Driven Generator Specifications

Output

Power

Efficiency (LHV)

Heat Rate (LHV)

Microturbine @ 50

or 60 Hz*

28kW net

26% (+/-0.5%points)

13,200 Btu/kWh

Emissions** (natural gas fuel): NOx

<9 ppmV / 6.7g/hr / 0.0147 lb/hr

Noise Level

65 dba @ 10 meters

Full Load Fuel flow (natural gas-HHV)

410,000 Btu/hr / 428,000 kJ/hr

Exhaust Gas Temperature

520ºF / 271ºC

Total Exhaust Energy (base @ 59ºF. 15ºC)

277,000 Btu/hr / 295,000kJ/hr

Dimensions

74.8"H x 28.1"W x 52.9"D

1900mm H x 714mmW x 1344mmD

Weight

1,052lbs / 478 kg

Voltage

400-480 VAC 3 phase, 4-wire wye or 3-wire wye, ungrounded delta, 43A max

*ISO conditions, 59º F (15º C) /sea level; for high pressure natural gas
**At full-load power