Generation of heat and power from biogas for stationary applications: boilers, gas engines and turbines, combined heat and power (CHP) plants and fuel cells - The Biogas: Science, Production and Applications - page 416

17.4 Gas turbine process with heat recovery (adapted from Deublein

and Steinhause, 2008, with permission from Wiley-VCH Verlag & Co.
KGaA, Germany).

heating the air that is sucked in (Fig. 17.4). Commercial units can range in
size from 500 kW to 250MW. A single-cycle turbine has an efficiency of 20-
45% at full load, with efficiency increasing with size (Chambers and Potter,
2002). The electrical capacity, and thus the efficiency of the gas turbine, can
be increased by changing the amount of biogas supplied to the combustion
chamber or increasing the turbine inlet temperature.
Gas turbines are available in medium to large capacities and are
characterised by low emission values. When fed with cleaned biogas, the
NO x emission in the exhaust gas is less than 25 ppmv (Deublein and
Steinhause, 2008). The CO content can be considerably reduced by installing
a downstream catalyst.

17.3.8 Generation of electricity in a micro gas turbine

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Micro (gas) turbines are small, high-speed, gas combustion turbines with a
power rating of 25-500 kW (Chambers and Potter, 2002). Micro turbines
are considered easy to handle and are relatively low noise and vibration free.
They can use various fuels, including natural gas, biogas, associated gas,
biodiesel and kerosene. Micro turbines are increasingly used for biogas
applications, especially in cogeneration at wastewater treatment plants,
codigestion plants, farms and landfills.
Micro turbines typically comprise an air compressor, combustor, turbine,
alternator, recuperator and generator (Fig. 17.5). Micro turbines have a
single shaft on which the compressor, turbine and generator are fixed. Gas
turbines are single-stage, radial flow devices with rotating speeds of 90 000
to 120 000 rpm (Chambers and Potter, 2002). The turbine propels the