Environmental Engineering Reference
In-Depth Information
17.5
Micro gas turbine process with heat recovery (adapted from
Deublein and Steinhause, 2008, with permission fromWiley-VCH Verlag
GmbH & Co. KGaA, Germany).
compressor, which compresses the air and, at the same time, the generator
(Deublein and Steinhause, 2008). In micro turbines, the compressor draws
the air into a recuperator, which acts as an air-to-air heat exchanger,
recovering the heat from exhaust gas. Heating of the combustion air
increases the micro turbine's electric efficiency. The heated air is passed into
the combustor chamber, into which fuel is also injected. For biogas
applications, the minimum methane content in the biogas should be 30%. In
the combustor chamber, the combusted mixture expands, which in turn
causes the turbine and shaft to rotate and thus generate electricity.
Micro turbines are generally regulated by varying the fuel supply. The
electrical efficiency of micro turbines is typically 15-30%; the higher range
efficiencies are obtained with pre-heated combustion air (Chambers and
Potter, 2002; Deublein and Steinhause, 2008). Micro turbine exhaust
temperatures are relatively low (about 200-300
C) and the waste heat can
only be used to generate low-pressure steam and/or hot water (Chambers
and Potter, 2002). Electrical efficiencies up to 50% are achieved when a
micro turbine is coupled with a micro steam turbine.
Micro turbines are more expensive than traditional gas engines, but their
maintenance requirements are much less and thus maintenance costs are
reduced. Their life time is also relatively long. The maintenance interval
ranges from 2000 to 8000 h, but can be longer if the turbine is operated
above the normal operating temperature of approximately 10
8
C (Deublein
and Steinhause, 2008). Like large gas turbines, micro turbines are tolerant to
humidity and corrosive gases in the fuel gas as long as condensation is
8
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