Gas Turbine Handbook : Principles and Practices

170 Gas Turbine Handbook: Principles and Practices
to a high of 500 kW. These units evolved from automotive and
truck turbocharger components, small jet engines (in turboprop applications),
and auxiliary power units commonly used for ground
power for aircraft. Microturbine components typically consist of a
centrifugal compressor and radial turbine components mounted on
the same shaft, a combustor, and a recuperator. In some designs a
separate turbine wheel, the power turbine wheel, is also provided.
The recuperator is used to capture exhaust waste heat to heat up
compressor discharge air. Heating the compressor discharge air reduces
fuel consumption, which reduces NO x formation (NO x formation
is discussed in detail in Chapter 9) and increases the overall
efficiency. Microturbines are coupled to alternators or generators
(inductive or synchronous generators) for the production of electricity.
In mechanical drive applications the microturbine may be coupled to
a compressor in refrigeration service or a pump in pumping service.
In single and split-shaft microturbine designs the electric generator
may be mounted on the same shaft as the compressor and turbine
components or a speed-reducing gearbox may be employed between
the gas turbine output shaft and the electric generator (or compressor
or pump depending on the application).
Due to the high speeds of the microturbines special attention
must be given to the electric generators. These generators are either
specifically designed to produce a 60 Hz output or have specialized
electronics (rectifiers and converters) to convert the power generated
to facilitate utility grid connection.
APPLICATIONS
Microturbines are used in distributed power and combined heat
and power applications. With recent advances in electronic, microprocessor
based, control systems these units can interface with the
commercial power grid and can operate “unattended.”
Table 11-2 list typical applications for microturbines and the
power range utilized for each application. 1
Table 11-3 demonstrates the relative cost of reciprocating engines,
microturbines, and fuel cells. Since microturbines and fuel cells
are relatively new to the marketplace their price & performance are
drawn from comparatively few samples.