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Industrial
gas turbines range in size from truck-mounted mobile
plants to enormous, complex systems. They can be
particularly efficient——up to 60%——when waste heat
from the gas turbine is recovered by a heat recovery
steam generator to power a conventional steam
turbine in a combined cycle configuration. They can
also be run in a cogeneration configuration: the
exhaust is used for space or water heating, or
drives an absorption chiller for cooling or
refrigeration. A cogeneration configuration can be
over 90% efficient. The power turbines in the
largest industrial gas turbines operate at 3,000 or
3,600 rpm to match the AC power grid frequency and
to avoid the need for a reduction gearbox. Such
engines require a dedicated enclosure.
Simple cycle gas turbines in the power industry
require smaller capital investment than either coal
or nuclear power plants and can be scaled to
generate small or large amounts of power. Also, the
actual construction process can take as little as
several weeks to a few months, compared to years for
base load power plants. Their other main advantage
is the ability to be turned on and off within
minutes, supplying power during peak demand. Since
they are less efficient than combined cycle plants,
they are usually used as peaking power plants, which
operate anywhere from several hours per day to a
couple dozen hours per year, depending on the
electricity demand and the generating capacity of
the region. In areas with a shortage of base load
and load following power plant capacity, a gas
turbine power plant may regularly operate during
most hours of the day and even into the evening. A
typical large simple cycle gas turbine may produce
100 to 300 megawatts of power and have 35–40%
thermal efficiency. The most efficient turbines have
reached 46% efficiency. |
