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Oil
or natural gas can run gas turbines. In a gas turbine, fuel burning in a
high-pressure combustion chamber produces hot gases that pass directly
through the turbine, which spins a generator to produce electricity. The
turbine also spins a compressor to provide high-pressure air to the
combustion chamber. This cycle is different from the steam turbine, where
the heat of combustion turns water to steam, which pushes the turbine.
Combined-Cycle System
The most efficient way for utilities to use gas or
oils is in a combined-cycle system, which combines two means of producing
electricity. Hot gases from the combustion chamber spin the gas turbine
and the generator to make electricity. The system then pipes the still-hot
exhaust gases leaving the combustion turbine to a 'waste heat' steam
boiler where their heat produces steam. The steam turns a turbine,
connected to a second generator, to produce electricity. Condensers
convert the steam to water that returns to the boiler to repeat the cycle.
Because steam
turbines can be built larger than gas turbines, a combined cycle system
often uses several gas turbines to feed hot exhaust to one steam boiler. |
