In a gas plant, the energy stored in combustible gases is converted into electricity.
In natural gas or biogas molecules, the chemical bonds are formed by the carbon atoms store energy. During the combustion of these gases in the presence of oxygen, carbon dioxide (CO2) and water vapor are formed. But it also releases a lot of heat.
In a gas plant, the combustion gases – those resulting from the combustion of combustible gases – are used to drive a gas turbine. But energy, originally stored in combustible gases, can still be used differently. That is why the combined cycle gas plants, which include a gas turbine and a steam turbine, were developed.
Use energy twice, it’s even better!
There is still a certain amount of usable heat in the combustion gases after they pass through the gas turbine. These hot gases are collected in a recovery boiler where they serve to heat water in the form of steam. This steam allows operating a second turbine. This steam turbine, like the gas turbine, is coupled to a generator, which produces electricity. Its operation resembles that of a hydraulic power station, where it is a water wheel that drives the generator.
In such a combined-cycle gas plant, the energy of the natural gas or biogas is thus used twice: the combustion of the gas with the oxygen of the air actuates a gas turbine, and the heat released makes it possible to heat steam water, which in turn operates a steam turbine. Both turbines are coupled to generators that produce electricity.
The exhaust gases of combined cycle gas plants are less polluting than those of coal-fired power plants. Nevertheless, these two types of plants release carbon dioxide into the atmosphere, which is responsible, along with other gases, for global warming.