|TYPE OF PLANT||FUEL|
|Combined Cycle||Natural Gas|
Table 3.1. Fuels used by Type of Power Plant In Figure 3.1 the relative proportion of pollutants emitted during the combustion of fossil fuels is shown. In this figure, coal has been taken as a reference; therefore, for each pollutant, emissions from coal are given a value of 100%. Natural gas is said to be the "cleanest" of the three types of fossil fuels, due to the significantly lower emissions generated before the post-combustion control equipment. Emissions of NOX are highly dependent on firing configuration, type of burners, flame temperature and to some extent on the nitrogen content of the fuel, although NOX is formed even when the fuel contains no nitrogen. In addition to the pollutants shown in Figure 3.1, there are other pollutants emitted by fossil fuel power stations, such as organic compounds that include volatile organic compounds (VOCs), semi-volatile organic compounds, and condensable organic compounds. There are also emissions of some metallic compounds (of which mercury is the only one considered in this report); other greenhouse gases besides CO2, such as methane and nitrous oxide; and some halogenated compounds.
Coal is the most widely used fossil fuel for electricity generation; its composition is a complex combination of organic compounds and inorganic, mineral matter.
Fuel oil is derived from crude petroleum and is the most widely used liquid fuel for power generation. Distillate and residual fuel oils are the two major categories of this type of fuel.
After coal and oil, natural gas is the third type of fuel most widely used for electricity generation. The main component of natural gas is methane (85–90%); it also contains propane, ethane, butane, some inert gases such as nitrogen, helium and carbon dioxide, and trace amounts of other gases.