What is coal gasification?

Rather than burning coal directly, gasification breaks down coal -- or virtually any carbon-based feedstock -- into its basic chemical constituents.

In a modern gasifier, coal is typically exposed to hot steam and carefully controlled amounts of air or oxygen under high temperatures and pressures. Under these conditions, carbon molecules in coal break apart, setting into motion chemical reactions that typically produce a mixture of carbon monoxide, hydrogen and other gaseous compounds.

Gasification may be one of the best ways to produce clean-burning hydrogen for tomorrow's automobiles and power-generating fuel cells. Hydrogen and other coal gases can also be used to fuel power-generating turbines, or as the chemical "building blocks" for a wide range of commercial products.

In a typical coal combustion plant, heat from burning coal is used to boil water, making steam that drives a steam turbine-generator. Only one- third of the energy value of coal is actually converted into electricity by most combustion plants, the rest is lost as waste heat.

A coal gasification power plant, however, typically gets dual duty from the gases it produces.

First, the coal gases, cleaned of their impurities, are fired in a gas turbine -- much like natural gas -- to generate one source of electricity. The hot exhaust of the gas turbine is then used to generate steam for a more conventional steam turbine-generator.

This dual source of electric power, called a "combined cycle," converts much more of coal's inherent energy value into useable electricity. The fuel efficiency of a coal gasification power plant can be boosted to 50 percent or more.

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