Entrained flow gasifier.
The most promising gasifier type for the power plant use is the entrained flow gasifier. Different commercial models are available and in development from various process technology companies.
The coal is first pulverised to a fine powder. This is fed into the gasifier and burned as a dry powder with steam , or as slurry with water. The oxygen required for combustion - less than the stoichiometric , is supplied as air or as oxygen from an air sepeartion unit.
The temperatures in the gasifier could go as high as 1600 °C. The pressures could be as high as 60 bar.
This temperature is higher than the coal ash fusion temperature resulting in the ash becoming molten slag. The hot gases and molten ash passes through a steam or water-cooled screen where the slag and ash particles separates form the gas stream. The slag cools and flows to the bottom of the gasifier for removal.
A typical molar gas concentration will be 30% Hydrogen, 50% Carbon monoxide, 10% Methane and balance CO2 percentage.
The hot gases are cooled in different heat exchangers and scrubbed for the removal of CO2, Sulphur Dioxide and other impurities.
The output is almost pure gas. This gas is fired in the gas turbine.