Underground Coal Gasification (UCG) is a method of converting unworked coal – coal still in the ground – into a combustible gas which can be used for industrial heating, power generation or the manufacture of hydrogen, synthetic natural gas or diesel fuel.

UCG technology allows countries that are endowed with coal to fully utilise their resource from otherwise unrecoverable coal deposits in an economically viable and environmentally safe way. UCG turns this resource into high value products:

• clean power
• liquid fuels
• syngas
• fertilisers and other chemical feedstocks.

UCG uses a similar process to surface gasification. The main difference between both gasification processes is that in UCG the cavity itself becomes the reactor so that the gasification of coal takes place underground instead of at the surface.

[Source:  http://www.worldcoal.org/]