Jaded, UCG works on the principal of heating a fuel to vapourise...

Jaded,

UCG works on the principal of heating a fuel to vapourise the gas the is then combustable. i.e. a coal fire heats the coal to vapourise the gas that can then burn to produce energy.

If you heat the coal in an atmosphere of restricted oxygen then the gas is released but not combusted. So by burning the natural occuring methane underground with restricted oxygen the coal is heated to release its contained energy (of which a good proportion is methane), and when combined with steam/oxygen instead of air you get a hydrogen rich gas.

CBM tries to collect the methane that is trapped in the coal, which then leaves the coal in the ground for mining. If the coal is deep then mining isn't an option, where UCG should be used.