Underground Coal Gasification (UCG)
Underground Coal Gasification (UCG) is a process by which underground coal in the seam reacts with oxygen to produce a combustible gas. It can be compared with the process at the heart of IGCC. Conceptually simple, it offers many practical difficulties. It is currently believed, although subject to further study, that UCG may be able to go deeper than the 1,200 m limit. UCG is the partial in-situ combustion of a coal seam to produce a gas for use as an energy source. It is achieved by drilling two boreholes from the surface, one to supply oxygen and water/steam, the other to bring the product gas to the surface. The gas can be used for industrial heating, combustion in gas turbines for power generation, or for the manufacture of hydrogen, synthetic natural gas or other chemicals.
In addition to being able to access deeper coal seams, the benefits of UCG are the absence of waste tips and ash at the surface, the elimination of surface plant for coal gasification and coal preparation, and the availability of the energy as a clean fuel gas. Furthermore it provides access to large-scale coal deposits which would not otherwise be exploited, including reserves at depths below those suitable for conventional mining and also substantial off- shore coal resources.
Historically, this technology has been developed in the US, France, Belgium, the UK and the former Soviet Union. Interest waned with the advent of natural gas and concerns about contamination of surface water by UCG but in the 1990s there has been a resurgence of interest in the process. Nevertheless, an initial trial of deep seam UCG in Spain in 1992-1998 using new oil and gas technologies suggested that it may offer an alternative to conventional mining. It is currently undergoing trials in Australia, China, the US and at various European sites. In 1999 the Coal Authority initiated a study of UCG as an exploitable option for UK coal.