UCG TECHNOLOGY
UCG EXPLAINED
Underground coal gasification (UCG) is the process by which coal is converted in situ into a combustible gas that can be used as a fuel or a chemical feedstock. UCG has the potential to exploit coal resources that are either uneconomic to work by conventional open cut or underground coal mining methods, or are inaccessible due to depth, geology or other mining and safety considerations.
The UCG process is initiated by drilling two adjacent boreholes into a coal seam, which is generally at a depth greater than 100 meters. Both vertical and/or deviated drill holes can be utilised to suit the size, shape and depth of the coal seam.
An oxidant such as air or oxygen mixed with steam is then injected under pressure into one of the boreholes (the injection well) and is ignited at the coal seam.The hot combustion gases flow through the coal towards the second borehole, with the resulting chemical reactions convertng the coal to a gas, which is then extracted through the second borehole (the production well).
Expansion of the process is achieved by the addition and linkage of further injection and production wells. The “coal gas” produced (referred to as “syngas”) has a low calorific value, and is a mixture of hydrogen, carbon monoxide, methane, carbon dioxide and higher hydrocarbons, along with nitrogen if air is used as the oxidant. After preparation, this syngas can be used to fuel a gas turbine, or as the feedstock for other chemical processing plant.
With an appropriate UCG technology, the cost of the gas per unit of energy is much lower than natural gas. When compared to current coal-fired power generation, these factors combine to provide a competitive cost of power at a smaller scale, with lower CO2 emissions, and longer term potential for CO2 removal and sequestration.