IN SITU COAL GASIFICATION: AN EMERGING TECHNOLOGY

Abstract

A literature review was conducted on in situ coal gasification with particular attention to environmental effects, benefits and process controls of this emerging technology. In situ coal gasification also known as underground coal gasification (UCG) appears to be both technically and economically feasible and exhibits many potential advantages over the conventional mining methods. The resource for UCG is principally un-mined coal seams. The gasification process creates synthesis gas that can be used as fuel, or feedstock for further chemical processes such as NH3 production or liquid fuels. An oxidant (usually air, oxygen, or steam) is injected into the coal seam and reacts with the coal and water present in the seam to produce syngas that is extracted through a production well. As the gasification process proceeds, the cavity grows radially outward and upward from the injection well. UCG has some environmental benefits relative to conventional mining including (1) no discharge of tailings, (2) reduced sulfur emissions (3) reduced discharge of ash, Hg and tar, and (4) the additional benefit of carbon capture and sequestration. Hydraulic control is the most important feature of UCG. It controls the gasification process and prevents groundwater contamination. Contaminants from the UCG process can affect water quality making sources for human and wildlife consumption unusable. Coal resources that are not suitable for conventional mining are ideally suited for UCG. Ultimately, UCG will compete in the marketplace with conventional and innovative gasification technologies to provide syngas for fuel and power applications, which will in turn compete against other fuels such as biodiesel and gasoline. In the coming years, these technologies will compete not just on an economic basis but on the costs and difficulties of managing CO2 emissions.