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Underground Coal Gasification (UCG)
Underground Coal Gasification (UCG)
• UCG is an in-situ gasification process carried out in non-mined coal seams using injection of oxidants, and bringing the product gas to surface through production wells drilled from the surface.
• The predominant product gases are methane, hydrogen, carbon monoxide and carbon dioxide.
• The technique can be applied to coal resources that are otherwise unprofitable or technically complicated to extract by traditional mining methods.
• UCG offers an alternative to conventional coal mining methods for some resources.
• Compared to traditional coal mining and processing, the underground coal gasification eliminates surface damage and solid waste discharge, and reduces sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions.
• UCG has the potential to exploit the coal resources regarded as either uneconomic to work by conventional underground coal extraction or in-accessible due to depth, geology or other mining and safety considerations.
• This is one of the identified Clean Coal Technologies.
• The UCG technology uses a variety of modern drilling methods, including high-precision directional holes, as well as conventional vertical and inclined (or angled) holes.
• In its arsenal are various methods of well-linking, the capability to inject different oxidants (air, enriched air, O2/H2O, CO2/O2 and so on), and a great variety of designs of underground gasifiers.
• It can be applied to coal in a wide range of geological conditions
• The basic UCG process involves drilling tube wells into coal; one for injection of the oxidants (water/air or water/oxygen) and other well some distance away to bring the product gas to the surface.
• The product gas is a combustible Syngas containing hydrogen, carbon monoxide and methane that can be used as a fuel or chemical feedstock.
• A cavity is formed as the coal burns and the roof is allowed to collapse. Eventually a stage is reached when gasification efficiency declines and a new gasifier must be initiated.
The principal UCG processes can be divided into two stages:
A. Pyrolysis: During pyrolysis coal is converted to char which releases tars, oils, low molecular hydro carbons and other gases.
B. Gasification occurs when water, oxygen, carbon dioxide and hydrogen react with the char.
The main gases produced are carbon dioxide, methane, hydrogen and carbon monoxide. Methane is a product of pyrolysis and its formation is favoured by low temperature and high pressure.
Economic Benefits of UCG:
• No need to transport the coal.
• No need for disposing of ash or slag.
• No need for an above ground gasification plant.
• No need to prepare the coal to be fed into a reactor.
• No need for coal handling.
• No need for the coal to be mined.
• Significantly lower capital cost for project development than that of above ground plants.
Environmental Benefits of UCG:
• No environmental impacts traditionally associated with coal mining and handling.
• All or a substantial portion of the sulfur, mercury, arsenic, tar, ash and particulates found in coal remain underground.
• Underground saline water is used.
• Significantly reduced use of groundwater or freshwater.
• No landfill disposal required for ash or slag.
• Coal seams being gasified are below the fresh drinking water supplies.
• Minimal land use.
• Significantly reduced criteria air pollutants.
• Any sulfur or metals that reach the surface do so in a chemically reduced state, making them easier to remove
UCG Policy Framework:
• The UCG policy framework has been framed in line with the existing policy for Coal Bed Methane (CBM) development on revenue sharing basis.
• Development of UCG has been envisaged to provide for energy security and will be adopted for offering the blocks through competitive bidding.
• Inter-Ministerial Committee under the Union Ministry of Coal with members from concerned Ministries will be responsible for identification of the areas.
• Central Mine Planning and Design Institute Limited (CMPDIL) will be the nodal agency for all business related proposals and regulations.