Underground Coal Gasification

Underground Coal Gasification (UCG) is a method of converting unworked coal - coal still in the ground - into a combustible gas which can be used for industrial heating, power generation or the manufacture of hydrogen, synthetic natural gas or diesel fuel.

UCG technology allows countries that are endowed with coal to fully utilise their resource from otherwise unrecoverable coal deposits in an economically viable and environmentally safe way. UCG turns this resource into high value products:

• clean power
• liquid fuels
• syngas
• fertilisers and other chemical feedstocks.

UCG uses a similar process to surface gasification. The main difference between both gasification processes is that in UCG the cavity itself becomes the reactor so that the gasification of coal takes place underground instead of at the surface.

UCG Process

The basic UCG process involves drilling two wells into the coal, one for injection of the oxidants (water/air or water/oxygen mixtures) and another well some distance away to bring the product gas to the surface.
The coal at the base of the first well is then heated to temperatures that would normally cause the coal to burn. However, through careful regulation of the oxidant flow, the coal does not burn but rather separates into the syngas. The syngas is then drawn out of the second well. Two different methods of UCG have evolved and are commercially available:

• Vertical wells combined with methods for opening the pathway between the wells.
• Inseam boreholes using technology adapted from oil and gas production that can move the injection point during the process

Tests in Europe in the late 1990s demonstrated it was possible to have greater control of deep drilling, to create larger cavities in the coal seam for the gases, and to provide more efficient combustion. In addition, while the process had previously been criticised for generating large quantities of hydrogen as a useless by-product, hydrogen is now in demand as a feedstock for the chemical industry and shows potential as an alternative fuel for vehicles.
The advantages in the use of this technology - especially in the emerging markets of China, India and South Africa - are the low plant costs (as no surface gasifiers are required) and the absence of coal transport costs.
UCG also presents the opportunity to reduce emissions as there are fewer surface emissions. UCG technology could also have synergies with CCS as the CO₂ could be stored in the coal cavity after gasification.

Developments, Projects & Interest

In the last few years there has been significant renewed interest in UCG as the technology has moved forward considerably.

• China has about 30 projects in different phases of preparation that use underground coal gasification.
• India plans to use underground gasification to access an estimated 350 billion tonnes of coal. In 2007 India compiled a 93-page status report on underground coal gasification that highlighted interest from many of the country's biggest companies.
• South African companies Sasol and Eskom both have UCG pilot facilities that have been operating for some time, giving valuable information and data.
• In Australia, Linc Energy has the Chinchilla site, which first started operating in 2000. Carbon Energy has completed a successful 100 day commercial scale study in Bloodwood Creek in 2008.

Demonstration projects and studies are also currently under way in a number of countries, including the USA, Western and Eastern Europe, Japan, Indonesia, Vietnam, India, Australia and China, with work being carried out by both industry and research establishments.
A number of issues remain to be resolved before wider deployment can be achieved.