Underground Coal Gasification

Underground Coal Gasification (UCG) is a method of converting unmined coal into combustible syngas – a combination of hydrogen and carbon monoxide.

This syngas can be used for industrial heating, power generation or the manufacture of hydrogen, synthetic fuels or other chemicals. The gas can be processed to remove its CO2 content, thereby providing a source of clean energy with minimal greenhouse gas emissions.

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 the 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 but 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
Demonstration projects are under way in a number of countries, including the USA, Australia, Western Europe, China and Japan.

Chinchilla Project
The Chinchilla project in Australia started in 1999 and is the largest underground coal gasification project outside the Former Soviet Union. The project ran for over thirty months with a total of 35,000 tonnes of coal gasified.

The technique demonstrated a 95% recovery of the coal resource, with 75% total energy recovery. The operators, Linc Energy, plan to expand their current Chinchilla project to include the production of coal to liquid fuels and electricity from the site.