Underground Coal Gasification: One Path to Clean Coal Power?

The reserve limits for coal, for China as well as the rest of the world, can be postponed for several generations if the technology to gasify coal underground can be commercialized. Underground Coal Gasification (UCG) enables the access of deeper coal layers hitherto unavailable through conventional mining. Several modern pilot projects have been successfully completed in recent years and commercial projects are underway. _Rembrandt

The writer known as "Rembrandt" provided a very useful article on underground coal gasification at the Oil Drum blog. The images shown below are all taken from Rembrandt's article.

The technology has gained substantial interest in the last ten years as fossil fuel prices increased and concerns over rising fossil fuel imports in Europe have grown. There are now over 30 pilot projects either operating or in the planning stage in more than 25 countries, including the U.K., Australia, the U.S., South Africa, and China. Of special importance are:

• The 1 km deep 5 MW coal pilot carried out by ENN in China that ran for 26 months. The Chinese government last month signed a 1.5 billion USD commercial partnership with the UK government for commercial development of the technology to be deployed in Inner Mongolia.

• The Swan Hills project supported by the government of Alberta in Canada that should start in 2012 and become operational in 2015. The 300 MW syngas electricity plant is intended to be equipped with a carbon capture and storage facility. The commercial project follows a trial project in the region which successfully gasified coal in-situ at 1.4 km’s of depth.

• The Chinchilla project in Australia operated by Linc Energy which since 2008 was combined with a Gas-to-Liquids plant to produce 20 barrels per day from the UCG syngas. The company is presently finalizing the engineering aspects to begin construction of a 20.000 barrels of oil equivalent per day UCG-GTL plant in 2012. Linc Energy claims it can commercially produce a barrel of oil equivalent at a price of 30 dollars. _Rembrandt

The latest standard of the technology incorporates horizontal directional drilling. To obtain the gas two wells are drilled, an injection well which brings steam and oxygen or air underground to ignite the coal seam and maintain the process, and a production well which pumps out the raw syngas. Previously vertical wells were used which are difficult to connect and limit control over the formation of the underground cavity as they cannot be steered. Today's horizontal wells can be connected using a magnetic target and detector positioned in the tip of the wells. The injection well is retracted along the borehole to gasify the coal which flows to the production well. The process is monitored above ground based on measurements of pressure, temperature, gas flow rates, gas composition at the wells. These are informed by simulations carried out to model the process. The control of the process comes from the injection of the oxidant, as too low or a halting of flows will stop the process.

The produced syngas varies in composition depending on the coal quality and for a standard horizontal two well retractable injection point technique (CRIP) includes hydrogen (11-35%), carbon monoxide (2-16%), methane (1-8%), carbon dioxide (12-28%) and other smaller components. Specific alteration of the gasification system can also result in a variance of the syngas composition. Yang et al. (2008) published about a field test to manufacture hydrogen using a two stage gasification process with multiple steam injection points to raise the temperature. In the test syngas was succesfully produced with on average 50%+ hydrogen content with a range between 40% to 73%, and both CO and CH4 contents of over 6%. _Rembrandt

Costs for Production and Electricity Produced

Costs for Natural Gas per MMBTU for Comparison
Several estimates have been made of the cost of an electricity plant based on UCG syngas. The main physical variables are the quality of the coal, depth and thickness of the coal seam, linking distance of the injection and production well, distance between the cavities, and sweep efficiency. The calculations based on theoretical and actual operations point to a cost range of 1 to 8 USD per GJ of produced syngas. The main cost variation is the usage of air or enriched oxygen for injection, the thickness of the coal seam, and the depth of drilling. The later two factors determine the number of wells that need to be drilled and their required length. Oxygen-blown gasification is preferred in case of adding Carbon Capture and Storage technology.

• The estimate of Marc Mostade of Clean Coal is a production cost of 2.5 to 4.5 USD per GJ of syngas, based on a 800 meter deep 500 MW thermal size UCG plant and a coal seam of 4 to 6 meters thickness at 800 meters of depth. The difference is caused by the usage of air-blown or oxygen-blown syngas. Information about the variables underlying his calculation can be found in his ASPO 9 presentation.

• Based on the Chinese ENN Pilot a total cost of 0.9 to 1.7 USD cents per cubic meters of syngas was documented, which translates into 1 to 1.9 USD per GJ of syngas assuming a higher heating value of 9 MJ/Nm3

• In 2007 GasTech carried out an analysis of costs based on coal in the US Powder River Basin using air-blown and oxygen-blown gasification. These were estimated at a cost of 1.5 to 2.4 USD per GJ of syngas.

• In 2011 the School of Public and Environmental Affairs of Indiana University calculated the production costs for air-fired syngas via UCG in the state of Indiana in the US at 4.6 to 7.7 USD per GJ of syngas for respectively syngas produced via enriched or air, assuming a coal seam thickness of 2 to 3.5 meters at 200 meters of depth or more.

These cost levels are when averaged equal to or below the present day price of natural gas in the US, EU and Asian markets, as shown in figure 4 below. The lower cost range is on par with today’s coal price on a GJ energy basis. _Rembrandt

Until the potential problem groundwater contamination with coal tars can be worked out, widescale adoption of this technology near populated zones is unlikely to take place outside of China and perhaps Africa. But it is quite likely that a variant of in situ coal gasification will be adopted within the next 20 years -- if crude oil prices continue to trend upwards and if national governments continue with their suicidal anti-nuclear policies and general policies of energy starvation.

The general technology approach is not that difficult to implement, and with further refinements over time it should be possible to prevent groundwater contamination. In selected locations where environmental concerns are not as widespread as in most western nations, this technology is apt to go forward within the next few years.

Underground Coal Gasification Moving Ahead in Alaska

Underground coal gasification (UCG) is the in-situ gasification of coal in the seam. It is achieved by injecting oxidants, gasifying the coal and bringing the product gas to surface through boreholes drilled from the surface. The gas is used for power generation, industrial heating or as chemical feedstock.UCG Engineering Ltd has recently undertaken reviews of the technilogy and provided designs of underground configurations for demnonstration and commercial applications. _UCG EngineeringLTD

Queensland-based LINC Energy has won new exploration licenses for development of underground coal gasification in Alaska.

January 27, 2011

Linc Energy is one step closer to becoming a significant part of the USA domestic energy market after winning further underground coal gasification (UCG) exploration licences in Alaska.

The Queensland-based company announced today it has been successful in its tender to the Alaska Mental Health Trust Authority for the grant of 181,414 acres of UCG licences.

The decision follows more than six months work in UCG geological assessment and competitive tender submissions from a unit spanning the Linc Energy Australian and United States offices.

Linc CEO Peter Bond says the outcome greatly advances the company’s strategic goal to bring commercial UCG development to Alaska.

“We have known for a long time that Alaska, the Cook Inlet Basin in particular, holds significant coal deposits,” Bond says.

“Importantly, the decision confirms that we were successful in obtaining 100 percent of the exploration areas we applied for in the competitive tender process,” he says. _qbr.com

Another likely site for commercial development of underground coal gasification (besides China) is Canada.

...Mr. Fallows says the only rational response for the U.S. is to use China as “a huge laboratory for deploying technology.” He cites the potentially game-changing technology known as underground coal gasification as an example of what a Sino-American technology partnership could achieve.

With this technology, jets of pure oxygen would be blasted, deep underground, into seams of coal. Under intense pressure, a controlled burn would take place. The heat would boil the saline water that occurs naturally far below groundwater. The resulting steam would set off the chemical reactions that turn coal into gas – which would be used (such as “natural” gas) to fuel “coal-fired power plants.” Yet no coal would ever be “mined.” The residual char and ash would remain put, along with the sulphur and nitrogen associated with dirty coal. Above ground, the C02 would be separated from the synthetic gas and recycled for use in the enhanced recovery of crude oil.

This is all marvellous science, but Mr. Fallows errs in thinking that China offers the only laboratory, or the best laboratory, to test it. The technology he describes in futuristic terms is already well advanced in the Swan Hills Synfuels development in Alberta – the largest coal gasification project in North America and the deepest underground coal-to-gas operation in the world. Beginning in 2015, Swan Hills will deliver synthetic gas from 1,400 metres underground – and, quite possibly, lead the entire world in clean coal technology. _GlobeandMail

Alaska, China, Alberta, and likely Australia. Four locations where underground coal seam gasification is likely to be developed, perfected, and commercially developed.

By eliminating the need for mining, UCG offers some benefits to the environment over traditional coal mining and coal gasification methods. Immediate benefits include the elimination of solid waste discharge and reduction in sulphur dioxide (SO2) and nitrogen oxide (NOx). In traditional coal mining, large quantities of coal ash, oxides, waste rock and radioactive waste are common discharges. In the case of UCG, this waste is either avoided or contained underground. Due to the absence of coal mining, Appalachian mountaintops are not stripped bare and remain largely preserved, hence there is no need for tailing and ash dams. For comparison, the ash content of UCG syngas is estimated to be approximately 10 mg/m³ compared to smoke from burning where ash content may be up to 70 mg/m³. _Sourcewatch

More information:
UCG Association
UCG Engineering LTD