By Julie Lauder & Phil Smith, Underground Coal Gasification Association

Reproduced from American Coal magazine

Underground Coal Gasification is finally coming into its own in many parts of the world, but the US market has yet to actively embrace this technology. Could this be about to change?

Many believe the term “clean coal” to be an oxymoron. Despite that resistance, the amount of coal available globally ensures that it will be a mainstay of our energy needs well into the future. Therefore, the challenge facing industry is to find methods that ensure we can extract the energy from coal in as low-cost, safe, and environmentally responsible ways as possible.

That Clean Coal, and Underground Coal Gasification (UCG) certainly has a part to play.

Many believe the UCG process of converting coal to energy offers huge potential to clean coal and enable economical access to stranded coal deposits, an estimated 1.7 trillion metric tones (1.9 trillion short tons) globally. It’s not a new idea, but one that is rapidly coming to the attention of policy makers, as an economical and politically acceptable method to meet growing energy needs.

Mining coal has environmental impacts; so extracting the energy from coal while it is still in the ground makes a lot of sense. Via UCG, coal is directly converted to a synthetic gas – suitable for industrial heating, power generation, hydrogen manufacture, synthetic natural gas, diesel fuel, liquid fuels, fertilizers and other chemical feedstock. Many experts believe UCG could triple or even quadruple recoverable coal reserves globally.

Converting just five percent of U.S.-based coal reserves to liquid fuels would provide an energy resource equivalent to crude reserves of 29 billion barrels!

One would expect the developing and energy-hungry nations of India, China and South Africa to be advancing and researching alternate technologies such as UCG. But other nations  Australia, Canada, New Zealand and many in Europe  are now also vigorously investigating commercial deployment of UCG, as the map above shows.

That is good news for the US, which like many western economies has seen a huge backlash towards coal production, while at the same time an increased demand for domestic energy.

Plus, UCG is not new to the US. Many recent technological and operational developments are a direct result of over 30 extensive US trials that were carried out between 1973 and 1989, in Wyoming, Colorado, and Pennsylvania, under the auspices of the DOE and Lawrence Livermore National Laboratory* (LLNL), which remains a leading authority on UCG.

Additionally, as UCG is a multidiscipline technology, many in the US already possess the skills, knowledge and expertise that the global UCG industry is seeking.

The process of converting coal to gas underground involves using horizontal and directional drilling techniques, where two wells are drilled into the coal. An oxidant – either air or oxygen or air/oxygen, with or without steam is fed into one well.

The coal is then ignited and partially combusted, and the resultant product gas is brought to the surface for processing via the second well. The process can be halted at any time by stopping the injection of the oxygen or air. Once a particular coal seam is exhausted, new wells are drilled to initiate the gasification reaction in a different section of the coal seam. A pair of wells can last as long as 15 years. The technology also lends itself easily to carbon capture, asthe process enables relatively simple, low-cost carbon removal from the syngas, prior to use.

Can all coal be gasified underground?

Alas, no. Many factors such as seam depth and thickness, coal grade, groundwater conditions, and seam inclination must all be considered; site selection is paramount for a successful project. Generally, seams between 120m and 2000m (390 to 6,600) deep are preferable.

After the coal is converted to syngas in a particular location, the remaining cavity (which will contain the leftover ash or slag from the coal, as well as other rock material) may be flooded with saline water and the wells capped. There is also growing interest in using these cavities to store the carbon dioxide captured from the aboveground processing.

UCG operates at pressures below that of the natural coal seam pressure, thus ensuring materials are not pushed out into the surrounding formations. This is in sharp contrast to hydraulic fracturing in oil and gas production, where pressures significantly above natural formation pressure are used to force fracking chemicals into the formation.

Despite many apparent benefits, obstacles to UCG remain.

One obstacle is a lack of funding (due to a lack of coherent licensing and regulatory frameworks) and lack of government interest (mainly due to negative connotations associated with coal). There are also environmental concerns, which hamper growth of the sector, such as possible groundwater contamination and subsidence  both of which can be mitigated through careful site selection, project design, and monitoring.

It is in the interests of all that the UCG process is safe and fully tested, so public and political concerns are acknowledged and explored. This is helped by live, active UCG projects currently being conducted in nations around the world and bolstered by a high level of interest in many others.

The Chinchilla and Bloodwood Creek sites in Queensland, Australia and Mecsek Hills site in Hungary have moved the process up a notch as they are now producing syngas for commercial use.

In India, the government is looking at UCG to utilize the 60 percent of its 270 billion tones of unminable coal. In neighboring Pakistan the Thar project in Sindh Province is expected to produce 100MW of electricity by the end of 2013.

In the US, a project at Cook Inlet, Alaska, plans to go commercial in 2015, as does the Swan Hills UCG site in Alberta, Canada. There is also substantial interest for projects in Wyoming, Montana, North Dakota, Colorado, Alaska and many commercial UCG companies are looking to expand operations in the US in the coming year.

As the industry grows, so too does the need to share knowledge surrounding national regulation and non-commercially sensitive technological advancements. The need has never been greater to show both investors and regulators that UCG can play a major role in alleviating the energy crisis by providing low cost, environmentally-sensitive energy for decades to come.

http://www.americancoalonline.com/features/underground-coal-gasification/