A project in the UK aims to combine the underground gasification of coal with fuel cell technology to produce extremely low carbon emission electricity from coal.
This is the aim of a memorandum of understanding (MoU) signed last month between two British companies, Thornton New Energy and Waste2Tricity, which is intended as the first step in the creation of a joint venture programme which will combine the two technologies to cleanly exploit deeper lying coalfields in Britain.
In January, Thornton New Energy was awarded the UK’s first underground coal gasification licence by the country’s coal authority, covering coalfields under the Firth of Forth, in Fife, Scotland. These reportedly cover more than 200 square miles (over 500 km2) and were previously unmineable, lying 500 m or more below the surface, which is deep by coal-mining standards.
Thornton New Energy is a subsidiary of another UK company, BCG Energy, while Waste2Tricity has the exclusive rights for the application of alkali fuel cells, developed by another British enterprise, AFC Energy, with any gasification techno- logy (including gas from waste) within Britain. The aim is to use hydrogen gas produced by the underground gasification of the coal to feed AFC Energy’s fuel cells, and so gene- rate electricity with water as the waste product. The extraction of hydrogen from the gas generated from the coal will allow the free capture of at least 99% of the carbon dioxide also produced by the gasification process, which can then be stored or sequestrated.
Underground coal gasification is very simple in principle: you gasify the coal in its seams underground, extracting just the gas – you are simultaneously extracting and processing the resource. This is done by drilling boreholes into the coal, and injecting mixtures of water and air or water and oxygen. The mixture plus the coal is ignited (through an ignition well) and the result is the burning of the coal, creating hydrogen-rich synthetic gas (syngas), which is extracted through a production well.
Thornton New Energy plans to use a process, called Controlled Retractable Ignition Point (Crips), to exploit the Fife coalfields. This will involve using the most recent long-reach and horizontal drilling and completion methods developed by the oil and natural-gas industry. A number of injection boreholes will be drilled and these will usually be long-reach wells with horizontal sections up to 500 m in length. A mixture of oxygen and steam will be injected down them. The ignition well will have an ignition source running down it, while the produc- tion well will be the simplest type of borehole, and will collect the syngas produced by the burning of the coal. When the coal around the ignition well is depleted, the ignition source will be retracted from the well and inserted into a new ignition well – hence, the term ‘Crips’ for this technique.
In terms of the MoU with Waste2Tricity, the resulting syngas will, after reaching the surface, be separated into two streams by a process known as pressure swing absorption; one stream will be pure hydro- gen, which will then feed the fuel cells, and the other stream will be pure carbon dioxide. (In other applications, the syngas could also be used to directly fuel modified gas turbines, although it has only one-third of the calorific value of natural gas, or it could be turned into liquid fuels using Fischer-Tropsch processes – perfected, it should be noted, by South African petrochemicals group Sasol).
The underground gasification of coal is not a new idea. The concept dates back to the nineteenth century, and is believed to have originated in 1868 with two German-born engineers, the brothers Werner and Wilhelm Siemens (although Wilhelm Siemens had emigrated to the UK in 1844 and became British in 1859, being knighted in 1883 and ending up as Sir William Siemens; Werner Siemens remained in Germany, founding what is now the global Siemens group, and was ennobled in 1888, becoming Werner von Siemens – the two brothers remained closely associated throughout their lives). The concept was further developed, including detailed design work, in the 1880s and 1890s by Russian scientist Dmitry I Mendeleev.
In 1928, the then Soviet Union became the first country to develop underground coal gasification in practice and opened its first commercial-scale plant in 1938. Technically successful trials were held in various countries after the Second World War, but very cheap oil and natural gas rendered the technology uncompetitive. But oil and gas are no longer very cheap, which is why underground gasification of coal is back in favour, with various projects under development, including those by Sasol in South Africa.