Подземная газификация угля: история и перспективы

Underground coal gasification (UCG) is an industrial process which converts coal into product gas. UCG is an in situ gasification process, carried out in non mined coal seams using injection of oxidants and steam. The product gas is brought to the surface through production wells drilled from the surface. The predominant product gases are methane, hydrogen, carbon monoxide and carbon dioxide. Ratios vary depending upon formation pressure, depth of coal and oxidant balance. Gas output may be combusted for electricity production. Alternatively, the gas output can be used to produce synthetic natural gas, or hydrogen and carbon monoxide can be used as a chemical feedstock for the production of fuels (e. g. diesel), fertilizer, explosives and other products. The technique can be applied to coal resources that are otherwise unprofitable or technically complicated to extract by traditional mining methods. UCG offers an alternative to conventional coal mining methods for some resources. It has been linked to a number of concerns from environmental campaigners.

The earliest recorded mention of the idea of underground coal gasification was in 1868, when Sir William Siemens in his address to the Chemical Society of London suggested the underground gasification of waste and slack coal in the mine. Russian chemist Dmitri Mendeleyev further developed Siemens' idea over the next couple of decades. In 1909–1910, American, Canadian, and British patents were granted to American engineer Anson G. Betts for "a method of using unmined coal". Between 1928 and 1939, underground tests were conducted in the Soviet Union by the state owned organization Podzemgaz.

After World War II, the shortage in energy and the diffusion of the Soviets' results provoked new interest in Western Europe and the United States. In the United States, tests were conducted in 1947–1958 in Gorgas, Alabama. The experiments were carried out in a partnership between Alabama Power and the US Bureau of Mines. The experiments at Gorgas continued for seven years until 1953, at which point the US Bureau of Mines withdrew its support for them after the US Congress withdrew funding. In total 6,000 tons of coal were combusted by 1953 in these experiments. The experiments succeeded in producing combustible synthetic gas. The experiments were reactivated after 1954, this time with hydrofracturing using a mixture of oil and sand, but finally discontinued in 1958 as uneconomical. From 1973–1989, extensive testing was carried out. The United States Department of Energy and several large oil and gas companies conducted several tests. Lawrence Livermore National Laboratory conducted three tests in 1976–1979 at the Hoe Creek test site in Campbell County, Wyoming. The National Coal Board abandoned the gasification scheme in summer 1959.

Cougar Energy and Linc Energy conducted pilot projects in Queensland, Australia based on UCG technology provided by Ergo Exergy until their activities were banned in 2016. Yerostigaz, a subsidiary of Linc Energy, produces about of syngas per day in Angren, Uzbekistan. The produced syngas is used as fuel in the Angren Power Station. In South Africa, Eskom (with Ergo Exergy as technology provider) is operating a demonstration plant in preparation for supplying commercial quantities of syngas for commercial production of electricity. African Carbon Energy has received environmental approval for a 50 MW power station near Theunissen in the Free State province and is bid ready to participate in the DOE's Independent Power Producer (IPP) gas program where UCG has been earmarked as a domestic gas supply option. ENN has operated a successful pilot project in China. In addition, there are companies developing projects in Australia, UK, Hungary, Pakistan, Poland, Bulgaria, Canada, US, Chile, China, Indonesia, India, South Africa, Botswana, and other countries. Compared to traditional coal mining and processing, the underground coal gasification eliminates surface damage and solid waste discharge, and reduces sulfur dioxide and nitrogen oxide emissions. For comparison, the ash content of UCG syngas is estimated to be approximately 10 mg/m3 compared to smoke from traditional coal burning where ash content may be up to 70 mg/m3. However, UCG operations cannot be controlled as precisely as surface gasifiers. Variables include the rate of water influx, the distribution of reactants in the gasification zone, and the growth rate of the cavity. These can only be estimated from temperature measurements, and analyzing product gas quality and quantity. Contaminants, such as ammonia and hydrogen sulfide, can be removed from product gas at a relatively low cost. However, as of late 2013, CCS had never been successfully implemented on a commercial scale as it was not within the scope of UCG projects and some had also resulted in environmental concerns. In Australia in 2014 the Government filed charges over alleged serious environmental harm stemming from Linc Energy's pilot Underground Coal Gasification plant near Chinchilla in the Queensland's foodbowl of the Darling Downs. When UCG was banned in April, 2016 the Queensland Mines Minister Dr Anthony Lynham stated "The potential risks to Queensland's environment and our valuable agricultural industries far outweigh any potential economic benefits. UCG activity simply doesn't stack up for further use in Queensland." Aquifer contamination is a potential environmental concern. Organic and often toxic materials (such as phenol) could remain in the underground chamber after gasification if the chamber is not decommissioned. Site decommissioning and rehabilitation are standard requirements in resources development approvals whether that be UCG, oil and gas, or mining, and decommissioning of UCG chambers is relatively straightforward. Phenol leachate is the most significant environmental hazard due to its high water solubility and high reactiveness to gasification. The US Dept of Energy's Lawrence Livermore Institute conducted an early UCG experiment at very shallow depth and without hydrostatic pressure at Hoe Creek, Wyoming. They did not decommission that site and testing showed contaminants (including the carcinogen benzene) in the chamber. The chamber was later flushed and the site successfully rehabilitated. Some research has shown that the persistence of minor quantities of these contaminants in groundwater is short lived and that ground water recovers within two years.