Gasification of Coal, Underground

the physicochemical process of converting coal into combustible gases by means of free or bound oxygen directly in the interior of the earth. The idea of underground gasification of coal was proposed by D. I. Mendeleev in 1888, with the British chemist W. Ramsay advancing the same idea in 1912. Research on the underground gasification of coal has been conducted in the USSR since 1930. In late 1933 the scientists I. E. Korobchanskii, V. A. Matveev, V. P. Skafa, and D. I. Filippov proposed conducting underground gasification of coal in a horizontal channel and preparing the gas generator by the shaft method. Between 1945 and 1948, Soviet scientists developed systems based on a shaft-free method of developing underground gas generators, which includes opening a section of a coal seam by boreholes and creating the initial gasification channels in a pillar of the seam. Depending on the geological conditions and the work system adopted, vertical, inclined, or inclined-horizontal boreholes are used.

The necessary reaction channels are created in a seam by percolation-fire or percolation linking of the boreholes, hydraulic fracturing of the seam, and directed sinking of boreholes along the coal seam. Reaction zones are formed in the gasification channels, where the gasification process, which usually occurs in an air draft, begins. The chemical reactions in underground gasification channels are analogous to the gas-generator process. As the coal seam is gasified, the reaction zones move and rock pressure causes the roof rock to shift and fill the gasified space. As a result, the dimensions and structure of the gasification channels remain relatively constant over a prolonged period; this is responsible for the constant composition of the gas obtained.

Two sequences of processes are used for underground gasification of coal. The draft may be fed from the direction of the coal pillar, with gas removal through the gasified space. Alternatively, the draft may be fed from the direction of the gasified space, with the gas removed from the direction of the coal pillar through the leading boreholes for heat treatment.

The lowest combustion heat for gas obtained in an air draft is 3.2–5 MJ/m³. The lowest combustion heat for gas obtained in an oxygen-enriched draft (60–65 percent oxygen) or a steam-oxygen draft is 7.6 MJ/m³. In terms of chemical composition, the gas is suitable for the synthesis of ammonia and hydrocarbons.

The use of fuel by the underground coal gasification method is also possible in cases when it is unprofitable to mine a coal deposit. Three underground coal gasification stations are in operation in the USSR: the Angren industrial station, which uses Middle Asian brown coals; the Shat industrial station, which uses brown coals from the Moscow Basin; and the Iuzhnoabin-skaia experimental industrial station, which uses anthracite coals from the Kuznetsk Basin. As of 1974, these three stations made about 1.5 billion m³ of producer gas a year.

Work on the underground gasification of coal is being carried out in the United States, the Federal Republic of Germany, Japan, and elsewhere. The construction of large industrial underground coal gasification stations was proposed in 1975 in the United States.

N. V. LAVROV and M. A. KULAKOVA