Underground Coal Gasification in the USSR

Summary

The interest currently displayed in this problem is due to the fact that the process offers a number of specific advantages:

• 1. Besides opencast coal mining this method is the only means of working coal which does not entail heavy labour underground.

• 2. By accomplishing in a single operation the extraction of coal and its conversion into a gaseous fuel, underground gasification makes it possible to avoid the heavy capital investments required for coal gasification in surface gasifiers, as well as to increase labour productivity.

• 3. Underground gasification substantially increases the volume of world energy reserves through the utilisation of substandard and high-sulphur coal reserves and of deposits which it is difficult to work by ordinary methods.

The paper reviews basic trends in the development of underground coal gasification in the USSR and discusses questions relating to the selection of deposits for the construction of plants in accordance with established criteria.

A short description is given of the operation of pilot and industrial plants located in areas with differing mining and hydro-geological conditions.

The underground coal gasification plants were used to make gas for energy production. Air injection was used in most cases. The process is carried out by the semi-conversion system, part of the volatile matter being burnt up by air oxygen. The heat of combustion of the gas obtained lies within the range 800–1,100 kcal/m, depending on the type of coal, the mining and hydro-geological conditions of the deposit and the technological characteristics of the process.

A description is given of a test aimed at obtaining process gas suitable for ammonia and petrol synthesis. In this case injection was by oxygen-enriched air with the addition of various quantities of steam. The combustion heat of the gas was, on average, 1,650 kcal/m³ throughout the test period. Removal of Co₂ and H₂ from the gas will raise the combustion heat to 2,300 kcal/m³. Emphasis is laid on the stability in time of the underground gasification process and on the fact that it can be regulated.

On the basis of the conclusions drawn from the extensive research carried out and in the industrial operation of underground coal gasification plants, the paper reviews the problems involved in the preparation of the coal seams: drilling different types of boreholes, various methods of creating reaction channels between the boreholes, and the principal technological process patterns for different coal deposit conditions. Information is given on the dynamics of gas formation in a reaction channel and an analysis is made of the effect of various factors on the heat of combustion of the gas and on the size of reaction areas.

Questions relating to the integrated utilization of the products of underground coal gasification, including production of sulphur, hyposulphite, etc., are also considered.

The existence of still unused possibilities of increasing the efficiency of the underground gasification process is noted.