Gasification underground

This section outlines the methods available for the in situ gasification of coal. In terms of the combustion process itself, both forward and reverse combustion are employed. Forward combustion is defined as movement of the combustion front in the same direction as the injected air whereas 

The concept of the gasification of coal in the ground is not new in 1868, Sianens in Germany proposed that slack and waste be gasified in the mine without any effort being made to bring this waste material to the surface. However, it was left to Mendeleev (in 1888) to actually propose that coal be gasified in the nndisturbed (in situ) state. 

A considerable volume of investigative work has since been performed on the in situ gasification of coal in the former USSR, but it is only in recent years that the concept has been revived in Russia, Western Europe, and North America as a means of gas (or even liquids) production (Elder, 1963 Gregg and Edgar, 1978 Thompson, 1978 King and Magee, 1979 Olness, 1981 Zvyaghintsev,1981). 

FIGURE 20.9 Underground coal gasification system. (From Berkowitz, N., An Introduction to Coal Technology, Academic Press, Inc., New York, 1979.) 

In addition, at the high temperatures that can frequently occur, moisture injected with oxygen or even moisture inherent in the seam may also react with the coal to produce carbon monoxide and hydrogen  

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Injection hole, Is used to Ignite the coal, and subsequent gasification then simulates underground gasification by the so-called stream method. 

Shuqin, L., Limei, Z., Xuedong Y. and Li Y. (2004) Leaching experiment of trace elements in lignite residue from underground gasification. Chemical Journal on Internet, 6(11), http //www.chemistrymag.org/cji/2004/ 06b081pe.htm, accessed October 13, 2008. 

Underground gasification eliminates much of the mining and its operational costs are relatively low. It can be used in seams which are thin or poor in quality. But the method produces no coke. 

Gubkin, I.M., 1953, Podzemnaia gazifikatsiia neftianykh plastov i termicheskii sposob dobychy nefti [Underground gasification of petroleum deposits and thermal methods of petroleum production]. Trudy n. Izdatel stvo AN SSSR. (professional paper). 

One example of a shaftless system for underground gasification of coal is the percolation or filtration method (Figure 21.30) in which two boreholes are drilled from the surface through the coal seam. The distance between boreholes depends on the seam permeability. 

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