Shaftless Methods

FIGURE 21.30 Shaftless method (percolation method) of underground coal gasification (a) section through boreholes and (h) plan of boreholes. (From Braunstein, H.M. et al., Environmental health and control aspects of coal conversion An information overview. Report ORNL-EIS-94, Oak Ridge National Laboratory, Oak Ridge, TN, 1977.) 

Air or air and steam are blown through one hole, and gas is removed from the second reverse combustion is permitted in this method. As the burning progresses, the permeability of the seam increases and compressed air blown through the seam also enlarges cracks in the seam. When combustion of a zone nears completion, the process is transferred to another pair of boreholes. 

and Lau, F.S. 1980. In Coal Processing Technology. American Institute of Chemical Engineers, New York, Vol. VI, p. 166. 

Baughman, G.L. 1978. Synthetic Fuels Data Handbook. Cameron Engineers, Denver, CO. 

Berkowitz, N. 1979. An Introduction to Coal Technology. Academic Press, Inc., New York. 

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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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