3698.     WILKINS, E. T.  Underground Gasification of Coal.  Fuel Econ. Rev., vol. 23, 1944, pp. 14-18, 58; Gas World, vol. 121, 1944, pp. 545-550; Am. Gas Assoc. Monthly, March 1945, pp. 119-123.

        Review of Russian prewar proposals.  3 methods of gasification are given:  Stream method applicable only to steeply dipping seams and requiring some preliminary hand labor; percolation method intended for use with horizontal seams, eliminates all underground labor and depends on the development of shrinkage cracks and fissures in the coal when heated, so that part of the seam becomes readily permeable to gas; and borehole-producer method, a combination of the 2 preceding methods.  A supply of O₂ for air enrichment is desirable for satisfactory gasification and would appear to add an appreciable, but not a prohibitive, amount to the cost of gasification.  3 different gases have been generated:  Producer gas obtained by continuous blowing with air; water gas generated by alternate 20 min. blasts of air and steam; and H₂-rich gas.  It is proposed to use the gas of lower calorific value as power gas for electricity generation and H₂-rich gas for chemical processes such as NH₃ synthesis and Fischer-Tropsch process.  Available details are given of trials carried out on 5 different coal seams.  No definite data have been obtained so far on the % of coal gasified.  The cost of producing gas by this method is said to be about 1/3 of that with normal producers -- 1-2 d. per therm as against 4-6 d.  Capital expenditure is about 60-70% as that of normal gas-producer plants, the principal costs being those of the blast- and power-supply installations.

        ----------.  See abs. 304.