Reverse combustion along a directionally-drilled horizontal channel 76 mm in diameter will be used in Hoe Creek No. 3. The enlarged channel at the bottom of the Felix No. 2 coal seam produced by the reverse combustion will allow high gas flow rates for the forward combustion phase of gasification. This paper discusses the experimental and mathematical modeling of reverse combustion along a horizontal bored channel in shrinking coal. The purpose of the modeling effort is to provide information to assist in planning the reverse combustion phase of the Hoe Creek No. 3 field experiment. In these experiments at one atmosphere reverse combustion did not propagate with air as the feed gas. Reverse combustion did, however, propagate when the feed-gas oxygen content was increased to 32%. An existing LLL model of underground coal gasification was modified and used to simulate the reverse combustion process. Preliminary results agree qualitatively with the experimental results. This model indicates that reverse combustion will propagate at a pressure of 5 atmospheres without enrichment of the air with oxygen. Simulations of field scale experiments are also discussed. The experimental and mathematical modeling results have yielded rather negative results to date, which serves as a warning of possible trouble in the Field Experiment. We have hopes that such trouble will not actually be encountered because the conditions for reverse combustion are somewhat more favorable in the field situation than those tested in the laboratory. A number of remedies have been conceived for use in case of trouble: (1) enrich the air with oxygen during reverse combustion, (2) add propane to the air, and (3) heat the air. These remedies and provisions for implementing them are being considered. (ERA citation 04:045808)
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