Reverse combustion along a bored hole (76 mm diameter) will be used during Lawrence Livermore Laboratory's next field experiment in underground coal gasification: Hoe Creek III. The enlarged channel produced by the reverse combustion will allow high gas velocities for the forward combustion phase of gasification.nIn the present experiments, reverse combustion along smaller boreholes (8.35 and 12.7 mm diameter) was investigated in coal blocks which were 0.5 m in diameter and 0.9 m long. In these experiments reverse combustion did not propagate with air as the feed gas. Three air velocities (14, 27, and 32 m/s) were tried in the 6.35 mm borehole and two velocities (7.5 and 21 m/s) were tried in the 12.7 mm borehole. All experiments were conducted at atmospheric pressure.
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