Exergy optimisation of reverse combustion linking in underground coal gasification

Underground coal gasification (UCG) is a gasification process carried on in non-mined coal seams using injection and production wells drilled from the surface, which enables the coal to be converted into product gas. A key operation of the UCG is linking the injection and production wells. Reverse combustion linking (RCL) is a method of linking the process wells within a coal seam, which includes injection of an oxidant into one well and ignition of coal in the other so that combustion propagates towards the source of oxidant thereby establishing a low hydraulic resistance path between the two wells. The new theory of the RCL in typical UCG conditions has been recently suggested, The key parameters of the RCL process are determined using the technique of intrinsic disturbed flame equations. The present study is concerned with extending the results of the RCL theory to incorporate hydrodynamics of air injection and flow during RCL operation to derive mass flow rate of air to the combustion front as a function of the injection pressure. The results enabled an optimisation procedure maximising the exergy efficiency of RCL process.