Effect of Non-Uniform Bed Properties on Cavity Wall Recession

摘要

Heat-transfer limited wall recession rates are of appropriate magnitude when calculated with average rubble-bed temperatures and gas fluxes, but can be much lower than observed values when calculated with detailed models for uniform beds. The possibility that this discrepancy is the result of non-uniform bed properties is investigated here for a bed model consisting of a low-permeability ash core surrounded by a thin, high-permeability wall layer. This model gives heat-transfer limited wall rates in good agreement with observed values. It predicts local wall rates generally proportional to local oxygen fluxes from the ash bed into the wall layer, over wide ranges of bed configuration, total gas flow, and injected gas composition. The results indicate the importance of accounting for non-uniformities in rubble-bed properties if cavity-growth modeling is to yield reasonable predictions of resource recovery in underground coal gasification. 7 refs., 11 figs., 2 tabs. (ERA citation 10:048041)