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Cavity growth occurring with crack extension and coal consumption during UCG processes directly influences the gasification efficiency and the estimated subsidence and gas leakage to the surface. This report presents an evaluation of the gas energy recovery, coal consumption, and gasification cavity estimation using a proposed stoichiometric method to analyze the coal gasification reaction process. We defined the evaluation parameters of rate of energy recovery and investigated the effects of different parameters using UCG trials conducted with coal blocks and coal seams, adopting different Linking-hole methods and operational parameters. Analyses of results obtained from laboratory experiments and small-scale field trials using V-shaped and L-shaped linking holes, and Coaxial-hole UCG models show that the gasification of Linking-hole models yielded average calorific values of product gas as high as 10.26, 11.11 MJ/m3 (lab.), and 14.39 MJ/m3 (field.). In contrast, the Coaxial-hole models under experimental conditions yielded average calorific values of product gas as: 7.38, 4.70 MJ/m3 (lab.) and 6.66 MJ/m3 (field.). The cavity volume obtained with Coaxial models was about half of the volume obtained from Linking-hole models. Results obtained for these UCG systems show that the feed gas and linking-hole types can influence coal consumption and product gas energy. Fissure ratios were also investigated. Results confirmed major factors underpinning gasification efficiency. Linking-hole types strongly influenced the development of the oxidization surface and fracture cracks for subsequent combustion in the gasification zone. Estimated gas energy recovery results support experimental observations within an acceptable error range of about 10%. Moreover, this stoichiometric approach is simple and useful for evaluating the underground cavity during UCG. Based on these results, we proposed a definition of the energy recovery rate, combined with the obtained volumes of gasification cavities that provide a definition of energy recovery and UCG effects. UCGにおいては炭層内のき裂進展に伴う燃焼空洞の拡大と石炭の消費が重要でありこれがガス化効率や安全性 (地盤沈下ガス漏洩等) に大きく影響する。本研究ではガス化効率回収エネルギーとガス化空洞の評価方法として化学量論および化学平衡に基づく評価手法を検討した。生成ガス組成と求めたガス化反応式から石炭の消費量ガス生産量等を推定する方法である。またエネルギー回収率を定義しUCG室内モデル実験及び露天炭鉱の炭層で行った小規模現場実験の結果を評価しリンキングの方式や注入ガス等のパラメータがガス化効率やガス化空洞の成長に与える影響を検討した。リンキングの方式としてL字V字同軸型のUCG実験を行いガス化効率の違いとその原因を明らかにした。すなわちリンキング型と同軸型モデルを比較するとリンキング型UCGモデルの方が発熱量が高く平均発熱量では前者が10.26/11.11 MJ/m3 (室内) 14.39 MJ/m3 (現場) であった。一方同軸型モデル試験では7.38/4.70 MJ/m3 (室内) と6.66 MJ/m3 (現場) と低い値であった。実験後の空洞体積の直接評価結果でもリンキング型の方がガス化領域が拡大していることを確認した。リンキング方式の方が炭層内にき裂を連続的に進展させやすいためと考えられる。またエネルギー回収率の評価では実験前後の供試体質量差から求めたエネルギー回収率と比較検討を行った。その結果両者の誤差は約10で検討した手法によりエネルギー回収率や燃焼ガス化領域の石炭消費量を推定できることがわかった。以上の結果より検討した化学量論法よる回収エネルギー評価手法は簡便で実用的であることが明らかになった。Special Edition for Coal Energy Technology; Development and Utilization of Coal Energ

Evaluation of Energy Recovery from Laboratory Experiments and Small-scale Field Tests of Underground Coal Gasification (UCG)