Enhanced-hydrogen gas production through underground gasification of lignite

Underground coal gasification is one of the clean technologies of in-situ coal utilization. Hydrogen production from underground gasification of lignite was investigated in this study based on simulation experiments. Pyrolysis of lignite, gasification activity, oxygen-steam gasification and the effect of groundwater influx were studied. As well, the advantages of lignite for stable underground gasification were analyzed. The results indicate that lignite has a high activity for gasification. Coal pyrolysis is an important source of hydrogen emission. Under special heating conditions, hydrogen is released from coal seams at temperatures above 350 °C and reaches its maximum value between 725 and 825 °C. Gas with a hydrogen concentration of 40% to 50% can be continuously obtained by oxygen-steam injection at an optimum ratio of steam to oxygen, while lignite properties will ensure stable gasification. Groundwater influx can be utilized for hydrogen preparation under certain geological conditions through pressure control. Therefore, enhanced-hydrogen gas production through underground gasification of lignite has experimentally been proved.