Forward and reverse combustion gasification of coal with production of high-quality syngas in a simulated pilot system for in situ gasification

This research focused on the feasibility and stability of applying the forward and reverse combustion approach to the in situ gasification of lignite and bituminous coal with oxygen or oxygen–steam mixtures as gasification agents, especially reverse combustion gasification. A high-quality syngas (H2 and CO) could be obtained using the reverse combustion gasification technique combined with forward combustion gasification in a pilot system for in situ gasification. The gasification time was extended more than 25% using the reverse combustion approach. The controlling conditions for reverse combustion gasification were obtained by comparing and analyzing experimental data. The results show the relationship between the inject gas flow within certain limits and velocity of the gasification flame was linear during reverse combustion. The underground conditions of the coal seam and strata were simulated in a pilot-scale underground gasifier during experiments. The combustion gasification of coal was carried out experimentally for over 5 days. The average effective content (H2 and CO) of syngas was in the range of 60–70%, meeting the requirement of synthesis gas. The optimal ranges of gasifying lignite and bituminous coal were found to be 1.5–2.0 and 1.3–1.75, respectively. The product gas flow was proportional to oxygen blast. These are expected to provide useful guidance on practical underground coal gasification operations and to give experimental evidence in support of theory.