Pure oxygen condition forced oxidation ignition process of underground coal gasification

Abstract Underground coal gasification without shaft is a technology that uses directional drilling technology to gasify deeply buried coal. The technology first needs to ignite the coal seam during drilling, but as the depth of the coal seam (drilling) increases, it is very difficult to ignite the underground coal seam. In order to ignite the underground coal seam more safely and effectively, the forced oxidation ignition technology has been developed; that is, the coal seam is heated by hot oxygen, and the coal seam is rapidly oxidized and released to ignite the coal seam. Due to the complex confidential environment, it is challenging to ignite underground coal seams. To ignite the underground coal seams more safely and effectively, this paper used a self‐made reactor to simulate the forced convection heating of the bituminous coal under different oxygen flow rates with hot oxygen and used a Fourier transform infrared spectrometer flue gas analyzer to detect the outlet gas, used ATR‐FTIR spectrometer to analyze the solid residues in different areas, and recorded the time and maximum temperature of coal ignition under other processes. The results showed that low‐flow high‐temperature oxygen could quickly burn coal seams. When the oxygen flow rate was 2.5 m 3 /h, and the coal seam was ignited when heated to 130°C for 170 min. Through GC‐MS analysis of nine flammable components in the tar components under different processes, the content of short‐chain aliphatic hydrocarbons in the tar decreases, and the content of benzene series tends to increase. Through ATR‐FTIR analysis, the solid sample near the gas injection port contained fewer oxygen functional groups; the middle of the furnace body included the most oxygen functional groups; near the gas outlet contained more oxygen functional groups than the raw coal. CO 2 would rise to 3% when coal was about to ignite.