Key technology and engineering demonstration for cascade utilization of gas in key coal mining areas of Shanxi Province, China

The key coal mining areas of Shanxi Province, including Jincheng, Yangquan, Xishan, Fenxi and Lu’an, are the main implementation sites of the “13th Five-Year” national science and technology major project “Demonstration Project of Coordinated Development of Coalbed Methane and Coal in Key Coal Mining Areas of Shanxi”. Relying on the high-end platform of the national science and technology major project, a series of technologies for cascade utilization of coal mine gas have been developed and demonstrated to guide the enhancement of gas drainage and utilization from 6.02 billion m³ and 2.23 billion m³ in 2015 to 6.403 billion m³ and 2.894 billion m³ in 2020 respectively, as well as the increasing of utilization rate from 37% to 45%, thereby greatly assisting to the realization of the goals of coal peaking and coal neutrality under the precondition of ensuring the safe mining of coal mine. Cascade utilization is mainly based on the comprehensive utilization of methane concentration of gas. Specifically, the high-concentration coal mine gas with the volume fraction of methane above 30% (including) can be used for power generation, civil and industrial utilization according to the principle of maximizing the benefits after gathering. For the low-concentration gas with the volume fraction of methane less than 30%, the utilization interval is divided into four levels according to the difference and adaptability of different gas utilization technologies. The low-concentration gas with the volume fraction of methane of 16%‒30% could be purified with the pressure swing adsorption technology, so that the volume fraction of methane reaches 30% or more, satisfying the subsequent requirements of civil utilization and gathering. In terms of this technology, a demonstration device with a processing capacity of 12 000 m³/h has been built in Chengzhuang Mine of Jincheng mining area. In the mining area with high-concentration coal mine gas, the mixing technology can also be used to directly increase the concentration of methane to more than 30% for gathering. The low-concentration gas with the volume fraction of methane ranging from 9% to 16% can be converted into electricity locally for local-use or access to the grid, for which the demonstration devices have been constructed in Zhaozhuang Coal Mine, Hudi Coal Mine and Changping Coal Mine in Jincheng mining area. The low-concentration gas with the volume fraction of methane within 6%‒9% can be converted into heat by direct combustion technology for the combined supply of electricity, heat and cold, for which the demonstration device has been built in Chengzhuang Coal Mine. In addition, the low-concentration gas with the volume fraction of gas in the range of 1% to 6% can be converted into heat by regenerative oxidation technology for the combined supply of electricity, heat and cold, for which the demonstration device is built in No. 1 Coal Mine and No. 5 Coal Mine of Huayang New Material Technology Group Co., Ltd. (the former Yangquan Coal Industry Group). The cascade utilization technology of low-concentration gas, successfully demonstrated in the key mining areas of Shanxi, still has many technical and economic challenges at present. Therefore, it is urgent to perform the research continuously and rapidly improve the utilization rate under the goal of coal peaking and coal neutrality.