Coal in-situ gasification _ A dreamlike yet real phenomenon

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This post was last edited by lgsan123 on 2017-4-26 at 15:07. China relies on coal as its main energy source; coal accounts for over 70% of its primary energy supply. According to incomplete statistics, by 2020 there will be over 500 \"closed\" mines in China, with abandoned resource reserves exceeding 50 billion tons; underground gasification technology can help recover some of these resources. According to incomplete statistics, China’s lignite resources amount to approximately 370 billion tons, mainly distributed in Inner Mongolia, Yunnan, and Xinjiang ； Due to its high moisture content, high ash content, low calorific value, and the presence of soft rock roofs, underground mining of lignite is less safe and economical. However, owing to its high reactivity and good air permeability, lignite is particularly suitable for underground gasification. It has been determined that China possesses approximately 2.9 trillion tons of coal resources buried at depths of less than 1,000 meters; alone in the Ningxia Autonomous Region, there are over 300 billion tons such resources. Along the West-East Gas Pipeline, there are about 477.64 billion tons of deep-seated coal resources suitable for shaftless gasification. As the mining depth increases, so do ground temperature and pressure, which makes underground mining more difficult. The basic principle of coal in-situ gasification is, similar to conventional coal gasification, to convert the solid organic matter in coal into combustible gases through thermal and chemical processes. The difference lies in the fact that this transformation takes place underground, without the need to extract the coal first. Coal in-situ gasification integrates three processes: well construction, coal mining, and surface gasification. It enables the recovery of coal resources left behind in old mines, as well as the extraction of low-grade coal seams (lignite, high-sulfur, high-ash, high-methane content) that are difficult to mine using conventional underground methods, or those where mining is not economically or safely viable. It also allows for the extraction of thin coal seams, deep coal seams, and coal seams located under infrastructure. **This approach improves the utilization rate of coal resources.** In the process of coal in-situ gasification, the ash and slag resulting from combustion remain underground, **which reduces surface subsidence and eliminates any solid waste emissions; thus, coal in-situ gasification lessens environmental damage to the surface. The gas emitted from underground gasification can be purified centrally, with harmful substances such as tar, sulfur, and dust removed, thereby producing clean gas. This gas can be used not only as a fuel for domestic purposes, power generation (including combined cycle power generation), and industrial boiler combustion, but also as a feed gas to produce synthetic ammonia, methanol, dimethyl ether, gasoline, diesel, etc., or for the extraction of pure hydrogen. Therefore, coal in-situ gasification technology focuses environmental protection at the source rather than through end-of-pipe treatment, and it is an environment-friendly green technology that meets the needs of sustainable development. At the same time, underground gasification is a coal mining method with a relatively high safety factor; it enables the safe extraction of coal resources. It has a positive impact on reducing the high accident rate in China’s coal enterprises, and brings significant economic and social benefits. After eight years of technical research and development, Newao Gasification Coal Mining Co., Ltd. has created an underground gasification furnace for surface mining units, as well as a mobile unit gasification process, both of which feature independent intellectual property rights. It primarily controls the movement of the air injection pipe in the air injection device through a mobile air injection system, thereby regulating the position and movement of the coal seam combustion zone. This approach can effectively prevent secondary combustion of gases at the working face, maintain relative stability in the oxidation zone and reduction zone, and enable stable radial expansion of the gasification reaction zone, thus solving the production challenges that have long hindered the stability of underground gasification processes. The produced syngas is transported through pipelines to chemical plants, where it undergoes further purification and synthesis to yield qualified products such as methanol and LNG. As a completely new coal mining technology, the mobile unit gasification technique is particularly suitable for the large-scale and efficient extraction of low-metamorphic bituminous coal and lignite deposits. It is also applicable to the clean extraction of unconventional resources such as deep-seated coal and high-sulfur coal.