As early as 1979 at the World Coal Vision Conference, the United Nations has clearly stated that the implementation of underground coal gasification mining is an important way to solve the problems of traditional coal mining and utilization. In terms of coal gasification technology, China has also formulated development plans, outlines, etc., and is one of the countries in the world that research on underground underground gasification technology is relatively early.
With the continuous development of the oil and gas industry, oil companies have begun to show a certain diversity in the exploration and development of fossil energy, and gradually extended to the coal field. Coal underground gasification mining and comprehensive utilization projects have gradually been favored by oil companies. PetroChinaâ€™s Liaohe Oilfield is the â€œfirst person to eat crabsâ€ among domestic oil companies.
Underground coal gasification is carried out under the conditions of an underground gasifier. There are currently two main types of this technology.
The first is the tunnel-type underground gasifier technology. It is to build an underground gasifier in the mined or abandoned coal mine, establish a gasification roadway in the coal seam by means of artificial excavation, and build a closed wall in the tunnel at the bottom of the air intake hole (to promote the directional combustion of the coal seam), and then it can be sealed. The coal point in front of the wall is gasified.
The single underground gasification furnace in this mode is composed of the gasification passage inlet hole, the auxiliary hole and the outlet hole, and the gasification passage communicates with each hole in the same coal seam, but the artificial shaft is restricted by the stress and temperature of the coal seam. Partial depth is limited.
The second is the drilling underground gasifier technology. That is, using conventional oil and gas drilling technology, an ordinary long-eye horizontal well is drilled and connected with the other two vertical wells in the same coal seam. A single underground gasification furnace is still composed of a gasification passage, an intake hole, an auxiliary hole and an outlet hole.
During the construction, the coal in the gasification hole at the bottom of the air inlet hole is first ignited, the gasification agent is blasted, the coal is continuously vaporized, and hydrogen gas is blown from the auxiliary hole, and an oxidation zone, a reduction zone and an oxidation zone are formed in the gasification channel. Dry distillation drying belt. Most of these technologies are used abroad. Liaohe Oilfield successfully built China's first drilling underground gasifier in 2005.
This coal gasification method has made good use of the drilling technology advantages of oil companies, and has eliminated the restrictions on the construction of underground gasification furnaces. However, due to the limited drilling borehole, it restricts the gasification scale of a single set of furnaces, and needs to carry out technical research on single-furnace multi-inlet, multi-gasification passage, multiple outlet holes, large borehole drilling and reaming completion.
According to statistics, from 1953 to 1989, there were 297 abandoned mines in China. From 1990 to 2020, 244 were scrapped. The amount of scrapped resources has exceeded 30 billion tons by the end of 2002. It is generally mined and mined (the workers are diverted into the well for resource extraction. Corresponding to open pit mining, the amount of coal that can be mined by the well can only account for 11.43% of the coal reserves. The remaining coal pillars, thin coal seams, inferior coal seams, high gas coal seams, etc., rich deep coal resources and coal resources in shallow sea areas are not Developed and utilized. The development and application of underground coal gasification technology provides a way for the effective use of these resources.
At present, Shandong, Shanxi, Inner Mongolia, Guizhou and other places are introducing underground coal gasification technology to make full use of the remaining coal resources.
According to experts, the underground coal gasification technology avoids the pollution caused by the traditional coal mining methods. The high temperature generated by underground combustion causes the gas and coal tar to expand violently and be volatilized. In particular, the high temperature can make the physical properties of lignite better, so that the coalbed methane is analyzed and easy to produce. The ash remains in the ground, and the risk of collapse of the stratum in the later stage of mining can be reduced.
Coal underground gasification mining also has the characteristics of quick effect. After ignition, it can be continuously produced by simply injecting a gasifying agent. The gasifying agent is composed of air, water vapor, oxygen, and hydrogen. Oxygen and hydrogen can be obtained by separating the crude gas. The water vapor can be obtained by cooling the produced high-temperature crude gas, and the overall process has obvious cyclic economic characteristics.
The more comprehensive the industry of underground coal gasification mining, the more obvious the reduction of mining costs, and the greater the comprehensive benefits obtained. The underground coal gasification mining industry can be large or small, can be operated independently, is more conducive to large-scale industrial operations, has less investment, short investment recovery period and high return on investment.
The focus of the future development of this technology is mainly on increasing the furnace type, increasing the production capacity, and improving the calorific value of the gas, so as to adapt to the underground coal gasification mining needs of deep coal seams below 1000 meters, and gradually realize the circular economy development of coal and other mineral resources. .
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