Application and effect analysis of water injection

2022-08-11
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Application and effect analysis of coal seam water injection in coal mine safety

1 coal seam water injection and methods

coal seam water injection is to drill several holes in the coal seam in advance before mining, inject pressure water through the holes, make it penetrate into the coal body, destroy the balance of the original coal gas two-phase system in the coal body, and form a coal gas water three-phase system, in which various media interact, Personalized customization and scope production change the physical and chemical properties, mechanical properties and thermodynamic properties of coal

coal seam water injection is divided into deep hole water injection and shallow hole water injection according to the drilling depth. Deep hole water injection is to drill holes in the air inlet or air return roadway in front of the mining work, which is inclined along the coal seam and parallel to the working face. The hole depth is generally 2/3 of the inclined length of the working face. The environmental protection supervision of enterprises will be more strict, with the hole diameter of 75 ~ 100mm. After sealing the hole with cement slurry or rubber hole sealer, water injection can be started. Compared with shallow hole water injection, deep hole water injection is more expensive and difficult to drill, which is only applicable to medium and thick coal seams. The advantage is that the pre wetting range is large, it can be fully wetted, and it does not affect the coal mining work. However, in some mining areas, water injection is difficult and the amount of water injection is small because the coal seams have not been damaged

2 mechanism and effect of coal seam water injection in coal mine safety

2.1 dust prevention

coal seam water injection is the most effective dust prevention measure in mining face. The dust removal mechanism of water includes the following three aspects:

(1) wet the primary coal dust in the coal body, and make it lose the ability to fly

(2) effectively wrap every small part of the coal body, and avoid the flying of fine coal dust when the coal body is broken during mining

(3) the wetting effect of water enhances the plasticity and weakens the brittleness of coal. When the coal is subjected to external forces, many brittle fractures become plastic deformation, which greatly reduces the possibility of the coal being broken into dust particles and reduces the amount of coal dust

after coal seam water injection in xinwensuncun mine and Benxi caitun mine, the dust removal rate reached 73% and 79% respectively. Table 1 shows the dust reduction rate of the "Three Soft" fully mechanized top coal caving face after the implementation of coal seam water injection and other dust prevention measures

Table 1 "Three Soft" fully mechanized top coal caving face dust reduction rate

2.2 prevention of coal and gas outburst

research and experimental investigation show that water injection to wet the coal body can significantly change the mechanical properties of the coal, reduce the elasticity and strength of the coal, and increase the plasticity, so as to change the pressure distribution in front of the roadway, that is, high pressure transfers to the deep part of the coal body, and the pressure concentration coefficient decreases. After the coal is wet, its permeability will also be reduced hundreds of times. Water has an obvious blocking effect on the movement of gas, and the amount and speed of gas emission in coal are greatly reduced. All the above changes show that water injection to wet the coal body can eliminate or reduce the outburst risk of the coal seam. After using shallow hole coal wall water injection in six fully mechanized mining faces with outburst risk in two pairs of outburst mines in Yangquan coal mine, the number of gas outburst and ejection is reduced by 72.2% and the average outburst intensity is also reduced by 36.5% compared with that before use

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