Talking about the important function of coal seam water injection to control coal mine underground disasters Abstract: This paper systematically analyzes the borehole layout of coal seam water injection and the reasonable determination of water injection parameters, and discusses the impact of coal seam water injection on dust prevention, prevention of rock burst, fire prevention, temperature reduction and improvement of top coal mining in combination with actual research projects. The important role of recovery rate and production. 1 Introduction With the increase in coal mining intensity, coal mine safety problems have become more and more prominent. Such as gas and coal dust explosion; rock burst, coal and gas outburst and fire under fire, etc. Once it occurs, it not only endangers the health and safety of workers, but even shuts down the mine, and will seriously destroy the mine. Therefore, domestic and foreign countries attach great importance to their research and management. Coal seam water injection is a comprehensive and ideal measure to control the above disasters in coal mines, and it is also an effective way to ensure underground safety. 2. Layout and parameters of coal seam water injection drilling 2.1 Drilling layout According to the permeability characteristics of the coal seam, the thickness of the coal seam, the length of the working face and the layout of the roadway, etc. There are unidirectional (Figure 1, Figure 5), bidirectional (Figure 2, Figure 3, Figure 4) and fan-shaped drilling layout (Figure 3, Figure 5) Way. The one-way drilling arrangement is an arrangement for drilling holes in the return air lane or the air intake lane. The two-way drilling arrangement is a way of arranging drilling holes evenly in the return air lane and the intake air lane. The fan-shaped drilling arrangement is because the thickness of the coal seam is too large. In the case of poor permeability of the coal seam perpendicular to the roof and floor, multiple holes are arranged on the same cross section (to facilitate drilling and prevent water flow between the drill holes) Layout. In the actual water injection, you can choose according to specific conditions. 2.1.2 Sealing In order to prevent the pressure water in the borehole from running away from the large cracks of the roadway being pressed, it is generally required that the hole sealing depth is greater than the width of the coal layer pressed by the pressure of the mine. For the fan-shaped drilling arrangement, in order not to cause water to cross each other, the depth of the sealing hole is generally between 10 and 2 intestines. Practice has proved that deep sealing is beneficial to improve the effect of coal seam water injection. Now the commonly used sealing methods are sealed. There are two kinds of holes and cement mortar. The sealing effect of the hole sealer is not good, and it is not suitable to realize long-term interrupted water injection. The sealing effect of cement mortar is good and reliable, which is an ideal sealing method. In order to solve the problem of sealing holes such as water injection or gas drainage, we developed the SLB type cement mortar sealing pump during the "Seventh Five-Year Plan" period. The maximum sealing depth of this pump is> 25m. When sealing the holes, mix the cement mortar with appropriate ratio [water: cement: sand ( 2.2 Coal seam injection parameters 2.2.1 Seepage equation of coal seam water injection For thin and medium-thick coal seams, one-dimensional infiltration is generally used to describe For thick and extra-thick coal seams, the infiltration of water in them is often described by two-dimensional nonlinear seepage. The equation is: The above equations are generally solved by the finite element method, and the results are in good agreement with the actual results. Not discussed in detail here, the following describes a method commonly used in the field. 2.2.2 Water injection pressure The coal seam water injection pressure is generally required to be greater than the gas (or other gas) pressure in the coal seam and less than the pressure of the coal seam being fractured by water, which can be given by the following formula. 2.2.3 Water injection t and water injection flow t For fan-shaped boreholes or other arrangements, the amount of water injected into the borehole is calculated using the amount of coal wetted by the borehole. Q = Kmq (5) In static pressure water injection, the water injection flow rate changes with the change of the water injection resistance in the borehole, which is an indefinite value; in dynamic pressure water injection, if the pump flow rate and the number of simultaneous water injection holes are fixed, the single-hole water injection flow rate is a certain value. According to the experience at home and abroad, if the water injection time permits, the effect of long-term small-flow water injection should be ideal for coal seam wetting. 3 Analysis of the effect of coal seam water injection on various disasters Coal seam water injection plays an important role in preventing rock burst, preventing dust, preventing fire and reducing temperature, and softening top coal to increase the recovery rate. It is described as follows. 3.1 Coal seam water injection to prevent rockburst Coal seam water injection is a very effective measure to prevent rockburst. It uses water injection to soften the coal body and change the structure and physical and mechanical properties of the coal body to improve the uniformity, instantaneousness and stability of energy release during coal mining. To achieve the purpose of preventing rockburst. 3.1.1 Impact analysis of a mine before and after water injection The ability of coal to accumulate elastic energy and produce impact failure when it is stressed is an inherent property of coal rock media, called impact tendency. The rock burst generated by coal seam is mainly related to coal seam geology, roof and floor conditions, mining method, coal strength, elasticity, cohesion and internal friction angle. If the strength, elasticity, cohesion, internal friction angle, etc. of the coal are small, and the failure process is slow and the plasticity is large, the impact tendency is small. After the coal seam is injected with water to wet the coal body, the strength, internal friction angle, etc. can be reduced, so that the coal body is significantly plasticized, thereby reducing its impact tendency. Table 1 shows the values ​​of various parameters before and after water injection in a mine. 3.1.2 Effect analysis The above test data shows that the elastic modulus of coal is reduced by 44.8%, and the values ​​of C (uniaxial compressive strength) and in-row friction angle are reduced by 11.2% and 70.6%, respectively. After the coal seam is injected with water, the stress concentration of the coal body is reduced, and the width of the stress reduction zone in front of the coal wall is increased, thereby increasing the lateral resistance of low damage resistance. In addition, the overlying rock layer is the same as the coal body before mining. System, the two restrict and interact with each other. The stress distribution characteristics of the overlying rock layer play a very important role in rock burst. After the coal seam is injected with water, the peak concentration of stress in the rock layer can be moved deeper, the distribution range is increased, and the peak value is reduced. Therefore, the stress within a certain range near the working face decreases. This change shifts the roof fracture position to the front of the coal wall, reducing the period The influence of the pressure on the coal wall of the working face reduces the possibility of the roof pressure to induce rock burst. In addition, after the coal seam is injected with water to soften the coal body, the energy release speed of the coal body is significantly reduced, and the damage form tends to be slow, which significantly improves the stability of the energy release when the coal body is destroyed. Tests have shown that the decrease in coal body strength has a negative exponential relationship with the water injection time, so long-term small-flow water injection should be used to reduce Coal body strength. In summary, coal seam water injection softens the coal body, which can reduce the physical and mechanical properties of the coal body, increase its plasticity, and reduce or prevent the harm of rock burst. 3.2 Coal seam water injection and dust prevention Coal seam water injection and dust prevention is the most effective measure to prevent dust generation. It is to use water pressure to inject water into the coal seam to be mined, and the water injected into the coal seam along the coal crack to the coal block divided by the crack Infiltrate and store in the fissures and pores, increase the moisture of the coal body, so that the coal body is pre-wet, to reduce the ability to generate floating dust during coal mining. 3.2.1 Increase effect of water injection water in coal seam Coal seam water injection reduces the dust concentration, which is mainly related to the moisture content of the coal body, the water increase after water injection and the uniformity of wetting. The top-coal working face of a mine adopts one-way drilling arrangement, combined with dynamic and static pressure water injection. The sealing hole is sealed with cement mortar. The working face is 160r long, flying, and the drilling length is 110nl. The porosity is 10.36%, 7GB-3.6 / 160 type coal seam water injection pump is used, and one pump injects three holes at the same time. The effect of coal seam water injection in this working face is very ideal. When the original moisture is as high as 3.914%, it also increases the average moisture by 1.202%, reaching 5.116%, and up to 7.72%. And the moisture is more even, so it has a better dustproof effect. 3.2.2 Dust reduction effect of coal seam water injection on main dust sources in top coal caving face Sampling every day within the range of 10nl around the water injection borehole to investigate the effect of coal seam water injection on the major dust sources, the results of which are shown in Table 2. It can be seen from Table 2 that the coal seam water injection in this working face has achieved a very good dust reduction effect. At the driver of the shearer, the dust reduction rates during downwind and upwind coal cutting were 83.% and 69% respectively; at 10m downwind of the shearer, the dust reduction rates for downwind and upwind coal cutting were 88% and 85%, respectively; At 27%; 31% at 10nl under the media outlet. Therefore, it is very important to do a good job of coal seam water injection to reduce the concentration of working flour dust and reduce its pollution. 3.3 Coal seam water injection fire prevention and cooling The above-mentioned mine was added with fire retardant and inhibitor in the coal seam water injection, which increased the ignition cycle from the original 3-6 months to 5-8 months. The average monthly advancement of the working face was more than 50m, and it was promoted after 5 months When the temperature is over 250rn, the working surface is far away from the ignition source, so that it does not have enough oxygen supply to fully burn and cause a fire, which solves the fire hazard problem. The temperature after injection is reduced from the original average staring to about 25.3 degrees. Improved working conditions. 3. The water injection of the Qi layer improves the effect of top coal caving In top-coal mining, if the coal seam is hard, especially top-coal is hard, many large blocks of coal will be produced during coal caving, which will easily block the coal caving port, thereby reducing the recovery rate and output. The coal seam can effectively wet and soften the coal body after water injection. Before the coal seam is injected with water, the coal seam is injected with water. Its unidirectional compressive strength is 20 MPa before water injection and 8. SMPa after water injection. After the water injection softens the coal mass is less, the top coal emission rate is increased from 74.8% before water injection to 86.3%, and the daily production is also increased from 2900t before water injection to 4700t, the work efficiency is increased by 38.2%, the unit failure and pick loss are greatly Decline, the labor intensity of workers is greatly reduced. 4 Conclusion Through the above analysis, the following conclusions are drawn: (1) Coal seam water injection is a comprehensive measure to prevent underground disasters. And it can reduce the cutting energy, improve the work efficiency and the output and recovery rate of the working face, which is a very effective measure. (2) The borehole layout of the coal seam water injection and the reasonable determination of the water injection parameters are the key factors affecting the coal seam water injection (for a certain coal seam). (3) Coal seam water injection can change the structure and physical and mechanical properties of the coal body, reduce the strength, elastic modulus, cohesion and friction angle of the coal body, improve the stress concentration and supporting pressure of the coal body and the influence of the overlying rock layer on the coal body, reduce Or prevent the harm of rock burst. (4) Coal seam water injection can increase the moisture content of the coal body, soften the coal body, and reduce the amount of dust generated. Practice has shown that coal seam water injection can make the coal mining driver and the downdraft dust reduction rate reach 80% at 10rn. (5) Coal seam water injection (addition of inhibitor) can increase the natural ignition cycle, avoid the hazards of fire, reduce the temperature and improve the working conditions. (6) The coal seam is injected with water to soften the top coal, which can increase the recovery rate, work efficiency and output, reduce energy consumption and labor intensity. In short, coal seam water injection is a comprehensive measure to prevent underground disasters and ensure the safety of mines and workers. Its promotion and application can effectively reduce the disaster accidents in coal mining face of coal mines, improve the environment, improve work efficiency, and promote safe production. Silicone Sheets,Silicone Gel Sheets,Thin Silicone Sheet,Silicone Sheet Nantong Boxin Electronic Technology Co., Ltd. , https://www.bosencontrols.com
