Prevention and control of corner gas on fully mechanized mining working surfaces
The wind flow state in the corners of the mining surface is an important reason for gas exceeding the limit.
The corners of the mining surface are close to the coal wall and the goaf side, and the wind flow speed is very low. Eddy current state. This vortex makes it difficult for the gas gushing out of the goaf to enter the main air flow, causing high-concentration gas to circulate near the upper corner and gather in the vortex area, forming an excess of gas in the upper corner. If a lagging back column appears in the corner of the working surface, in addition to the vortex area that exists in the upper corner, a breeze area will appear near the top cut row. The gas leaked from the goaf will accumulate here, making it easier to form the upper corner. Gas exceeds the limit.
The pressure difference between the two sides at the corners of the mining surface is one of the reasons for the gas exceeding the limit.
Any section in the tunnel air flow has static pressure, potential pressure, Dynamic pressure, the sum of the three pressures is the total pressure, and the size of the total pressure difference determines the direction and speed of the wind flow. Since the static pressure and potential pressure on both sides at the upper corner are the same, the speed of the wind flow is different, so the coal mining face The wind flow turns here, causing the wind speed at the upper corner to slow down, and the wind speed difference on both sides of the upper corner to decrease. The wind flow speed here is greatly reduced, and there is no speed difference at the upper corner, or even turbulence in the wind flow.< /p>
Methods to prevent and control gas exceeding the limit in the upper corner
For the situation where gas exceeds the limit in the upper corner, there are 10 common prevention and control methods, namely: ① Set up temporary wind protection in the upper corner ② Increase the air volume of the mining working face; ③ Set up air curtains in the goaf area; ④ Install local ventilators on the coal mining working face; ⑤ Install air and water ejector in the return air lane of the coal mining working face; ⑥ Install special exhaust Fan; ⑦ High-level gas drainage; ⑧ Establishing a tail discharge system for the coal mining face; ⑨ Three-phase foam squeezing the corner gas; ⑩ Changing the ventilation mode, etc. Now analyze them respectively.
1 Set up the mining face Upper corner windshield curtain
When gas exceeds the limit in the corner of the coal mining working face, hang a windshield curtain near the corner of the coal mining working face to prevent the wind flow from the working face. Divide it into two, and use air curtains to guide more air flow through the upper corners to dilute high-concentration gas. The air curtains can be made of soft air duct cloth, and the length is generally not less than 10m.
A mine *During the production process of the working surface, an abnormal gas phenomenon occurred in the upper corner, and the CH4 concentration reached 2%, so a windshield was added near the upper corner. According to on-site observations, it was found that after using the windshield, the upper corner The CH4 concentration in the corner quickly dropped to less than 1%; however, due to the existence of the windshield, the shearer cut coal, and the branches and return pillars near the corner, as well as pedestrians and transportation materials at the upper exit were greatly affected. The windshield curtain was damaged and lost its function, causing the gas concentration in the upper corner to quickly rise above the over-limit concentration. As a result of repeated operations, the gas concentration in the upper corner will inevitably rise and fall, which is extremely unstable. , forming a major hidden danger in production safety. At the same time, the existence of the windshield increases the ventilation resistance of the working surface and reduces the air volume of the working surface.
Therefore, this method is mainly used in There is not much gas in the upper corner, and it can only be used as a temporary measure. This method is actually to increase the pressure difference between the two sides of the corner on the mining surface to solve the problem of eddy currents in the upper corner.
2 Increase the air volume at the mining working face
The working face wind flow dissipates the accumulated gas in the upper corner vortex area, mainly relying on the convection between the working face wind flow and the air in the upper corner gas accumulation area and the diffusion of the main wind flow. After a long period of on-site observation, it was found that under the condition of normal air supply to the working face, it is impossible to rely on limited speed wind flow to disperse the high concentration of gas in the vortex accumulation area in the upper corner. The method of increasing the air volume is adopted at the working face. Although The convection effect between the wind flow in the upper corner accumulation area and the main wind flow in the working face can be increased. However, as the air volume increases, the negative pressure increases, and the wind flow speed in the goaf area increases, which makes the gas streamlines in the goaf area deepen. , which strengthens the exchange of air flow and gas in the goaf. If there are other air leakage channels in the goaf, the air leakage volume will increase. In short, if the air volume at the mining surface is increased, the amount of gas carried out by the wind flow will increase. At the same time, excessive air volume has the following disadvantages: ① It causes the air supply volume adjacent to the mining working face to decrease, affecting the stability of the mine ventilation system; ② It increases the dust concentration in the air flow at the mining face, worsens the working environment of the working face, and increases The difficulty of dust prevention work; ③ Excessive air volume on the working face can easily cause the wind speed in the tunnel to exceed the provisions of the "Coal Mine Safety Regulations", affecting the quality standardization of the mine.
3 Set up the air curtain in the goaf area
According to the reasons for the excessive gas in the corners of the mining surface, if the air volume entering the goaf area can be reduced, the amount of gas outflow in the goaf area can be reduced, so that Avoid excessive gas in the upper corner. On the side of the goaf area of the working face, set up air curtains along the top row from the outlet of the working face to the upper corner, so as to minimize the amount of air leakage into the goaf area. Especially at the exit of the working face, since the wind flow enters the working face and directly hits the goaf area, it should be ensured that the wind screen in this section is tightly sealed.
It can be seen that this treatment method can be Fundamentally, the amount of gas emission in the goaf is reduced. However, because the wind curtain is located at the edge of the goaf, the gangue falling from the goaf can easily destroy the wind curtain, causing the air leakage to increase; at the same time, because the wind curtain changes with the direction of the work It moves forward gradually, which increases the difficulty and workload of workers.
Therefore, this method is restricted by a variety of conditions, and the effect is not ideal. It can only be used when the corner of the mining working surface is The application effect is obvious only when the corner accumulation gas velocity is not large (2~3 m3/min) and the gas concentration is not too high (about 3%).
4 Install local ventilators
In the working face, install a small local ventilator of 5.5kw or 2×2.2kw at a position 10 to 15m away from the corner of the coal mining face, and use a colloid air duct to guide the wind to the return air Corner, a positive pressure area is formed at the corner of the coal mining working surface, and fresh air flow is introduced through the local fan to dilute the gas in the corner of the coal mining working surface, so that the gas concentration there drops below the specified level. The local ventilator works as This treatment method has the following advantages: ① The gas in the corners of the coal mining working surface can enter the interior of the air duct as quickly as possible and be discharged into the return air tunnel; ② The corners of the coal mining working surface can be increased The air volume can dilute the high concentration of gas here in time; ③ Because the air duct is small and takes up little space, it can greatly reduce the impact of construction on the working face; ④ When the fan is operating normally, this method of extracting coal Corner gas control on the working surface is a safe and reliable process.
5. Install Feng Shui ejector
When gas exceeds the limit in the corner of the coal mining working surface, install A Feng Shui ejector uses high-pressure water and wind as power together, or high-pressure water or wind as power separately to form a large negative pressure area. The main air flow on the working surface will increase due to the pressure difference. The air volume in the corner is adjusted to meet the requirements of the fan. In this way, the high-concentration gas in the upper corner enters the interior of the air duct after being diluted by the air flow flowing through the working surface, and is discharged into the return air lane. This method has the following advantages: ① Using high-pressure water and wind as power, the wind and water ejector itself has no mechanical moving parts, and there is no hidden danger of sparks; ② The air volume can be adjusted by changing the wind and water pressure; ③ The structure is simple and easy to install and move. However, management needs to be strengthened. Prevent the sudden stop of the power source (water, wind), causing sudden accumulation of gas in the corners of the coal mining working surface.
6 Install special exhaust fans
(1) Pulsation ventilation technology .Pulsating ventilation technology is a set of technologically reliable, economical, reasonable and practical pulsating fan usage technology developed by utilizing the theory related to the turbulent diffusion coefficient of air flow and the pulsating characteristics of air flow. The pulsating air flow is superimposed on the normal ventilation air flow, thereby increasing the efficiency of the air flow. The turbulent diffusion coefficient improves the ability of wind flow to dissipate local accumulation of gas, and fundamentally solves the problem of gas accumulation in corners of the mining working surface.
(2) GDS-1 automatic gas emission system. Made of coal The GDS-1 automatic gas emission system developed by the Chongqing Branch of the General Academy of Science and Technology consists of a pull-out non-sparking fan, a gas sensor, a control device, an air damper, an air suction device and several air ducts. The main structure is shown in Figure 2. Above High-concentration gas in the corner enters the hard air duct Y through the air suction device switch, and the size of the switch angle, thereby changing the air volume mixed with "fresh air" so that the gas concentration in the gas discharge duct does not exceed the limit.
(3) Small hydraulic fan. Hydraulic fans are divided into monitoring devices and execution device. The monitoring device includes a control processor and a gas sensor. The execution device includes a small hydraulic fan and a hydraulic power system. The working principle of the monitoring device is to place it at the corner of the working surface.
The gas concentration sensor detects the gas concentration in real time, and converts the detected gas concentration signal into an analog electrical signal, which is transmitted to the control processor. The central processing unit processes and judges the detected analog signal, and issues instructions to control the opening and closing of the relay. , real-time control of the hydraulic fan. When the gas concentration exceeds the limit, the fan starts to blow away the gas accumulated in the upper corner; when the gas concentration drops to a safe limit, the fan automatically stops.
(4) Installation Compressed air blower to extract gas. This method has the characteristics of air and water ejector and gas mobile pump to extract gas. A rigid air duct is laid along the return air lane of the working surface, and the suction port of the air duct is located 0.5m away from the upper corner. The exhaust outlet is installed in the wind eye or in the return air lane of the district. The fans are installed in the return air lane, in groups every 200 to 300 m, using compressed air as power.
(5) Installation A mobile drainage pump is used to drain the gas in the upper corner. One rigid air duct is laid along the return air tunnel of the working face, and a drainage flower tube is laid in front of the air duct (in the goaf area). The length of the drainage flower tube is 15-20m. Left and right, low negative pressure drainage is required. The pipe is connected to the rigid air duct of the return air system, so as to form a negative pressure area at the corner, allowing the gas in the corner to flow to the drainage pipe, and finally be discharged to the mining area. Air tunnel.
7 High-level gas drainage
(1) Hole layout method. Arrange the drilling field directly in the return air tunnel of the working face, open holes from the roof, and move upward to the working face Drill holes in the fissure zone to drain the gas in the adjacent layers and nearby coal lines. The drilling holes are arranged in the opposite direction of the working face. The spacing between drilling sites is 15m. Three drilling holes are drilled in each drilling field. The coal in front of the working face is used. The body protection boreholes are drilled, and the working face is withdrawn when the mining is in place. Gas drainage pipes are installed in the return air tunnel to drain the gas in the empty area and form a negative pressure area at the corners of the coal mining working face, which makes the coal mining working face The gas at the corner flows to the drainage pipe.
(2) Hole layout parameters. The drilling design is based on two principles. One is that the final hole layer of the drilling is located at the upper limit of the fracture zone; The layer where the hole enters the pressure relief zone is located above the top of the caving zone and the lower limit of the fissure zone. According to the mine pressure theory, after the coal seam is mined, its roof and floor rock layers camber and move. When the overlying rock layer sinks and stabilizes, the overlying rock layer will be mined. Dynamic fracture zones can be divided into "three vertical zones" and "three horizontal zones", that is, the mining zone is divided from bottom to top along the vertical direction into caving zones, fissure zones and curved subsidence zones; The areas facing the wind tunnel and the machine tunnel are divided into the coal wall support affected area, the separation zone and the re-compaction area. As the working face continues to advance forward, the "three horizontal areas" along the direction of work advancement will alternately move forward. .
(3) The best position for the roof drainage port. The normal distance is located at 8 to 25m, (10 to 15m) upward from the roof of the vertical coal seam (located at the top of the caving zone and the lower part of the fissure zone), and the horizontal distance is at The internal deviation of the return air tunnel is 8 to 30m (8 to 17m). The specific mine should be comprehensively determined based on its actual situation. The final hole position of the drilled hole can be obtained through calculation using geometric knowledge.
8 Others Method
(1) Establish a tail drainage system at the mining face. Lay a non-metallic pipe along the return air tunnel (goaf area) of the working face. Cement can be used. This pipe is connected to the return air system. (Not the return air tunnel with the coal mining face), a negative pressure zone is formed at the corner of the coal mining face, so that the gas in the corner of the coal mining face flows along the pipe to the return air flow.
(2) Three-phase foam extrusion corner gas on the working surface. Using three-phase foam technology, the three-phase foam is used to occupy the space occupied by the gas to reduce the gas concentration. The three phases are water, ash, and nitrogen. The ash can be made of yellow mud, The slag and other materials used in coal power generation have a water-cement ratio (mass ratio) of 1:4:1. This method has the characteristics of fast processing speed and obvious results, which is a development trend.
(3 ) Change the ventilation method. Most of the ventilation methods in China's coal mines adopt upward wind. Since the gas gushing out of the coal mining face is lighter than the air, its natural flow direction is consistent with the direction of the upward wind. At normal wind speed (greater than 0.5~ 0.8m/s), gas may have stratified flow and local gas accumulation, which may easily cause gas to accumulate in upper corners. The direction of the downwind is opposite to the natural flow direction of gas. The two are easy to mix and are less likely to form gas layers. The phenomenon of flow and local accumulation can prevent the accumulation of gas in the upper corner. However, Article 115 of the "Coal Mine Safety Regulations" stipulates that downward gas shall not be used in coal mining working faces with the risk of coal (rock) and gas (carbon dioxide) outbursts. ventilation
.So when using downward ventilation, you must be cautious.
After the above analysis, combined with the actual situation on site, once the gas exceeds the limit at the corner of the mining surface, immediately hang air curtains and air curtains at the corners of the mining surface. Install wind screens; increase the air inlet volume of the working surface, increase the pressure difference on the working surface, check whether all seals related to the working surface are leaking, and if there is air leakage, seal it in time. The above methods cannot solve the problem, so install it as soon as possible. Set up a special extraction fan (wind and water ejector) for extraction.
The above methods are temporary and acute measures. The main method to control the excessive gas in the upper corner should be: high-level drainage, Tail row and upper corner gas extraction. The fundamental method is to mine the liberation layer and perform tunnel extraction or pre-extraction in advance to reduce the gas content of the coal seam to less than 8m3/t. Other methods are uncertain and unstable. ; Therefore, the control of upper corner gas should be considered in advance, constructed in advance, invested early, and effective early.