Prevention and control of spontaneous combustion h

Geting coal mine is a new mine that was put into operation in January 2001, with a design production capacity of 600000 T/A. the mine is located in the northwest of Jining City, Shanxi Province, with a minable reserve of 42.9 million T and a service life of 51 years. The average thickness of the three layers of coal currently mined is 8.03m, which belongs to gas coal with ultra-low sulfur, ultra-low phosphorus, low ash, high calorific value and good coking performance. The first working face is 1301 working face in mining area 130, with a buried depth of 240m, a strike length of 150m and a dip length of 900m. The average dip angle of the coal seam is 8 °, and the maximum is 21 °. The mining method is dip longwall retreating fully mechanized top coal caving mining method

the ventilation mode of the mine is central parallel extraction, the main shaft is lifting and return air, and the auxiliary shaft is air intake. The main ventilator of the mine is bdk-62no 22 counter rotating fan, motor power 110 × 2kW。 The actual inlet air volume of the mine is 3800m3/min, the effective air volume rate of the mine is 86%, and the ventilation resistance is 810pa. The relative gas emission of the mine is 0.825m3/t, and the appraisal grade is low gas mine; The explosion index of coal dust is 40.54%, which is explosive; The shortest spontaneous combustion period is 34 days, which belongs to a spontaneous combustion mine

due to the annual national major industrial special energy-saving supervision and special supervision carried out by the mine coal natural organization, the ignition period is short, the ground pressure is high, and the mining method is large dip mining, which brings great difficulties to the prevention and control of coal spontaneous combustion. When the mining speed of face 1301 was slowed down for some reasons, the CO concentration increased and continued to rise. At the same time, 1301 work is located between F2 and F3 faults. Affected by the faults, the gas content in the coal seam is high, and the gas concentration in the blast hole reaches about 25%. During the mining process, the return air corner of the working face is easy to cause gas accumulation. The two hidden dangers of gas and coal spontaneous combustion exist at the same time, which poses a serious threat to mine safety production. The mine is currently equipped with a set of KJ95 safety monitoring system; A set of mk-400 underground mobile membrane separation nitrogen generation system; A set of kss-200 beam tube chromatography microcomputer monitoring system; A set of ground grouting system

2 analysis of difficulties in Preventing Spontaneous Combustion Hazards in fully mechanized top coal caving face

(1) the conditions of oxygen supply for spontaneous combustion of coal lost in goaf are good. Because the mining direction of the top coal caving face is from high to low, the goaf is located in the upper part of the working face. In the process of mining, under the action of the air flow velocity and pressure of the air intake channel, the negative pressure of the mine and the self lifting force of the air, the air leakage air entering the goaf cannot have a line pressure line. The depth of the air entering the goaf is larger than that of the overhead face, and the goaf of the overhead face should not be flooded. The air is dry, making the coal lost in the goaf easy to undergo oxidation reaction

(2) the conditions for the accumulation of heat in the spontaneous combustion of abandoned coal in the goaf are good. The heat generated in the oxidation process of abandoned coal in the goaf of the overhead mining face is easy to accumulate in the goaf under the action of its thermal expansion and lifting force, creating conditions for the spontaneous combustion of coal

(3) it is difficult to implement the grouting measures in the goaf. When grouting in the goaf is carried out, once the grouting amount is greater than the bearing capacity of the goaf, the slurry flooding accident will occur. Even if the gob bearing capacity is carried out, the mud flooding accident will occur. Even if grouting is carried out in the goaf, the slurry only covers a small range of coal loss at the bottom of the goaf, and a large number of coal fall at the top of the goaf cannot be covered by the slurry

3 comprehensive treatment measures to prevent natural hazards in the fully mechanized caving face

preventing coal spontaneous combustion in the fully mechanized caving face is currently a difficulty in the work of "one ventilation and three prevention". If the measures are unfavorable, there will be signs of coal spontaneous combustion or spontaneous combustion in the mining process, which will pose a great threat to the normal production of the mine, especially in the coal seam, the gas content is large, the gas concentration in the goaf is high (up to about 7%), and the accumulation is large, Once there is a high temperature point or natural ignition point in the goaf, it may cause gas explosion accidents and cause immeasurable economic losses and casualties to mine safety. Therefore, it is particularly important to take comprehensive treatment measures in the case of both coal spontaneous combustion tendency and a large amount of gas

(1) development and application of non corrosive Magnesium Silicon Valley gel inhibitor. The white non corrosive magnesium silicate gel inhibitor developed by geting coal mine is mainly used in coal face opening, mining roadway and pedestrian roadway with small air volume. In goaf pillar roadway and other places, the covering and blocking of exposed coal and the air leakage of coal pillar cracks near the goaf mainly prevent the coal exposed in the air from accumulating heat due to coal oxidation under the condition of small air volume and sufficient oxygen supply, resulting in coal spontaneous combustion accidents. Silicate colloidal inhibitor is composed of silicate main agent + magnesium silicate + accelerator + water colloidal inhibitor. The main functions and functions are: ① colored, easy to control the spraying range and uniformity in the spraying process. ② The glue forming speed can be configured according to the flow and pressure of the spraying equipment, so that the inhibitor sprayed from the spraying equipment can be installed with different fixtures to form glue when sprayed on the coal surface. ③ The colloid is uniform, non-toxic and tastes small. ④ Long water fixation time: since about 90% of the colloidal inhibitor is water, the water should not be dehydrated under the action of the main agent and auxiliary water retaining agent. Through experiments, the water fixation time of the colloidal inhibitor is between 35 and 60. ⑤ Good heat absorption and cooling: the colloidal inhibitor has an endothermic effect during the gelation process. It can absorb heat after being sprayed on the coal, especially when it is sprayed on the open cut and goaf, it can absorb a large amount of heat generated by coal oxidation, reduce the temperature in the goaf and prevent heat accumulation. ⑥ The effect of blocking air leakage is good. When the mining is close to the working face of the goaf, when the pressure of the working face increases, there is bound to be air leakage in the cracks along the goaf coal pillar. At this time, the colloidal inhibitor is sprayed on the top of the coal pillar. Because the colloidal inhibitor is a flowable colloidal body, it will block these cracks under the air leakage pressure, playing the role of blocking air leakage

(2) build a fire-retardant wall to prevent air leakage in the goaf. The spontaneous combustion of coal in goaf is caused by the continuous supply of oxygen and the continuous thermal storage environment. By building fire-retardant walls at the air inlet and return corners of the working face at the same time, reduce air leakage in the goaf, change the scope of "three zones" and oxygen supply conditions, and make the oxidation zone enter the asphyxiation zone in advance

(3) implementation of yellow mud grouting measures in goaf of overhead mining face. Goaf grouting is also an effective fire prevention and extinguishing measure. At present, the mine has 1 mud station and 2 mud pits with a capacity of 2 × 40m3。 In view of the difficulties of grouting in the downdip mining face and the inability to retain slurry in the goaf, we adopted the pre buried pipe grouting method, that is, the grouting pipeline is buried in the goaf along the face, and the grouting pipeline is the same length as the working face. The pipeline is provided with a slurry outlet every 15m. The slurry outlet changes from small to large according to the direction of slurry flow, and the diameter ranges from 50 to 108mm. Using the ground, combined with the actual situation of the high dip mining face, the slurry water soil ratio is prepared as 5:1, At the same time, add about 15%~20% of the inhibitor into the mud, so that after the mud is poured into the goaf and part of the water is separated, the yellow mud mixed with the inhibitor is stored in the goaf and covered on the residual coal in the goaf, which plays the role of inhibiting, covering and increasing the humidity in the goaf. In order to prevent the air in the grouting pipeline from being squeezed and rushed into the goaf by the slurry during the grouting process, and form an oxygen supply source for coal spontaneous combustion in the goaf, through research and transformation, a three-way vent valve is set within the advance control range of the working face, and a stop valve is set at the rear of the three-way vent valve. During grouting, close the stop valve first, open the three-way vent valve, and the slurry flows from the ground grouting pool to the working face through the grouting pipeline, The air in the grouting pipeline is discharged from the three-way vent valve. When the three-way vent valve sees the mud, it will be closed immediately, and the stop valve will be opened immediately, and the formal grouting of the working face will begin

(4) pressure equalizing ventilation. Pressure equalizing ventilation is an important measure of fire prevention and extinguishing technology in coal mining face. Taking pressure equalizing measures can change the pressure distribution in the ventilation system, reduce the air pressure difference at both ends of the air leakage path, reduce the air leakage in the goaf, and achieve the purpose of restraining coal spontaneous combustion. In order to ensure the air flow stability and pressure equalization effect of the coal mining face, we mainly adopt the pressure regulation principle of the air window: that is, a air window to control the air volume is set in the return air chute of the coal mining face to improve the ventilation pressure of the coal mining face. According to the pressure equalization research and application carried out in 1301 working face, when the air distribution of the working face is about 450m3/min and the ventilation resistance of the working face is 29pa, it is most beneficial to the fire prevention and extinguishing of the working face; Therefore, when the air distribution of the working face is about 600m3/min and the ventilation resistance is about 35PA, it is most beneficial to prevent the corner gas from exceeding the limit. Therefore, the air distribution of the working face is controlled at about 500m3/min. In order to ensure the effect of pressure equalizing ventilation and realize the stability of the ventilation system, we have set up locking devices on all air doors of the mine, and set up the start and stop display of the air station on the main air doors near the working face. Especially during the tunnel connection, the ventilation facilities are built in advance, the three shifts are specially assigned to guard, and the ventilation system is adjusted in time after the connection, so as to ensure the stability of the mine ventilation system and sufficient air volume

(5) the application of new fire-proof materials of eglawney. Eglani is an expandable foam material composed of two components, which is used to seal air and gas and fill voids without mechanical resistance. This product uses a pump and a mixing gun. The resin and foaming agent are mixed in the volume of 20:15 or 1:1, and the foaming is automatically activated by compressed air in the gun. The advantages are that it can quickly generate foam, has good expansion capacity, uses less when filling, is simple and economical to use, quickly eliminates air leakage, and antistatic foam can be used in a large area without spreading flames. By using the new fire-proof material eglani before and after the withdrawal of the 1301 fully mechanized top coal caving face, the air leakage in the goaf was significantly controlled. Using the breeze tube test, the air leakage in the wall was basically eliminated, and the CO concentration in the return air corner decreased significantly. Especially after the stoppage of the working face, the CO concentration inside the fire-retardant wall in the return air corner decreased continuously, from 15010 when the mining was just stopped, by using the material eglani ×- 6, down to 110 ×， The goaf 25m away from the stoping line enters the suffocation zone after stoping mining for 15 days. After the closure of the working face was withdrawn, the O2 content in the goaf decreased to less than 6% after 20 days due to the use of the upper eglani material for sealing, which fully shows that the eglani material has a significant air leakage blocking effect

(6) application of monitoring system. In order to do a good job in gas management and prevent coal spontaneous combustion prediction work. We mainly use the method of combining kss-200 mine safety monitoring system with KJ95 safety monitoring system and manual detection to actively carry out prediction and prediction. Kss-200 mine safety beam tube monitoring system realizes the monitoring of CO, CO2, CH4, C2H4, C2H6, O2, N2 and other gas contents, and its analysis results are automatically stored in the database while providing data in real-time monitoring report and analysis, so as to analyze the bending trend of a certain gas content in the future; When sampling and analysis are required for individual sites, gas sampling can be carried out manually, and gas analysis can be carried out by Chromatograph after being put into the well, and data printing and storage can be realized at the same time. The system can carry out constant analysis and microanalysis at the same time, with many kinds of monitoring gases, large linear range, high accuracy and 24h monitoring. It lays a foundation for summarizing comprehensive and accurate technical data for mine fire prevention and extinguishing work. The use and further improvement of KJ95 safety monitoring system, whether in the mine gas management or in the prevention of coal spontaneous combustion