Coal spontaneous combustion prevention technology in fully mechanized caving and open goaf

Extinguishig colloidal slurry injection is to open Gob: Gob "three zones", i.e. with heat, with the risk of spontaneous combustion, asphyxiation with, spontaneous combustion of coal with a risk of spontaneous combustion inside. The most easy to spontaneous combustion depth is generally 30~60m. If the colloidal mud is injected at a fixed point in front of the most spontaneous combustion zone in the goaf from 30 to 60 m from the working face, the flow range of the colloidal mud is controlled by controlling the gel ratio and gelation time. The colloidal mud and the vermiculite form a wide separation zone, which is supplemented by grouting in the separation zone. The barrier can prevent the yellow mud from flowing to the working surface, forcing the yellow mud to flow deeper into the goaf and to the point of ignition. As the working face advances, the roof of the goaf swells gradually and gradually, the space gradually decreases, the air leakage in the goaf gradually decreases, and the fire source points gradually move downward; as the isolation belt increases, the flow to the fire The amount of grouting at the source point is also gradually increased, so that the filling of the goaf is more strict and the temperature is gradually reduced, so that the anti-fire extinguishing effect of grouting can play a better role.

In a nutshell, it is to inject the colloidal mud in the most spontaneous combustion zone in the goaf, forming a separation zone, and grouting a lot in the isolation zone, thereby destroying the air supply and oxygen storage environment and eliminating spontaneous combustion of coal. Colloidal mud is the core technology, which plays the role of forming the isolation belt, which plays: 1 blocking function, which prevents the grouting slurry from flowing to the working surface and affects normal production; 2 isolating effect, blocking the fire source to extend to the working surface; 3 sealing Function, sealing and blocking air leakage.

2 Colloidal mud fire protection characteristics

Colloidal mud fire prevention technology, which is commonly used to control coal spontaneous combustion in open goaf and closed coal gob area (closed goaf) in open gob area and no coal pillar (or small coal pillar), with material saving and low construction intensity. The fire prevention effect is remarkable. In Yaoqiao Coal Mine, the colloidal mud fire prevention technology was used to successfully control the spontaneous combustion of coal in the adjacent goaf (closed goaf) of 7513 fully mechanized caving face, 7003 fully mechanized caving face and 7507 fully mechanized caving face.

Characteristics of colloidal mud:

Colloidal slurry is binder (water glass), coagulant (ammonia and carbon dioxide, sodium aluminate, etc.) and the yellow slurry (pulp or fly ash slurry and the gangue) mixing certain proportion can be controlled within a certain time The gel solidifies and absorbs heat and cools down; adding a filler to the colloid can increase the strength, heat resistance and prolong the expiration date. Colloidal mud mainly has the following properties: 1 high solid water, solid water content is above 80%; 2 strong permeability, penetration distance can exceed 5 m; 3 heat absorption and temperature drop fast, base material concentration is 6%, the colloid heat absorption is 4×104 kJ/m3; 4 seal sealing effect is good; 5 resistance performance is high; 6 heat stability is good; 7 high strength, stable for more than 1 a time in the well; 8 low cost, simple process, light equipment, Easy to operate.

3 Application of ammonia-free colloidal mud fire prevention technology to control spontaneous combustion of 7005 fully mechanized caving face

3.1 Overview of fully mechanized caving work

The 7005 fully mechanized caving face is the first mining face of the central mining area of ​​Yaoqiao Coal Mine. The strike length is 1649m, the slope length is 159m, the coal seam thickness is 5.8~4.27m, the coal seam dip angle is 9~19?, the elevation is -676~-730m, and the working face is adopted. Downstream "U" ventilation system, the normal air supply is 741 ~ 639m3 / min. There are more than 10 large faults on the surface, and the coal at the fault is loose and easy to spontaneously ignite. During the excavation process, the material path, the cut-eye and the scraper conveyor track have experienced spontaneous combustion of the coal seam in many faults. There were 2 spontaneous combustions during the recovery process.

3.2 Analysis of spontaneous combustion of goaf in upper corner

Advancing to 1190 m on the working surface of 7005, it was suddenly found that there was CO in the corner of the working face, and it was as high as 220×10-6. There was also a small amount of CO in the end of the working surface of the 85#~110#, and then it was rising. The corner CO of the working face has been stable at (20~50)×10-6. After investigation and analysis, the main reasons are:

(1) There are 3 to 5 brackets near the exit of the working face.

Or the amount of coal released is very small, and the amount of coal left in the old empty area is large, leaving a hidden danger of spontaneous combustion.

(2) Although the advancement speed of the working face in January is 156m, the roof is still not tight, and the amount of grouting in the goaf is small (because the working face is slightly submerged for a long time, it is impossible to grout normally) There is a serious hurricane in the area, that is, it has the condition of oxygen storage and heat storage.

(3) In the near future, there are many roadways in the surrounding area, the ventilation system is unstable, the air volume on the working surface changes greatly, and the air volume is less than 300 m. /min (At that time, the air volume of the working face was 620 m3/min), which formed a bellows effect, which induced spontaneous combustion of the residual coal in the goaf.

3.3 Treatment of spontaneous combustion

Since the working face is slightly subtly, it is decided to use the glue injection mud and the grouting technology to extinguish the fire. One of the key technologies of this measure is to determine the proportion of colloidal mud. After experiment, it is selected: 1 the ratio of water to soil of yellow mud is 3:1 (volume ratio); 2 the ratio of gel is water: water glass: no ammonia promotes condensation Agent = 94:4:2 (mass ratio), the gelation time is about 4 to 5 minutes. The process is to add a coagulant to the grouting pipeline in a certain proportion in the existing static pressure buried pipe grouting system to form a colloidal mud separation belt and grout in the separation belt. .

The specific implementation scheme and process are as follows: assault transport, filling glue pump, and adding 2 趟 76 mm grouting pipeline about 600 m, wherein the first 趟 pipeline is opened at the 798# shed for the injection of colloidal mud, the first The second pipeline is used as a grouting mud reserve pipe at the opening of the 732# shed. The original 108 mm pipeline is still used as a grouting pipe at the opening of the 884# shed. Take 1 kg of colloidal mud in the morning shift, 3 hours of grouting in the middle and night shift, strengthen the coal, maintain the normal propulsion and stabilize the working face and increase the air volume to 830m3/min. The co-injected colloidal mud is 1382 m3 and grouted. 4436m3, working face advancement 86 m, CO in the old empty area of ​​Shangyujiao fell below 15×10-6, no CO in the tail of 106#, 96#, 85# bracket, the hidden dangers were basically eliminated, and it was maintained until the working face was recovered. End the closure.

3.4 Comprehensive analysis of fire prevention and control

The 7005 fully mechanized caving face is a non-standard “U” type ventilated working face (there is a water draining lane at the rear of the working face, and there is a tailway at the rear of the material. Although the tailgate is closed, it is affected by the dynamic pressure of the mining, and the wall is pressed and leaked. When the 760 m was pushed for 11 months, the rear end of the scraper conveyor (small lane) appeared spontaneous combustion. The main cause of spontaneous combustion was the large amount of air leakage from the work to the rear of the old empty area. At the same time, the bandwidth of the spontaneous combustion danger zone of the 7005 goaf is far from 35 to 110m. Before the coal spontaneous combustion, although the propulsion speeds of the working face were 110 m / month, 150 m / month and 156 m / month, far > 60 m, it still failed to avoid spontaneous combustion in the goaf of the working face.

In view of this, the air distribution of the 7005 fully mechanized caving face is 830 m3/min. For example, the air leakage rate of the goaf is calculated at 1%, and the air leakage of the goaf corner can reach 8.3 m3/min, so that the air leakage is so large. It needs to be injected with nitrogen above 300m3/h. The maximum nitrogen production capacity of the 7005 nitrogen generator is less than 300 m3/h, and it is difficult to inertize the goaf for fire prevention. Therefore, it is impossible to achieve nitrogen injection and fire prevention. Only the method of plugging air and destroying the heat storage environment is feasible.

Therefore, the colloidal mud is injected at the 798# shed (fixed location) before the most spontaneous ignition point of 40 m from the working face, and the yellow mud is pressed at the 884# shed at 51.6 m from the working face in the goaf. In this way, in the vicinity of the 798# shed, the colloidal mud is formed to form an isolation belt; the most spontaneous combustion zone in the isolation belt is grouted to prevent the spontaneous combustion from extending to the working surface; as the working surface advances, The gradual tightening of the roof of the goaf makes the grouting fire prevention effect better, achieving the purpose of plugging the air and destroying the heat storage environment, thus finally extinguishing the fire.

The colloidal mud acts as a separation belt: 1 the partition fire source extends in the direction of work; 2 seals the air leakage; 3 prevents the grouting slurry from flowing to the working surface, forcing the grouting slurry to the fire source point, destroying the heat storage environment, and cooling Extinguishing.

4 Fireproof technology of two flame retardant walls in goaf

The internal air leakage in the goaf of the working face is mainly caused by the pressure difference between the upper and lower channels. The upper and lower roadways are unsuccessful in the mining process due to support reasons, especially the roadway in the form of anchor net and anchor cable support, and the lag behind after mining, which makes the air leakage depth of the goaf increase. When the wall is built up and down, the air leakage caused by the two lanes is effectively blocked, which plays a role in narrowing the air leakage width of the goaf.

During the mining process, the working face will establish a flame-retardant wall at the next two landings on the working surface for every 10~15 m of propulsion. The wall material can be used to take crushed coal in situ, and the whole layer is built in proportion to the flame retardant in the crushed coal. The wall is sprayed with polyurethane or treated with yellow mud to inject the gel material or Rox For materials, it is strictly forbidden to leak or leak airflow from two channels, reduce the amount of air leakage in the goaf, and reduce the width of the air leakage.

5 Conclusion

(1) The basic measures for preventing spontaneous combustion of coal in open goaf are the degree of propulsion, the design of a reasonable working face length, and the management of the working face to ensure that the monthly propulsion is not less than 60 m.

(2) The injection of colloidal mud can form a separation zone in the goaf, which is convenient for a large amount of grouting in the goaf, and can prevent coal spontaneous combustion in the goaf when the working face is propelled slowly.

(3) Whether the colloidal mud can achieve the expected effect, the key is the control of the gelation ratio. Therefore, in the implementation of the technical measures of the injection of colloidal mud, according to the specific conditions of different goafs, different proportions are taken in a targeted manner, and the gelation time is strictly controlled to achieve the intended purpose.

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