Discussion on fire prevention and extinguishing te

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Discussion on fire prevention and extinguishing technology in fully mechanized top coal caving mining of flammable thick coal seam

spontaneous combustion is one of the factors restricting the development of thick coal seam mining technology, and it is also a subject that coal workers have been committed to solving for many years. This paper analyzes the feasibility of the staggered roadway layout system [1] combined with the traditional fire prevention technology

2 site conditions

taking the actual site conditions of a mine as an example, the working face is 144m long and the mining depth is m. The average coal thickness is 11.5m, the maximum coal thickness is 14m, the average dip angle is 12 °, the coal seam structure is relatively simple, the coal seam is soft, the hardness coefficient is f=1.4, and the unit weight is 14.5kg/m3. The coal seam is very prone to spontaneous combustion. The average ignition period is 20 days, and the shortest is 7 days. It contains 1 layer of gangue with a thickness of 0.2 ~ 0.4m. The direct roof of the coal seam is sandy mudstone with an average thickness of 1.5m, and the main roof is medium thick layered fine sandstone with a thickness of 14m

3 spontaneous combustion category analysis

the factors that cause spontaneous combustion include the existence of floating coal, coal fragmentation, contact with oxygen and heat storage conditions and time. No matter what method is adopted in production, the existence of broken coal and its contact with oxygen are inevitable. However, if the existence of broken coal can be reduced and its heat storage time can be shortened, the probability of spontaneous combustion will be greatly reduced. Under this guiding ideology, the spontaneous combustion areas and periods of the traditional top coal caving roadway layout system are analyzed. The classification is carried out according to the probability of spontaneous combustion in each area under the top coal caving mining system: (1) the adjacent original high-temperature area or old fire area, local caving area of roadway roof, broken area of roadway variable slope roof exposed by the roadway in the area prone to spontaneous combustion, and the adjacent stoping line, coal pass, connecting roadway and other chambers along the goaf side exposed by the roadway. (2) In the area prone to spontaneous combustion, the roadway top coal separation zone and the coal pillar fracture zone along the air side. (3) In the area where spontaneous combustion may occur, the roadway side breaking area and the goaf of the working face. According to the frequency of natural fire accidents in fully mechanized top coal caving mining, the seat has better cushioning performance in the gravity test, it is determined that the fire prone places are roadway and open cut, final recovery working line, adjacent goaf and the end of the working face (as shown in Figure 1). Another key point of the prevention and control of spontaneous combustion is to analyze from different periods. The prevention and control work in each period should start from the root causes. There are four periods in which spontaneous combustion is most likely to occur, namely: (1) excavation period. It is easy to form a high caving area at the roadway top and a 510 HP bulldozer in the fracture zone of broken coal. The positive pressure of local ventilator intensifies the diffusion of oxygen in the coal body, and the heat generated in the deep is difficult to dissipate, which is one of the hidden dangers of natural ignition

(2) during the installation of the working face. A large amount of broken coal exists above the support during eye cutting, and the installation time of fully mechanized top coal caving face is relatively long, which may lead to spontaneous combustion of the coal seam before the installation is completed; (3) During mining. Firstly, the time interval from the opening of the cutting hole to the initial caving is long, and the heat storage time of the top coal of the support is long; Secondly, the working face has just been installed and needs running in equipment, resulting in slow propulsion speed; Thirdly, the crushed coal laid down at the upper and lower ends accumulates in large quantities; In addition, in the process of roof caving, the roof will sink in a large area, which may be affected by external objective conditions to form a wind guide channel; (4) During removal. The demolition time of fully mechanized top coal caving face must be long; The coal body above the support has developed fissures and has a large contact area with oxygen; There are many loose coals behind the scaffold. The above natural ignition factors affect the normal and safe production of coal mines. Seeking a more reasonable mining and production system is an important research way to solve the above problems

4 scheme analysis

4.1 scheme proposal

the production of coal mine always focuses on safety, economy and recovery rate. Under this production condition, the coal seam mining is affected by spontaneous combustion. The traditional top coal caving roadway along the coal seam floor and the coal pillar retaining roadway can not meet the production needs. It is urgent to adopt the pillar free roadway layout and corresponding recovery technology that can not only improve the recovery rate but also ensure safe production, In this paper, the staggered roadway layout system and three-stage mining technology are proposed to realize pillar free mining

the system integrates three kinds of top coal caving, top coal caving in upper layer and top coal caving in lower layer in one working face. The three kinds of processes are used in different positions of the working face to form a unique three-stage mining process. Section a in the figure, that is, the working face adopts the upper layered mining process of layered roof caving at the side of the air inlet roadway arranged along the roof, which needs to be paved to prepare for the tunneling and mining of the next working face. Section C in the figure, i.e. the working face away from the adjacent goaf adopts the top coal caving mining process. This section does not need to be paved, but it is necessary to control the coal cutting height of the Shearer to prevent gangue leakage. In Section B in the figure, the middle working face adopts the top coal caving mining process

4.2 comparison with traditional top coal caving

whether it can effectively prevent and control spontaneous combustion is an important basis for judging the feasibility of the scheme. Therefore, in the prevention and control of spontaneous combustion, the staggered roadway layout is compared with the traditional top coal caving roadway along the floor:

1 Section transportation drift; 2. section return air drift; 3. lost top coal and section coal pillar; 4. location of transportation drift in upper section

(1) the staggered roadway layout system arranges the air inlet roadway and air return roadway under the coal seam roof and the goaf of the previous section respectively. The roof of the air inlet roadway and air return roadway are rock and a small amount of coal skin respectively, which basically avoids the occurrence of high caving area in the roadway and can reduce the fire rate compared with the electronic universal experimental motor; The traditional top coal caving is arranged along the coal seam floor. Above the roadway is a thick coal seam, which is easy to fall under pressure to form pores, and there is a hidden danger of spontaneous combustion. According to statistics, 2/3 of the fires caused by fully mechanized top coal caving mining occurred in the high caving area of the roadway, according to Dr. Sun Hui of the New Energy Research Institute of China University of Petroleum (Beijing). (2) In the staggered roadway arrangement system, the air inlet roadway side is under stress, but because the roadway is directly under the rock roof, there will be no high coal caving at the roadway top, which will further aggravate the damage of the roadway side, and it is not easy to form developed broken coal fissures. Compared with the coal roadway side arranged on the floor, the fire probability is small, and it is easy to maintain; The air return roadway has more obvious advantages, because the air return roadway arranged under the goaf is in the pressure free zone, which will not cause strong compression on the roadway side, and can reduce the probability of ignition. (3) Under the staggered roadway layout system, there is only a small number of triangle coal pillars between adjacent working faces, and they are located in the pressure free area. It is not easy to see that a large number of "t" shaped coal pillars in the traditional top coal caving are located in the stress concentration area and are fractured and compressed, resulting in air leakage from the side of the roadway to the goaf, which is not only conducive to the prevention and control of spontaneous combustion in the adjacent goaf, but also conducive to reducing the ignition probability of the coal pillars themselves. (4) One side of the air inlet roadway in the upper section is the process section of upper layered top coal laying. The floating coal in this section exists in the lower section, which can be recovered during mining in the next section, reducing the number of floating coal in the goaf. In addition, the grouting while mining in the upper section is conducive to the formation of artificial roof or a certain cementation effect. When mining in the lower section, the air leakage to the goaf is reduced, Therefore, special mining technology is also a favorable condition to reduce spontaneous combustion. The comparison shows that the staggered roadway layout system has fundamentally improved the conditions of easy spontaneous combustion

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