1 Basic conditions of gas explosion
The occurrence of gas explosion must have three basic conditions. First, the gas concentration is within the explosion limit, generally 5% to 16%; second, the ignition source with sufficient energy; and third, the oxygen concentration in the mixed gas is not less than 12%. . A gas explosion cannot occur in any of the three conditions.
1.1 Gas concentration
Gas concentration overrun is the root cause of gas explosion accidents. The gas concentration causing the gas explosion has a range. Any gas mixture whose concentration is lower than the lower explosion limit or higher than the upper explosion limit will not cause the flame to propagate spontaneously when it comes into contact with the ignition source. When the gas concentration is lower than the lower explosion limit, excessive air is used as an inert medium to participate in the combustion reaction, which consumes a part of the reaction heat, which acts as a cooling function and hinders the flame from self-propagating. On the contrary, when the gas concentration is higher than the upper explosion limit, the air is excessive due to the combustible material. Insufficient oxygen, resulting in incomplete chemical reactions, the heat released by the reaction is less than the heat lost, thus hindering the spread of the flame.
1.2 Oxygen concentration
The concentration of oxygen must reach more than 12%, otherwise the underground gas explosion reaction cannot continue. In the closed area, goaf and other cracks in the underground, oxygen concentration may be less than 12% due to oxygen consumption or no oxygen supply. The general oxygen concentration of other roadways and working faces will be higher than 12 %.
1.3 Fire source
Fire source is one of the necessary conditions for causing mine gas explosion accidents. Fire sources can be divided into weak fire sources and strong fire sources. Under normal circumstances, a weak fire source cannot form a shock wave, and the deposited coal dust cannot be converted into a floating state; on the contrary, a strong fire source generates a shock wave and converts the deposited coal dust into a floating state. In order to cause a gas explosion, the source of the fire must have sufficient energy, that is, the temperature is generally not lower than 650 ° C, the energy is generally greater than 0.28 mJ and the duration is greater than the explosion induction period. This condition is usually easy to satisfy. In coal mining, measures are taken for some inevitable sources of ignition, making it an ignition source that cannot satisfy the ignition of gas.
2 The main cause of gas explosion
2.1 Analysis of thought factors
The root cause of the gas explosion accident lies in the lack of ideological understanding and the idea of ​​truly establishing safety first [1]. Especially in the case of favorable coal market in the past two years, many coal enterprises have expanded their production capacity and increased coal production. It is not possible to properly handle the relationship between safety and production, safety and efficiency. The concept of “safety first†is weakened and is the biggest hidden danger in the current safe production of coal mines.
2.2 Analysis of technical factors
With the adoption of intensive production technology characterized by high production and high efficiency, existing gas disaster prevention technologies and equipment have been unable to effectively control the occurrence of major gas disasters in mines [2]. The main reasons are: 1 gas disaster prevention technology is scattered, there is no system to form a complete system; 2 gas disaster prevention technology lacks corresponding equipment support; 3 there are many common key technical problems that need to be solved, especially under the conditions of intensive production technology Common technical issues of commonality.
2.3 Analysis of management factors
The safety management method of coal mines lags behind, and the phenomenon of “three violations†sometimes occurs. The occurrence of gas explosion accidents has a certain direct relationship with the way of safety management. In many cases, the management of gas is often subject to human subjectivity and experience. As the depth of coal mining continues to increase, the geological conditions of gas are becoming more and more complex, and this traditional safety management method is limited by people's experience, knowledge and responsibility. Therefore, management factors are also the cause of frequent gas accidents. one.
2.4 Analysis of safety input factors
Safety investment is crucial to the safety of coal mines. In the past few years, due to the poor economic benefits of coal mines and the difficulty in maintaining the lives of coal mine workers, many coal mining enterprises have reduced their safety investment and have more safety debts. Many mines have different levels of ventilation systems and inadequate supporting facilities, "one-way three-proof" monitoring system is imperfect and equipment facilities are aging. Taking the statistics of 1999 as an example, only 191 of the large and medium-sized coal mines in the country have investment in safety research, accounting for only 36.77% of the total number of large and medium-sized coal mines, and the total investment in safety research is 58.78 million yuan, with an average of about 100,000 yuan per mine. In 2002, the US Occupational Safety and Health Supervision Bureau had a total budget of US$426 million, and the Mine Safety and Health Supervision Bureau had US$246 million. A total of 672 million US dollars, China's budget in this area can not be compared, as the annual budget of China's coal mine safety supervision bureau is only 1 / 60 of the United States, and the number of coal mines is about 300 times that of the United States [3]. In the past two years, the benefits of coal mines have improved. Many enterprises only pay attention to production inputs. There are still serious shortages in safety investment, and the safety production conditions have not been significantly improved.
2.5 Analysis of natural factors
After entering the 1990s, with the increase of mining depth, the geological conditions have become more and more complicated, and the gas content and gas emission of coal seams have increased, and coal and gas outburst have become more and more serious. At the same time, due to the increased mining depth, the existing partial gas control theory can no longer adapt to new production conditions. The above two reasons make the gas management difficult.
3 Basic measures to prevent gas explosion
From the gas explosion conditions, the concentration of oxygen is one of the factors causing gas explosion, but there is generally no oxygen concentration below 12% in coal mines. Therefore, the prevention and control measures for gas explosions are reflected in two aspects: strict control of gas concentration in various areas of the mine, elimination of fire sources and exercise plans.
3.1 Control the concentration of gas in the well
3.1.1 Establish a reasonable ventilation system to dilute the gas concentration in the underground space
Ventilation is the primary means of discharging gas. Doing a good job in ventilation safety technology management is a prerequisite and key link in the prevention and control of major accidents in coal mines. Therefore, all mines must establish a safe and reliable, independent mine ventilation system. Establishing a reasonable ventilation system can ensure that there is enough air volume at all working places in the well to dilute the gas from the underground and discharge it out of the well to avoid gas accumulation. Therefore, establishing a reasonable ventilation system is the most effective and basic way to prevent gas explosion. Measures. Pingdingshan Coal Industry Group No. 10 Mine has reformed the ventilation system of the 9-10-21170 working face, established a reasonable ventilation method, improved the gas concentration of the return air flow and avoided the gas over-limit of the working surface angle (see Table 1). .
3.1.2 Do a good job of gas drainage to reduce the amount of gas in the coal seam
Gas drainage is an effective measure to prevent gas accumulation [5]. As the depth of coal mining continues to deepen, the amount of gas emission becomes larger and larger, and the ventilation system becomes more and more complicated. The ventilation method is used to reduce the concentration of gas to the requirements of coal mine safety regulations, from a technical and economic point of view. , are unreasonable. Gas drainage can not only effectively use gas, but also reduce the amount of gas in the coal seam. The implementation of gas drainage is a fundamental measure to control gas concentration in mining space, reduce gas accumulation, and prevent coal and gas from protruding. It also reduces gas pollution to the atmosphere and increases resources and energy. However, due to the fact that China is generally a low-permeability coal seam, it is difficult to implement gas pre-extraction, and the effect is very poor. Pingdingshan Coal Industry Group Shitou 10-20120 working face and Wu 9-10-20190 working face actively use gas drainage technology, the coal seam gas pressure and gas emission are significantly reduced after pumping (see Table 2), better The ground controls the possibility of gas overrun.
3.1.3 Strengthening daily management of gas
Strengthening the daily management of gas is an important part of coal mine safety work. The daily management of gas is to establish a patrol inspection gas system. It is necessary for the inspectors to check the ventilation and the concentration of gas in an uninterrupted underground well. When local gas accumulation is found, it must be dealt with immediately. Therefore, when the inspectors work underground, they must strictly implement the coal mine safety regulations, and it is strictly forbidden to miss the empty class. The "Safety Regulations for Coal Mines" stipulates that the number of inspections of gas concentration in all mining face: at least 2 inspections per shift in low gas mines; at least 3 inspections per shift in high gas mines; coal (rock) and gas (CO2) For the dangerous mining face, the individual mining face with large gas emission and abnormal changes must have a special person to check the gas or CO2, and automatically set the alarm power-off device according to the gas. For prominent mines, the prediction of gas outburst should also be done. Gas daily management is one of the important measures to prevent gas explosion accidents.
3.1.4 Establish a gas monitoring system to detect gas overruns in time
The establishment of a gas monitoring system plays a very important role in controlling the concentration of gas. The gas monitoring system can realize continuous monitoring of gas, timely grasp the change of gas concentration, and also provide reference for accident emergency rescue decision and accident investigation. The monitoring of gas by people is an intermittent process, which has its inevitable shortcomings. The accident is characterized by a unity of randomness and contingency. This determines that relying solely on people to manage gas can obviously not be achieved. The purpose of controlling the concentration of gas. However, because the gas monitoring system can realize the advantages of continuous monitoring of gas, the establishment of the gas monitoring system can achieve the purpose of monitoring gas at any time. The gas monitoring instrument is installed underground, and the abnormal situation of the gas in the main roadway of the underground is continuously monitored, which can prevent and control the occurrence of gas explosion accidents.
3.2 Eliminate the source of fire
The fire source is a basic condition that causes the mine gas explosion. It is necessary to conscientiously implement coal mine safety regulations, and eliminate all non-production fire sources in the underground; strictly manage and limit the fire sources and heat sources that may occur in production. It is strictly forbidden to use the overhead electric motor vehicle in the underground. In the production, the separate power supply, the three special two locks, and the dual fan dual power supply are adopted to limit the occurrence of the fire source.
3.3 Walk the gas explosion plan
The drill plan is very important for preventing gas explosion accidents. Coal mining enterprises should conscientiously formulate special emergency plans for gas explosion accidents under the guidance of the principle of "resistance prevention and prevention, prevention first", and conduct exercises on their plans. The formulation of the gas explosion emergency plan will not only help the employees of Daping Coal Mine to familiarize themselves with the situation of the enterprise, but also be able to guide the prevention of gas explosion accidents and emergency rescue of accidents. The exercise through the pre-plan will not only enable the majority of coal mine workers to master various emergency skills, improve the resilience of emergency rescue personnel, but also find the lack of gas explosion prevention measures during the exercise, thus improving gas explosion measures and avoiding gas explosions. The possibility of an accident.
4 Conclusion
Preventing coal mine gas explosion is a complicated system project. All production in coal mines should be placed in an important position to prevent gas explosion accidents, and conscientiously implement the 12-character policy of “first pumping, monitoring, monitoring, and wind productionâ€. Starting from the conditions, it is analyzed and proposed that the prevention of gas explosion should be based on the control of gas concentration, the elimination of fire sources and the practice of gas explosion, and the corresponding preventive measures should be taken to make the production of the mine intrinsically safe.
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