In recent years, coal production has developed rapidly and the level of mechanization has been greatly improved. Coal mines generate a large amount of dust in the process of excavation, coal mining and transportation, which seriously threatens the safe production of mines and the health of employees. Effective control of dust, reduction of dust concentration, improvement of working environment and elimination of coal dust accidents are an important part of coal mine safety production. Grasping the mine's comprehensive dust prevention work is of great significance for promoting mine safety production and ensuring the health of workers.

1 Coal mine dust hazards

Coal mine dust refers to the fine particles of rock and coal that are produced during the production process of coal mine development, excavation, mining and lifting transportation, and can be suspended in the air for a long time, also referred to as mine dust. The hazards of coal mine dust are mainly manifested in four aspects. One is the spontaneous combustion and explosiveness of coal dust. The danger of coal dust explosion is widespread and the damage is serious. The danger of coal mine explosion in China is widespread. In 2007, there were 548 coal mine dust explosions in state-owned key coal mines, accounting for 87.4%. Second, serious occupational hazards. According to statistics, at present, the number of pneumoconiosis patients in the coal industry alone has exceeded 200,000, which is close to half of the number of lung patients in various industries in China, and is still growing every year. The annual death from pneumoconiosis is 2,500 to 3,000. The third is to reduce the visibility of the workplace. The coal dust concentration is high in some working faces in the underground, and its visibility is extremely low, which often leads to misoperation and increases the occurrence of industrial accidents. The fourth is to accelerate the impact of mechanical wear and dust on mechanical equipment. It is manifested in accelerating the wear of machinery and shortening the life of precision instruments. Controlling coal mine dust has become a top priority in the coal industry, and the most effective measure to control dust is to significantly reduce the dust concentration in the workplace air.

2 Dust prevention measures currently adopted by coal mines in China

2.1 Coal seam water injection Coal seam water injection is to inject high pressure water into the coal body through drilling, so that the coal body is pre-wet, the original coal dust is wetted, so that it loses the ability to fly, and the water can effectively wrap each small part of the coal body. When the coal body is broken during mining, the presence of water can avoid the flying of fine coal dust. This kind of dust reduction measure is effective, and generally reduces the dust concentration by about 60% to 90%. The number of working faces that use water injection abroad is a high percentage of the total number of working faces, while the number of working faces that use coal seam water injection in China is relatively small. This gap is not due to water injection technology equipment, but due to the lack of strict management of dust control and the ineffective promotion of effective water injection technology measures. Some countries add humectant calcium chloride to coal seam water to improve the degree of wetting and dust reduction. There are three main types of water injection in coal seams: 1 short-hole water injection is vertical coal wall in the mining face or obliquely intersected with coal wall to inject water, the length of water injection hole is generally 2-3.5m; 2 deep hole water injection is in mining The working face is perforated and filled with water in the direction of the vertical coal wall. The length of the hole is generally 5-25m. 3. The long hole is filled with water. It is from the transport roadway or the return airway along the mining face. The coal seam tends to be parallel to the working face. Water injection, the hole length is 30-100m, and sometimes the upper and lower combined drilling water injection method is adopted. The long hole water injection method has the advantages of uniform coal body moisture and large wet range, and it is preferred as the main water injection method at home and abroad.

2.2 Spray sprinkler Dust spray spray is achieved by a sprayer or sprinkler. When the water passes through the sprayer, it is sprayed into the air to form a misty water droplet due to the rotation and impact. When the misty water droplets meet the dust particles suspended in the air, the dust particles are wetted, some of them fall directly, and some of them collide with the wind flow, and the dust particles collide with each other, and then fall into the dust particles. Spray watering is one of the simplest, easy and extremely effective measures to reduce the amount of dust in the mine. It can be used not only for dust removal in mining face, but also for other operations such as transportation, transfer, purification of wind, etc. . Spraying when shooting at the mining face can also eliminate the gun smoke and shorten the ventilation time. At present, the spray dust removal technology used in coal cutting machine shearing machine mainly has the following aspects: 1 radial shear screen of rocker drum rocker arm and hydraulic support beam auxiliary spray dust reduction; 2 internal and external spray dust reduction of coal mining machine ; 3 coal mining machine high pressure spray negative pressure secondary dust.

Hydraulic Support Transfer Automatic Spray Dust Reduction Technology The self-moving hydraulic support in the process of lowering the column and moving forward accounts for about 30% of the dust generated by the entire working surface. At present, the automatic spray control of the hydraulic support has been developed in China. The valve realizes the automatic spray dust removal of the hydraulic support in the process of descending column, moving frame and pushing and sliding, and has good effect and wide application.

2.3 Establishing a reasonable ventilation and dust removal system Mine ventilation is to continuously supply the ground fresh air to the working point under the action of mechanical or natural power, dilute and eliminate toxic, harmful gases and dust, adjust the climatic conditions in the mine, and create safe and comfortable work. surroundings. The ventilation and dust removal of mines is based on fluid mechanics and thermodynamics. The principles of momentum, mass and heat transfer are applied to study the laws of wind movement and pollutant transport and settlement, as well as various safety and sanitary engineering technical measures. The main factors that determine the effect of ventilation and dust removal are wind speed, direction of wind flow and density of mine dust, particle size, shape, and degree of wetting. When the wind speed is too low, the coarse-grained dust will separate from the air and sink, it will not be discharged and stay in the mining space, increasing the concentration of coal dust; the wind speed is too high, although the dust can be taken away, but the dust in the mining space is blown again. Instead, it will increase the concentration of coal dust. In general, the optimal dust-removing wind speed of the tunneling face is 0.4-0.7 m/s, and the wind speed of the mechanized coal mining face is 1.5-2.5 m/s. The "Safety Regulations for Coal Mines" stipulates that the maximum allowable wind speed of the mining face and the driving coal roadway is 4m/s. This not only considers the requirements of ventilation on the working face, but also considers the secondary flight of coal dust.

2.4 Improve the strict inspection and management system, and do a good job in dust prevention and labor protection for workers in dust prevention knowledge training. It is necessary to establish a sound and strict inspection management system and specialized organization. The first is to strengthen the maintenance and management of the established ventilation and dust removal system and ventilation equipment to ensure good ventilation. Regularly measure the dust concentration in the air in the dust-producing space to see if it meets the Industrial Hygiene Standard. The second is to regularly check the body of people exposed to dust, to detect the patient early, to treat in time, and to adjust the position of exposure to dust poisoning work early. Dust prevention and control work, both technical work and organization management work, both are indispensable. While increasing anti-dust technology, dust and increase investment capital, the use of advanced equipment and anti-dust measures, we must strengthen technical training, improve the quality of workers, the vast majority of workers to realize that dust on the human body, anti master Dust knowledge and technical measures.

2.5 Personal protection Personal protection refers to measures to reduce the inhalation of dust by wearing various protective masks. At present, the personal protection has a self-priming dust mask, a filtered air dust mask, a airflow helmet, etc., the purpose of which is to enable the wearer to breathe the cleaned clean air without affecting normal work. The high efficiency of dust prevention by individual protection measures is one of the important technical measures to solve the harm of mine dust to the health of miners. Actively promoting individual protection technology will definitely promote dust prevention work in mines and protect mine workers from dust.

3 Development trend of coal dust control technology

In recent years, China has made great progress in the prevention and control of dust. New technologies, new processes, new methods, new designs, new products, and new materials have been continuously introduced, but there is still a gap with the on-site needs. The next step should be focused on the following aspects. Research and Development:

3.1 The physical and chemical dust prevention technology should be strengthened. For example, technologies such as ultrasonic dust removal, ionized water dust removal, microbial dust removal, sonic atomization and dust removal are discussed;

3.2 Improve the existing coal seam water injection technology level. According to the specific conditions of the fully mechanized mining face, choose the reasonable drilling arrangement, sealing process, water injection method and water injection equipment to achieve the best water injection effect and achieve the purpose of dust prevention and dust reduction.

3.3 The dustproof side of the bracket. The hydraulic support and coal injection nozzle are still at low pressure. In the future, our work will focus on the research and application of medium and high pressure spray dust reduction.

3.4 It is necessary to vigorously develop various equipment such as high-efficiency and low-energy utility model dust collectors, and air conditioners that are suitable for mine characteristics. Dust removal systems and purification equipment should be developed in the direction of systemization, large-scale, intelligent and energy-saving.

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