(1) Dust-proof measures. Under normal circumstances, the concentration of floating coal dust in the production site is much lower than the lower limit of the explosion. However, due to air turbulence (the shock wave of the shot), the deposited coal dust is re-flyed, and the concentration of coal dust at this time greatly exceeds the lower explosion concentration. It is estimated that on the periphery of the 4m2 section small roadway, as long as a layer of coal dust of 0.04mm thick is deposited, when it is all flying up, the lower explosion limit is reached. In fact, the deposited coal dust in the underground exceeds this thickness. Therefore, it is the simplest and most effective explosion-proof measure to reduce the amount of deposited coal dust in the roadway and remove the well.
Effective dust-proof and dust-reducing measures are adopted in each production process to reduce the generation of coal dust and reduce the concentration of coal dust in the air, thus reducing the amount of deposited coal dust. Therefore, comprehensive dust prevention measures are not only measures to reduce the health hazards of workers, but also measures to prevent coal dust explosions.
(2) Eliminate the source of fire. The sources of ignition that can cause coal dust explosions are electric sparks, friction sparks, friction heat, high temperature points formed by spontaneous combustion of coal, deflagration in blasting operations, and high temperature products generated by gas explosion. The main technical measures to eliminate this kind of ignition sources are: to maintain the integrity of the mine explosion-proof electrical equipment, electrical equipment to strengthen management to prevent loss of critical phenomena; the choice of non-ignition of the light alloy material to avoid the risk of friction sparks; tape, wind Common non-metallic materials such as cylinders and cables must have flame retardant and antistatic properties; use resisting agent, gel or nitrogen to prevent self-ignition of coal pillars and residual coal in goaf, and strengthen gas management to prevent gas explosion accidents. .
(3) The method of spreading rock powder. Due to the complex natural conditions of coal mines and the randomness of coal dust explosions, in addition to the above-mentioned general safety technical measures, in view of the characteristics of coal dust explosions, countries have also studied the expertise to prevent coal dust explosions. The long-term, simple and easy-to-use technical measure to prevent coal dust explosion is the slag powder method.
This method is to periodically spray inert rock powder around the roadway to cover the deposited coal dust deposited on the periphery of the roadway. When the rock powder layer has a low wind speed in the roadway, its viscosity plays a role in hindering the re-flying of the deposited coal dust.
When an abnormal situation such as a gas explosion occurs, a huge air turbulent wind blows both the rock powder and the deposited coal dust to form a rock dust-dust dust cloud. When the explosion fire enters the mixed dust cloud area, the rock powder absorbs the heat of the flame to cool the system, and the rock powder particles also play a shielding role, preventing the flame or the burning coal particles from transferring heat to the unexposed coal dust particles, and finally reaching Prevent the purpose of coal dust from catching fire. This measure has been widely applied in major coal-producing countries such as the United Kingdom, the United States, and Russia, and the effect is remarkable.
Prevention of coal dust explosion propagation technology
The technology for preventing coal-dust explosion propagation is also called the technology for isolating coal-dust explosion propagation (hereinafter referred to as explosion-proof technology). It refers to the technical measures to control the explosion that has already occurred within a certain range and extinguish it to prevent the explosion from spreading outward. This technology is not only suitable for the control of coal dust explosion, but also for the control of gas explosion and gas coal dust explosion. The technology is divided into two categories, passive flameproof technology and automatic flameproof technology.
(1) Passive flameproof technology (also known as explosion-proof measures). At the beginning of the explosion, the peak of the explosion flame is ahead of the explosion pressure wave. As the explosion reaction continues and strengthens, the pressure wave gradually catches up and advances ahead of the flame peak. There is a time difference between the two. Passive explosion-proof technology is to use this law, using the energy of the pressure wave to make the explosion-proof measures act, forming a flame-damping flame cloud in the roadway to extinguish the flame, and the subsequent flame is extinguished when it enters the inhibitor dust cloud, preventing it. The explosion continued to spread forward. The passive explosion-proof technology mainly includes: rock powder shed, water tank shed and water bag shed, collectively referred to as passive explosion-proof shed.
There are three forms of passive explosion-proof sheds, centralized layout, decentralized arrangement and centralized decentralized hybrid arrangement. According to the role and protection scope of the explosion-proof shed in the mine roadway system, they can be divided into the main explosion-proof shed (heavy shed) and the auxiliary explosion shed (light shed). The function of the heavy shed is to protect the safety of the whole mine. The main transportation roadway and the return air main road connected to the wellbore of the mine are connected; the transportation lane and the return stone gate between the adjacent coal seams; the concentrated transportation lane and the return airway between the adjacent mining areas. The role of the light shed is to protect the safety of a mining area, the air inlet and return air passages in the coal mining face; the coal and semi-coal rock roadway in the mining area; and other roadways with independent ventilation and danger of coal dust explosion Settings.
(2) Automatic flameproof technology. The principle of action of the passive explosion-proof technology determines that the technical measure can only suppress the explosion within the range of 60-200 m from the explosion source (300 m in the rock meal shed). Therefore, this technique was ineffective at the beginning of the explosion. In addition, the use in low, narrow and curved lanes is extremely unfavorable and does not exert a detonation effect. In response to these shortcomings, countries have studied and used automatic flameproof technology.
The sensor, controller and spraying device are the three major components of the automatic explosion-proof device. The explosion-proof system consisting of several automatic explosion-proof devices is the automatic explosion-proof device. The sensors used mainly have three types: the gas explosion is accepted. A power effect pressure sensor, a pyroelectric sensor that utilizes the thermal effect of the explosion, and a photoelectric sensor that utilizes the light effect of the explosion flame. The controller is an instrument that issues an action command to an actuator that sprays the inhibitor; the spray mechanism typically consists of an actuator, a sprinkler, and an inhibitor storage container. Its role is to diffuse inhibitors (rock powder, dry powder or water) into the roadway space to form dust clouds or water mist zones. Its movements should be fast, reliable, and adaptable to the rapid development of the explosion.
The selection principle of the inhibitor is to suppress the amount of flame, the effect is good, and the price is cheap. Although rock powder is the most widely used in coal mines, its suppression effect is not satisfactory under weak gas and coal dust explosion conditions and in severe explosions. Inhibitors suitable for use in automatic flameproof devices are mainly liquid inhibitor water, water plus halogenated alkane, powdered inorganic salt inhibitors and alkyl halides. The powder inorganic salts are powders of (NH4)H2PO4, NaCl, KCl, KHCO, NaHCO3, CaCO3 and the like. Haloalkoxy has a bromine-difluoro-methane chloride, although a good extinguishing effect, but it has the disadvantage of damaging the ozone layer, has begun disabled.
Mine dust detection method
Dust detection is a scientific method for measuring, analyzing and inspecting the content of dust and its physical and chemical properties in the air of production environment. From the perspective of safety and hygiene, daily dust testing projects are mainly dust concentration, free silica content in dust and dust dispersion (also known as particle size distribution).
1. Determination of mine dust concentration
(1) Mine dust concentration standards. The allowable concentration of dust in the air of workplaces in China is defined as: mines with a free silica content greater than 10% in rock ore, a dust allowable concentration of 1 mg/m3; mines with a free silica content of less than 10% in rock ore, dust The allowable concentration is 4 mg/m3.
(2) Determination of dust concentration. The dust concentration of the mine is mainly determined by the membrane dust measuring method and the fast direct reading dust meter method.
1 filter film sampling dust. The principle of dust measurement is to collect a certain volume of dusty air by using a dust sampler (or a respiratory dust sampler). When the dusty air passes through the filter membrane, the dust is trapped on the filter membrane and calculated according to the weight gain of the filter membrane. Dust concentration.
2 Quick direct reading dust meter. Dust measurement with a filter sampler is a method of indirectly measuring dust concentration. Due to the long preparation time, dust sampling and sample processing time, the results cannot be obtained immediately, which is inconvenient when the health supervision and evaluation of dustproof measures are effective. In order to meet the needs of practical work, countries have developed a rapid tester that can immediately obtain dust concentration.
2. Determination of dust free silica
Determination of national standards is pyrophosphate mass method is also useful for measuring infrared spectrophotometer assay. Determination of free silica content in respirable dust, coal mine dust using infrared spectroscopy, non-coal mine dust using X-ray along the way.
(1) Pyrophosphoric acid method. At a temperature of 245 to 250 ° C, pyrophosphoric acid can dissolve silicates and metal oxides, and it is almost insoluble in free silica. Therefore, after treating the dust sample with pyrophosphoric acid, the mass of the residue obtained is free dioxide. The amount of silicon, expressed as a percentage. In order to obtain more accurate results, the residue can be treated with hydrofluoric acid, and the quality that is mitigated by this process is the free silica content.
(2) Infrared spectroscopic analysis. When infrared light interacts with matter, its energy is equivalent to the vibration or rotational energy level of the material molecule, and the energy level transition occurs, that is, the molecular low energy level transitions to a high energy level. As a result, certain wavelengths of infrared light are absorbed by the substance molecules to produce an infrared absorption spectrum. The absorption spectrum of free silica has a wavelength of 12.5 μm, 12.8 μm, and 14.4 μm.
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