Chapter I: Mine Ventilation Section I: Why the mine ventilation Why ventilate underground coal mine? Without ventilation can not I? Practice has proved that without ventilation is not acceptable. Because mine will be producing some, people can not live without oxygen. Second, people in the underground production process continuously produce toxic or harmful gases, such as: carbon monoxide, carbon dioxide, nitrogen dioxide, sulfur dioxide, hydrogen sulfide, methane, etc., if you do not rule out that people can not produce these gases. Underground due to temperature and other factors, adverse weather conditions need to be adjusted downhole. The basic tasks of ventilation: (1), supply fresh air underground sufficient to meet the oxygen needs of staff. (2), dilute the toxic and harmful gases and dust underground, to ensure safety in production. (3), regulating underground climate, to create a good working environment. Mine must be ventilated, no ventilation can not guarantee security and maintain production. Therefore, ventilation is the most basic aspects of mine production part of it during mine construction and production has always occupied a very important position. Section II of the type of mine ventilation Impact of the mine ventilation system consists of the main factors of production safety decisions. According to the mine ventilation system related factors are divided into different types. According to gas, coal combustion and high temperature of the main factors in mine production safety requirements on the mine ventilation system, in order to facilitate the management, design and inspection, the mine ventilation system is divided into general type, cooling type, fire type, emissions of gas type, fire and the cooling type, and cooling type gas emissions, emissions of gas and fire-type, emission type of gas and fire and some cooling, followed by eight grades 1-8. Section: Air First, the air: The air is the surface of the earth we live on the ground surrounded by the atmosphere, which consists of dry air and water vapor mixture formed in the dry air under normal conditions of several of the following composition: Name of the gas volume concentration Nitrogen (N2) 78.13% Oxygen (O2) 20.90% Carbon dioxide (CO2) 0.03% Argon (Ar) 0.93% Other 0.01% Second, the underground air: The air into the mine, the result of both physical and chemical changes occur, so ingredients and concentration change. 1, the physical changes: Gas mix: coal contains gas, carbon dioxide and other gases, mine gases in the production process of these will be mixed with mine air. Solid mixed: Underground produced part of the job rocks, dust and other small miscellaneous dust mixed with mine air. Climate Change: As downhole temperature, pressure and humidity caused by mine size and concentration of air. 2, the chemical changes: The slow oxidation of all the material underground, blasting fire zone of oxidation, these changes have an impact on the air underground. After the physical and chemical changes in underground air compared with the air changed greatly, composition increased, the concentration change of oxygen concentration decreased. Species composition of underground air there: O2, N2, CH4, CO, CO2, H2S, SO2, H2, NH3, NO2, water vapor and dust twelve. However, due to different conditions of each mine, the mine's underground air and the type and concentration are not the same. Third, the main component of underground air: 1, oxygen (O2) The nature of oxygen: a colorless, tasteless, odorless gas, it is 1.11 the proportion of the air, its chemical nature is very lively, can be combined with all of the gas phase, oxygen to support combustion, oxygen is not human and animal metabolism the lack of substance, people can not survive without oxygen. Oxygen effects on human beings as follows: Oxygen concentration% Symptoms of human response 17 No effect at rest, work, causing wheezing, difficulty breathing, heartbeat. 10 - 12 Loss of consciousness, of a serious threat to human life. 9 Following Suffocation in a short time. "Coal Mine Safety Regulations" provides that: In the mining face in the inlet air flow, by volume, the air was 20%. 2, nitrogen (N2) The nature of nitrogen: a colorless, tasteless, odorless gas, it is 0.97 the proportion of air, no combustion, unable to maintain respiration. Under normal circumstances, nitrogen is harmless, when too much nitrogen in the air, it will reduce the oxygen content, can be suffocating from lack of oxygen. Underground source: the decay of organic materials such as prop will produce nitrogen, dynamite explosions can produce nitrogen, coal and rock will be emission of nitrogen within the cracks. 4, carbon dioxide (CO2) The nature of carbon dioxide: a colorless, inert gas Luedaisuanwei, it is 1.52 the proportion of air, easily soluble in water, not combustion, can not maintain breathing, slightly toxic, eye, throat and nasal mucosal irritation effect. "Coal Mine Safety Regulations" provides that: In the mining face in the inlet air flow, by volume, carbon dioxide concentration should not exceed 0.5%. Underground Source: prop substances such as coal and oxidation of coal and rock in the emission, blasting, gas and coal dust explosion, human respiratory and so on. Fourth, the main underground air and preventive measures of harmful gases Underground mine production of air due to the physical and chemical changes, the underground air, there are some poisonous and harmful gases: First, the main harmful gases: A), carbon monoxide (CO) 1, nature: Carbon monoxide is a colorless, tasteless, odorless gas, accounting for 0.97 of its air, slightly soluble in water. Under normal temperature and pressure, carbon monoxide, inert chemical properties, but the concentration of 13% - 17% of a fire can cause an explosion. The reason why is because the highly toxic carbon monoxide in the body of its blood-red ball contained hemoglobin oxygen affinity than the large 250 - 300 times. Therefore, after carbon monoxide inhalation of oxygen and hemoglobin prevented the normal combination of the various parts of the body tissues and cells of oxygen, causing suffocation and poisoning. 2, the concentration of carbon monoxide poisoning the relationship between the degree: Carbon monoxide 0.016 0.048 Degree of intoxication time poisoning symptoms Hours without symptoms or mild headache Mild poisoning within 1 hour tinnitus, headache, dizziness, heart 0.128 0.5 - 1 hour addition to the above serious poisoning symptoms weakness, vomiting, feeling Late nap, loss of mobility Loss of consciousness within a short time of 0.4 fatal poisoning, convulsions, respiratory pause, play dead "Coal Mine Safety Regulations" provisions of the concentration of carbon monoxide in the air underground not more than 0.0024%. 3, the underground sources of carbon monoxide in: (1), underground fires; coal combustion. (2), methane and coal explosion. (3), blasting work. B), carbon dioxide, see above section. III), hydrogen sulfide gas. 1, nature: Hydrogen sulfide gas is a colorless sweet, a rotten-egg smell of gas, accounting for 1.19 of its air, soluble in water, can burn, when the concentration of 4.3% - 46% Shihai explosive. 3, underground sources: (1), prop Analysis of decay. (2), sulfur-containing minerals (such as: pyrite, gypsum, etc.) water decomposition. (3), from gob or coal waste rock in the tunnel emission release. (4), the work of blasting. ; D), sulfur dioxide: 1, nature: Sulphur dioxide is a colorless with a strong smell of sulfur combustion gases, it accounted for 2.2 air, soluble in water. It has a strong eye and respiratory stimulation. "Coal Mine Safety Regulations" provisions of the concentration of sulfur dioxide in the air underground not more than 0.0005%. 3, underground sources: (1), the spontaneous combustion of sulfur mineral or slow oxidation. (2), released from coal in the surrounding rock. (3), sulfur minerals in the blast generated. Fifth, nitrogen dioxide (NO2) 1, nature: red-brown nitrogen dioxide gas, accounting for 1.57 of its air, easily soluble in water, nose to the eyes, respiratory tract and lungs have a strong stimulating effect, nitrogen dioxide combines with water produce nitric acid, so corrosion damage of lung tissue from the role, can cause lung edema. 2, the concentration of nitrogen dioxide poisoning relations between the degree: "Coal Mine Safety Regulations" provisions of the concentration of nitrogen dioxide gas in the air underground not more than 0.00025%. Underground Source: Produced mainly shooting. F) Biogas: Biogas total number of coal mine gas accounts for about 90% or more, focus on the next chapter described. Second, measures to prevent harmful gases: 1, to enhance ventilation. Appropriate increase in air volume, the discharge of harmful gases or dilute them to the "Coal Mine Safety Regulations" the following provisions of the safe concentration is also effective against common hazardous gases underground hazards of the most fundamental measures. 2, strengthen inspection, using a variety of swimming see that most of bribery mane skeleton clock diarrhea ζ Mi mu ? For timely and appropriate action. 3, if a high content of harmful gases drainage measures can be taken. Such as gas drainage. 4, poorly ventilated areas or underground ventilation of the old roadway is not a lot of accumulation of harmful gases. Therefore, to be located in the old alley fence, hanging police standard, to prevent others from being diverted. If you must enter the required detailed examination of a variety of harmful gases to enter. 5, if a person suffocation from lack of oxygen or breathing toxic gas poisoning would immediately move to fresh air poisoning the roadway or ground and artificial respiration (NO2, H2S poisoning excluded) first aid. Third, the mine ventilation facilities: In order to flow underground distribution of air flow along the designated route, to be guided in some roadway construction of structures that control the ventilation airflow, which guide the air flow and cut off air flow into the facility. A) guide the air flow facilities: 1, Wind Cave: Wind Cave is well join Fan for a section of wind tunnel equipment. Wind Cave multi-purpose concrete, masonry and other building materials to build into a round form of rectangular tunnel, which is determined by the characteristics of the duct. 2, wind bridge: the bridge is two shares of the wind to pay * the new plane, dirty air flow across the body _set_ up to pay * a new, polluted air of a separate ventilation. Structural characteristics of the bridge under different wind can be divided into three types: (1) Bypass-type air bridge. (2), concrete air bridge. (3), Tietong air bridge 3, the wind window (card) Windshield features in the tunnel in the wall or door, the door in the wall or window, leaving space for an adjustable, by adjusting the spatial window area so as to achieve the purpose of regulating air flow. 4, wind barrier: Use of wood in the roadway, Wei Xi, cloth fabric duct air flow barrier play a guiding role. This method is commonly used in treatment of high risk at the downhill angle, etc. gas accumulation. 5, Hair Dryers: In the tunnel ventilation using positive pressure or negative pressure through the pipe to force air flow to the destination specified, the pipe is called duct. B), cut off air flow facilities: 1, the blast doors (cap) Explosion-proof doors are installed in the fan cylinder, to prevent the occurrence of coal dust underground gas explosion destroyed a shock wave generated when the fan machine safety. Mine occurred when coal dust, gas explosion, the blast doors that can be red open air waves, the explosion wave directly into the atmosphere, thus helping protect the Fan for effect. 2, break wall Does not allow airflow in the passage of the Mine will not allow pedestrian traffic, such as mined areas, Old Lane, the fire area and into the air and return air contact between the roadway must be _set_ small eyes break wall will cut off air flow. To avoid leakage, short circuit of the ventilation system air flow to form a reasonable stability of the accident loss. Break wall is divided into: temporary break wall, permanent wind wall. 1) Temporary break wall: generally in the column on the nail board, Wong rubbed into the temporary wooden wall of wind. Terms of use: length of service is not long, the pressure surrounding rock is small, air leakage rate is not strictly required to use. 2) permanent break wall: the general use of stone material, brick earth, cement, concrete building. Terms of use: length of service length, surrounding rock pressure, air leakage rate of the use of strict requirements. 3, throttle: In does not allow airflow through, subject to pedestrian or vehicle in the roadway, you must _set_ the throttle. By the structure: ordinary throttle and throttle-and-carry. 4, the ventilation regulations: (1), ventilation system, adjustment of departments do to minimize the air card to the natural distribution of air flow based. (2), ventilation love to do: throttle non-car collision at the same time to open or throttle, throttle damage to the timely reporting of ventilation schedule, if the air volume of the system power outage affected areas, rehabilitation of people after the withdrawal of the production and safety monitoring, analysis and processing scheduling organization. (3), ventilation by the ventilation department management, other units of the right to move, remove and other powers, such as the need to remove, move in advance and the ventilation department. (4), is strictly prohibited into railings, removal of railings, closed walls, ventilation air cards. Fourth, the determination of air flow: Mine ventilation air flow is one of the main parameters, namely: unit time the volume of air through the roadway. A), wind station requirements: 1, must be located in the straight roadway. 2, wind owners of not less than 4m. 3, anemometers within 10m around the bend and no other obstacles. 4, anemometers should be linked to a record card, indicate the number, location, basal area, average wind speed, wind, wind date, wind measurement points. 5, anemometers should be located in the absence of air leakage, supports complete, little change in the roadway section. B), wind methods: Wind measurement using fixed-point method, nine law and line method, calculated the average wind speed. Wind in the same section of not less than three times the error of measurement should not exceed 5%, and then take three times the average. After the average wind speed measured by anemometers to calculate the basal area wind tunnel. "Coal Mine Safety Regulations" provides that at least every 10 days to conduct a comprehensive determination of air volume. 4, the ventilation regulations: (1), ventilation system, adjustment of departments do to minimize wind card for the main natural distribution of air flow. (2), ventilation love to do: throttle non-car collision at the same time to open or throttle, throttle damage to the timely reporting of ventilation schedule, if the air volume of the system power outage affected areas, rehabilitation of people after the withdrawal of the production and safety monitoring, analysis and processing scheduling organization. (3), ventilation by the ventilation department management, other units of the right to move, remove and other powers, such as the need to remove, move in advance and the ventilation department. (4), is strictly prohibited into railings, removal of railings, closed walls, ventilation air cards. Fourth, the determination of air flow: Mine ventilation air flow is one of the main parameters, namely: unit time the volume of air through the roadway. A), wind station requirements: 1, must be located in the straight roadway. 2, wind owners of not less than 4m. 3, anemometers within 10m around the bend and no other obstacles. 4, anemometers should be linked to a record card, indicate the number, location, basal area, average wind speed, wind, wind date, wind measurement points. 5, anemometers should be located in the absence of air leakage, supports complete, little change in the roadway section. B), wind methods: Wind measurement using fixed-point method, nine law and line method, calculated the average wind speed. Wind in the same section of not less than three times the error of measurement should not exceed 5%, and then take three times the average. After the average wind speed measured by anemometers to calculate the basal area wind tunnel. "Coal Mine Safety Regulations" provides that at least every 10 days to conduct a comprehensive determination of air volume. IV: Driving Ventilation In the roadway, in order to supply the breathing, eliminate or dilute the heading face after blasting gas harmful, harmful gases and mineral dust to the air. Roadway excavation of ventilation is called ventilation. All sub-heading ventilation negative pressure ventilation, air ejector and the local fan ventilation. The company is mainly because I use local fan ventilation, it is mainly about local fan ventilation. First, the local fan ventilation: Local fan ventilation is widely used in China coal mine ventilation of a tunneling method, which is the auxiliary fan and duct to fresh air flow into the excavation face. A), local fan ventilation: Pressed into; out type; hybrid 1, pressure-in: is the fan in the fresh air into the face by the duct pressure, while the pan-air discharged by the roadway. Bureau forced ventilation fan installed in the fresh air flow in the wind without a fan in Pan, which fan in the event of electrical discharge, are unlikely to cause gas and coal dust explosion, so security is good, can also be used rigid flexible duct air duct , strong adaptability. The downside is: the work of the wind along the single entry Mianfan back row the wind Lane, is not conducive to roadway workers breathe. Shooting from the roadway after the gun smoke emitted slow, long time, affect the driving speed. 2, exhaust ventilation: Exhaust ventilation and forced ventilation contrary, fresh air from the tunnel into the working face, the pan from the local fan air discharged by the duct. Exhaust ventilation duct after the discharge of polluted air, fresh air to keep it working gateway to better health conditions, need to smoke after shooting faster, helping improve the driving speed. However, due to the effective end of the suction duct relatively short, easy to collapse when the duct blasting, such as the absorption path length of the ventilation is not good, polluted air through the fan in poor security, exhaust ventilation must use rigid duct, poor adaptability. 3, mixed: Hybrid ventilation ventilation to both of the two mix. Although overcome some of these shortcomings, but because of equipment, large power consumption, management of complex, not widely used. Forced ventilation is good for safety, simple equipment and good adaptability, good results have been widely used. B), local ventilation management: 1, the local fan: 1), designate a person responsible for the management (listed management), not allowed to start any fan stop, keep running. 2), the Council must be installed on a dual-fan dual-fan power supply and the installation opening stop monitoring devices. 3), install the fan in the inlet roadway. Airflow from the back of not less than 10m, not allowed to place wind circulation. 4), local fan installation and electrical equipment must be driving face a delay of wind power locking device. 5), local fan outage for any reason, must withdraw and tacked fence, gas emissions in accordance with relevant regulations. 2, Hair Dryers: 1) promote the use of flame-retardant duct Φ700mm soft, the wind increased rate of local fan. 2) to improve the joint quality, reduce joint leakage, stick with a bilateral joint anti-edge style. 3), hair dryer to hang straight, taut suspension stability, every ring will be suspended and improve the local fan for air flow. 4) to strengthen the inspection and management, and timely repair. And put someone responsible. 5), regular and timely access duct to ensure duct is not exported to the head of coal at a distance. Chapter II Mine Safety Section I: coal mine gas The main component of coal gas is generally methane and other harmful gases, these gases are referred to as gas. Because the hazards of gas is mainly methane, so the narrow sense refers specifically to mine methane gas to run. First, mine gas generation: Second, the gas properties: Methane is colorless, tasteless, odorless gas can burn and explode, not for people to breathe, to causing suffocation, it is easy to spread, diffusion rate is 1.34 times that of air, gas permeability is 1.6 times the air, methane the proportion of air to 0.544, so easy to accumulate in the tunnel roof collapse of the roof space within the Cave. Chemical properties of the gas extremely lively, almost combined with other substances, insoluble in water. Amount of gas mixed with air has a burning explosive. This is the gas into the mine so the reason why the major disasters. Third, the gas explosion conditions: 1, the gas concentration: In the standard conditions of gas by volume concentration of 5-16%, the percentage of high temperatures encountered in fire occurs after the gas explosion. Exploded in the 9.1-9.5% concentration of the most powerful. Gas explosion limit is not fixed, it is affected by temperature, pressure and other combustible coal seam gas, inert gas mixed with other factors. 2, ignition temperature: gas ignition temperature is generally in the 650 ℃ -750 ℃, but it is by the gas density and the nature of fire 1), delayed detonation gas has practical significance of the blasting. The instant when the temperature of the blasting of explosives up to 2000 ℃, but the flame there for a short time, only thousandths of a second, it does not cause gas explosion. However, if the deterioration of explosives, charge stemming non-compliance, there is likely to lengthen the duration of the flame ignition kits even cause fire or explosion of gas, so great care should be underground blasting. The existence of high-temperature fire caused by gas explosions the necessary conditions. Electrical sparks, illegal shooting, spontaneous combustion, fire and so easy to cause the gas explosion. 3, sufficient oxygen content: Experiments show that reduce the concentration of oxygen in the air when the gas explosion limit reduced, when the oxygen concentration decreased to below 12%, the gas will not explode. Mine Safety Technology: 第一章概述 Mine ventilation is the basic guarantee of safety. Ventilation refers to the aid of mechanical or natural air pressure, wind point to the continuous use of underground transmission of the amount of fresh air, supply the breathing, dilution and discharge of harmful gases and dust, to reduce the ambient temperature, to create a good climate conditions and In the event of disaster relief when the person according to the needs of withdrawal and control of air flow regulation, flow path of the operation. 80 years since the 20th century, along with raising the level of coal mining mechanization, mining methods, roadway layout and supporting the reform, electronic and computer technology, China's coal mine ventilation technology has made great strides, increasing ventilation management standardization, serialization and institutionalized, ventilation equipment, new technology and new applications more and more people to vote. To low consumption, high efficiency, safety guidelines modified ventilation system to be implemented in a number of coal mines so that it can better serve the high-yield, efficient and safe intensive production to provide security. Section Optimization Reconstruction of ventilation system Mine ventilation system is to supply the fresh air with the wind point, the ventilation exhaust polluted air (into the back to the way air shaft arrangement of a central type, diagonal, mixed-type), ventilation (out type, pressure on people-style , hybrid pumping pressure), ventilation network (through the tunnel by the romantic and associated facilities form) and ventilation control facilities (ventilation structures) in general. First, the reform of ventilation Second, the main fan's economic performance capabilities To improve the capacity of the main fan running the economy, mainly in the following work. (1) to adapt to changes in the ventilation system requirements and production intensification, of the 20th century, 80 years, China has emerged 2K60 series and GAF series of axial fans, and G4-73 and K4-73 series centrifugal fan. 90 20th century, relying on the national "Eighth Five-Year" off the project, developed a rotating type FD fan. Fans of the series with low energy consumption, high efficiency, thus promoting the rapid coal mines in China. In the former Ministry of Coal, "Ninth Five-Year" research project, no hump the successful development of axial fans of the fan increases the stability of the work area. (2) development of renunciation and fan speed control devices such as thyristor speed, fluid coupling, and frequency control devices. (3) to strengthen the fan and its subsidiary device management and reduce the wind tunnel, fan, and the proliferation of towers resistance loss and leakage and improve the fan efficiency. The old mine in the production, transformation of the old machines running, the main features and identified the ventilation fan drag characteristics of the network matches the poor, mainly larger fan _select_ion, fan speed high, the motor capacity is too large, the fan a long period inefficient zone operation and other issues, a comprehensive _set_ of measures of economic operation fan of the old, old fan to the technological transformation of a variety of methods, such as to replace the movement, transformation of the impeller and the fan blades and other ways to improve operating efficiency. Third, the optimal layout mining ventilation system Optimization of mining area and the face of the ventilation arrangements, can improve the ventilation capacity and the effect of exhaust gas. With the intensification of production and development to deep mines, mining areas and coal mining face dramatic increase in the absolute volume of gas emission, requires mining area and the coal face of the ventilation capacity rapidly. Ventilation system in the mining area layout, the emergence of three mountain layout, mining district with an independent wind up the hill into the wind and return, which will help mining coal face and the heading face area of independent ventilation, improved mining district of the stability of ventilation capacity and airflow, but also to ensure that the local anti-mining area of the wind and the safety of workers provided favorable conditions for escape. Ventilation arrangements in the coal face, the U-ventilation in the conventional arrangement, based on the proposed U + L-type way (or End Lane layout), changed the flow of gob distribution, more effective in the prevention coal face corner gas accumulation, and promoted the gob gas emissions. Special gas emissions in order to prevent gas overrun Lane, and proposed and adopted the Y-type ventilation arrangement, a separate supply of fresh air flow diluted gob gas emission. In addition, using the W-and Z-other arrangement, under suitable conditions have achieved an ideal ventilation, greatly improved the coal face ventilation, to ensure the safety of mining. Fourth, the use of new ventilation Mine disaster period to meet the needs of air flow control, developed the use of mines in the ground environment monitoring system or remote control system of automatic throttle control system of underground main to solve the disaster period, when the miners and rescue personnel is difficult to reach the affected area and smoke invaded region while the relief requested must be turned on or off throttle problems.
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kuangjing tongfeng Mine ventilation mine ventilation Continuous delivery of fresh air to the underground, dilution and discharge of toxic and harmful gases and dust, the mine microclimate regulation, to create a good working environment, ensuring safety and health of miners and improve labor productivity. China's mine safety regulations and safety rules of order: the underground supply of fresh air volume of not less than the general person 4m □ / min, inlet air flow in the mining face, press the volume calculations, O □ no less than 20%, CO □ shall not exceed 0.5%; In addition to the underground parts of the air composition, wind speed and temperature, also have the corresponding provisions (see mine heat injury, the mine air, mineral dust, gas). Mine Ventilator by the scope of work in three: one for the whole mine or mine-wing (region), called the main fan unit, referred to as the main fan; to mine some of the branches in the conditioning air duct air volume, to help the main fan to work, called the auxiliary fan machine, referred to as the auxiliary fans; for mine in some areas (mainly on heading Mine) ventilation, and called the local fan machine, referred to as the local fan. Main fan and axial separation of two types of mind: ① centrifugal fan machine, the drive wheels, spiral shell, suction tube and diffuser etc., fixed to the driving wheel and the axle of the wheel hub and the blades on the composition of its (Figure 1, centrifugal fan drives). Leaves sub-forward type, radial-and three post-tilting, mining multi-purpose centrifugal fans, after the main tilting. When the driving wheel rotates, the air from the suction pipe into the central part of the driving wheel, turn off after 90 □, thrown into the road along the leaf spiral casing, and then the diffuser outflow. ② axial fan machine, equipped with a blade from the drive wheels, cylindrical shell, _set_ the wind, rectifiers, streamlined body and diffuser and so on. To improve air pressure, and some can be placed two drive wheels. When the driving wheel rotates, the wing blade along the axial flow of air driven by the exhaust diffuser. Axial flow fan blades, in order to install certain that the mounting angle on the drive wheels, adjust the installation angle can change the fan performance. Centrifugal Fan for simple structure, low noise, stable operation range, but the air volume control inconvenience, must be anti-air anti-air channel. Axial-flow fan unit structure is more compact, easy adjustment, a larger adjustment range, can reverse the anti-wind; but the noise, the small range of stability. Council also has axial fan and centrifugal types. The former small size, use the easy installation, easy series, widely used, but noisy. Rotating axial flow fan in the opposite direction by the blade twisted form of the two drive wheels, respectively, driven by two electric motors, rotating in the opposite direction, no rectification leaves. The fan in high efficiency, low noise. Long Lane and the big dig dug shaft section, the commonly used centrifugal fan in ventilation. Axial fan blower By local ventilation
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