Mine ventilation

In the underground, due to mining operations and mineral oxidation and other reasons, the air composition will change, mainly manifested as oxygen reduction, toxic and harmful gases increase, mining dust mixed, temperature, humidity, pressure changes. These changes have caused harm and impact on the health and safety of workers. In order to ensure the health of workers and suitable working conditions, to ensure safe and sustainable production, it is necessary to send the fresh air on the ground to the mine, and discharge the dirty air from the mine to the ground, which is the purpose of mine ventilation.

(1) Mine ventilation system

In order to send enough fresh air to the underground mining face in a certain direction and route, and at the same time to discharge the dirty air from the mining face in a certain direction and route, it is necessary to require a reasonable ventilation system in the mine.

1. Unified or zoned classification according to the whole mine

A mine forming a whole ventilation system is called unified ventilation. A mine is divided into a number of relatively independent ventilation systems, each system has its own air intake, exhaust shaft and ventilation power, although there is a connection between the shaft and the alley, but the wind does not interfere with each other, independent of each other, called zoning ventilation.

Unified ventilation has the advantages of more concentrated exhaust air, less ventilation equipment and easy centralized management. For mines with small mining scope and few surface exits, especially deep mines, it is reasonable to adopt unified ventilation of the whole mine.

Zone ventilation has the advantages of short wind path, small negative force, less air leakage, low energy consumption, simple network, easy control of air flow, and beneficial to reduce the series of dirty air and air volume distribution on demand, and can receive better ventilation effect. Therefore, zonal ventilation is widely used in some mines with shallow and scattered ore bodies or mines with more shallow ore bodies and shafts through the ground.

Zoning ventilation can be divided according to orebody zoning, mining area zoning and stage level zoning.

2. Classification according to the layout of air inlet and exhaust shafts

Every ventilation system must have at least one reliable intake shaft and one reliable exhaust shaft. The cage lift shaft is usually used as an air intake shaft, and some mines also use a special air intake shaft. Because the exhaust air flow contains a lot of toxic gases and dust, the exhaust shaft is generally dedicated.

According to the relative position of air inlet shaft and exhaust shaft, it can be divided into central type, diagonal type and central diagonal mixed type.

1) Central type

The air inlet shaft and exhaust shaft are located in the center of the ore body, and the flow route of air flow in the mine is returnable

The central layout has the advantages of less capital construction cost, fast production, centralized ground construction, easy management, convenient shaft deepening work, easy to realize wind reversal and so on. The central arrangement is mostly used for mining layered ore bodies.

2) Diagonal

As shown in Figure 3-8, the intake shaft is in the center of the orebody, and the return shaft is in the two wings, which is called the two-wing diagonal type. As shown in Figure 3-9, when the orebody has a long strike, the intake shaft and exhaust shaft are arranged at intervals along the strike or the orebody is thick, the intake shaft and exhaust shaft are arranged at intervals around the orebody, which is called the spaced diagonal type. In diagonal ventilation, the flow path of air flow in the mine is straight.

Diagonal layout has the advantages of short air flow circuit, small wind pressure loss, less air leakage, stable wind pressure during mine production, more uniform air distribution, and far away from the industrial site. Diagonal layout is generally adopted in metal mines.

3) Center diagonal hybrid type

When the ore body is long and the mining range is wide, the central development is adopted, and the air inlet shaft and exhaust shaft can be arranged in the middle of the ore body to solve the ventilation during the mining of the central ore body. The exhaust shaft can be dug in the two wings of the mine to solve the ventilation during the mining of the remote ore body. The whole ore body has both a central and diagonal type, forming a central diagonal mixed type.

Although the layout forms of air inlet and exhaust shafts can be summarized into the above several kinds, due to the complex occurrence conditions of ore bodies, different development and mining methods, in the mine design and production practice, it is necessary to arrange according to the specific conditions of each mine, and not subject to the limitations of the above several kinds.

3. Classified by fan working mode

The working mode of the fan has three kinds: pressure type, extraction type and pressure pumping mixed type.

1) Press the person

Pressurized ventilation is to make the whole ventilation system under the action of the main man-pressured fan, forming a positive pressure state higher than the local atmospheric pressure. Because the air flow is concentrated and the air volume is large, the pressure gradient in the air intake section is high, and the fresh air flow can be quickly sent into the well along the specified ventilation route, avoiding pollution from other operations and having good wind quality.

The disadvantage of pressurized ventilation is that air flow control facilities such as air doors need to be located in the air intake section. Due to frequent transportation and pedestrians, it is not easy to manage and control, and the wind leakage at the bottom of the well is large. In the exhaust section, the main fan forms a low pressure gradient, which can not quickly discharge the dirty air from the air shaft according to the specified route, so that the underground air flow is disordered. Coupled with the interference of natural air flow, the phenomenon of air flow reversal and pollution of fresh wind will even occur.

2) Withdrawable type

Extraction ventilation is to make the whole ventilation system under the action of the main extraction fan, forming a negative pressure state below the local atmospheric pressure. Because the exhaust air is concentrated and the exhaust air volume is large, the extraction ventilation causes a high pressure gradient on the exhaust air side, so that the dirty air of each operation surface is rapidly concentrated in the exhaust air duct, and the smoke of the exhaust system is not easy to spread to other roadways, and the smoke exhaust speed is fast. This is a major advantage of extraction ventilation. In addition, the adjustment and control facilities of air flow are installed in the exhaust duct, which does not hinder pedestrian transportation, convenient management and reliable control.

The disadvantage of extraction ventilation is that when the exhaust system is not tight, it is easy to cause short circuit suction phenomenon. This phenomenon is more serious when the caving method is used and the surface subsidence area is connected with the goaf. In addition, the operating surface and the whole air inlet system have low wind pressure, and the air inlet path is affected by natural wind pressure, which is easy to reverse air flow, resulting in the disturbance of underground air flow. The extraction ventilation system makes the main lifting shaft in the position of air intake, and the northern mines should consider the anti-freezing of the lifting shaft in winter.

Most metal and other non-coal mines in our country use extraction ventilation. 3) Pressure pumping mixed type

Pressure pumping mixed ventilation is controlled by the main fan on both the intake side and exhaust side, so that the air flow in the intake section and exhaust section can flow according to the specified route under the action of higher wind pressure and pressure gradient, smoke exhaust is fast, air leakage is reduced, and it is not easy to be disturbed by natural air flow and wind flow reverse. This kind of ventilation is an important way to improve the effect of mine ventilation because of the advantages of both manual ventilation and extraction ventilation.

The disadvantage of pressure pumping mixed ventilation is that more ventilation equipment is required, and the air flow in the required air section cannot be controlled. The air leakage in the shaft bottom yard on the inlet side and the subsidence area on the exhaust side still exist, but to a much smaller extent.

When choosing a ventilation method, the presence of subsidence areas or other difficult to isolate passages on the surface is a very important factor. For mining mines containing radioactive elements or where there is a risk of spontaneous combustion of ore and rock, the press-in type or press-in type based pressure pumping mixed type should be used, and the multi-stage machine station controllable type should also be used. For the mine without surface subsidence area or the mine with subsidence area but can keep the exhaust duct with good tightness through filling and sealing, the extraction type or the pressure pumping mixed type based on extraction type should be used. For mines that have a large number of surface subsidence areas and are not easily isolated between the exhaust duct and the goaf, or the mines that are transferred from the open pit to underground mining, the pressure pumping mixed type or the multi-stage machine station controllable type should be used.

The installation site of the main fan is generally on the ground, but also can be installed in the underground. The advantage of installation on the ground is that installation, overhaul, maintenance and management are more convenient and not easily damaged by underground disasters. The disadvantages are the sealing of the wellhead, the high capital construction cost of the anti-wind device and the wind tunnel, and the short circuit leakage; When the mine is deep and the working face is far away from the main fan, the air leakage along the way is large. In the case of complex terrain conditions, the installation and construction costs are high. The main ventilator installed in the underground has the advantage of less air leakage from the main ventilator device. The fan is closer to the required air section, and less air leakage along the way can simultaneously utilize more inlet air or exhaust air from the shaft and lane, which can reduce the ventilation resistance. Its disadvantages are inconvenient installation, inspection and management, and easy to be damaged by underground disasters.

(2) Mine ventilation equipment

1. Fan classification

At present, there are two kinds of fans used in mine, one is axial fan and the other is centrifugal fan. The axial flow fan is characterized by a straight line between the air inlet direction and the air outlet direction, and is parallel to the axis. When the working wheel keeps rotating, because the blade is an airfoil shape and has a certain Angle with the rotating surface, a low pressure area is generated behind the advancing blade to inhale air, and a high pressure area is generated in front of the advancing blade to press out air. The centrifugal fan is characterized by the air inlet direction and the air outlet direction are perpendicular to each other. When the working wheel rotates in the spiral housing, due to the centrifugal force generated by the blade, the air flows in the housing along the path of the blade movement from the tangential direction of the working wheel. In this way, a low pressure area is generated in the central part of the working wheel to inhale air; The rim creates a high pressure that pushes air out of the diffuser.

Compared with the centrifugal fan, the axial fan has high efficiency and light weight, and the Angle of the driving wheel blade can be adjusted. At present, the metal mine is widely used, but its noise is large and its maintenance is complicated.

The fans used in the mine are divided into the following types according to their uses: the fans used for the ventilation of the whole mine, that is, the main fans; A fan used to enhance the ventilation of a certain section, that is, an auxiliary fan, that is, a fan used for ventilation of a single-head working face, that is, a local fan.

2. Working mode of the fan

The working mode of the fan can be divided into three kinds: pressing type, pulling type, pressing and pulling combined type.

3. Anti-wind device

The main ventilator must have a reverse air device. When the mine fire and mine dust explosion occur, in order to prevent the expansion of disaster and adapt to the requirements of rescue work, sometimes it is necessary to change the direction of mine air flow. The air reflux device is related to the fan type. Figure 3-10 shows the common air reflux device of the axial fan. Lift gate 1 and lower gate 2 on reverse wind.

(3) Mine ventilation structures

Devices used to guide, interrupt and regulate air flow are collectively referred to as ventilation structures.

Ventilation structures can be divided into two categories, one is the structure that passes through the air flow, including wind bridge, wind deflector, wind barrier and regulating wind window; the other is the ventilation structure that interrupts the air flow, including sealing walls and air doors.

1. Wind Bridge

When the inlet air duct and exhaust air duct cross in the ventilation system, in order to separate the fresh air and the dirty air, it is necessary to build a wind bridge. The requirements for the wind bridge are strong, tight, less air leakage, small wind resistance, and the wind speed through the wind bridge should be less than 10m/s.

The wind bridge cut in the upper mine rock at the intersection of the roadway is called the bypass type wind bridge, which has the least air leakage and can pass through a large air volume, and is suitable for the main wind road.

At the intersection of the roadway, concrete wind bridge can be built, it is relatively strong, can be used for the air volume of not more than 20m³/s roadway can also set up simple iron drum wind bridge, iron drum can be made of round or torch shape, iron plate thickness is not less than 5mm, suitable for the air volume of less than 10m³/s in the secondary wind path.

2. Air deflector

The following types of air deflectors are used in mine ventilation.

(1) Air guide plate. In order to prevent air leakage at the bottom of the mine, the air guide plate is installed at the intersection of the air inlet stone door and the stage transportation roadway, and the direction of the wind flow pressure is used to reduce short circuit air leakage. The wind deflector can be made of wood, iron or concrete. The intersection Angle between the air inlet roadway and the transport roadway should be 45°, the roadway Angle and the air deflector should be rounded, and the length of the air deflector should exceed a certain distance (0.5~1m) from the roadway intersection.

(2) reduced resistance wind deflector. In order to reduce the ventilation resistance at the right-angle transition of the roadway with large airflow volume, the airfoil or ordinary curved wind deflector can be made of iron plate to reduce the energy loss of airflow impact. The open Angle of the air deflector at the right corner can be 100°, and the installation Angle can be 45° to 50°. After the installation of the air guide plate, the local resistance coefficient of the right Angle turn can be reduced to 1/4 to 1/3 of the original.

(3) Bus deflector plate. At the fork of the shaft and lane, when the two air currents meet and converge together, a herring-shaped wind deflector can be installed to reduce the impact energy loss when the air currents collide.

3. Longitudinal wind barrier

The longitudinal wind barrier is a wind wall laid along the length of the roadway. It divides the roadway into two compartments, one for air intake and the other for air exhaust. The longitudinal wind barrier can be used in the ventilation of long single-head roadway. The longitudinal wind barrier is used to form a comb ventilation network in Pangushan tungsten mine to eliminate the series of polluted air. Longitudinal wind barriers can be constructed with wood, masonry or concrete.

4. Airtight walls

Closed walls, also known as wind walls, are structures that block air flow, usually laid in non-production laneway, which can be masonry or concrete. Temporary airtight can be nailed by wooden posts, boards and waste duct cloth.

The sealing of the patio can be made of wood, steel or cement board at the upper entrance of the patio. In the place affected by blasting shock wave, suspension sealing can be used. Place two steel beams horizontally at the mouth of the patio, suspend the lifting plate with steel rope, go 1~1.5m below the wellhead, pile several layers of broken bags on the lifting plate, and then fill the gaps with soil and gravel. This kind of suspension sealing has certain seismic ability.

5. Damper

In the ventilation system, it is necessary to cut off the air flow, and it is necessary to establish the air gate for pedestrians or traffic. In the process of exhaust air, only pedestrians do not traffic or traffic is not much, can build a common damper. Automatic air damper should be constructed in the main transportation lanes with frequent traffic and pedestrians.

Ordinary damper can be made of wood or iron plate. The slanted contact between the door and the door frame of the wooden damper is relatively tight and the structure is solid. The opening direction of the damper should face the wind flow, so that after the damper is closed, it is kept tight by the wind pressure. The door frame and door shaft should be tilted 80°~85°, so that the damper can be closed by its own weight. In order to prevent air leakage and maintain a stable air flow, two or more air doors should be set up at the same time.

6. Wind measuring station

In order to measure the air volume accurately, wind measuring stations should be set up in each main inlet and exhaust roadway of mine. There are the following requirements for establishing an anemometer station.

(1) The anemometer station shall be located in the straight roadway, there shall be no obstacles in the station, and the surrounding wall of the roadway shall be smooth and smooth.

(2) The length of the anemometer station should be greater than 4m, and the section should be greater than 4m².

(3) The length of the roadway in the straight section before and after the station should be greater than 10m.