Problems and Improvement Measures of Coal Mine Ventilation System in China

The main task of the mine ventilation system in the coal mine is to deliver a proper amount of fresh air to the windy location for the personnel to breathe, dilute and discharge various toxic and harmful gases and floating dust, reduce the ambient temperature at the working place, and create good climatic conditions, especially In the event of a disaster, wind flow can be controlled and scheduled according to the needs of disaster relief. In order to achieve the above tasks, each mine, mining area and coal mining face must have a complete ventilation system. Reasonable ventilation, reliable wind control, efficient local ventilation and corresponding ventilation are the basis for safe production in coal mines.

1. Ventilation status of coal mines in China

At present, although China's mine ventilation technology has achieved remarkable results, there is still a big gap compared with developed countries. Overall, the technical level of mine ventilation in China is still relatively backward, and the reliability of the ventilation system needs to be improved. In particular, in recent years, the fully mechanized caving coal mining method adopted in coal mine production has the advantages of large mining intensity, good economic benefit, and high degree of mechanization, but it also leads to a large amount of gas emission and a large amount of wind required for the working face. At present, traditional ventilation technology and ventilation equipment cannot adapt to this production mode.

2. Problems in the ventilation system

2.1 The ventilation system is unreasonable.

Whether the mine ventilation system is reasonable or not will have a long-term impact on mine safety production. Unreasonable mine ventilation methods can not effectively supply wind to avoid disasters, and can not effectively control and mitigate disaster losses in the event of disasters. Threatening the safety of the workers in the underground.

2.2 The ventilation facilities are unreasonably set and of poor quality.

At present, some coal mines should be constructed without sealing and replaced by dampers, which makes the number of downhole dampers increase. Some dampers are located between the main inlet and return air passages, and the pressure difference between the two sides is large, resulting in serious air leakage, thus causing a The hazards of the series.

2.3 Ventilation resistance is large and the resistance distribution is unreasonable.

According to statistics, the maximum ventilation resistance of China's low gas mines is 1962Pa, the medium mine is 1177.2Pa, and the small mine is 735.75Pa. The maximum resistance of large mines in high gas mines is 2452.5Pa, and the maximum size of medium mines is 1962Pa. The maximum size of small mines is 1569.6 Pa. According to statistics in 1982, 40% of the national key coal mines have ventilation resistance of medium and high resistance mines, and the main ventilators of the high-resistance mines (93 pairs), which account for 14.9% of the total number of mines, account for national key national power. Half of the total electricity consumption of coal mines, the ventilation power consumption of a few mines accounts for more than half of the electricity consumption of raw coal. In the case that the total wind volume of the state-owned key coal mines is 52,300 m3/s, the mine ventilation resistance can be reduced by 9.8 Pa per year, and the annual electricity saving can be 9 million kW·h, saving electricity costs of more than 720,000 yuan. The statistical analysis of the newly built mine designed by the design institute shows that in the ventilation system, the resistance of the inlet section accounts for 25% of the total resistance, the resistance of the wind section accounts for 45% of the total resistance, and the resistance of the return section is 30% of the total resistance. The measured results show that the ventilation resistance of most mine return air sections accounts for 60%~85% of the total resistance, and only a few mines have a ventilation resistance of 40%~50% of the total resistance. The reasons for the excessive ventilation resistance of the return airway in the mine are the sudden expansion or contraction of the section, the turning of the roadway, the splitting, the meeting, the roofing, the gang, the incomplete removal of the ventilation facilities and the blockage of the slime.

2.4 The main ventilator operates at low efficiency.

Due to the inefficient efficiency of the selected equipment, or the poor matching of the performance of the fan with the resistance of the mine ventilation, the working efficiency of the fan is generally low, and at the same time, the unnecessary consumption of electric energy is caused.

2.5 Drive fan motor rated power is too large, motor efficiency is low

The efficiency η and the power factor cosφ of the motor vary with the change in the load factor (the ratio of the actual output power to the rated power). When the load factor is around 1.0, η and cosφ are the largest; when the load rate is below 0.5, η and cosφ are rapidly decreased. At present, the mine motor capacity is too large, forming a phenomenon of “large horse-drawn car”, and the motor load rate is lower than 50%, resulting in low power of the motor.

2.6 Insufficient ventilation.

In some mines, due to insufficient air supply in the whole mine or mining face, or too many times the air volume is used in series, the gas accumulation in some places and the concentration of dust in the mines often exceed the standard, directly supporting the safety production. The survey conducted by the former Ministry of Coal Industry at the end of 1996 showed that there are still 48 mines with insufficient air volume in the state-owned key coal mines. As for local coal mines and township coal mines, mines with insufficient air volume or excessive number of series are more common.

2.7 Mines have more air leakage.

Sending sufficient air volume that meets the quality requirements to the wind location, with less air leakage and high effective air volume rate, is one of the effectiveness of the ventilation system and the main measure to ensure the safe production of the mine. However, some mines have large air leakage or internal air leakage, resulting in low effective air volume rate. Some mines account for more than 25% of the total airflow of the ventilator, accounting for about 35% of the total return air volume of the entire system.

2.8 Mine air volume adjustment method is inadequate

In the early stage of production, some mines used the method of lowering the gate to reduce the air intake of the mine due to the overcapacity of the main ventilator. This method of adjusting the wind is simple and easy, and it can save a part of the electric energy to the centrifugal fan, but it consumes a lot of electric energy and reduces the ventilation than the method of adjusting the fan capacity (such as reducing the fan speed or using a small capacity motor). The economic benefits of the system. For example, if a fan installed in a mine shaft is equipped with a motor with a power of 1250 kW, the initial air volume of the mine is 6700 m3/min, which is only half of that at the time of production. The method of lowering the gate is used to adjust the wind, so that the ventilation resistance of the mine is increased from 1000 Pa to 4600 Pa. The measured power consumption per hour is 760kW·h; after that, a motor with a low speed of 550 kW is installed, and the gates are all lifted up to keep the air volume at 6700m3/min. The measured hourly power consumption is 160kW·h, and the annual energy saving is 525.6. 10,000 kW·h. The main ventilator gate resistance of a mine in our city is 4535Pa, and the total resistance is 6672.7Pa, resulting in the efficiency of the main ventilator unit being only 19.9%~21.3%. The high negative pressure not only increases the difficulty of ventilation management, but also increases the amount of air leakage on the ground and reduces the effectiveness and economy of the ventilation system.

2.9 Some mines perform malignant adjustment during actual operation.

Some mine ventilation systems use the method of increasing resistance, which is easy to reduce the total air volume of the mine. The air volume in the mining area that needs to increase the air volume is insufficient. For this reason, the area of ​​the adjustment windshield is arbitrarily reduced, and even the roadway is blocked, causing malignancy. adjust.

2.10 Mine lacks management and normal maintenance.

According to the design of our institute, the mines of some mines are in an unmanned or nominal management state. Some wind turbines are in the “disease work” or unreasonable operation state for a long time. Corrosion or deformation, which not only greatly reduces the performance of the fan, but also has serious safety hazards.

3, the solution of the ventilation system

3.1 Reasonable selection of the main fan model.

In order to ensure the normal operation of the main fan and reduce the economic cost, the first choice of fan model must be scientific and reasonable. In recent years, whether it is mine expansion or design and construction of new coal mines, many coal mining companies have focused on selecting some more efficient ventilators to ensure that the newly-introduced ventilation instruments are energy-efficient and efficient.

3.2 Replace the motor.

In the design of the mine, most of the motor equipment and the main fan are selected according to the maximum demand and negative pressure of the air supply during the two periods of easy and difficult periods. At the initial stage of production, the production scale is small and the output is low. Some coal mines are affected by geographical conditions. The design production volume is quite different from the actual production volume. Therefore, enterprises can replace the low-power and low-speed motors according to actual production requirements. Improve the motor operating load rate to achieve economic operation.

3.3 Adjust and modify the mine ventilation system.

The use of a reasonable and scientific ventilation system in the mine is a key condition for ensuring the normal economic operation of the main ventilator. In order to reduce the ventilation resistance, the entire mine ventilation system should be comprehensively surveyed and tested for resistance, and relevant measures should be taken to reduce the resistance. The main methods are as follows: (1) expand the ventilation passageway section; 2 reduce the local ventilation resistance of the roadway; 3 develop new wells and shorten ventilation Distance; 4 increase parallel air duct; 5 change mining layout to achieve reasonable and stable production.

3.4 Establish a reasonable ventilation network structure.

The reasonable ventilation network structure can achieve the best matching effect between the main fan and the mine wind network, so that the mine ventilation system is stable and reliable, and can achieve the purpose of energy saving and consumption reduction. The optimization of the mine wind network structure specifically includes the following aspects: 1 Determine the optimal position of each adjustment facility of the mine, so that the total ventilation power of the mine is minimum; 2 Optimize the cross section of the air duct; 3 Use parallel ventilation as much as possible to reduce the angle connection and shorten the ventilation process.

3.5 Correctly adjust the mine air volume.

Mine air volume adjustment is an important part of mine ventilation technology management, and the effect of air volume adjustment depends on the location of air volume adjustment facilities, the size of adjustment parameters and the rationality of the number of adjustment facilities. By controlling the amount of return air in the mining area and the air volume of each mining face, the air volume distribution is reasonable, thus ensuring the air volume of each wind location, especially the newly-produced mining face. The main methods for adjusting the air volume of the mine include local supercharging, decompression and leakage reduction, and changing the ventilation mode.

3.6 Use a reasonable method to evaluate the safety performance of the mine ventilation system.

At present, the proportion of disasters such as poisoning and suffocation of toxic and harmful gases such as coal spontaneous combustion and gas in underground coal mines is still high and the damage is high. The main reason is that the mine ventilation system is imperfect. Therefore, we should use the verified safety performance rating and other methods to evaluate the safety performance of the mine in an all-round way, and then strive to improve the safety of the mine ventilation system and enhance the mine's ability to prevent and resist accidents. At present, in the safety evaluation of mine ventilation system at home and abroad, fuzzy comprehensive evaluation method, grey system evaluation method and neural network based method are often used. We can use these methods to evaluate the function value and various indicators to improve the ventilation condition of the mine. Good protection of the safe production of mines.

3.7 Renovation of the main fan attachment

The main ventilator attachments are a key component of the main ventilator installation, including diffusers, pneumatic picks and anti-wind installations. Whether the auxiliary equipment and equipment mechanism is scientific and reasonable and the quality of construction is directly related to the operation efficiency and energy saving efficiency of the ventilation system.

3.7.1 Reconstruction of the diffuser

Currently, centrifugal fan diffuser vertical some small power machine using plate iron welding material is formed, using some of the mine in the open angle of the diffuser 15 ~ 30 °, in order to reduce the height of the diffuser, but it resulted in a wide range of reflux Suction wind zone to reduce the efficiency of the diffuser. If the internal expansion angle of the diffuser is adjusted to 4 to 6°, the external expansion angle becomes 8 to 10°, which prevents the reverse reflow at the outlet of the diffuser device, thereby improving the working efficiency of the diffuser. For some large-scale centrifugal fans and large and medium-sized axial flow fans, they are generally horizontal external diffusers, with internal angles of 70-80° and external rotation angles of 60°. According to the long-term investigation, the diffuser has a reverse suction zone and a vortex zone on the side of the fan. The presence of these zones reduces the exhaust area of ​​the diffuser and increases the resistance of the exhaust side of the fan. The efficiency of the ventilator. A mine in our city has modified the diffuser of its main fan, reducing the outer corner of the diffuser from 56° to 45°, and the inner corner from 70° to 50°. Other dimensions have also been changed accordingly. To achieve the obvious effect, the power consumption of the fan is reduced by 60.2 kW, and the annual energy saving is 520,000 kW·h, which effectively reduces the production cost of the mine.

3.7.2 Wind reform

The wind and hurricane resistance in China's mine ventilation system is generally large, accounting for 15% to 20% of the total wind pressure loss of the entire mine ventilation system, and even the resistance loss of individual winds is more than 29%, far exceeding the normal design of the mine. The assumed 200Pa wind pressure loss. Therefore, when digging a new mine or adjusting the wind of an unreasonable old mine, the following points should be noted: 1 The section of the wind should be ensured, and the wind speed of the wind is maintained within 15 m/s. The shape of the section is recommended to be semicircular. Or round, the surface of the wind is recommended to use cement mortar to wipe the surface to ensure the smoothness of the surface to reduce the friction coefficient of friction. 2 The form of the wind raft should adopt the unified oblique type to connect it with the hoistway, and minimize the number of turns to make the local resistance smaller. 3 The obstacles stored in the wind should be removed in time to keep the ventilation tunnel smooth and reduce the wind resistance, so that the total resistance is less than 200Pa and less than 9% of the resistance of the entire shaft ventilation system.

3.7.3 Reconstruction of anti-wind facilities and explosion-proof cover

Some of the gates of the anti-wind system are not tight and not in place, the wind wells or explosion-proof covers are not tight, and due to surface cracks, the main ventilator devices leak outside the wind all year round, resulting in unnecessary power consumption. According to the actual investigation, the total air leakage of a mine shaft in the city accounts for 20% of the total exhaust volume of the whole mine. After the replacement of the door panel to prevent leakage, the air leakage is reduced by 15m3/s, the total air intake of the mine is increased by 9.95m3/s, and the total negative pressure is increased by 137Pa, thereby improving the efficiency of the main fan. Therefore, in order to save the energy consumption of the main fan in actual operation, the wind leakage of the anti-wind facility and the explosion-proof cover should be minimized as much as possible, and the length of the wire rope of the gate should be reasonably adjusted so that the gate can be in place.

3.8 The mine must have a complete and independent ventilation system, and the ventilation method and ventilation network should be used reasonably. At the same time, the ventilation system of the mining area must also have the following basic requirements.

3.8.1 Partition ventilation must be implemented in the mining area.

1 Preparation of the mining area must be constructed in the mining area to dig the other lanes.

2 The coal mining face must be harvested after the mining area forms a complete ventilation system.

3 A high-gas mine, a mining area with coal (rock) and gas (carbon dioxide) outburst danger, and a mining area that is easy to self-ignite coal, must have a dedicated return air duct.

4 In the low-gas mine mining coal seam group and layered mining, a dedicated return air lane must be set up in the joint mining area.

The entry and return wind lanes of the 5 mining area must run through the entire mining area. It is strictly forbidden to enter the wind tunnel and a section as the return air lane.

3.8.2 The mining face should be independently ventilated.

3.8.3 In the ventilation system of the mining area, to ensure the stability of the flow of the wind, the mining face should be avoided in the corner wind path.

3.8.4 In the ventilation system of the mining area, the ventilation system should be simple to control the airflow and evacuate personnel in the event of an accident.

3.8.5 For ventilation facilities (dampers, wind bridges, etc.) and ventilation equipment (local ventilation machines, etc.) that must be set up, it is necessary to select the proper position, strictly control the quality specifications, and strictly abide by the quality system to ensure the safe operation of the ventilation equipment. The main damper switch state, local ventilator start-stop state and airflow change parameters are incorporated into the mine safety monitoring system for timely detection and processing.

3.8.6 In the ventilation system of the mining area, it is necessary to ensure that the ventilation resistance is small, the ventilation capacity is large, the wind flow is smooth, and the air volume is distributed as needed.

3.8.7 In the ventilation system of the mining area, minimize the air leakage in the mining area.

3.8.8 Set up fire sprinkler pipes, evacuation diverticulum and facilities to control wind flow during fires, and clarify the route and safety signs. If necessary, establish a gas drainage system and a fire-fighting grouting system.

3.9 Improve mine technical documents and technical data management.

The mine must have a complete ventilation system diagram, ventilation network diagram and dustproof pipeline layout. For mines with safety inspection systems, coal mine fire grouting and gas drainage systems, safety monitoring and control system diagrams, fire grouting and gas drainage are also required. The piping system diagram, etc., should collect and store the performance curve of the main ventilator, the model of the local ventilator and its performance parameters. The wind report of the mine should be complete, reliable and timely. In addition, the mine should have complete construction safety technical measures, each work type has a post responsibility system and technical operation procedures, and establish and improve various technical files.