Nearly 90% of coal in China is produced by underground mining. A series of wells and lanes must be dug from the ground to the underground (Figure 1-2). The production process is underground and the natural conditions are complicated. The main feature of mining is the need for mine ventilation, and there are five major disasters: gas, coal dust, roof, fire and water.
Figure 1-2 Underground Coal Mining
(1) Mine ventilation. Because the underground production of coal mine is underground operation, the surface air will be mixed with harmful gases and mine dust in the process of entering underground and flowing through various workplaces, and its composition will gradually change. At the same time, due to geothermal effect, artificial and mechanical heat dissipation, water evaporation and so on. The temperature and humidity of underground air will increase significantly, resulting in unfavorable climatic conditions. Therefore, the mine must be ventilated.
(2) Gas and mine dust disasters. In the process of coal mining, gas and mine dust will be produced. Gas and mine dust will explode under certain conditions, causing casualties and property losses; Mine dust will also make miners suffer from coal silicosis, which will bring pain to miners.
(3) Roof disaster. In the process of underground mining, the roof will collapse due to the action of mine pressure. If there are loopholes in roof management, roof accidents will occur.
(4) Mine fire. Mine fire is also one of the main disasters in coal mine production. Once a mine fire happens, it will not only cause the loss of coal resources and disrupt the layout of all work, but also often cause gas and coal dust explosions, expanding the degree and scope of disasters.
(5) Mine flood. In the process of mine construction and production, surface water and groundwater will flood into the mine through various channels. In order to ensure the normal construction and production of the mine, various measures must be taken to prevent water from entering the mine or to discharge the water entering the mine to the ground. However, when the mine water gushes out beyond the normal drainage capacity, or when underground water bodies such as old pond water or karst water are dug through in the excavation work, it will cause water disasters.
1.2.2.2 Main operation contents of underground mining
(1) underground mining method and technology
The continuous improvement of coal mining methods and technology is the theme of mining development, and the development of coal mining technology has led to changes in all aspects of coal mining. Because longwall mining is one of the most economical underground mining methods, at present, wall mining method is widely used in underground mining all over the world, occupying a core position.
In longwall mining technology, aiming at gently inclined and inclined coal seams, the coal mining methods and technologies currently adopted include single longwall fully mechanized mining in gently inclined thin and medium thick coal seams, inclined layered longwall fully mechanized mining in gently inclined thick coal seams, fully mechanized mining in gently inclined thick coal seams at one time, fully mechanized mining in gently inclined thick coal seams and fully mechanized caving longwall fully mechanized mining in gently inclined thick coal seams.
At present, longwall work is developing in a centralized and efficient direction, and the length of working face is increasing. On 20 10 and 12, Shangwan Coal Mine built the second fully mechanized mining face with a mining height of 7m in the world. The heavy fully mechanized mining face with a mining height of 7m is 3 19m long, which is 18m longer than the first mining face in Bulianta Coal Mine of Shenhua Shendong Coal Group Company, and the strike length is 4231m.. It is the longest mining height working face in the world at present. Under normal circumstances, each shearer can cut 2700t of coal, which is 300t more than that of fully mechanized mining face with 6.3m mining height, and the resource recovery rate is increased by 14%, which is more than that of fully mechanized mining face with 6.3m mining height, and the resource recovery rate is increased by more than 8%. 20 1 1 year, the monthly output of fully mechanized mining in the world is 1.265 million t, and the annual output of fully mechanized mining reaches1.40 million t.
Daliuta Mine of Shendong Company of Shenhua Group has a working face length of 2,000 ~ 6,200m, with an average of 4 100m and a working face length of 240m. In 2002, the annual output of fully mechanized mining face reached 8.74 million tons, exceeding the world advanced level of 6.4943 million tons maintained by 20-mile mine in the United States. In Xinglongzhuang Mine of Yankuang Group, the output of No.1 fully mechanized top-coal caving team reached 6,399,200 t, which set a new record for the annual output of fully mechanized top-coal caving face, and the unit output of thin coal seam planing face exceeded one million t mark.
At present, the pseudo-inclined flexible shield support mining method is widely used in thick and medium-thick steep coal seams. Aiming at steep and extra-thick coal seam, horizontal sublevel caving mining method is adopted. Inverted bench mining method and roadway short-wall small-stage mining method are also widely used in steep seam mining. No.84 steeply inclined coal seam is mined in Goujian Mine of Xinjiang Wukuang Group, and the horizontal slicing caving method is adopted. The annual output of working face reached 459,000 t, which set a new record for the output of steeply inclined working face in China.
China is one of the earliest countries to apply hydraulic coal mining in the world, and its output ranks among the top in the world. It has a good application prospect in low gas mines with dip angle above 10, medium-thick coal seam and stable roof and floor, especially in irregular coal seams with large changes in coal seam thickness and dip angle.
(2) Technical equipment
The general trend of underground mining technology and equipment is to develop into large-scale, intensive, automatic control and unmanned working face with the goal of high yield, high efficiency, safety and reliability according to coal mining conditions.
Fully mechanized mining face: The main equipment is mechatronics, with self-diagnosis function and communication function, which lays a foundation for the automation of production in the working face, improving the start-up rate of the system, ensuring the safe and reliable operation of the system and the automatic control and information management of the whole mine. Using the multi-channel rapid moving technology of auxiliary roadway, it takes only seven days to realize the fast, safe, high-quality and efficient from the old working face mining, hanging nets and the withdrawal and relocation of heavy fully mechanized mining equipment to the installation and debugging of new working face equipment and reaching the trial production conditions as soon as possible. Many working faces use high pressure (3300V or 4 160V).
Unmanned face: China imported fully-automatic plough fully-mechanized mining system (plough, conveyor and computer remote control technology) from German Mining Technology Company (DBT), and other supporting equipment was assisted by domestic manufacturers. It can adapt to thin and medium-thick coal seams below 35, the economic length of the working face is more than 2 10m, the production capacity is 900t/h, and the motor power is 630kW. At present, the system is being applied in Tiefa Coal Industry (Group) Company and other mines in China.
Coal mining machinery: 6LS 5 shearer imported from Daliuta Mine in China, with total installed power 1500kW and production capacity of 2,800 t/h, with electric traction speed regulation; Microcomputer control adopts advanced information processing and sensing technology to collect, process, display, store and transmit the operating conditions and various technical parameters of the shearer, and comprehensively control, monitor and protect the shearer through programming, so as to realize the functions of automatic adjustment of the electrical system of the shearer, automatic balance of cutting motor power and automatic search and diagnosis of mechanical faults. The unmanned coal mining technology of spiral drilling rig is also relatively mature in China, and its development prospect in thin coal seam mining is very broad. Recently, a new type of three-drill spiral shearer has been successfully developed in China. The shearer is applied to thin coal seam, which has obvious effect on improving the recovery rate of coal seam resources. The once mining width of this machine is 1.9m, and the mining depth can reach 85m.. It is suitable for thin coal seams with various hardness, such as coal seam thickness of 0.5~0.9m, coal seam dip angle of-15 ~+ 15, coal seam strike dip angle of less than 8, and daily output can reach 250~350t.
Hydraulic support: Two-column shield support with high height and strong strength is mostly adopted, and the working resistance is above 6000kN, with the maximum of 9800kN.
Scraper conveyor: It requires large capacity, long distance, high power, long service life and high reliability. Almost all scraper machines use double middle chains, and the power of scraper machine reaches 1790kW, and the transportation capacity per hour can reach more than 2500t t t. ..
Belt conveyor: long distance, large capacity and high power are required to ensure the smooth transportation of large coal flow. The laying length of retractable belt conveyor in some working faces has reached 5000m, the transportation capacity is 2000 ~ 3000 t/h, the belt speed is 5m/s, and the total installed power is 1 125kW. The bridge loader has a conveying capacity of 2500t/h, a length of 27m and a motor power of 3 15kW.
(3) Surrounding rock control technology of stope
In large coal mines in China, heavy hydraulic supports are mostly used in stope support, and bolt support is the main support in roadway support. Single hydraulic prop and metal prop are mostly used in mining faces of small and medium-sized coal mines, and the roadway is mainly supported by bolts, supplemented by self-closing and metal supports.
Support technologies and materials for different conditions such as hard roof, broken roof, steep slope, large mining height and large mining depth stope are continuously introduced. Anti-explosion light single hydraulic prop, anchor cable and telescopic anchor rod in thick coal seam roadway are produced one after another.
Monitoring instruments tend to be intuitive, portable and miniaturized.
1.2.2.3 Analysis of problems existing in underground mining
(1) The coal mining technology level is low, the technical equipment is poor, and the coal machine manufacturing technology is backward [3]
Compared with the same industry abroad, there is still a big gap in electromechanical integration, intelligent and automatic control technology, product reliability technology, digital integration technology, computer-aided design technology and so on.
Blasting is still the main way of coal falling in small and medium-sized mines, and the length of working face is short; Most coal mining methods are longwall mining, and the roof is managed by full caving method, which has serious damage to overlying strata and surface.
In the coal mining mechanization system, the transportation system, stope surrounding rock control system, roadway preparation system and auxiliary transportation system have poor technical equipment, low power and production capacity, and generally low mechanization degree and efficiency.
It is not enough just to introduce and digest foreign advanced equipment. In the underground self-rescue system, the level of disaster avoidance system and personal protective equipment is still very low, the instruments and meters for predicting major disasters such as gas can not fully meet the requirements, and the prevention technology and equipment for safety accidents can not completely effectively prevent disasters or minimize disasters.
(2) major scientific and technological research projects are difficult to achieve and major safety and technical problems are difficult to solve.
At present, there are many technical problems in "one ventilation and three prevention" (mine ventilation, gas prevention, coal dust prevention and fire prevention), water prevention, deep mine ground pressure, rock burst, high temperature disaster and support, which seriously threaten coal mine safety production. These are basic and forward-looking major scientific and technological work topics related to the development of industrial technology, and the scope and intensity of state support are greatly reduced compared with the past. After the decentralization of key coal enterprises, it is difficult to carry out technical research because of the economic strength of individual enterprises and research institutes.
Underground coal gasification technology and underground coal slurry (liquefaction) technology have not been effectively promoted and applied due to economic costs and other factors.
(3) Professional and technical personnel are faced with the situation of green and yellow.
In state-owned coal mines, technicians with college education or above only account for 3% of the total number of employees, while the proportion of corresponding technicians in individual coal mines is even lower, accounting for more than 60% in developed countries. In nearly 40 large and medium-sized coal enterprises with an annual output of more than 5 million tons, there are less than 2,000 engineers and technicians. Due to the particularity of coal industry safety, the proportion of students majoring in geology and mineral resources is decreasing year by year. According to the incomplete statistics of nine former coal universities, less than 10% of the graduates are employed in the coal industry. A mining group lost more than 900 talents in recent 10 years, including 270 technical talents, and did not recruit college students 10 years. The lack of technical personnel and low level make technical measures not in place, which restricts the improvement of coal mine safety production technology and management level.