Research on new technology of preventing hidden fi

Research on new technology for prevention and control of hidden fire sources in fully mechanized top coal caving goaf

spontaneous combustion fire in coal seam is one of the main disasters in coal mine, which seriously threatens the safety of coal mine personnel and causes significant economic losses. 56% of the coal mines in the country have the risk of spontaneous combustion of coal seams, and 182 spontaneous combustion fire accidents have occurred in 220 fully mechanized top coal caving faces that have been mined. Coal seam spontaneous combustion fire has become one of the main factors restricting the safety production and development of high-yield and high-efficiency mines, such as torque/axial force rotation angle and other experimental curves

2 characteristics of spontaneous combustion fire in coal seams in fully mechanized top coal caving goaf

the fully mechanized top coal caving face adopts retreating mining, "U" ventilation mode, and implements coal pillar free mining. Zhao Wei believes that the area is connected with the adjacent goaf (closed), forming a relatively complex air leakage pattern. The internal air leakage of the stope is closely related to coal spontaneous combustion, which directly affects the distribution of oxidation "three zones" in the goaf, The specific performance is as follows:

2.1 most coal seams have the tendency of spontaneous combustion, and because the unit yield of fully mechanized top coal caving face is high and the strike length is large, some working faces have exceeded 2000m at present, the mining time of working faces exceeds the shortest spontaneous combustion period of coal seams, and the exposure time of coal bodies in the air is long

2.2 during fully mechanized top coal caving mining, there are more coal losses in the goaf, and these floating coals are in a broken state, which provides conditions for the occurrence of spontaneous combustion fire in the goaf

2.3 spontaneous combustion fires mostly occur in the middle of a certain depth from the exposed surface, where the air leakage intensity is moderate, the wind speed is slow, and the oxygen concentration is appropriate, which is easy to meet the spontaneous combustion conditions of coal and form the spontaneous combustion high temperature point, and the oxidation zone and spontaneous combustion zone of the residual coal in the goaf are generally 30m behind the working face

2.4 the top coal at both ends of the fully mechanized top coal caving face is difficult to recover, and the top coal caving lost at both ends is backward and piled up. When there is no adjacent goaf, the air leakage of fully mechanized top coal caving face is the small parallel air leakage of goaf. The two ends of the fully mechanized top coal caving face are the source and sink of air leakage in the goaf, and the air leakage at these two places is relatively large

2.5 the risk of spontaneous combustion in the groove, cut hole and stoping line of the fully mechanized top coal caving face is relatively high. The roadway of the fully mechanized mining face is excavated along the coal seam floor, and there is usually a few meters thick (generally more than 3m) top coal on the top. Under the influence of the dynamic pressure of tunneling and the dynamic pressure of mining in the adjacent mining face, the top coal is crushed and separated, and the section coal pillar is also compressed. During the tunneling process, the top coal often falls, and after support, a certain amount of loose floating coal is accumulated on the shed

3 current main fire prevention and extinguishing technologies and comments

with the rapid development of the coal industry, coal seam spontaneous combustion fire control technology has made remarkable achievements. At present, preventive grouting technology, chemical inhibitor technology, water injection technology, inert gas technology, etc. are often used in fire prevention and extinguishing technology at home and abroad, and plugging technology and gel technology are also used in some conditions

in the 1950s, grouting technology became the main means of coal mine fire-fighting technology in China, and has been used until today. The so-called preventive grouting technology, which has been widely implemented, refers to mixing water and grouting materials in an appropriate proportion to prepare a certain concentration of slurry, which is sent to the area where coal spontaneous combustion may occur through the laid slurry pipeline using natural pressure difference or slurry pump, so as to prevent the occurrence of natural fire. Inhibitor technology has been well applied in the United States, Poland, the former Soviet Union and other countries; In recent years, inhibitor technology has also been popularized and applied in China. This technology mainly allows the aqueous solution to adhere to the surface of coal that is easy to be oxidized, inerts the active structure of the surface of coal, and prevents the contact between coal and oxygen. In recent years, gel technology has been widely used in China. Gel can be divided into two categories: inorganic gel and polymer gel. Its fire-fighting mechanism is that gel enters the high-temperature area through drilling holes or coal cracks. When a part of it is not gelled, the water vaporizes rapidly at high temperature, which reduces the coal surface temperature rapidly. At the same time, the residual solid forms an isolation layer, which hinders the contact between coal and oxygen and further oxidizes and spontaneously ignites; With the rise of the temperature of the coal, some of the flowing mixed liquid forms colloids not far away and in the pores of the coal, wraps the coal, isolates oxygen, and terminates the oxidation and exothermic reaction of the coal; The dried colloid can also reduce the porosity of raw coal, greatly reducing the amount of air passing through, thereby inhibiting re ignition