The geology of coal mines is complex and variable. Coal mining, including digging tunnels and arranging work surfaces, is carried out underground for hundreds of meters or even kilometers. With the continuous advancement of coal mining and excavation work faces, the coal seams and rock formations that have been recovered have been damaged. For this reason, how to mine safely and efficiently is particularly important. At present, the first is based on the characteristics of coal mine engineering, through the prediction and forecast of mine pressure, control design and control effects, and achieve scientific and safe mining; the second is to carry out physical filling of the goaf to avoid collapse, achieve safe production, and increase the amount of mining. 1 Guided safe mining with mine pressure theory 1.1 Related concepts of mine pressure theory The basis of mine pressure prediction and forecasting is the practical mine pressure theory system established by Academician Song Zhendu of the Chinese Academy of Sciences. The theoretical system includes the following main contents: First, it explains various mine pressure phenomena and uses the obtained “mine pressure display†to infer the mine pressure distribution and Overlying rock movement. The second is to reveal the relationship between "mine pressure" and its "appearance" and the overlying rock level and its development and change law with the stope. The field observation is used to infer the roof movement of the stope and analyze the size distribution of the supporting pressure for the correct establishment. The mining pressure and control design of the stope provides the basis. The third is to point out the range of overburden affecting the mine pressure and the appearance, generally including “direct roof†and “old roofâ€, which can artificially control the mining conditions such as mining height, mining procedure and roof treatment method. The fourth is to establish the position equation, the roof control design criterion and the corresponding mechanics guarantee conditions at the production site. The fifth is to put forward the concept of the effective support capacity of the stope support, which provides a basis for rational selection of the support form and the determination of the support density. 1.2 The guiding role of theory in production practice The technicians of our company directly use the mine pressure theory to guide the on-site production practice. The following methods are mainly used: Firstly, according to the technical conditions of specific coal seam mining, the mining and mining pressure and the prediction, control design and control effects of roof activity are combined. Formed a relatively complete control method. Secondly, aiming at solving the problem of engineering control practice, the unity of theory and practice is realized. The main methods: First, by observing the dynamics of the roof, the control range and structural parameters of the roof are determined; secondly, the “top dynamic meter†has been successfully developed to improve the measurement accuracy; thirdly, the “top board dynamic monitoring computer system†has been successfully developed. 1.3 Combination of engineering theory and high technology China's coal industry has a large gap compared with developed coal-producing countries. The main reason is that coal mine accidents are frequent, the casualty rate is the highest in the world, and the surface subsidence is serious. Accidents and disasters occur because they do not understand and master the laws governing the development of rock strata movement and stress fields along the stope, and the construction of roadways and mining operations at the wrong time and in the wrong position. The reliable control of various accident disasters can only be realized on the basis of understanding the overburden movement and stress field stress magnitude and distribution law of different mining conditions. Therefore, it is necessary to grasp the fundamentals of controlling rock formation movement and stress conditions caused by accidents, and select the mining conditions (including controlling the length of mining face, mining height, etc., selecting the correct mining procedure and the treatment method of the goaf, etc.) by correct design. Achieve unified control of all types of accidents and disasters, and achieve the goal of safe and efficient coal mining. In view of the complicated mining conditions in China, the level of mechanization is low, and the quality of technical and management personnel is low, the situation of large-scale mining of coal is carried out. Therefore, it is necessary to use the theory of mining engineering in China, especially the theory of mine pressure and rock movement control. Relying on practical achievements, making full use of the achievements of modern information technology, establishing a scientific decision-making system, realizing the informationization, intelligence and visualization of safe mining decision-making, completely reversing the long-term relying on experience and statistics, low-level artificial decision-making, and making coal mine safety and high efficiency Mining decision-making is advanced to the scientific and quantitative development stage of specific coal seam geological conditions. 2 to ensure safe mining by coal mining and mining technology China's village coal has a large amount of surface, and the mining of coal under the village involves land, environmental protection, workers and peasants and other social aspects. Therefore, it is necessary to solve the problem of large-scale coal mining under village buildings and realize coal mining in non-removed villages. The use of filling mining is the most effective way to reduce surface subsidence, ensure safe mining and increase coal recovery rate. 2.1 Commonly used non-removed village coal mining methods The large amount of coal under the villages and other buildings not only causes huge waste of coal resources, but also seriously restricts the normal production and connection of the mine. At present, the main methods for realizing coal mining in non-removed villages are strip mining and filling mining. Strip mining is based on the premise of not changing the coal mining process, using strip interval mining to reduce surface subsidence and increase coal production, but the mining rate is low, the resource waste is serious, and the production efficiency is low, so it is no longer recommended. Filling mining is the physical filling of the goaf, which is equivalent to the filling to replace the coal from the rock formation to reduce surface subsidence, ensure safe production and increase coal output. 2.2 Coal mine filling and mining technology At present, the filling and mining processes used are water sand filling mining and paste filling mining. 2.2.1 Water sand filling and mining Water sand filling and mining has been widely used, and the effect is good, but the water sand filling technology is complicated, which is not conducive to mechanized production, and the efficiency is low. This technology is basically not used in China. 2.2.2 Paste filling and mining Paste filling mining technology is developed on the basis of water sand filling and mining. China has applied paste filling technology since the 1990s and achieved good economic results. The paste filling is made of solid waste such as coal gangue, fly ash and industrial slag near the coal mine, and is made into a paste slurry without dehydration. It is pumped to the underground through pumping or gravity, and the gob is filled in time. Methods. According to the different conditions of coal seam occurrence, the requirements for the filling degree of goaf are also different. The filling of coal paste can be divided into all filling, short wall filling, long wall filling, separation in the separation zone, and filling in the goaf. And other methods. The filling process of coal mine paste is divided into four parts: material preparation, batch pulping, pipeline pumping and working surface filling. The specific process requirements for paste filling are as follows: First, the material requirements: the material with smaller particle size is sieved (screening blocks and linear debris larger than 20 mm), and when using large pieces of material such as coal gangue, appropriate crushing treatment is also required. In order to reduce the amount of cement, it is also possible to stimulate the chemical activity of the fly ash by means of mechanical grinding and alkaline excitation. Second, the matching requirements: coal mine filling paste is made up of a variety of materials, must be mixed evenly, accurate ratio, in order to ensure the fluidity of the filling, condensation and solidification. This requires that the mass fraction of the filling slurry must be controlled within 0.5%, and the material weighing error is less than ±2%. According to the characteristics of the filling material of the coal paste, the periodic concrete mixer is selected, the stirring is forced, the mixing and the discharging are cycled in order to control the mixing ratio and the mixing quality. The third is pipeline pumping: pumping with concrete vacuum pump, requiring cleaning before and after using the pump and pipeline, cleaning in time after use, the pump is filled with clean water. The fourth is the filling of the working surface: the coordination of the paste filling system and the coal mining system is the key to the filling and mining of the paste. The general working face is filled with paste. First, a wall is built in the top surface of the working surface and the filling area to form a wall. "closed" space. Plastic woven cloth isolation and combined steel formwork isolation are commonly used. After the isolation installation is completed, the working surface and the pipe provided on the wall are pumped into the space to be filled. 3 Conclusion In summary, with the continuous development of science and technology, coal mining technology will be more safe and efficient, regardless of the use of mine pressure theory system prevention and control or coal mining and filling, are aimed at safe production and resource extraction.
Retort technology means food is pre-cooked, needing little (if any) additional preparation. And for those consumers that appreciate convenience, the less cooking, the better! Today`s consumers demand convenience, so the flexible retort pouch is appealing because it can be re-sealed. Someone who opens a can of tuna and prepares half of it must then find a way to store what remains. With a re-sealable zip seal pouch, there`s no need for other storage methods. Believe it or not, retort technology makes food taste better. Here, food is spread out evenly, so it cooks faster than in a can. In cans, product at the edges can overcook, while product in the center can undercook. This problem is eliminated by the flexible pouch.
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Traditionally used for coffee and tea, this side-gusseted bag is now growing in popularity in the food, snack and baked good industries. Its side-gusset feature allows your package to be displayed vertically or horizontally, giving retailers more options for shelf display.
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Coal is the food industry, accounting for 70% of China's energy structure. At present, China's proven coal reserves amount to 900 billion tons, which can be extended for at least 400 years according to the annual mining of 1.5 billion tons. China's oil and natural gas resources are limited, and in the future, it will only be supplemented by coal-to-oil and coal-to-gas . Therefore, coal safe and economic mining plays an important role in China's national economy.