The formation of coal and how to mine it.

Under the normal temperature and pressure of the surface, the plant residues accumulated in stagnant water are transformed from peat or sapropelic mud into peat or sapropelic mud; After peat or sapropelic mud is buried, it sinks into the deep underground due to the decline of basin basement and is transformed into lignite by diagenesis. When the temperature and pressure gradually increase, it is transformed into bituminous coal to anthracite by metamorphism. Peatization refers to the process that the remains of higher plants accumulate in swamps and are transformed into peat through biochemical changes. Sapropargization refers to the process of transforming the remains of lower organisms into sapropelic mud through biochemical changes in swamps. Asphaltene is a kind of argillaceous material rich in water and asphaltene. Glaciation may contribute to the collection and preservation of coal-forming plant remains.

Coal mining is the hardest work and efforts are being made to improve working conditions. Due to the different burial depths of coal resources, mining methods are generally divided into mine mining (deep burial) and open-pit mining (shallow burial). Among them, the proportion of open-pit mining resources to total resources is an important index to measure the advantages and disadvantages of mining conditions. China's open-pit mining reserves only account for 7.5%, while that of the United States is 32%. The quality of mine mining conditions is inversely proportional to the amount of gas in coal mines. The proportion of gas in coal mines in China is relatively high, and high gas and gas outburst mines account for more than 40%. China's coal mining is mainly based on mining, such as Shanxi, Shandong, Xuzhou and Northeast China, and there are also open-pit mining, such as Pingshuo Coal Mine in Shuozhou, which is the largest open-pit coal mine in China.

More than two-thirds of underground coal production is mined by room-and-pillar method using continuous mining machinery. The continuous shearer with tungsten alloy bit cuts coal from the surface side by side, and then it is transported to the car waiting to pick up the car, transported to the conveyor belt and transferred to the ground. The shearer moves forward for a certain distance, stops moving, and then puts it into the support. This process is repeated until the coal seam is mined. No blasting is used.

Another underground mining method is longwall mining, which accounts for about 20% of the output. This method uses a cutting machine that spans 400 to 600 feet of coal seam (longwall). This machine has a rotary cylinder tungsten drill to cut coal, and then the coal is sent to the conveying system, and then it is taken out of the mine. The roof is supported by large steel and connected to the machine. As the machine moves forward, the roof bracket will also move forward. This method can be used in nearly 80% coal mining.