Basic knowledge of coal

Coal is a solid combustible mineral gradually formed by ancient plants buried underground through complex biochemical and physical-chemical changes. What do you know about coal? The following is my coal knowledge, I hope you like it!

Coal application history

Although the important position of coal has been replaced by oil, it will inevitably decline for a long time because of the gradual depletion of oil. Because of the huge coal reserves, the rapid development of science and technology, the maturity and wide application of new technologies such as coal gasification, coal will surely become one of the irreplaceable energy sources in human production and life.

According to the different original materials and conditions of coal formation, coal in nature can be divided into three categories, namely humus coal, residual humus coal and sapropelic coal.

China is the first country in the world to use coal. Coal handicrafts were found in Xinle ancient cultural site in Liaoning, and coal cakes were also found in gongyi city, Henan. In Shan Hai Jing, coal was called Shi Nie, while in Wei and Jin Dynasties, coal was called graphite or Carboniferous. The name coal was first used by Li Shizhen in Compendium of Materia Medica in Ming Dynasty. Greece and ancient Rome were also countries that used coal earlier. About 300 BC, the Greek scholar Theophrastos wrote The History of Stones, which recorded the nature and origin of coal. About 2000 years ago, ancient Rome began to use coal for heating.

Cause of coal formation

Coal is a very thick layer of black humus, which has been accumulated on the ground by the branches and roots of plants for millions of years. Due to the change of the earth's crust, it has been buried underground for a long time and isolated from the air. After a series of complex physical and chemical changes at high temperature and high pressure, a black combustible sedimentary rock is formed, which is the formation process of coal. The thickness of coal seam in coal mine is related to the speed of crustal decline and the accumulation of plant residues in this area. The earth's crust is falling rapidly and the plant remains are piled thick, so the coal seam in this coal mine is thick. On the contrary, the earth's crust is slowly falling, and the plant remains are piled very thin, so the coal seam of this coal mine is very thin. Due to the tectonic movement of the earth's crust, the original horizontal coal seam was folded and fractured. Some coal seams are buried deep underground, while others are pushed out of the surface or even exposed to the ground, which is easy to be found. There are also some coal seams that are relatively thin and small in area and have no mining value. So far, there is no updated statement about the formation of coal. Is coal formed in this way? Whether some expositions should be further studied and discussed. Large coal mines have thick coal seams and excellent coal quality, but the area is generally not very large. If the leaves and roots of plants have accumulated naturally for millions of years, their area should be very large. Because the earth was full of forests and grasslands in ancient times, there should be traces of coal storage everywhere underground; The coal seam is not necessarily very thick, because the leaves and roots of plants rot into humus, which will be absorbed by plants. If it is repeated, it will not be so concentrated when buried underground, and the boundary between soil layer and coal seam will not be so clear. However, the undeniable fact and basis is that coal is indeed formed by the systematic evolution of plant residues, which is an unbreakable truth. As long as you look at the coal carefully, you can see the traces of leaves and roots of plants; If you slice coal and observe it under a microscope, you can find a very clear plant tissue structure. Sometimes things like tree trunks are still preserved in coal seams, and some coal seams are still wrapped with complete insect fossils. 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.

Environmental problems caused by coal

1, flue gas desulfurization

SO2 pollution in the atmosphere is mainly caused by fuel combustion including coal. Desulfurization before combustion can be completed by coal washing and conversion. Combustion desulfurization can remove some sulfur by adding desulfurizers, such as dolomite and limestone.

The commonly used desulfurization technology is flue gas desulfurization, that is, the discharged sulfur-containing flue gas or waste gas is introduced into absorbent and adsorbent to remove sulfur oxides, which are divided into dry method, semi-dry method and wet method. The dry method uses solid adsorbent and absorbent, which has huge equipment and high cost. Semi-dry method is to blow semi-solid desulfurizer into flue, or blow waste gas and air into semi-solid desulfurizer at the same time to remove SO2 from flue gas. Wet process adopts liquid absorbent, including alkaline absorbent method and alkaline earth metal absorbent method. The former uses ammonium, sodium and potassium solution, while the latter uses calcium and magnesium oxide or hydroxide solution.

2, smoke pollution and prevention and control

Smoke particles produced during coal combustion will cause environmental pollution. Its pollutants can be divided into two categories, namely aerosol pollutants and gaseous pollutants. Smoke belongs to the former.

Coal goes through three stages in the combustion process: first, drying and volatilization stage, second, combustion stage, and finally, burnout stage. Different stages need different air volume. Too much or too little air volume will make the combustion incomplete, and carbon particles will be discharged into the air to form black smoke. Some non-combustible components in coal, such as ash, remain in the ash during combustion, and some of them are discharged into the atmosphere with flue gas to form smoke. There are also great differences in the amount of coal dust with different ash content. According to the different particle size of smoke, it can be divided into dust suppression and floating dust, the latter can not fall for a long time and can be transported farther.

Smoke and dust can cause human respiratory diseases, or become carriers of other pollutants and bacteria. It will also affect plant growth and reduce atmospheric visibility. The prevention and control methods are to improve combustion equipment and combustion mode, reduce smoke and dust emission, install dust removal equipment and reduce smoke and dust emission concentration.

coal mining method

Gangue discharge

The solid waste with the largest discharge in coal mine production is also the solid waste with the largest output and accumulation in China's industrial solid waste, and the output is generally about 10% of the coal output. The annual discharge of coal gangue in China is about1.500-200 million tons. By the end of 2002, the national coal gangue storage was about 3.4 billion tons, covering an area of 20,000 to 60,000 hectares, and it was the largest solid waste in China. In 2004, the comprehensive utilization of coal gangue in China was 1 and 3.5 billion tons, with a utilization rate of 54%.

mine drainage

In the process of coal mine construction and production, various types of source water will enter the roadway and working face through different ways. In order to ensure the safety of coal mine and prevent water disaster, it is necessary to drain the mine water inrush. According to incomplete statistics, in the process of coal mining, the national coal mine water inflow in 2004 was about 3 billion m? The average water inflow per ton of coal is about 2m? . The utilization rate of resources only accounts for about 22%.

Gas drainage and mine ventilation

Gas drainage before and during coal mining is an important measure to ensure coal mine safety. However, the emission of gas into the atmosphere will have a strong greenhouse effect, and the greenhouse effect of methane contained in gas is 20 times greater than that of carbon dioxide. In addition, in the process of coal mine production, underground tunnels need hundreds of thousands or even millions of cubic meters of air per second, mainly by mine ventilation, which also contains gas and a lot of dust. According to the relevant evaluation and estimation in recent years, the national coalbed methane resources are 3? 106 。 In 2002, the output of coalbed methane in national key coal mines was 9773 and 37, of which the gas utilization was 5 17 and 49, and the utilization rate was about 5%.

Ecological damage caused by mining

Traditional coal mining ignores the mining, processing and utilization of other biological sources and associated minerals, resulting in a waste of resources. There are more than 20 kinds of minerals associated with coal measures in China, most of which are not used. In addition, the random storage and discarding of minerals will also cause environmental pollution and destroy the ecological environment.