Which is an ancient plants buried in the ground has experienced a complex biochemical and physical and chemical changes gradually formed the solid combustible minerals.
So?
Coal” means raw coal, excluding coal washing, coal preparation and other coal products.
Raw coal refers to the coal just extracted from the mine without screening, washing, selection and other processes, which needs to be levied resource tax.
There is no need to levy resource tax on coal washing, coal preparation and other coal products.
Coal includes raw coal, coal washing, coal preparation and other coal products, that is, coal includes coal (raw coal: unprocessed coal) and coal washing, coal preparation and other coal products (processed coal).
Coal is a flammable black or brownish-black sedimentary rock that usually occurs in a rock formation or vein called a coal bed or seam.
Because of later exposure to elevated temperatures and pressures, the harder forms of coal can be considered metamorphic rocks, for example.
Coal is composed mainly of carbon, together with various amounts of other elements, chiefly hydrogen, sulfur, oxygen and nitrogen.
Historically, coal has been used as a resource, mainly to be burned for production and/or heat, but also for industrial purposes, such as refining metals, or for the production of fertilizers and many chemical products.
As a kind, coal was formed when ancient plants were buried in the ground before they decomposed into peat, then into lignite, then sub-bituminous coal, then bituminous coal, and finally anthracite.
The hydrocarbons produced by coal act under the pressure and temperature conditions of the earth’s crust movement, and the carbonized fossil minerals are produced, that is, coal is the fossil plant.
It involves biological and geological processes over a long period of time.
Coal is the most abundant and widely distributed fossil fuel on Earth.
The elements of coal organic matter are mainly carbon, hydrogen, oxygen, nitrogen and sulfur, etc. In addition, there are a very small amount of phosphorus, fluorine, chlorine and arsenic and other elements.
Carbon, hydrogen and oxygen are the main parts of coal organic matter, accounting for more than 95%.
The deeper the coalification, the higher the carbon content and the lower the hydrogen and oxygen content.
Carbon and hydrogen are elements that generate heat during coal combustion, while oxygen is a combustion-supporting element.
When coal is burned, nitrogen does not produce heat, and is converted into nitrogen oxides and ammonia at high temperature, which are precipitated in a free state.
Sulfur, phosphorus, fluorine, chlorine and arsenic are harmful components in coal, among which sulfur is the most important.
When coal is burned, most of the sulfur is oxidized into sulfur dioxide (SO2), which pollutes the atmosphere, endangers animal and plant growth and human health, and corrodes metal equipment;
When sulfur rich coal is used in metallurgical coking, it also affects the quality of coke and steel.
Therefore, sulfur content is one of the important indexes to evaluate coal quality.
The combustible gas produced by thermal decomposition of organic matter in coal at a certain temperature and under certain conditions is called “volatile”, which is a mixture of hydrocarbons, hydrogen, carbon monoxide and other compounds.
Volatile matter is also the main coal quality index, in the determination of coal processing and utilization ways and technological conditions, volatile matter has an important reference role.
The coal with low degree of coalification has more volatile matter.
If the combustion conditions are not appropriate, volatile high coal combustion easy to produce unburned carbon particles, commonly known as “black smoke”;
And produce more carbon monoxide, polycyclic aromatic hydrocarbons, aldehydes and other pollutants, the thermal efficiency is reduced.
Therefore, the appropriate combustion conditions and equipment should be selected according to the volatile matter of coal.
The content of inorganic substances in coal is very small, mainly water and, their existence reduces the quality and utilization value of coal.
Minerals are the main impurities of coal, such as sulfide, sulfate, carbonate, and so on, most of which belong to the harmful components.