1. Carbon and hydrogen

Carbon is the most important constituent element in coal. The carbon content (Cr) increases with the degree of coalification. The Cr of peat is 50-60%; Brown coal accounts for 60-77%; 74-92% for bituminous coal; Anthracite is 90~98%. Among coals with the same degree of coalification, Cr in fusinite is the highest, followed by vitrinite, and stable group is the lowest. Hydrogen middling coal is the second heavier

The hydrogen content (HR) of humic coal is higher than that of humic coal, generally above 6%, sometimes up to 11%. This is due to the lower biological hydrogen content that forms humic coal. In humic coal, the stable group has the highest HR, followed by the vitrinite group, and the silk group has the lowest. As the degree of coalification increases, their HR gradually decreases

2. Nitrogen

The nitrogen in coal is mainly converted from proteins in coal forming plants. People believe that the nitrogen in coal is usually organic nitrogen, some of which are heterocyclic The NR in coal is usually about 0.8~1.8%, but it also slightly decreases with the increase of coal maturity. In China, the NR of weakly bonded coal and non bonded bituminous coal is mostly less than 1%, which may be due to different degrees of oxidation during the peatification stage, causing protein oxidation and decomposition in coal plants, resulting in generally lower NR

3. Oxygen

Oxygen is one of the main elements in coal, and its total amount and form directly affect the properties of coal. The elemental composition of coal is mainly composed of organic matter, and the main components of organic polymers are carbon, hydrogen, oxygen, nitrogen, and other elements. There are dozens of elements present in coal, but the commonly referred to element composition of coal is mainly five elements, namely carbon, hydrogen, oxygen, nitrogen, and sulfur. Other elements with low content and diverse types in coal are generally not considered as elemental components of coal, but only as accompanying or trace elements in coal.

1、 Carbon in coal

It is generally believed that coal is composed of large aromatic rings and fused rings with fatty side chains. The skeleton of these dense rings is composed of carbon elements. Therefore, carbon is the most important element in the organic polymers that make up coal. Meanwhile, there is also a small amount of inorganic carbon in coal, mainly derived from carbonate minerals such as limestone and calcite. The carbon content increases with the increase of coalification degree. The dry ash free carbon content in peat in China is 55-62%; After becoming lignite, the carbon content increases to 60-76.5%; The carbon content of bituminous coal is 77-92.7%; Until the highly metamorphosed anthracite, the carbon content is 88.98%. Individual anthracite coal with higher coalification degree often has a carbon content of over 90%, such as anthracite coal in Beijing, Siwangfeng and other places, with a carbon content as high as 95-98%. Therefore, the entire coal formation process can also be said to be a process of increasing carbon.

2、 Hydrogen in coal

Hydrogen is the second important constituent element in coal. In addition to organic hydrogen, coal minerals also contain a small amount of inorganic hydrogen. It mainly exists in the crystalline water of minerals, such as kaolin (Al203 · 2SiO2 · 2H2O), gypsum (CaS04 · 2H20), etc., which all contain crystalline water. Throughout the entire metamorphism process of coal, as the degree of coalification deepens, the hydrogen content gradually decreases. Coal with low degree of coalification has a higher hydrogen content; Coal with high coalification degree has low hydrogen content. The general rule is hydrogen content

3、 Oxygen in coal

Oxygen is the third important constituent element in coal. It exists in both organic and inorganic states. Organic oxygen mainly exists in oxygen-containing functional groups, such as carboxyl (-- COOH), hydroxyl (-- OH), and methoxy (-- OCH3); Inorganic oxygen mainly exists in coal, including water, silicates, carbonates, sulfates, and oxides. The organic oxygen in coal decreases and even tends to disappear as the degree of coalification increases. When the carbon content of dry ash free base is less than 70%, the oxygen content of brown coal can reach over 20%. When the carbon content of bituminous coal is around 85%, the oxygen content is almost always less than 10%. When the carbon content of smokeless coal is above 92%, its oxygen content decreases to below 5%.

4、 Nitrogen in coal

The nitrogen content in coal is relatively low, generally around 0.5-3.0%. Nitrogen is the only element in coal that exists entirely in an organic state. Organic chlorides in coal are considered to be relatively stable heterocyclic and complex non cyclic compounds, and their original organisms may be animal and plant fats. The cyclic structures of plant alkaloids, chlorophyll, and other tissues all contain nitrogen, which is quite stable and does not change during coal gasification, becoming nitrogen compounds retained in coal. Nitrogen in the form of proteins is only found in peat and lignite, and is rarely found in bituminous coal, with almost no discovery. The nitrogen content in coal decreases with the deepening of coal metamorphism. Its relationship with hydrogen content is that it increases with the increase of hydrogen content.

5、 Sulfur in coal

Sulfur in coal is a harmful impurity that can cause steel to become brittle, equipment to corrode, and sulfur dioxide (SO2) generated during combustion to pollute the atmosphere, posing a threat to the growth of animals, plants, and human health. So, sulfur content is one of the important indicators for evaluating coal quality. The amount of sulfur in coal seems to have no obvious relationship with the depth of coal gasification. Whether it is coal with high or low degree of metamorphism, there is more or less organic sulfur in coal. The amount of sulfur in coal is closely related to the ancient geographical environment during coal formation. Coal seams or shallow deposits formed in inland or coastal triangular training plain environments and deposited at the intersection of sea and land

Coal seams in marine sediments have a relatively high sulfur content, with most of them being organic sulfur. According to the occurrence forms of sulfur in coal, it is generally divided into two categories: organic sulfur and inorganic sulfur. The sum of various forms of sulfur is called total sulfur. The so-called organic sulfur refers to the sulfur that combines with the organic structure of coal. Organic sulfur mainly comes from proteins in coal plants and proteins in microorganisms. Inorganic sulfur in coal mainly comes from various sulfur-containing compounds in minerals, which are generally divided into sulfide sulfur and sulfate sulfur, and sometimes there are also trace amounts of elemental sulfur. Sulfide sulfur is mainly composed of pyrite, followed by white iron ore, magnetite (Fe7S8), sphalerite (ZnS), and galena (PbS). Sulfate sulfur is mainly composed of gypsum (CaSO4 · 2H20), with a small amount of green alum (FeSO4 · 7H 20), etc.