Coal classification and elements

Coal classification

There are several coals such as lignite, bituminous coal, anthracite coal and semi-anthracite coal.

lignite

Mostly massive, dark brown, dark in luster, loose in texture; containing about 40% of volatile matter, low ignition point, easy to catch fire, fast on ignition, large flame, and black smoke; low carbon content and calorific value ( Because of the different grades of coal at the place of origin, the calorific value varies greatly.) The burning time is short, and coal must be added frequently.

bituminous coal

Generally granular, small, also powdery, mostly black and shiny, fine texture, containing more than 30% of volatile matter, burning point is not too high, easier to ignite; carbon content and heat is higher, when burning The blaze is fast, the flame is long, there is a lot of black smoke, and the burning time is long; most of the bituminous coal is sticky and easy to slag when burned.

anthracite

There are two kinds of powder and small pieces, showing a black metallic luster and shiny. Less impurities, tight texture, high fixed carbon content, up to more than 80%; low volatile content, less than 10%, high ignition temperature, not easy to catch fire; but high heat, just when the fire is lit slowly, after the fire is relatively large , Strong firepower, short flame, less smoke, long burning time, weak adhesion, and slagging when burning. Should be mixed with appropriate amount of coal to burn, in order to reduce the intensity of firepower.

In October 1989, the National Bureau of Standards issued the "National Standard for Coal Classification in China" (GB5751-86), based on the dry ash-free volatiles Vdaf, the bonding index G, the maximum thickness of the gelatinous layer Y, the Oia expansion degree b, and coal The light-transmitting P, coal's constant humidity, ash-free high-level heat generation Qgr, maf and other six categories of indicators, the coal is divided into 14 categories. Namely lignite, long flame coal, non-stick coal, weakly coal, 1/2 medium coal, gas coal, coal gas, 1/3 coking coal, fat coal, coking coal, lean coal, lean coal, poor coal, and anthracite .

Coal contains elements

The elements that make up the coal's organic matter are mainly carbon, hydrogen, oxygen, nitrogen, and so on. In addition, there are very few elements such as phosphorus, fluorine, chlorine, and arsenic.

Carbon, hydrogen and oxygen are the main components of coal organic matter, accounting for more than 95%. The deeper the degree of coalification, the higher the carbon content and the lower the content of hydrogen and oxygen. Carbon and hydrogen are elements that generate heat during the combustion of coal, and oxygen is a combustion-supporting element. When coal is burned, nitrogen does not generate heat, and it is converted into nitrogen oxides and ammonia at high temperatures and precipitates in a free state. *, Phosphorus, fluorine, chlorine and arsenic are harmful components in coal, of which the * is the most important. Most of the coal* is oxidized to sulfur dioxide* (SO2), which emits fumes, pollutes the atmosphere, and jeopardizes animal and plant growth and human health. It also corrodes metal equipment. When more coal is used for metallurgical coking It also affects the quality of coke and steel. Therefore, the “* points” content is one of the important indicators for evaluating coal quality.

The combustible gas produced by the decomposition of organic matter in coal at a certain temperature and condition is called “volatile matter”. It is a mixture of various hydrocarbons, hydrogen, and carbon monoxide. Volatile matter is also a major coal quality indicator. When determining the processing and utilization methods and processing conditions of coal, volatile matter has an important reference role. Coal with low coalification has more volatiles. If the combustion conditions are not appropriate, coal with high volatile content tends to produce unburned carbon particles when burned, commonly known as "black smoke"; and produces more pollutants such as carbon monoxide, polycyclic aromatic hydrocarbons, and aldehydes, resulting in lower thermal efficiency. Therefore, the appropriate combustion conditions and equipment should be selected based on the volatile content of the coal.

The content of inorganic substances in coal is very small, mainly including water and minerals. Their presence reduces the quality and utilization value of coal. Minerals are the main impurities of coal, such as sulfides, sulfates, carbonates, etc. Most of them are harmful components.

"Moisture" has a great influence on the processing and utilization of coal. Water changes to steam when it is burned to absorb heat, thereby reducing the calorific power of the coal. The moisture in coal can be divided into external moisture and internal moisture, and internal moisture is generally used as an indicator for evaluating coal quality. The lower the degree of coalification, the greater the internal surface area of ​​the coal and the higher the moisture content.

“ash” is the solid residue left after the coal is completely burned, and is an important coal quality indicator. Ash mainly comes from the incombustible minerals in coal. When minerals are burned, they must absorb heat during ashing. A large amount of slag should remove heat, so the higher the ash content, the lower the thermal efficiency of coal combustion. The more ash, the more ash from coal combustion, the more fly ash will be discharged. . In general, high-quality coal and clean coal have relatively low ash content.