Coal: classification, types, grades, characteristics, characteristics of combustion, places of production, application and importance for the economy

Coal is a very diverse and multifaceted compound. Due to its particular formation in the bowels of the earth, it can have very different characteristics. Therefore, it is customary to classify coal. How this happens is described in this article.

Fossil coal is mostly mined from the bowels of the earth, but sometimes, as a result of seismic activity, coal seams come to the surface where open-pit mining is possible. But where does the coal in the earth's crust come from? The formation of coal is a very long and complex process that originates from ordinary plants. When plants die, peat is formed from them with a lack of oxygen and high humidity. For millions of years, this peat has settled in the ground, where, thanks to high temperature and pressure, it slowly turns into coal. This process is called coalification.

Fossil coal can be found by man at various stages of coalification, so there are many types of this resource. There are several types of coal classifications: in composition, in terms of origin, in size, in moisture, in the presence of impurities, and also in many other characteristics. Let us examine some of them in more detail.

Coal classification by size of pieces

To get coal out of the ground, it must be crushed and delivered to the surface. The resulting pieces can be of different sizes, which is important enough for future use. For this reason, there is a state standard (GOST R 51586-2000), which defines the classification of coal by the size of the pieces. These sizes are sometimes called grades of coal, so as not to be confused with brands, which will be discussed later.

If coal is not yet sorted and has in its composition pieces of completely different sizes, then such coal is called ordinary (P).

There are also mixed varieties, that is, mixtures of coals of different sizes within certain limits. But the percentage of coal of each class in this case is not regulated. A mixture may consist, for example, of a 95% seed and 5% bayonet, in which case the variety will be called a seed with a bayonet.

Grade classification of coal

As already mentioned, coal may vary in composition. It is extremely difficult to isolate specific compounds in coal, therefore, in order to characterize coal, they use only some characteristics: concentration of volatile substances, humidity, carbon content, calorific value, etc.

Usually all of these characteristics are related. The higher the carbon content in the coal and the less volatiles, the more heat the fuel can produce. According to these characteristics, coal is divided into grades.

Brown coal (B)

It is the youngest and therefore the least useful brand of coal. It looks like a brown stone mass. Sometimes it even has a woody structure. The heat output is only 22 MJ / kg. The reason for this is the low carbon content, a large amount of moisture, volatile substances and mineral impurities. All this does not provide effective combustion.

Such coal is formed directly from peat and lies at a shallow depth (from 10 to 200 meters). In Russia, it is mined at the Solton deposit, in the Tunguska and Kansk-Achinsk coal basins.

Long flame coal (D)

Usually has a gray-black color. It burns with a long smoking flame, which gave it its name. It contains 70-80% carbon, which makes it a slightly better fuel, compared to brown coal. It is also affected by less moisture and impurities. But the advantage of long-flame coal is not that. This fuel can burn without blowing, which makes it easy to use in furnaces and boilers. This type of coal is very common. Its mining is carried out in the Minusinsk, Kuznetsk, Donetsk and many other basins.

Gas Coal (G)

Very similar to the previous brand, but is characterized by low humidity and high burning rate. Because of the latter, it is often used as a fuel in boiler rooms. This coal is common in Donetsk, Kuznetsk, Kizelovsky and some other coal basins. It is also found in deposits of Sakhalin Island.

Fat Coal (W)

This is already quite high-quality coal. Despite the fact that it lights up harder than the previous two brands, it has a high calorific value (35 MJ / kg). The disadvantage is the high content of volatile substances, which complicates the control of the combustion process, so this brand of coal is rarely used as fuel. The main areas of its use are the production of building materials, activated carbon and other useful substances, as well as in the coke and chemical industry. Such coal is mined in the Osinovsky, Baidaevsky, Leninsky and Tom-Usinksky deposits.

Coke coal (K)

This is a very valuable type of coal due to its low prevalence. This brand produces very high-quality coal coke, which follows from the name. Such coal is formed at a sufficiently large depth (5500 m), where there is a lot of pressure. The color of this coal is gray with a glass sheen. It has a very uniform structure and a minimal number of pores. The content of volatile substances is moderate (22-27%), and carbon already reaches 88-90%, which has a positive effect on heat transfer, although such coal is rarely used as fuel. Coke coal is mined in the Kuznetsk coal basin, in Angersky, Tom-Usinsky, Prokopyevsky-Kiselevsky and other areas.

Sintered Coal (OS)

This brand of coal is not very different from coke coal: the content of carbon and inorganic impurities is at about the same level. Its main advantage is its high calorific value. It is 36 MJ / kg, so sometimes it is used as fuel in power plants. But its main use is the coke industry. True, this coal is difficult to coke, so you have to use it in a mixture with other types of coal. Such a mixture of several grades is called a coal charge. Mining of sintered coal is mainly carried out in the Kuzbass, in the Kemerovo region and in the South Yakut coal basin.

Lean coal (T)

This brand of coal received such a funny name because of the relatively thin seams with which it lies in the rock. The reason is the great depth (6600 m) and great pressure. Unlike the previous two types, lean coal does not have the ability to sinter, and it is almost impossible to produce coke from it.

But it has a very high calorific value of up to 40 MJ / kg. This leads to its use as a fuel, as well as in metallurgy, where extremely high temperatures are needed in furnaces for melting metals. The main lean coal mining areas are the Aralichevsky, Baidaevsky and Kemerovo districts.

Anthracite (A)

This is the highest quality coal, in terms of calorific value. The carbon content in it can reach 98%. Only graphite has more. And in appearance, anthracite is very different from other brands. It has a dark black color with a pronounced metallic tint. It also has increased heat resistance and electrical conductivity. The combustion temperature of anthracite is quite high, so it can not be used as fuel in all types of furnaces. In addition, it is used in metallurgy, for the manufacture of filters, electrodes, calcium carbide, microphone powder. This coal does not sinter, therefore, it did not find application in coking, although even without this process it can replace coke in some processes.

Other types of classifications

In addition to the grades presented above, there are many intermediate grades, for example, coke fat (QL), gas sintering (HS), long-flame gas (DG).

Also, coal of each brand can have different sizes of pieces. In this case, the letter denoting the variety is located after the letter denoting the brand. For example, anthracite-nut (AO), fatty-plate (ZhP), coke seed (KS).

There is a classification of coal by origin. All coal, as already mentioned, is formed from plants over millions of years. But plants can have a different nature. So, coals are divided into humic (from wood, leaves, stems) and sapropelite (from the remains of lower plants, such as algae).