Coal: classification, types, grades, characteristics, combustion features, extraction sites, application and importance for the economy

2024 Author: Howard Calhoun | [email protected]. Last modified: 2024-01-17 18:37

Coal is a very diverse and multifaceted compound. Due to its peculiarity of 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 depths of the earth, but sometimes, as a result of seismic activity, coal seams come to the surface, where 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, with a lack of oxygen and high humidity, peat is formed from them. Over millions of years, this peat settles into the ground, where, due 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. In total there are several types of coal classifications: by composition, byfeatures of origin, size, humidity, the presence of impurities, as well as many other characteristics. Let's take a closer look at some of them.

Classification of coal by size of pieces

To extract coal from underground, it must be crushed and delivered to the surface. The resulting pieces can be of different sizes, which is quite important for further use. For this reason, there is a state standard (GOST R 51586-2000), which defines the classification of coal according to the size of the pieces. These sizes are sometimes referred to as coal grades so as not to be confused with grades, which will be discussed later.

Class name (abbreviation)	Size in mm
Slab (P)	From 100
Large (K)	50-100
Nut (O)	25-50
Small (M)	13-25
Seed (C)	6-13
Shtyb (Sh)	Up to 6

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

There are also mixed grades, 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. The mixture may consist, for example, of 95% seed and 5% cultivar, in which case the variety will be calledseed with a lump.

Class name (abbreviation)	Size in mm
Large with slab (PC)	From 50
Walnut with large (KO)	25-100
Small walnut (OM)	13-50
Small seed (MS)	6-25
Seed with a stone (SS)	Until 13
Small with seed and trout (MSH)	Up to 25
Walnut with small seeds and chips (OMSSh)	Up to 50

Classification of coal by grades

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

Usually all these characteristics are connected. The higher the carbon content of the coal and the lower the volatile matter, the more heat the fuel can provide. According to these characteristics, coal is divided into grades.

Brown coal (B)

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

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

Long Flame Coal (L)

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

Gas Coal (G)

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

Fat Charcoal (W)

This is already a fairly 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 volatilesubstances, which complicates the control of the combustion process, so this brand of coal is rarely used as a fuel. The main areas of its use are the production of building materials, activated carbons and other useful substances, as well as in the coke industry. Such coal is mined in the Osinovskoye, Baidaevskoye, Leninskoye and Tom-Usinkskoye deposits.

Coke Coal (C)

This is a very valuable type of coal due to its low prevalence. This grade produces very high quality coal coke, as the name implies. Such coal is formed at a sufficiently large depth (5500 m), where there is great pressure. The color of such coal is gray with a glassy sheen. It has a very uniform structure and a minimum 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 a fuel. Coking coal is mined in the Kuznetsk coal basin, in Anzhersky, Tom-Usinsky, Prokopyevsko-Kiselevsky and other areas.

Skinny Caking Coal (OS)

This brand of coal is not much different from coking coal: the content of carbon and inorganic impurities is approximately at the same level. Its main advantage is its high calorific value. It is 36 MJ / kg, so it is sometimes used as a fuel in power plants. But its main use is the coke industry. True, this coal is hardly coked, so it has to be used in a mixture withother types of coal. Such a mixture of several grades is called coal charge. The extraction of lean coal is mainly carried out in the Kuzbass, in the Kemerovo region and in the South Yakutsk coal basin.

Lean Coal (T)

This brand of coal received such a funny name because of the relatively thin layers with which it lies in the rock. This is due to 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 up to 40 MJ/kg. This leads to its use as a fuel, as well as in metallurgy, where extremely high temperatures are required in furnaces for melting metals. The main areas for the production of lean coal are the Aralichevsky, Baidayevsky and Kemerovo regions.

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 sheen. It also has high thermal stability and electrical conductivity. The combustion temperature of anthracite is quite high, so it can not be used as a 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, so it has not found use in coking, although even without this process it canreplace coke in some processes.

Other types of classifications

In addition to the grades presented above, there are many intermediate grades, such as coke fat (KZh), gas sintering (GS), long-flame gas (DG).

Also, coal of each brand can have different sizes of pieces. In this case, the letter denoting the grade is placed after the letter denoting the brand. For example, anthracite-walnut (AO), bold-slab (ZHP), coke seed (KS).

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