Wood has been used used as fuel by humans for a long time, but in order to ensure steady combustion, it is necessary to keep adding logs constantly; which is quite inconveniencing. With the development of the coal industry, people began to use more effective options that give more heat and burn longer. If the furnace is laid properly, a portion of coal which has been placed in the burner by evening will maintain a stable temperature all night. Would you like to know more? In this article we will consider different types of coal and their uses.
Process of formation of different types of coal
The entire process of coal formation can be divided into two main stages: the formation of peat and the actual process of coalification (the transformation of peat into coal). Peat is formed from plant remains of varying stages of decomposition on extensive water-covered spaces. When plants decompose, some of its parts rot completely to a gel-like state, while some other parts preserve their cellular structure. Their remains are accumulated on the bottom of water bodies, which gradually turn into swamps.
A necessary condition for the formation of peat is the absence of oxygen, which makes water convenient for this process due to its thickness. The decomposition of residues releases hydrogen sulphide, methane and, carbon dioxide, which contribute to solidification of residues, enabling the formation of peat.
But not all the peat get converted to coal. For the process of coalification, high pressure, temperature and a long period of time are needed. Depending on the availability of these conditions, formation of coal will or will not happen.
A long time ago, coal got formed from peat deposited by sedimentary rocks; the high pressure and temperature in the area then transformed the peat into lignite - this is the first stage of coalification.
In some areas that experienced earth movement, these lignite beds fell (some of the discovered deposits are at a depth of more than 6,000 meters), causing a rise in magma and volcanic eruptions in some areas.
High pressure, lack of oxygen and high temperatures are factors that contributed to the fact that moisture and natural gas in the lignite became less, forming more carbon. As water and gases were displaced, lignite turned into bituminous coal, and then, because of the presence of high temperature, into anthracite.
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Today, the amount of coal deposits is determined by plant residues. The oldest ones date back to the Carboniferous period (345-280m years ago). During this period, most of the coal basins of North America (the east and the center of the USA), center and west of Europe, southern Africa, China, India were formed. In Eurasia, most of the coal deposits were formed in the Permian period, some of the small coal basins in Europe date back to the Triassic period.
The increase in coal formation happened at the end of the Jurassic period and in Cretaceous; at this time, deposits were formed in east of Europe, Rocky Mountains of America, Indochina and in the center of Asia.
What are the different types of coal and their uses?
Coal is classified according to moisture, natural gases and carbon content. With an increase in the amount of carbon, its calorific value rises. The less moisture and volatile substances it contains (gases), the easier it can be stored and transported.
This is the coal of the first stage of coalification. The structure is fibrous and its color ranges from brown to black (higher quality). It is mostly used in power engineering (for thermal power plants). The use of this type of coal for heating private houses is rare, as it is difficult to store and has a low calorific value in conventional furnaces.
By means of distillation, lignite can be processed into a hydrocarbon fuel of liquid consistency. Residues of processed coal are used to produce soot. In addition, during the processing, mountain wax and hot gas are obtained. Mountain wax is used in paper, textile and woodworking industries.
Lignite is also used to produce a gas consisting of hydrogen, methane and carbon monoxide. Lignite is heated in gas generators at high temperatures (up to 1000 C) and the resulting fuel is processed into a synthetic gas, which serves as an analog of natural gas. Specialists in the mining of minerals invented a fairly effective method for extraction of this gas, which does not require direct extraction of coal; they drill a vertical hole and insert a pipe into the lignite deposits, through which heat is passed to increase the the temperature of the lignite. Accordingly, gas is discharged from another pipe, which is a product of the underground processing of lignite.
Another area where lignite is used is the production of high-quality gasoline by hydrogenation. This process is simple: coal is mixed with heavy oil and then combined with hydrogen at a high temperature (450C), with the help of a catalyst. As a result, liquid fractions of fuel and synthetic gas products are obtained as output. Then another hydrogenation process takes place, and as a result, high-quality gasoline is obtained.
Lignite is also used to produce semi-coke (this fuel is used in the production of phosphates, ferroalloys, calcium carbide).
Also, lignite is used in agriculture; the fact that it contains humic acids makes it good for fertilizing soil.
2. Subbituminous coal
It is black and has a less obvious fibrous structure, higher calorific value and less moisture content (30%) than lignite. When being transported, it is susceptible to crumbling and getting eroded outdoors. During combustion, it releases 5-6 kW/kg. It is used in power engineering, housing and communal services for heating.
3. Bituminous coal
This type of coal has the highest calorific value and does not lose its qualities during transportation or storage. It emits 7-9 kW/kg of heat during combustion. Some of its types are used for cooking.
This is a type of resin black coal. It has the highest content of hydrocarbon and is hard to ignite, but burns for a long time without soot; it also releases a large amount of heat (more than 9 kW/kg). Anthracite is most often used for heating.
Metallurgy currently uses about 13%, which is 717 million tons, of the world’s production of the best grades of coal. About 70% of steel in the world is smelted with its application.
The use of pulverized coal injection technology gains is very popular in large metallurgical enterprises. Natural gas has been fully replaced with coal dust. Non-coking coals are alternative to coke; this technology significantly increases the productivity of blast furnace, reducing the cost of finished products.
A significant part of anthracites is used in the production of thermoanthracite - carbon filler for the manufacture of cathode blocks for electrolyzers, which is extremely necessary in the aluminum industry. Anthracites are also used for the production of silicon carbide and aluminum carbide.
Coal anthracite, having its own special properties, is used as a filter for primary water purification, and is widely used in water treatment systems of energy and heat generating companies, oil refineries, chemical industries, metallurgical plants, and in a multi-stage cycle for preparing water from underground sources. Anthracite coal is also used in pressure filters for wastewater treatment of auxiliary and basic shops of metallurgical companies.
Now, you know about the major types of coal and their uses. We hope this information was interesting and useful to you.
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