Today, coal is one of the most necessary minerals.
This resource is formed naturally, has huge reserves and a lot of useful properties.
What is coal and what does it look like?
Construction of a mine is a very expensive investment, but over time all costs are fully recouped. When coal is mined, other resources also come to the surface.
There is a possibility of mining precious metals and rare earth elements, which can later be sold and receive additional profit.
Oil is practically the most precious resource and the main source of fuel today. However, not a single company or country that mines coal will neglect its extraction in the name of oil, because solid fuel is also of great importance and high value.
Formation of coal
Coal in nature is formed by changing surface topography. Tree branches, plants, leaves and other natural remains that have not had time to rot are saturated with moisture from the swamps, which is why they are converted into peat.
Next, seawater reaches the land, and when it leaves, it also leaves a layer of sediment. After the river makes its own adjustments, the ground becomes swamped, again forms or covers the soil. Therefore the composition coal depends greatly on age.
Hard coal is intermediate in age between brown, the youngest, and anthracite, the oldest.
Types of coal, their composition and properties
There are several types of coal:
- long flame;
- gas;
- fat;
- coke;
- low-caking;
- skinny.
Also common are species consisting of several, so-called mixed, having the properties of two groups.
Coal is distinguished by its black color, hard, layered, easily destructible structure, and has shiny inclusions. The combustible properties are quite high, since the material is used as fuel.
Let's consider physical characteristics:
- Density (or specific gravity) varies greatly (the maximum can reach 1500 kg/m³).
- The specific heat capacity is 1300 J/kg*K.
- Combustion temperature - 2100°C (1000°C during processing).
Coal deposits in Russia
About a third of the world's reserves are located on Russian territory.
Coal and oil shale deposits in Russia (click to enlarge)
The largest coal deposit in Russia is Elginskoye. It is located in the Yakutia region.
Reserves, according to approximate calculations, amount to more than 2 billion tons.
The terrain close to the Kuznetsk coal basin (Kuzbass) was severely damaged due to large-scale resource extraction operations.
The largest coal deposits in the world
Map of coal deposits in the world (click to enlarge)
In the United States, the most famous coal basin is the Illinois. The total reserves of deposits in this field amount to 365 billion tons.
Coal mining
In our time, hard coal is mined in three fundamental ways. Such as:
- career method;
- mining through adits;
- mining method.
The quarry mining method is used when coal seams lie on the surface, approximately one hundred meters deep or higher.
Quarries involve simply digging up the ground or sand pit from which mining is carried out; usually in such cases the coal seam is quite thick, which makes its extraction easier.
Adits mean wells with a large angle of inclination. All mined minerals are transported upward along it, without the need to use serious equipment or dig out a basin.
Typically, deposits in such places are thin and not buried particularly deep. Therefore, the method of mining through adits allows for rapid production without special costs.
Extraction through mines is the most common method of extracting minerals, at the same time the most productive, but at the same time dangerous.
The mines are drilled to great depths, reaching several hundred meters. However, this requires a permit confirming the justification for such large-scale work and evidence of the presence of deposits. Sometimes the mines can reach a kilometer or more in depth, and stretch for several kilometers in length, forming interconnected webs of corridors underground. In the 20th century, settlements even formed around the mines and small towns
, in which miners lived with their families.
It is precisely because of the mining conditions that work in the mines is considered very difficult and dangerous, because a huge number of times the mines collapsed, burying dozens or even hundreds of people working there.
Application of coal Hard coal is used in a wide variety of fields. It is widely used as solid fuel (main purpose), in metallurgy and in, plus many other components are made from it.
It is from coal that some aromatic substances, metals, chemicals are produced, and more than 360 other processed products are obtained.
In turn, the substances produced from it have a market value tens of times higher; the most expensive method is considered to be the method of processing coal into liquid fuel.
To produce 1 ton of liquid fuel, 2-3 tons of coal will need to be processed. All industrial waste obtained during processing is often used for the production of building materials.
Conclusion
There are many coal deposits on earth that are still being actively mined to this day. In biology lessons in the 5th grade and even earlier, in natural history lessons in the second grade, children are introduced to this concept. In this work, we briefly repeated the basic facts about coal - origin, formula, grades, chemical composition and use, extraction and more.
Coal is one of the most important resources widely used in industry. However, you should still be careful when disrupting the natural flow of substances, because development disrupts the relief and gradually depletes natural reserves.
The content of the article
FOSSIL COAL, combustible sedimentary rock of organic (plant) origin, consisting of carbon, hydrogen, oxygen, nitrogen and other minor components. Color varies from light brown to black, gloss - from matte to bright shiny. Usually, layering or banding is clearly expressed, which causes it to split into blocks or tabular masses. The density of coal ranges from less than 1 to ~1.7 g/cm 3 depending on the degree of change and compaction that it has undergone during the process of coal formation, as well as on the content of mineral components.
Coal formation.
Since the Devonian period, in ancient peat bogs, under anaerobic conditions (in a reducing environment without oxygen), organic matter (peat) was accumulated and preserved, from which fossil coals were formed. The primary peat deposit consisted of a mass of plant tissues ranging from completely decomposed (gelified) to well-preserved cellular structure. Under aerobic conditions, when plant remains were exposed to oxygen-enriched waters or in contact with the atmosphere, complete oxidation (decomposition) of organic matter occurred with the release of carbon dioxide and light hydrocarbons (methane, ethane, etc.), not accompanied by peat formation.
The transformation of peat into fossil coal, called carbonification, occurred over many millions of years and was accompanied by a concentration of carbon and a decrease in the content of the three main coal-forming elements - oxygen, nitrogen and hydrogen. The main factors in carbonization are temperature, pressure and time. In Russia, it is customary to distinguish the following stages of coalification: lignite (with an early substage - lignite), coal, anthracite and graphite. At the same time, there was a sequential formation of brown coals, hard coals, anthracite and graphite. In the USA, Canada, Germany, Great Britain and many other countries, it is generally accepted that in the process of coalification, lignites, subbituminous coals, bituminous coals, anthracite and graphite are formed from peat (which does not contradict the Russian classification).
Modern peat formation occurs on different scales within all continents except Antarctica. Large peat bogs are known in Canada, Russia, Ireland, Scotland and other countries.
Coal formation that took place in past eras varied in intensity, as well as in the conditions for the formation of primary peatlands. As now, in ancient times peat accumulated both in the interior of continents and on their outskirts. Climatic and tectonic factors played a major role. Intense coal formation occurred in eras with a warm and humid climate, the Carboniferous, Permian, Jurassic, Paleogene and Neogene, and weak - in the Devonian and Triassic. Tectonic pulsation fluctuations of the continental margins were accompanied by the accumulation of coal-bearing strata several kilometers thick, including up to 200–300 coal seams and interlayers. During marine transgressions, peat bogs were flooded, and sediments of various types, washed away from adjacent higher land areas, were deposited on top of the peat. mechanical composition. Then, during marine regression under conditions of land subsidence, bog formation resumed and peat accumulated. As a result of repeated repetition of these processes, layered sedimentary strata were formed. The thickness of such coal-bearing strata ranges from several tens of meters to 3000 m or more (for example, in the Appalachian basin over 2000 m, in the Ruhr basin - 2500-3000 m, in the Upper Silesian basin - 2500-6000 m, in the Donetsk basin - up to 18,000 m).
Age of coal.
The study of plant remains preserved in coals made it possible to trace the evolution of coal formation - from more ancient coal seams formed by lower plants, to young coals and modern peat deposits, characterized by a wide variety of higher peat-forming plants. The age of a coal seam and associated rocks is determined by determining the species composition of plant remains contained in the coal.
The oldest coal deposits were formed in the Devonian period, approximately 350 million years ago. The most intense coal formation occurred in the range from 345 to 280 million years ago, and therefore this period was called the Carboniferous. It includes most of the coal basins in the eastern and central regions of the United States, Western and Eastern Europe, China, India and South Africa. During the Permian period (280–235 million years), intensive coal formation occurred in Eurasia (coal basins of Southern China, Kuznetsk and Pechora in Russia). Small coal deposits in Europe were formed during the Triassic period. A new surge in the intensity of coal formation occurred at the beginning of the Jurassic period (185–132 million years). Approximately 100–65 million years ago, during the Cretaceous period, coal deposits of the Rocky Mountains of the USA, Eastern Europe, Central Asia and Indochina were formed. During the Tertiary period, approximately 50 million years ago and later, deposits of mainly brown coal arose in various areas of the United States (in the northern Great Plains, northern Pacific coast and coastal areas of the Gulf of Mexico), in Japan, New Zealand and South America, and also in Western Europe. In Europe and North America, peat formation occurred during warm interglacial periods and postglacial periods.
Occurrence conditions.
As a result of movements of the earth's crust, during which there was a change in the relative position of land and sea, thick strata of coal-bearing rocks experienced uplift and folding. Over time, the uplifted parts of the strata (anticlines) were destroyed by erosion, and the downhill parts (synclines) were preserved in wide, shallow basins where the coal is at a depth of at least 900 m from the surface. For example, in the USA in the Rocky Mountains and in the north of the Pacific coast, coal deposits occur mainly at depths of 1200–1850 m and in exceptional cases reach a depth of 6100 m. In the UK, Belgium, Germany, Ukraine and Russia (Donbass) coal in some In some places it is mined from a depth of more than 1200 m. Coal seams that continue to a depth of 5–8 km are currently unprofitable to develop.
Coal seams.
The thickness of individual coal seams ranges from 10 cm to 240 m (as, for example, in the state of Victoria in Australia). Strata 120 m thick occur in China; 60 m – in the USA (Wyoming) and Germany; 30 m – in the USA (Wyoming), Canada (British Columbia) and other areas. Such thick layers usually occupy a small area. The most common seams are 90–240 cm thick. They extend over large areas and are associated with significant reserves of mined coal. The strata of coal-bearing rocks contain from two to three to several dozen coal seams. For example, in the United States, 117 coal seams were identified in a detailed study of the coal-bearing strata in West Virginia.
Classifications.
Fossil coals are assessed according to three parameters: the degree of metamorphism, which is defined as the degree of change in the carbon content of coal; quality, assessed by the content of the combustible component, the amount of ash-forming substances, the content of moisture, sulfur and other elements and the composition of fossil coal-forming plants, chemical transformations that occurred during the process of coalification.
Stages of metamorphism.
The main classes of coal (accepted in the USA and some European countries) in increasing stages of metamorphism include lignite (in Russia lignite is a loose term), subbituminous coal, bituminous coal and anthracite. Differences in metamorphic stage are determined on the basis of chemical analyzes indicating a consistent decrease in moisture and volatile matter, as well as an increase in carbon content. The strength of coal during transportation and storage, as well as combustion activity, depend on the relative amount of moisture, volatile substances, carbon and calorific value (heat of combustion). Large consumers it is necessary to know the properties of various coals and the comparative costs of mining and transporting different categories of coal in order to decide which category best suits their needs.
Lignite
has a distinct fibrous structure of wood, most often light brown and brown, less often black. Its properties and composition differ from real brown coal, which is found mainly in Canada and Europe. Compared to peat, lignite contains less water and has a higher calorific value. Most young (recently formed) coals are represented by lignite, but where they have undergone high blood pressure or intense thermal exposure, their quality is higher.
Subbituminous coal
characterized by a black color, little or sometimes no fibrous woody structure, contains less water and volatile substances compared to lignite and has a higher calorific value. Subbituminous coal easily erodes in air and crumbles during transportation.
Bituminous coal
It is distinguished by its black color, relatively low moisture content and the highest calorific value among all coals. In most highly developed countries, bituminous coal is used in industry in larger quantities than coal of other categories, since its quality does not decrease during transportation and it has a high calorific value; In addition, some varieties of bituminous coal are used to produce metallurgical coke.
Anthracite
characterized by a very high carbon content, low humidity and low yield of volatile components. It has a pitch-black color and does not produce soot when burned. Anthracite requires more heat and effort to ignite, but once ignited, it produces a steady, clean, hot, blue flame and burns longer than coal of lower stages of metamorphism. Anthracite was widely used to heat homes until the 1920s, and was later replaced by oil and natural gas.
Grade.
During the process of peat formation, various elements enter coal, most of which are concentrated in the ash. When coal burns, sulfur and some volatile elements are released into the atmosphere. The relative content of sulfur and ash-forming substances in coal determines the grade of coal ( see table). High-grade coal has less sulfur and less ash than low-grade coal, so it is in greater demand and is more expensive.
The grade is determined by the quality of the coal, and not by the stage of coalification, which characterizes the degree of its change. Coal at a low stage of coalification, such as lignite, can be of high grade, and coal at a high stage, such as anthracite, can be of low grade.
The amount of ash-forming substances (mineral component) contained in coal can vary from 1 to 50 weight percent, but for most coals used in industry, it is 2–12%. Ash-forming substances add additional weight, which increases the cost of transporting coal. In addition, some of the ash enters the air and pollutes it. Some ash components sinter to form slag on the grates and impede combustion.
Although the sulfur content of coals can vary from 1 to 10%, most coals used in industry have a sulfur content of 1–5%. However, sulfur impurities are undesirable even in small quantities. When coal is burned, most of the sulfur is released into the atmosphere in the form of harmful pollutants called sulfur oxides. In addition, sulfur impurities have a negative impact on the quality of coke and steel produced using such coke. Combining with oxygen and water, sulfur forms sulfuric acid, which corrodes the mechanisms of coal-fired thermal power plants. Sulfuric acid is present in mine waters seeping from waste workings, in mine and overburden dumps, polluting environment and preventing the development of vegetation.
Resources.
Total world coal resources, i.e. the amount of coal that was in the depths before it began to be mined is estimated at a total value of more than 15,000 billion tons; Of these, approximately half are available for mining. The bulk of the world's coal resources are in Asia and are concentrated primarily in Russia and China, which are the largest coal producers. North America and Western Europe occupy second and third places, respectively, in terms of coal resources and are also very large producers.
COAL MINING
Coal is mined by open-pit (quarries) and underground (mines and adits) methods. The choice of mining method depends mainly on the location of the coal seam relative to the earth's surface. Open pit mining is usually carried out at a depth of no more than 100 m. Depending on the direction of approach to the coal seam, there are methods of opening the deposit: adits (horizontal underground workings) and vertical or inclined mine shafts. Sometimes coal is mined from deposits that extend far out to sea. Subsea coal mining occurs in Canada, Chile, Japan and the UK.
UNDERGROUND DEVELOPMENT
Opening of the deposit by adits.
If the formation comes out to the surface on the mountainside, then a horizontal tunnel called an adit is drawn to it. The adit, as a rule, is driven along the dip (slope) of the formation. If the seam is almost horizontal, then development begins slightly below its level and, having already reached the seam, they follow its dip. If the thickness of the formation is small, then part of its soil (rocks lying below the formation) or roof is removed.
To determine the lowest and most convenient entry point into the adit, small wells are drilled and short adits are made, in which surveyor measurements are carried out. The sides and top of the adit mouth are concreted, especially near the surface. If the adit is designed to last for several years, then they are limited to installing wooden support.
Inclined workings.
Coal seams often lie at an angle. The dip angle of the formation is sometimes more than 90° (in the case of an overturned bedding), then the base of the formation becomes its roof. Such seams are often exploited in the coal fields of France.
In cases where the formation drops steeply from the point of exit to the day surface, inclined underground workings are carried out. If an economically viable formation does not have a convenient outlet, then mining is carried out along the strike of the rocks. As a rule, opening a deposit with inclined workings is economically feasible with a length of no more than 800 m.
Mine shafts.
It is most convenient to open many coal deposits using a vertical opening - a mine shaft. The cost of constructing and operating a mine shaft is higher than an adit, but when underground watercourses cross the coal seam in different directions, the total cost of operating the mine may be lower. This method allows for more rational planning of mining operations; In addition, the mine shaft lasts longer than scattered adits. However, ventilation and drainage are more expensive, and there are costs associated with lifting coal.
Opening up coal seams with a mine shaft is used when their depth is more than 45 m. In the USA, the depth of mine shafts rarely exceeds 300 m, in other coal-mining countries it sometimes reaches 1200 m, and in India and South Africa mines with a depth of more than 4 km are known.
Underground mining systems.
In underground mining of coal deposits, a room-and-pillar system and longwall mining, or longwall mining, are used. In the United States, room-and-pillar mining is more common (about 65% of all underground coal mining), since most of the developed coal seams, especially bituminous coals, are characterized by significant thickness. In the case of thin, heavily disturbed and deep-lying formations, the long stope method is preferable. Room and pillar development is not very economical; it typically recovers only 50% of the available coal. Longwall mining is safer and allows you to extract up to 80% of coal and distribute it more evenly.
Room and pillar development system.
With such a system, a number of chambers pass through the formation, separated by pillars supporting the roof of the formation. After the working faces of a given area are moved in accordance with the plan, the miners either leave this area or carry out a reverse excavation, excavating pillars with the collapse of the roof behind them. In some cases, during preparatory tunneling of chambers, only 10–15% of coal is removed.
The formation is usually broken up into large blocks by primary and secondary groups of chambers, sometimes called a face drift, across which smaller groups of chambers (sections and end drifts) run. Areas are called the actual production front, since the pillars of the main and secondary groups of chambers are rarely removed.
Coal pillars are left in place for an indefinite period in cases where the need for their preservation is dictated by the condition of the roof and soil of the seam or environmental regulations. Mining supervisory authorities do not encourage such a system, since it results in large losses of coal.
In some cases, coal pillars, under the weight of their own enormous weight and the weight of the roof, are pressed into the softening clay soil of the seam, swelling it. If the soil and roof are made of hard rock, then the settlement of the roof can lead to crushing of the pillars with their spalling into chambers. Sometimes pillars in this state are destroyed instantly with the release of great mechanical energy (rock burst). Mass destruction of pillars rarely occurs, but once it begins, it is difficult to stop. Such a destructive process can cover a large area and even lead to the complete collapse of the mine, in which people, coal, materials and equipment remain buried. True, modern technical standards on pillars generally guarantee the prevention of their massive destruction.
The extraction of inter-chamber pillars - the second stage of excavation - is carried out in short runs in the opposite direction. If carried out correctly, there is no danger to the lives of miners, losses of coal and materials are insignificant and the cost of production is reduced. True, if the excavation of pillars is carried out over a large area, then subsidence of the thickness is possible rocks over the mine field.
Longwall mining.
With this mining system, a large block of coal is excavated by moving equipment along a wide surface of the face under a continuous line of support sections. The pillars are not left. Excavation is carried out either forward or reverse. In both cases, the working space (at the face) is secured with steel sections along the entire length and the support is removed after coal is removed along the entire excavation panel. During the excavation process, the roof of the formation collapses behind the mechanical support.
Initially, longwalls were used to mine shallow seams or disturbed seams at depths of more than 300 m, especially in European coal mines. In the case of moderately deep horizontal layers, preference was given to the room-and-pillar development system. Then in the United States, longwall mining began to be widely used for moderately deep horizontal seams, since it is safer for miners and allows for a 4-5 times increase in coal production.
Anthracite mining.
In the case of steeply dipping anthracite seams, horizontal, often winding, haulage and ventilation workings are carried out and underground workings called coal slopes are brought directly to the seam. After breaking, anthracite rolls down in the direction of the formation's fall by gravity. At the narrow end of the coal slope, such an amount of coal is left so that its surface is at the level necessary for the work of the blasting miners. Miners work by standing on the surface of crushed coal, part of which is removed each time as the face moves forward. In this way, the surface of the loosened coal is maintained at a convenient distance from the face at all times. Breaking is carried out using pneumatic drilling hammers or explosive methods. The coal is so hard that it crumbles very little when passing through the magazine (storage) zone in the chamber. With a slight dip (slope) of the seam, miners work on a bed of hard rock. The steel chute through which the coal “flows” is equipped in the lower part with a section suspended on hinges, when lifted, the flow of coal is interrupted. Where, due to the steepness of the seam, crushed coal flows down too quickly, racks are fixed in the soil and roof near the funnel-shaped mouth of the coal mine to restrain the pressure. If the layer is not steep enough, then the steel trench can be brought up almost to the working surface. Previously, coal was manually pushed down; now vibrating and other conveyors are used.
With a low slope of the seam, where coal does not flow by gravity, miners stand on the ground and a storage area is not needed. If magazine storage is necessary, then passages with wooden supports are made on both sides of the chamber. One of them is intended for people, and the other serves as a return ventilation duct and emergency exit. When the chamber is completely mined out, the pillars are removed using the drilling and blasting method, in which the coal rolls into the lower part of the chamber.
Sometimes coal is torn from the face without drilling and blasting, after which further exploitation of the seam is impossible. In such cases, a new working is carried out to the face through another chamber or at a higher height. The pillars are excavated without breaking, as they themselves collapse under the pressure of the roof. However, at the same time, the roof rock also collapses, sometimes in such quantities that the operation becomes unprofitable, since most of the mined coal must go to a washing plant, where the rock is separated manually or mechanically.
Mining of bituminous coal.
Underground mining of soft and loose bituminous and sub-bituminous coal deposits can be carried out using a continuous system with long longwall faces. The drilling and blasting method is often used for breaking. Each of them provides for a certain cycle of operations of excavation, loading, hauling of coal and fastening the roof. Once upon a time, the first operation was the bottom notch, performed with hand picks along the entire width of the face. Currently, cutting is done by machines, then holes are drilled in the face to place explosives (explosives) in them.
Solid notch.
A powerful mining machine removes coal from the mass on the surface of the face, dumps it on the soil of the working horizon for loading by another machine, or unloads it directly into mine cars, which move the coal to the loading site onto a conveyor. After the excavation has been completed over the entire area, the combine moves to the new face surface; the former bottomhole space is secured with anchor rods. Sometimes additional support is used if the condition of the formation roof requires it. This cycle is repeated four to 12 times per work shift, depending on the efficiency of the overall production system. A typical continuous excavation site is serviced primarily by one shearer, one bolting machine and two trolleys. An extended version is also possible, in which two combines, one or two bolting machines and three or four trolleys operate on the site. This method is very productive and often produces 2000–2500 tons of coal per shift.
Longwall mining.
In a mechanized longwall system, a mining machine with a working body (bar, drum) moves along a scraper conveyor along the face. The crushed coal is loaded by the combine ploughshare directly onto the conveyor, which transports it through the loader to the main conveyor system. When making the next cut, the face conveyor is pressed against the coal mass by hydraulic jacks attached to the steel supports of the mechanical support with an overlap. When the pressure pressing the support slabs to the seam roof drops, the jacks move to the moving face conveyor line and are pressed against the roof in a new place, and the loose roof behind the slab collapses. This sequence of operations is repeated in forward and reverse directions along the face, which can have a length of up to 300 m. The entire excavation panel of a longwall with a length of up to 3000 m can be completely developed in six months. During longwall mining, on average, up to 5,000 tons of coal are mined per shift. Such a system can operate using software control, requiring only two to three operators per face.
Drill and blast excavation.
The sequence of operations consists of the excavation itself (creating a cut, drilling and blasting) and the subsequent operations of loading, hauling away coal and fastening the roof. First, the shearer makes a cut across the face area with a width of approx. 50 cm to a depth of 2–2.7 m to create a free surface. The cut can be made at the top, bottom, middle or side of the face; Any paired combinations of these options are also possible. Typically, cutting, drilling, blasting, coal loading and roofing are carried out in parallel in at least five faces. Individual operations are repeated cyclically in the faces of the site.
OPEN DEVELOPMENT
In cases where the coal seam lies shallow and is not covered by a thick layer of waste rock, mining is carried out using an open pit method. After removing the overburden, drilling and blasting of coal begins and loading it into dump trucks or railway cars.
Stripping works.
First, drilling is carried out with core selection to analyze the hardness of the cap rock, its layering, fracturing and degree of weathering. If the top layer of rock is thin and loose, then stripping operations are carried out with bulldozers and scrapers; Mechanical shovels, draglines and bucket wheel excavators are used in combination with smaller types of equipment to remove large quantities of overburden and coal. Drilling and blasting is generally required when there is a thick layer of hard cap rock or narrow and steep openings 20–30 m wide are required.
Capital trench.
If the relief is flat and the coal seam does not reach the surface, then the opening of the deposit is carried out by an excavator, laying a capital trench approximately wide to the coal horizon. 20 m, which can be flanking (along one side of the quarry contour) or central. The overburden is placed in a dump along the perimeter of the quarry. Sometimes the coal covered with the first overburden is simply left, since its small amount does not justify the cost of re-removing the overburden. In other cases, the overburden, as it is unloaded by a powerful excavator, is moved and leveled over a larger area by bulldozers, scrapers and small mechanical shovels to facilitate its further removal. Since a mechanical shovel, dragline or rotary excavator stands at a distance of at least 7–8 m from the place where the bucket picks up the overburden loosened by the explosion, and people are not allowed there, the bench of such a capital trench can be almost vertical. This requires a special technique of explosive breaking, in which the rock is not thrown down by an explosion, but is loosened in such a way that it can be easily removed by an excavator bucket. To do this, explosive charges are placed in wells drilled vertically almost to the coal horizon or horizontally 1–1.5 m above the coal seam.
To open deep-lying layers, you need very powerful equipment, otherwise the work will be unprofitable. Diesel and electric shovels of any required size are used, which can scoop 225 tons of overburden and move them over a distance of up to 130 m. Draglines are used to work on steep bench slopes leading to a flat coal seam. The largest of them have a bucket volume of almost 120 m3 and move the rock on a boom over a distance of approx. 170 m at the height of a 14-story building. Giant excavators are capable of moving up to 2,700 m 3 of rock per hour over a distance of up to 150 m. Such machines can work on ledges more than 30 m high.
Stripping operations in mountainous areas.
On mountain slopes, the trench that exposes the coal seam usually follows the profile of the slope. In this case, the same machines are used as mentioned above. Another possible way– removal of the top of the mountain with laying of overburden in the valley.
Transport trenching.
When developing bituminous coal deposits, trenches are usually passed using a non-transport method, in which all the rock from the trench is laid out by an excavator directly onto the sides. When extracting anthracite, a transport method is more often used, in which the overburden is loaded into railway cars or dump trucks and moved a considerable distance from the trench - to old quarries or to completely mined-out areas of the same deposit. This method allows you to open several layers of coal lying one above the other in one operation, performed from one place. It makes it possible to cost-effectively develop formations located at depths of up to several hundred meters.
Reclamation of a spent quarry.
After mining, the entire quarry is a series of long trenches, and on the surface there is often a subsoil layer randomly mixed with rock (the soil layer is stored separately for subsequent restoration of vegetation). Quarries often form reservoirs with orange or rusty (due to high acidity) water, which must be isolated from nearby rivers and lakes. With careful planning, the soil cover of fully mined quarries can be restored, albeit at significant cost. In some areas, after reclamation, the earth's surface may be in even better condition than before stripping operations, and can be used for growing crops, grazing livestock, planting forests, creating a recreation area or a reserve for wild animals and birds.
Auger excavation.
In hilly areas, where thick overburden makes it economically unprofitable to mine the formation from the surface, auger miners are used. Huge (up to 2 m in diameter) drills of such machines (single, paired or triple) cut into the ledge along the dip of the formation. The broken coal is carried by an auger and poured onto a conveyor that moves it to dump trucks. This method can remove up to 25 tons of coal per minute. The choice of miner depends on the length of the coal seam, its angle of incidence and the strength of the surrounding rock.
Currently, remotely controlled harvesters with a continuous mining cutter head, a laser guide and a continuously running transport conveyor exist and are in use. The combine is controlled via a computer by an operator located outside the underground mine.
HAZARDS ASSOCIATED WITH COAL MINING
Coal mining is associated with such dangerous factors as the collapse of the roof and walls of mine workings, coal dust, the release of methane and other harmful gases generated during the mining process. The impact of many of the hazardous factors can be eliminated or significantly reduced by strictly complying with mining standards, labor protection requirements and safety regulations.
Explosion hazard.
Various gases are released in coal seams: most often methane (CH 4), less often hydrogen sulfide (H 2 S) and carbon dioxide (CO 2). These gases rarely cause death or serious illness. The exception is explosive methane, although its explosions are quite rare. To prevent explosions of methane and coal dust in coal mines, it is necessary to continuously monitor the methane content in the air and ensure the removal of dust from mine ventilation ducts. A mixture of air with methane and coal dust, which is highly flammable, is also explosive. An explosion releases a lot of heat and produces highly toxic carbon monoxide (CO). In addition, due to combustion, the oxygen content in the mine air decreases and excess carbon dioxide is formed. All this leads to accidents, sometimes fatal.
Fire hazard.
Coal, especially with a high content of volatile components, ignites quite easily, even if it is still in the seam. When it burns, it produces carbon oxides, gaseous sulfur compounds and flammable gaseous hydrocarbons. Due to the intense heat of a fire (and exposure to water, which is sometimes used in fire extinguishing systems), the roofing rocks crack and the roof collapses. Such fires can lead to death, mainly due to roof collapse, asphyxiation and explosions of the resulting gases. Currently, special fire prevention systems are installed in the main ventilation ducts underground, consisting of carbon monoxide detectors or temperature sensors connected to a computer through a network covering all underground workings. This system makes it possible to detect a fire at a very early stage. In exhausted mines, coal residues can burn for years and sometimes even require the evacuation of residents of adjacent settlements.
Occupational diseases.
Coal miners are more likely than others to suffer from respiratory diseases associated with inhalation of coal dust. Among miners who worked 15–20 years underground, pneumoconiosis (anthracosis, or “black lung,” silicosis, etc.) and pulmonary emphysema are common. Pulmonary silicosis, caused by inhaling silica particles, is more common among miners working in anthracite mines. Statistical research occupational diseases miners were carried out in the UK, where a model of the influence of hazardous factors was developed. As a result of compliance with the established norms for dust content in the air of coal mines (no more than 2 mg per 1 m 3 of air and no more than 5% SiO 2), the number of deaths and cases of complete disability of miners is reduced to a minimum. In Russia, standards for various harmful factors have been developed and put into effect long ago.
Miners also experience nystagmus (convulsive twitching of the eyeball associated with damage to the central nervous system) and some fungal diseases.
Environmental consequences.
Underground mining can cause subsidence of the earth's surface, which can be prevented by selectively removing coal and filling the openings with waste rock and other materials. Many countries have laws and federal programs for the reclamation of the area after mining operations, technologies have been developed for filling the mined-out space with household and construction waste.
If mining operations do not comply with mining regulations or safety requirements, undesirable consequences such as underground fires, fires in dumps, contamination of watersheds with water containing acids, metals or suspended solids, and landslides of unstable slopes are possible. Many countries, including the United States, have a number of laws covering almost all aspects of coal mining and providing for continuous monitoring during mining operations to ensure that there is no possibility of undesirable environmental consequences.
COAL ENRICHMENT
Sorting by size.
The mined coal is sent to a coal processing plant, where it is sorted by size and enriched. Commercial (enriched) coal is transported to loading points for shipment to consumers. Raw (unenriched) coal is first screened - sifted through vibrating screens with several sieves of different mesh sizes, then cleaned and enriched. There are known classifications of coal by size, for example, bituminous coal - “oversized” (with a diameter of 12 cm or more), “egg” (4 cm), “nut” (2 cm), “peas” (1 cm) and “fines”; anthracite - “stove” (6 cm), “peas” (1 cm), “grain” (0.5 cm), “rice” (less than 0.5 cm) and “dust”. Longwall mining usually produces finer run-of-mine coal than continuous mining.
Impurities and inclusions.
Coal contains microscopic, practically inseparable mineral impurities (associated with coal-forming plants), as well as inclusions that are easily removed by crushing and subsequent enrichment.
Lenticular inclusions form pyrite (FeS 2), marcasite (also FeS 2), lead carbonate (PbCO 3) and zinc sulfide (ZnS). Inclusions may also appear as thin layers or fill cracks and crush zones that run at an angle to the coal seam. The third type of inclusion consists mainly of sandstone, shale and calcite (CaCO 3). Coal mined in underground mines often contains impurities from the mine soil and roof rocks, which the miner is required to remove at all (except steeply located) workplaces.
Wet enrichment.
The most common enrichment systems are based on differences in the density of pure coal (1.4 g/cm3 or less), which is almost always lighter than impurities (more than 2.0 g/cm3) and therefore remains near the surface of intensively stirred water, while heavier impurities settle. This process is carried out in jigs or other gravity enrichment devices that process mixtures of intermediate densities.
With the advent of improved processing equipment, the difficulties of sorting by size have been significantly reduced. Aqueous suspensions of sand or iron oxides with a density intermediate between those of coal and impurities provide more efficient enrichment than pure water. Sorting by size, although a labor-intensive operation, is always necessary; Often, each size gradation has its own beneficiation machine.
Enrichment in a jigging machine.
In a jigging machine, water rises through a sieve onto which coal slowly flows. Commercial coal is carried away by the stream. The more contaminated material located below goes to the dump after unloading. The heaviest impurities, mainly fine pyrite, fall through the sieve holes into a collection container and are mechanically discharged from it.
Sand separation.
In cases where sand is used to form a heavy suspension, enrichment is carried out in a large stationary separator cone, the rotating blades of which drive water with sand and coal (coal size 0.6 cm or more). Commercial coal is collected in the upper part of the cone, and contaminated coal is lowered into the lower cylinder, where it is periodically unloaded along the outlet tray. The sand fraction is separated by wet screening for reuse in the plant.
Enrichment in a difficult environment.
This is the most common method of coal preparation. An aqueous suspension of magnetite powder with a density necessary for the enrichment of coal with a particle size of 0.6 cm or more is used as a heavy medium. Commercial coal appears on the surface and is discharged through a threshold device or transported by a conveyor belt, the waste is unloaded from the bottom of the installation. Magnetite is separated by wet screening and removed from the water by magnetic separators. Commercial coal is dried on vibrating screens and unloaded onto a belt conveyor.
Cyclone with heavy environment.
In a cyclone, enrichment is carried out due to centrifugal forces exceeding the normal acceleration of gravity. In this case, commercial coal is collected at the top, waste – at the bottom. Magnetite is captured in the same way as described above. Coal of different sizes is enriched in cyclones of different diameters.
Concentration table
– a corrugated inclined plane performing a rapid back-and-forth movement, on top of which water flows, carrying coal (with a particle size of 0.6 cm or less). The cleaner coal easily overcomes the corrugation ridges and is quickly separated from the gangue, which moves laterally along the chute and collects at the periphery of the table. Impurities that do not contain coal (pyrite, calcite, etc.) are concentrated in an even more distant area. There are various modifications and more complex versions of concentration tables for the enrichment of coals that require special processing.
Froth flotation.
In this method, used for beneficiation of fine coal, coal particles treated with a hydrophobic flotation reagent are captured by foam air bubbles and float to the surface. Waste hydrophilic rock settles to the bottom.
Separation from water is carried out by screening coarse coal, centrifuging medium-sized coal and filtering or drying fine coal.
Use of coal.
In the past, coal was used mainly for heating homes and in the furnaces of steam locomotives. Its use has now increased for power generation as well as for coke production in the steel industry. From the volatile substances released from coal during the production of coke, coal tar, light oils, chemicals, gas, etc. are obtained. These components serve as the basis for the manufacture of a large number of different substances, including drugs, preservatives, dyes, paint thinners, nylon, ink, explosives, fertilizers, insecticides and pesticides.
Methods are being developed to convert coal into flammable gases underground without extracting it (underground gasification). The possibility of generating electricity through chemical reactions using coal is also of significant interest.
FUEL.
Literature: Bondarenko A. D., Parshchikov A. M. Technology
coal industry
. Kyiv, 1978 Burchakov A. S. et al.
. M., 1982 Coal reserves of the world
. M., 1983 Kiyashko I. A. Underground Mining Processes
Coal is a sedimentary rock that forms in the earth's formation. Coal is an excellent fuel. It is believed that this is the most ancient type of fuel that our distant ancestors used.
How is coal formed?
To form coal, a huge amount of plant matter is needed. And it is better if the plants accumulate in one place and do not have time to decompose completely. The ideal place for this is swamps. The water in them is poor in oxygen, which prevents the life of bacteria.
Plant matter accumulates in swamps. Without having time to completely rot, it is compressed by subsequent soil deposits. This is how peat is obtained - the source material for coal. The following layers of soil seem to seal the peat in the ground. As a result, it is completely deprived of oxygen and water and turns into a coal seam. This process is long. Thus, most of the modern coal reserves were formed in the Paleozoic era, i.e. more than 300 million years ago.
Characteristics and types of coal
(Brown coal)
The chemical composition of coal depends on its age.
The youngest species - brown coal. It lies at a depth of about 1 km. There is still a lot of water in it - about 43%. Contains a large amount of volatile substances. It ignites and burns well, but produces little heat.
Hard coal is a sort of “middle peasant” in this classification. It lies at depths of up to 3 km. Since the pressure of the upper layers is greater, the water content in coal is less - about 12%, volatile substances - up to 32%, but carbon contains from 75% to 95%. It is also flammable, but burns better. And due to the small amount of moisture it gives more heat.
Anthracite- an older breed. It lies at depths of about 5 km. It contains more carbon and virtually no moisture. Anthracite is a solid fuel and does not ignite well, but the specific heat of combustion is the highest - up to 7400 kcal/kg.
(Anthracite coal)
However, anthracite is not the final stage of transformation of organic matter. When exposed to more severe conditions, coal transforms into shuntite. At higher temperatures, graphite is obtained. And under ultra-high pressure, coal turns into diamond. All these substances - from plants to diamonds - are made of carbon, only the molecular structure is different.
In addition to the main “ingredients,” coal often includes various “rocks.” These are impurities that do not burn, but form slag. Coal also contains sulfur, and its content is determined by the place where coal is formed. When burned, it reacts with oxygen and forms sulfuric acid. The less impurities in the composition of coal, the higher its grade is valued.
Coal deposit
The location of hard coal is called a coal basin. There are over 3.6 thousand coal basins known in the world. Their area occupies about 15% of the earth's land area. Most large percentage deposits of the world's coal reserves in the USA - 23%. In second place is Russia, 13%. China closes the top three countries with 11%. The largest coal deposits in the world are located in the USA. This is the Appalachian coal basin, whose reserves exceed 1,600 billion tons.
In Russia, the largest coal basin is Kuznetsk, in the Kemerovo region. Kuzbass reserves amount to 640 billion tons.
The development of deposits in Yakutia (Elginskoye) and Tyva (Elegestskoye) is promising.
Coal mining
Depending on the depth of coal occurrence, either closed or open mining methods are used.
Closed or underground mining method. For this method, mine shafts and adits are built. Mine shafts are built if the depth of coal is 45 meters or higher. A horizontal tunnel leads from it - an adit.
There are 2 closed mining systems: room and pillar mining and longwall mining. The first system is less economical. It is used only in cases where the discovered layers are thick. The second system is much safer and more practical. It allows you to extract up to 80% of the rock and evenly deliver coal to the surface.
The open method is used when the coal lies shallow. To begin with, they analyze the hardness of the soil, determine the degree of weathering of the soil and the layering of the covering layer. If the soil above the coal seams is soft, the use of bulldozers and scrapers is sufficient. If the upper layer is thick, then excavators and draglines are brought in. The thick layer of hard rock lying above the coal is blasted.
It is precisely because of the mining conditions that work in the mines is considered very difficult and dangerous, because a huge number of times the mines collapsed, burying dozens or even hundreds of people working there.
The area of use of coal is simply enormous.
Sulfur, vanadium, germanium, zinc, and lead are extracted from coal.
Coal itself is an excellent fuel.
Used in metallurgy for iron smelting, in the production of cast iron and steel.
The ash obtained after burning coal is used in the production of building materials.
From coal, after special processing, benzene and xylene are obtained, which are used in the production of varnishes, paints, solvents, and linoleum.
By liquefying coal, first-class liquid fuel is obtained.
Coal is the raw material for the production of graphite. As well as naphthalene and a number of other aromatic compounds.
As a result chemical treatment Today, more than 400 types of industrial products are produced from coal.
Coal mining is complex technological process, which requires a lot of resources and equipment. It is used in industry, for agricultural needs, and for electricity production. It has a very high value in the world; the fossil is called black gold, hard oil. What does coal mining and processing look like, and how did this industry develop in countries from antiquity to the present day?
The coal industry began to develop in antiquity. The first countries that began to use it as fuel are Greece and China. Most often it was used for heating premises, and later for smelting metals. 3000 years ago in China they realized that its combustion is much more efficient than obtaining heat from wood and other raw materials. In 315, the first person to study its properties was the scientist Theophrastus, who gave it a telling name - anthrax, which translated from Greek meant “burning stone”.
There have been many theories about the origin of this fossil fuel. Some believed that it was formed as a result of exposure to high temperatures during a volcanic eruption. The first deposits were found precisely in their vicinity - near tectonic faults, where the deposits were closest to the ground. Given its flammable properties, some scientists have suggested that it is solidified oil.
Subsequently, scientists determined that coal is of plant origin; they were even able to establish which tree species predominated in a particular fossil layer.
We found coal by accident; during the weathering and collapse of rocks, pieces of a strange material appeared on the surface, which was black in color and shimmered in the sun. It was mined by hand, using primitive technology. Children also collected pieces on the coasts, especially after high tides and storms. They began to produce it using the mine method only in 1113, but even then production was far from modern times. Coal activity was considered one of the most dangerous; the lower strata of the population worked in the mines, receiving mere pittance.
The most extensive use of coal was in blast furnaces: in forges, in metal processing, in brick factories. It was valued because of its heat capacity during combustion; with its help it was possible to maintain a high temperature for a long time.
With the advent of steam engines, this fuel became part of propulsion systems on ships, in cars and other equipment operating on this principle. Nowadays, not only people are involved in mining, but also a huge amount of equipment, and the amount of raw materials that is produced annually is billions of tons.
The first data on the search for coal deposits for industrial use date back to 1491, when the Grand Duke of Moscow Ivan III organized expeditions to the mountain ranges. He chose the Pechora region, one of the largest coal mines in Russia today.
The most large-scale development of coal mines took place under Peter the Great; he initiated the creation of mines in the Urals, Donbass, Kuznetsk, the Far East and in the vicinity of Moscow. He spared no expense on financing mining industry, sought to introduce new technologies that made people's work easier and increased output.
During the Soviet era, fossil fuel extraction played a special role. The workers were highly valued, even an all-Union holiday was introduced - Miner's Day - to pay tribute to their difficult and dangerous work. Coal was called the “bread of industry”; it was already used to generate energy at thermal power plants.
Now the coal mining industry has reached great heights, but many countries, along with the introduction of all kinds of innovative developments, are trying to withdraw this resource from use. It's all about the environmental danger that arises from its use. When burning fuel, a huge amount of carbon dioxide is formed, one of the culprits of the greenhouse effect.
It turns out that brown and black coal got its name not because of the color of the raw materials. Previously, to determine the “fat content” of a rock, it was carried out on a white surface. The result was a black or brown stripe, which gave the fossil its corresponding name.
How coal is mined in modern mines
Despite the fact that production has never stood still, constantly modernizing, some countries still extract it using manual force. One can highlight India, where residents of towns near deposits collect coal. Even young children are involved in this process, trying to help their parents earn money. The village of Jharia was even called hell on earth, because the air there is filled with coal dust and toxic gases, and raw materials often spontaneously ignite.
Main methods of coal mining
In more developed countries this problem is not so pronounced. Deposit development is carried out using specialized equipment; humans do not even take part in some processes.
Nowadays, 3 types of coal mining are widely used:
- Quarry or cut;
- Mine;
- Hydraulic.
Their use depends on the depth of the mineral layer, rock hardness and accessibility.
Comparative table of coal mining methods.
| Career | Shakhtny | Hydraulic | |
| pros | Low cost Safety Rapid field development |
Relatively environmentally friendly High quality coal Large workings |
Eco-friendly Does not require a huge amount of human resources Relatively cheap Does not harm the foundation of the planet |
| Flaws | Quality of mined coal Not eco-friendly |
Not a safe way Labor intensity The cost is very high |
Using huge amounts of water Low productivity |
Career way
Open pit mining Coal mining is carried out where it lies underground at a depth of no more than 500 meters. To develop such deposits, cranes are used to remove a layer of waste rock. They are called draglines. The cranes consist of a cabin, a boom and a bucket. They are mounted on rails for movement around the quarry or stand on tracks.
Explosives are also used to loosen rock, but due to the danger, they are now abandoned in most industries. After the deposit is devastated, the empty land is filled back up, the area is leveled and enriched with fertilizers. Trees are planted from above to restore or improve the ecosystem of the area. Open-pit mining of coal still causes harm to nature - the ecological situation is disrupted and groundwater dries up.
Brown coal does not lie relatively deep, at a depth of 300-400 meters, so the open-pit method is also used for its extraction. Field development sites are usually called open-pit mines, because they are long and narrow, this is especially noticeable from space. Perhaps this is their only difference from quarries, because the technology for obtaining raw materials is the same.
Then smaller machines come into operation, loosening the rock and loading it into wagons that are sent to production. Coal is poured onto a conveyor unit and sent to production, enrichment stations or thermal power plants.
Mine method
Underground coal mining is an older and technological method obtaining raw materials. A large amount of the fossil lies at a depth of more than 500 meters, and removing the top rock will be an unprofitable, time-consuming and expensive process. The construction of the mine is carried out in this way - a shaft is made, the main shaft, along which all the equipment and workers will descend in the future.
When it reaches the maximum possible depth, horizontal cuts are made in the formation, rails are laid and the main equipment is started. All walls are reinforced with pillars or rings to prevent collapse from vibration.
The deepest coal mine is located in the Donetsk coal basin in Ukraine. Now it reaches 2043 meters.
For the safety of workers, it is very important to ensure constant ventilation of the mine in order to reduce the concentration of methane and warm the air if climatic conditions require it.
Coal mining in mines is carried out using equipment that crushes the layers and sends them to the surface. Mastodon in this area - roadheader. He beats the raw material from the formation and sends it to the surface along a conveyor belt. In areas where hard rock occurs, slightly different equipment is used.
The shearer is equipped with an analogue of a drill with huge teeth that crush the rock, moving deeper and deeper into the mine. Additionally, a shearer is installed, which removes excess chips and crushes large pieces of rock so that they can move along the conveyor to the top.
Another important part that cannot be ignored in the closed coal mining method is pumping out water. Even underground rivers can pass through these areas; they greatly impede production and are dangerous for workers. If the rules are violated or the equipment that pumps out water fails, it can break into the mine shaft, flooding the branches. This will lead to the breakdown of equipment and the death of workers or their imprisonment underground.
Hydraulic method
The hydraulic method is the newest and is currently being modernized to minimize water consumption for coal production. The first device was invented back in the USSR in the 30s. This installation is called a mechanical-hydraulic combine. It is used to loosen the rock, breaking it off from the main layer.
The flowing water passes through gutters, along which it is transported to a low-pressure pump. There, the mined coal is dehydrated, fed to the conveyor and moved outside. The water is purified to prevent any remaining particles from damaging the hydraulic equipment. This method. Despite the huge number of advantages, the hydraulic method is less productive.
Copanca or coal mining at home
Despite the fact that coal mining is carried out in industrial scale, this is a complex and time-consuming process. Residents of areas where there are deposits develop them independently, using it for their own purposes. It is very simple to build, but to implement this method, the coal must not lie deep.
In many countries, this method is used only illegally, to sell coal on the black market. A large number of workers may also be involved there, but the use of advanced industrial technology is out of the question. This is the most dangerous and hard labour Moreover, the norms are not regulated in any way, because the owner of the digging cares only about his own profit.
The most effective ways
It is impossible to say which type of mineral extraction is more profitable to use, because all this is influenced by many factors. You can dig a quarry 1 km deep in the ground, but this requires a huge amount of equipment, time, and can also greatly damage the ecosystem. But making a mine in a coal deposit that lies 300-400 meters away will be too expensive, and such places do not always produce high-quality coal.
Only 8% of raw materials in the world are currently extracted using hydraulic methods, while it is still more experimental.
Places and methods of coal mining are not chosen at random. Initially, the size of the deposit, the quality of raw materials, and terrain features are assessed. Only after this, equipment is brought to the territory and trial fences are made to ensure the profitability of production.
