Coal is a black or brown rock that can be ignited and burned. As coal burns, it produces energy in the form of heat. The heat from coal can be used to heat buildings and to make or process various products. But the heat is used mainly to produce electricity. Coal burning power plants supply about half the electricity. Coal burning power plants supply about half the electricity used in the United States and nearly two –thirds of that used throughout the world. Coal is also used to make Coke an essential raw material in the manufacture of iron and steel. Other substances obtained in the coke making process are used to manufacture such products as drugs, dyes, and fertilizers.
Coal was once the main source of energy in all industrial countries. Coal burning steam engines provided most of the power in these countries from the early 1800’s to the early 1900’s. Since the early 1900’s petroleum and natural gas have become the leading sources of energy throughout much of the world. Unlike coal, petroleum can easily be made into gasoline and the other fuels needed to run modern transportation equipment. Natural gas is often used in place of coal to provide heat. But the world’s supplies of petroleum and natural gas are being used up rapidly. If they continue to be used at the present rate, petroleum supplies may be exhausted by the early 2000’s, and natural gas by the mid – 2000’s. The world’s supply of coal can last about 220 years at the present rate of use.
Increased use of coal, especially for producing electricity, could help relieve the growing shortage of gas and oil. However, the use of coal involves certain problems. The burning of coal has been a major cause of air pollution. Methods have been developed to reduce the pollution, but these methods are costly and not yet fully effective. They must be improved before the use of coal can be increased greatly. In addition, some coal lies deep underground and so is difficult to mine.
In the past, few jobs were harder or more dangerous than that of an underground coal minor. During the 1800’s many had to work underground ten or more hours a day, six days a week. Picks were almost the only equipment they had to break the coal loose. The miners shoveled the coal into wagons. In many cases, children as young as 10 years, thousands of men, women, and children as young as 10 years of age hauled the coal from the mines. Women worked as loaders and hailers. Over the years, thousands of men, women and children were killed in mine accidents. Thousands more died of lung diseases from breathing coal dust.
Today, machines do most of the work in coalmines. Mine safety has been improved, work hours have been shortened, and child Labour is prohibited. The death rate from mine Accidents in the United States has dropped dramatically since 1900. However, coal mining remains hazardous occupation.
This article discusses how coal was formed, where is found, its uses, and how it is mined. The article also discusses the cleaning and shipping of coal, the coal industry, and the history of the use of coal.
Coal developed from the remains of plants that died 400 million to 1 million years ago. For this reason, it is often referred to as a fossil fuel. The coal – forming plants probably grew in swamps. As the plants died, they gradually formed a thick layer of matter on the swamp floor. Over the years, this matter hardened into a substance called peat. In time, the peat deposits became buried under sand or other mineral matter. As the mineral matter accumulated, some of it turned into such rocks as sandstone and shale. The increasing weight of the rock layers and of the other overlying materials began to change the peat into coal. Coal, sandstone, and other rocks formed from deposited materials are called sedimentary rocks.
The first stage in the formation of coal produces a dark brown type of coal called lignite. Lignite develops from buried peat deposits that have been under great pressure. The pressure results from the weight of the overlying materials and from movements within the earth’s crust. As the pressure increase, lignite turns into a harder coal called bituminous coal. Intense pressure changes bituminous coal into anthracite, the hardest of all coals.
Anthracites are the oldest coals in most cases, and lignites are the youngest. Some anthracites began to form as long as 400 million years ago. Some lignite’s developed within the last 1 million years ago. The greatest period of coal formation occurred during a time in the earth’s history called the Carboniferous Period, from about 360 million to 290 million years ago. Swamps then covered much of the earth. Tall ferns and other tree like plants grew in the swamps and produced huge amounts of peat forming matter after they died. Today’s plentiful deposits of bituminous coal developed largely from the vast peat deposits formed during the Carboniferous Period. It took about 3 to 7 feet (0.9 to 2.1. meters) of contact plant mater to produce a bed of bituminous coal 1 foot (0.3 meter) thick.
Plant materials are still accumulating in such coal forming environments as the Everglades, the huge swamplands of southern Florida. Under the proper conditions, these materials could eventually develop into peat and then, over hundreds of thousands of years, into the various kinds of coal.
Coal beds are also called coal seams or coal veins. Present day seams range in thickness from less than 1 inch (2.5 centimerters) to 400 feet (120 meters) or more. The thickest seams are sub bituminous coals and lignites. Many coal deposits consist of two or more seams separated by layers of rocks. These formations were produced by new coal – forming swamps developing the buried ones. Each new swamp became buried and developed into a separate seam of coal.
Some coal beds lie nearly parallel to the earth’s surface. Other beds have been titled by earth’s movements and lie at an angle to the surface. Most of the deepest beds consist of anthracites or bituminous coals. In many beds, earth movements have uplifted deep anthracite and bituminous beds to a position nearer the surface. Such movements also account for coal seams in hills and mountains.
The development of coal
The formation of coal involved three main steps. (1) The remains of dead plants turned into a substance called peat. (2) The peat became buried. (3) The buried peat was subjected to great pressure. After thousands or millions of years under pressure, the peat turned into coal. Each of these steps is illustrated below :
Coal is found on every continent Deposits occur as far north as the Arctic and as far south as Antarctica. Some coal deposits occur off ocean coastlines. However, deep underwater deposits have little value at this time because they are difficult to mine.
Coal deposits that can be mined profitably are called coal reserves. In most cases, a coal seam must be at least 24 inches (30 to 61 centimeters) thick. But such thin beds would probably be mined only after more productive deposits were exhausted. Most estimates of coal reserves may actually be somewhat larger or smaller than the estimates.
To estimate coal reserves, mining engineers drill into the ground in suspected coal – bearing areas. A drill brings up samples of the rock formations in the order in which they occur. The depth and thickness of a coal seam can thus be estimated. By taking a number of such samples, engineers can estimate the extent of a particular deposit. A large area of tested reserves is called a coal field.
World Coal Reserves
Estimates of world coal reserves range from about 1 trillion short tons (910 billion metric tons) to about 2 trillion short tons (910 billion metric tons) to about 2 trillion short tons (1,820 billion metric tons). The lower figure includes only the reserves that can be mined economically. The higher figure includes deposits that cannot now be mined profitably. The United States has 30 per cent, and China has about 10 per cent. Most of the remaining reserves are in Australia, Canada, Great Britain, India, Poland, South Africa, and West Germany.
Location of U.S. and Canadian Reserves
About half of all U.S. coal reserves lie in the eastern half of the nation, from the Appalachian Highlands to the eastern edge of the Great Plains. The rest are in the western part of the country, especially the Rocky Mountain States, the northern Great Plains, and Alaska. The Eastern reserves include nearly all the nation’s anthracite deposits and more than four –fifths of its bituminous deposits. The western reserves include almost all the sub bituminous coal and lignite in the United States.
Canada’s coal reserves consist of bituminous coal. The nation also has large fields of sub bituminous coal and lignite. But the deposits are much thinner than the bituminous deposits. More than 95 percent of Canada’s reserve are in its western provinces British Columbia, Alberta, and Saskatchewan.
The way in which coal is used depends on its chemical composition and moisture content. Coal is often referred to as a mineral. But unlike a true mineral, it has no fixed chemical formula. All coal consists of certain solids and moisture. The solids are composed chiefly of the element carbon, hydrogen, nitrogen, oxygen, and sulfur. However, coal varies widely in the amount of each element it contains as wall as in its moisture content. In fact, no two deposits of coal are exactly alike in their make up.
Coal is usually classified according to how much carbon it contains. Coal can thus be grouped into four main classes, or ranks (1) anthracites; (2) bituminous coals; (3) subbitminous coals; (4) lignite’s or brown coals. The carbon content of the coals decreases down through the ranks. The highest – ranking anthracites contain about 98 per cent carbon. The lowest – ranking lignite’s have a carbon content of only about 30 per cent. The amount of moisture in the coals increases down thorough subbituminous coals and lignite’s. These coals have a lower heating value than do anthracites and bituminous coals. Heating value refers to the amount of heat that is produced by a given amount of coal when it is burned.
Bituminous coals are by far the most plentiful. They are also the most widely used of the major ranks of coals. They have a slightly higher heating value than do anthracites and are the only coals suited to making coke. Anthracites are difficult to ignite. They also burn slowly and therefore they are unsuited to today’s standard method producing electricity from coal. Anthracites are also the least plentiful of the four ranks of coals. About 2 per cent of the coal found in the United States is anthracite.
Coal as a fuel
Coal is a useful fuel because it is abundant and has a relatively high heating value. However, coal has certain impurities that limit its usefulness as a fuel. These impurities include sulfur and various minerals. As coal is burned, most of the sulfur combines with oxygen and forms a poisonous gas called sulfur dioxide. Most of the minerals turn into ash. The coal industry refers to ash production substances in coal as ash even before the coal is buried.
Some coals have a sulfur content of less than 1 per cent. These low – sulfur coals can be burned in fairly large quantities without adding harmful amounts of sulfur dioxide to the air. However, many coals have a sulfur content of more than 1 per cent. These medium and high – sulfur coals can cause serious air pollution if they are burned in large quantities without proper safe – guards. The difficulty and the high cost of developing safe – guards have greatly restricted the use of coal as a fuel. Some of the ash produced by burning powered coal may also escape into the air. Like sulfur dioxide, such fly ash can contribute to air pollution. However, devices have been developed to trap fly ash in smoke stacks and to prevent it from polluting the air.
Coal is used as fuel chiefly in the production of electricity. Electricity power plants use more than two – thirds of the coal mined in the United States.
Electric power production.
The great majority of electric power plants are steam – turbine plants. All nuclear power plants and almost all plants fueled by coal, gas, or oil are steam – turbine plants. They use high – pressure steam to generate electricity. The steam spins the wheels of turbines, which drive the generators that produce electricity. Steam – turbine plants differ mainly in how they create the heat to make steam.
A conveyor system at a power plant removes coal from a stockpile and carries it to the plant’s boilers. Coal – burning power plants produce most of the electricity used in the world.
Nuclear plants create the heat by splitting uranium atoms. The other plants earn coal, gas, or fuel oil. Steam – Turbine plants produce about 80 per cent of the electricity used in the United States. Coal – burning plants account for most of this output.
Bituminous coals have long been the preferred coals for electric power production because they are the most plentiful coals and have the highest heating value. Sub – bituminous coals and lignite’s have the lowest heating value. However, nearly all the subbituminous coal and about 90 per cent of the lignite in the United States have a sulfur content of less than 1 percent. On the other hand, about 50 percent of the nation’s bituminous coal has a medium – or – high – sulfur content. To meet federal and state pollution standards, more and more power plants have switched from bituminous coal to subbituminous coal or lignite.
Other uses of coal as a fuel. In parts of Asia and Europe, coal is widely used for heating homes and other buildings. In the United States, natural gas and fuel oil have almost entirely replaced coal as a heating fuel. However, the rising cost of oil and natural gas has led some factories and other commercial buildings to switch back to coal. Anthracites are the cleanest burning coals, and so they are the preferred coals for heating homes. However, anthracites are also the most expensive coals. For this reason, bituminous coals are often preferred to anthracites for heating factories and other commercial buildings. Subbituminous coals and lignite’s have such allow heating value that they must be burned in large amounts in order to heat effectively. As a result they are seldom used to heating.
In the past, coal was also to provide heat for the manufacture of a wide variety of products, from glass to canned foods. Since the early 1900’s, manufactures have come to prefer the use of natural gas in making most of these products. Coal is used mainly by the cement and paper industries. However, some industries have switched back to coal to avoid paying higher prices for natural gas.
Coal as a raw material
Many substances made from coal serve as raw material in the manufacturing. Coke is the most widely used of these substances. Coke is made by heating bituminous coal to about 2000º F. (1100ºC) in an airtight oven. The lack of oxygen prevents the coal from burning. The heat changes some of the solids in the coal into gases. The remaining solid matter is coke – a hard, foam like mass of nearly pure carbon. It takes about 1½ short tons (1.4 metric tons) of bituminous coal to produce 1 short ton (0.9 metric tone) of coking process.
The coal used to make coke is called coking coal. To be suitable for coking, the coal must have various characterstics, such as a low – sulfur content and a specified amount of ash. Only certain types of bituminous coals have all the necessary characteristics.
About 90 per cent of the coke produced in the United States is used to make iron and steel. Most coking plants are a part of steel mills. The mills burn coke with iron ore and limestone to the ore into the pure iron required to make steel. It takes about 3/5 short
A coking Plant heat coal in airtight ovens to make coke an essential raw material in the manufacture of steel. This batch of red – hot coke is being released from an oven into a railcar. The car will carry it to another part of the plant of cool.
(0.5 metric ton) of coke to produce 1 short ton (0.9 metric ton) of pure iron. For a description of the role of coke in the iron – making process.
The coke making process is called carbonization. Some of the gases produced during carbonization turn into liquid ammonia and coal tar as they cool. Through further processing, some of the remaining gases change into light oil. Manufacturers use the ammonia, coal tar, and light oil to make such products as drugs, dyes, and fertilizers. Coal tar is also use for roofing and for road surfacing. Some of the gas produced during carbonization does not become liquid. This coal gas, or coke oven gas, burns like natural gas. But coal gas has a lower heating value and, unlike natural gas, gives off large amounts of soot as it burns. Coal gas is used chiefly at the plants where it is produced. Coal gas provides heat for coke – making processes.
Gas can be produced from coal directly, without carbonization, by various methods. Such methods are known as gasification. The simplest gasification method involves burning coal in the presence of forced air or steam. The resulting gas, like coke oven gas, has a low heating value and produces soot. It is used chiefly in some manufacturing processes. Coal can be used to make high – energy gas and such high – energy liquid fuel as gasoline and fuel oil. But the present methods, of producing these fuels from coal are costly and complex. Researchers are working to develop cheaper ad simpler methods.
Coal mines can be divided into two main groups (1) surface mines and (2) undergrounding mines. In most cases, surface mining involves stripping away the soil and rock that lie over a coal deposit. This material is known as overburden. After the overburden has been removed, the coal can easily be dug up and hauled away. Underground mining involves digging tunnels into a coal deposit. Miners must go into the tunnels to remove the coal.
Surface mining is usually limited to coal deposits within 100 to 200 feet (30 to 61 meters) of the earth’s surface. The more overburden that must be removed, the more difficult and costly surface mining becomes. Most coal deposits deeper than 200 feet are mined under ground. Surface mines produce about 60 per cent of the coal mined in the United States. Underground mines produce the rest.
Surface Mining
Nearly all surface mining is strip mining that is, mining by first stripping away the overburden. Many coal seams are exposed on the side of hills or mountains. In some cases, these seams are mined from the surface without removing any overburden. Miners use machines called augers to dig out the coal. This method of surface mining is known as anger mining.
Strip Mining
It depends on powerful machines that dig the overburden and pile it out of the line of work. The dug – up overburden is called spoils. In time, a strip digging up of vast areas of land has caused serious environmental problems in the past. As a result, the United States government now requires that all new stripped land must be reclaimed – that is, returned as closely as possible to its original condition. Strip mining thus involves methods of [1] mining the coal and [2] reclaiming land.
Mining the coal Most strip mines follow the same basic steps to produce coal. First, bulldozers clear and the mining area. Many small holes are then drilled through the overburden to the coal bed. Each hole is loaded with explosives. The explosives are set off, shattering the rock in the overburden. Giant power shovels or other earth moving machines then start to clear away the soil and broken rock. Some of these earthmovers are as tall as a 20 storey building and can remove more then 3,500 tons (3,180 metric tons) of overburden per hour. After a fairly large area of coal is exposed, smaller power shovels or other coal – digging machines scoop up the coal and load it into trucks. The trucks carry the coal from the mine.
Although most strip mines follow the same basic steps, strip – mining methods vary according to whether the land is flat or hilly. Strip mining can the be class as [1] area mining or [2] contour mining. Area mining is practiced where the land is relatively level. Contour mining is practices in hilly or mountainous country. It involves mining on the contour – that is, around slopes.
In area mining, an earthmover digs up all the broken overburden iron a long, narrow strip of land along the edge of the coal field. The resulting deep ditch is referred to as a cut. As the earthmover digs the cut, it piles the spoils along the side of the cut that is away from the mining area. The piled spoils form a ridge called a spoil bank. After the cut is completed, the coal is dug, loaded into trucks, and hauled away. The earthmover then digs an identical cut alongside the first one. It piles the spoils from this cut into the first cut. This process is repeated over and over across the width of the coal field until all of the coal has been mined. The spoil banks form a series of long, parallel ridges on the land that can later be leveled.
Area mining is impractical where coal seams are embedded in hills. If a seam lies near the top of a hill, an earthmover may simply remove the hill top and so expose the coal, fi a seam lies near the base of a hill, it must be mined on the contour.
In contour mining, an earthmover removes the shattered overburden immediately above the point where a seam outcrops its exposed all around a hill. The resulting cut forms a wide ledge on the hillside. The spoils may be stored temporarily on the hillside or used to fill in the cuts. After the exposed coal has been mined and hauled away, the earthmover may advance up the slope and dig another cut immediately above the first one. However, the depth of the overburden increases sharply with the rise of the slope.
After the first or second cut, may be too great for a coal company to remove profitably. But if the seam is thick enough, a company may dig an underground mine to remove the rest of the coal.
Reclaiming the land.
The chief environmental problems that strip mining can cause results from burying fertile soil under mining can cause result from burying fertile soil under piles of rock. The rocks tend to give off acids when exposed to moisture. Rainwater runs down the bare slopes, carrying acids, and mud with it, the run – off from the slopes may wash away fertile soil in surrounding areas and pollute streams and rivers with acids and mud.
The first step in reclaiming strip – mined land is to reduce the steep slopes formed by the spoils. The spoil banks created by area mining can be leveled by bulldozing. The spoils from contour mining can be used to fill in the cuts in the hillside. As much topsoil as possible should then be returned to its original position so that the area can be replanted.
Mining companies have reclaimed much strip – mined land, which has been turned into farms and recreation areas in many cases. But much land has not been reclaimed. In 1977, the U.S. Congress passed a law requiring mine owners to reclaim all the land they use for strip mining after 1978. In every case, the mine owners must restore the land as nearly as possible to its original condition.
Auger mining
A coal auger is a machine shaped like an enormous corkscrew. It bores into the side of a coal outcrop on a slope and twists out the coal in chunks. Contour mines often use augers when the over burden in a slope is too great to remove. An auger can penetrate the outcrop and recover coal that could not otherwise be mined. Some augers can bore 200 feet (61 meters) or more into hillside.
A few companies specialize in auger mining, chiefly to mine outcrops of high quality coal that cannot be mined economically by other methods. However, auger mining can recover only a small portion of the coal in a seam. The method is most efficient when used in combination with contour mining.
Underground Mining
Underground mining is more hazardous than surface mining. The miners may be injured or killed by cave INS falling rocks, accidental explosions, and poisonous gases. To prevent such disasters, every step in underground coal mining must be designed to safeguard the workers.
Underground mining requires more human Labour than does surface mining. But even so, underground mines are highly mechanized. Machines do all the digging, loading, and hauling in nearly all the mines. Non – mechanized mines produce only about 1 percent of the coal mined underground in the United States.
In most cases, miners begin an underground mine by digging two access passages from the surface to the coal bed. One passage will serve as an entrance and exit for the miners and their equipment. The other passage will be used to haul out the coal. Both passages will also serve to circulate air in and out of the mine. As the mining progresses, the workers dig tunnels from the access passages into the coal seam.
Underground mines can be divided into three main groups according to the angle at which the access passages are dug into the ground. The three groups are [1] shaft mines, [2] slope mines, and [3] drift mines. Some mines have two or all three types of passages.
In a shaft mine, the access passengers run straight down from the from the surface to the coal seam. The entrance and exit shaft must have mines. In a slope mine, the access passages are dug on a slant. They may follow a slanting seam or slant down through a hillside to reach a seam under the hill. Drift mines are used to mine seams of coal are embedded in hills or mountains.
The access passages are dug into a seam where it out – crops on a slope. They thus parallel the ground.
Two main systems of underground mining are used : [1] the room – and pillar system and [2] the longwall system. Each system has its own set of mining techniques. Either system may be used in a shaft, slope, or drift mine. The room – and pillar system is by far the more common system of underground mining in the Unites States. The long wall system is more widely used elsewhere, especially in European Countries.
The room – and – pillar system.
It involves leaving pillars of coal standing a mine to support the overburden. Miners may begin a room – and – pillar mine by digging form the access passages. These tunnels are called main entries. In most cases, the walls of coal separating the main entries are 40 to 80 feet (12 to 24 meters) wide. Cuts are made through each wall every 40 to 80 feet. The cuts thus form square or rectangular pillars of coal that measure 40 to 80 feet on each side. The coal dug in building the entries is hauled to the surface.
The pillars help support the overburden in the main entries. But in addition, the tunnel roofs must be bolted to hold them in place. To bolt the roof, the miners first drill holes 3 to 6 feet (0.9 to 1.8 meters) or more into the roof. They then insert a long metal bolt into each hole and fasten the free end of each bolt to the roof. The bolts bind together the separate layers of rock just above the roof and so help prevent them from falling. The miners must also bolt the roof in all other parts of the mine as they are developed.
A railroad track of a conveyor belt is built in one of the main entries to carry the coal to access passages. Mine railroad may also provide transportation for the miners along the main entries. At least two main entries serve chiefly to circulate air through the mine. An underground mine may also need such facilities as water drainage ditches, gas drainage pipes, compressed air pipes, and electric power cables. These facilities are built into main entries and later extended to other part of the mine.
After the main entries have been constructed, the miners dig sets of subentries at right angles form the main entries into the coal seam. Each set of subentries consists of three or more parallel tunnel, which serve the same purposes as the main entries. Cuts are made through the walls separating these tunnels, forming pillars like those between the main entries. At various points along each set of subentries, the miners dig room entries at right angles into the seam. They then begin to dig rooms into the seam from the room entries.
As the miners enlarge a room, they leave pillars of coal to support the overburden. A room is inked only a certain distance into seam. When this distance is reached, the miners may remove the pillars. The room roof collapses as the pillars are removed, and so they must be removed in retreat – that is, from the back of the room toward the front. The miners exit from the room thus remains open as the roof falls. Pillars are also some times removed from entries. Like room pillars, they must be removed in retreat to protect the miners.
All room and pillar mining involves leaving pillars in place. Room and pillar mines differ, however, in our mining methods Mechanized room and pillar in use two main methods [1] the conventional method and [2] continuous mining.
The Conventional mechanized method
It produces about 30 per cent of the coal mined underground in the United States. This method was more widely practiced during the 1930’s and 1940’s than it is today. During the 1930’s, it largely replaced the earlier method of digging coal by hand. Since about 1950, continuous mining has increasingly replaced the conventional method.
The room – and pillar system
Most underground mines in the United States use the room – an – pillar system of mining. First the miners dig channels called main entries into the coal bed from the entrance and exit passages. They then dig sets of subentries into the bed from the sub – entries. Pillars of coal are left standing in all the entries to support the mine roof. As the room entries are extended. They create large panels of coal. The miners evenly dig rooms into the panels to recover as much coal as possible from the bed. This floor plan of a room and pillar mine shows how the entries are developed.
TYPES OF UNDERGROUND MINING EQUIPMENT.
The type of equipment that an underground mine requires depends on the method of mining 4 uses. Mechanized mines use three main methods (1) The Conventional method (2) Continuous mining, and (3) Longwall mining. Each of the three methods calls for different type of equipment.
Conventional mining equipment . The conventional method of mining involves a series of steps, three of which require special machinery. First a cutting machine, left, cuts a deep slit along the base of the coal face (coal exposed on the surface of a mine wall). Another machine, center, drills holes into the face. Miners load the holes with explosives and then set the explosives off. The undercutting along the bottom of the face causes the shattered coal to fall to the floor. A loading machine, right gathers the coal onto a conveyor belt.
Continuous mining equipment eliminates the series of steps in mining a face. A continuous mining machine, right gouges out the coal and loads it onto a shuttle car in one operation.
Longwall mining equipment . Longwall mining differs from the other methods of underground mining in its system of roof support. The other methods are used only in room and pillar mines, where pillars of coal are left to support the mine roof. In the longwall method, movable steel props support the roof over one long coal face. The miners move a cutting machine back and forth across the face, shearing off coal. The coal falls onto a conveyor. As the miners advance the cutter into the bed, the roof supports are moved forward. The roof behind the miners is allowed to fall.
The conventional method involves five main steps : (1) machine that resembles a chain saw cuts a long, deep slit along the base of the coal face. (2) Another machine drills a number of holes into the face (3) each hole is loaded with explosives. The explosives are set off, shattering the coal. The undercutting along the bottom of the face causes the broken coal to fall to the floor. (4) A machine loads the coal onto shuttle cars or a conveyor (5) Miners bolt the roof that has been exposed by the blast.
A separate crew of miners carries out each of the five steps. After a crew has completed its job on a particular face the next crew moves in. The miners can thus work five faces of coal at a time. But there are frequent pauses in production as the crew change places.
Continuous Mining
It accounts for about 65 percent of the output of U.S. underground coal mines. The method uses machines called continuous miners. A continuous miner gouges the coal from the coal face – that is, the coal exposed on the surface of a wall. One worker operating a continuous miner can dig as much as 12 short tons (11 metric tons) of coal per minute. The machine automatically loads the coal onto shuttle cars or a conveyor belt, which carriers it to the railroad or conveyor in the main entries.
A continuous miner can usually dig and load coal much faster than the coal can be hauled out of a mine. The machine can work faster than the roof – bolting, ventilation, and drainage systems can be installed. As a result, a continuous miner must frequently be stopped to allow the other mine systems to catch up.
The Long wall system
The long wall system of underground mining involves digging main tunnels or entries like those in a room – and – pillar mine. However, the coal is mined from one long face, called a longwall, rather than form many short faces in a number of rooms.
A longwall face is about 300 to 700 feet (91 to 210 meters) long. The miners move a cutting machine back and forth across the coal falls onto a conveyor belt. Movable steel props support the roof over the immediate work area. As the miners work the machine further into the seam, the roof supporters are advanced. The roof behind the miners is allowed to fall. After a face has been dug out 4,000 to 6,000 feet (1,200 to 1,800 meters) into the seam, a new face is developed and mined. This process is repeated over and over until as much coal as possible has been removed from the seam.
The longwall system originated in Europe and is far more common there than in the United States. Underground mines in Europe are much deeper, on the average, than The Pressure of the overburden becomes intense in an extremely deep mine. Longwall mining relieves the pressure by allowing the roof to cave in throughout most of a mine. In a European longwall mine, the roof remains in place only over the main entries, over the longwall face, and over two tunnels leading to the face. The mines can thus recover up to 90 per cent of the in a seam.
Mine safety laws in the United States require longwall mines to have fully developed subentries as wall as main entries Thus U.S. longwall mining includes some of the main features of the room – and pillar system. But in many cases, the mines are most productive than room – and – pillar mines because less coal may be left in place.
Longwall mines produce about 5 per cent of the coal mined underground in the United States. However, more and more U.S. mines are adopting longwall techniques. Experts believe this trend will continue into the 1980’s as mines are dug deeper and deeper to recover more coal. A few American mines have adopted a variation of the longwall method called short wall mining. A shortfall face is only about 150 to 200 feet (46 to 61 meters) long, and it is mined with continuous mining machines rather than with longwall equipment. This system, which was developed in Australia, is suited to coal seam whose structure prevents them form being divided into long faces.
Much coal is shipped to buyers exactly it comes from the mine without any processing. In the coal industry, such coal is called run – of – mine coal. It ranges in size from the fine particles to large chunks. About 40 per cent of the coal sold by U.S. mining companies is run – of mine coal.
The two largest users of coal, the electric power industry and the coking industry, have definite quality requirements for the coal they buy. Much run – of – mine coal does not meet these requirements because it contains unacceptable amounts of impurities. Mining companies must clean this coal by removing the impurities before they can sell it. About 60 per cent of the coal mined in the U.S. is cleaned before it is shipped to buyers.
Cleaning Coal.
Mining companies clean coal in specially designed preparation plants. Most large coal mines have a preparation plant on the mine property. The plants use a variety of machines and other equipment’s to remove the impurities form coal.
Ash and sulfur are the chief impurities in coal. The ash consists chiefly of mineral compounds of aluminium, calcium, iron and silicon. Some of the sulfur in coal is also the form of minerals, especially pyrite, or fool’s gold. The rest is organic sulfur, which is closely combined with the carbon in coal. Run – of – mine coal may also contain pieces of rock or clay. These materials must be removed in addition to the other impurities.
Preparation plants rely on the principle of specific gravity to remove the impurities from run – of mine coal. According to this principle, if two solid substances are placed in a solution, the heavier substance will settle to the bottom first. Most of the mineral impurities can be separated from run – of – mine coal that is placed in a solution. The entire coal cleaning process involves three main steps (a) sorting (b) washing, and (‘c) drying.
Sorting – large pieces of pure coal may settle to the bottom of a solution faster than small pieces that have many impurities. Therefore, the pieces must first be sorted according to size. IN many preparation plants, a screening device sorts the coal into three sizes – coarse, medium, and fine. Large chunks are crushed. The crushed pieces are then sorted into the three main batches according to size.
Mining companies remove mineral impurities from coal by a process called cleaning. The process involves three main steps [1] A screening device sorts the coal into batches of three sizes [2] Each batch is piped into a separate washing device and mixed with water. The impurities in coal are heavier than pure coal. As a result, the first pieces of coal to settle to the bottom of each solution are those that contain the most impurities. Any loose piece of rock or clay mixed in with the coal also sink to the bottom. All the waste pieces are discarded [3] The clean pieces are dried with vibrators or hot air blowers. The coal is then ready for shipment to buyers.
(Unit Trains carry most large overland shipments of coal in the United States. A unit train normally carriers only one kind of freight and travels non stop from its loading point to its destination).
Washing – The typical preparation plant uses water as the solution for separating the impurities from coal. Each batch of sorted coal is piped into a separate washing device, where it is mixed with water. The devices separate the impurities by means of specific gravity. The heavy pieces – those containing the largest amounts of impurities drop into a refuse bin. Washing removes much of the ash form coal. But the organic sulfur is so closely bound to the carbon that only small amounts can be removed.
Drying – The washing leaves the coal dripping wet. IF this excess moisture is not removed, the heating value of the coal will be greatly reduce. Preparation plants use various devices, such as vibrator and hot – air – blowers, to dry, coal after it is washed.
In most cases, the separate batches of coal are mixed together again either before or after drying. The resulting mixture of various sizes of coal is shipped chiefly to electric power companies and coking plants. All coking plants many power companies grind coal to a powder before they use it. They therefore accept shipments of mixed sizes. Some coal users require coal of a uniform size preparation plants that supply these users leave the cleaned coal in separate batches graded according to size.
Shipping coal
Most coal shipments within a country are carried by rail, barge, or truck. In many case, a particular shipment must travel by two or all three of these means to reach the buyer. Huge cargo ships transport coal across oceans, between coastal ports, and on large island waterways, such as the Great Lakes.
Barges provide the cheapest way of shipping coal within a country. But they can operate only between river or coastal ports. Trucks are the least costly means of moving small shipments of coal short distances by land. Much, coal, however, must be shipped long distance over land to reach buyers. Railroads, offer the most economical means of making such shipments. About two – thirds of the coal shipped from mines in the United States goes by rail.
Many large shipments of coal in the United States are delivered to electric power companies and coking plants by unit trains. A unit train normally carries only one kind of freight and travels non stop from its loading point to its destination. A 100 – car unit train may carry 10,000 short tons (9,100 metric tons) or more of coal. To meet the need for low – sulfur coal, more and more power plants east of the Mississippi River are importing subbituminous coal from the West Unit trains help speed such long – distance shipments.
A 273 – mile (439 Kilometer) underground pipeline carriers coal from a mine in Arizona to a power plant in Nevada. The coal is crushed and mixed with water to form a slurry (soupy substance) that can be pumped through the pipeline. The coal and power industries are considering building other such pipelines are most costly and less efficient than the traditional methods of shipping coal.
In the past, nearly all coal shipments consisted of anthracite, bituminous coal, or subbituminous coal. It costs as much to ship a given amount of lignite as it costs to ship the same amount of a higher – ranking coal. But lignite has the lowest heating value of the four ranks. It therefore could not formerly compare worth the higher – ranking coals in different markets. Lignite was used chiefly by power plants built in the lignite fields. Conveyor belts or small railways carried the coal from the mines to the plants. However, the growing need for low sulfur coal has increased the demand for lignite. Some lignite is now shipped by rail from mines in the Western United States to power plants in Midwest.
In most countries, the central government owns all or nearly all the coal mines. The major exceptions are Australia, Canada, South Africa, the United States, and West Germany. In West Germany, the mines are jointly owned by the federal government, various state Governments, and private investors. All or nearly all the coal mines in Australia, Canada, South Africa and the United States are privately owned. In each of these countries, however, the central government regulates certain aspects of the coal industry.
The United States is the world’s leading coal exporter. About one – fourth of all coal exports come from U.S. mines. Other leading exporters include Australia, Canada, Poland, South Africa, and the Soviet Union, Japan buys about a third of the world’s coal exports – far more than any other country.
This section deals chiefly with the coal industry in the United States. However, much of the information also applies to other country.
Coal Producers
The United States has about 4,400 active coal mines and about 3,000 coal – mining companies. A majority of the companies are small, independent firms that own and operate one or two small mines. All the small companies together supply less than a third of the coal mined in the United States. The 50 largest U.S. coal companies produce more than two – thirds of the nation’s coal. Some of the companies are independently owned, but many are owned by corporations outside the coal industry. The chief outside owners include oil companies, railroads, and ore – mining firms.
Steel companies and electric utilities own may coal mines. These companies produce coal chiefly for their own use. Their mines are known as captive mines.
(Coal miners provide the labour on which the coal industry depends. These miners have just finished their day’s work in an underground mine. The train will carry them to the mine exit).
The National Coal Association (NCA) works to promote the interests of the major coal producers. The NCA is jointly sponsored by the producers and the firms that supply them with equipment, technical advice, and transportation. The association tries to increase efficiency within the industry, to encourage favorable legislation, and to inform the public about the industry. The National Independent Coal Operators Association represents the smaller coal producers.
Mineworkers
Most large coal – mining companies have a full – time staff of professional workers, including engineers, lawyers, and business experts. They also employ electricians, mechanics, and construction workers. Skilled miners, however, provide the labor on which the industry depends. Underground mining requires more miners than does surface mining. The United States has about 155,000 coal miners. About two – thirds of them work in underground mines.
Mechanization has helped miners become more productive. In 1950, each coal miner in the United States produced, on the average, about 7 short tons (6.4 metric tons) of coal daily. Today, the production rate averages about 25 short tons (23 metric tons) per miner per day. On the average, a strip miner produces approximate three times as much coal as does an underground miner.
Increased mechanization has also made miner’s jobs are specialized. The job of most miners is to operate certain type of machine, such as a continuous miner or a power shovel. A beginning miner must work as a apprentice for a specified period to qualify for a particular job. Miner supervisors must have a license from the department of mining in their state. Generally, the licenses are granted to miners who have two to five year’s experience and who pass a written examination.
Most mining engineering jobs call for a college degree in engineering. If the job is directly related to miss safety, it may also require a state engineering license called a P.E. (professional engineer) certificate. Some mining engineering jobs require a P.E. certificate only. The states grant P.E. certificates to applicants who meet certain educational requirements, have a certain amount of on – the – job experience, and pass a written examination. In some states, applicants must have and engineering degree. Other states require only a high school education.
Labour Unions
About 70 per cent of all coal miners the United States belong to the United Mine Workers America (UMW). The UMW was organized in 1890. At that time, the nation’s coal miners lived and worked under miserable conditions. The mines were dangerously unsafe, and the miners earned barely enough to live on. Most miners and their families lived in company towns, which were owned and run by the mining companies. IN many company towns, the housing and other facilities were far from adequate. Frequently, miners were not paid in cash. Instead, the mining companies gave them coupons that could be exchanged for goods at company – owned house. The store prices and rents are unreasonably high in many cases, and some mines were always in debt to the mining companies.
During the first half of the 1900’s, the UMW did not improve the wages and working conditions of American Coal miners. Through strikes and hard bargaining the union forced the mining companies to grant the miners increasingly favorable work contracts. The UMW owed much of its success to the vigorous leadership of John L. Lewis, who headed the union form 1919 to 1960. During Lewis long term as UMW president, the union had the overwhelming support of its members.
Although the UMW is still strong, its influence has declined. This change partly reflects the rapid growth of strip mining. Strip mining requires fewer miners than does underground mining. It also requires a different type of miner. Strip miners are chiefly heavy machine operators. Unlike underground miners, they have little need for traditional mining skills. Some strip miners are members of the UMW. But many belong to various building trades unions or to no union.
The UMW has also lost influence among its member. Many UMW members feel that their contracts with the mining companies are still far from satisfactory. The miners want better health and retirement benefits and stricter mine safety measures. During the 1970’s small groups of miners frequently took matters into their own hands and went out on wildcat strikes, which did not have the approval of union leaders.
Mine Safety
Since 1900, more than 100,000 workers have been killed in coal mine accidents in the United States. Many more have been injured or disabled. Because of this extremely high accident rate, more and more aspects of mine safety have been brought under government regulation. The federal government and the government of the coal mining states set minimum health and safety standards that the coal companies and miners have to follow. TO make sure that all miners know their responsibilities, the companies must give every new miner a course in mine safety. The improvements in mine safety have greatly reduced the death rate from mine accidents. In the early 1900’s, about 3.5 miners per 1,000 were killed in mine accidents annually. The annual death rate has dropped to about 5 today is an improvement of about 85 per cent.
(Bolting the roof is an essential safety practice in an underground mine. Roof bolts are long metal rods that are inserted into the mine roof. After a bolt is fastened to the roof, above it helps prevent the rock layers immediately overhead from falling).
Mine safety involves four main types of problems. They are [1] accidents involving machinery, [2] roof and wall failures, [3] accumulations of gases, and [4] concentrations of coal dust.
Accidents involving machinery – kill or injure more U.S. coal miners in a typical year than does any other kind of mining accident. Most strip mine accidents involve machinery. The machines in underground mine must often operate in cramped, dimly lit spaces. The miners must therefore be doubly alert to prevent accidents.
Roof and wall failures – can be prevented in may cases if a mining company carries out a scientific roof support plan. The federal government requires all U.S. mining companies to draw up such a plan for nay new mine. The government must then approve the plan before mining is begun. Mining engineers make a roof support plan after studying all the rock formations surrounding the coal bed. The plan deals with such matters as the number of pillars that must be left standing and the number of roof bolts that must be used.
Accumulations of gases – Certain gases that occur in underground coal mines can become a serious hazard if they accumulate. Methane and carbon monoxide are especially dangerous. Methane is an explosive gas that occurs actually in coal seams. IT is harmless in small amounts. However, a mixture of 5 to 15 percent methane in the air can cause a violent explosion. Carbon monoxide is a poisonous gas produce by the combustion of such fuels as coal and oil. Blasting in an underground mine may produce dangerous levels of carbon monoxide if the mine is improperly ventilated.
The air vents in a mine normally prevent harmful gases from accumulating. A powerful fan at the surface circulates fresh air polluted air to the surface. As an added precaution against methane, federal law requires all underground mines to have automatic methane detectors. A mine must shut down temporarily if a detector shows a methane accumulation of more than 2 per cent.
Concentration of coal dust.
Anyone who breathes large amounts of coal dust over a period of years may develop a disease called pneumoconiosis of black lung. The disease interferes with a person’s breathing and may eventually cause death. Thousands of coal miners have been victims of the disease. In addition, high concentrations of coal dust are explosive. A mixture of coal dust and methane is especially dangerous.
Proper ventilation removes much of the coal dust from the air in a mine. However, mines must also use other dust control measure. In the United States, federal law requires that underground mines be rock dusted. In this process, the miners spray powdered limestone on all exposed surfaces in the mine entries. The limestone dilutes the coal dust and so lessens the chance of an explosion. Mines use water sprays to hold down the dust along a face that is being mined.
Government regulation
State departments of mining have traditionally set and enforced safety standards for American Coal Mines. In the past, the U.S. Bureau of Mines had this responsibility at the federal level. On occasion, Congress had made urgently needed standards a matter of law, as in the Federal Coal Mine Health and Safety Act of 1969. This act strengthened the safety standards for mine ventilation, coal dust concentrations, roof supports, and mining equipment. It also established a program to provide financial benefits to miners disabled by black lung. The Mine Safety and Health Administration enforces federal mine safety standards. The United States Department of the Interior, the United States Environmental Protection Agency (EPA), and state environmental protection agencies regulate the environmental aspects of coal – mining activities in the United States.
Leading Coal producing Countries.
Coal Research – has become increasingly important. The U.S. Department of Energy and the EPA are the chief federal organizations that sponsor coal research. Leading industry sponsors include coal and oil companies.
The goals of most coal research are (1) to find ways to burn more coal without increasing air pollution and (2) to develop economical methods of converting coal into liquid fuels and synthetic natural gas.
Pollution control – in 1977, Congress passed a law requiring all U.S. electric power plants built since 1971 to meet federal pollution standards by 1982. These standards prohibit the burning of medium – or high sulfur coals without a means of controlling sulfur dioxide pollution. Medium – and – high sulfur coal make up more than a third of all U.S. coal reserves. These resources can be used for electric power production only after ways are found to control sulfur dioxide pollution.
Researchers are also working on a experimental sulfur control process called fluidized –bed combustion. In this process, crushed coal is burned in bed of limestone. This limestone captures sulfur from the coal and so prevents sulfur dioxide from forming. The heat from the burning coal boils water that is circulated through the bed in metal coils. The boiling water produces steam, which may be used to produce electricity.
Coal Conversion – To turn coal into high – energy fuel, the hydrogen content of the coal must be increased. Bituminous coals have the highest hydrogen content of the four ranks of coal. On the average, they consist of about 25 per cent to produce synthetic natural gas.
The process of converting coal into a liquid fuel is called coal hydrogenation or liquefaction. Various methods of coal hydrogenation have been developed. IN the typical method, a mixture of pulverized coal and oil is treated with hydrogen gas at high temperatures and under great pressure. The hydrogen gradually combines with the carbon molecules, forming a liquid fuel. This proceed can produce such high – energy fuels as gasoline and fuel oil if sufficient hydrogen is added.
Coal can easily be turned into low – energy gas by the carbonization and gasification methods described in the section the uses of coal. Low energy gas can also be produced form unmined coal. This process, called underground gasification, involves digging two widely spaced wells from ground level to the base of coal seam. The coal at the bottom of one well is ignited. Air is blown down the second well. The air seeps through pores in the seam, and the fire moves toward it. After a passage has been burned between the two wells, the air current forces the gases up the first well to the surface. Compared with natural gas, low – energy gas must be enriched with hydrogen for its heating value to equal that of natural gas.
The present methods of obtaining high – energy fuels from coal cost too much for commercial use. Hydrogen is expensive to produce. In addition, most fuels made from coal contain unacceptable amounts of sulfur and ash. Researcher are trying to develop cheaper methods of coal conversion. In 1980, which provides federal funding for coal conversion research and for the construction of synthetic fuel plants. In 1984, two commercial – sized coal gasification plants began operating in the United States. However, both plants rely heavily on the federal government for financial support.
No one knows where or when people discovered that coal can be burned to provide heat. The discovery may have been made independently in various parts of the world during prehistoric times. The Chinese were the first people to develop a coal industry. By surface deposits and using it to heat buildings and smelt metals. Coal had become the leading fuel in China by the 1000’s.
Commercial mining developed more slowly in Europe. During the 1200’s, a number of commercial mines were started in England and in what is now Belgium. The coal was dug form open pits and used mainly for smelting and forging metals. But most Europeans regarded coal as a dirty fuel and objected to its use.
Wood, and charcoal made from wood, were the preferred fuels in Europe until the 1600’s. During the 1600’s, a severe shortage of wood occurred in Western Europe. Many western European countries, but especially England, then sharply increased their coal output to relieve the fuel shortage.
Development in England – During the 1500’s English factories burned huge quantities of charcoal in making such products as bricks, glass, salt, and soap. By the early 1600’s that most factories had to switch about 80 per cent of the world’s total coal output. The country remained the leading coal producer for the next 200 years.
Charcoal had also been widely used in England as a fuel for drying malt, the chief ingredient in beer, Brewers tried using coal for this process. But the gases it produced were absorbed by the malt and so spoiled the flavor of the beer. The brewers found, however, that the undesirable gases could be eliminated if they preheated the coal in an airtight oven. They thus developed the process for making coke. About, and English iron maker named Abraham Derby succeeded in using coke tosmelt iron. Coke then gradually replaced charcoal as the preferred fuel for iron making.
(A Pennsylvania mine of the late 1800’s was like coal mines everywhere before mining became mechanized and child labor was abolished. Boys and mules provided much of the labour).
The spread of the new/iron making process became part of much larger development in England – the Industrial Revolution. The revolution consisted chiefly of a huge increase in factory production. The increase was made possible by the development of the steam engine in England during the 1700’s. Steam Engines provided the power to run factory machinery. But they required a plentiful supply of energy. During the 1800’s, the Industrial Revolution spread from England to other parts of the world. IT succeeded chiefly in countries that had an abundance of coal. Coal thus played a key role in the growth of industry in Europe and North America.
Development in North America – The North American Indians used coal long before the first white settlers arrived. For example, the Pueblo Indians in what is now the Southwestern United States dug coal from hillsides and used it for baking pottery. European explorers and settlers discovered coal in eastern North. American during the last half of the 1600’s. in the 1700’s a dew small coal mines were opened in what are now Nova, Scotia, Virginia, and Pennysylvania. The mines supplied coal chiefly to blacksmiths and ironmakers. Most settlers saw no advantage in using coal as long as wood was plentiful. Wood and charcoal remained the chief fuels in America throughout the 1700’s.
The Industrial Revolution spread to the United States during the first half of the 1800’s. By then, coal was essential not only to manufacturing but also to transportation. Steamships and steam – powered railroads were becoming the chief means of transportation, and they required huge amounts of coal to fire their boilers. As industry and transportation grew in the United States, so did the production and use of coal. By the late 1800’s, the United States had replaced England as the world’s leading coal producer.
The United State led in coal production until the mid – 1900’s. It demand for coal then declined as the use of petroleum and natural gas increased. The Soviet Union surpassed the United States in coal production from the late 1950’s through the late 1970’s. During the 1980’s the United States has usually ranked first.
Recent developments – The growing scarcity of the petroleum and natural gas has led to a sharp rise in the demand for coal. As a result, U.S. coal production increased output was used mainly to produce electricity.
Today, electricity can be produced more cheaply from coal than from either natural gas or fuel oil. However, the cost of coal – generated electricity will almost certainly increase for several reasons. To meet environmental standards, power plants that burn medium or high – sulfur dioxide scrubbers. To obtain low – sulfur coal, power plants must pay to have it shipped from the major producing areas. As coal deposits near the surface are used up, mines must be dug deeper and deeper. The high operating costs of extremely deep mines will add to the price of coal. Power companies, like other businesses, pass their added costs on their customers. Thus, even though coal is plentiful, the energy it produces will become increasingly expensive.