Coal and energy production

Summary: Coal has been one of the most widely used of the fossil fuels since the 19th century, driving industrial growth and modernization, although concerns about its environmental impacts slowed its growth in the 20th century.

Coal is a fossil fuel formed over centuries through the compaction and heating of decaying plant materials in oxygen-poor environments. It is mined from the earth through either surface or subsurface methods. Coal has been one of the most widely used fossil fuels since the Industrial Revolution of the nineteenth century; the leading fuel for electricity generation, it accounted for nearly 36 percent of the world’s primary energy production in 2021. In the United States it accounted for 22 percent in 2021, behind natural gas at 38 percent. Coal is used for heating, generating electricity, and industrial processes such as the manufacture of coke and steel.

Coal’s powering of the Industrial Revolution in Britain, Germany, and elsewhere led to its emergence as the driving force behind economic expansion well into the twentieth century. Usage rates declined mid-century as a result of environmental concerns and the development of cleaner energy sources. However, coal usage rates have undergone a resurgence since the late twentieth century because of the rising expense and energy security issues surrounding oil, the rising demand in developing countries such as China and India, and to a lesser degree the development of clean-coal technologies.

Coal formed when ancient plant materials accumulated in layers over the centuries in environments such as swamps, where they failed to decay completely due to lack of oxygen. Anaerobic bacteria, which survive without oxygen, converted the plant materials into simpler forms such as minerals including carbon. Centuries of heat and pressure converted this decaying organic material into the combustible, rock-like substance known as coal, which is mainly carbon. Scientists believe that most of the earth’s coal was formed during the Carboniferous period, approximately 300 million years ago, with other large deposits forming during the Upper Cretaceous period, approximately 100 million years ago.

The dead vegetative material first forms into peat, which is soft and wood-like. Peat itself is burned as a fuel source, but its poor burning capacity and smoky output have limited its use, especially in modern times. If peat remains in the ground, layers of sediment gradually build on top of the peat, resulting in additional heat and pressure. This process slowly converts the peat into coal. Coal is most often found in lengthy horizontal layers of varying thickness known as seams or beds, which may lie at or near the surface or deep underground. There are various types of coal, depending largely on the amount of time it has remained in the ground. The three main classifications of coal are lignite, bituminous, and anthracite.

The first type of coal formed is known as lignite coal, also known as brown coal; followed by bituminous coal, also known as soft coal; and anthracite coal, also known as hard coal. (Bituminous coal can be further divided to include the lower-value sub-bituminous coal.) The types are ranked in value, with lignite at the lowest part of the scale and anthracite at the highest. Lignite is the most abundant type of coal; has the highest moisture, oxygen, and ash contents; and has the lowest carbon content and heating value, or energy content. Anthracite is the least abundant type of coal; has the lowest moisture, oxygen, and ash contents; and has the highest carbon content and heating value, or energy content. Bituminous is the most common and widely used type of coal and falls in the middle of the scale.

Coal is classified in terms of heating value, with anthracite at the top of the scale, followed by bituminous, sub-bituminous, and lignite. The higher the percentage of pure carbon, the higher the heating value or rank of the coal. There is usually a direct correlation between age and pure carbon percentage. Anthracite tends to have a 90 percent or greater carbon content, bituminous ranges from 70 percent to 90 percent, and lignite from 40 percent to 70 percent. Coal may also be evaluated by grade, based on the amount of ash or sulfur content. Coal also contains a number of other minerals, chemicals, and trace elements that vary among different coal seams and even within individual coal seams. Examples include aluminum, zirconium, hydrogen, oxygen, nitrogen, and sulfur, as well as heavy metals such as mercury, arsenic, and uranium. These minerals are noncombustible and remain behind as ash or are released into the atmosphere as emissions when coal is burned.

Coal is defined as a fossil fuel, meaning it is an energy source of organic origins. Coal is one of the world’s most common and commonly used fossil fuels, alongside oil and natural gas. It is the most carbon-intensive of the fossil fuels, releasing its energy through the combustion of carbon. Burning coal oxidizes the carbon, causing a chemical reaction known as an exothermic reaction, which releases energy. Coal is considered a nonrenewable energy source because no more significant quantities of coal are expected to form in the human-scale present or future, meaning that the world will eventually exhaust its supply of this energy resource.

Coal Production

Although coal is classified as a nonrenewable energy resource, it exists in very large quantities throughout the world, including both proved and potential reserves. Proved coal reserves are spread over approximately 70 countries around the world and found in every continent. However, the United States, Russia, China, Australia, and India combined hold about two-thirds of global proved recoverable coal reserves, according to the World Energy Council in its Survey of Energy Resources 2010. Not all known resources are extractable with current technology; this adds to the uncertainty in the widely varying estimates of potential global coal resources. Estimates by the World Coal Institute indicate that current production rates and reserve estimates will allow for approximately 119 more years of coal production, far more than estimates for other fossil fuels. This figure could change with new discoveries and technological developments.

Coal is one of the most economical fuels, leading to its popularity since the 19th century. All types of coal are mined and utilized as fossil fuels; all types are used in the generation of electricity. Sub-bituminous and anthracite are also used for space heating. The leading coal producers are China—which alone accounts for about half of global production—the United States, India, the European Union, Australia, Russia, and Indonesia. Coal-mining operations exist in more than 60 countries across the globe, with output by the United States and China amounting to two-thirds of annual global production. Most of the coal produced is destined for the domestic market, with a small percentage sold on the international market. Coal export is more likely to dominate in less densely industrialized nations; in recent years Australia and Indonesia together have accounted for half of world coal exports.

The first step in the production of coal is exploration and discovery of coal seams, usually accomplished through geological mapping, geochemical and geophysical surveys, and exploratory drilling. Next, the extent and quality of the coal seam are determined, and a decision is made regarding whether or not it is technologically possible and economically feasible to begin mining operations. The two major types of coal mining are subsurface mining, also known as underground or deep mining; and surface mining, also known as strip, opencast, or open-cut mining. The decision is determined based on the geographical and geological features of the coal seam. Subsurface mining is dominant in global coal production overall, although surface mining is the most prevalent form in some leading coal production countries such as Australia and the United States. Subsurface mining is more dangerous but less environmentally damaging.

Surface or strip mining is utilized to obtain coal seams that lie close to the surface through the explosive breakup and removal of overlying sediment layers known as overburden. Miners then drill and recover the coal in strips. Miners employ different types of surface mining based on the geography and geology of the individual coal seam and surrounding area.

Types of surface mining include contour mining, mountaintop removal, area mining, and open-pit mining. Equipment involved includes draglines, power shovels, and trucks for the removal of overburden and bucket-wheel excavators, conveyors, and trucks to move the coal. Finally, the coal is transported to a processing plant or primary consumer. Surface mining provides coal recovery rates at or above 90 percent of the total deposits.

Subsurface or underground mining is utilized to extract coal from seams that lie deep below the surface through the construction of tunnels into the earth. Different types of mines are constructed based on the depth and slope of the coal seam. Types of subsurface mines include drift mines, slope mines, and shaft mines. The main types of subsurface mining are room-and-pillar and longwall mining.

Room-and-pillar mining involves carving a series of rooms into the coal seam to allow for mining while leaving behind pillars of coal as roof supports. Longwall mining involves excavating all coal from a section of the seam known as a face. Miners use mechanical shearers to remove the coal and temporary hydraulic roof supports during the course of removal. Coal is brought to the surface through tracks, conveyor belts, coal trucks, or electric hoists.

Coal mining safety concerns include health risks such as lung diseases, the need for proper ventilation, and the potential for explosions, cave-ins, or flooding. Explosions are a concern because of the release of methane during subsurface mining. Although mining safety standards, worker training, and oversight have improved in modern times, mining remains a dangerous occupation, especially in countries with poor mining safety records, such as China.

Negative environmental impacts associated with coal mining include land and habitat destruction; soil erosion; dust, noise, water, air, and soil pollution; mine subsidence; and acid mine drainage. Mine subsidence occurs when subsurface coal mining results in the lowering of the surface ground level. Acid mine drainage results when rocks containing sulfur-bearing minerals react with water, forming an acidic runoff that dissolves heavy metals into the water. Measures to reduce or repair environmental impacts include project planning and monitoring, pollution control measures, and reclamation projects at abandoned mines.

After exploration and mining, the recovered coal then moves to the transportation and storage stage of production; these add to production expenses. Transportation of coal is most often by train or ship; other modes include trucks and coal slurry pipelines. Coal must be stored along the supply chain routes from producers to consumers, which can be dangerous if not done with care. Storage problems can include oxidization of improperly stored coal, and subsequent heat content and economic value losses, or the spontaneous combustion of coal piles due to heat buildup over time, which can cause dangerous explosions.

The World Coal Association estimated that approximately 7 million people are directly employed in the coal industry. Indirect employment through related services and industries is also significant. In developing nations, many local mine enterprises result in the development of multi-use infrastructure, such as roads, water distribution, and communications systems. Coal exports provide countries with foreign hard currency as well as more cost-effective domestic energy sources and greater access to electricity than is typical in developing nations. Many have thus targeted coal as an important component of their strategic development programs, despite its environmental drawbacks.

Uses of Coal

Coal is a fossil fuel energy source that provides both a direct and an indirect source of fuel. Coal can be directly burned to provide heat or can be used as a secondary heat source, such as in the creation of steam to power engines. Humans have utilized coal as an energy source throughout much of recorded history, with readily visible surface outcroppings providing the first preindustrial sources. Recorded uses of coal in China date back to the 4th century c.e., and it had emerged as one of that nation’s leading fuel sources by the 11th century. Large-scale underground coal mining began later, around the 13th century.

The emergence of coal as an important domestic heating source in Europe beginning in the 13th century was driven in part by the destruction of wide swaths of forest for wood energy. When this traditional energy source was endangered, the resulting crisis drove the search for alternative energy resources. European nations such as Britain found an answer through the available supplies of coal. During the Middle Ages, coal powered such preindustrial applications as smelters and forges. By the 15th century, coal-burning stoves, furnaces, and fireplaces were heating homes.

The advent of the Industrial Revolution was in part powered by new developments in coal use technology. Britain led the way in the 18th century because of its large coal deposits and growing coal production rates. British inventor Thomas Newcomen introduced the first steam engine powered by coal in 1712. Another British inventor, James Watt, devised a revolutionary steam engine that was also sometimes coal-powered. The Newcomen, Watt, and other coal-powered engines were first used to pump water from mines and later powered factories, ships, and trains. Britain’s abundant coal supplies and production, as well as its technological innovations, soon gave it the lead in energy-intensive manufacturing, notably in the textile and steelmaking industries. Britain gained military as well as economic advantages, as iron and steel were used in the manufacture of advanced weapons and armaments.

As a result of its industrial and domestic applications, coal had supplanted wood as a global energy source by the end of the 19th century and continued to grow into the first half of the 20th century, although at a slower rate. Coal-burning stoves, furnaces, and fireplaces also continued to heat homes, businesses, and institutions. Coal also proved important in the manufacture of coke, a nearly pure carbon that results when soft coal is heated in the absence of air. Coke has a higher heat value than coal and produces carbon monoxide when heated, reducing iron oxides contained within ore to iron, making it vital to the steel industry as well as other chemical and metallurgical processes.

Coal also became essential in the manufacturing of electricity. Coal burning provides the heat source necessary for creating pressurized steam, which is then used to power turbines. The turbines turn generators and produce electricity. Coal never dominated the automotive or other transportation industries—except for a period in rail transport—because coal-fired steam combustion engines lacked the success of their gasoline- or diesel-powered counterparts.

Coal began to lose ground to oil and natural gas during the course of the 20th century, although it remained a dominant source of energy for home heating and lighting. Coal consumption’s downward trend accelerated after World War II. Natural gas provided a cleaner and better-smelling fuel source than coal distillates, while many industries began switching to relatively convenient and economical petroleum as their dominant fuel source. Key uses of oil and natural gas included the powering of transportation such as trains and automobiles, residential heating, and certain industrial processes. Nuclear, hydro, and renewable energy sources have also increased in use since the 1950s, although at a slower rate than the fossil fuels. Some renewable resources, such as wind power, provide a less expensive alternative to coal and other fossil fuels, are not limited by finite supplies, and continue to benefit from technology growth. Coal has maintained its dominance in other areas, such as electrical power generation.

Coal Use Resurgence

Coal enjoyed a resurgence in the mid- to late 1970s, during US oil shortages resulting from an oil embargo imposed by the Organization of Petroleum Exporting Countries in 1973 and the Iranian Revolution in 1979. The shortages and effects of global politics on oil supply forced the concentration of oil for transportation industry needs, and sparked efforts to diversify energy sources in other areas, revitalizing interest in coal. Ongoing oil crises and politics, rising oil prices, and concerns over energy security have sustained the renewed interest in coal. Coal demand is expected to rise by more than 50 percent by the year 2030.

Coal currently provides more than 35 percent of the world’s primary energy supply, and coal usage is rising at a faster rate than that of any other fuel source. Much of the rising demand for coal comes from developing countries such as China, India, and South Africa, where it is used to increase electrification rates. As construction booms in such nations, other key industries utilize more coal, such as the concrete, iron, and steel manufacturers. The advent of cleaner combustion methods and other clean-coal technologies in the late 20th century has provided some answer to the environmental objections over the pollution generated by coal burning. Despite environmental concerns, coal is expected to maintain its dominance in part because of its lower costs in comparison to other energy sources.

Upon the emergence of the global COVID-19 pandemic in 2020 and the Russian invasion of Ukraine in 2022, renewed focus was placed on coal as an energy source as economic stagnation and war led to sharp increases in the price of natural gas. In 2022, the International Energy Agency estimated that global coal consumption will rise throughout the remainder of the year to match a record high of 8 billion tons previously set in 2013.

Environmental Concerns and the Development of Clean-Coal Technologies

One of the biggest drawbacks to continued production and consumption of coal, besides its nonrenewable status as a fossil fuel, is its associated negative environmental impacts. Environmental problems associated with its use include soil, air, and water pollution, acid rain, and emissions of soot, sulfur oxide, nitrogen oxide, carbon monoxide, carbon dioxide, mercury, methane, cadmium, uranium, lead, and other particulates and trace elements. The ash remaining after coal combustion either escapes into the atmosphere as a pollutant or must be disposed of as a hazardous waste. These toxic emissions mean that coal is regarded as a so-called dirty fuel; its emissions have been linked to respiratory and other diseases. The carbon dioxide and other so-called greenhouse gas emissions produced by coal burning are also associated with climate change or global warming due to the greenhouse effect.

Historical uses of coal as a primary domestic heating source, coupled with growing factory use during the Industrial Revolution of the 19th century, often produced heavy black smog during periods of stagnant, humid weather that held pollutants close to ground level. Well-known examples included the 1952 Great London Smog and the 1948 Donora, Pennsylvania, smog. Modern urban, industrial areas have also seen a rise in pollution-related health issues and deaths, such as those documented in the international port city of Yokkaichi, Japan, resulting in victims’ lawsuits against industrial ownership and more stringent government pollution regulations. Many nations have imposed environmental regulations designed to reduce carbon and other emissions.

Recent environmental concerns have centered on the release of greenhouse gases such as carbon dioxide and methane, and their association with global warming. Coal is more carbon-intensive than other fossil fuels; it produces greater amounts of carbon emissions. International agreements such as the United Nations Framework Convention on Climate Change and the Kyoto Protocol have targeted coal as a leading producer of carbon dioxide. Signatory countries have some incentive to reduce coal usage to meet required reductions in carbon dioxide and other greenhouse gas emissions. Some national governments have also moved toward cleaner and renewable energy resources in response to the growth of the green culture movement and consumer demand for sustainability, which have made it more difficult to mount coal-based projects and to expand the coal industry.

One area of initiative involves reducing or utilizing the dangerous waste products associated with coal production and use. Methane gas is created during coal formation and released during the coal-mining process. Although methane poses a danger because of its combustibility and classification as a greenhouse gas, it is also a potential source of natural gas energy that could be recovered from coal seams. Coal combustion generates waste in the form of the noncombustible minerals found naturally within coal as well as small amounts of carbon that are left behind. Processes have been developed to remove a number of these impurities before the coal is burned, improving the quality of the coal itself while reducing levels of waste and inefficiency at power-generating stations.

Two key techniques involve coal cleaning, also known as washing, and coal pulverization, to separate and remove the mineral and chemical materials often found within the coal and released as emissions during the burning process. Coal washing or pulverization techniques are standard in many developed countries but are lagging in many developing countries. Waste can be further reduced through high-efficiency coal combustion technologies. Potential uses for generated waste are also under consideration, with industrial uses in construction and civil engineering showing promise.

Another area features processes to convert solid coal into a liquid or gaseous state to produce alternate forms of coal fuel. The gasification process involves pulverizing coal and introducing it to steam combined with air or pure oxygen, which produces a reaction converting the coal into a mixture of gaseous hydrocarbons. The liquefaction process involves converting coal into a liquid form similar to that of petroleum. Liquefaction could allow for the use of coal as a motor vehicle fuel, which has proved impractical in the past and led to reliance on oil to fuel the transportation industry.

Other developments have focused on the removal of waste products from the smoke produced during the coal-burning process before it is released into the atmosphere. Key technologies for the reduction of harmful emissions include particulate control devices, various fluidized bed reactors, activated carbon injection, and flue gas desulfurization. Flue gas desulfurization (FGD) systems, known as scrubbers, work within the furnace or smokestack of a coal-fired plant. Traditionally, wet scrubbers have been employed, but the implementation of dry scrubbers utilizing the dry injection of compounds into the furnace is under experimentation.

Challenges to overcome include the cost of developing and implementing clean-coal technologies. Clean-coal-burning technologies began to emerge in the late 20th century in response to increased awareness of the environmental damage caused by traditional coal-burning methods. These technologies include chemical, physical, and biological methods and center on the reduction of pollutants released into the atmosphere through the coal-burning process. The World Coal Association, an industry group, asserts that the average new coal-fired electric generation plant emits about 40 percent less carbon dioxide than the average such plant did in the 20th century. Carbon capture and geological storage (CGS) is a promising avenue for the reduction of carbon dioxide emissions from the use of fossil fuels such as coal at an affordable cost. The use of these technologies currently ranges from full implementation to experimental trials.

By 2021, the Global CCS Institute estimated that the global capacity of CCS technology had reached 40 million tons of carbon dioxide, but more than $1 trillion in funding for the technology by 2050 was required to limit global warming to 2 degrees Celsius. Additionally, Carbon capture and utilization (CCU), an offshoot of CCS technology, emerged as a method of capturing the carbon dioxide released from burning coal and recycling it for future use in other industries. As the concern surrounding global warming increased throughout the twenty-first century, increased focus has been placed on CCU technology as a means of limiting the damage done to the environment by reducing the overall output of carbon emissions.

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