Coal is a flammable sedimentary, organic rock. Coal is a fossil fuel that has been consolidated between the other rock strata and is formed from vegetation. It is mainly composed of carbon, as well as other elements such as hydrogen, sulphur, oxygen, and nitrogen. To form coal seams, the combined effects of heat and pressure over millions of years were altered. The energy received by coal today is the same energy that was absorbed by the plants millions of years back. The majority of coal is used in power generation and metallurgy.
Coal reserves are widely dispersed around the world. However, the United States, Russia, China, and India collectively hold more than half of the world's recoverable coal reserves. Coal is also the cheapest source of electricity if used near coal mines as its transportation to remote locations is expensive due to its size. As a result, industries that need a significant amount of coal are located near coal mines.
Coal is used to fuel machines, trains, ships, etc. It is also needed for the production of iron and steel, as well as a variety of chemicals. Coal-tar and chemicals such as ammonia, benzol, and others are generated as by-products of the iron and steel manufacturing process when coal is burned to produce coke.
Occurrence of Coal
Coal is a widespread resource of energy. Around 358.9 million to 298.9 million years ago after the Carboniferous time, the terrestrial plants which are necessary for coal development became abundant. The large sedimentary basins that contain the rocks of the Carboniferous age and younger are virtually known on every continent, including Antarctica.
Regions such as Alaska and Siberia, which have arctic and subarctic climates have large coal deposits due to the climatic changes and the tectonic motion of the crustal plates that are moved by the ancient continental masses above the earth’s surface. Areas including most of northern Canada and Greenland do not have coal, as the rocks that are found in these areas are from before the Carboniferous period.
Formation of Coal
Coal first appeared about 300 million years ago, during the Carboniferous era. The Earth was covered in large, shallow seas and dense forests at the time.
To begin with, plant matter in wetlands, such as ferns, shrubs, trees, and algae, died and accumulated on the soil.
This plant matter was then buried underneath the earth's crust, with no exposure to sunlight.
As the plant matter got buried deeper under the Earth's surface, it experienced higher temperatures and pressure.
The organic plant matter was then decomposed by anaerobic bacteria, which emitted carbon dioxide and methane.
This continued for thousands of years, resulting in many metres of partly decayed plant matter known as peat.
Several metres deep inside the Earth, these peat layers store vast quantities of carbon. The resulting peat can be burned as fuel and is a major source of heat energy in countries such as Scotland, Ireland, and Russia.
When this peat is deeply buried, water and other compounds are forced out by increasing pressure, resulting in the formation of lignite, the lowest quality of coal.
Growing pressures and temperatures turn lignite coal into better quality "black coals."
Lignite is converted into sub-bituminous coal, followed by bituminous coal, and finally anthracite.
Major Varieties of Coal
Coalification is a process by which 4 different types of coal are created which include bituminous, lignite, sub-bituminous, and anthracite. The degree of changes that coal undergoes as it matures from peat to anthracite is referred to as the process of coalification. The different types of coals are listed below-
Anthracite is the best quality of coal. It is composed of 80-90% per cent carbon. It's hard coal. It is mostly located in the district of Reasi in the state of Jammu and Kashmir in India.
Bituminous coal is the most common and widely used type of coal. It's of average size. It is composed of 40-75 per cent carbon. It's made of soft coal. Most of the coal in India falls into this group.
Lignite is of poor quality. It has a brown colour to it. It is composed of 30 to 40% carbon.
Peat is the intermediate stage in the coal formation phase. It is composed of less than 40% carbon. It contains more impurities. The wood pieces are surprisingly present in it.
The determination of the quality of each of the coal that is deposited is done by-
Depths of burial.
The length of time taken by the coal to form in the deposit.
The types of vegetation the coal has originated from.
The level of pressure and temperatures at those depths.
The composition of coal, in addition to carbon, consists of oxygen, hydrogen, nitrogen, and varying amounts of sulfur. The carbon content in the low-rank coals is low but the content of oxygen and hydrogen is high, while the carbon content in high-rank coals is high but the content of oxygen and hydrogen is low.
World Distribution of Coal
More than 90% of the world's proven coal reserves are concentrated in only ten countries. The United States tops the list, with more than one-fifth of total proven coal reserves, while China ranks third as the largest producer and user of coal. Mining Technology examines the ten countries with the most coal reserves, as measured by total proved reserves. Here is a table of the largest coal reserves in the world.
After many centuries of exploration, location, size and also the characteristics of most of the countries, the coal deposits in the world now are quite well known. What varies much more than the resource's measured amount – i.e. the potentially accessible coal in the field – is the level known as proved recoverable reserves. Improved exploration activities and improvements in mining methods will increase the availability of coal in the world, allowing previously inaccessible reserves to be reached.
Distribution of Coal in India
Now that we have discussed coal reserves by country, let’s learn about the distribution of coal in India.
As of December 2018, India's proven coal reserves accounted for more than 9% of the world's total. The country's main hard coal deposits are in the eastern states of Jharkhand, Chhattisgarh, Orissa, and West Bengal, which account for more than 70% of the country's coal reserves. The other major coal-producing states in India are Andhra Pradesh, Madhya Pradesh, and Maharashtra. The majority of the country's lignite deposits are located in the southern state of Tamil Nadu.
After China and Indonesia, India is the world's third-largest producer and user of coal. In 2018, it produced 771 Mt of coal (7.9% of the global total). India also consumes 12% of the world's overall coal use. In 2018, it imported 240 Mt of coal, making it the world's second-largest coal importer. Coal accounts for more than 70% of India's electricity production. That’s why distribution of coal in India is vital.
Detailed Distribution of Coal in India
The Damodar Valley Coalfield is India's largest coal reserve. Jharkhand and West Bengal are included in this coalfield area. Jharia in Jharkhand is India's largest coalfield. The majority of India's coking coal comes from here. Jayanti, Bokaro, Karanpura, Ramgarh, Giridih, Auranga, Hutar, Daltonganj, and Deogarh are also coalfields in Jharkhand. West Bengal's major coalfields are Raniganj (India's oldest coalfield) and Dalingkot in the Darjeeling district.
The Mahanadi Valley Coalfield includes areas in Chhattisgarh and Odisha. Korba, Jhilmil, Chirmiri, Bishrampur, Lakhanpur,Birampur, and Sonhat are the major coal mining areas in Chhattisgarh. The most important coalfields in Odisha are the Talcher, Rampur-Himgir, and Ib river coalfields.
The Son Valley Coalfield includes parts of Madhya Pradesh and parts of Uttar Pradesh. Singrauli, Sohagpur, Umaria, Pench, Ramkola, and Tatapani are prominent coalfields in the Son Valley.
The Godavari Valley Coalfield is located in the Indian states of Andhra Pradesh and Telangana. Singreni, Tandoor, and Sasti are the region's major coalfields.
The Wardha Valley Coalfield, which includes Kampti, Wunfield, Chandrapur, Yavatmal, and Nagpur, is a major coal-mining region in Maharashtra.
The Satpura Coalfield is located south of the Narmada River in the Satpura range. Ghorbari, Mahapani, and Patharkheda are major coal-mining areas.
The Rajmahal Coalfield (Lalmatia) is a major coal-mining centre in the Rajmahal range, where open-cast mining is practised.
World distribution of coal shows a significant amount of the world's energy supplies. The estimated coal reserve is 860 billion tonnes. These resources are widely dispersed globally, and current output accounts for 29% of global primary energy consumption. In recent years, the classification of coal resources and reserves has been redefined, with the criteria and codes of conduct followed by the major coal-producing countries being equated on a global scale.
Undiscovered coal resources are hypothetical coal reserves that are either distinct from or an extension of the estimated, suggested, and inferred coal resources. Undiscovered coal resources are classified as hypothetical or theoretical based on their degree of certainty. Estimates of hypothetical coal resources are based on very little geologic certainty and typically exist in unmapped and unexplored areas.
Coal Deposits World Map
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Problems in Estimating World Coal Reserves
The largest coal reserves in the world are difficult to assess. While a lack of reliable data for individual countries contributes to some of the difficulty, two fundamental issues make these estimates challenging and subjective.
The first issue is that there are different definitions of terms such as proven reserves and natural resources. Any commodity's proven reserves should provide a fairly reliable estimation of the amount that can be recovered under current operational and economic conditions.
A coal bed must have a minimum thickness and be buried no deeper than a certain depth below the Earth's surface in order to be commercially mineable. These thickness and depth values are not constant and vary depending on coal quality, demand, the ease with which overlying rocks can be extracted or a shaft sunk to enter the coal seam, and so on.
New mining techniques can increase the amount of coal that can be extracted in comparison to the amount that cannot be removed. In underground mining, for example, traditional mining methods leave huge pillars of coal behind to support the overlying rocks while recovering just about half of the coal present. Longwall mining, on the other hand, in which the equipment removes continuous parallel bands of coal, can recover nearly all of the coal present.
The rate at which coal is consumed is the second problem in estimating its reserves. When it comes to global coal supplies, the number of years coal would be available could be more significant than the overall amount of coal resources.
Problems Associated With the Use of Coal
Coal is cheap and abundant. Assuming that current rates of consumption and output remain constant, estimates of reserves suggest that there is enough coal to last more than 200 years. However, there are a number of issues associated with the use of coal.
Mining activities are risky. Every year, hundreds of coal miners are killed or critically injured. Roof crashes, rock blasts, and fires and explosions are also major mine hazards. The latter occurs when flammable gases trapped in coal (such as methane) are released during mining operations and inadvertently ignited. Methane can be extracted from coal beds prior to mining by using hydraulic fracturing (fracking), which involves injecting high-pressure fluids underground to open fissures in the rock, allowing trapped gas or crude oil to escape through pipes that carry the material to the surface.
Coal mines and coal-preparation plants have wreaked havoc on the climate. Surface mining, also known as strip mining, kills natural habitats, while surface mining, known as mountaintop removal mining, changes the topography of the region significantly and irreversibly. Surface areas exposed during mining, as well as coal and rock waste (which was often deposited indiscriminately), weather rapidly, creating a large amount of sediment as well as soluble chemical products such as sulfuric acid and iron sulphates. Sedimentation can cause nearby streams to become clogged.
Coal use is associated with different types of air pollution. Many compounds are formed during the incomplete burning or conversion of coal, some of which are carcinogenic. Coal combustion also releases sulphur and nitrogen oxides, which react with atmospheric moisture to form sulfuric and nitric acids, resulting in acid rain. Furthermore, it generates particulate matter (fly ash) that can be carried hundreds of kilometres by winds and solids (bottom ash and slag) that must be disposed of.
Coal as an Energy Source
Coal is an abundant resource that can be used as an energy source, a chemical source from which many synthetic substances can be derived, and in the manufacture of coke for metallurgical processes. Coal is a significant source of energy in the generation of electrical power through steam generation. Furthermore, coal gasification and liquefaction provide gaseous and liquid fuels that can be easily transported and stored in tanks.
After a massive increase in coal usage in the early 2000s, fueled mainly by the expansion of China's economy, global coal use peaked in 2012. Since then, coal consumption has steadily declined, partially offset by rises in natural gas use.
While the availability and affordability of coal are advantageous, these considerations must be weighed against the negative environmental effects of its use. Coal's future will be determined by the use of low-sulfur varieties, advancements in renewable coal technology, and the procurement of lower-cost alternatives. While the drawbacks of coal energy will reduce demand over time, the lack of a cost-effective substitute could hold this fossil fuel in demand for many years to come.
Coal is a strong carbon-rich substance that is commonly brown or black and occurs in stratified sedimentary deposits. It is one of the most significant primary fossil fuels. Coal is characterised as having more than 50% carbonaceous matter by weight formed by the compaction and hardening of altered plant remains, i.e. peat deposits.
Different types of coal exist due to variations in plant content, degree of coalification, and impurity range. While the majority of coals is found in stratified sedimentary deposits, the deposits may later be subjected to elevated temperatures and pressures caused by igneous intrusions or deformation during orogenesis, resulting in the formation of anthracite and even graphite. While the concentration of carbon in the Earth's crust is less than 0.1% by weight, it is essential for life and is the primary source of energy for humans.