What is Coal?
This article deals with the different aspects of coal like its properties, chemistry, types, and distribution in the world. But before going into the various aspects of coal, let us find out “what is coal”. Coal is a sedimentary rock that is blackish or brownish-black in colour and is developed from start rock also referred to as coal seams. This is assumed to have developed from the residue of the algae plants. Coal is composed of a maximum amount of carbon with other organic elements chiefly hydrogen followed by sulphur, oxygen, and nitrogen.
When the dead and decayed matter of plants and animals undergo heat and pressure of deep burial for millions of years, they convert into peat and finally into coal. Wetlands are the hub of coal, and therefore, the region is also referred to as coal forests. It covers much of the topical land of the Earth during the late Permian and Carboniferous times. But most of the coal that is found today has been studied to be much younger than the times mentioned, and therefore, it is assumed that the coals have originated from the matters of the Cenozoic and Mesozoic eras.
Coal rock is always primarily preferred as fuel. Though coal has been in use for thousands of years, its usage was limited until the industrial revolution began. With the invention of the steam engine, the usage of coal has abruptly increased. In 2016, coal made up a quarter of the total primary energy of the world and one-fifth of the electrical energy required by the world. Some of the industrial applications like that of the formation of iron and steel require the burning of coal.
Permanent death and illness are caused by the extraction and use of coal. It is an anthropogenic source of carbon dioxide that contributes largely to climate change, and thus, the increased use of coal affects the environment adversely. In the year 2020, with the burning of coal, about 14.5 billion tonnes of carbon dioxide was generated around the globe. It contributes to 25% of the greenhouse gas emissions and 40% of the total fossil fuel emissions. China is the largest importer and consumer of coal.
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Formation of Coal
Coalification is a process in which dead matters like plants and vegetation convert into coal over a prolonged period of time. In the past geological times, the Earth was covered with dense forests, especially in the wetland areas. Now the dead plants in these areas were prevented from decomposition and oxidation by the acidic water and mud. This results in the formation of peat. Now, the coalification process started when the bogs accumulating the peats trapped the carbon in large amounts that were eventually deeply buried by the sediments. Now, over millions of years of pressure and heat resulting in the escape of the water, carbon dioxide and methane, and the matter were left with carbon content. The gradation of the coal depends on the amount of heat and pressure the dead matter underwent to convert into coal. Thus, Lignite is formed under relatively mild conditions; sub-bituminous, bituminous, and anthracite coals are formed under high temperature and pressure.
Temperature is one of the prime factors that are most important as compared to other factors like pressure or even the time of burial. Sub-bituminous coal can be formed at a very low temperature of 35℃ to 80℃ while anthracite is formed under a very high temperature of at least 180℃ to 245℃. Also, favourable geology does not only contribute to the formation of coal but other factors like the presence of oxygen also contribute to the high coal deposition. Thirty per cent of the wildfires were contributed by the presence of high oxygen levels in the atmosphere resulting in the formation of charcoal. The nature of the Carboniferous forests and promote plant growth are the contributors to the high level of carbon dioxide.
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How is Coal Obtained?
Now that we know how coal is formed, it is essential to understand: how do we get coal? Coal is extracted by different kinds of mining activities on the Earth’s surface. The most common ones are surface mining and underground mining. Surface mining is done when coal is less than 200 feet below ground level. In this process, mineworkers have to remove all kinds of rocks and soil-forming the top layer. It is cheaper than underground coal mining. There are three types of surface mining – strip mining, where explosives are used to remove the top layers; open pit mining when a pit is dug; and MTR mining where a whole mountain summit is destroyed. Underground mining is performed when the coal is deeper than 300ft below ground level. Coal mine workers have to carry out mining activities then.
Properties of Coal
The physical properties of coal are as follows:-
The Density of Coal: The degree of mineral impurity and the rank of the coal determine the relative density for the specific gravity of the coal. In order to determine the properties of the composites and the blend, it is very important to have a thought knowledge of the density of each coal. For the conversion of the resources into reserves, the density of the coal seam is necessary. The loss of weight of the sample in water determines the relative density. This can be achieved by using finely ground coal as bulk samples get white porous in nature. It is important to however preserve the white space when measuring the specific gravity so as to determine the in-place coal tonnage.
Particle Size Distribution: The rank of the coal determines the particle size distribution of the coal which in turn determines the brittleness, and the handling, crushing and milling it has undergone. Generally, a certain size of coal is required for the furnace and the coke oven and therefore, its crushability needs to be determined and its behaviour quantified.
The chemical properties of coal are as follows:-
Moisture: As all the coals are mined in wet conditions, thus the moisture content in the coal is an important factor. Groundwater and other extraneous moisture is known as adventitious moisture and can easily be evaporated. The coals trapping the moisture in itself is known as inherent moisture and undergoes quantitative analysis. In coal, moisture may occur in four forms, namely:
Surface moisture is the water held on the surface of the coal.
Hygroscopic moisture is the water held by the microcapillary within the microfractures of the coal.
Decomposition moisture is the water that is held within the decomposed organic matter of the coal.
Mineral Moisture is the water that comprises part of the crystal structure of hydrous silicates such as clays.
Thus, the total moisture content is determined by the total mass of the untreated coal minus the total mass of the treated coal once the sample is analysed. This is achieved by:-
Heating the coal with Toluene.
Within a nitrogen atmosphere, the drying is done in minimum-free space over 150℃.
Drying in the air at 100℃ to 105℃ and then the loss of mass is analysed.
Volatile matter: The component of the coal except for moisture is referred to as the volatile matter in coal which is liberated at high temperature in absence of air. It is usually an amalgamation of long and short-chain hydrocarbons and aromatic hydrocarbons along with sulphur. In order to evaluate the absorption application of activated carbon, volatile matter comes into play. Under rigid control standards, the volatile matter of the coal is determined.
Ash: The non-combustible residue that is left after the coal has been burnt is known as ash. After the carbon, oxygen, sulphur, and water have been driven off, during conversion, the bulk matter that is left behind is represented by ash. The determination of the percentage of ash is very simple. It is evaluated when the coal is thoroughly bonded and is expressed as the percentage of the original weight. It also gives a fair idea about the nature of coal. The air-dried basis on the oven-dried bases is the two ways of determining the ash content. The difference between the two processes is determined after the entire moisture in the coal has been expelled.
Fixed Carbon: The fixed carbon can be found determined as the carbon which is left after the entire volatile materials are driven off. This is different from the ultimate carbon content of the coal because some carbon is lost in hydrocarbons with the volatiles. To estimate the amount of coke that would be either from a sample of coal, fixed carbon is taken into consideration. When the mass of volatile is removed, it is only then the fixed carbon is determined. Therefore, it is determined by the volatile test from the original mass of the coal sample.
Types of Coal
Coal is divided into four main types and these are anthracite, bituminous, sub-bituminous, and lignite. The ranking of the coal is done by the amount and the type of carbon that is present in the coal and its ability to produce heat when it is burned. The rank of the coal deposit determines the amount of pressure and the heat that has acted on the dead and decayed matter over a prolonged period of time.
Anthracite: It has the highest heating value of all the other coal types as it contains about 86–97% carbon. It summed up to less than 1% of the coal mined in the USA in the year 2020. Northeastern Pennsylvania and the United States are the two major anthracite coal mines in the world. In the United States, anthracite coal mines are generally used for the metal industries.
Bituminous: The carbon content in bituminous coal is 45–86%. It is the most abundant type of coal that is found in the United States that accounting for about 44% of the total production of coal in the USA in 2020. In order to generate electricity, bituminous coal is used as it is an important fuel and raw material for making coking coal.
Sub-Bituminous: The carbon content in sub-bituminous coal is about 35–45% and it has a lower heating value than bituminous coal. In the United States, a total of 46% of the coal production in 2020 was sub-bituminous among which 88% of it was produced by Wyoming and 8% was in Montana. The remaining was produced in Alaska Colorado and New Mexico.
lignite: The carbon content in lignite coal is about 25–35% and has a low energy content among all the coal types known. Lignite has a high moisture content which contributes to its low heating value. Only 9% of the lignite coal was mined in the USA in the year 2020 among which 54% was mined in North Dakota and 39% was mined in Texas. Another 7% was in Louisiana Mississippi and Montana.
Under suitable conditions, as geological processes apply pressure to dead biotic material over time, its metamorphic grade or rank increases successively into:
Peat, a coal precursor.
Lignite, or brown coal, the lowest rank of coal and the most hazardous to one's health, is almost solely utilised to generate electricity.
Jet, is a polished form of lignite that has been utilised as a decorative stone since the Upper Palaeolithic period.
Sub-bituminous coal, which has qualities that fall in between lignite and bituminous coal, is largely employed as a fuel for steam-electric power generation.
Bituminous coal is a solid sedimentary rock that is normally black but can sometimes be dark brown and has distinct bands of bright and dull stuff. It is principally utilised as a fuel in the production of coke and in the manufacture of steam-electric power. In the United Kingdom, it's known as steam coal, and it was once used to generate steam in steam locomotives and ships.
Uses of Coal
Coal is a very widely used natural resource because of its unique characteristics.
Because of its affordability, it is used in several countries for electricity and power generation.
Generally, powdered coal is used to create steam, which in turn generates electricity with high pressure.
Coal also serves as a raw material in the making of several things like steel and iron, which we use in our everyday lives.
Coal is available easily in countries like India and China and is used by many households, especially in rural areas, for activities like cooking.
Electricity Production: Coal is commonly used in thermal power generation, which aids in the generation of energy. Powdered coal is burned at a high temperature, turning water into steam in the process. In a strong magnetic field, this steam is used to turn turbines at high speeds. Then, and only then, is electricity generated.
Steel Manufacturing: Coal is used indirectly to create steel in the steel industry. Coal is baked in furnaces to produce coal coke in this process. Manufacturers utilise coal coke to smelt iron ore into iron and make steel after this is generated. In the meantime, ammonia gas is recovered from coke ovens and utilised to make nitric acid, ammonia salts, and fertilisers.
Industries: Coal is used in a variety of sectors to make a variety of products. Cement, paper and aluminium manufacturing, chemical and pharmaceutical manufacturing are just a few of the industries that use coal. Chemical businesses rely on coal for a variety of raw materials such as benozle, coal tar, sulphate of ammonia, creosote, and so on. The majority of industries rely on coal as a source of energy.
Disadvantages of Coal
Coal has a set of disadvantages: coal mining accidents, coal pollution, etc. There are a large number of accidents that take place in coal mines because it is a dangerous and challenging activity involving heavy equipment. Moreover, coal emissions are very harmful to human beings, especially to the lungs. Coal pollution is widespread in areas that lie near coal reserves. When coal is burnt, it releases carbon dioxide in vast quantities, which is harmful to human beings. Moreover, coal is a non-renewable and exhaustive natural resource which implies that we should not depend on it for everyday activities. Coal is also one of the biggest contributors to global warming today.
Coal Distribution in the World
The distribution of coal across the world is as follows:-
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Most of the coal fuel of Russia that is trapped in the Siberian Region is unexplored.
The Carboniferous coal that helped us become a leading industrial nation came from two places namely great lakes and Appalachian wetlands.
The coal reserves that have made Germany the leading industrial superpower of Europe are in Ruhr and Rhineland which are coupled with rich iron deposits.
From the coal reserves of South Wales auction Manchester and Liverpool acceptor England also benefited immensely as the industrial revolution began here mainly due to the rich reserves of the coal.
In South America, Brazil is the leading producer of coal. Most of the coal goes into power generation and the axis produced is imported by China.
The highest producer of coal in Australia and most of its course is exported either to Japan or China. Australia is famous for its rick coking coal deposits. Australia exports this coking coal mainly to India.
As the quality of the coal in China is very poor, thus it imports metallurgical grade coal from Australia.
The only region in Africa that has an abundance of coal reserves in South Africa.
FAQs on Coal
1. Where is coal produced?
Coal reserves are large geographical areas where coal is deposited. These reserves are spread across the globe in all continents except in Antarctica. There are enormous amounts of coal – mostly in countries that have the largest land masses, for example, Russia, North America, China, Australia, etc. These countries, along with 6 more countries – India, Germany, Ukraine, Kazakhstan, South Africa, and Serbia, have 90% of the world's source of coal. In India, the state of Jharkhand has an estimated reserve of 80,716 million tonnes, with Jharia Mines in Dhanbad being one of the primary coal reserves.
2. Can coal be reused or recycled?
Once burned, coal cannot be reused or recycled. On burning coal, coal ash is formed. This coal ash comprises several minerals like calcium and aluminium, which can be reused. About 40% of coal ash produced each year is effectively reused to fill coal mines that are abandoned. Sometimes, coal ash is used as the topmost layer on roads and foundations of high rise buildings. Another advantage of reusing coal ash is that it lowers emissions from greenhouse gases by putting carbon to use.
3. Is coal a natural resource?
Yes, coal is a natural resource as it is generated from the dead and decayed vegetation and plants when they are under high temperature and pressure for millions of years under deep burial.
4. State the origin of coal.
The origin of coal is the vegetation and the plants that were present in the wetlands during the Mesozoic era.
