What are Coal Types?
There are different types of coal that are all rocks and minerals composed largely of carbon. This fossil fuel produces ~40% of the planet's electricity and approximately 25% of the world's primary energy. Perhaps, not all coal used is the same. There are different types of coal and their uses. Moreover, there are different quantity levels of carbon—which pronounce the quality of the coal. Higher quality coal or the best variety of coal yields less smoke, burns longer, and renders more energy than lower quality coal.
Coal is Which Type of Rock
Wanting to know coal is what type of rock? Coal is typically organic sediment which contains a complex mixture of compounds. Depending upon the evolutionary phase of coal formation there are essentially four types of coal. The variety of coal types is based on energy density and the carbon contents of coal. Furthermore, it reflects the moisture content before drying, and the amount of mercurial content, after it's dried.
Types of Coal and their Uses
As mentioned above, there are primarily 4 types of coal that are distinguished from one another based on their process of formation.
1st Stage - Peat
The first evolutionary phase of coal formation is Peat that is a bit more than wood pulp which has been poorly decomposed. There are huge deposits of Peat in the Greenland and Scandinavian countries. Peat coal can strip mine it because it is usually very close to the ground level. The issue with Peat is that it consists of a very low British Thermal Units (BTU) production per pound of the fuel burned. Moreover, strip mining is ecologically very devastating unless the mining operative makes a deliberate effort to restore the countryside. Strip mining is a phenomenon of scraping the coal from the top surface of the ground.
2nd Stage - Lignite
The second in an evolutionary phase of coal is lignite. Lignite is found in a huge amount in the Western part of the United States. Again lignite is not specifically efficient in yielding energy per mass of fuel. There has been a little effort recently in the gasification and liquefaction of lignite. Liquefaction transforms lignite into liquid crude petroleum. Gasification plants transform lignite into natural gas products. The transformation process is very expensive, and with the current cost of other forms of fuel, it is economically impractical. However, if other fuels get too expensive, this could become a more economical process. Other research has been carried out scrutinizing other uses of lignite like a fertilizer in hydroponic plant growth. Hydroponics is the use of nutrients containing water in place of soil for the growth of plant life.
3rd Stage - Lignite
The third phase included in the coal development is bituminous (soft coal) which is one of the two stages used as a fuel in producing electrical power. The fourth and the final phase outcomes in the formation of anthracite (hard coal). If anthracite coal is put under more heat and pressure, it would in the de course be compressed into a diamond.
4th Stage - Anthracite Coal
In this fourth stage in the coal formation, coal is formed due to the high pressure and high temperature for a long duration of time. It is hard, lustrous and has the greatest percentage of carbon among all the 4 coal types. This is also known as hard coal. Petroleum and natural gas deposits are generally found in the coastal areas.
Best Type of Coal
The best variety of coal is Anthracite It is also known as the hard coal and attained its name due to the compact carbon variety with a submetallic luster. It contains the greatest carbon content, minimal impurities, and massive energy density of all coal types, and is the top coals ranking. Moreover, anthracite is also the oldest variety of coal, having created from biomass that was buried 350 million years ago
Where is Coal Formed?
The energy in coal arises from energy stored in jumbo plants, which lived in wetland forests hundreds of millions of years ago, even before the dinosaurs! When those colossal plants and ferns perished, layers at the bottom of the swamps were formed. Water and soil started to amass around the remains of the dying vine.
FAQs on Coal Types
1. What are the four main types of coal, and how are they classified?
The four main types of coal are ranked based on their carbon content, moisture level, and heating value. The classification reflects the stage of formation, a process known as coalification. The types are:
- Anthracite: The highest rank of coal, with the highest carbon content (over 85%) and the highest heating value. It is hard, black, and lustrous.
- Bituminous: The most abundant type, with a carbon content ranging from 45% to 85%. It is widely used for electricity generation and making coke for the steel industry.
- Sub-bituminous: A lower-grade coal with 35-45% carbon content and higher moisture than bituminous coal.
- Lignite: Also known as brown coal, this is the lowest rank with the lowest carbon content (25-35%) and highest moisture, giving it a lower heating value.
2. Which type of coal is considered the best quality and why?
Anthracite is considered the best quality coal. This is because it has the highest carbon content and the lowest percentage of impurities and moisture. As a result, it produces the most energy (high calorific value) when burned and generates the least smoke, making it a very clean and efficient fuel source.
3. What is the main difference between peat and lignite in the context of coal formation?
The main difference is that peat is not actually a type of coal but the precursor to it. Peat is an accumulation of partially decayed vegetation and organic matter. Over millions of years, under immense heat and pressure, peat undergoes a transformation (coalification) to become lignite, which is the first and lowest rank of coal.
4. How do the uses of bituminous coal differ from other types?
Bituminous coal is extremely versatile due to its balance of high heat output and abundance. Its primary uses include:
- Electricity Generation: It is the most common type used in thermal power plants to produce steam for turbines.
- Coke Production: A specific type, coking coal (metallurgical coal), is heated to produce coke, which is essential for smelting iron ore in the steel manufacturing process.
- Cement Manufacturing: It is used as a fuel source in cement kilns.
In contrast, anthracite is often used for residential heating, while lignite is primarily used for power generation in plants located very close to the mines due to its low energy density.
5. Why is coal often called the 'Black Diamond'?
Coal is called the 'Black Diamond' as a metaphor for its immense economic value. Just as diamonds are precious, coal has been a cornerstone of industrial development and energy production for centuries. Its black colour and vital role in powering industries, generating electricity, and manufacturing essential goods like steel and cement make it an extremely valuable resource, hence the comparison to a precious gem.
6. How does the geological process of formation affect the quality of coal?
The quality of coal is a direct result of the intensity of its formation process, known as coalification. The deeper the organic matter is buried and the longer it is subjected to high heat and pressure, the more its chemical and physical properties change. This process drives out moisture and volatile compounds, increasing the concentration of pure carbon. Therefore, minimal pressure and heat result in low-quality lignite, while intense, prolonged pressure and heat create high-quality anthracite.
7. If anthracite is the highest quality, why is bituminous coal more commonly used in industries worldwide?
Although anthracite is superior in terms of energy content and cleanliness, bituminous coal is far more widely used for two main reasons: abundance and cost. Bituminous coal deposits are much more common and widespread globally than anthracite deposits. This greater availability makes it significantly cheaper to mine and transport, rendering it the more economically viable option for large-scale industrial applications like power generation and steel production.
