Coal is a fossil fuel. The energy we get from coal today comes from the energy that plants absorbed from the sun millions of years ago. All living plants store solar energy through a process known as photosynthesis. When plants die, this energy is usually released as the plants decompose. Under conditions favorable to coal formation, the decaying process is interrupted, preventing the release of the stored solar energy. The energy is locked into the coal.
Coal formation began during the Carboniferous Period - known as the first coal age - which spanned 360 million to 290 million years ago.
Coal is used primarily as an energy source, either for heat or electricity. It was once heavily used to heat homes and power locomotives and factories. Bituminous coal is also used to produce coke for making steel and other industrial process heating.
Coal is a complex resource and can vary in composition even within the same deposit. Generally, there are different types or ranking levels of coal, each with differences in energy output as a result of increased pressurization, heat, and time.
Anthracite:
This is the highest ranked, hardest, oldest, and least common type of coal. It possesses a high energy content, high percentage of carbon (85%) and relatively little moisture or volatiles. Anthracite produces nearly 15,000 Btu's per pound. This type of coal is what you might burn in your home. There are 7.3 billion tons of anthracite reserves in the United States, mainly in Pennsylvania.
Bituminous:
This is the second rank of coal, softer and younger than anthracite, and containing a lower percentage of carbon (45-85%) and therefore more moisture and volatiles. Bituminous coal is the most plentiful type of coal in the United States. It is mainly found in the eastern and middle parts of the North American continent. Bituminous coal is primarily used to generate electricity and to make coke for the steel industry. Bituminous coal has a heat value of 10,500 to 15,500 Btu's per pound.
Subbituminous:
This is the third rank of coal, possessing 35-45% carbon and more moisture than bituminous coal. Sub bituminous coal is used primarily for electricity generation and possesses an average "as-received" energy content of 17-18 million BTU /ton. This coal is found in the western states and Alaska. It is a clean burning coal.
Lignite:
This is the softest, youngest, and wettest rank of coal, often referred to as "brown coal" with a carbon content of only 25-35% and correspondingly lower energy content. Lignite is used almost exclusively for electricity generation and possesses an average "as-received" energy content of 13 million BTU /ton.
Sub-bituminous coal
Its properties range from those of lignite to those of bituminous coal, is used primarily as fuel for steam-electric power generation and is an important source of light aromatic hydrocarbons for the chemical synthesis industry.
Peat
It is considered to be a precursor of coal, has industrial importance as a fuel in some regions, for example, Ireland and Finland. In its dehydrated form, peat is a highly effective absorbent for fuel and oil spills on land and water. It is also used as a conditioner for soil to make it more able to hold on to and slowly release water.
Graphite
It is technically the highest rank, is difficult to ignite and is not commonly used as fuel — it is mostly used in pencils and, when powdered, as a lubricant.
Steam coal
It is a grade between bituminous coal and anthracite, once widely used as a fuel for steam locomotives. In this specialized use, it is sometimes known as "sea-coal" in the US. Small steam coal (dry small steam nuts or DSSN) was used as a fuel for domestic water heating.
Coal has many important uses worldwide. Since 2000, global coal consumption has grown faster than any other fuel. The five largest coal users - China, USA, India, Russia and Japan account for 76% of total global coal use.
The biggest market for coal is Asia, which currently accounts for over 67% of global coal consumption; although China is responsible for a significant proportion of this. Many countries do not have natural energy resources sufficient to cover their energy needs, and therefore need to import energy to help meet their requirements. Japan, Chinese Taipei and Korea, for example, import significant quantities of steam coal for electricity generation and coking coal for steel production.
Coal formation began during the Carboniferous Period - known as the first coal age - which spanned 360 million to 290 million years ago.
Coal is used primarily as an energy source, either for heat or electricity. It was once heavily used to heat homes and power locomotives and factories. Bituminous coal is also used to produce coke for making steel and other industrial process heating.
Coal is a complex resource and can vary in composition even within the same deposit. Generally, there are different types or ranking levels of coal, each with differences in energy output as a result of increased pressurization, heat, and time.
Anthracite:
This is the highest ranked, hardest, oldest, and least common type of coal. It possesses a high energy content, high percentage of carbon (85%) and relatively little moisture or volatiles. Anthracite produces nearly 15,000 Btu's per pound. This type of coal is what you might burn in your home. There are 7.3 billion tons of anthracite reserves in the United States, mainly in Pennsylvania.
Bituminous:
This is the second rank of coal, softer and younger than anthracite, and containing a lower percentage of carbon (45-85%) and therefore more moisture and volatiles. Bituminous coal is the most plentiful type of coal in the United States. It is mainly found in the eastern and middle parts of the North American continent. Bituminous coal is primarily used to generate electricity and to make coke for the steel industry. Bituminous coal has a heat value of 10,500 to 15,500 Btu's per pound.
Subbituminous:
This is the third rank of coal, possessing 35-45% carbon and more moisture than bituminous coal. Sub bituminous coal is used primarily for electricity generation and possesses an average "as-received" energy content of 17-18 million BTU /ton. This coal is found in the western states and Alaska. It is a clean burning coal.
Lignite:
This is the softest, youngest, and wettest rank of coal, often referred to as "brown coal" with a carbon content of only 25-35% and correspondingly lower energy content. Lignite is used almost exclusively for electricity generation and possesses an average "as-received" energy content of 13 million BTU /ton.
Sub-bituminous coal
Its properties range from those of lignite to those of bituminous coal, is used primarily as fuel for steam-electric power generation and is an important source of light aromatic hydrocarbons for the chemical synthesis industry.
Peat
It is considered to be a precursor of coal, has industrial importance as a fuel in some regions, for example, Ireland and Finland. In its dehydrated form, peat is a highly effective absorbent for fuel and oil spills on land and water. It is also used as a conditioner for soil to make it more able to hold on to and slowly release water.
Graphite
It is technically the highest rank, is difficult to ignite and is not commonly used as fuel — it is mostly used in pencils and, when powdered, as a lubricant.
Steam coal
It is a grade between bituminous coal and anthracite, once widely used as a fuel for steam locomotives. In this specialized use, it is sometimes known as "sea-coal" in the US. Small steam coal (dry small steam nuts or DSSN) was used as a fuel for domestic water heating.
Coal has many important uses worldwide. Since 2000, global coal consumption has grown faster than any other fuel. The five largest coal users - China, USA, India, Russia and Japan account for 76% of total global coal use.
The biggest market for coal is Asia, which currently accounts for over 67% of global coal consumption; although China is responsible for a significant proportion of this. Many countries do not have natural energy resources sufficient to cover their energy needs, and therefore need to import energy to help meet their requirements. Japan, Chinese Taipei and Korea, for example, import significant quantities of steam coal for electricity generation and coking coal for steel production.