How is coal formed?

Coal is a fossil fuel, formed from vegetation, which has been consolidated between other rock strata and altered by the combined effects of pressure and heat over millions of years to form coal seams. The energy we get from coal today comes from the energy that plants absorbed from the sun millions of years ago.

Types of coal

There are four types of coal; lignite, sub-bituminous, bituminous and anthracite, which are created during a process known as ‘coalification’.

Coalification means the degree of change undergone by coal as it matures from peat to anthracite. This has an important bearing on coal’s physical and chemical properties and is referred to as the ‘rank’ of the coal. Ranking is determined by the degree of transformation of the original plant material to carbon.

The quality of each coal deposit is determined by:

  • Types of vegetation from which the coal originated
  • Depths of burial
  • Temperatures and pressures at those depths
  • Length of time the coal has been forming in the deposit

In addition to carbon, coal contains hydrogen, oxygen, nitrogen and varying amounts of sulphur.

  • High-rank coals are high in carbon and therefore heat value, but low in hydrogen and oxygen.
  • Low-rank coals are low in carbon but high in hydrogen and oxygen content.

Where is coal found

Coal is abundant – there’s over 1.06 trillion tonnes of proven coal reserves worldwide.

This means that at current rates of production, there is enough coal to last us around 132 years. The biggest reserves are in the USA, Russia, China, Australia and India.

After centuries of exploration, the location, size and characteristics of most countries’ coal resources are quite well known. What tends to vary much more than the assessed level of the resource – i.e. the potentially accessible coal in the ground – is the level classified as proved recoverable reserves.

Reserves can be extended further through improved exploration activities and advances in mining techniques – allowing previously inaccessible reserves to be reached.

RESOURCE

The amount of coal that may be present in a deposit or coal field

RESERVES

Reserves can be defined in terms of proved (or measured) reserves and probable (or indicated) reserves

PROVED RESERVES

Reserves that are not only considered to be recoverable but can also be recovered economically

How is coal found?

Coal reserves are discovered through exploration activities. The process usually involves creating a geological map of the area, then carrying out geochemical and geophysical surveys, followed by exploration drilling. This allows for an accurate picture of the area to be developed. The area will only ever become a mine if it is large enough and of sufficient quality that the coal can be economically recovered. Once this has been confirmed, mining operations begin.

As coal reserves are found across the globe, the largest coal producing regions are not confined to one region – the top five hard coal producers are China, India, USA, Indonesia and Australia. Most coal production is actually used in the country in which it was produced.