Coking black coal

Metallurgical coal is a high quality kind of black coal that is mostly used to make coke, which is a material used in the steel making process. In Australia, the term black coal covers a wide range of coals varying from the most mature form of coal, anthracite, and includes the next grades of coal, bituminous and sub bituminous coals. Metallurgical coal is a bituminous coal. Black coal is older than brown coal (thermal coal), and since it has been pressurised for many millions of years longer than brown coal, it has a lower moisture and higher carbon content. Metallurgical coal is thus much harder than brown coal, and more economically valuable due to its relative scarcity. Metallurgical coal contains 60-80% carbon, with the remaining parts made up of water, oxygen, minerals and gasses.

Formation
All coal starts as peat, which is a mixture of organic materials buried in a peat bog. The peat turns into lignite (brown coal), then takes many years to mature into black coal, and finally anthracite. And we do mean many years – each stage of coal has millions of years between it. Brown coal is between 15 and 50 million years old, whereas the oldest deposits of black coal in Australia are between 180 and 220 million years old. There are other black coals mined in Australia that are on the younger end of the spectrum, as young as 140 million years old, however there is still a huge age gap between these coal seams and the brown coal seams that are mined in Victoria.

Australia’s Resources
Metallurgical coal is found all around Australia, with the major deposits in NSW and Queensland. Australia is one of the few countries that exports metallurgical coal, because most countries consume what little they produce. Australia, on the other hand, exports the majority of the metallurgical coal it produces, with almost 40% of exports going to Japan. Globally, the biggest reserves of metallurgical coal are found in China, and they produce over half the global output of metallurgical coal. While estimation of resources is difficult and depends on exploration and inference, recent estimates show that Australia has 6-7% of global recoverable black coal resources, ranking it 5th behind the USA, Russia, China and India. Australia also produced 6% of black goal globally in 2010, ranking it fourth, far behind China’s 51%, but not so far from the USA’s 16% and India’s 9%.

Mining
Metallurgical coal is mined the same ways as other coals, however bituminous coal tends to contain larger amounts of gas than other coal. This gas can lead to underground explosions, hence mining black coals takes greater care and management. The same methods are still used, and depending in the depth of the coal being mined, open cut or underground mining is chosen. The most effective of these is the longwall approach, which uses hydraulic supports to hold the roof of a mine while large blocks of coal are removed. The roof is then allowed to fall, closing the mine. Open-cut mining is useful when the coal seam is close to the surface, and recovers higher amounts of coal than underground mining methods.

Uses
Metallurgical coal is mostly turned into coke, which is used for making steel. Metallurgical coal is categorised into coking coal or PCI, which is pulverised coal injection; both of these are used in making steel. Of all the metallurgical coal mined globally, nearly 75% of that goes into steel production. The remaining amount goes into smelting other metals.

The coking process removes volatile parts of the coal by heating the coal to temperatures exceeding 1,000 degrees Celsius. This process fuses the carbon and residual ash, while removing water, gasses and material impurities that cause volatility. This heating is done in the absence of oxygen so that the gasses being removed do not burn or explode. The coke that is formed through this process is a tough, grey, porous product that is then put into a blasting furnace, where it converts iron ore into molten iron, which is called pig iron. When the resulting pig iron is fed into a blast oxygen furnace, it becomes crude steel.

The other kind of metallurgical coal used in in steel manufacture is PCI coal, which is crushed to a powder then injected into blast furnaces. This replaces the coke in producing pig iron. Both coking coal and PCI coal have very high carbon contents.