Metallurgical coal is a grade of low-ash, low-sulfur and low-phosphorus coal that can be used to produce high grade coke. Coke is an essential fuel and reactant in the blast furnace process for primary steelmaking. The demand for metallurgical coal is highly coupled to the demand for steel. Primary steelmaking companies will often have a division that produces coal for coking, to ensure stable and low-cost supply.
Metallurgical coal is distinguished by the strong low-density coke produced when the coal is heated in a low-oxygen environment to reduce mineral impurities (e.g. less sulfur, phosphorus). On heating, the coal softens, and volatile components evaporate and escape through pores in the mass. On cooling, the resultant coke has swollen, becoming a larger volume. The coking ability of coal is somewhat correlated with its physical properties such as its rank, but laboratory testing is required to completely evaluate the coking ability of the coal. The strength and density of coke is particularly important when it is used in a blast furnace, as the coke supports part of the ore and flux burden inside the furnace.
Coking coal is usually Bituminous coal. Some grades of Anthracite coal are used for sintering, PCI, direct BF charge, pelletizing, and in production of ferro-alloys, silicon-manganese, calcium-carbide and silicon-carbide. Metallurgical coal contrasts with thermal coal, and has different sources (produced mainly in Canada, the United States, and Australia) and industrial significance; prices for the two may vary.
The suitability for conversion to coke is also referred to as the caking ability. Metallurgical coal is harder, blacker, produces less ash when burned, and contains less moisture. 
There are several types of metallurgical coal:
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