Metallurgical coal is low in ash, moisture, sulfur and phosphorus content, and its
rank is usually
bituminous. Some grades of
anthracite coal are used for
sintering,
pulverized coal injection, direct
blast furnace charge,
pelletizing, and in production of ferro-alloys, silicon-manganese, calcium-carbide and silicon-carbide. Metallurgical coal produces strong, low-density coke when it is heated in a low-oxygen environment. On heating, the coal softens, and volatile components evaporate and escape through pores in the mass. During coking, the material swells and increases in volume. The coking ability of coal is related to its physical properties such as its rank, but laboratory testing is required to completely evaluate the coking ability of a coal. The strength and density of coke are particularly important when it is used in a blast furnace, as the coke supports part of the ore and flux burden inside the furnace. Metallurgical coal contrasts with
thermal coal, which does not produce coke when heated. Because of their different end-uses, prices for the two types of coal are usually quite different. The suitability of coal for conversion to coke is also referred to as the
caking ability. == Types ==