Coal breaker remaining. The sorting by size is particularly important for anthracite coal. In order to burn efficiently, air must flow evenly around anthracite. Subsequently, most anthracite coal is sold in uniform sizes. In the 1910s, there were six commercial sizes of coal (with the smallest size having three subsets): Coal pieces smaller than in size were considered "culm," and unable to be separated from the impurities (and thus useless). The grade of coal ranged from a low of 5 percent impurities for steam or broken coal to a high of 15 percent for pea-size coal and its subsets. Coal breakers were
Metallurgical coal Metallurgical coal 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