Which among the following types of coal produces the most heat per unit?
(1) Coal
(2) Lignite
(3) Anthracite
(4) Pit
Answer: (3) The heat content of anthracite ranges from 22 to 28 million Btu per short ton (26 to 33 MJ/kg) on a moist, mineral-matter-free basis. Anthracite (“coal-like”) is a hard, compact variety of mineral coal that has a high lustre. It has the highest carbon content, the fewest impurities, and the highest calorific content of all types of coals, which also include bituminous coal and lignite. Anthracite is the most metamorphosed type of coal (but still represents low-grade metamorphism), in which the carbon content is between 92.1% and 98%.
