Coal Rank Classification

The rank of a coal is characteristic of the stage reached by it in course of coalification. The development from peat through the stages of lignite, subbituminous, and bituminous coals to anthracite and meta-anthracite is termed coalification. Coalification or coal metamorphism is a function of heat and pressure acting over a period of time. Among the three primary factors, heat is generally considered to be the most important. Increased heat at greater depths of burial has been considered the primary factor (Hilt’s Law, after Hilt 1873).

Rank or maturity of coal indicates its coalification stage which can be determined by reflectance measurement studies of vitrinite (Ro%), estimation of moisture, volatile matter, and carbon hydrogen content.

Fundamental and technological properties of coal depend primarily on the rank of coal.

Exact determination of rank always has been one of the most important subjects of coal science and research. It is universally accepted that rank determination...