Petrographic Studies in Interpreting Chemical Behaviour of Coals

The paper review the validity of formulae relating primary tar yields of coals with hydrogen content and petrographic composition developed by one of the authors. From these formulae, hydrogen content of a 100% vitrinite is derived. An interpretation of the Spooner’s formula leads to estimation of “reactive” or tar-yielding hydrogen in coals, Various manipulation of the formulae and their interpretation show that composition of vitrinites (85% C) is practically constant, after which a predictable change follows the rank. The composition of inertinites possibly changes little till 92% C level is reached. The significance of these deductions is discussed in terms of geo-chemical metamorphism of coals and a general formula is developed which enables primary tar yields to be predicted for all ranks of coals provided petrographic composition of the coal in terms of vitrinites and inertinites is known. It is shown that although such formulae are statistically derived, they are based on predictable structural changes of the chemical constitution of coals. The rank evolution of coal is solely guided by the changes in vitrain and petrographic corrections are necessary for interpretation of common chemical parameters defining the rank of coal. As a corollary, it is suggested that inertinites are of biological origin and do not play any significant part in geo-chemical evolution of coal till perhaps the end