ABSTRACT
Coals are classified based on various parameters like proximate analysis, calorific value, maturity (rank), ultimate analysis, caking properties etc.
There is no universal classification system of coal because
– Coal is composed of diverse elements i.e., it is a heterogeneous mixture of organic mass, mineral matters and moisture in uncertain proportions
– The organic mass itself being heterogeneous comprises of many microcomponents which means that the coals of same ultimate analysis do not necessarily have the same properties while coals of different compositions may in some respect behave alike
– Both the amount and composition of mineral matters in coal varies widely which greatly influence the properties of the whole coal
– The quality and quantity of the microcomponents vary from coal to coal. The quality of microcomponents is determined by the initial plant material and the coalification processes both of which vary from place to place and time to time
Because of the above reasons, large number of coal classification systems exist. Indian coal is classified into two main categories, namely, coking and non-coking. Although for commercial gradation, ash percentage is the sole criterion, for semiweakly-coking coal, along with ash percentage, moisture percentage too is considered as an added criterion. For non-coking coal, an empirical formula is used to determine Useful Heat Value (UHV) of coal in kcal/kg. The classification of coal as per the Ministry of Coal is given in Table 4.1.
