JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV SOLID FUEL TECHNOLOGY Previous Question Paper (July/August - 2022 - R18)

The classification of coal is based on the following four parameters:

• Type: Refers to the physical constitution of coal based on the specific plant debris and organic matter from which it was formed. It distinguishes coals like humic coal (derived from woody material) from sapropelic coal (derived from spores, algae, and resins).
• Rank: Indicates the degree of coalification or metamorphism that the original plant material has undergone. It represents the transformation from peat to lignite, sub-bituminous, bituminous, and finally anthracite, characterized by an increase in carbon content and a decrease in moisture and volatile matter.
• Class: A broad grouping based on the rank of coal, typically used to categorize coals into major divisions like low-rank (lignite/sub-bituminous) and high-rank (bituminous/anthracite) for industrial application suitability.
• Grade: Refers to the quality of coal based on the amount of impurities present, such as ash, sulfur, and moisture content. It is a measure of the economic value and utility of the coal, independent of its rank.

Petrological constituents of coal, known as macerals, are the organic components analogous to minerals in inorganic rocks. They are classified into three main groups:

• Vitrinite: Derived from woody tissues and bark. It is the most abundant maceral, acting as the primary binding agent during carbonization.
• Liptinite (Exinite): Derived from spores, pollen, cuticles, and resins. These are hydrogen-rich and contribute significantly to the volatile matter content of coal.
• Inertinite: Derived from oxidized or charred plant material. These are carbon-rich and chemically inert during the coking process.

These constituents significantly affect coal properties:

• Coking behavior: Vitrinite provides the necessary fluidity for coke formation, while high proportions of inertinite reduce the strength and swelling properties of the resulting coke.
• Calorific value: Macerals rich in hydrogen (liptinite) generally yield higher calorific values compared to inertinite-rich coals.
• Reactivity: The maceral composition determines the chemical reactivity during combustion and gasification; for instance, liptinite increases volatile yield, whereas vitrinite influences the softening temperature and plastic range of the coal.