Coal classification table is a critical step in describing the coalification process of coalification, which classifies the various stages of coalification, from the initial unaltered plant remains to the ultimate metamorphic transformation and coking properties sequentially.
The coal distinguished into various types such as anthracite, bituminous, subbituminous and lignite based on the levels of metamorphism, alteration and coal component composition. Anthracite is the highest rank coal and ranges in reflectance between 0.7 0.85. It is highly durable and specialized material having volatile component range 8-10%. Bituminous coal is rich in carbon content, C 83.3-86.7%, and has volatile component range 8-17%. Furthermore, volatile component range of subbituminous coal is 17–25%, whereas it’s lower than bituminous type, its calorific value increases dramatically. Lignite is the lowest grade of coal which contain 65-75 % of carbon content and distinct compositional character due to its higher water content, volatile component range and low calorific value.
The vitrinite is the main constituent of high rank coal, generally exhibiting reflective values from 0.6 to 0.95 or even greater. In lower rank coals, vitrinite may decrease its reflective value while increased in amount due to increased thermal alteration as a consequence of coalification. The other particles that make up coal include mineral matter, liptinite and inertinite. Mineral matter consists of clay minerals, quartz and pyrite, whose amount varies in each coal. Liptinite components, such as exinite, inertodetrinite, semifusinite and a great amount of cutinite are present in the high rank coal. On the other hand, inertinite components such as fusinite, semifusinite and waxes are found mostly in subbituminous coals.
The caking properties of coal is an important feature which is responsible for its capacity to undergo self-heating and is used in many industrial applications such as power generation and metallurgy. Caking properties of coal vary with its rank, maturity and structure. Vitrinite, liptinite, and minor amount of well-distributed mineral matter are important parameters of caking properties. The lumpiness, caking points and size distribution of coals also directly illustrate caking properties.
In conclusion, classification of coal is a critical step in determining the coalification process and its commercial aspects. The coal is segmented into various types based on its physical and chemical properties which directly influence the cost, calorific value and stability of the coal. The caking properties of coal also play an important role in commercial applications and should be taken into consideration for industrial applications.
