Coal is fuel that is mostly used as fuel of steam generator in industries and power plant. Based on its hardship, coal fuel can be classified in three types namely anthracite, bituminous and lignite.
Anthracite coal is usually known as hard coal that shiny and black. Semi anthracite coal has ashen color and it is not as hard as anthracite coal. Bituminous coal is usually known as soft coal and it is often used in industrial world because its ignition is easy with long burning. Sub bituminous is also soft coal type but this coal type has lower carbon content than bituminous coal type. Lignite coal has low heating value and high moisture; furthermore this type is seldom used as fuel in steam boiler.
Further analysis is required to find suitable coal as fuel to perform well combustion. Proximate or ultimate analysis is required to identify the best characteristic of coal type. Proximate analysis is used to know humidity, substance that easily evaporate, ash, carbon and sulfur content in coal. Ultimate analysis is used to know elements such as nitrogen, sulfur, oxygen, carbon, ash and hydrogen in coal.
Coal fuel classification is used as consideration to do purchase contract. The method that is used is standard ASTM D 388-38. Coal fuel classification is based on physical properties, carbon value, moisture, mineral matter content in coal.
Coal fuel classification can be categorized in each class and group based on carbon content and volatile matter as follow:
- Coal fuel classification if carbon content more than 69% and volatile matter content less than 31%.
Class : Anthracite coal ===> Group : Meta anthracite
Class : Bituminous coal ===> Group : Low volatile
- Coal fuel classification if carbon content less than 69% and volatile matter content more than 31%.
Class : Bituminous coal ===> Group : High volatile A
High volatile B
High volatile C
Class : Sub bituminous coal ===> Group : Sub bituminous A
Sub bituminous B
Sub bituminous C
Class : Lignite coal ===> Group : Lignite
Description of each group:
- Meta anthracite has carbon content 98-100% and volatile matter content 0-2%.
- Normal anthracite has carbon content 92-98% and volatile matter content 2-8%.
- Semi anthracite has carbon content 86-92% and volatile matter content 8-14%.
- Low volatile has carbon content 78-86% and volatile matter content 14-22%.
- Mid anthracite has carbon content 69-78% and volatile matter content 22-31%.
- High volatile A has heating value more than 14.000 btu/lb.
- High volatile B has heating value 13.000-14.000 btu/lb.
- High volatile C has heating value 11.000-13.000 btu/lb.
- Sub bituminous A has heating value 11.000-13.000 btu/lb.
- Sub bituminous B has heating value 9.500-11.000 btu/lb.
- Sub bituminous C has heating value 8.300-9.500 btu/lb.
- Lignite has heating value less than 8.300 btu/lb.
- Brown coal has heating value less than 8.300 btu/lb.