A system based on proximate analysis in which coals containing less than 31% volatile matter on the mineral-matter-free basis (Parr formula) are classified only on the basis of fixed carbon; i.e., 100% volatile matter. They are divided into five groups: above 98% fixed carbon; 98% to 92% fixed carbon; 92% to 86% fixed carbon; 86% to 78% fixed carbon; and 78% to 69% fixed carbon. The first three of these groups are called anthracites, and the last two are called bituminous coals. The remaining bituminous coals, the subbituminous coals, and the lignites are then classified into groups as determined by the calorific value of the coals containing their natural bed moisture; i.e., the coals as mined but free from any moisture on the surface of the lumps. The classification includes three groups of bituminous coals with moist calorific value from above 14,000 Btu/lb (32.5 MJ/kg) to above 13,000 Btu/lb (30.2 MJ/kg); three groups of subbituminous coals with moist calorific value below 13,000 Btu/lb to below 8,300 Btu/lb (19.3 MJ/kg); and two groups of lignitic coals with moist calorific value below 8,300 Btu/lb. The classification also differentiates between consolidated and unconsolidated lignites and between the weathering characteristics of subbituminous and lignitic coals. See also: coal classification systems
Source:
Dictionary of Mining, Mineral, and Related Terms










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