Glossary
ADB - Air-Dried Basis. In coal sample analysis, ADB neglects the presence of moistures other than inherent moisture while DB (dry-basis) leaves out all moistures, including surface moisture, inherent moisture, and other moistures.
ARB - As-Received Basis. In coal sample analysis, ARB puts all variables into consideration and uses the total weight as the basis of measurement. ARB is the most widely used basis in industrial applications.
Ash content - Ash content is the non-combustible residue that remains after coal is burnt. Ash reduces handling and burning capacity, affects combustion efficiency and boiler efficiency and therefore increases handling costs.
ASTM - American Society for Testing and Materials
GAR - Gross As Received. Thermal coal is quoted on a GAR basis, except for Europe/ARA, Richards Bay 6,000 kcal/kg, and Japan and Korea West CIF, which are quoted on a NAR (Net As Received) basis.
Fixed carbon - Fixed carbon is the solid combustible residue that remains in the furnace after volatile matter is distilled off, comprised mostly of carbon but also containing some hydrogen, oxygen, sulphur and nitrogen not driven off with the gases. It provides a rough estimate of the heating value of coal.
HGI - The relative ease with which coal can be pulverised depends on the strength of the coal and is measured by the Hardgrove Grindability Index (HGI). This empirical test indicates how difficult it would be to grind a specific coal to the particle size necessary for effective combustion in a pulverized coal fired boiler
Inherent moisture - Inherent moisture (or bed moisture) means moisture that exists as an integral part of the coal seam in its natural state, including water in pores, but excluding that present in macroscopically visible fractures.
Sulphur - Sulphur content in coal presents problems with utilization and resultant pollution, as it causes corrosion and fouling of boiler tubes, and atmospheric pollution when released in flue gases.
Total moisture - Total moisture in coal is represented by measuring weight loss from aggressive drying in an air atmosphere under rigidly controlled conditions of temperature, time and air flow. The presence of moisture is an important factor in both the storage and the utilization of coal, as it adds unnecessary weight during transportation, reduces the calorific value, and poses some handling problems.
Volatile matter - Volatile matter is the material that is driven off when coal is heated to 950 °C in the absence of air under specified conditions. It consists of a mixture of gases, low-boiling-point organic compounds that condense into oils upon cooling, and tars. In general, coals with high volatile-matter content ignite easily and are highly reactive in combustion applications.