Coal quality parameters (moisture, ash, volatile matter, sulphur, HGI)
Besides calorific value, the value of thermal coal is set by total moisture (TM), ash, volatile matter (VM), fixed carbon, total sulphur (TS), the Hardgrove grindability index (HGI) and ash fusion temperature. High ash and moisture raise transport and burning costs; sulphur affects flue-gas treatment and emission limits; HGI determines mill capacity. For coking coal, CSR, CRI and fluidity also matter. Contracts give “typical” and “rejection” limits plus price-adjustment formulas for deviations in each parameter.
Related terms
Calorific value (gross and net, GAR / NAR)
The energy released by the complete combustion of a unit mass of fuel, in kcal/kg or MJ/kg. Gross calorific value (GCV) includes the latent heat of the water vapour formed; net calorific value (NCV) excludes it and is closer to the energy a boiler can actually use. For coal the figure also depends on its basis: GAR (gross as received, including total moisture), ADB (air-dried) or NAR (net as received). Indonesian coal is mostly priced on GAR, European and South African coal (API2, API4) on NAR 6,000, so offers must be converted to the same basis before comparison.
Sampling (representative sample)
Taking samples so that they represent the whole lot, following standard methods – e.g. ISO 24333 for grain, ISO 3082 for ores, ASTM D4057 for liquids. In bulk loading, increments taken at intervals are combined and divided, and usually three or four identical samples are sealed: one for the seller, one for the buyer and one retained for umpire analysis. At the quotation stage, small type samples are tested for suitability; the contract should commit that the shipment will match the approved sample.
Draft survey
A method of calculating the weight of bulk cargo loaded or discharged by reading a ship’s draughts at six points before and after cargo work and correcting for seawater density, ballast, fuel and fresh water. For coal, ores, grain and fertiliser the bill of lading quantity is usually set this way, with an accuracy of about ±0.5 %. Having it performed by an independent surveyor such as SGS, Intertek or Bureau Veritas increases confidence on both sides.