Last checked by Coal Boss
Coal holds water, and how much depends on rain, washing, storage and how long it has been lying. So a lab has to say which condition its numbers refer to — the 'basis'.
As received (ARB, or 'ar'): the coal as it arrived, with all its moisture (total moisture). Air-dried (ADB, or 'ad'): after the sample has been dried in air to steady conditions — only the inherent moisture is left. Dry basis (DB): as if all moisture were removed. Dry ash-free (DAF) goes further and takes out the ash too.
Because moisture adds weight but no heat, the same coal shows a higher GCV and ash percentage on air-dried basis than as received. Converting between bases uses the moisture figures: for example, a value on air-dried basis is multiplied by (100 − total moisture) ÷ (100 − air-dried moisture) to express it as received. The international method is set out in ISO 1170.
What it means if you trade coal
Before you compare a supplier's report with your own lab's, check that both are on the same basis — and write the basis into purchase and sale terms. An 'ADB' GCV against an 'ARB' GCV is not a quality difference, just a different yardstick.
Hinglish mein, short mein
ARB (as received) mein coal ki poori nami shamil hoti hai; ADB (air-dried) hawa mein sukhane ke baad — sirf andar ki nami bachti hai; dry basis mein saari nami hata di jaati hai. Nami wazan badhati hai par garmi nahi deti, isliye ek hi coal ka GCV aur ash ADB pe ARB se zyada dikhta hai. ADB ko ARB mein badalne ke liye (100 − total moisture) ÷ (100 − air-dried moisture) se guna kijiye — tareeka ISO 1170 mein hai. Do report hamesha ek hi basis pe milaiye.
Sources
- StandardISO 1170:2020 — Coal and coke: calculation of analyses to different bases
- StandardBureau of Indian Standards — IS 1350 Part 1 (Proximate analysis)
Coal Boss explanation, based on the sources above.
