What the two bases mean
As-received (AR) reports a value as a percentage of the sample's mass including its water content — the state in which it was sampled, shipped or delivered. Dry basis (db) reports the same quantity as a percentage of the sample's mass after moisture has been driven off, so water no longer dilutes the other components.
Because water is dead weight, as-received figures for ash, volatile matter and fixed carbon are all slightly lower than their dry-basis equivalents for the same material — the fixed percentages are diluted by the moisture fraction.
A worked illustration
Take a charcoal with 10% moisture and, on a dry basis, 80% fixed carbon. Stated as-received, that fixed-carbon figure becomes 72% (80% of the remaining 90% that is not water). Neither number is wrong; they answer different questions. The dry-basis figure describes the fuel's composition, while the as-received figure describes what you actually bought per tonne.
Why it changes a purchase decision
If you are paying by weight, the as-received basis is the commercially honest one: it tells you how much of each delivered tonne is water and how much is fuel. The dry basis is the technically honest one: it lets you compare the fuel's intrinsic composition across suppliers and batches without moisture confusing the picture.
A supplier quoting a dry-basis ash figure while a competitor quotes as-received can make an identical product look different. Ask every supplier to state the basis next to every percentage, and where possible to restate the whole proximate analysis on one agreed basis.
How to spot an unstated basis
- A moisture figure with no basis is ambiguous — moisture is itself usually stated as-received.
- Fixed carbon should reconcile with moisture, volatile matter and ash on the same basis; if the four do not sum consistently, the basis is likely mixed.
- A datasheet that reports ash "as-received" but fixed carbon "dry" without saying so is internally inconsistent.