Fixed carbon from proximate analysis measures non-volatile carbon remaining after combustion, while total carbon from ultimate analysis includes some organic carbon lost as emissions. Fixed carbon content rises with increasing coal rank, and is used to define ranks above medium-volatile bituminous coal based on the non-volatile carbon percentage.

1. Fixed carbon from proximate analysis is a different
value than total carbon from ultimate analysis.
Total carbon includes some organic carbon that
escapes as volatile matter emissions during
combustion.
Fixed-carbon content increases with rank, and is used
to define ranks above medium-volatile bituminous
coal.
Difference between
Fixed carbon Proximate analysis
AND
Carbon in Ultimate analysis