• Unburnt loss indicates how well the firing equipment and furnace are sized and matched such that

— The three Ts—time, temperature, and turbulence—are adequately addressed.

— Heat release rates of the firing equipment and the volumetric heat release rate of furnace are judiciously selected to burn the fuel optimally.

— Air pressures, temperatures, and distribution are selected properly to help release the fuel heat fully. For example, hot air is necessary for proper burning of biofuels. It is also good for coal but depending on the coal properties, the temperatures should be limited to less than certain limits to avoid clinkering or caking.

• Sizing of solid fuel is of paramount importance in the firing to limit the unburnt carbon in the ash.

• Selecting proper bed temperatures in FBC or firing temperatures in PF is another factor for reducing the unburnt carbon.

• Proper arches in stoker firing deflect the gases on to the bed and aid ignition and effective burnout.