[Stoves] Stoves Digest, Vol 22, Issue 10

[Crispin Pemberton-Pigott]

Dear AD and All

The complete combustion of biomass involves adding energy to the ash because
that fraction is endothermic, actually. The 'standard' calculation is
-0.0211 MJ/kg. The same is also true for Nitrogen which is -0.0151 MJ/kg and
Oxygen in the form of O2 is -0.1034 if there is any. These are extracted
from the general formula 

HHV (in MJ/kg) = 0.3491C + 1.41 H  - 0.1034 O + 0.1005 S - 0.0151 N - 0.0211
A where A is Ash.

When creating char at a low temperature several processes may be incomplete
and the true heat content of the char over-estimated.

The difference is minor relative to the initial heat value but rises as the
combination of a small residual mass gets smaller, if the low formation
temperature leaves the ash un-roasted.

Regards

Crispin

 

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