[Gasification] wood energy content

[AJH]

On Sat, 13 May 2006 08:05:46 -0500, Greg Manning wrote:

>In Energy Balance factors only, 16Kg of wood at 15% Mc would have 81 Kw/th
>or so...

If you're used to imperial units you need to watch your units when
quoting SI units. Also beware the difference between the total heat
liberated and the sensible heat liberated, this difference between
Higher Heating Value and Lower Heating Value is in the steam formed as
the hydrogen in the fuel turns to water vapour.

16kg of wood will have a calorific value (LHV) of the dry wood (18.6MJ
per kg for hardwood seems to be an accepted average) minus the energy
in the moisture it contained at the temperature at which it is dumped.
This will normally be as steam in the flue gas so we can use 2.7MJ/kg
of water dumped as a ball park figure, 2.3MJ/kg of this is the latent
heat necessary to turn the liquid water to vapour.

Thus the 16kg of wood at 15% mc wwb (i.e. the moisture expressed as a
% of the whole wet weight) will have 2.4kg of free water and 13.6kg of
oven dry wood. This will liberate 253MJ of sensible heat and "waste"
6.5MJ in the steam from the free water (plus of course the steam
produced in burning the hydrogen component of the wood).

This 253MJ of energy is equivalent to a power of 68kW(t) running for
one hour, hence 68kWh(t).

Again all subject to my maths being correct.

AJH