[Stoves] Fuel equivalents

[AJH]

On Tue, 5 Jun 2007 10:37:57 -0400, Sharon Gordon wrote:

>To begin with I was hoping for at least a rough rule of thumb such as
>10 kilograms of freshly cut oak limbs

10kg of freshly cut oak limbs would be about 5kg of bone dry wood and
5kg of water, so burning this would release about 93 MegaJoules
(26kWhrs)of heat but the water would "steal" 13.5MJ (3.75kWhr) of this
to discard as steam leaving a net 80MJ (22kWhrs) of heat.



> -> Xk of wood dried for one year ->Yk

Well this is a variable, it depends on the size of the piece of wood,
the local humidity and temperature. In UK it wouldn't lose much
moisture in the winter but a split piece that you could pick up in one
hand would probably dry to 30% moisture content in a summer. Even so
the heat released doesn't change much except the fire burns a *lot*
better and cleaner.

>turned into charcoal fuel 

Traditional methods don't get much better than 25% of the dry wood
into charcoal and though the charcoal now contains ~28MJ/kg the total
energy remaining from the initial 10kg of wet wood is now 1.25kg of
char with 35MJ (9.7kWhr) of heat.

>->Zcharcoal debris/ashes

It's hard to guess how much char remains in the ashes but with clean
wood well burned out the ash should be no more than 1% of the dry
matter, buds, bark and leaves will push this up by a bit.

AJH