[Stoves] LannyPan cooking module and the TLC burner

[ajheggie at gmail.com]

[Default] On Sat, 10 Aug 2013 16:10:56 -0400,"Lanny Henson"
<lannych at bellsouth.net> wrote:

>It does take a long time for dry wood to totally absorb water but 50 min is 
>not insignificant,  and concrete block soaks up water a lot faster.  I am 
>thinking that even the water on the surface of wood or even dry wood is a 
>problem for most top lit batch burners.

Yes anything that robs the pyrolysis front of heat will compromise a
TLUD burn. As has been shown in the past primary air has to increase
to provide oxygen to burn nascent char to provide the heat to drive
off moisture, such that at 25%mc there is no residual char.

>
>Green wood is a problem, it stinks up the place and smuts the pot but it 
>will still burn fresh green wood after the fire heats up. Green wood 
>probably takes away more energy than it provides but it will burn fist size 
>chunks.

Yes but this is the acid test, it takes a lot of time and energy to
get heat into the middle of a bit of green wood to drive off the
moisture which is why solar/air drying is very useful even if slow.
>
>I will weigh the wood before and after soaking next time.

Good
>
>How much moisture content is the break even point?

Theoretically we can postulate that you need about 0.75kWh(t) to drive
off 1kg of water and raise it to flue exhaust temperature, this is
energy lost. Each kg of dry wood burned completely will yield about
5kWh(t) so the break even point is when the energy content of the wood
equals the energy loss of the vapour. This point is 86% moisture
content. Of course in practice this is unattainable and even on the
industrial scale sustaining combustion at more than 66% (green poplar
or spruce) is difficult and will not be clean. The reason is that the
combustion chamber cannot ever get hot enough for a clean burn with
high moisture content fuel, the char will burn out but the offgas
never gets hot enough to sustain a flame.

AJH