[Stoves] Changing rate of pyrolysis front in TLUDs

[AJH]

On Thu, 12 Apr 2007 09:07:49 -0400, Crispin Pemberton-Pigott wrote:

>Height of chimney
>initially 40mm and later 200mm as the fuel burns down
>Heat content of wood/biomass
>19.300MJ/Kg
>
>The draft changes from 0.312 to 1.56 Pascals.   OK, so it appears to go up 
>by a factor of 4,

This is true for a small cooking stove, I was referring to a long
stack method of tlud making char from a bulky material, the reasoning
was the flare would be clean and have possible uses and the char could
then be incorporated into a cooking fuel, either on its own as a
briquette or with other waste. The reduction to char makes transport
more economic.

Anyway to my mine a pressure difference that changes by a factor of 4
isn't insignificant, what is interesting is that Dale's report doesn't
indicate there is a big change in power, and power should directly
relate to primary air (even though this is just the driver for
pyrolysis in a tlud and the char is retained and not completely
gasified).


>The radiant heat from the pyrolosis zone surely heats the fuel chunks 
>underneath and the temperature of the inside air is not 'ambient'.  Heat 
>conducts down the metal skin on the inside assisting this further. 

In fact this doesn't happen, the metal stays about 600C on a single
skinned device and the incoming air keeps the column below the
firefront at near ambient.

AJH