[Default] On Sat, 10 Aug 2013 16:10:56 -0400,"Lanny Henson" <[email protected]> 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 _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] to UNSUBSCRIBE or Change your List Settings use the web page http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org for more Biomass Cooking Stoves, News and Information see our web site: http://stoves.bioenergylists.org/
