[Gasification] Fwd: RE: Whole log pyrolysis for char production was Re: W...

Henri Naths c_hnaths at telusplanet.net
Sun Jan 5 10:50:48 CST 2014


Hi Ken
Thank you for your good analysis of your wood stove. I know there is a better design and I'm not sure if my stove is better or not. 
Here is the thing. I burn spruce. My supply comes in 5 to 8 inch round logs dried  for ~3 years. Not sure mc but guess around 15%.-20 % I try to maintain a very hot temp so the entire logs gasify and burn over a 12 hr period. (Absolutely no fuel prep. splitting etc is mandatory lol ) It's very fickle in setting damper and air intake but for the most part I am successful. The refractory bricks helps a lot. So that is 2 burns over a 24 hr period. ( it's been averaging minus 20 c over the last two months here so not much choice)Ive run numerous test of my  theory for max efficiency under which this stove operates and settled on this operation because when the stove is shut down anywhere at the height of its max temperature and burn cycle and allowed to cool to 20 c it can be relight with a single match.  
The volatile gases including h2o could be better used for sure. They cool and condensate on the inside walls of the stove and flue before they frac. completely resulting in biochar.  The problem being the gases should be reheated, frac.ed with a catalyst and burned where the heat would be a benefit to the logs for pyrolysis.  Thus enhancing the entire burn + 20%. ( +++  considering the exponential advantage of said catalysis and resulting heat) 
A fluidized bed would also be an advantage. 
 I hope this helps. 
Yours truly 
Henri Naths

On 2014-01-05, at 4:11 AM, Ken Boak <ken.boak at gmail.com> wrote:

> Jason,
> 
> Thanks for the interesting comments. I suppose that firebricks are a simple capacitive thermal mass, to prevent the outer casing of the traditional cast iron stove from seeing the worst effects of thermal cycling, and to prevent excessive surface temperature.  
> 
> Taking this capacitive idea to the max, I guess is the masonry stove, which is all thermal mass intended to absorb and slowly release the heat from a brief but intense fire.  
> 
> I have magnetite bricks left over from an electric storage heater (common in the UK). My intention was to experiment with these for heat retention.
> 
> What is the problem with pyrolysis occurring too early?  Is it simply because fuel is pyrolysing in the wrong place, and there is no means to transfer the pyrolysis gases to the combustion chamber, or is the problem tar generation in the fuel magazine?
> 
> My motivation for design is a more efficient woodstove, which radiates more heat into the room in which it's located - say the living room, plus provides adequate hot water via a heat exchanger to provide heating for some additional rooms and hot water.
> 
> The nominal 8kW stove I have at the moment fails to produce much radiant heat, and I am sure that the simple heat-exchanger tank at the back of the combustion chamber seriously effects the combustion temperatures resulting in more emissions and poor, inefficient combustion. For this reason I believe that the only way to control emissions and combustion temperatures, is to first gasify the wood fuel and then burn the wood gas at high temperature with preheated secondary air.
> 
> Traditional stoves generally lose a lot of heat straight up the chimney. Whilst this generates draft, it is a major cause of inefficiency. Some heat could be recuperated for secondary air pre-heating, using a simple concentric heat exchanger made from twin-wall fluepipe.
> 
> A good stove should be easy to light, be easy to load, easy to clean out ash. Additionally it should have a convenient batch burn time, and the ability to control the heat (turn down), without too much loss of efficiency.  The stove should be capable of handling the predominant fuel type (say split logs) without additional fuel preparation.  
> 
> There may be good reason to have the stove non-reliant on electrical power, relying on natural draft and thermosyphoning for it's normal operation.
> 
> These are the features that I consider necessary to meet customer expectations.
> 
> Having intensively run my existing stove for around 14 hours per day for the last 16 days, as the primary source of heat over the festive holiday period, I am tolerating its less than ideal performance, but am now certain that there must be a better design.
> 
> 
> regards
> 
> 
> Ken
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