[Stoves] Top lit updraft combustors

[Gordon West]

Regarding the question of top lighting being cleaner burning, my understanding is that when you light the bottom of a pile of biomass the heat/flames spread up through the pile and quickly involve all of the fuel. There is not enough air accessible to the burn, especially when it is an updraft situation, to fully combust the gases. 

When lighting the top, the fuel involvement is “regulated” and the progress of combustion downward is a result of radiant heat gasifying biomass below it. Lower biomass is shielded from the radiant heat until the layer above is gone. 

This principle holds even in pile burning of logging slash — light the bottom and you get smoke problems, light the top and it burns clean.
 
Gordon 




> On Dec 14, 2017, at 6:23 AM, Norbert Senf <norbert.senf at gmail.com> wrote:
> 
> On Wed, Dec 13, 2017 at 7:57 PM, Ronal W. Larson <rongretlarson at comcast.net <mailto:rongretlarson at comcast.net>> wrote:
> Norbert and list:(snip)
>> 
>> As an outsider to the TLUD scene, I'd note that we make a top lighting updraft combustor,
>> in the form of a heating appliance indigenous to northern Europe. The top lighting is 
>> not mandatory or traditional, but has been found through testing to be a preferred mode
>> of operation for combusting a batch load of cordwood in the 10 - 40 kg range with very low
>> particulate (PM) emissions.
> 	[RWL:  Can you give a lead to look this up?   Makes char?  Probably not as you say “combustor”.  Any theory on why top lighting is cleaner?  Do you always operate batch load only?
> 
> >>>Ronal: It is a combustor. It is similar to a masonry fireplace, except burns a 60 lb batch and stores the heat. Two 50 lb fires per day gives you 6 kW continuous for house heating. Because of thermal storage, you can use an optimized single burn rate which makes it easy to burn clean. The trick is the cold start, and getting the firebox up to temperature so you have your 3T's. Top ignition gives you a small hot fire right away, whereas bottom ignition results in quenching of the flames by the cold fuel pile above.
> http://heatkit.com/ <http://heatkit.com/>
>> 
>> A newly developed combustion air system from Austria can be configured to
>> produce biochar as a byproduct. I fooled around with this last winter, and was able to 
>> make around 300 kg, as a byproduct of heating our house. We have conducted EPA-style
>> dilution tunnel PM testing on this as well as on pellet (heating) stoves, and are burning cordwood with
>> about half the PM emissions of pellet stoves.
> 	[RWL:  Can you give us a lead on the Austrian group?
> 
> Here is the specification, from the Austrian tile stove association:
> mha-net.org/docs/codes/austria/MB_10_eco-friendly%20combustion%20chamber_20120424Version2.pdf <http://mha-net.org/docs/codes/austria/MB_10_eco-friendly%20combustion%20chamber_20120424Version2.pdf>
> Here is some info on the testing that we have done on it:
> http://www.heatkit.com/research/lopez-2014-03-01.html <http://www.heatkit.com/research/lopez-2014-03-01.html>
> 
> 		Can you say a bit more about your own 300 kg of char-making?  I pull char (with tongs) regularly (when I think of it) out of my very small wood stove.  What sort of char-making efficiency in your method?  (I have no idea on mine, but it is not hard to do - and is my concept on how char was produced for the Terra Preta soils.)
> 
> A rough guess is 5% - 10% of the (wet) weight of the 20% moisture cordwood. When the yellow flaming has stopped on the batch and there is a big coal bed, I shut off the air. The next morning, I scoop out the ash + coals, some of which are still live, into a metal ashbucket with a tight lid. I keep the ash + char mix in bags until the spring, when I screen it all to separate the charcoal. 
>> 
>> You can find some details here:
>> http://heatkit.com/research/2006/lopezm02.htm <http://heatkit.com/research/2006/lopezm02.htm>
> 
> 	[RWL:  I thought you did a nice job in explaining your whole lab process.  I tried to learn more about Condar - but no web site was found.  Is this a method or a product?
> 
> It used to be an official method in Oregon, OM41. It was a commercially produced product in the 1980's, and used to develop all of the first generation of clean burning EPA-certified stoves. We have an original, and have had copies made. Here is a transcript of a workshop that was prepared for us by OMNI Environmental, one of the top EPA-accredited labs:
> heatkit.com/docs/OMNIcourse.pdf <http://heatkit.com/docs/OMNIcourse.pdf>
> 
> It features the late Dr. Stockton (Skip) Barnett, the inventor of the Condar.
> 
> We have a repository of some technical documents here:
> http://heatkit.com/html/lop-arc.htm#Condar_Sampler <http://heatkit.com/html/lop-arc.htm#Condar_Sampler>
> 
> 
> 	I stumbled on the stove decathlon.  Any comments for us on whether that could help our interests with much smaller stoves?
> 
> I don't know. John Ackerly of Alliance For Green Heating has attended some of the cookstove conferences
> http://forgreenheat.blogspot.ca/2014/02/experts-gather-in-northwest-to-design.html <http://forgreenheat.blogspot.ca/2014/02/experts-gather-in-northwest-to-design.html>
> 
> There seems to be a real divide between the EPA heating stove certification scene in the US, and the international cookstove/biochar scene.
> Any connections that can be formed to harmonize test methods, or even emissions definitions, would be beneficial to everybody.
>> Norbert
> 
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