[Stoves] Inverted top lit updraught

Tue Jan 17 02:30:28 CST 2012

Charcoal making was not an important objective of the Eindhoven 
Woodburning Stove Group; even clean burning was not initially considered 
important by the Steering Committee. The objective was saving fuel in 
the preparation of food.
The Downdraft stove was the first clean burning stove we developed. It 
could be fed continuously but utilising the heat was not straightforward.
There was no deliberate partitioning of primary and secondary air; the 
layer of burning char was not thick enough to deplete the air completely 
of oxygen; whatever oxygen was left after passing through the char bed 
was used to burn the volatiles. If the fuelbed was not too thick, enough 
oxygen passed through to burn the volatiles downstream.
If the fuelbed thickness was increased the stove worked for a short 
period as a gasifier but only while the chimney was very hot from the 
proper burning period. After that there was smoke everywhere.
We did have a shot at producing charcoal in a stove that would burn only 
the volatiles. Wood sat in a vertical cylinder, closed at the top with 
an opening at the bottom. Air was drawn into that opening to burn the 
wood in that vicinity. Around the wood filled cylinder an insulated 
chimney surrounded it. The idea was that burning part of the wood would 
produce hot gas which could be burned at the top under a pan. The hot 
gas heated the cylinder, charring the wood inside.
It didn't work and we had no time to look into proper dimensioning which 
might have resulted in something that did work.

Peter (smoke) Verhaart

On 13/01/2012 14:25, rongretlarson at comcast.net wrote:
> Tom  (cc Andrew and list):
>
>      Thanks.    Professor Prasad is certainly one of my heroes in 
> stove work.  It was fun to read (I need to re-read) this report on a 
> helpful down draft design.   But char production was not a part of his 
> analysis.   I will look more closely to see if there is something 
> there to allow for a char-making design.  I think the main issue is 
> predicting something on needed chimney heights - which seems to be in 
> there.   But it appears to me that both primary and secondary air were 
> traveling through the fuel - whereas I presume a need to separate the 
> air supplies - as in the TLUD.
>
>      The message (below) by Andrew to the stoves list was at least in 
> part generated by some off-list conversation that we have been having 
> on BLDD and char-making.  The issue is why are almost all gasifiers  
> (which can be operated to give sizeable char output) based on BLDD, 
> but (apparently) all (?) char-making stoves are TLUD?
>
>     I hope anyone knowing of a BLDD char-maker will let us know.
>
>   Few items below also on Andrew's e-mail..
>
>
> ------------------------------------------------------------------------
> *From: *"Tom Miles" <tmiles at trmiles.com>
> *To: *"Discussion of biomass cooking stoves" 
> <stoves at lists.bioenergylists.org>
> *Sent: *Thursday, January 12, 2012 5:23:21 PM
> *Subject: *Re: [Stoves] Inverted top lit updraught
>
> Krishna Prasad described the downdraft stove in a presentation to ETHOS in
> 2004
> http://www.vrac.iastate.edu/ethos/ethos05/proceedings2004/presentations/pras
> adbiomasscookstoves.pdf
>
>
> A picture and WBT for Peter Verhaart's down draft barbeque can be 
> found at:
> http://www.stoves.bioenergylists.org/verhaartbarbeque
>
> Tom Miles
>
> -----Original Message-----
> From: stoves-bounces at lists.bioenergylists.org
> [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
> ajheggie at gmail.com
> Sent: Thursday, January 12, 2012 2:48 PM
> To: Discussion of biomass cooking stoves
> Subject: [Stoves] Inverted top lit updraught
>
> One for Peter Verhaart to comment on perhaps: we probably all know by now
> the genesis of the inverted down draught stoves which Ronal and Tom Reed
> expounded early on this list and  concurrently Paal was developing 
> with his
> early Peko Pe and we understand how burning the pyrolysis offgas can offer
> very low particulates compared with  burning whole wood in a conventional
> updraught stove but is the same true of a down draught stove if the 
> primary
> air is similarly controlled?
> *[RWL:  I think Piet Verhaart's thoughts would be excellent (for 
> others:  Piet's doctoral work was on a BLDD stove).  But for this 
> purpose, I am interested right now in whether any BLDD is providing 
> (lots of) char.*
>
> The advantage of stratified down draught ( i.e. where the air moves down
> through the charge of wood as that also descends through the grate) would
> seem to be that  the fire can be continually stoked. The disadvantage 
> is all
> the extra pipe work and either needing a hot plate or sunken pots to
> maintain the chimney depression required to suck the primary air down.
>     [RWL:  I think Professor Prasad's paper shows a BLDD design that 
> doesn't suffer from these two drawbacks.  But also it doesn't seem to 
> produce char.
>
> Down draught devices are normally intended to gasify all the fuel, often
> with extra air supplied in the "throat" but what if one was not 
> particularly
> concerned if a high char ash were left?
> [RWL:  I have recently been talking with Agua Das [cc'd] about his 
> "Dasifier" - which is incredibly efficient (very high temperatures) 
> with an "ejector" supplying this extra air.  He says he can produce 
> lots of char as well.   This is not what I have had in mind - but 
> could be attractive if that intermediate secondary air can be 
> introduced and controlled economically.
>
> For the sake of staying on topic can we avoid the "b" word and just 
> discuss the concept?
> [RWL:  Hmm.   "b" word ?   I trust it is OK to talk of saved char 
> (intended for a "b" purpose).
>
>     Andrew - thanks for these thoughts.
>
> Ron
>
> AJH
>
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