[Stoves] Inverted top lit updraught

[rongretlarson at comcast.net]

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.. 


----- Original Message -----
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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