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" <[email protected]> To: "Discussion of biomass cooking stoves" <[email protected]> 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: [email protected] [mailto:[email protected]] On Behalf Of [email protected] 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 _______________________________________________ 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://www.bioenergylists.org/ _______________________________________________ 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://www.bioenergylists.org/
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