[Stoves] Role of secondary air on wood burning and charcoal stoves

Ronal W. Larson rongretlarson at comcast.net
Thu Aug 22 10:16:41 CDT 2013


Sarbagya and iist

   I am mainly going to pass, as I have only been involved with char-making stoves, which of course has everything to do with secondary air (and almost no-one controlling it - only allowing for it).

   As near as I can tell, the rocket stove dimensions (which I don't even know where to find) make no effort to supply secondary air, except for encouraging a grate.   Some of the air flowing above and below the grate has a primary air function (pyrolyzing), some a secondary air function (combusting pyrolysis gases) and much a gasifying function  (consuming the char).   Maybe there is a fourth role for the air.   Some for sure has to be present as excess air, since we are talking random encounters;  we will miss some combustible particles if only the theoretical (stoichiometric) amount is somehow entered.   All four (or five?) functions going on at the same time,  but any one entering O2 molecule does only one of these four (or five) functions.  My point here only is that I don't see any rocket stoves, only TLUD type (char-making at one stage; Philips is one) working on preheating secondary air.  I think you can help the TLUD community a lot with a study on secondary air hole location and dimensions, preheating, etc - but I will leave it to rocket stove designers to answer your main question.

   On charcoal using stoves,  I see something very similar:  no (?) use of secondary air holes.   There may be some and well designed, but the recent paper by Bentson, Still, etal shows results for 14 different char-consumers, and it doesn't appear any use secondary air supply.  This paper is #10 in a list I gave a week or so ago.  [  Energy for Sustainable Development:   Volume 17, Issue 2, April 2013, Pages 153–157]  As Crispin said, you want to burn up the CO, and so far none of the char-burners are passing the CO part of the water boiling test.  I have no idea how to do it when users are (usually, not always)  placing the cook pot right on the char.  Maybe you can figure something by looking at the 14 stove results.  Maybe the authors at Aprovecho have CO and efficiency data to go with the interesting fuel load data in that paper.

    My conclusion - If you want to study the size and shape secondary air questions you first proposed - you might want to join the TLUD tribe.

Ron


On Aug 22, 2013, at 6:26 AM, "Sarbagya R. Tuladhar" <sarbagya007 at gmail.com> wrote:

> Hi Ron,
> 
> I am basically looking at natural draft front loading continuous feeding wood stoves and natural draft charcoal stoves. The reason I am investigating these is that for a wood stove, having secondary air component "really" did impact on the CO and PM production. The two stoves similar in design had the same thermal efficiency but then differed a lot with the emissions. The secondary air supposedly used was via the exterior gap ( I am guessing similar to the Philips TLUD). However, I am not talking about the TLUDs here but just normal front feeding wood cookstoves. 
> 
> Heard from Crispin regarding the role of secondary air in charcoal cookstoves. So it is used to burn the evaporated volatiles and the CO to CO2. Designs of the Benin charcoal stove have a simple concept of having holes on the bottom of the outer body which allows air to flow through it and then this pre-heated air is exited out to the combustion chamber to aid in the combustion of the volatile unburnt gases. Does this feature work?
> 
> Looking to hearing from you.
> 
> Cheers
> 
> Sarbagya
>  
> On 21/08/2013, at 1:25 AM, Ronal W. Larson wrote:
> 
>> Sarbagya:
>> 
>>    Can you narrow down the type of stoves you are looking at?  And why?  
>> 
>>    You seem to be talking of TLUDs, and when mentioning consuming char is that in a TLUD?
>> 
>>    We have seen some nice designs with secondary being preheated with a central pipe, not the exterior gap you describe.
>> 
>>    At least one stove developer (Kirk Harris) has argued for using that exterior space for added insulation.  A topic fairly easy to compare in the lab you appear to have available.
>> 
>> Ron
>> 
>> On Aug 20, 2013, at 6:44 AM, Sarbagya R. Tuladhar <sarbagya007 at gmail.com> wrote:
>> 
>>> Hi stovers,
>>> 
>>> The debate on the role of secondary air both for natural draft and forced draft has been raging for quite some time now. Obtaining secondary air in pre-heated form has been the research area for me in the laboratory for the past few weeks. However, one conclusion I obtained was that secondary air if not pre-heated would have the tendency to put off the fire by blowing in cold air. 
>>> 
>>> Hence my question is:
>>> 
>>> What is the role of secondary air for wood burning stoves ? Is there an optimum gap for the secondary air to travel between the jackets of the combustion chamber before ejecting out into the combustion chamber ? How does this effect the performance of the cookstove ? I know a few cookstoves which have secondary air concept included and which seemed to decrease the CO and PM up to some extent. 
>>> 
>>> What is the role of secondary air for charcoal burning stoves ? Quoting Crispin "Secondary air is necessary to burn charcoal in a low O2 environment at a high temperature." How does this effect the performance of the charcoal cookstove?
>>> 
>>> Waiting for the responses.
>>> 
>>> Cheers
>>> 
>>> Sarbagya Tuladhar
>>> Pondicherry, INDIA
>>> _______________________________________________
>>> Stoves mailing list
>>> 
>>> to Send a Message to the list, use the email address
>>> stoves at lists.bioenergylists.org
>>> 
>>> 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://stoves.bioenergylists.org/
>>> 
>> 
>> _______________________________________________
>> Stoves mailing list
>> 
>> to Send a Message to the list, use the email address
>> stoves at lists.bioenergylists.org
>> 
>> 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://stoves.bioenergylists.org/
>> 
> 
> _______________________________________________
> Stoves mailing list
> 
> to Send a Message to the list, use the email address
> stoves at lists.bioenergylists.org
> 
> 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://stoves.bioenergylists.org/
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20130822/5bd0ef1d/attachment.html>


More information about the Stoves mailing list