[Stoves] Blue Flame -- Natural Draft -- Rice Husk

[Paul Anderson]

Dear Jaakko,

Thank you for your excellent message.   It is also helpful about 
understanding charcoal-burning stoves, which tend to have a rather 
shallow thickness of char.

Can you please elaborate more about the
> two different stable (quasi)steady state solutions for the temperature 
> and species distributions in the char bed, a high temperature solution 
> and a low temperature solution. 

Paul

Paul S. Anderson, PhD  aka "Dr TLUD"
Email:  psanders at ilstu.edu   Skype: paultlud  Phone: +1-309-452-7072
Website:  www.drtlud.com

On 9/3/2013 8:56 AM, Saastamoinen Jaakko wrote:
>
> Dear all,
>
> I have seen blue flames in my heat storing stove under natural draft 
> using wood logs in char combustion stage, when the logs have been 
> broken into pieces. It is CO burning as has been discussed here by 
> others. Later the blue flame disappears due to lower bed temperature 
> so that CO cannot burn but goes to chimney.
>
> I have also calculated this phenomena. One can see blue flames  (CO is 
> burning) if the thickness of bed of char particles and air rate are 
> suitable.  If the bed is too thick, blue flames are inside the bed, 
> increasing gas temperature and gasification takes place above 
> producing CO from the bed. (This CO could be burned if somehow oxygen 
> could be mixed and temperature of the gas is high enough). If the bed 
> is too thin, excess air (due to lower flow resistance) cools the gas 
> so that CO is not burning or it burning rate is very low.  So it needs 
> suitable bed thickness and air rate which are difficult to maintain 
> with natural draft.
>
> As Richard Stanley has experienced, blue flame is very sensitive to 
> air rate.  I noticed this when calculating the burning with a model. 
> The calculation was based on iteration and on an initial guess. I was 
> astonished that depending on this initial guess I got, not a chaotic 
> solution, but two different stable (quasi)steady state solutions for 
> the temperature and species distributions in the char bed, a high 
> temperature solution and a low temperature solution.  Conclusion is 
> that both solutions could be right (CO is either burning or it is 
> not). It depends on the burning history of the stove which solution is 
> the right one. It the fire is disturbed and cooled down a little, CO 
> does not burn but if it remains hot, CO can burn.
>
> I throw small twigs in the end stage to get some CO escaping to 
> chimney to burn in the volatiles flames, increase the draft and speed 
> up the burning of residual char at the end of the heating.
>
> Jaakko
>
> *From:*Stoves [mailto:stoves-bounces at lists.bioenergylists.org] *On 
> Behalf Of *Erin Rasmussen
> *Sent:* 24. elokuuta 2013 0:15
> *To:* 'Discussion of biomass cooking stoves'
> *Subject:* Re: [Stoves] Blue Flame -- Natural Draft -- Rice Husk
>
> Hey that's exciting.  I've seen blue flame with wood pellets on 
> occasion, but only on the edges of my stick built fires.
>
> Nice work Marc!
>
> Erin
>
> *From:*Stoves [mailto:stoves-bounces at lists.bioenergylists.org] *On 
> Behalf Of *Marc-Antoine Pare
> *Sent:* Thursday, August 22, 2013 8:34 PM
> *To:* Discussion of biomass cooking stoves
> *Subject:* [Stoves] Blue Flame -- Natural Draft -- Rice Husk
>
> Hi everyone,
>
> I've managed to repeat blue flames consistently in a rice husk stove 
> using only natural draft.
>
> Anyone seen this before? I am only aware of forced air stoves that 
> achieve blue flames.
>
> The photo below is just a teaser. The lighting is terrible and you 
> can't make out the column of blue flame because I'm shooting straight 
> down.
>
> The smell is also quite motivating. Usually you get acquainted with 
> the "smell of defeat" with rice husk, since poor combustion smells 
> quite strong. So far, achieving odor on par with forced air units.
>
> More soon...
>
> This will be part of a completely Open Source project
>
> Inline image 1
>
> marc
>
> notwandering.com <http://notwandering.com>
>
>
>
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