[Stoves] Charcoal stove design
Alex English
english at kingston.net
Wed Sep 18 20:55:51 CDT 2013
AT ETHOS a few years back (2010 I think), Bryan Wilson gave an excellent
presentation on an improved combustion charcoal stove. The ETHOS website
doesn't seem to have a link for it.
I believe this is the the one,
http://www.envirofit.org/products/?sub=cookstoves&pid=12
Alex
On 18/09/2013 5:37 AM, Saastamoinen Jaakko wrote:
>
> Dear Frank and Crispin,
>
> the main DIRECT product in the reaction of carbon with oxygen is CO
> but also some CO2 is directly formed. CO that is formed can be
> oxidized to CO2 (CO+½O2=CO2) at high enough temperatures in the
> vicinity of carbon particle or in later stage in the gas flow. So
> there are different zones along the gas flow in carbon particle layer
> when air (or gas) is flowing upwards through it:
>
> I)Zone where exothermic reaction C+½O2=CO takes place (but some CO2 is
> also formed). Here the gas temperature is rather low because it is
> close to the inlet and the gas has not heated up enough. So CO is not
> burning well.
>
> II)Zone where the gas temperature becomes high enough so that also the
> exothermic reaction CO+½O2 =CO2 (enhanced by H2O) takes place in the
> gas. This leads to even higher local temperature along the gas flow so
> that exothermic reactions (C+½O2=CO and CO+½O2=CO2) take place at even
> higher rate. Here also the endothermic reaction CO2+C=2CO takes place
> because the char temperature is high enough. This rrwaction adjust the
> temperature level preventing it to increase very high. Then at the
> location, where all oxygen is consumed, the gas temperature and CO2
> concentration reach the maximum values.
>
> III)After that the carbon reacts with CO2 producing carbon monoxide in
> endothermic gasification reaction CO2+C=2CO. The gas is cooled due to
> this endothermic reaction. If the layer is very thick, the gas is
> cooled to a temperature at which the reaction rate C+CO2=2CO becomes
> very low.
>
> So some conclusions:
>
> 1.For a thin layer, there is only zone I producing CO.
>
> 2.For thicker layer (zone II), the exit gas contains much CO2 and some
> CO. The exit gas is hot and CO may be burned introducing (preheated)
> secondary air. The exit gas is hottest if the thickness of the layer
> is just in the intermediate transfer regime from zone II to III.
>
> 3.For a thick layer, the gas contains much CO and some CO2. Its
> temperature is low and it is difficult to burn CO without highly
> preheated secondary air.
>
> The reaction CO+½O2=CO2 can take place also in the other direction.
> This reverse reaction (dissociation) of carbon dioxide is not
> significant at temperatures <1800 K.
>
> Regards
>
> Jaakko
>
> *From:*Stoves [mailto:stoves-bounces at lists.bioenergylists.org] *On
> Behalf Of *Frank Shields
> *Sent:* 18. syyskuuta 2013 0:55
> *To:* 'Discussion of biomass cooking stoves'
> *Subject:* Re: [Stoves] Charcoal stove design
>
> *Dear Crispin,*
>
> **
>
> *So the CO2 > CO is endothermic. But still needs carbon. As I see it
> the only difference is the temperature changing as the gases move
> around the pot. Wondering if the reading could be affected by
> temperature? Perhaps amount of gas entering the instrument or
> something? Interesting. Could hydrogen react with one of the oxygen in
> CO2 making water leaving CO? *
>
> **
>
> *Frank*
>
> **
>
> *From:*Stoves [mailto:stoves-bounces at lists.bioenergylists.org] *On
> Behalf Of *Crispin Pemberton-Pigott
> *Sent:* Tuesday, September 17, 2013 2:01 PM
> *To:* 'Discussion of biomass cooking stoves'
> *Subject:* Re: [Stoves] Charcoal stove design
>
> My conclusion is the CO splits endothermically. It does not happen in
> stoves with high EA.
>
> Crispin
>
> *Dear Crispin,*
>
> **
>
> *<snip>*
>
> I found that directly above the middle of a good stove (under the pot)
> there is zero CO -- I was amazed. But nearer the edges there is more.
>
> */[Frank >] How is that possible? I thought going from CO2 > CO could
> only occur be in a bed of char. This is very strange. /*
>
> *//*
>
> */Regards/*
>
> *//*
>
> */Frank/*
>
>
>
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