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:[email protected]] *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:[email protected]] *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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