[Stoves] Smoke-free biomass pellet fueled stove

Paul Anderson psanders at ilstu.edu
Sun Nov 11 20:01:02 CST 2012


Crispin and all,

I think that the char being created in a TLUD  is not hot enough to 
cause the water gas reaction.

Also, there is no net increase in energy.   The water gas reaction just 
takes energy from the reacting carbon plus water and puts it (saves it) 
into the desirable gases (H2, and CO mainly) that permits the energy to 
be moved to a different place where it is needed when the gases are 
combusted.   That makes sense in the larger gasifiers where the gases 
can be moved many meters, cooled,  and put into internal combustion 
engines.   But in a TLUD, the gases would be moved only 5 to 20 cm 
upward before being combusted under the pot.

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 11/11/2012 6:46 PM, Crispin Pemberton-Pigott wrote:
> Is this not exactly the reaction taking place as the moisture comes 
> out of the fuel particles and passes through the charred surface?
>
> The point of discussion is that it consumes the char in doing so.
>
> Regards
> Crispin
> ------------------------------------------------------------------------
> *From: * rongretlarson at comcast.net
> *Date: *Sun, 11 Nov 2012 20:56:14 +0000 (UTC)
> *To: *Discussion of biomass cooking 
> stoves<stoves at lists.bioenergylists.org>; Andrew Heggie<ajheggie at gmail.com>
> *Cc: *paul anderson<psanders at ilstu.edu>; Crispin 
> Pemberton-Pigott<crispinpigott at gmail.com>
> *Subject: *Re: [Stoves] Smoke-free biomass pellet fueled stove
>
> Andrew, list, Paul, Crispin
>
>    I can agree with the various explanations offered in this thread 
> vis-a-vis fuel moisture.  But I think there is another fundamental 
> chemical 'WATER GAS" explanation.   One can find this chemistry 
> explanation many places, for example:
>       http://www.webelements.com/carbon/chemistry.html
> which says:
>
> */"Reaction of carbon with water/*
>
> /Carbon, either as graphite or diamond does not react with water under 
> normal conditions. Under more forsing conditions, the reaction becomes 
> important. In industry, water is blown through hot coke. The resulting 
> gas is called water gas and is a mixture of hydrogen (H_2 , 50%), 
> carbon monoxide (CO, 40%), carbon dioxide (CO_2 , 5%), nitrogen and 
> methane (N_2 + CH_4 , 5%). It is an important feedstock gas for the 
> chemical industry./
>
> /C + H_2 O ? CO + H_2 /
>
> /This reaction is endothermic (?H° = +131.3 kJ mol^-1 ; ?S° = +133.7 J 
> K^-1 mol^-1 ) which means that _*the coke cools down*_ during the 
> reaction. To counteract this, the steam flow is replaced by air to 
> reheat the coke allowing further reaction." /_*(Emphasis added)*_/
> /
>
>
>         Ron
>
> ------------------------------------------------------------------------
> *From: *ajheggie at gmail.com
> *To: *"Discussion of biomass cooking stoves" 
> <stoves at lists.bioenergylists.org>
> *Sent: *Sunday, November 11, 2012 3:17:24 AM
> *Subject: *Re: [Stoves] Smoke-free biomass pellet fueled stove
>
> [Default] On Thu, 8 Nov 2012 23:01:44 +0000,"Crispin Pemberton-Pigott"
> <crispinpigott at gmail.com> wrote:
>
> >Dear Andrew
> >
> >I an becoming convinced that the char disappears for other reasons as 
> well. The heat needed to get rid of the moisture is far less than the 
> charcoal. That leads me to think there is some reaction involving 
> water that breaks the carbon out of the char.
> >
> >Any ideas what that would be?
>
>
> Crispin I think Jaakko has nailed that one and I completely agree,
> it's the heat required to dry the particle below the pyrolysis front
> before it reaches pyrolysis temperature, all the while the bulk of the
> heat is rising through the already charred layers as sensible heat of
> the offgas. The more of the char burns at the pyrolysis front because
> the downward movement of the front has slowed and it remains in
> contact with air for longer. When the wood is dry the front moves
> downward from the fresh char and the offgas, being devoid of oxygen,
> shields the hot char from further oxidation.
>
> Jaakko that's an interesting cite with regard to the autogasification,
> I haven't found the original yet, I'm not sure it is relevant to tlud
> as generally the burn is complete before larger particles are
> pyrolysed, also the watergas reaction needs a higher temperature at
> equilibrium that we normally see in the pyrolysis front ( which is
> about 600C I think).
>
>  I have also in the past pointed out that large logs of dry wood burn
> differently from the same log when green as pyrolysis moves quickly
> through the log evolving offgas which again forms a shield as it burns
> preventing oxygen reaching the outer parts of the log, once the offgas
> slows down the char then burns. With the green log because the heat
> required to dry successive layers of the log is large and offgas
> evolution is slow air does reach fresh char on the surface, so the log
> gradually disappears. Also as the  water vapour and CO2 given off
> dilute the offgas often this does not burn and the log smoulders away
> with little or no flame but lots of acrid smoke.
>
> Sorry to be a bit slow on the response but I'm glad Jaakko chipped in.
>
> AJH
>
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