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<div class="moz-cite-prefix">Crispin and all,<br>
<br>
I think that the char being created in a TLUD is not hot enough
to cause the water gas reaction. <br>
<br>
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. <br>
<br>
Paul<br>
<pre class="moz-signature" cols="72">Paul S. Anderson, PhD aka "Dr TLUD"
Email: <a class="moz-txt-link-abbreviated" href="mailto:psanders@ilstu.edu">psanders@ilstu.edu</a> Skype: paultlud Phone: +1-309-452-7072
Website: <a class="moz-txt-link-abbreviated" href="http://www.drtlud.com">www.drtlud.com</a></pre>
On 11/11/2012 6:46 PM, Crispin Pemberton-Pigott wrote:<br>
</div>
<blockquote
cite="mid:372955295-1352681217-cardhu_decombobulator_blackberry.rim.net-1075835766-@b13.c10.bise6.blackberry"
type="cite">
<style type="text/css">p { margin: 0; }</style>Is this not exactly
the reaction taking place as the moisture comes out of the fuel
particles and passes through the charred surface?<br>
<br>
The point of discussion is that it consumes the char in doing so.
<br>
<br>
Regards<br>
Crispin
<hr>
<div><b>From: </b> <a class="moz-txt-link-abbreviated" href="mailto:rongretlarson@comcast.net">rongretlarson@comcast.net</a>
</div>
<div><b>Date: </b>Sun, 11 Nov 2012 20:56:14 +0000 (UTC)</div>
<div><b>To: </b>Discussion of biomass cooking
stoves<a class="moz-txt-link-rfc2396E" href="mailto:stoves@lists.bioenergylists.org"><stoves@lists.bioenergylists.org></a>; Andrew
Heggie<a class="moz-txt-link-rfc2396E" href="mailto:ajheggie@gmail.com"><ajheggie@gmail.com></a></div>
<div><b>Cc: </b>paul anderson<a class="moz-txt-link-rfc2396E" href="mailto:psanders@ilstu.edu"><psanders@ilstu.edu></a>; Crispin
Pemberton-Pigott<a class="moz-txt-link-rfc2396E" href="mailto:crispinpigott@gmail.com"><crispinpigott@gmail.com></a></div>
<div><b>Subject: </b>Re: [Stoves] Smoke-free biomass pellet
fueled stove</div>
<div><br>
</div>
<div style="font-family: Arial; font-size: 12pt; color: #000000">
<style>p { margin: 0; }</style>
<div style="font-family: Arial; font-size: 12pt; color: #000000">Andrew,
list, Paul, Crispin<br>
<br>
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:<br>
<a class="moz-txt-link-freetext" href="http://www.webelements.com/carbon/chemistry.html">http://www.webelements.com/carbon/chemistry.html</a><br>
which says:<br>
<br>
<b><i>"Reaction of carbon with water</i></b>
<p class="p_first"><i>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<sub>2</sub>, 50%), carbon monoxide (CO, 40%),
carbon dioxide (CO<sub>2</sub>, 5%), nitrogen and methane
(N<sub>2</sub> + CH<sub>4</sub>, 5%). It is an important
feedstock gas for the chemical industry.</i></p>
<p class="equation"><i>C + H<sub>2</sub>O → CO + H<sub>2</sub></i></p>
<p><i>This reaction is endothermic (ΔH° = +131.3 kJ mol<sup>-1</sup>;
ΔS° = +133.7 J K<sup>-1</sup> mol<sup>-1</sup>) which
means that <u><b>the coke cools down</b></u> during the
reaction. To counteract this, the steam flow is replaced
by air to reheat the coke allowing further reaction." </i><u><b>(Emphasis
added)</b></u><i><br>
</i></p>
<h3 class="p"> Ron<br>
</h3>
<hr id="zwchr"><b>From: </b><a class="moz-txt-link-abbreviated" href="mailto:ajheggie@gmail.com">ajheggie@gmail.com</a><br>
<b>To: </b>"Discussion of biomass cooking stoves"
<a class="moz-txt-link-rfc2396E" href="mailto:stoves@lists.bioenergylists.org"><stoves@lists.bioenergylists.org></a><br>
<b>Sent: </b>Sunday, November 11, 2012 3:17:24 AM<br>
<b>Subject: </b>Re: [Stoves] Smoke-free biomass pellet fueled
stove<br>
<br>
[Default] On Thu, 8 Nov 2012 23:01:44 +0000,"Crispin
Pemberton-Pigott"<br>
<a class="moz-txt-link-rfc2396E" href="mailto:crispinpigott@gmail.com"><crispinpigott@gmail.com></a> wrote:<br>
<br>
>Dear Andrew<br>
><br>
>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. <br>
><br>
>Any ideas what that would be?<br>
<br>
<br>
Crispin I think Jaakko has nailed that one and I completely
agree,<br>
it's the heat required to dry the particle below the pyrolysis
front<br>
before it reaches pyrolysis temperature, all the while the
bulk of the<br>
heat is rising through the already charred layers as sensible
heat of<br>
the offgas. The more of the char burns at the pyrolysis front
because<br>
the downward movement of the front has slowed and it remains
in<br>
contact with air for longer. When the wood is dry the front
moves<br>
downward from the fresh char and the offgas, being devoid of
oxygen,<br>
shields the hot char from further oxidation.<br>
<br>
Jaakko that's an interesting cite with regard to the
autogasification,<br>
I haven't found the original yet, I'm not sure it is relevant
to tlud<br>
as generally the burn is complete before larger particles are<br>
pyrolysed, also the watergas reaction needs a higher
temperature at<br>
equilibrium that we normally see in the pyrolysis front (
which is<br>
about 600C I think). <br>
<br>
I have also in the past pointed out that large logs of dry
wood burn<br>
differently from the same log when green as pyrolysis moves
quickly<br>
through the log evolving offgas which again forms a shield as
it burns<br>
preventing oxygen reaching the outer parts of the log, once
the offgas<br>
slows down the char then burns. With the green log because the
heat<br>
required to dry successive layers of the log is large and
offgas<br>
evolution is slow air does reach fresh char on the surface, so
the log<br>
gradually disappears. Also as the water vapour and CO2 given
off<br>
dilute the offgas often this does not burn and the log
smoulders away<br>
with little or no flame but lots of acrid smoke.<br>
<br>
Sorry to be a bit slow on the response but I'm glad Jaakko
chipped in.<br>
<br>
AJH<br>
<br>
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