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<div class="moz-cite-prefix">Marc,<br>
<br>
All of the other comments are useful. I only add a couple of
thoughts:<br>
<br>
1. If you have some (even one) irregularly larger piece of fuel
at the bottom, it will continue to give gases (potential smoke)
for a while after all of the surrounding fuel pieces have become
char. That very small amount of pyrolytic gase sometimes is not
sufficient to sustain the upper flame, and the result will be
smoke.<br>
<br>
2. When the MPF (migratory pyrolytic front) approaches the
bottom, the radiant heat that goes downward has no "next layer" of
biomass to dry, torrify and pyrolyze. Instead, it radiates to
the grate and back to the already hot fuel, making it hotter and
pyrolyzing faster. That is why there is a slight upward spike in
the pyrolytic gases and the resultant flame at the top. Seeing
that, the cook has the tendency to try to turn down the flame,
which is exactly the wrong thing to do. The pyrolysis needs to
finish strongly at the very end, to avoid that small amount of
final gases from being TOO small to sustain the upper flame
(similar to the comment in #1 above).<br>
<br>
We all hope that this helps. Please (everyone) submit comments
on experiences that support or refute the comments made to the
readers. <br>
<br>
Paul<br>
<br>
<pre class="moz-signature" cols="72">Doc / Dr TLUD / Prof. Paul S. Anderson, PhD
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 12/12/2014 9:33 AM, Dean Still wrote:<br>
</div>
<blockquote
cite="mid:CA+tShZu+q2u=ZRsBsXosj=Lwi7-PqP_ObsUwb-urPehE=QLtzg@mail.gmail.com"
type="cite">
<div dir="ltr">Hi All,
<div><br>
</div>
<div>We added more bottom air until all the wood had turned to
charcoal so there was no smoke at the transition.</div>
<div><br>
</div>
<div>Best,</div>
<div><br>
</div>
<div>Dean</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Fri, Dec 12, 2014 at 4:32 AM, Ray
Menke <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:ray.menke@gmail.com" target="_blank">ray.menke@gmail.com</a>></span>
wrote:
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">If the
fuel is not dry, or doesn't let enough air through, the
stove<br>
will need more primary air. A small computer fan mounted in
the<br>
bottom of a tin can or 2 liter juice bottle will provide
that excess<br>
air. (I use an old motorcycle battery with clip-clip
leads.) Most of<br>
the time, it is not needed, but it does solves the problem
in a hurry.<br>
It also melts grates and the walls of the burn chamber. A
sacrificial<br>
burn chamber liner from scrap metal or old stovepipe works
well, and<br>
grates can be made from 1/8" thick steel.<br>
Another solution might be to mix some pencil size torrefied
wood in<br>
with the almond husks. (one or two inches in length.) The
torrefied<br>
wood is guaranteed dry, and will loosen the packing of the
husks so<br>
more air can enter.<br>
My stoves are based on Paul Anderson's Champion TLUD design,
and have<br>
a 2" tube at the bottom for primary air. A funnel to direct
air into<br>
the tube can be made by taping tin or cardboard around the
open end of<br>
the olive can.<br>
Ray<br>
<br>
On Fri, Dec 12, 2014 at 4:57 AM, kgharris <<a
moz-do-not-send="true" href="mailto:kgharris@sonic.net">kgharris@sonic.net</a>>
wrote:<br>
> Marc,<br>
><br>
> I have also been struggling with this transition
problem. It has become<br>
> more pronounced since the rains started, so humidity
may be a contributing<br>
> factor. Also, the ND-TLUD I am using has turn-down
capability and the<br>
> transition problem seems to share some similarities
with turn-down problems.<br>
> This makes sense because in both cases the wood gas
production is being<br>
> reduced and the temperature of the flame is lower.
This made me think that<br>
> perhaps the problem could be addressed in the same way
that turn-down is<br>
> addressed, with either hot char or pilot flame
support. This has so far not<br>
> worked with pilot flame support. What has helped is
giving the stove lots<br>
> of primary air to get the char hot before the flame
reduces. Entering this<br>
> phase with the stove turned to a low setting always
results in smoke. This<br>
> is in keeping with something that Crispin wrote about,
using paper to cover<br>
> excess primary holes. When the pyrolysis front reaches
the bottom, it burns<br>
> the paper and lets extra primary air in to heat the
char, which helps get<br>
> through this phase without smoke. It might be a pain
to add this paper to<br>
> each burn.<br>
><br>
> Fuel depth may have some input here. With a large load
the char will start<br>
> burning at the bottom and will not be near the
decreasing wood gas to heat<br>
> and ignite it. Directing air down onto the top of the
char and heating some<br>
> of it to red hot may help. This is one of the methods
of supporting<br>
> turn-down by using red hot char. Julian Winter once
suggested a purched<br>
> char method for turn-down which did work. Placing a
small amount of char or<br>
> wood which will become char in a wire basket inside the
reactor just below<br>
> the secondary air inlet provides red hot char to
support the secondary flame<br>
> during turn-down. This would have the deminishing
transition wood-gas<br>
> passing through red hot char to be heated and ignited.
This might work for<br>
> the transition and also provide turn-down.<br>
><br>
> The primary air in this phase will be used mainly for
the last bit of<br>
> pyrolysis and the char will gradually increase burning
as the pyrolysis<br>
> slows down. This produces a temperature low point
before the char heats up.<br>
> Excess primary air just before this phase can heat the
char to keep the<br>
> temperature up. Keeping the temperature up is
important.<br>
><br>
> Please post anything you might learn.<br>
><br>
> Kirk<br>
> Santa Rosa, CA. USA<br>
><br>
> ----- Original Message -----<br>
> From: Marquitusus<br>
> To: <a moz-do-not-send="true"
href="mailto:stoves@lists.bioenergylists.org">stoves@lists.bioenergylists.org</a><br>
> Sent: Friday, December 12, 2014 1:01 AM<br>
> Subject: [Stoves] Smokeless transition<br>
><br>
> Hi Stovers,<br>
><br>
> There is a point in the TLUD process that I find
specially difficult to<br>
> understand and control: the transition from wood
gasification to char<br>
> gasification. Maybe you can help me to do it.<br>
><br>
> At this point, when the hydrocarbon fuel is near to
finish, my experiments<br>
> with almond husks as fuel for ND-TLUD shows 2 possible
endings:<br>
> 1- The flames in the burner turns to blue
color (due to high CO<br>
> presence in gases) and the char pyrolisis continues
until ashes. No smoke<br>
> present.<br>
> 2- The flames in the burner extinguishes and
the smoke appears.<br>
><br>
> I made a lot of tests, with variations in ND-TLUD
design (riser height,<br>
> quantity of primary and secondary air, type of
concentrator, etc.) and<br>
> still I'm not able to say which factor combination is
the answer for a<br>
> smokeless transition. Sometimes I have smoke, and
sometimes I don't.<br>
><br>
> I suspect the answer has to do with chemical fuel
composition, as when I use<br>
> wood pellets, almost never have smoke.<br>
><br>
> So this is the point where I am today. When char
gasification begins, I have<br>
> to lower the primary air? Lower the secondary air? How
I can ensure the<br>
> flame won't extinguish?<br>
><br>
> It would be very useful for me to read your comments
about this.<br>
><br>
> Thanks very much,<br>
><br>
> Marc<br>
><br>
><br>
><br>
</blockquote>
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