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<div class="moz-cite-prefix">Stovers,<br>
<br>
Truth: TLUD stoves are very different in combustion from simply
turning a down-draft gasifier upside down.<br>
Myth and misconception: That TLUD and DD combustion is the same
except upside down.<br>
<br>
My comments are stimulated by what Crispin Pemberton-Pigott who
wrote:<br>
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">A
TLUD is an upward burning downdraft stove and there is a
great deal in common with them. There are investigations
and patents going back to the 17<sup>th</sup> century.
FD-downdraft stoves are rare though known. There is a
good reason why Dr Tom’s stove was called an upside down
downdraft combustor. It was a downdraft stove turned
over, burning the same fuel in the same manner
internally, with the fire on top. <o:p></o:p></span></p>
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Tom Reed called his innovation "Inverted Down-Draft" or IDD for
short in the 1980s and 90s. He was inspired by what he knew about
true Down Draft (DD) gasifiers. But names and reality are not
always clearly matching. In 2004 - 05 I re-named it Top Lit
UpDraft (TLUD) which is also not totally accurate. None of the
names acknowledge the Migratory Pyrolytic Front (MPF) that is the
dominant feature of what is commonly called TLUD micro-gasification.<br>
<br>
Note:<br>
A DD gasifier is ignited at the BOTTOM, and the fire (hot zone of
gasification) REMAINS at the bottom, and the unit can be operated
with continuous fuel entry into the top.<br>
<br>
A IDD or TLUD or MPF gasifier is ignited at the TOP, and the fire
(hot zone of gasification) slowly MOVES to the bottom, after which
time the fire zone stays at the bottom and the unit operates as if
it were a regular UpDraft (UD) gasifier if anyone puts more fuel
into the top. <br>
<br>
Fundamentally different.<br>
<br>
Because of Tom Reed and also Paal Wendelbo who worked totally
independently, we have something new for cookstoves. They did not
invent pyrolysis. They were not the first people to have a fire in
a barrel making gases and have the flames only up at the top where
secondary air was available. (I saw that in the 1950s in a burn
barrel at my home.) But Reed and Wendelbo were the ones who
CONTROLLED it and understood it and made it all small enough to be
useful in a cookstove. And the rest is history. And TLUD history
is still being made.<br>
<br>
Paul<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>
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<p class="MsoNormal"><o:p> </o:p></p>
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<div>
<p class="MsoNormal"><span style="color:#1F497D">></span>For now
what we need are some very basic empirical studies on
ND-TLUD performance, so that builders of stoves can make
more deliberate decisions, so that rural extension workers
can have confidence that their advise is well-grounded,
and so that both can respond effectively to unexpected
situations.<span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">That
would be great. I wouldn’t second-guess what people are
doing or have done, and not published it in a way you
could find it. There is a lot in Chinese which is not
very accessible. <o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><o:p> </o:p></p>
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<div>
<p class="MsoNormal"><span style="color:#1F497D">></span>We
need to start building ND-TLUD science at a very basic
empirical level. Nobody has actually measured primary and
secondary air flow, so nobody really knows the their
optimum proportions for low emissions and how that changes
with gasification temperature, types of burner and fuel. <span
style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I
believe that has been done for BLDD gasifiers long ago.
Such gasifiers were used for making town gas. It is (as
I understand it) not wise to estimate that the gases
produced somehow set the emissions of the fire. That is
a bit like saying ethanol is a ‘clean fuel’. I can
suggest that you try two sets of experiments: use a
fixed burned design and vary the gas production
parameters, then see how the burner handles the gaseous
fuel.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Then
leaving the gas production in one of several starts,
vary the burner to get the best burn for the gas it
happens to produce. What you will find is that there are
dozens of combinations that produce very low emissions.
The combination of a gas generation method (creating a
significantly different gas composition) will burn best
in a particular architecture of burner, mixing and
secondary air pre-treatment regime. <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">></span>Nobody
has actually proven that preheating secondary air is
effective; it is just assumed to work, even though we are
taking heat from the reactor to create more viscous and
less dense air. <span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I
have personally conducted many tests involving this and
so has Roger Samson who has been manufacturing rice hull
gasifiers for years. I have been making downdraft stoves
more than 10 years and they all have (now) preheated
secondary air because the benefit is so great. The
effect of preheating is strong, reproducible, and is
best demonstrated when using a gas analyser which tracks
the CO/CO2 ratio. Completeness of combustion is a good
metric. Taking heat out the combustion process generates
CO sooner than PM.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">ND-TLUD
design has been investigated by me and Prof Lodoysamba
many times in Mongolia, first over a period of 18
months, and later for several shorter periods. We have
many hours of tests showing the clear advantage of
preheating the secondary air and how to introduce it,
and more hours of showing the poorer results of not
doing so. Two stoves that failed to make the cut this
year were failed precisely because they did not
incorporate secondary air preheating, combined with
poorly conceived operating instructions.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">></span>If
preheating makes no difference, then it becomes easier to
design the gas burner and the gasification reactor as
separate modules, that are mixed and matched according to
need. <span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Yeah,
but it is a big damper on combustion efficiency (pun
intended). Cold air entering the gas stream simply
cannot compete with hot air entering the same gas
stream. Cold air injection produces a combustion
efficiency that will meet US and EU CO targets, but the
approved stoves in Ulaanbaatar demonstrate a far lower
sustained CO level – often 0.03% or lower. This is only
achieved in those TLUD’s that have preheated secondary
air and have it injected in the right amount in the
right manner.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">></span>Nobody
has shown that TLUD biochar has safe levels of polycyclic
aromatic hydrocarbon and dioxins. <span
style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">No
idea. I have not researched what is in biochar though I
think the Japanese have been looking at that for some
time. <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">></span>All
this, and more, needs clarification in replicated,
controlled experiments ... and open access publication.<span
style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">There
is a significant problem with that in that as the money
pool spent on stoves drives the creation of larger
private participants, they have proven to be less likely
to share as openly as in the past (unless it is in the
patents they file). This group is far more likely to
participate in a sharing exercise, but even here, times
they are a-changing. <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I
appreciate your willingness to share your work and
thoughts about your investigations. <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Regards<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Crispin<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
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