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<div class="moz-cite-prefix">Crispin,<br>
<br>
Thanks for your well informed (by much experience) comments.
Short flames are to be desired, but different approaches are still
being studied. Some other quick replies:<br>
<br>
1. I do not have a high regard for the Mayon rice husk stove.
My experience was limited and several years ago, but I have not
read of any substantial changes to the stove since then. And we
do not hear that it is being well accepted somewhere. I hope we
can hear from some others who can add their comments.<br>
<br>
2. Where do I go to read the results of what stoves have passed
the requirements of the Indonesia project? Did I miss an
announcement? IMO, things like that should be announced with
glee and fan-fare!<br>
<br>
3. I am glad to hear that some TLUDs are approved in Indonesia,
EVEN THOUGH THERE IS NO RECOGNITION FOR THE CHARCOAL PRODUCED
(unless it is somehow consumed later in the same stove). It will
be very interesting to have some study done (even if rather
informal observations) about what the users of those stove
actually will do with the charcoal, and if the char is
acknowledged by the users as having some value or importance. I
agree with Crispin that char is no longer the same as the original
biomass fuel. Kg of biomass into the stove is gone (when
calculating FUEL efficiency) even if there is about 20% of the Kg
weight coming out as char (which is about 30% of the energy value
of the biomass and about 50% of the carbon atoms of the
biomass.). But the ENERGY efficiency calculations would give
credit for the energy value to the char. And the FINANCIAL
"efficiency" (relating to cost of fuels or to benefits of possible
increases in crop production because of biochar) could also be
calculated, but would be more debated because of differing
perceived values.<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>
On 12/17/2014 1:03 AM, Crispin Pemberton-Pigott wrote:<br>
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Dear Ron</div>
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There two issues I have seen with the central pipe method of
supplying secondary air. I have of course tried it on several
designs to see what the effect is for updraft, side draft and
downdraft configurations. It is often suggested as a solution to
an air supply problem - the problem typically is that of poor
mixing. I can describe the most typical case as follows:</div>
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Consider a TLUD with a diameter inside the fuel chamber of 200
or 250mm. The designer, having read material on line, places a
number of holes above the fuel to let secondary air in. The
holes are small and many, copying photos found here and there. </div>
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The unit makes gas, has a tall flame, burns clean to the eye and
it is claimed to be a success. </div>
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<br>
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Putting a pot on it chills the tall flame, it smokes a lot and
the flames come out well past the pot. The heat transfer
efficiency is low, maybe 30% and it makes a lot of charcoal.
The fuel consumption is as high or higher than an open fire. The
designer reads that it is "ok" to deduct the char energy and
report the energy used in the form of a 'dry fuel equivalent'
which is of course interpreted to mean the 'fuel consumption'. </div>
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<br>
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Now we have a stove that in use (not just burning on its own)
makes a lot of smoke and CO, saves no fuel, costs more and is
much less controllable than an open fire, and needs special
preparation of fuel each time it is used. That, Ron is a VERY
hard sell, save for one thing: so many claims for superior
performance have been made for stoves like this that they get
attention, sales and subsidies. I am from time to time asked to
'fix it'. </div>
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What to do? Well the obvious problem with these stoves is the
tall flame which is directly caused by poor secondary air
mixing. I have written about it a lot as you know. If it is not
preheated it chills the gasses and the general result is worse.
Adding preheating is not enough because the problem was mixing,
not always temperature. Adding a 'concentrator disk' is a
compensation for poor mixing. It is an extra part which burns
out quickly. It does not necessarily reduce the flame length
required to burn completely. The target is to reduce the flame
length which to get it completed before it hits the pot. Many
people assume this is not necessary, assuming that the heat
'gets into the pot' best when the flames are running against
it. </div>
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<br>
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To get the flame length down is helped by the concentrator disk
but not necessarily if it delays the combustion during the
mixing process. What is ideal, everything else remaining the
same, is to place a pipe in the centre that feeds air into the
centre, passing through the fuel and providing the critically
needed air in the centre. </div>
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<br>
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Different methods of doing this are tried: a simple tube with an
open bottom and top passing through the fuel as is done by Roger
Samson in his rice hull gasifier: the Mayon Turbo Stove - one
of the first available designs. He uses two open tubes. They
shoot secondary air into the gas stream well below the pot. It
is a downdraft gasifier with a moving pyrolytic front. It has
continuous char removal, can be refuelled and is very clean
burning. It has been manufactured in Third World conditions for
a decade, I think, by now. It surprises me that this design is
not used more because it is an available product that uses rice
hull and doesn't require a fan and can be operated continuously.
Anyway...I worked on improving it at the request of Roger and it
involved reducing the amount of air passing through and
spreading it around and reducing the flame height. It still
remained an uncontrolled secondary supply. </div>
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<br>
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A problem introduced by this approach is the pipes are corroded
easily because they are in a very hot zone. </div>
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<br name="BB10" caretmarkerset="INVALID"
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</div>
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A capped pipe is often used as an alternative. Holes are
usually drilled in the side and the air is bled into the centre
portion of the gas stream. This has the right effect but let's
in more secondary air as the fuel uncovers the holes - a
significant problem. Because most people can't check the excess
air level, they don't know when the conditions are good. The
stove is declared clean anyway. </div>
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<br>
</div>
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Two problems are introduced by the stove add to the corrosion
problem. They are the variable secondary air supply that is
technically difficult to control and the creation of a
donut-shaped fuel charge. The ring-shaped burn is a continuous
source of problems. It is much harder to light 'evenly' as there
iis no 'centre' in which to place the ignition material. The
fire tends to get going on one side first and it takes time to
spread to the other side, and even longer to burn evenly. The
tube is a source of cooling right at the place where it should
be hottest. When the stove burns wood, it has to be chopped and
stacked in such a way that it is evenly spaced around the pipe
or else one side finishes well before the other. It makes
Everything harder to burn consistently. </div>
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<br>
</div>
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The use of a pipe with holes cause the least problems with
pelleted or very small fuel largely because the problems with
fire distribution tend to be minimal. Lighting is accomplished
with a liquid splash and the main issue is only the variable
airflow, lack of control and corrosion. </div>
<div style="width: 100%; font-size: initial; font-family: Calibri,
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initial; background-color: rgb(255, 255, 255);">
<span style="font-size: initial; text-align: initial;
line-height: initial;"><br>
</span></div>
<div style="width: 100%; font-size: initial; font-family: Calibri,
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initial; background-color: rgb(255, 255, 255);">
<span style="font-size: initial; text-align: initial;
line-height: initial;">This of course required a processed
fuel, pellets or rice hull. Wood, with a central pipe, is hard
to get to run properly.
</span></div>
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caretmarkerset="INVALID" class="markedForCaretMarkerRemoval">
</span></div>
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Usually the addition of the pipe is not accompanied by a
reduction in the supply from the side. The typical result is a
much shorter flame but with higher excess air. This is also
declared 'improved' (and it is, I guess). </div>
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<br>
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The best way to use a central pipe is with a flat, elevated top,
and no holes in the side. The biggest remaining problem is
uneven burning taking place on opposite sides of the pipe.
</div>
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<br>
</div>
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One could make a plan for controlling the air getting to the
pipe which would allow the power to be controlled while
maintaining the correct primary/secondary split. Bit is is not
easy to do in a way that is cheap and convenient to operate. </div>
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<br>
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What else can be done to overcome these problems - the lighting,
uneven burn, variable flow, uncontrolled flow, corrosion and
cost?</div>
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<br>
</div>
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Put the secondary air in properly in the first place, from the
outside!</div>
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<br>
</div>
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If the secondary air was fed in correctly, there would be no
need for a concentrator disk, no central pipe, easy control,
self-balancing primary/secondary split, easy central ignition,
self-spreading fires that balance well and quite importantly, a
short flame without high excess air. </div>
<div style="width: 100%; font-size: initial; font-family: Calibri,
'Slate Pro', sans-serif; color: rgb(31, 73, 125); text-align:
initial; background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="width: 100%; font-size: initial; font-family: Calibri,
'Slate Pro', sans-serif; color: rgb(31, 73, 125); text-align:
initial; background-color: rgb(255, 255, 255);">
I described in detail how to alter the design shown to the group
a couple of days ago. I estimated the EA% and suggested a
target value and hole sizes to achieve it. The approach works
for all fuels. One of the biggest advantages is the creation of
the same effect as a concentrator disk using only airflow. </div>
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<br>
</div>
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The swirl you speak of can be created using this air entry,
avoiding if at all possible, any metal in the gas or flame path.
Metal chills the flow. End of short story. It makes it harder to
burn really clean. Metal corrodes. Metal costs a lot. Metal
requires assembly. Why bother?</div>
<div style="width: 100%; font-size: initial; font-family: Calibri,
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initial; background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="width: 100%; font-size: initial; font-family: Calibri,
'Slate Pro', sans-serif; color: rgb(31, 73, 125); text-align:
initial; background-color: rgb(255, 255, 255);">
Paul: message for you. Don't you think the Mayon turbo stove has
all the features you are seeking in a char maker? It seems to me
to do a lot of things that are oft-stated goals. </div>
<div style="width: 100%; font-size: initial; font-family: Calibri,
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<br>
</div>
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'Slate Pro', sans-serif; color: rgb(31, 73, 125); text-align:
initial; background-color: rgb(255, 255, 255);">
For TLUD builders I can report (now that it is public) that
there are a couple of models commercially available which are
controllable, used wood fuel, have very low emissions, make char
and exceed the minimum 25% system efficiency requirement of the
CSI-Indonesian Pilot program. Thus when calculated correctly
and built well, stoves can still be char-makers and save fuel
(compared with an open fire). </div>
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<br>
</div>
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Regards </div>
<div style="width: 100%; font-size: initial; font-family: Calibri,
'Slate Pro', sans-serif; color: rgb(31, 73, 125); text-align:
initial; background-color: rgb(255, 255, 255);">
Crispin </div>
<div><br>
</div>
<div><br>
</div>
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caretmarkerset="INVALID" class="markedForCaretMarkerRemoval">
</span></div>
<div style="word-wrap:break-word">Crispin, cc list
<div><br>
</div>
<div><span class="x_Apple-tab-span" style="white-space:pre"></span>1.
Yesterday you said this:</div>
<div><span class="x_Apple-tab-span" style="white-space:pre"></span><i>Personally
I don’t think a ratio is a good design approach. You need a
certain vertical space to burn the gases before you attempt
heat transfer. A total of 125-150mm is normally OK assuming
you have the fuel deck covered with secondary air and it is
burning hot near the fuel bed. If you bleed in secondary air
through a lot of small holes, there will be no secondary air
in the middle. Some try to compensate for this by putting in
a vertical tube. That tube is a sign that he secondary air
entrance has not been handled correctly. It is a common
‘solution’ to a problem that should not be there in the
first place. Try to avoid it.</i></div>
<div>
<div>
<div><br>
</div>
<div><span class="x_Apple-tab-span" style="white-space:pre"></span>2.
Re the “vertical tube”: I have been involved in several
off-list discussions where central secondary air seemed to
be providing turbulence benefits (benefits that including
reducing the height and therefore lowering costs. A
central pipe can also prevent gases from rising in the
center, which can be a benefit if one has swirl. Can you
give a cite on where a central secondary pipe was shown to
not be of value?</div>
<div><br>
</div>
<div>Ron</div>
</div>
</div>
</div>
<br>
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