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Dear Crispin,<br>
<br>
On 22/01/2012 10:36 PM, Crispin Pemberton-Pigott wrote:
<blockquote cite="mid:02fd01ccd980$31566a90$94033fb0$@gmail.com"
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<div class="WordSection1">
<p class="MsoNormal"><span style="color:#1F497D">Dear Alex<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">This
is interesting news. The grate looks great, and if there is
a pile of char that is maintained in front, we must conspire
to burn it.</span></p>
</div>
</blockquote>
Not so fast. I rather like the idea of a naturally formed biochar
venturi:)<br>
<blockquote cite="mid:02fd01ccd980$31566a90$94033fb0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">To review, it
is a crossdraft fire with all the advantages inherent in it:
refuellable and lots of room for flames. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">If
the char builds up in front of the hopper but self-limits
(i.e. burns away) then it has to be eaten by the passing
flame and available O2. That being so, I see a couple of
options. One is to admit air through some small holes (1.6,
2.0mm) drilled under the early part of the pile (on the
grate side of the pile). That will bleed air under the char
which is a good way to burn it. Another is to change the
shape of the pipe in that area to allow ash to drop. I
presume at the moment the ash is blown into the larger
chamber of the stove. </span></p>
</div>
</blockquote>
I see the odd spark or glowing particle fly into the stove. This is
what you see in most pellet stoves which do tend to have relatively
low PM emissions. In part that has to do with the way the size of
the particles in the pellet ('sawdust' is really tiny wood chips)
and how they tend to hold together. When the hopper does runs out
of fuel the added air flow literally blows whole charred pellets
into the stove. A chimney draft is nothing to sneeze at, so to
speak. <br>
<blockquote cite="mid:02fd01ccd980$31566a90$94033fb0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">It
is highly likely you have a fairly large PM10 number
compared with the same fuel burned in a pile in that larger
chamber because of lofted ash.</span></p>
</div>
</blockquote>
<blockquote cite="mid:02fd01ccd980$31566a90$94033fb0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span style="color:#1F497D">I am really
pleased to hear that the flow is so reliable. I have some
really short fat pellets here which are probably going to
feed well because they are nearly marbles. Probably made
with one of those trochoid, concentric-ring pellet formers.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">As for the fire
rising into the hopper, that is not going to happen if the
air velocity is high enough. Conditions we have observed it
is when the velocity is quite low. If the heat is enough, a
rising current of heated air and gas circulates in the fuel
immediately above the burning layer and the fire works its
way up. That can only happen if a) there is some air
(especially from above) or b) the fuel is volatile enough to
run an air-free charring burn in the present of enough heat.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">The advantage
of coal, even with a highly volatiles one like the lignite
from Nalaikh mine, it is still less volatile than wood. The
talk of torrefied pellets intrigues me for that reason. It
is more likely to behave like slow roasting coal. Very
controllable. There are small coal pellets, say 16mm
diameter which might feed well too.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">Is
there any reason you can think of that the hopper, feed tube
and burning chamber should be round?</span></p>
</div>
</blockquote>
No.<br>
<blockquote cite="mid:02fd01ccd980$31566a90$94033fb0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">If you pass by
the house I can show you a stove body that your burner will
directly attach to with several novel features. It won’t be
shown until March and sort of solves the ‘rest of a stove’
for you. I am pretty sure you will like it. It <i>might</i>
address the PM10 issue, or not, and solves the heat
extraction issues for cooking and heating.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I have some
Kanthal wire here which we are recommending for grate
material. It will work well for you and will hardly get hot
at all. If some small bits of fuel drop through (being ahead
of the grate) a pocket can be provided underneath to let
them smoulder, feeding CO and C and H2 into the beginning of
the fire. No problem.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">The arrangement
is made similarly on the SeTAR BLDD5 with the smoulderings
fed into the flaming portion of the pipe. The reason I
mention a wire grate is it is cheap and easy to make. But
like the layered flats too. It should be possible to punch
that in a single stroke with the right tool.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">How
deep is the fuel in the hopper?</span></p>
</div>
</blockquote>
40 cm. I have materials to go up to 100cm, and I could take it up to
near the ceiling with some stove pipe, though I might have to
counter balance the stove:)<br>
<br>
<blockquote cite="mid:02fd01ccd980$31566a90$94033fb0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">I
tried a number of things with hopper shape and decided there
is a general rule about bridging which is the following: if
the hopper tapers inwards the point of burning, there is an
upper limit to the height of the fuel for each degree of
narrowing. I tried shoulders too and they are OK further up
(for example, within 1 hopper width of the top of the fuel
pile). On all cases, if the fuel is compressed by pushing
down on it or by stacking lots of fuel up, bridging occurs
just above the beginning of the taper.</span></p>
</div>
</blockquote>
These pellets are highly resistant to bridging. On the other hand I
have seen chips defy gravity:) <br>
<blockquote cite="mid:02fd01ccd980$31566a90$94033fb0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">The solution is
agitation or a non-tapering hopper bottom.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">This
is bound to be affected by the surface smoothness of the
fuel particle. If the pellets are shiny and hard that has to
be a help avoid bridging, right? I am impressed that you are
able to keep it feeding so well with such a significant
narrowing.</span></p>
</div>
</blockquote>
It is difficult to measure but the pellet flow is in fact air (wind)
assisted. However they are more bullet than sail. Small dry wood
chips are sails and if they make it down through the hopper, they
blow right out of the tube.<br>
<blockquote cite="mid:02fd01ccd980$31566a90$94033fb0$@gmail.com"
type="cite">
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<p class="MsoNormal"><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">To
you think it is necessary to tilt the flame tube downwards
at all? If the char pushed ahead it would be burned by the
continuous heat of the flame. Using wood, I can report that
I have seen flames reaching more than 24 inches along the
tube so you may get better combustion efficiency by
lengthening the one you have.</span></p>
</div>
</blockquote>
Yes, a view of the flame is useful for understanding the process but
is not ideal for combustion.<br>
<blockquote cite="mid:02fd01ccd980$31566a90$94033fb0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color: rgb(31, 73, 125);">Thanks
for an interesting (tiny) burner idea. If you bring it here
I have some 5mm switchgrass pellets I have had difficulty
burning it anything yet. Maybe…</span></p>
</div>
</blockquote>
I suspect the ash would bung it up, but maybe...not.<br>
<br>
Alex<br>
<blockquote cite="mid:02fd01ccd980$31566a90$94033fb0$@gmail.com"
type="cite">
<div class="WordSection1">
<p class="MsoNormal"><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Crispin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<div>
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1.0pt;padding:3.0pt 0mm 0mm 0mm">
<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext;mso-fareast-language:EN-CA"
lang="EN-US">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext;mso-fareast-language:EN-CA"
lang="EN-US"> <a class="moz-txt-link-abbreviated" href="mailto:stoves-bounces@lists.bioenergylists.org">stoves-bounces@lists.bioenergylists.org</a>
[<a class="moz-txt-link-freetext" href="mailto:stoves-bounces@lists.bioenergylists.org">mailto:stoves-bounces@lists.bioenergylists.org</a>] <b>On
Behalf Of </b>Alex English<br>
<b>Sent:</b> Sunday, January 22, 2012 7:02 PM<br>
<b>To:</b> Discussion of biomass cooking stoves<br>
<b>Subject:</b> Re: [Stoves] The upside of Down feed<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Dear Crispin,<br>
The pellets are 6mm dia. 1-2.5 cm long. The hole is 5cm in
diameter. I tried a few chips to block the hole. It usually
took more than one to stop it, and put out the fire. There
isn't much evidence of the fire mving up into the hopper. The
attached picture shows the position of grate in relation to
the hopper. It is adjustable. A mount of glowing charred
pellets form in the bottom half of the tube (6.2 cm ID pipe)
out in front of the grate. This seems to be self limiting, at
least over the five hours it ran today.<br>
<br>
I ran it with a second hopper tube such that the air flowed
outside the inner 14cm diameter hopper (with lid) and inside
the outer15.5cm diameter hopper. The air has to pas through
pellets in the cone portion only.<br>
<br>
Shutting off the grate air does reduce the burn rate by as
much as half, but that is a guess and I am unsure if it works
for hours.<br>
<br>
but wood pellets are cheating...<br>
<br>
next, a complete redesign for chips...<br>
<br>
courting failure....<br>
Alex<br>
<br>
<br>
<br>
<o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif";mso-fareast-language:EN-CA"><o:p> </o:p></span></p>
</div>
<br>
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