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<DIV><FONT size=2 face=Arial>Crispin,</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>I have been following your insights as you have
shared them with us. I value what you are saying. I like your
earlier statement that the pipe is a solution for a problem that should not
exist in the first place. If my stove was providing adiquate air and
mixing then my Wonderwerk Strata combustor would have no effect. It would
not be necessary.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Reading through this responce to Dr. Anderson I can
follow your logic until I get to the last paragraph. I do not disagree
with you, I just wonder how it works. The heat of pyrolysis rises through
the fuel in a BLDD, heating the fuel and driving out moisture. I wonder
what the mechanism is for this raising heat in a down draft stove. Is the
gas not moving down, carrying the heat downward? Heat is a property of
material, not material itself, and so it is independent of gravity and
buoyancy. The only mechanism I can see for heat to move upward is radiant
heat, just like a TLUD MPF radiates heat downward. I would like to know
more about how this works. I mean no contention here, I just want to
know.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Thank you,</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Kirk</FONT></DIV>
<BLOCKQUOTE
style="BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=crispinpigott@outlook.com
href="mailto:crispinpigott@outlook.com">Crispin Pemberton-Pigott</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=stoves@lists.bioenergylists.org
href="mailto:stoves@lists.bioenergylists.org">'Discussion of biomass cooking
stoves'</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, December 15, 2014 12:39
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [Stoves] Correcting a
misconception that approaches myth status</DIV>
<DIV><BR></DIV>
<DIV class=WordSection1>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">Dear
Paul<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US">You
can’t just jump in with such classifications without asking first.
<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt; mso-fareast-language: EN-US"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><B><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"
lang=EN-US>>…</SPAN></B>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><SPAN
style="COLOR: #1f497d"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">I
think you should have a look at a BLDD working and watch the migratory
pyrolytic front rising through the fuel instead of descending into it. You
might change your opinion.<o:p></o:p></SPAN></P>
<P class=MsoNormal><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><SPAN
style="COLOR: #1f497d"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">No
that is not necessarily true at all! One could make the same claim for
<I>all</I> top lit stoves with a high superficial air velocity. In a
BLDD there is a gas production process started by a fire at the bottom. Same
as TLUD. There is a migratory pyrolytic front that works its way
upwards. Same as a TLUD. When it reaches the top, there is a fuel chamber full
of char, same as a TLUD. The gas produced can be burned immediately under the
grate or taken elsewhere to be burned in a gas burner. Same as a
TLUD.<o:p></o:p></SPAN></P>
<P class=MsoNormal><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.<SPAN
style="COLOR: #1f497d"><o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">Again,
no. It is the same! When the migratory pyrolytic front reaches the top
of a BLDD fuel chamber the combustion continues at the top drafting air in (if
allowed) and does exactly what you describe but upside down. The <I>big
difference</I> is that the BLDD can be refuelled by placing more fuel on top
and the MPF continues to work its way into the new fuel, upwards, until it
again reaches the fully charred condition.<o:p></o:p></SPAN></P>
<P class=MsoNormal><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><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><BR>That
may all be true, but the BLDD stoves with MPF have been in use literally for
centuries. BLDD combustors with large fuel chambers were used for making coal
gas and the only way a useful gas can be created is by having a MPF in the
fuel bed. Obviously it was controlled or they would not have been able to get
a reliable product.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">A
TLUD is a bottom-lit downdraft stove turned upside down so that can’t be
refuelled. Deal with it.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">The
only practical difference is that the heat from pyrolysis in a DD stove rises
within the fuel supply, heating it and driving out moisture sooner than it
would in a TLUD where the heat all rises, save by radiation. There is an
advantage to this with coal or wet charcoal or wet wood. Otherwise, not really
any practical difference. I find that with a BLDD and wood pellets, for
example, the airflow velocity through the interstitial spaces becomes more
important in a DD stove than an UD one in order that the rising heat does not
create run-away gas generation inside the fuel bed. If too much gas is
produced it is hard to burn it all. Apart from this small consideration, and
having built lots of each, I observe no difference at all between these
architectures in terms of how the fuel is pyrolysed and the options for
burning the gas.<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">Regards<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt">Crispin<o:p></o:p></SPAN></P>
<P class=MsoNormal><SPAN
style="FONT-FAMILY: 'Calibri',sans-serif; COLOR: #1f497d; FONT-SIZE: 11pt"><o:p> </o:p></SPAN></P></DIV>
<P>
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