<html><head></head><body lang="EN-CA" bgcolor="white" vlink="#954f72" link="#0563c1" data-blackberry-caret-color="#00a8df" style="background-color: rgb(255, 255, 255); line-height: initial;"><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);">Dear Kirk</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);">Within the small spaces between lumps of fuel there is normal buoyancy for the hot air or hot gases so it circulates and convects heat upwards, no matter what the direction of the burn. Generally for very dry biomass this is a problem with a DD stove if an attempt is made at the same time to make char. Either it 'cooks' a lot of fuel at once making wet gas or it races through it and is not able to properly pyrolyse the fuel. </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);">Consider this: in a TLUD with a very low flow of primary air, or with damp fuel, or a combination of the two, there is a real possibility it just stops pyrolyzing. It is a limit. The problem is the heat radiated (and a small amount conducted) downwards is not enough to sustain a continuous reaction. Taking those identical conditions and flipping it upside down one finds the pyrolysis continues because more heat, under the same conditions, rises into the fuel bed. </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);">At the other extreme is the high gasification rate. If the fuel is really dry and full of oxygen it can burn quite well with no air at all. This was reported in the news a couple of months ago in Colorado whereby the roots underground kept burning long after the forest fire was 'out'. It makes charcoal doing this. It does it with a combination of water gas shift reaction and combusting the O2 in the carbohydrates. </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);">Well, in a DD burner this situation arises pretty easily if the gap size is right. When the condition arises and the fuel is setting itself alight upward and uncontrollably, turn it upside down. It turns into a TLUD with the heat rising away from the new fuel. That is a second limit. </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);">So depending on whether you want to make char, make gas and not, burn all the <span style="font-size: initial; line-height: initial; text-align: initial;">fuel in one go, use low or high density fuel, high or low moisture, and importantly, high or low Oxygen content, you choose the burner that is best suited to the range of conditions anticipated. </span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;"><br></span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;">Consider: suppose you want to run a higher air flow rate in the physical space available and the fuel is relatively dry and you want to make char. A DD stove would give a good yield and work well in those conditions. An UD would in the same conditions burn much more of the char. I hope that is explanation enough. </span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;"><br></span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;">On another note don't worry about Paul and me yelling ultimatums at each other. We know each other very well and have cooperated for years. He is enthusiastic which I appreciate but sometimes gets things askew. People think we are overly hostile but it is OK - he will tell you the same thing. We communicate frequently and he is a guy I can count on to want things done right. </span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;"><br></span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;">As things stand, Paul put a decade into TLUD investigation and I put it into BLDD work. I am going to post a few small pictures showing the movement of the MPF vertically in a DD stove fuel hopper. A significant advantage of a DD combustor is that the secondary combustion can be maintained directly next to the pyrolysed fuel because the fuel is always falling against the grate. It means the combustion is very stable once it is running. It doesn't change for hours on end. This is very well suited to process heating and home heating. Cooking is more difficult. </span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;"><br></span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;">With a TLUD cooking is easier and and space heating for a long time is difficult because of the refuelling. </span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;"><br></span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;">I have seen drawings for a Russian combustor the fed fuel into a conical TLUD fire that was continuous, burning on a round steel plate that rotated slowly. It could do what a DD burner does in terms of long term burns. </span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;"><br></span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;">Regards </span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;">Crispin </span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;"><br></span></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);"><span style="font-size: initial; line-height: initial; text-align: initial;"><br name="BB10" caretmarkerset="INVALID" class="markedForCaretMarkerRemoval"></span></div><br><div id="_originalContent" style="background-color: white;">
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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>
</p><hr>
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