Dear Paul
The concept of a "Migrating Pyrolysis Front" is very interesting, but
it is not at all confined to TLUD Systems. I can operate my JXQ-10
Stratified Downdraft gasifier in a manner where it either produces
char, or where it "burns" char to produce more fuel gas. A "migrating
pyrolysis front" is a characteristic of many downdraft gasifiers. Dr.
Tom explains the phenomenon quite well, with his concept of
"Superficial Velocity." Basically, if the "Superficial Velocity" (SV)
is below a given level, then one will have a "char making stove",
while if the SV is above a given level, then one will have a "char
burning stove."
Imbert solved the problem of a "migrating pyrolysis front", in the
1920's or 30's, simply by closing off the top of a gasifier (so that
air cannot flow down through the fuel bed), and by introducing the
necessary "reaction air" into the reaction zone, by introducing the
air at the level of the desired for the reaction zone. This technique
"anchors" the reaction zone toward the bottom of the gasifier. Below
teh "Reaction Zone", where the wood is pyrolized, is teh 'Reduction
Zone", where pyrolysis tars and products of combustion are reduced
back to a gas that is high in CO and H2, and tar levels are low enough
to permit use as "Engine Grade gas."
If one was to describe Imbert's Gasifier Design, it would be:
"A Top Fueled, Mid-Aired, Downdraft" gasifier. Note that there is
also a "Bottom Fueled, Mid-Aired, Updraft" system... the common
"Underfed Stoker" system.
Concerning the "Deep History" of TLUD's, rather than look to the
Romans, perhaps we can look even further back in History, to the time
of the Amazonian Terrapretians. Nobody seems to have determined how
the Amazonians made thir charcoal for Terra Preta. Given that they had
the technology to make pottery, is it possible that they simply put
their dried "jungle clearing waste" and put it in vertical pottery
cylinders, that were top lit, to provide cooking heat, and charcoal,
for biochar? One very good reason supporting this hypothesis is the
fact that it would be much easier to feed wood into teh top of a
pottery cylinder, than it would be to dig a hole in the ground, fill
it full of wood, set fire to it, cover it over with soil to partially
smother it, and then dig out the hole to recover the charcoal. With
the proven understanding of combustion they had, as is evidenced by
their ability to design, build and operate pottery kilns, it is very
likely they could have configured a Top Lit Above Ground (TLAG)
charcoal producer. They may have used it simply as a "smudge pot" to
dispel insects at night, and they may have ignited the smoke for
cooking during the day.
Best wishes,
Kevin
Quoting Paul Anderson <[email protected]>:
Dear Crispin and all,
First, the quote:
Designed by Paul Anderson, the top light upward draught (tlud)
gasifying cook stove works o
This statement can be correct if referring to a specific TLUD stove
that I designed, which I think is the case of the author who is
quoted. However, it should NOT be taken that I originated the
TLUD stoves. The originators are Thomas Reed and Paal Wendelbo,
working independently in the 1980s and 1990s. Note that we do not
credit the Norwegian resistance fighters who influenced Wendelbo as
originators of TLUD stoves. Those men were doing top-lighting of
open fires, that is, fires that were NOT contained inside the walls
of stoves. We needed Wendelbo to accomplish that!!!
Second, Crispin wrote:
The TLUD was invented centuries ago as a way to burning with little
smoke. The Romans used TLUD fires.
Until Crispin or others can produce hard evidence to support such a
statement, please consider the above to be utterly false and should
NOT be quoted.
Crispin, let's have the documentation or a retraction or at least
stop writing such nonsense. Maybe the Romans did. Maybe cavemen
did. But no proof, no credit. Forty years ago I observed a
"TLUD-like" fire in the top of a burn barrel on an windless day. But
I did not understand it, and I did not develop the
concept/technique, and I do not take any credit for the original
work about TLUDs. If some Roman or caveman ignited some pile of
brush or wood on the top, that does not constitute inventing TLUD
gasifier cookstoves.
By the way, I did coin the term "top-lit updraft" and the acronym
"TLUD" back in 2004 and 2005 respectively, but that is not the
same as originating it or initially identifying it. Wendelbo had
no name for what was happening. (Peko Pe is the stove name.) And
Tom Reed called it "inverted down-draft" or IDD, which actually it
is not, because down-draft gasifiers have their hot zones at the
bottom all of the time. Actually, with hindsight, I should have
called it something like "Top-Lit, Downward Migrating Pyrolysis
Zone" (maybe " TLDMPZ") because the MIGRATING PYROLYSIS FRONT is by
far the most distinctive feature of TLUD gasifiers. The real
important feature is that the hot spot does not stay in one
position, but migrates downward. In that way it is unlike any
other up-draft or down-draft or cross-draft gasifiers, in which the
fuel moves and the hot spot stays in one position (which is at the
bottom on up-draft AND down-draft gasifiers.)
I hope this helps clarify some of the background about TLUD stoves.
Paul
Paul S. Anderson, PhD aka "Dr TLUD"
Email: [email protected] Skype: paultlud Phone: +1-309-452-7072
Website: www.drtlud.com
On 9/18/2012 11:24 AM, Crispin Pemberton-Pigott wrote:
Dear Steve
That was an interesting excursion. To be brief, there are a great
number of technical misconceptions contained in the document
http://www.soil-carbon-regeneration.co.uk/biochar/wp-content/uploads/2012/05/Biochar-Rocket-Stove-building-instructions.pdf so my advice is to try to gain some knowledge from the general approach and from the unusual layout of the product but not take it all as literally
true.
It is interesting that anything with a side feed is being termed a
Rocket Stove. That rather undermines the actual Rocket Stove as a
unique design, in my view. I guess people will call it what they
want.
I have copied here a paragraph from a the document:
*The tlud*
Designed by Paul Anderson, the top light upward draught (tlud)
gasifying cook stove works on more than just one level. It is a
very efficient cook stove, producing a lot of heat from a small
amount of wood. It is smokeless and it produces biochar. Paul
Anderson has also been instrumental in getting these stoves
distributed and used in developing countries where wood or charcoal
is otherwise used in conventional fires for cooking. By being more
efficient, less wood is needed. By being smokeless, diseases and
deaths caused by smoke in living spaces are reduced. By producing
biochar, subsistence growers are able to [maintain] soil fertility
and improve soil structure, biological activity and moisture
holding capacity. Atmospheric carbon is also being sequestered by
the use of these stoves.
So, I have some issues with some of this and because the whole list
was referred to it there is merit in correcting some of the
impressions given.
The TLUD was invented centuries ago as a way to burning with little
smoke. The Romans used TLUD fires. A TLUD cooking stove may or may
not be 'efficient' depending entirely on how well it transfers heat
from the flame to the pot and whether or not the remaining char( if
any) is counted as 'consumed by the stove' or not.
The heat produced by a TLUD is no greater than the heat released by
burning the same amount of fuel to the same extent in any other
stove. That is, if you gasify wood in some other device the heat is
exactly the same. TLUD's are renowned for making lots of smoke when
things are not working properly, like in the beginning and at the
end of a burn there can be lots of smoke. Mitigation of this
involves timely intervention by the cook. They are, after all,
smoke producing devices that then burn the smoke.
You have no doubt seen Paul Anderson throwing a lit match into a
smoke bomb of a stove re-lighting the fire when it has blown out. I
have done it myself dozens of times. When they are running well,
especially during the main part of the burn, they are amazingly
smokeless, like any other really good biomass stove. I hope that
the products evolve to the extent that they really are smokeless.
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