[Stoves] Misconceptions about TLUD origins and operations-- was Re: biochar rocket stove

[Kevin C]

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 <psanders at ilstu.edu>:

> 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:  psanders at ilstu.edu   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.
>>
>>
>
>