[Stoves] "Young-adult" TLUD research Re: List of woods for TLUDs?

Sat Apr 29 15:16:40 CDT 2017

Dear Paul

In general I support your points about hardness of fuels and pyrolysation. I think a missing element of the advice is that the preheating of primary air is an important element when it comes to burning different fuels in a TLUD.

If the fuel is a dense fuel with a high salt content (the salt tends to extinguish the fire continuously) then out need to run the pyrolysis zone at a higher temperature than usual. This improves the rate of combustion allowing it to thrive. The surface area to volume ratio should be increased (use smaller particles).

With one or both of these tricks a TLUD can burn dense fuels, or those with a higher heat conduction rate.  If the heat penetrates the fuel rapidly, the whole particle has to be raised to the pyrolysis temperature instead of just the surface. If this is the case, the particles should be smaller (which increases the surface to volume ratio).

Incidentally, while preparing some material on the cross draft coal gasifier I came upon two mentions of TLUD's from long ago. One Harold Annegarn found in a book written about 1900 which refers to the use of the 'Scotch Method' (previously discussed her as the TLUD ignition promoted in the 1970's in South Africa). The book is one of those 'home keeping' manuals. Low smoke long0burning was a good idea and the TLUD method was advised. I later found a reference to a 1707 patent on the production of char from coal that may be the source of the name itself (by which I mean Scotch Method). It was known for at least 300 years by that moniker. It is also known in South Africa as Basajengo Magogo (lighting it as an old woman does) which dates from the 1990's.  In the 70's and 90's and again in the 00's it was promoted as a method of limiting the smoke produced in Highveld township cooking fires, something still being addressed.

There was also a patent issued in about 1695-ish for a similar method of producing coke. I haven't found either original document yet. When I do I will let you know what they say.  In both cases the drive was to find a way to produce a higher yield of char from the input material. The patent of 170 raised the yield from 33 to 65%.

Regards
Crispin

To all,                   29 April 2017     [This note contains some new content and explanations for the advancement of TLUD stoves.]

1.  Ron:    I and probably some others have successfully used dung as the input fuel into TLUDs.    I am not recommending dung, but if it is being burned, then a TLUD is preferred for cleaner burning.

2.  AD:   I agree with Ron that the TLUD stoves are better with both light and hard (heavy) wood than direct burning of them in any direct-burning (ICS) stove.

3.  Main point, to Neil and all:   TLUDs are not burning wood directly.   TLUDs turn wood into gases.   THEN the gases are burned.   So poplar, maple, maize cobs, dung, etc. are ALL becoming gases first.   THEN the burning of those gases might be somewhat different (but not as much as the direct burning of those diverse fuels).

TLUD stoves are just arriving into their "young-adult stage."   In contrast:  not infancy, not childhood, maybe still "youth", but certainly not full maturity, and a long way from  the "old age" of the ICS "Inproved or Inadequate" direct-burning cookstoves.  This is because we are still learning about better and better ways of mixing the combustible gases with  the incoming secondary air (SA)  (This is where the BURNING takes place to make the heat that goes to the pot.  TLUDs are DIRECTLY burning GASES, not solid fuels. )    (Please see my "Classification of Stove Technology and Fuels" documents (1-page and 4-page versions) at  http://www.drtlud.com/2017/04/11/classification-stove-technologies-fuels/  )

The solid wood and dung etc are an intermediate stage of the fuel.   Sort of a "storage" stage.  Then pyrolysis "transforms solids into gases plus charcoal".  The created gases are then burned SEPARATELY (by centimeters and seconds, but certainly separately) from where the gases were created.  We do not have clear terminology for this, in layman's terms.  The closest might be "gas burning stoves that make their own gases."

So, what development is happening in the early "young-adult" stage?  Control of primary air, learning about solid "intermediate" fuels, and improving combustion of the gases, as well as "new clothes" with sizes and mateials.

Consider this:  We have known of FA (forced air or fan assisted) TLUD stoves from the 1990s.  And there has been much progress.  But NO TLUD on the market has SEPARATE controls for "variable flows" of primary air (PA) and secondary air (SA).   THAT control is what will make the difference regarding Neil's initial question that pointed to differences in the initial fuels (and therefore differences in the resultant gases and quantities of gases that are being burned.)

Note that TLUDs can be made with different flows of PA ans SA by changing the sizes and number of holes.  That is a form of "tuning" the TLUD for a specific fuel.   This works great for one initial fuel, but only good but acceptable with other fringe fuels.  I am NOT referring to that work as being "variable flows".   I am referring to when the user can change the flows, even during one batch of fuel.

There has been some researach (mostly unreported and set aside) on variable control of primary and secondary air, using fans.  I have experimented several times.  The "million-dollar-grants" have had laboratory equipment with controlled and measured separate air flows.  Nathan Puffer did it when we were looking at Jatropha SEEDS as a fuel.  Seeds give off additional gases from the vaporization (not pyrolysis) of combustible vegetable oils (carbohydrates), which are much more plentiful in seeds than in stems and branches and leaves, thereby overwhelming the insufficient supply of SA in a "regular" TLUD-FA.

There is a good reason to not have separate control of PA and SA.   That reason is the user, the cook.  To need to "dial-in" the right flow of SA (assuming PA flow stays the same) is, for the most part and for most non-scientist cooks, an extra task that could easily be done incorrectly.  And there are the financial reasons of increased cost and maintenance.

But with "separate air-flow control" (not an established term and NOT justifying an acronym like SAC, as in TLUD-SAC), Neil or anyone could put many very different initial fuels into a TLUD and have greater control of the burning of the gases.

More work is needed before TLUD stoves can reach their full potential, while growing in "young-adulthood".  Today (2017), maybe 40% of what can be known about TLUD stoves is now known (but not necessarily put into practice by stove manufacturers).

(This note is being placed at the EPosts section of my website  www.drtlud.com<http://www.drtlud.com>   so that it can  be accessed continually instead of only one time on the Stove Listserv.)

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD

Email:  psanders at ilstu.edu<mailto:psanders at ilstu.edu>

Skype:   paultlud    Phone: +1-309-452-7072

Website:  www.drtlud.com<http://www.drtlud.com>

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