[Stoves] Accidental TLUD technique discovery

kgharris kgharris at sonic.net
Tue Nov 15 14:44:54 CST 2016


All,

It occurs to me that one point needs clarification.

The statement: ">...there is an undesirable layer of
> char above the hot area, resulting in less heat reaching the pot."

could be mistaken as magical thinking.  Energy and matter cannot be created 
or destroyed, only changed from one form into another other.  This heat does 
not just vanish.  It must go someplace.  In this case it probably is out the 
sides and bottom of the stove.  If the stove was designed so no (minimal) 
heat escapes, at some point the heat must reach the pot, just slower and 
cooler (and less effective) because of the char layer.  Energy in (chemical 
stored in the charcoal and O2) must equal energy out (heat).

Reducing the amount of heat lost out the sides of the stove, whether by 
radiation, convection, or conduction will increase both the heat in the fire 
(helping combustion, draft and cleaner burning) and the heat at the pot. 
This will also help with moist fuel, with more heat to keep the fire going 
in spite of the water vapor absorbing heat and displacing O2.  Keep the heat 
in the fire until it finishes burning, then take it out.  This concept made 
a big difference in my stove.

Kirk H.

----- Original Message ----- 
From: "Paul Anderson" <psanders at ilstu.edu>
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>
Sent: Tuesday, November 15, 2016 9:41 AM
Subject: Re: [Stoves] Accidental TLUD technique discovery


> Neil,
>
> I will bring some of your questions to the top and answer them here, with 
> other comments mixed in:
>
> 1.  A stove that is short and wide has advantages as a charcoal stove so 
> that the charcoal is spread out and close to the bottom of the pot. 
> However, we are discussion TLUD stoves, and in them the advantage of the 
> height is the longer time of combustion (and with less fire tending.) 
> Unless using the TChar concept (see it at my website), taller TLUD stoves 
> actually are NOT good for charcoal combustion.   The char is at the bottom 
> (near the incoming air) and there is an undesirable layer of char above 
> the hot area, resulting in less heat reaching the pot.   Charcoal cooking 
> utilizes radiant heat, and any obstacle (char or otherwise) is not good.
> Neil wrote:
>> There can be at the end of a burn, a quarter full of
>> char, all aflame. And I can't see why this wouldn't be occuring all the
>> way down?
> But it will not be all aflame UNLESS there is O2 reaching that upper 
> amounts of char, which would be a forge down in the bottom and not good 
> for the stove or for cooking.
>
> 2.  you wrote:
>> Are you saying that a mid fire's MPF will not consume char below it, left
>> from the original MPF?
> Yes, it will not consume that char that is below the middle fire.
>
> And note that the middle fire was NOT a TLUD fire so there is no MPF 
> funtioning in the middle fire.   Also remember that WHERE the air enters 
> to sustain the MPF is an influencial factor.
>
> The MPF in a regular TLUD has some flame (combustion of gases) pressent. 
> But if raw fuel is placed above the hot char but is without spark or 
> flame, then that raw fuel is pyrolyzing in a RETORT-fashion without 
> burning in that area.  Pyrolysis does occur, but it is different from the 
> pyrolysis in TLUDs.
>
> 3.  Neil wrote:
>> my experience of the smaller ones is that invariably the fire is
>> hottest towards the end of pyrolysis, which conversely may coincide with
>> wanting a more simmer heat.
> The increase in fire is with all the TLUDs (operated normally) at the end 
> of the batch.   What happens is the MPF reaches the bottom and there is no 
> fuel below to take in the DOWNWARD RADIATING heat, so all that heat is 
> available to boost the pyrolysis of the last fuel at the bottom, giving a 
> spike in gases created, and a larger secondary flame.   But that is rather 
> short lived (less than a minute usually), and then the secondary fire cuts 
> back or even dies because much less gases are coming to the top.
>
> Note:   adding dry fuel on top of the charcoal bed at that time can get 
> pyrolytic gases (and water vapor) that are NOT being combusted by the 
> secondary flame IF the secondary flame is no longer there. THAT results is 
> smoke escaping.   Throw in a match or flaming fire brand.  Something needs 
> to restart that secondary combustion.   At the risk of having smoke, some 
> blowing ONTO THE TOP OF THE NEW FUEL might get an ember to glow and ignite 
> the gases.  It can be done, but if done incorrectly, it can get a bunch of 
> smoke, and irritated (maybe drunk) husband who then beats his wife because 
> of the smoke.   She needs practice and success, or she will not be doing 
> that "add fuel to the top" stunt more than once.
>
> 4.  Neil wrote:
>> I three quarters filled the pot with chunked
>> hazel which has remained outside uncovered and was damp/wet, and I
>> deliberately left the bark on and didn't split it!  I then filled up the
>> rest with 'stove top' dried and split wood.  So unused to doing things
>> this way, and with hindsight not really leaving enough working room for
>> the top fire, the thing reached the damp wood and went out very suddenly
> This is different from what you described of having damp fuel SOMEWHAT 
> FUNCTIONING in TLUD mode, and then puttin the middle fire onto it.  What 
> you describe (above) give NO heat to the damp fuel to help dry it out 
> because all of the heat is going up, and not impacting the lower, damp 
> fuel.
>
> Neil, I do not normally (because of lack of time) do this much explanation 
> for an individual.  However, in this case,
> 1.  you raised interesting new-ish questions about damp fuel
> 2.  you are actually doing the experiments and reporting your results to 
> all of us, and
> 3.  this is a public forum and our Stoves Listserv discussion is preserved 
> for later use.  (I would not do this on a one-to-one private basis.)
>
> However, most postings of emails are not collected as in prepared 
> documents that have titles and can be more easily accessed.  I hope that 
> you (or others?) might take the time to pull this info together into a 
> document.   I know from experience that I will not get to that task.
>
> Keep the discussion going.
>
> Paul
>
> Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
> Email:  psanders at ilstu.edu
> Skype:   paultlud    Phone: +1-309-452-7072
> Website:  www.drtlud.com
>
> On 11/15/2016 9:57 AM, neiltm at uwclub.net wrote:
>> On 14 Nov 2016 at 12:12, Paul Anderson wrote:
>>
>>> Neil,
>>>
>>> This is a very informative conversation.  I hope a number of Stovers are
>>> reading the messages.
>>>
>>> 1.  Your last comment is answered first:  An open fire on top of some
>>> damp fuel.  (or maybe even a contained fire (in a cylinder but ignited
>>> at the bottom, NOT a TLUD).   Much would depend on whether air can
>>> actually pass through the lower pile.   I suspect that very little air
>>> could be coming up through the damp fuel even if with rather loose or
>>> largeish pieces.   (Also seen in open bonfires that air cannot get into
>>> the central area, but that is partly because of the conventive flame on
>>> the outer edges and comsumption of the O2.)
>>>
>> When I built what I imagined might have been the structure of Pal
>> Wendelbo's ww2 Norwegian resistance stealth TL fire, I crossed sticks in
>> a right angle layered grid, thus maximising air flow potential through
>> the bottom of the stack. This worked impressively well, and I was even
>> able to observe the way in which the PF also migrated sideways to
>> completely consume the stack against the mild side breeze.  Not an
>> unburnt fragment of wood remained without touching the fire once lit,
>> quite unlike any conventional fire. A wonderful and so simple experiment
>> anyone can easily conduct, and there is no better 'teacher'.  I stood
>> there feeling I had just discovered the 'right' place to light a fire,
>> and why doesn't everyone do it that way?! With my little trekker stove
>> simply charging the pot with large pieces ensures a robust, barely
>> impeded primary air flow through from the grate at the bottom.  If I want
>> a slower burn, more moderate heat, then using very fine woodchip de facto
>> restricts the primary air flow, thus avoiding the towering inferno in
>> what is in all other respects the identical chip, merely size graded.  I
>> use a 'riddle' (seive?) with 3 different mesh sizes when I want to
>> experiment with uniform sized fuel, or simply use up a fine residue.
>>
>>> 2.  Very interesting that your work is with a short small "camping
>>> stove" type that is not even marketed as a TLUD.   Yes, shortness does
>>> limit the ability to have observations related to height issues.  My
>>> responses are in regard to taller units.
>>>
>> Yes.  Rechecking the measurements now that the breakfast stove has cooled
>> down, distance from ground to bottom of secondary air holes is 4 1/4".
>>  From bottom of fuel chamber to bottom of secondary air holes is 3 1/8" !
>> If this seems ridiculously short, Tom Reeds first woodgas campstove, the
>> SL, measures 2 7/8" on fuel depth!  This ND stove is slighter larger in
>> the fuel chamber.  The internal diameter is 4 1/4" so the chamber is
>> actually wider than it is deep.
>>
>>> 3.  It is easy for having two fire zones or pyrolysis zones with solid
>>> fuels in a normal TLUD operation with appropriate dry fuel (not
>>> discussing damp fuel at this moment).  (Secondary burning is with
>>> gaseous fuel.)
>>> Let the MPF decend a distance (3 to 5 inches) so that
>>> there is a layer of charcoal.  Then put additional fuel onto the top of
>>> the char layer (and sufficiently below the entry of the secondary air).
>>> The rising hot gases (maybe 400 to 500 deg C) will dry and then start to
>>> pyrolyse the new upper fuel layer.  That creates additional gases that
>>> all rise to the level of the secondary combustion.
>> Ah, thank you for that.  This is outside my experience, so I didn't know
>> this.  So are you saying that the smoke as it builds up from the
>> eventually pyrolising "additional fuel onto the top of the char layer" is
>> simply burned cleanly at all stages at the secondary air flame front?
>> This must be a nice versatility if so, since doing so would presumably
>> give you a hotter fire? This is perhaps then a potential in a tall enough
>> stove, presumably such as your Champion?  The closest I've come to this
>> has been with Tom's XL woodgas campstove, the big one, where I found that
>> when I wanted an extra hot fire for stir frying in a wok, I could get a
>> useful extra boost by adding more fuel during normal full fan operation
>> of the stove.
>>
>> But....
>>> 4.  But if there is any surplus O2 getting past the MPF (as could be the
>>> case with the damp fuel) or entering downwards or through a side
>>> hole/leak, and if hot enough or with a spark, there could be some small
>>> combustion of some of the gases (similar to the MPF) at the level of the
>>> middle fire.
>>>
>> Yes, that makes sense.  Interesting possibilities.
>>
>>> 5.  Concerning the possibility of the "middle fire" and the MPF being
>>> together all the way to the bottom, I doubt it.  IF the MPF is
>>> functioning at all, it moves downward and SOME char is created.
>> Yes, but so little in terms of thickness of layer in the case of the
>> trekker stove surely as to be insufficient to separate out separate
>> combustion layers? (see above dimensions).  Yet just as with the even
>> shallower Reed SL stove it clearly does make sense to say that there must
>> be a MPF since these stoves can be batch loaded, top lit, and burn
>> relatively steadily and smokelessly for up to half an hour, and much
>> longer still with pellets.
>>
>> The trekker stove, as I seem to be calling this nameless Chinese offering
>> (do they understand branding in China?), also makes an excellent charcoal
>> burning stove, and sometimes the only way to tell when pyrolysis has
>> finished is by the colour of the still substantial flame when it turns
>> entirely blue.  There can be at the end of a burn, a quarter full of
>> char, all aflame. And I can't see why this wouldn't be occuring all the
>> way down? The larger, deeper stack of char resulting from burning fines
>> remains cool until the char has burned down, and only then can you
>> successfully add a little thin dry fuel to revive a fire.
>>
>>> Tom
>>> Reed showed many years ago the reduced amount of char that results from
>>> using moist fuels (such as char production being only 10% or 8 % by
>>> weight of the initial fuel instead of about 20%.)  But I recall no
>>> mention of zero char being left behind.   And the "middle fire" has no
>>> conditions for somehow combusting (char-gasifying) charcoal that is
>>> below that middle fire.
>>>
>> Are you saying that a mid fire's MPF will not consume char below it, left
>> from the original MPF?
>>
>>> 6.  Significance:  When a person is desparate and needs a fire with
>>> dampish wood, the person will meticulously tend to the fire, nursing it
>>> with small pieces.  But in common everyday usage, the cook commonly does
>>> NOT want to be tending the fire with great frequency (hence the appeal
>>> of the batch operations of TLUD stoves with rather consistent fire
>>> without much tending).  In that case, the "middle fire" over damp fuel
>>> in a TLUD is not likely to be of much interest.
>>>
>> One has to hope not, I agree.  The goal must be as you rightly state.
>> Yet it might be worth considering those situations of emergency,
>> displacement, migration, refugee camps, and of course the entire
>> backpacking/camping uses where sufficient dry wood will not always be
>> available.  Also as Tony Vovers wrote: " a lot of the local found Biomass
>> is not dry and storage is not easy in the tropics."  I expect we may
>> experience this for ourselves when we visit Dominica this coming
>> April/May.
>>
>> Also, if as I hope to discover, there can be only advantages in
>> stratifying a bottom layer of damper wood in conjunction with top feeding
>> for the added heat level control and/or longevity and stability of the
>> burn then this could simply become another way of getting finer control
>> over the stove.  Perhaps it is not so with the larger taller NDTLUDs?,
>> but my experience of the smaller ones is that invariably the fire is
>> hottest towards the end of pyrolysis, which conversely may coincide with
>> wanting a more simmer heat.  Is it the case that this would be no
>> different in a larger taller stove, but for a primary air control as part
>> of the stove, or is the "consistent fire without much tending?" you
>> describe a characteristic of the stove design independent of any primary
>> air control?
>>
>> This is outside my personal experience, but would it not be useful to
>> know how to burn wet wood successfully without undue struggle and even
>> perhaps to the advantage of a steadier burn in disaster/displacement
>> situations of any kind where the weather is wet?  If SOME wood can be
>> dried, or prepared from dry heartwood, but not enough so easily for the
>> entire fuel needs, then certainly this would be of interest to
>> backpackers with their Bush Buddy 5oz weight stoves I'm sure.
>>
>> This morning's breakfast was cooked in similar fashion to yesterdays, but
>> this time intentionally!  I three quarters filled the pot with chunked
>> hazel which has remained outside uncovered and was damp/wet, and I
>> deliberately left the bark on and didn't split it!  I then filled up the
>> rest with 'stove top' dried and split wood.  So unused to doing things
>> this way, and with hindsight not really leaving enough working room for
>> the top fire, the thing reached the damp wood and went out very suddenly
>> while I was paying more attention to the cooking.  So some smoky mess
>> reviving it again, but not on the scale of yesterday!  I am confident
>> that I will soon have this just right.  A bit more smoke as things
>> settled down with the burn improving and needing less tending as it went
>> down. Leaving a kettle on for coffee untended was an added bonus, just
>> needing a little reviving after I'd eaten, but with sufficient char still
>> to bridge that time gap, something I really appreciate.
>>
>> For doing things this way a deeper burn chamber would definitely be an
>> advantage, and I hope to try this soon, but by settling on maybe a half
>> fill of the damp/wet wood I think things should turn out well next time.
>>
>> You have definitely inspired me to fresh experiments with and
>> modifications of my tallest, largest tincanium TLUDs, and I feel humbled
>> in such exalted company that you have found my experiences of some
>> interest.  Thank you,
>>
>> Best wishes,    Neil Taylor
>>
>>> On the other hand, it is well known that people do throw (place) new
>>> fuel into an operating TLUD, either while the MPF is still advancing
>>> downward in TLUD style, or after the MPF has reached the bottom and has
>>> become a charcoal burner with the primary O2 consumed in the char
>>> layer.)  In either case, the new fuel will first dry, then torrify, and
>>> then pyrolyze, producing gases that can be burned in the stove.  In some
>>> ways, this is like the "Flame Cap" method of producing charcoal.  Flame
>>> Cap is discussed on the Biochar Listserv because it is not with a
>>> cookstove emphasis  (unless we choose to have that discussion here also,
>>> with cookstove focus).  My website    drtlud.com   has some documents.
>>> Or search the Internet for   Flame cap .
>>>
>>> Personal note:  Even just a few years back I was fiercely defensive of
>>> the purity of designating TLUD stoves WITH MPF as the key distinguishing
>>> feature.   I still am in many ways.   But TLUDs have recently received
>>> such widespread recognition and "acceptance" in some circles that I am
>>> much more open to discussions about "fringe" topics and things like
>>> adding additional fuel during the MPF operations.
>>>
>>> Neil's contributions are of interest and considerable potential.
>>>
>>> Paul
>>>
>>> Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
>>> Email:  psanders at ilstu.edu
>>> Skype:   paultlud    Phone: +1-309-452-7072
>>> Website:  www.drtlud.com
>>>
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