Re: Pull embers from three-stone cookstove to use as biochar.

Paul S Anderson



1.  I refer here to your statement:    “… why are we so excited about biochar when the alternative of using charcoal is so close at hand?”


In common usage the  word “charcoal” CAN refer to  all types of chars (regarding temp at time of production and different equipment) ranging from low-temp to medium temp to high temp (think of activated charcoal made in special equipment).   And  all types have their uses / advantages.   So,  when there is no designation of low, medium or high, the word “charcoal” is insufficient.    So the word “biochar” (once proposed to be “agrichar” but it was somebody’s trademark) was created, initially regrading chars (charcoal) that was appropriate for placement into soils.    More recently it is also for chars into construction materials and other long-term sequestration destinations (which maybe should have a separate name, but that is a different discussion.)  


So, to compare “charcoal” with “biochar” means comparing one Undefined charcoal  vs. one that is defined.   Better to be called “low-temp charcoal” or “commonly made charcoal” or maybe some other name, but not just unspecified charcoal.  


2.  Your other phrase raises a question about:    “ … the problem with charcoal is that it never gets hot enough (a) to burn out all of the tars and other aromatics and (b) to form the carbons into the necessary sheets of ring structures.”


I would say that the problem with “common charcoal” (as taken from an open fire, including rock-bed fires) is that it gets TOO hot at its edges of the piece of biomass because of extra oxygen (more than needed for pyrolysis) reaching the outer layer of created charcoal, resulting in some (more than minimal) combustion of the charcoal (char combustion or char-gasification that leaves behind ash).   And this happens before the pyrolysis is completed in the interior of that piece of biomass.


Certainly this occurs, so the question is about the timing of the removal of the embers from the fire (or the quenching of the fire).   Too soon and there is much (more than desired) LOW-temp char or even torrefied wood or raw wood in the middle of ember.   Too late and there is much (more than desired) ash on the outside, with the ash falling off so it might not be seen or weighed (but such a small weight that it would hardly be included in the careful  calculations of weight).  


About weight (could be grams or kg or pounds):  If a biomass piece of wood is 100 gm, the well-made mid-temp biochar is about 20 grams% , and the “only ash” weight is 1 gm.      [Typical wood pellets are sold claiming less than 1% ash.]


3.  Comment:   Yes, there are differences between chars (I prefer to say chars instead for charcoal) made in “open fires” compared to those made in arrangements with constrained oxygen supply, ranging in order from open-top flame-cap (trenches, troughs, cones,  etc.) and (mostly) covered flame-cap (RoCC kiln), to TLUD with limited air flow, to sealed retorts.    And each degree of air control adds an amount of expense or required labor.   All have their places and roles and resultant chars.   Are the differences worth the efforts and expenses?   Subject to the desires of the involved people and their resources (labor, money, time, biomass, etc.)   


I am sure that the Amazonian Indians of 500 to 4000 years ago did not speak in terms of oxygen and pyrolysis, but they could have understood about quenching chars having advantages.  Using simple practices largely unknown to us, they left behind for us the  “terra preta” soils.   Unfortunately, modern society does not have thousands of years to build its soils.




Doc / Dr TLUD / Paul S. Anderson, PhD --- Website:

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         Phone:  Office: 309-452-7072    Mobile & WhatsApp: 309-531-4434

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Inventor of RoCC kilns and author of Biochar white paper :  See  

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         with pages 88 – 94 about solving the world crisis for clean cookstoves.


From: <> On Behalf Of d.michael.shafer@... via
Sent: Sunday, March 28, 2021 3:40 AM
To: Ronal Larson <rongretlarson@...>
Cc: K McLean <kmclean56@...>; Biochar Listserv <>; Stephen Joseph <joey.stephen@...>
Subject: Re: [Biochar] Pull embers from three-stone cookstove to use as biochar.


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Would be very interested in results. My understanding is that the problem with charcoal is that it never gets hot enough (a) to burn out all of the tars and other aromatics and (b) to form the carbons into the necessary sheets of ring structures. If this is not true, why are we so excited about biochar when the alternative of using charcoal is so close at hand?



Dr. D. Michael Shafer
Founder and Director, Warm Heart

+1 732-745-9295 | +66 (0)85 199-2958 | d.michael.shafer@... | Skype: live:d.michael.shafer53

61 M.8 T.Maepang A.Phrao 50190 Chiang Mai Thailand



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On Sun, Mar 28, 2021 at 8:18 AM Ronal Larson <rongretlarson@...> wrote:

Michael,  cc Kevin


It should be fairly easy to test with seed sprouting at a kitchen window.


I view all char as pretty much the same (if. The interior reaches the same temperatures.  The reason is that all combustion is two-stage.  The first stage is char-mkaing - followed by a second stage where the char is combusted.  In the first stage, gases exiting through the outer layer of char prevents oxygen to get to the char itself.  After all the internal gases are released (as the interior comes up to a final temperature) - then the oxygen can finally hit the hot outer layer of char.




On Mar 27, 2021, at 8:02 AM, K McLean <kmclean56@...> wrote:


Hi Ron,


Michael thinks that because the char from three stone is not made without oxygen, it will not work as biochar.  What do you think?


On Fri, Mar 26, 2021 at 11:45 PM Ronal Larson <rongretlarson@...> wrote:



No.  Some soils will be wrong of course.  I think the temperature range produced by most TLUDs is like 3 stone fires and TLUDs have some good reports (thinking of Bangladesh)


I’m almost finished with.a drawing of new idea for replacing multiple stones below the wood supply. Can use your existing tripod potholders.   Might add 70-80%.   A skirt seems worthwhile and cheap here also.




On Mar 26, 2021, at 2:21 PM, K McLean <kmclean56@...> wrote:




Do you know of any reason that embers pulled from three stone would not make good biochar?  Maybe not perfect biochar but good biochar?  Someone from SNV suggested they would not make good biochar but I don't think this SNV person is an expert on biochar.



On Thu, Mar 25, 2021 at 11:21 AM K McLean <kmclean56@...> wrote:



Here is the SNV embers report.  It is very encouraging.  Pulling embers out of the fire resulted in a negligible increase in fuel usage.  The weight of the char exceeded the weight of the additional wood.


The problems (cook time, tending, smoke) referenced by SNV are not problems that have been expressed by the women in Africa.  We are exploring.


We are already training farmers to crush the char, mix with urine and ashes and apply to their fields.  This is at a small scale now but can be expanded easily.


I see great potential for this, especially where farmland is degraded, like most of SS Africa.  I'm talking with SNV about more testing.


We are shifting to metal tongs (35x2 cm).  They are simple to make, use very little metal (140 sq cm), are cheap ($0.15 - 0.20) and durable.


On Thu, Mar 11, 2021 at 9:14 AM K McLean <kmclean56@...> wrote:

Hi Ron,


We are seeing promise in this.  Tongs are made from bamboo, very cheap and easy.  Women pull the embers out as they cook.  Here is a photo.  A video is attached.


<Pile of char from tongs - Kasese.jpeg>



This woman collected 400g in a day.  She did not notice any change in fuel usage or smoke.  


SNV Vietnam is going to do a water boil test to determine whether there is a change in fuel usage.  It seems like it should require more wood.



Kevin McLean, President




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