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I ask as a question, It may be instructive to know what temperature the char in Terra Preta was as even after a long time that char should (?) fit into one (or all?) of the temperature categories, - certainly if the Terra Preta char is mainly in one area of heating, that would be significant.
Anyone know of such research?
Whatever methods the highly populated civilisations that colonised the Amazon using Terra Preta to transform the soil in the Amazon so that they could live there in their cities, we can be reasonably sure that they knew what they were doing.
I use the words Highly populated on that statement in "guns germs and steel", by Jared Diamond, that 95% of the South American population was killed by the eurasian diseases brought by the spanish.
That the argument that theTerra Preta found in the Amazon was deliberately placed is in that it had the same pottery shards as the Incan or Aztec Terra Preta.
In regards to Paul’s comment that we have not thousands of years to re carbonise our soil, (if indeed that it took thousands of years for the South American civilisations to so do..), but whatever, the modern city has enormous waste streams, containing huge amounts of carbon, - some is not suitable for agriculture, but suitable for feeding to cattle, - ie Doug Pow achieved spectacular results from feeding his cattle charcoal derived from Aluminium production, and of course the toxic carbon from other processes can be used in concrete, steel making , road surfacing, etc.
Cheers, Geoff Thomas.
On 29 Mar 2021, at 7:19 am, Tom Miles <tmiles@...
The tarry residue is exactly the concern about health and soil effects of products of incomplete combustion. The engineered TLUDs and Kon Tiki’s can generally make a clean char product. PAH contaminant levels are usually lower than expected. If you do a traditional proximate analysis you will find that biochars generally have less than 20% volatile matter compared with cooking charcoals at 20%-35% volatiles. The volatiles help ignite the cooking charcoal. I think the European requirement for volatile matter in cooing charcoal is something like 40%. Charcoal producers have complained that it is more costly to cook out the volatiles to make biochar compared with cooking charcoal.
Using char from open-fire cookstoves or campfires as biochar must have been done. Can anyone report their experiences?
TLUD (GASTOV) flame temp: 738
Three stone flame temp: 648
The spontaneous breakdown or carbonization of the wood above a temperature of 280°C liberates energy and hence this reaction is said to be exothermic. This process of spontaneous breakdown or carbonization continues until only the carbonised residue called charcoal remains. Unless further external heat is provided, the process stops and the temperature reaches a maximum of about 400°C. This charcoal, however, will still contain appreciable amounts of tarry residue, together with the ash of the original wood. The ash content of the charcoal is about 3-5%; the tarry residue may amount to about 30% by weight and the balance is fixed carbon about 65-70%. Further heating increases the fixed carbon content by driving off and decomposing more of the tars. A temperature of 500°C gives a typical fixed carbon content of about 85% and a volatile content of about 10%.
It seems that char from three stone cookstoves should work as biochar. But I would love to hear about actual experiences.
Also, has anyone actually tested the use of low-temp charcoal as biochar? I've spent hours researching this and found comments that it works and comments that it does not work but no references to actual testing.
Some women in Africa have been pulling embers from their three stone cookstoves. They've reported that removing embers does not increase the amount of firewood needed for cooking. This seems implausible so SNV did a WBT and found that the increase in firewood was negligible. Here is the SNV report.
On Sun, Mar 28, 2021 at 9:59 AM Anderson, Paul <psanders@...
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.
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with pages 88 – 94 about solving the world crisis for clean cookstoves.
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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
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.
Michael thinks that because the char from three stone is not made without oxygen, it will not work as biochar. What do you think?
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.
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.
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.
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.