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Containers for making biochar inside a wood burning stove?

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Location: Cantabria, N Spain

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I'm looking to experiment with biochar in our garden, and to do this, I want to make quantities of finely divided biochar. Also I want to do this as efficiently as possible in terms of effort, mess, emissions (smoke) and also if possible capture the heat from the process.

The best way I have found so far is to use an old metal tin (normally paint or varnish tins) filled with the feedstock (which is mostly wood shavings that we get for free, but could equally be sticks from the garden). I punch a few holes in the lid and put it in the fire when it's nice and hot. The feedstock evaporates, the gas emerges and is burnt, then I take the tin out when it's finished and Bob's your uncle.

I can't make very much at a time because it's hard to find used metal tins that are bigger than 1 litre. But it's a reliable method that works, is no hassle, and over a winter can produce a fairly large amount. Since we light the fire most days for about 3-4 months a year, and we can probably produce about 2 litres worth of biochar a day, that should make a couple of hundred litres over the course of a winter. Theoretically.

The problem I have found, though, is that the tins don't last very long. As in, about a week of intensive use. The intense heat and the wood acids just eat them up. Of course I might be able to find a regular source of used tins, but that isn't really the principle of the thing. Also, I would love to be able to make 5-10 litres at a time (which is about all that would fit inside the stove) instead of just one litre.

I would love to know if anyone else has tried this method of biochar production and if so, what solutions you have found. Is there a kind of biochar-making insert for a woodstove that you can actually buy? Or do you use some other material for the container? Or just keep getting more tins? Any suggestions are more than welcome.

Thanks a lot!

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Not much help I'm afraid but I do the same thing! Old tins with a few small holes in or a not-quite-closed lid. As you do, I get through tins quite quickly- I collect the chocolate tins that float around the office at christmas and use those- but I'll be interested if you do find a better method that produces less burnt out tins.

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One bonfire in the garden, quenched with water at the right moment, gets me about 100 litres of char and takes about 2 hours total.

The scale of production is just so unfavourable in an ordinary wood stove that it doesn't seem worthwhile in comparison. Plus I don't need to find tins to do it in!

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Robert Alcock

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Thanks for your replies!

Michael, I have also tried the bonfire method. I have found that the result is a mixture of all stages of charring (from uncharred wood to partially charred to ash) and is too coarse, so it would not be any good to add to the composting process, which is the next stage of using the biochar. I think you would need a very big bonfire to make 100 litres of usable char. Also you are producing a lot of smoke and CO2 and wasting the resulting heat. So it doesn't work for me, I'm afraid.

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Bryant RedHawk

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Hau, Robert; I like stainless steel stock pots, if you want to do this in an oven look for a cheep stainless steel roasting pan with lid. Spring clips like you can find at office supply houses will work for holding the lid in place.

Don't forget that biochar can be just about anything that is carbon based. I do cow chips along with wood pieces, even grass can become biochar if you want to use it, as can straw, leaves, etc.

Using the cook method to derive your biochar is the way it should be done, burning in the open is not going to give the best results, but can be used. Jack Daniels makes charcoal by ricking maple wood and using a misting nozzle to keep the heat in the proper range to make charcoal not a bon fire. It requires at least one person is present at all times to regulate the flames so it doesn't go willy-nilly and make a lot of ash.

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Michael Cox wrote:One bonfire in the garden, quenched with water at the right moment, gets me about 100 litres of char and takes about 2 hours total.

The scale of production is just so unfavourable in an ordinary wood stove that it doesn't seem worthwhile in comparison. Plus I don't need to find tins to do it in!

Around here I do this with hemlock bows doing the wet season. The pitch makes them burn supper hot and you just keep layering soaking wet bows on top. All the energy goes to boil off the water and you are left with a substantial amount of char. Of course the energy is wasted with this method.

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Robert Alcock wrote:Is there a kind of biochar-making insert for a woodstove that you can actually buy? Or do you use some other material for the container?

I use a dutch oven. It ruins the seasoning.... But whatever.

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Robert Alcock

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Bryant, that's a good suggestion. I will try and find an old stainless steel pressure cooker or similar, that should work fine. Of course it will take longer to get up to temperature.

Joseph, I'm not sure what you mean by using a dutch oven... can you elucidate?

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Around here, we use the term "Dutch Oven" to refer to a cast iron cooking pot. They are often used for cooking directly in a fire. I use them in my day to day cooking for anything that needs to be fried, steamed, or stir-fried. The term "seasoning" refers to the layer of burnt on oil that makes cast iron cookware non-stick. Here's what one of mine looks like.

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Bryant RedHawk

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Robert, I make most of my biochar in 55 gallon steel drums these are lidded and have 5-8 holes around the bottom edge that are around 1" in size, I load the drum up with what ever I am going to cook, light a small fire in the bottom and let it get going good then slap the lid on (it has one 1" diameter hole in it) and walk away. The fire doesn't consume but a little of the fuel I am turning into biochar, it makes quite a few pounds per load. I did one oven type production and was told "NEVER AGAIN" by the wife, since then I have moved to the steel drums and the great outdoors.

Just thought I would mention this for an other reference for you.

Robert Alcock

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That sounds a very interesting idea, Bryant. Have you got any photos?

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Bryant RedHawk

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Yes I have some photos but no way to get them posted up here. Sadly I have no internet access at the farm and my office doesn't allow me to do things like up loading photos. We are hoping that next year we will have internet on the farm and when that happens, I will be able to post photos here.

Robert Alcock

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Thanks anyway, it sounds pretty clear the way you describe it!

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Michael Cox

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Robert Alcock wrote:
Michael, I have also tried the bonfire method. I have found that the result is a mixture of all stages of charring (from uncharred wood to partially charred to ash) and is too coarse, so it would not be any good to add to the composting process, which is the next stage of using the biochar. I think you would need a very big bonfire to make 100 litres of usable char. Also you are producing a lot of smoke and CO2 and wasting the resulting heat. So it doesn't work for me, I'm afraid.

Managing nearly 9 acres of largely wooded gardens/field/hedges produces a LOT of woody waste, just simply in defending the remaining open spaces from in growth. Anything larger than about 2" diameter goes in the wood pile, smaller gets piled and eventually burned - we don't have the means to use the waste more productively at the moment. On the whole it is pretty much fully charred, light weight and friable... but there is a fair size difference. The variable size is no problem as far as I can see; plant roots colonise the larger pieces just fine and they break down over time in the soil. I don't compost the biochar first but I do spread both compost and biochar on the soil together (topdressing), and also periodically wee on the biochar pile while it ages in the open before using it.

I would prefer to make biochar as a bi-product of some constructive process - cook stoves are the obvious ones - but that is not compatible with our current kitchen arrangements. If I were to try and make char in a stove designed for heating I would probably do it by letting the fire build up a big bed of embers then shovel some of the embers into a sealed heavy metal container (dutch oven as mentioned earlier would work well) or dump it into a bucket of water. No extra process needed here.

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William Bronson

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For making it inside a woodstove how about an ammo can with the rubber gasket replaced with a suitable gasket?

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Bryant RedHawk

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William Bronson wrote: For making it inside a woodstove how about an ammo can with the rubber gasket replaced with a suitable gasket?

That should work nicely. Might not even need a gasket (you do need to let the gasses get out or you will have an explosion).

Jack Edmondson

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Robert,

If your can is not lasting, try putting the container on the fire towards the end of the burn. It sounds like too much heat is causing fabric fatigue. You don't need a lot of heat to burn off the gases and the temp will rise when the gases start to burn. I would suggest trying it on the coals of the waning burn. If you can hold your open palm over the fire for less than 7 seconds, the fire is too hot.

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Morgan Barker

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How about a large diameter iron pipe with threaded ends and end caps? You could make one(or have it made by a plumber friend, if you have one of those) that is log diameter and the length of your firebox. You might want to make several and load all of them because the mass of the pipe will make for a long cool down period.

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Morgan,

Good idea. Just make sure to vent both caps. Expanding flammable gases trapped inside a rigid enclosure with no vent is a recipe for a bomb. The same vented on only one end is the basic design of rocketry.

Morgan Barker

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I was thinking that the drilled holes would work well if done equally spaced in a single row down the length of the pipe so if you did want to char sawdust, the gasses wouldn't have to push through all that material to get to one end.

Michael Helmersson

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I must have read this thread 5 years ago because I've been charring in my sauna stove for years. I assumed it was my own idea but I guess not. I started with a cast iron pot with lid but after a few years it was too warped and cracking to keep the lid on and I lost too many batches to full combustion. Last year I acquired a 24" length of 1/4" wall 4" diameter pipe with a welded cap on one end. I fill it with wood shavings (about 15-20liters) and pack it in as tightly as I can with a tamper, then I put it in the sauna stove tucked up against one side. It's just slightly shorter than the firebox so the open end of the pipe sits against the end wall of the firebox with an 1/8" gap. We use our sauna for showers every day and in winter I keep it heated all the time to avoid freezing our shower plumbing. In super cold weather I can get a batch cooked in about 2-3 days, in the heat of summer it's about 2-3 weeks. The 15-20 liters of loose shavings produce about 3-4 liters of dense char, so I probably generate about 150 liters per year. Pretty slow and not a lot, but zero waste. I'd love to produce a mega batch of a cubic yard or two but can't imagine the process required for that.
Belated thanks for the idea!

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Jay Angler

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I also found that metal tins didn't last long and I gave up making biochar for several years because of it. However, there are things I really want at least small quantities of char for, so I re-read many threads like this one and realized that I had an old stainless pot with a lid that was taking up space and wasn't going to get used for cooking.

It is just slightly too tall to fit through the opening on our Pacific Energy wood stove, unless we feed it in and out with the lid off. A little annoying, but manageable.

Much of my recent reading has been about the benefits of biochar for carbon capture and long term storage, so I got curious. Hubby found a Government of Canada document which is intended to educate the public about the amount of CO2 produced by a liter of gasoline. It claimed that 1 liter of gasoline contains about 0.63 kg of carbon. So we weighed the results of one pot of wood that had "cooked" in our wood stove and the result weighed 0.350 kg. Since our local town is a round trip of 10-11 kilometers and we have a fairly fuel efficient car, it will take two rounds of filling and cooking in the pot shown to offset a trip to town. Of course that's simplified the whole issue a great deal, as there's a lot of CO2 produced before I ever buy my liter of gas, not to mention all that went into building the car in the first place, but Hubby figured that our char making was totally insignificant, and now is much more convinced that it is worth making the effort because the biochar is useful mixed in with our duck bedding, mixed in with our compost pile, and from both those places, eventually it's added to our soil to create and maintain fertility, as well as off setting at least part of our fossil fuel footprint.

biochar-pot.JPG

Pot filled and ready to go in the wood stove.

biochar-results.JPG

Cooled and poured into a bucket for distribution.

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Michael Helmersson

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posted 4 years ago

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"Cooled and poured into a bucket for distribution."

I used to put my finished char into a plastic pail outside my sauna. Once, while distracted and stupid, I put the char in without cooling it overnight and went back to what I was doing. An hour later my peripheral vision and subconscious mind caught something unusual and it turned out that my sauna was on fire. The bucket of char had heated up and melted a hole through its side allowing the hot char to get oxygen. The char and melting plastic ignited and proceeded to ooze out down the wall and collect at the floor joist where it eventually started to burn under the sauna. This was when I caught it, luckily, because in my above-mentioned distracted stupidity I had placed the bucket of char on top of a 200L plastic barrel of dry wood shavings covered with a plywood lid. The whole scenario could not have been better laid out if I were an arsonist.
Now, I use a metal bucket with tight sealing lid and keep it away from anything that I would be stupid to leave it near. God knows what other stupid things I've gotten away with.

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Mike Sved wrote:

Once, while distracted and stupid, I put the char in without cooling it overnight and went back to what I was doing.

Yes, let's not do that! Normally, the pot get's carried out of the house on an old metal cookie tray, then we quench it with enough water to get good steam cooling happening without drowning it, and then leave it on a concrete pad which at this time of the year is reliably wet. We cheated a little for the measurements I wanted - watering the outside of the pot and leaving water in the tray until it was cool enough to transfer. The trouble was that to get some idea in real life of our "gasoline offset", I needed dry biochar and a matching bucket to tear off the bucket mass on our scale.

I have another friend with essentially the same stove as us, and I'm trying to convince him that it's worth the trouble to at least start on a small scale to learn what works, rather than immediately thinking "ginormous project that we don't have time to tackle so it will take 5 years". His wife drives to town at least once/week, and further afield every Saturday to run errands and visit her brother. She also drives a larger vehicle. If they did a pot of similar size once/day, they might off-set at least 50% of her gasoline use, and their heavy clay soil would love the byproduct after it's been composted with the horse shit they collect. Stacking functions! So far he's resistent - but I'm going to weigh a second pot of it to see how consistent it is and then send him the data and see if I can get some movement there! He's got easy access to raw material, although it hasn't been tested yet to see how easy it is to work with. I think that's going to land on my plate, but since I'll keep any char that I produce, I'm good with that. Yes, I'd love a large scale biochar/electricity producing burner that can heat the greenhouse I also don't have - but I'll settle for a pot in my wood-stove!

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Jack Edmondson wrote:Morgan,

Good idea. Just make sure to vent both caps. Expanding flammable gases trapped inside a rigid enclosure with no vent is a recipe for a bomb. The same vented on only one end is the basic design of rocketry.

What if you had a TLUD setup and the flame heated an iron box with two (one?) pipe that actually connected back into the secondary air source, and this was all used basically to heat a building with then air intakes being from the outside?

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I’ve done a couple of successful batches in our wood stove, using a paint can with holes punched in the non-lid end. I bought a brand new paint can, not wanting to have paint residue. Not sure how long it will last, I am placing it in the stove at the end of the burn when there are just embers left.

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I've found that stainless steel steam pans (from buffet lines and restaurants) work really well. Just set the lid on the pan and the gasses escape but the fire can't get to the char. I've got about 50 burns out of a pan and it is still in good shape. They come in a variety of sizes so you can find one that will sit to the side in your stove and allow for a good fire next to it to heat and and char the feedstock.

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Faye Mogensen

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We're on 30 acres with lots of wood waste so, despite the emissions, feel the bonfire method is our way to go too. I attended a biochar workshop a couple of years ago but the details have escaped me. Can you elucidate me on the "right moment" to quench the fire???

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I've made some biochar in my wood stove with nesting cans. Pretty small amount like you say, though.
I've also done the thing with steel drums, several ways. But a couple years ago I was determined to make a Kon-Tiki burner (see Ithaka Institute for the design and theory of operation), basically a big cone. I was lucky because my welder friend had just gotten a discarded fertilizer hopper (from a tractor implement). We closed the bottom and put three legs on it. It works great. I mainly burn brush of which we have plenty of, feeding fuel to it for 3-4 hours, and get about 5-6 buckets of char per use. You can also dig a conical fire pit and burn in it. I always keep a bucket of char in my woodshed to pee in. I just inoculated several buckets with fish emulsion as an experiment. And I throw it my my compost, and feed some to my cows.

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Faye Mogensen wrote:We're on 30 acres with lots of wood waste so, despite the emissions, feel the bonfire method is our way to go too. I attended a biochar workshop a couple of years ago but the details have escaped me. Can you elucidate me on the "right moment" to quench the fire???

All the tutorials I have watched say that once you start seeing gray ashes on top of black sticks, add another batch of wood, repeat until you've filled the bucket, and when the last sticks show some ashes, it's time for cooling.
Charcoal is made in absence of oxygen, but good biochar must achieve high temperatures too. Otherwise, you are making just charcoal.

Maybe someone who actually makes it can give you better advice.

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Jason Thomas

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One of my podcast guests, Justin Dolan, is making massive amounts of biochar. He digs a large hole (2x2x4 meters, for example), fills it with wood, gets it burning, covers the top with palm leaves and sand, and lets it smolder. He makes a couple hundred gallons at a time. After harvesting the biochar from the hole, he fills the hole back up with more wood, covers it with earth, and has a hugelkultur bed!

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Jim Morris

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You might try a cheap used pressure cooker, handle, seal and jiggler, off, and put in stove upside down. I think they are about 5L.

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Jim Morris wrote:You might try a cheap used pressure cooker, handle, seal and jiggler, off, and put in stove upside down. I think they are about 5L.

Many old pressure cookers are aluminium which doesn't handle the heat the way stainless steel or regular steel does. I melted an old aluminium pot on a fire once, although it may have been quite a hot fire - it was years ago.

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Mark Brunnr

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posted 3 years ago

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Edible Acres has a Youtube channel and they use stainless steel hotel pans, in

he mentions having used them for several years so far without issues. He fills them up and puts them in when the stove is already running, and the lids sits on top with gravity only. The gasses escape and once done he pulls it out, sits it on a metal tray, and places it in the garage on concrete to cool. Sounds like that prevents heat shock to the metal and it doesn't warp, he said each pan has had thousands of burns.

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Emilie McVey

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Location: central Pennsylvania

posted 3 years ago

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Showing my ignorance here: what's the difference between charcoal and biochar? I thought biochar is simply charcoal that has been inoculated with helpful microscopic organisms.

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Bryant RedHawk

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Location: Arkansas - Zone 7B/8A stoney, sandy loam soil pH 6.5

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Regular charcoal has remaining volitile compounds present. What most people are talking about when referencing biochar is a carbon matrix with no remaining volitile compounds left. This carbon matrix is then inocculated either by design or by natural migration of soil microbes.

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Edward Lye

Posts: 187

posted 3 years ago

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Emilie McVey wrote:Showing my ignorance here: what's the difference between charcoal and biochar? I thought biochar is simply charcoal that has been inoculated with helpful microscopic organisms.

Wood does not burn. It is the escaping gases that burn. The process continues until you get a lump of red glowing ember that produces no flame even when you fan it really hard{another way to tell is if you see white ash appearing on its surface}. It has exhausted its fuel supply and is basically carbon. You then quench it and get biochar. If you do not quench it, it slowly oxidizes into fine white ash. While it still has fuel, that makes it charcoal. You buy charcoal for your barbeque because it has energy to give off. Biochar will not work for a barbeque or heat up your cabin in winter or cook your stew. WARNING some wood/trees/organics give off toxic fumes when burnt. The Manchineel tree is but one example.

Edward Lye

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posted 3 years ago

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Robert Alcock wrote:The problem I have found, though, is that the tins don't last very long. As in, about a week of intensive use. The intense heat and the wood acids just eat them up.

I stumbled on this:

I might replicate my ARS-C using this if the cob doesn't work. This will certainly protect your tin but also prevent the heat from entering. Win some, lose some.

Charlotte Fairchild

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posted 3 years ago

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There are wonderful YouTube videos on making Biochar. Some people use the metal box found for buffet tables at Sam's Club. Some people get a section of tin, dig a pit, burn in the pit, cover the fire with the tin & soil and add water so it stops turning to ash.

There are many people who make biochar in rocket stoves. I do not have one. Many people are experimenting and teaching on YouTube.

Ellendra Nauriel

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Edward Lye wrote: I stumbled on this:

I've been pondering better ways to fireproof buildings for a while now, even more so after watching my neighbor's house burn down. That video gave me some ideas.

Thank you for finding that!

I agree. Here's the link: https://woodheat.net