Slash char and burn accelerants

40 acres nearby was clearcut in Dec. One day it was down, the next day the "waste" was burning in 4 massive slash piles. It's wet here in winter and the wood couldn't have been greener.

Last week I visited the site. It's covered with piles of char. There must be at least 2 pickups worth, maybe as much as 4, hard to tell the way it's mixed in. The implications of slash pile carbon being usable as char would be huge.

I've wanted to learn how to execute a conservation burn, turning a slash pile into biochar, but have not been able to find any workshops or videos about it.

Biochar purists will tell you the wood has to pyrolize at 500 degrees, be feedstock of a certain type and size, and be dry. None of that is present here, obviously, so is the resulting char of any value as an amendment? It was burned with liberal lashings of accelerants, probably diesel. The smoke was godawful for days, hard to tell if it was the green, the accelerant or something else. I'd like to think that burns off completely but think that must be naive.

You could test it yourself.

A simple method would be taking some in cheesecloth or a strainer and a funnel and passing water through it, catching the runoff. If it is clear and free of obvious contaminants (oily residue, rainbow colours, funny smell/taste) then it's probably good to go.

As to ways to make larger pieces and quantities of wood into biochar, while I am personally wanting to do experiments on retort-style burns, the best way I have seen yet is the one I have posted below.



I saw it on another biochar thread, but I have forgotten which one, and had little luck searching, but was able to find it on YouTube.

At the end, you'll see the water test I described.

I like how they describe the thermodynamics involved, and how the shape of the cone essentially starves the finished charcoal that falls to the bottom of oxygen, and the fact that the format is essentially one that allows for a constant feed up until there's no more room for more contained burning.

Which brings up my final point. By whatever method, if you thought it was contaminated, you could either use it in a burning application, or you could put it through the oxygen-free part of the biochar process again. Just heat it up, say in a 55 gallon drum. Set up some rocks to support it with a fire underneath. You could use some of the worst looking char to fuel the fire. I would make sure that the drum can vent escaping vapours down back into the fire, and also to make sure it can neither really pressurize itself, nor draw any air in.

If you had equipment, I would use the trench approach. Dig a trench, reserve the topsoil, and start a fire with some of the most contaminated-looking char. When the bed is hot enough, fill the trench the rest of the way with the char you wish to later inoculate for biochar and cover that over with the fill that was in the trench to begin with. Just let it cook.

When the temperature drops below that useful for making good charcoal, I would quench it, let it drain, and then dig it up for use.

When I last did this, I put the trench on the future site of an on-contour hugelbeet, which was the purpose for the biochar. I basically dug it all out and piled in the rotting, punky wood that wouldn't have burned well and was also already inoculated with healthy wood decomposers, on and around the largest trunk rounds that wouldn't have burnt without further work, and that I had reserved for structural reasons of the hugelbeet.

I hope you can make use of that waste as a resource. That's a lot of long-term carbon sequestration and serious soil-building if you can make it happen, and work for you.

Let us know how you do, and good luck.

-CK

If there was a complete burn then there wouldn't be any char or wood ash. I'd guess there wasn't a complete burn of the diesel. There's said to be residue of an accelerant as evidence of arson. I'd also guess that there's more residue from diesel than from gasoline. I seem to remember it said that after an arson the residue will improve the chances of reignition. Besides it's not yours.

I don't think you need to be worried about contaminants. Mix the char in with plenty of organic material, and water. Fungi and bacteria will break down anything that might be of concern.

Regarding the use of accelerants; if the burn really was on the tonnage you describe then the accelerants will have been a negligible proportion of the original mass, and would have been on the outside of all the woody material so burned first. Combustion itself creates all sorts of nasties and we don't concern ourselves overly with them, beyond avoiding breathing the smoke.

If it was me I would be up there getting as much as I could - even imperfect char is better than no char at all!

Fredy Perlman wrote:40 acres nearby was clearcut in Dec. One day it was down, the next day the "waste" was burning in 4 massive slash piles. It's wet here in winter and the wood couldn't have been greener.

Last week I visited the site. It's covered with piles of char. There must be at least 2 pickups worth, maybe as much as 4, hard to tell the way it's mixed in. The implications of slash pile carbon being usable as char would be huge.

I've wanted to learn how to execute a conservation burn, turning a slash pile into biochar, but have not been able to find any workshops or videos about it.

Biochar purists will tell you the wood has to pyrolize at 500 degrees, be feedstock of a certain type and size, and be dry. None of that is present here, obviously, so is the resulting char of any value as an amendment? It was burned with liberal lashings of accelerants, probably diesel. The smoke was godawful for days, hard to tell if it was the green, the accelerant or something else. I'd like to think that burns off completely but think that must be naive.

I've been reading a lot about the new fangled Biochar ideology and find a lot of it good practice but the proponents seem to forget that in the beginning of terra preta, there were no oxygen free furnaces, no gas jets to create the heat, and metal was a prized commodity.
While it is great to have the new techniques and the ability to incorporate them they really can't be as necessary as the "new wave" ideology insists, otherwise there never would have been a discovery of hundreds of years old terra preta, it would not have been able to be created.

I've used (and do use) a crude set of tools when I make my charcoal for terra preta experiments and use in gardens. I also use primitive methods (burn pit or just a lot of junk wood stacked up on the soil surface), all will produce decent quality charred wood.
The first people, who created terra preta as a necessity of being able to produce enough food for masses, in an area that it still is difficult to raise food plants, seem to have come up with the system by accident.
It was the result of burning the "Trash Dump" then they would spread the charred remains over the soil so they could build a new trash dump in the same spot without having to walk over heaps of charred trash dump remains.
Over time (probably at least 50 to 100 years) the raked out remains sank into the soil and microorganisms inhabited the nooks and crannies since they were an easy source of carbon for the organisms food.

In the Amazon basin if you start a fire in the morning, around noon it will be put out by the daily rain.
To make char in a similar way we pile up our fuel, set it on fire and grab the garden hose, occasionally spraying water over the burning pile to cool it down some, so there ends up being more charcoal than ash and what ash there is, is washed into the soil beneath the heap of burning  fuel wood.
That would be the most authentic method of making the char for building terra preta.
From there, you can get as efficient as you feel you have too.

Redhawk

Bryant RedHawk wrote:While it is great to have the new techniques and the ability to incorporate them they really can't be as necessary as the "new wave" ideology insists, otherwise there never would have been a discovery of hundreds of years old terra preta, it would not have been able to be created.

I generally agree with you, but would argue that the new techniques are necessary if you must achieve the biggest energy-return-on-energy-invested. The ancient Amazonian people probably had vast biomass resources on their doorstep and also a lower sense of economic and environmental urgency than we have today.

Edited for clarification.

I don't think we need to argue Matt. I like the fast methods too.

I was just pointing out that if you don't have the money to build a retort furnace, don't worry, you can still make good char.
To actually get "the biggest energy-return-on-energy-invested" wouldn't you need the energy used to create the char do something else at the same time, other than heat the atmosphere?  (I'm just asking, not trying to be a smart ass, I have not actually done a lot of thinking about that aspect)

It's great to see others thinking about this method of soil improvement.

Redhawk

I agree with the whole idea of not letting the perfect be the enemy of the good.

I also think that the best possible biochar operation would involve a drum retort as I have detailed, but powered by the exhaust stream of another, more energy-intensive project. For me, because my much better half is a glassblower, my heat will come as the exhaust of a 1950-to 2200-degree glass furnace.

-CK

Bryant RedHawk wrote:To actually get "the biggest energy-return-on-energy-invested" wouldn't you need the energy used to create the char do something else at the same time, other than heat the atmosphere?

I agree, and would love to see somebody make that. I've been tinkering with the idea myself but it is taking a long time.

The trouble with a system designed to both reclaim energy and make char is that it ends up being an inefficient compromise between two things. For example, if I am trying to heat the water for my house, then I want a system that burns very cleanly, and gives me good yield of energy for the amount of fuel I load. By definition, making biochar is not fuel efficient (because, obviously, the char is not burned away). And then simultaneously, I'm adding all sorts of awkward design constraints to the boiler part as well. How do I extract the heat, exactly? What are the implications of needing to periodically empty the char? If this water is to be useful, it needs to be in or near the house - what are the implications for house safety (fire, carbon monoxide from restricted combustion etc...)?

Thus I am not really surprised that we haven't seen a dual purpose arrangement yet, that meets with wide acceptance.

My personal experience, for what that is worth, is that these systems - when/if they evolve - are going to be very small units used in daily tasks. For example, I have use a rocket cook stove - fueled with dry twigs - that burns hot and clean, and more powerfully than a gas fire. After cooking for 15 minutes or so, about 1 large cup worth of char builds up in the bottom of the burn channel. That doesn't sound a lot, but it is a fire you might have anyway, and the char is a waste product at the end of your cooking. Over a year of use you could build up quite a bit. The rocket stove I used would need to be slightly adapted to make it a more convenient collector of the char. Just a removable steel collection cup beneath the burn tunnel, for the char to drop into.

I should also point out that a device of this sort would do nothing for the "I have huge amounts of brash to dispose of quickly" problem!

I took the charred wood from the remnants of one logging slash pile and buried it in the bottom of my hugulkultur, packed with sod and subsoils.  A couple to four feet of uncharred decaying cottonwood was put over top, topped with subsoils and then manure, and top soil.

My guess is that the quality of the char from slash piles is not optimum, but it will still have some of the honeycomb porous qualities for nutrient / biological reservoirs, and at the same time, making the bottom of the hugulkultur a stable nutrient sink over a longer period of time than simply burying wood.  

Biochar hits the big time in my valley!    :)

The implications of slash pile carbon being usable as char would be huge.  

As it so happens, there are two potential projects doing just this in my valley.  

-Today I bumped into my friend Ray who is the manager of the local community forest for my little community.  Our woodlot is partnering with a guy with a gassification/pyrolysis power plant machine to test a pilot project with some of it's logging slash, creating biochar and energy rather than burning huge slash piles to carbon the atmosphere.  Oh Yeah!  !!! :)  

Some of the wood will power the unit's initial and continuous firing, while most would be turned to high quality char.  Some of the wood gas that is produced would be fed back into the firing chamber, while the rest is used to fire a generator for producing surplus electricity for other uses, like small industry manufacturing.  The unit is a patented prototype that has been in operation regionally for a few years.The Local Dude's enterprise  The connection of these two entities has been something that I have been hoping for for a while.



-At the same time, a much larger industrial system is set to be built in Mcbride by an Albertan company, which will produce what amounts to char pellets to be marketed to fire energy plants in Japan instead of Coal.  Last week's Newspaper Article about this bigger project  This one will use it's excess power to heat greenhouses to grow trees, furthering it's carbon offsetting.  

Pretty Freakin cool, if you ask me.

@Chris: I saw a Kon-Tiki demoed and was impressed by its simplicity and effectiveness. I am hoping to find the parts I need at a scrapyard to make one on the cheap, adapting some existing thing like a tank or cauldron. Washing machine drums will probably figure into my plan somehow. In the video here it shows a quenching from the top, but the one I saw had an input at the bottom; Paul Taylor or one of his congeners there said quenching from the bottom was better because the char falls through the incompletely-burned material to collect at the bottom, so you'll extinguish the char before putting out the stuff that's still burning.

But next time I have an excavator onsite I will dig a trench for trench burns. I was thinking of controlling the burn rate with a big sheet of steel, rather than burial. Weld an eyelet on it and pull it around with a hooked pole.

@Michael, you're right, I remember that fungi have broken down used motor oil, diesel, and runoff from interstates. And if there's anything we have, it's fungi. I've not seen anyone doing a burn with even an N95 particle respirator on, and I strongly recommend it, just as I did in the welding shop when I was the only one wearing a P95. But after one welder resurfaced a 3'x10 steel slab with an angle grinder, everyone wore one. Burning without breathing gear is a bad idea imo.

In "The Biochar Revolution" there is a lot of material about cookstoves produced for the developing world, that turn cookfires into small biochar furnaces. They're cheap and durable, but their point is to cook, not make biochar: the volumes produced are trifling for our purposes. The first person to dial in a rocket mass stove&heater that produces biochar is gonna be the Elon Musk of permaculture.

@Bryant, thanks for the very hands-on description of your process. That's something I can do right now, which makes use of my slash piles without further handling. Though I've read most of Paul Taylor's book and other bits about biochar production, I've kept in mind that the technology is very old and, in a place like the PNW, we needn't worry about total feedstock efficiency. There is always too much supply, and it is only completely dry for about 3 months of the year -- during which burns are banned!

@Roberto: would you have the char in the trench of the hugel, or at the base of it? I had thought green wood in the trench, raw char on top of that mixed with clay, then sand, soil and rotting wood with leaves on top of that. Probably mix charged char into the upper layers.

The super-tech biochar of the future is almost upon us, with hugely expensive industrial plants such as you describe. This Finnish guy's company is an example of current development. I'm ambivalent, because I want biochar to be an open-source, local process and product. The materials and energy and labor that go into making an industrial plant also create a huge initial carbon footprint to offset. And making biochar a market-driven commodity may provide perverse incentives like deforesting areas where labor and fuel are cheap to provide biochar to remote customers, which rather defeats the big-picture environmental purpose of biochar.

Roberto: would you have the char in the trench of the hugel, or at the base of it? I had thought green wood in the trench, raw char on top of that mixed with clay, then sand, soil and rotting wood with leaves on top of that. Probably mix charged char into the upper layers.  

 I'm not saying that what I did was right, but this is how I was thinking it.  Since it's going to take a real long time to break down, I put the charred 'green' wood at the bottom of my trench, but the trench was not too deep: about a foot, so it pretty much filled the trench, so it was basically also at the base of the mound.  So we are thinking the same there and generally on all points.  

I didn't have biochar made up for the project.  If I did, considering that I live pretty far north and don't get ton's of sun (as I'm on the wet side of the Rockies) and we need all the solar gain and heat that we can get, I would have placed biochar in the outer soil horizons, in the compost mix, on the south side and top of the hugulkulture (My Hugul was built as a sun scoop, facing South), so that it would darken the mound on that side.

If I had raw char (not inoculated with nutrients such as compost), I would have put it in the deeper layers, so that they would not draw down too much of the much needed surface nitrogen.  

These days I'm about to be compost rich.  I am in the process of making about 3 to 4 tons of it, so no char should go un-inoculated for long around these parts.    

I tried making biochar last fall on a pretty big scale using my bulldozer without success at all.

I made a perfectly shaped pit, then put in 1-1/2 cords (full cords) of wood, and lit it on fire. It burned well enough, then I quenched it using soil over the top, and ended up with almost nothing. Most turned into fine ash, with what did not burn completely up, into big chunks of wood. I was REALLY discouraged.

This spring I burned some logging slash just to get rid of it. It burned down to nothing in no time, but I think I can get more use out of the ash as a natural fertilizer than I could as biochar. I do have a lot more to burn, but it is located on the edge of the woods so during the height of fire season it was NOT okay to burn, but after the first snowfall this winter, I'll light it, and let it burn all winter. Maybe the shear volume, and snow burn from the dirt, debris and snow will give me some biochar. If not, I will at least get rid of the logging debris, and if not that, then have cheap fertilizer.

My few attempts at burying to quench the burn failed as well. Quenching with water on the other hand works very well.

Michael Cox wrote:My few attempts at burying to quench the burn failed as well. Quenching with water on the other hand works very well.

I can see how that would be true, but when a person gets into larger volumes, that gets problematic.

I wonder if a special biochar pit could be built, next to a pond or other water body. It would be coned shaped, but have a grate at the bottom so that as the wood burned down, it would fall through the grate. Water would then be pumped down to the tank below so that the biochar would be quenched as it did so.

Now the only problem I see is the wood floating on the water. Hardwood does not float, but I am not sure if hardwood floats after its been turned into biochar...I would think it probably would (pun intended). I suppose a spray of water could be given on both sides of the grate so that as the biochar falls down it quenches the biochar. That water would then run down to the bottom of the biochar settling tank, filtered, then pumped back for the cooling process again.

It is kind of an elaborate system, but would save a lot of water, allow for higher volumes of biochar burned per burn-cycle and not be all that expensive to set-up. Steel or concrete would have to be used to form the pit, steel obviously for the grate that was hinged or removable so biochar could be removed, then concrete or steel for the biochar/water accumulating chamber. A tank perhaps, pump, lines, filter and spray nozzles would complete the system. I am not sure what the size would be. I would think maybe a cord? (4 feet high, 4 feet wide, by 8 feet long). It would be an initial cost outlay, but maybe all the controls would net better, more consistent biochar for not a whole lot of money, making it worthwhile.


Thoughts???

We have the advantage of having our own borehole, so water volume in no issue for us. If you are trying to minimise water then I would consider some kind of metal drum (for the guaranteed abilityu to exclude air).

Also, you mention cord wood. Personally I avoid making biochar from anything that would be better served as fuel for in the house, so our burns are smaller diameter brash. Smaller diameter means each branch chars quickly and completely in just a few minutes, and breaks up into nice find pieces of char. My experience of burning larger diameter wood is that you end up with more waste - the fire has to burn for longer for complete charing of large diameter pieces, so more char burns away to ash.

There is a design based on oil drums that I have wanted to try, with the drum in a horizontal position. It looks like it would minimize water and be very cheap.

Also, If i were to do a design like that I would adapt it to be mobile - think like an oversized wheel barrow - so that you can wheel it around while still lit. You can take your bonfire with you while you are working, and minimise the distance of hauling your bits of wood.  A lot of our woody scraps are tree prunings around paths, hedges, dropped deadwood from trees etc... and then prunings from various bushes and the like. I can't keep making more and more bonfires in convenient locations, so a mobile burn barrel would be great.

I saw something like this being used at a vineyard in france - the workers pushed the barrow along the row while they were pruning, and the trimmings just got chucked straight in. That design wasn't aimed at making biochar, however - it had vents at the bottom so the char would have burned away completely.

A portable kiln like this one from Byron Biochar is ideal for stuff that would otherwise be burned in large slash piles. If water availability is limited I have read that they can also be snuffed with a cloth that is kept damp so you don't need to fill the whole kiln with water.


As mentioned in previous comments only burning smaller diameter wood is best, some people say up to 3 inches but I would recommend up to two inches and cut everything that is thicker into firewood.


@Fredy
Yesterday I made a post about my indoor TLUD stove that could also be connected to a thermal bench and heat exchanger for hot water as well, not sure if I will include the thermal bench but hooking one up to a hot water system will be part of my next stove build/design for sure. So I'd like to reserve the title of becoming the Elon Musk of permaculture :p

Michael Cox wrote:For example, I have use a rocket cook stove - fueled with dry twigs - that burns hot and clean, and more powerfully than a gas fire. After cooking for 15 minutes or so, about 1 large cup worth of char builds up in the bottom of the burn channel. That doesn't sound a lot, but it is a fire you might have anyway, and the char is a waste product at the end of your cooking. Over a year of use you could build up quite a bit. The rocket stove I used would need to be slightly adapted to make it a more convenient collector of the char. Just a removable steel collection cup beneath the burn tunnel, for the char to drop into.

This is exactly the type of dual purpose I was referring to Michael, as I said I haven't put much if any thought into such a design. I leave that to others with more time and experience in the field of combustion.