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Angelika Maier
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I started this other thread weather or not it is feasible to use garden debris like twigs etc. too small to heat for producing biochar. I have some more questions:
1. How long do you have to burn in order to get biochar?
2. Does smoke develop and how much?
3. I read that biochar is very good in a composting toilet - does anyone tried to use it? Did it help with the smell?
4. How did your soil improve with biochar? Any soil tests?
5. How much do you produce say m3 of material ratio to biochar and how much do you put into the soil (best in handfulls per square meter)? How often?
6. I tend to think that digging a hole in the ground to burn would be the best and most practical way to do it?
 
Travis Johnson
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The problem you will have with trying to burn smaller pieces of wood and debris is, they would almost instantly convert into ash instead of charcoal. That is not all that bad as Ash has some "fertilizer: properties in it, 0-1-3 in NPK if you want to run the numbers based on your soil samples. As you can see though, it is very weak fertilizer so you would need a lot of it.

I am not an expert on biochar however as my first try at it was an utter failure. In my case I did not have small wood, but rather big wood. I heard anything over 4 inches was hard to char through and I was using wood 12-18 inches in diameter. I used the burn pit method and the guy I saw try it used water to stop the burn process and get his biochar. Since water stops a fire by removing the heat part of the fire tetrahedron, I thought I would use another method; removing the oxygen. So I got a 2 cord pile of wood really cooking then smothered the fire by bulldozing soil over it in the hopes that the heat would continue to char through, but not consume the wood. After three days I bulldozed off the soil and sadly the majority of the wood had turned to ash even underground without oxygen. DRAT!

I wish I could answer more of your questions, but in all honestly, all I can tell you is what NOT to do. Maybe there is a lesson in that though for others?
 
Michael Cox
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For small diameter material take a look at the cone-kilns for biochar making.





 
Todd Parr
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Angelika Maier wrote:I started this other thread weather or not it is feasible to use garden debris like twigs etc. too small to heat for producing biochar. I have some more questions:
1. How long do you have to burn in order to get biochar?
2. Does smoke develop and how much?
3. I read that biochar is very good in a composting toilet - does anyone tried to use it? Did it help with the smell?
4. How did your soil improve with biochar? Any soil tests?
5. How much do you produce say m3 of material ratio to biochar and how much do you put into the soil (best in handfulls per square meter)? How often?
6. I tend to think that digging a hole in the ground to burn would be the best and most practical way to do it?


Using small twigs and such works great if you use a retort.  If you use an open pit, as Travis said, you will just get ash.
1)  It depends on the size of the wood.
2)  If you do it right, you will have some smoke at first but it will go away quickly.
3)  It is, and I have.  It works great in a bucket toilet.  It even works great in a bucket with just urine and that smell is much harder to control.
4)  I don't have an answer to that yet, but I can tell you that it increases worm activity greatly, so just with the additional worm castings, I don't see how it could fail to produce good results.
5)  That is open to debate and I don't think anyone knows the answer. 
6)  I haven't had good results with the pit method, but it may be that I just need more practice.  I use the barrel-in-a-barrel method most successfully.

Travis, maybe you still had too much air getting thru and more soil is the answer? 

 
Roberto pokachinni
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Hi Angelika

I used this website as the foundation of my own biochar thoughts and system:   Biochar Retort  There is a lot of good information in this article/site, including enough to build a simple double barrel retort which Todd mentioned in his post, but also that which will answer most of your questions.  By going there, and reading all of this guy's stuff, you will have a much better grasp of biochar.  I cram a lot of small material in my barrel, as dense as I can.  I like using small material as it takes a lot less work to crumble it up into the size of granules that I like in my garden. 

When you do it right:  Good char (fully released of volatile gasses) will be extremely light, will clink like glass, and will come off your skin without dark staining/smearing, unlike regular char from wood which makes your fingers black. Some of the fine biochar dust might stain your skin still.  

As for ratios of char in your soil, that seems to be up to debate.  I don't have a fixed ratio. Some say 5% others as high as 30%!  A handful in a square meter would be helpful, a few handfuls would probably be better.    You want to incorporate it into your soil.  It works great as a compost amendment and that inoculates the char.  It's super important to inoculate the char with nutrients before incorporating it with your soil; that's what makes it biochar.  Urine is a great inoculation. 

If you had added it when building your compost, then it gets incorporated when you are laying out your compost.  You could toss some in the holes when you are transplanting, put it in your potting mix, put it down in a dusting before mulching, lay it down on top of a bed before doing vigorous harvesting, such as with potatoes or garlic, drop it into carrot/parsnip etc holes after harvesting.  Lots of ways to get it in there. 

 
Bryant RedHawk
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The easy way to make charcoal (which is what biochar starts out as) from small, twigs and actually any wood size, is to put it into an air tight container and apply heat to that container at a low intensity and check the progress every hour or two.

Wood heated in the presence of air, burns, it turns from wood to charcoal to ash, this is the process of fire, it consumes a combustible material in the presence of oxygen.

There are many containers for fire, but the best ones for creating charcoal limit the oxygen available. This is how a retort does it's job.

Charcoal is wood minus the combustible materials (resins, gases and so on). If you burn some wood and watch it burn you will see gasses coming out the ends of the log and igniting, sometimes these compounds come out as a liquid and hiss, pop and sizzle, once all those compounds are used up, you have carbon (charcoal) which will then burn and turn to ash. What we want is to stop that process right after all those combustible compounds have burnt up.

I have used a TLUD type of retort and I have used a simple 55 gallon drum with removable lid with just a few 1/4 inch holes drilled in it, built a fire around it. Both create good charcoal with little ash formation, which is what we want.
If you are going to make a lot of charcoal to turn into biochar, you need to use the method that produces the most charcoal with the least ash so you get maximum benefit for the efforts put out.

My TLUD has burned out now and I have gone to the simpler drum method, both work great as does any retort style. The choice is yours.  small stuff turns to charcoal faster and at lower temps than big stuff.

Redhawk
 
Roberto pokachinni
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I went to the retort site that I posted and did not see as much information as was there before.  There is still the making and use of the retort, but I could not find the descriptions of what is going on with the char, and his use of inoculation.

So I will answer your questions as best I can if they are not answered on the retort site.

1.)He describes this on the site, but for reference, I have cooked a pot of long grain brown rice on top of the center of the retort, with a grill over the system, and had time to cook up some veggies as well.
2.)There is some smoke at the initial lighting, but not much as the air holes in the burn barrel draw quite powerfully creating a very hot combustion, burning off the smoke.
3.)Like Todd said, this is very effective at eliminating odors.  It is also great at absorbing moisture from humanure.
4.)No soil tests but it seems to promote bio-activity.  As Todd indicated with the worm activity.  Worms thrive in biologically rich systems, and further them.
5.)I answered in my previous post.
6.)The problem with the hole method if you are using fine material is that the fine material has too much air.  The hole method is better with wrist sized pieces, which can be laid on the fire, continuously covering the coals so that the coals are deprived of oxygen and then wont continue the process towards ash.  I have not used the hole method, but have watched several videos on it.
 
Travis Johnson
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Todd Parr wrote:Travis, maybe you still had too much air getting thru and more soil is the answer?


I don't think that was the case. I used my bulldozer so I had a lot of soil over the pile. I even expected occasional whips of smoke to poke through, but they never did. I am wondering if the heat from the fire caused the big wood to collapse and when it did it created air pockets that the fire could feed upon?

I honestly did not think this thing could fail that bad. I figured I might be disappointed with the quality, but figured at the heart of the pile I would dig in and get at least a bucketful of charcoal. There was almost nothing. By nothing I mean maybe a 5 gallon pail? I will try it in my wood stove to see how they burn as a coal replacement (I have hundreds of acres of woods, but not one coal seam) so it was not a complete waste.

Maybe if the charcoal burns well enough in my wood/coal stove I will build a retort and try again.

I am not one to give up easily, but drat, what a colossal failure!

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Todd Parr
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You could very well be right about that. I think I would try again but lay logs down next to each other like a pulp pile so there aren't really any large air gaps between the logs. With big chunks like you are burning the gaps between pieces may be big enough that there is a lot of air in there.
 
Roberto pokachinni
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I honestly did not think this thing could fail that bad
  I wouldn't think so either. Strange.  You would think that with a fire raging like that, the lower oxygen would have been sucked out of the pit and consumed by the fire too.  What sort of wood were you burning?  Not that I can see that it should make any difference.
Maybe if the charcoal burns well enough in my wood/coal stove I will build a retort and try again
So you are planning to burn the char?  Is there a reason that you want to do that instead of burning the wood?  Anyway, with your welding skills you might want to consider building a woodgas generator to create your char, while generating gas for heating, for machinery, or for generating electricity. 
 
Tj Jefferson
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Travis,

I know your bulldozer is near your heart, but the secret to pit burns is depth. I make mine in a pit about 4' deep and only 2' across. I also have a sacrificial layer on top of small stuff that is burning when I add the clay- yes, clay. And it is damp. That seals the top very well.

I think you can totally do your method and make it in bulk, but I would suggest a deep pit from an excavator, small stuff in the bottom to seal your pit, big stuff in the middle, and small stuff on top- with a big clay cap on it. Judging by your prior posts you may have a hard time finding the clay, I can mail you as much as you want for just the cost of shipping! The clay cap bakes hard on the interior but not all the way through, preventing cracks. I do not significantly quench, which keeps the temps inside pretty high for a long time. I use about a foot (or 25% of the depth) of clay soil as a cap. I think you could get complete pyrolysis even with some big timbers but you need a big pit, so the walls reflect the heat back into the pit. Mine is totally glazed like pottery after several burns.
 
Fred King
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If you are interested in charcoal and or biochar you might try the Drive on Wood site. It is mainly for wood gratification but many people run small engines (and some not so small) on charcoal and the charcoal section of the site shows several ways of making it. They often use larger pieces in a charcoal gasifier to run an engine and the fines as biochar.
 
Angelika Maier
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Thanks for all the answers! I think we go with a barrel. The idea came to my mind because we have a lot of twig piles and we have a lot of blackberries to clear. The only thing is that we have to cram these sticks and blackberries and no I don't want to cut them with the secateur! It seems fantastic to bring all that debris to a good use.
 
Travis Johnson
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The pit dimensions must have been the problem. I had the depth at 4 feet, but my blade on my dozer is 8 feet wide, and of course it was 16 feet long. I can bring down the excavator and dig it, and in hindsight I probably should have, but it would have taken longer to drive it down then the3 swipes to dig the hole, so i used my bulldozer instead.

Ultimately I think I will have to built a retort, I just do not have anything ideally sized kicking around. A 1000 gallon tank would be perfect, but I don't have one. I was hoping to use the old method to make some charcoal just to see how it would work for biochar/heating charcoal.

On the last point, today I started the first fire of the season and used what little charcoal I did produce. It was not a good test because this is also the first fire kindled in our new-to-us-stove. It is actually an antique, but new to us so I am not sure of all the control measures for the draft. It worked pretty good though,; long burn times, low stack temperatures (like burning coal) and seemed too throw plenty of heat. I would burn more of it for sure if I could produce it faster/better/more of it.

 
Bryant RedHawk
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Another way to make charcoal is to use an old trailer. I know a company that uses 4 40 foot long trailers (dead 18 wheeler boxes) they load them up, start the fire and once it is just starting to roar they shut the doors. There is one small hole at the front for gasses to escape from.
This is a company that makes oak charcoal that they sell in 50 lb. bags for grill use and they make a lot of charcoal (the money  isn't bad either).
 
Tj Jefferson
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Bryant RedHawk wrote:Another way to make charcoal is to use an old trailer.


That would be a really good technique for huge amounts, especially using a CONEX. I would expect it would last under ten burns before becoming structurally unsound, but that would make a lot. That would require a Travis-size pit! Do they pile wood on the outside too to provide the heat or just have a contained burn?
 
Bryant RedHawk
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Their trailers are old, steel sided trailers they use fire only on the inside of the trailers which do have double side walls, floor and roof.

When I was there to learn how they did their "natural" charcoal they were getting ready to fire up one of the trailers, the wood was just thrown in, the box was full but there were spaces (air pockets).
The guys said that all the air that was there when they lit the twig bundle was there because they had found out just how tightly they could pack the trailer and still get the most charcoal out.
These are not used like a retort, they are more like a burn barrel. The "chimney" is a four inch by two foot long slit at the top front of the box, the doors do not have any type of seal but they are shut and locked down so very little draft effect occurs.
The burns are around 8 hours long and there is very little ash produced and there are very few pieces that aren't completely turned to charcoal, those that aren't, they put into a pile for a re-burn.
 
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