I've made batches of biochar at various points, using various different methods.
Periodically I like to look around and see if any new ideas have come up in kiln designs, as I have yet to be satisfied with the methods I have tried. They make batches that are too small, or too labour intensive, or require nicely dried wood (which I don't have). Basically I've been looking for something that can take big chunky prunings from our 6+ acres - a mix of hedge trimming, fruit tree prunings, heavier branches, general pruning waste, etc... without needing complex tools, or lots of labour. Most especially, I don't want to have to cut everything down to nice 6 inch lengths to stack in a kiln, given most of it is woody stuff a meter or so long.
I have used open fires and pit - they meet the need for minimal processing of fuel wood, but are inefficient and tend to be a bit smokey.
The cone kilns which were first appearing two or three years ago looked promising, but a lot of our wood is long and would still need cutting to fit into a reasonably sized cone.
Today I came across these ones:
They use the same principals as the cones but are a rectangular cross section, and substantially longer in one direction, so you can fit your long logs without the whole thing being excessively oversized. Given that I haven't already gone ahead and had a cone made, i think I might go for something like this.
Tempatures should not be high enough to need refractory materials.
Maybe just sheet metal would be enough,thus keeping it light.
If I understand the way this and the cones work, a carefully dug trench can do the same job.
I am just starting my biochar journey, so I will watch this subject with great interest.
As I understand it the raised metal construction does have benefits when it comes to clean burning and consistency of product; air outside the kiln is preheated by the contact with hot metal then is sucked into the flame front as it rolls over the lip of the metal. Preheated air burns more consistently, with fewer smoke problems. There are also advantages when it comes to quenching as a leaky dug pit will need a lot more water to guarantee a full quench than a sealed metal tank.
Michael Cox wrote:Hi Folks,
The cone kilns which were first appearing two or three years ago looked promising....
I can see the benefit of a trench pit to handle longer pieces, encourage exploring that approach. The cone kin=ln better fits my situation. Some permie friends of mine, Best Biochar Kiln, in Stevens County, Washington, USA, make shippable cone kiln kits. I have two of the BBK kilns, typically running both simultaneously in a very urban backyard setting. With two and three story apartments on the downwind side, one has to deeply appreciate cone kilns for the ease with which they can maintain smokeless runs. A cone-kiln shaped pit in the dirt would work quite well also. A big wok, there are a number of ways to get the benefit of an open pan shaped firepit. I previously relied on enclosed barrel-in-a-barrel retorts, but the smoky start up, and the smoky hand off when transitioning from primary (outer sleeve) to secondary (inner vessel / retort) gases 20 minutes or so into the run. That meant I had to choose my days and times more carefully, needing to avoiding cold air temperatures and high humidity conditions that the cone kiln handles easily. That said the cone kiln is more sensitive to wind, I avoid 5 mph and above, whereas the barrel retorts were good up to 12 mph days. A windscreen can really help.
A cone kiln can throw sparks that an enclosed retort will retain. With climate disruption, and increasing incidence of red flag fire warning days of high temperatures, high winds, and extremely low humidity, open burn methods for making biochar deserve an added measure of caution.
This one just cries for a drop into place lid which would make the burn far more efficient for creating char, just a few holes (maximum of 4 - 1/4") drilled at one end for air to enter the burn chamber should give good results.
Making charcoal is more science than art, you just need to have a fire that can not get so much O2 that the flames run away and leave you with more ash than charcoal.
Bio char is fully cooked charcoal (no volatile compounds left behind) that has then been soaked with a good compost tea or just added to a compost heap so the microbiome finds places to live in your fresh carbon supply)
Properly activated biochar is a boone to all soils since it performs many functions; carbon sink, microbiome housing development, mineral source, water holding ability, O2 holding ability are among the impressive list of things biochar can do for soils.
Use a steel 55 gal. drum with a retaining ring held in place lid, this is your oven (they last long enough to off set the small cost of buying a used one every time one wears out).
take a 2 foot piece of steel pipe (or anything that is usually used as a flue pipe, even the ones used for venting hot water heaters work well) set it in the center of the lid and mark around it so you can see the line.
remove the pipe and use a 1/4" drill bit to make a dozen or so holes in the lid inside the pipe's line you just made.
next is fastening the section of pipe you used to make your circle mark to the lid of the drum. (I used tin snips to make 8 tabs, remove the "waste" and then I drilled and pop riveted the vent pipe to the lid)
Use 4 8x16 inch concrete blocks spaced around the bottom rim so the drum will sit up off the ground (set these so the drum sits on the center reinforcement of the blocks)
Take the barrel off the positioned blocks and dig out the soil in the center so you have a pit for building a fire.
To use this for making charcoal or biochar you just fill the drum with your wood, packing it in as tightly as possible.(this is easiest to do if the drum is laying on its side, then stood up on top of the blocks and more sticks pushed in to really pack the drum)
stand the drum on the concrete blocks after laying the wood for the fire, place the lid on and use the clamp ring to fasten the lid to the drum.
Light the fire under the drum, keep the fire as hot as you can make it, once the wood heats up use a long match or stick to ignite the fumes that will be coming out of the "stack".
This is a pretty simple TLUD type of setup and it works.
Post 1/22/2017 2:13:22 PM Subject: Biochar making - various kiln designs
"[...] I have used open fires "
Two weeks ago I made about 150 gallons of charcoal in two hours using the open fire method aka "when the coals begin to turn white, put more wood on top of it." I really liked how quickly I could produce a huge batch - much faster than any containerized methods i've tried.
After I hosed the fire out and soaked the coals real good, i drove the front wheels of my truck back and forth over it, picked out the few un-crushed pieces (mostly knots & super thick pieces that didn't char all the way through) with a pitch fork, hosed it down again and drove over it again. End product is a very fine material, largest pieces being about 1/4 inch.
I think open fire / truck crush is my favorite method for making charcoal to go in the compost.
Making dry charcoal for blacksmithing on the other hand... I don't see any way around using a kiln of some kind.
I fill it to almost an inch of the lid , douse the top with accelerant and light.
When I'm sure its lit, I cover it with the lid/chimney.
It burns about 45 mins, or an hour, I think, its been a while.
Lately I have only made char in the bonfire.
An old steel tool box stuffed with bones, bread, willow, cardboard, etc, goes in the bottom of the pit.
The willow turned out well, I hoping to monetize that in the future.
Bryant, does your setup continue to burn once the chimney gasses are lit?
The trough style has the advantage that you could add to it as the material reduces.
If you put a lid on that, you lose that feature.
I can see wanting a lid to starve the coals of air at the end of a burn but not otherwise.
I'm building a batch rocket powered black oven.
It occurs to me that it could make a fine biochar kiln.
One would want to burn off the gasses produced.
If you build it as white oven, you could re-route the gas produced into the rocket itself, for a self perpetuating process.
I wouldn't do this with a black oven, as the pyrolysis gasses would be mixed with the finished rocket exhaust, probably not a good mix.
Bada bing . . . done . . . and no expensive equipment needed. When you are done, you don't have to find a place to store that big steel contraption.
One of the reasons I'm so drawn to permaculture is because of the sustainability and transferability of these principles to the developing world where resources are scarce. appropriate technology doesn't get any more simple than a dish-shaped hole in the ground that is rimmed with basic mud bricks. I would find it expensive to have a big steel biochar burner made. How much more so if you are a simple farmer living on the side of a hill somewhere in Latin America or Africa?
If I recall, its just a matter of what works for you.
Digging a hole when and where you need to make some bio-char is one way.
Bringing your kiln with you, or bringing your feed stock to the kiln might work better in some situations.
Me, I bring my feed stock to the kiln, as I do not have acres of woods.
I do have a couple of yards, and I will probably build one on each property, with a emphasis on easy of loading , unloading, and utilizing the heat generated.
Happily living in the valley of the dried frogs with a few tiny ads.
Two part roundwood timber framing workshop sep 24-29 and oct 1-5https://permies.com/t/91267/permaculture-projects/part-roundwood-timber-framing-workshop