Rocket Stove for Biochar

Hey gang...
I couldn't find a suitable thread for this question, so I'm winging it.

The Kansas & Nebraska Forestry Services are offering grant funding for biochar production.  I've done some looking at biochar in the past as a personal soil amendment pathway, but had this random thought.  

IS A ROCKET STOVE A SUITABLE MEANS OF HEATING A BIOCHAR KILN?

Bearing in mind that my knowledge of both biochar kilns and rocket stoves are largely theoretical, and that I have no practical experience, my thought is this.  Normally, a biochar kiln has an inner chamber for the biocharring materials and an external chamber where a fire is built to create the chemical/physical reactions to create the char.  Would it be possible to build a rocket stove with a char reservoir on top/around the horizontal chamber?

I'm not even positive I know what I'm talking about, so if this is TOO crazy to work, please feel free to shoot me down.  

Hi Chris;  I don't have any direct answers on how exactly you would accomplish this but after a little reading and watching the attached video i"m sure it could be done and I suspect it already has.[youtube]RXMUmby8PpU[/youtube]

I'm working on a prototype for this right now.  I just put a small drum full of wood directly over the chimney of my rocket stove.  At first I tried it with the drum just sitting over the chimney on an old stove burner grate from a gas stove, but I couldn't generate enough heat.  The next time, I put another barrel on top of the rocket stove barrel surrounding the charcoal drum and it worked better, but I didn't get a complete char.  Next step will be to insulate around the outer drum with rockwool to keep more of the heat in.  At that point I think it will work really well.  Once I'm sure, I'm going to use a barrel of 35 gal or so to hold the wood with a 55 gal barrel around it.  Right now my charcoal drum is small, only 7 gallons I believe.  I'll have to do some testing to find the "sweet spot" with regards to the size of the charcoal barrel I can use and still generate enough heat to char it completely.

I love the idea, but two things come to mind when I try to solve for this problem.

First is the capacity. Any retort going into a Rocket Stove will suffer from a loading and capacity problem.

The second is accessibility. Unless you just have a J-tube with the retort on the top of the riser and the woodgas redirected back to the burn tunnel, getting at the retort to either empty it by hand/shovel, or lifting it out of a rocket stove enclosure to dump the biochar you've created will not be an easy task you'll want to do over and over.

I really like the Kon-Tiki design. It's essentially a funnel with a closed bottom end. You fill it up with wood and start the fire on the top, and keep adding as it goes. The fire on top keeps oxygen away from the bottom of the pile, so as it burns, the coals eventually drop to where there's no oxygen, so they essentially self-quench. You can see a great video on this thread.

I think that wide adoption of biochar techniques requires fast, easy ways to make lots of biochar from windfall resources like slash piles and waste biomass. I think that small batch production, while interesting and perhaps an ice-breaker for biochar newbies (or a way to catch and direct the attentions of pyromaniacs), presents its own stumbling blocks.

Now maybe if it was just a dedicated biochar retort with an integrated J-tube to power it, a riser running up the centre of a drum of wood scraps, woodgas fed back to the burn tunnel, and the ability to tip the drum out when cold, maybe that would be different. But I still like the cone retort. If you check out the video, you'll probably see why.

-CK

Chris, mine has a drum that is just sitting on top of the rocket stove drum with only short metal tabs holding it on.  The inside drum has holes drilled around the bottom so the vent gases escape.  I don't have the rock wool insulation on the outside of the outer barrel yet, so when the burn is done, I lift the outer barrel off with welding gloves.  You have to do it fast or it will burn your hands anyway.  As I said, it's a prototype :)  The inner drum is lifted off and set on the ground and then I cover the holes with dirt so the charcoal doesn't burn to ash.  There are obvious issues with the design at this point and I wouldn't suggest it to people, but when I get the bugs worked out, I think it will be a viable option.  I need to come up with a some sort of device to help with lifting the inner barrel.  I came up with a couple ways, but they are a two-person operation, so still not ideal.

I haven't used the cone as it is, but I have tried to duplicate it using a hole in the ground, as well as the trench method.  I wasn't happy with my results.  I get a lot of brands, or if I let it burn longer to get all the brands, I get large amounts of ash. To quench it, you need water.  A lot of water.  With the kiln, I can see some of that not being an issue, but the kilns are pretty expensive if I remember correctly.  To quench a retort, you just need to cover the vent holes and let it sit until the next day.  Dry charcoal is also easier to work with in my experience.  It's much lighter and you can wet it with a pretty small amount of water to keep the dust down.  Like many things permie, I think it is a matter of personal preference and I wouldn't try to dissuade someone from using another method, but for me personally, I like the results of a retort.

Did you see the drum and basket version of the cone kiln? Essentially, everything smaller than the grating falls into the oxygen-deprived space in the barrel below the fire. No water, no smouldering, and a half-barrel or more of capacity.

The cone kiln is similar in function. It's an oxygen deprivation quench, no water required. The water shown in the video illustrates how clean the resultant charcoal is.

As to your prototype, shouldn't it be possible to have some kind of closure on the vents themselves? Seal the vents and you don't even need to take the retort off the heat first. Sounds like a one-person solution to me.

-CK

Chris Kott wrote:Did you see the drum and basket version of the cone kiln? Essentially, everything smaller than the grating falls into the oxygen-deprived space in the barrel below the fire. No water, no smouldering, and a half-barrel or more of capacity.

The cone kiln is similar in function. It's an oxygen deprivation quench, no water required. The water shown in the video illustrates how clean the resultant charcoal is.

As to your prototype, shouldn't it be possible to have some kind of closure on the vents themselves? Seal the vents and you don't even need to take the retort off the heat first. Sounds like a one-person solution to me.

-CK

I did see it.  I think that large cone would be expensive, but it looks very interesting, and it may be able to be recreated by a barrel or a hole in the ground as you mentioned in that other thread.  I have many experiments and tests going at any given time, but if I could use that method with something I can cobble together to create large amounts of charcoal, I would certainly try it.  I can't see myself as ever having to much charcoal, so if there is a good efficient way to make larger batches I'm certainly in favor of it.

If you or a friend has any welding gear, the cone should be pretty cheap to craft. I had pondered a setup in the past, where a J-tube is setup on a slope, with a platform so you can walk to the top of the riser and slide a 55 gallon retort into position (or fill it up on its side and then stand it up and attach the lid) and there is a pipe coming out of that retort barrel which you connect to a pipe that feeds back into the bottom of the J-tube riser so you can use the retort gasses to fuel the burn after the initial load gets the process started. Having a second barrel attached to the top of the riser which is a little larger than the retort, with a small gap all around for the exhaust to travel up the sides, and insulation on the outside I think would help heat it up faster, perhaps even using the rocket oven designs of recent kickstarter fame? Open the lid on the side, fill the barrel with wood, close the door and "cook", then open the lid afterwards and pull all the charcoal out?

Mark Tudor wrote:If you or a friend has any welding gear, the cone should be pretty cheap to craft. I had pondered a setup in the past, where a J-tube is setup on a slope, with a platform so you can walk to the top of the riser and slide a 55 gallon retort into position (or fill it up on its side and then stand it up and attach the lid) and there is a pipe coming out of that retort barrel which you connect to a pipe that feeds back into the bottom of the J-tube riser so you can use the retort gasses to fuel the burn after the initial load gets the process started. Having a second barrel attached to the top of the riser which is a little larger than the retort, with a small gap all around for the exhaust to travel up the sides, and insulation on the outside I think would help heat it up faster, perhaps even using the rocket oven designs of recent kickstarter fame? Open the lid on the side, fill the barrel with wood, close the door and "cook", then open the lid afterwards and pull all the charcoal out?

That is sort of how mine works.  I like the idea of the door.  that would be a big improvement over mine.

Chris Kott wrote:

As to your prototype, shouldn't it be possible to have some kind of closure on the vents themselves? Seal the vents and you don't even need to take the retort off the heat first. Sounds like a one-person solution to me.

-CK

Forgot to reply to this the first time.  I'm sure you're right, there should be a way to do it.  A small handful of mud might even work.  If I used an actual closure, I think it would need to be fairly airtight to keep the char from smoldering away to ash.

To speak to the question of accessibility:
I grew up around my grandfather's welding shop, and learned quite a bit but it's been 25+ years.  It seems to me that some of the same techniques we used to construct portable cattle panels would work here, ergo short sections of 1" pipe coupled with "L" shaped lengths of 3/4" rod to make a hinge joint.  If one side of the retort were completely removable, it would allow easy loading/unloading/reloading of biomass for charring.  Obviously, it would be necessary to treat it as you would a top-loading retort with a high-temperature caulk-type material, but again, this particular wild hare only recently flushed, so I haven't gotten the entire concept worked out.  

There's a biochar forum here https://permies.com/f/190/biochar which I have posted to before.

Graham Chiu wrote:There's a biochar forum here https://permies.com/f/190/biochar which I have posted to before.

Thanks for the link, Graham.  I overlooked the forum when searching for a concept similar to what I've envisioned.  There's some intriguing stuff in it.  

Maybe one of the admins can add the biochar tag to this thread so it appears in both topics ( Is that how it works? )

The James Hookway biochar retort can be found on YouTube.
It has a fair amount of development behind it, and it essentially is a rocket built into the middle of a container of feedstock.
The rocket is insulated by the feedstock, which begins to offload,  feeling into ports in  the rockets combustion chamber.
The whole shebang is insulated.

This video shows an old technique for making charcoal and wood vinegar.
A small fire is built in one chamber,and the exhaust products and heat flow into an adjoining chamber filled with feedstock.
Exhaust from that chamber is diverted and condensed.
By measuring the exhaust tempatures,  the operator selects only the products she wants,  venting off simple steams and burning off dangerous tars.
Subsituiting a 4" batch box or 6" J tube for the small fire in the original design could improve efficiency.
Redirecting the combustible gasses into the burn chamber could be more efficient
still.
The design could lend itself to easy loading and unloading.
One could build it like a low bell,out of masonry.
Top loading, slopped bottom, emptying on one side.

https://youtu.be/fTOHBrFuh68