I was burning biochar again today and one of my neighbors, who makes ceramics, was asking me questions. He wanted to know how hot it got in there. I don't actually know. I just tried it and it made good biochar. I have mentioned before that I don't feel that I use the energy of the burn very efficiently, and I'd like to find a practical use for it. I use a 55 gallon barrel, with a TLUD and chimney. I drench it with water when it is ready.
Has anyone on this forum used their biochar set up to make ceramics?
A flame cap burn reaches about 750 C in the active combustion zone. A TLUD, during the most rockety phase of its burn, could do the same, I think. The trick would be setting up a firing shelf that didn't shift or settle as pieces of fuel around it get either consumed or pyrolysed. Someone somewhere must have tried this.
I've thought about a box that would go into the middle of the burn in a kontiki with pottery inside it for firing, but this never went past the brainstorm stage. I'm more partial to the rocket kiln ideas coming out of Wheaton Labs at the moment. Looks more controlled and manageable to me.
Great info and perspective, Phil. I was also thinking that with my TLUD barrel with chimney, some kind of retort metal box might work best. I had forgotten to think about how the wood inside falls after burning and that might not be optimal ! for pottery. Yes, probably one of the flat burning methods like a trench or a kon tiki might be better. I don't know if it would get hot enough. I'm not really much of a ceramicist. I'll have to ask him.
A tlud could vent into a kiln, taking the place of or supplementing the rocket stove used in the experiments cited above.
Properly designed, the tlud powering the kiln could be swapped out with an identical one,to have continuous heat with only intermittent tending.
The pit or trench methods have the usual advantage of needing little or no fuel prep.
They also allow for bigger peices to be fired.
It would be boon to self sufficiency if one could fire sections of clay pipe successfully.
A huge earthen ware cauldron would be a sought after work of art, more so if it could be cooked in.
My favorite use would be the creation of rocket stove cores, something that Flip and Jon Anderson pioneered using unfired rocket stoves to power the kiln that made fired rocket stoves.
I think I can see one way to do what you're talking about William.
If I put another 55 gallon barrel on top of mine, that has the wood in it, I could use the one above, fill it with clay and then it would fire. I could put my chimney above the second barrel. My friend suggested bisque fires (pure clay) instead of the glaze.
In other kilns, that were actually designed for clay, I have stacked the clay pots with ceramic shelves. My main concern is that they would fall over. One would have to be careful. Is this what you were talking about? I have known for some time that your metalworking skills are way above mine, so I might not be getting the idea.
There are other techniques that seem even better adaptable to use with a tlud.
Sawdust kilns seem to be very bad tluds, filled with sawdust and pottery to be fired.
The reason I call them bad tluds is they are lit and left to smolder.
I like that they use regular bricks plus metal mesh to stack the peices to be fired.
The sawdust protects the peices from direct heat, from the metal mesh and from each other.
There is a pit (trench)kiln method that uses sawdust to surround the peices at the bottom of the pit, then covers that with metal mesh to protect the wares from the solid fuel.
After the fuel is burned down to embers they pit is covered with steel roofing and left to cool.
It's very much like a trench charcoal burn.
Instead of the bottom up of a charcoal making process, the fuel in the pit kiln is burned from the top down, which might add need thermal protection to the process.
Even so, I think firing pottery in the bottom of a charcoal making trench would work.
Edit: I wonder if the Amazonians were actually firing their ceramics in their terra preta pits?
Ask the ceramics guy to give you different rated cones to test.
They re like incense cones and at certain temps they bend or break.
Start with low temp ones maybe in different places in the barrel.
It would be good for you to know as well. There's a sweet spot for the best biochar and I think I read that it's about 700F much higher than that gives poorer quality.
I've just started to learn about it.
I'd like to find an affordable way to build one that I could operateinside a greenhouse with 30 ft of chimney running through a rocketstyle bench to salvage virtually all of the heat, which is just a free byproduct of the biochar.
And I have much more free time in the winter for making it.