Wood Burning Kiln

Hi Everyone,

I have been reading the forum here for a while and love all the valuable information and input.  I have started off building rocket stoves and experimenting.  My latest project is to build a kiln for firing pottery.  

I have been doing some research on the web and came up with my own design, but will it work??   Would love some valuable input from anyone here with experience.

Have based it upon a Bourry Box as in the pic below:

Bourry Box



However I want the Ware Chamber Stacked on top of the Firebox, like a shoebox rocket design. Other design alternatives I have looked at are Wood Boilers which are fan operated or the Walltherm range:

Wallterm



I would like the flames to go down the way, but then travel up the sides of the firebox into the ware chamber.   See my "cruddy" sketches:

Sketch


Lots of queries I'm sure, but what anyones initial impression, will this work,  Maybe have a Fan blowing air into the Firebox, or some kind of arrangement at the exhaust with the fan blowing up the chimney to create a suction?!?!?

Open to questions and insights, propbably looking to start a trial soon.

Best Regards

Duncan

Hi Duncan,   Welcome to Permies!

I wasn't able to see most of your photos. Only the last one showed up. Could you try to re-post them again?
In the meantime, here are a few links I found that may help:

Ideas-future-rocket-ovens-rocket

small-Stoneware-Kiln-Designs

Rocket-Stove-Kiln

They are planning on building a rocket kiln at the upcoming Jamboree. Perhaps something you may be interested in:
Rocket-Mass-Heater-Jamboree-Wheaton Labs

Thanks Gerry, they are great posts.  I particularly like the double rocket.  

I was mainly looking at Batch Box rockets and Masonary Heater type arrangements, but this thing needs to get up to 1100 deg Celcius.

I|'ll see ig i can get the pics to work

Pics posted, hopefully they work and it makes sense.  I love the idea of the inverted "shoebox" design of the walltherm and think it could be designed to be made into a bourry box Kiln.

Duncan Pirie wrote:Pics posted, hopefully they work and it makes sense.  I love the idea of the inverted "shoebox" design of the walltherm and think it could be designed to be made into a bourry box Kiln.

Something's not working with your images.

trying again, apologies.  was using google photos, but now trying Imgur.  thats why i dont post much

another sketch for a batch style, not a bourry box.

try image again...

I'm not sure a batch box is really going to work well for a pottery kiln. You need fine control of the rate of firing for a lot of the early hours, and a batch box is pretty much a set-it-and-go thing.

I build medieval-style earthenware kilns (getting to cone 02 on a good day) on a demo scale, and even these small kilns need a firebox about 16" wide x 14" high x 4' long, with the fire started outside the firebox and gradually moved inside and made more intense. At the peak, you need to add a log every few minutes and cannot add too much at once or the temperature will fall and you will get heavy reduction and lots of black smoke. I am in favor of a rocket-style combustion core for a kiln, but I think the variable rate of fire needed would necessitate an L-tube or maybe a large J-tube rather than a batch box.

Thanks for the input Glenn,  You are absolutely correct about the steady and low temps at the start of the firing cycle.  

I have already tried an L-Shaped rocket stove, made out of firebricks, held together with clay.  This rocket had a small chamber for pots etc...on my first attempt I lit a small fire and then continued to stoke it.  Within about 1 hr, I heard the familiar "popping" of the clay pots.    

On my second attempt, I started small fires with cardboard and paper, each hour for 4 hours until things started to heat up.  I think I still fired too quickly as although the pots survived , looked like they had vitrified and sounded like ceramic when I tested them, some were grey in the middle..I forget the name for this, but means it was fired too quickly and not enough heat work.

The small Kiln was then destructed and I built a new chamber for a Weed Burner on propane to be the heat source.  Similiar to a raku kiln, but with firebricks on the outside and ceramic fibre on the inside.  This also heated up too quickly, but was certainly more controllable. I actually managed to bisque and glaze some earthenware pots with this.  Although I ran out of propane very quickly.

I think my intention would be to have propane burners incorporated into my design, to allow for slow early heat up to around 400 / 500  Celcius and then use wood.  I love the look of wood fired pots and would expect each firing to take 24-36 hours.  

I would use modern materials to retain the heat within the kiln.

I would also like to avoid that black smoke each time the firebox is loaded.  With this in mind the best options are gasification (pre heated secondary air), complete combustion and the bourry box is an excellent example of achieving this.  

I have also experimented with TLUD Gasifications stoves (small ones, made out of a SS flue section) and they didn't smoke at all, I might even put one of these into the firebox at early stages to slowly heat the kiln up to temps.  Only issue with these is that once the fuel is in, you cant add more, easily.  

I wanted the ware chamber to be approx, 2ft x 2ft x 2ft, the firebox would be similiar size or larger.  I did run out of stoking room on the first wood kiln, but mostly from the embers building up.  

Dont know if my vids will work:

Fire Kiln, in Oxidation - Just make out the blue flames here, didnt have a temp gauge, but think around 800 celcius

Video- Oxi


Same Kiln in reduction (i Think)

Video - Reduct


Would love to trial build this and have some input into this, before committing to the cost of the modern materials.  
Maybe a clay brick built one without all the insulation etc would let me know if its gonna work.  

Anyone have any experience of Fast Fire Kilns, such as Olsen Fast Fire Kiln, this one is pretty much a L Tube Rocke Stove on a large scale

    Howdy Duncan,

          I like your project and the advice offered so far. It's an interesting take on the rocket stove concept. Perhaps a comparison is in order, in the sense of understanding what wood fired kilns do as compared to the RMH. The Kiln Book by Frederick Olsen seems is a good reference point for the comparison. It's full of those kind of measurements of space, mass and flow of gasses that make a wood fired kiln work. Of course, if you're doing this as your own fantastic exploration without any specific desired result, such as kiln efficiency concerning wood or controlling heat as in work well, please disregard the above unless it fits with your goals.

      Best of luck in your project!

      Thomas


       

Thanks Thomas, I have been trying to get hold of that book for a reasonable price, but are unfortunately like hens teeth. Especially here in the uk.

Done a wee bit of research to date and trying to make this as efficient as a wood kiln can be.
Would love to have attended a permies workshop and see the great work that’s happening. Hopefully in the future.

Those are good videos of good oxidation and heavy reduction firing. When reducing like that, the temperature is actually falling in my experience.

The kilns I build have ware chambers close to 2' diameter x 2' high, with the 16" x 14" x 4' firebox below. They are made entirely from cob, with dried grass clippings mixed in for wet strength and to improve the insulating qualities (the more grass, the better insulation but the weaker the cob). They take 8 to 12 hours to fire and can be opened (carefully) the next morning. I candle for up to 3 hours before starting to ramp up the temperature. Using good sized logs for most of the firing (typical commercial firewood), the logs hold together long enough to mostly burn up before collapsing into coals, and I can avoid the firebox choking or having to rake out coals. At the end I use smaller wood that burns faster and hotter but tends to build up a coal bed and choke the flow. It is a matter of experience to balance the feed rate. The wood must be really dry (like seasoned off the ground under cover for a full year) to burn hot enough. Damp wood will never get the ware to cone 06 no matter how long you fire.  With good dry wood, I need around 20 cubic feet more or less of wood for a firing.