Experimental Stove for Ceramic Glazing

[Robert]

Dear All.

Rocket stoves becoming more popular in Poland:) I have been ask for another one. This time by my friend ceramic maker. He wants me to build him the one for making Glazing for his ceramic work.

Now he uses a lot of wood and he heard that rockets are very efficient and they use much less wood. So time for the experiment. We will be building it in may, but i would like to gather some information and hear some of advice from you guys.

The most important thing is that we need to maintain the temperature beetwen 1160 - 1300C since this is required for proper glazing.

So I came with this kind of an idea:



For the doors i want to use some sort of a vermiculite plug.

And now some questions:

1. Which one i should choose for the project. J-Tube or Batchbox? I now that J-Tube will use less fuel, but if this will be enough for the heat in the chamber? Batchbox is more powerfull machine but also uses more wood... so what would you think...

2. The chamber for burning should be build in 2 layers as i think? The first one more accumulating, and the second one more insulative - just like it is been done in pizza ovens? Am i thinking right way?

[colinsaengdara]

I like this design Robert! I think you are on the right track with dense interior and insulative exterior, but I would suggest less density than a pizza oven or it will require too much time and too much fuel to get up to the 1160 - 1300C. I think making the interior from dense cast refractory 2.5 - 3 cm thick might be great and then insulate the box extremely well. From what I understand, you wont want to let the chamber heat or cool too quickly. That's where the higher density seems appropriate.

Have you seen this from Dragon Heaters? donkey32.proboards.com/thread/854/dragon-heater-outdoor-kitchen-oven

I think they have a great design, not so heavy that it will take forever to heat up, and should be maintainable with the right burner (I think). Maybe Sandy can chime in about maintaining such a high temperature. They designed it for baking, not ceramics. Maybe she could suggest whether you should go for a higher or lower density refractory mix.

Batchbox or J? You can easily use a larger j to get the amount of heat you want, and I think it's easier to control because you are always feeding fresh material in. Batch box burning might be too up and down for this project. Just my take on it.

[doggy1969bc]

i would go with a solid 6" heatriser and for the befor i think a batch box would do but a j -tube whit a feed of pellets would be more controabel
by that i mean an normal j-tube but with an insert 5"outer tube an 3" inner blocked on the end 5% pchannel 20% back opening in a sq 6" by 6". The pellet holder would rest on top of the feed and give room for the air to flow , channeling the pellets to the holder (i know the rocket stove is a bad exampel but i like the pellet burner )look from 3.00 there it becomes intersting youtu.be/_mAi5Omd_UQ i hope it heled

[Deleted]

Sorry to disappoint you, but in this respect a rocket cannot be a single % more effective than a traditional wood fired kiln,
not even a half %. To save wood kilns are usualy huge beasts fired only a few times per year.

You get this temperature range only when the chamber is filled with burning gas and the exit temperature still about 1000 ° C.
Waste heat could be recuperated at the chimney to preheat air.

Professional plans for a Small Instructional Wood Kiln.
ceramicartsdaily.org/firing-techniques/kiln-plans-and-diagrams/an-experienced-wood-firer-shares-kiln-plans-for-a-small-instructional-wood-kiln/

Fuel Efficient Kiln Design, forced air required due to cooling the chimney.
www.bartelart.com/firing/ecokiln.html

[calcifer]

Hi karl,

I'm also interested in building such a kiln, could you elaborate on your answer?

I am assuming that there is no efficiency to be gained because a traditional wood kiln burns its produced gases to completion, due to the high temperatures in the system.

Actually I have multiple goals for my burn system.
1. high temperature ( ~ 900C ) kiln for ceramics production.
2. medium temp. ( ~ 400 to 600C ) for pyrolysis and charcoal/biochar production
3. reuse waste heat for drying fuels... i want to fire with coconut husks.

If there is indeed no added benefit for a rocket stove burner, then I'll focus my efforts on recovering heat from #1 to achieve goals 2 and 3.

[Deleted]

Feb 2, 2014 0:03:13 GMT -8 calcifer said:

I am assuming that there is no efficiency to be gained because a traditional wood kiln burns its produced gases to completion, due to the high temperatures in the system.

Yes.

[ridder]

Hello,

If it is true that if all the gasses are burned the thing is efficient? Is it not also important that the exact amount of oxygen is applied. The manner of burning the gasses should be right to?

sorry for my english i am from holland

[pinhead]

Mar 12, 2014 12:37:21 GMT -8 ridder said:

Hello,

If it is true that if all the gasses are burned the thing is efficient? Is it not also important that the exact amount of oxygen is applied. The manner of burning the gasses should be right to?

sorry for my english i am from holland

Efficiency can refer to thermal and chemical efficiency.

Chemical efficiency rates how well the volatiles burn.

Thermal efficiency rates how much energy is utilized. In other words, how much heat stays in the building versus how much heat is lost through the chimney.

[pyrophile]

Wood fired kilns may have very different designs but many of them have not a very good efficiency. Even at high temperature, mixing gases and oxygen can be bad (too much velocity of the gases, or no dedicated place for mixing place, etc).

I think that a problem with rocket ceramic kilns is to be powerfull enough.

In opposite to what has been supposed for a long time, it is not necessary with ceramic kilns to bring inertia in the kiln structure : many professionnal types use refractory wool for the body of the kiln, surrounded by metal or bricks. The inertia is given by the objects being fired. It is true for little objects but also for bricks. The professionnal kilns I am thinking about are using gas, not wood but it does not make any difference.
Bell kilns exist in Europe since the 18th century (much before in China) and have efficiency and homogeneity. I should add that chinese or japanese (or korean) kilns are still choosen nevertheless, for various reasons.

A vault or simili vault is better than a flat roof.
Benoit

[stephenson1]

Does anyone know the maximum exit temperature of flue gasses at the top of the heat riser in a rocket stove? In my imagination, the taller the riser the more heat one can get, provided one can keep up with feeding the fire and not get bogged down with coals blocking the tunnel. But there must be a practical top end temperature. Is it even theoretically possible to sustain 2500 degrees F -for say eight hours- with a rocket stove.

If so, I'm definitely interested.

[pyrophile]

I visited a big round inverted draft kiln dedicated to tiles and perforated bricks (built in the 1930's, I think).







It was surrounded by wood/coal vertical feeders/entries connected insides to vertical "heat risers"! They were actually J rocket burners!
You can hardly see two of them on each side of the door, just below small arches.


I tried a rotation without success!



I add that wood was used first to warm the kiln then coal was used for big heat phase (gives more heat, lress expensive, more convenient, etc.).
But wood only have also been used in those kilns, without coal.
I am planning to build a kiln for bread oven firebricks : with friend, we make compressed earthen bricks and we fire a few of them in a ceramic wood kiln to sell them as bread oven bricks. The other are sold for building (inside the house as they are crude and don't like water).

[pyrophile]

Here is another brick kiln.
You can see that there are different ducts for secondary air (I found three! and one for primary air).







Here is the link to be able to enlarge the image and see the full patent : www.google.com/patents/US508003

[Robert]

Dear all. I just would like to inform you that we did it. We build the experimental rocket kiln for ceramic glazing during the Festival Of High Temperatures organized in Poland. Our aim was to check if we can get around 1100C to properly burn one type of glazing. So we build a very simple stove based on Winiarski L-Tube design. Results was quite amazing. The highest temperature measured was 1160 and our thermocouple died. I am quite convinced that with the batch-box design we could get much more... next year we are invited too, and our goal will be 1260:)

Check out few pictures from our build. And stay tuned for some more in a near future

1. So we started our construction based on two barrels. Yes we all love those barrels, dont we?

2.Modeling input and output.

3. This will be the chamber for burning. Just a barrel insulated with 5cm ceramic blanket.

4. Simple l-tube design. Later the barrel will be filled with perlite.

5. And here it is. Our beloved perlite...

6. Few objects are placed on the shelve... We used the glazing that supposed to be used for "raku" technique... a low temp ones (they need 1100C).


7. Our chamber is placed on top and we are preparing small, chopped pieces of wood.

8. Fire!!!

9. And this is a proof We reached 1123!!! Later we came up to 1160. And we used very little wood. Everyone was excited


So we are happy to find out that rocket kilns can be used and we can burn ceramics in a very efficient way. I would like say thanks to all of you who has inspired me, and biggest thank goes to Ed van Dijk from NL whom i had wonderfull exchange of thoughts:) Thank you ED.

[Dan (Upstate NY, USA)]

Hey I wanna see the pottery that came out, any cracks from getting to that temp so fast?!

[photoman290]

he did say it was a glazing kiln,so presumably the bisque firing was done in another kiln? if so there shouldnt be any cracking?