riserless core recycled ceramic kiln experimental project

Hey Rocketeers

It been a while since my last post but I thought Inwould share something I am experimenting with.

Using the Tiny Cook stove, (thanks Walker Stoves) riserless core and an old kiln that I picked up for free I want to combine these two.

I have included some photos of how it is currently looking.

I was wondering about how to position the exhaust.

I have the option to go out of the top through the lid of the kiln.

However I am also considering going out the bottom or bottom side to allow stratification.

I have only my rocket mass heater to draw on previous knowledge. However I would love to hear other people's thoughts on how they would make the exhaust.

looking forward to hearing from you

Fraser

I would not go out the lid if you can help it.  Mud’s kiln videos mentioned they kept getting dust and debris falling onto the pottery as they messed with the chimney.

Simon leach has a lot of videos about converting electric kilns to propane, there is a lot of good info on exhaust flow and heat distribution. You may or may not want stratification, depends how you load and run the kiln.

Thanks man. was unaware of Simon leach. just checked out some videos.
looking at his videos his solution is stratification right.
I mean that he has the flue gasses existing out of the bottom of the kiln by constructing a wall with an opening at the bottom.

I am really sceptical of whether I will reach the temperatures with wood but I guess I have to try.

does anybody know what temperatures are generated by riserless core.
probably a stupid question that depends on many factors but I'm curious

It would depend on the system size but you could expect around 1000 -1200c in the  hottest mid air stream and around 500c on a cooktop.

I moved my setup outside today  and got some wood.
The wood I had is admittedly not dry enough but it's what I had. probably setting myself up for issues.

With the temperature probe I could only reach

240C
464F
it's currently slowly climbing
off a small batch of wood.

I have kept everything to 225cm2 for the CSA

I am considering if adding more wood will keep raising the temperture  

Or whether insulating the core with ceramic wool would make a big difference. It's something I was planning to do next.

anyways. please share your thoughts and ideas.

Not sure If I can reach the temperatures for baking ceramic

some ideas of the inside of the kiln

exaust

Hi Fraser,
Some observations from your photos:
I don't see an external chimney. Are you relying on the kiln to act as the chimney coming out that slot in the top? If so, then that would be a problem. A riserless core still requires a tallish exhaust chimney that will provide the necessary draft for a hot, clean burn.
Matt Walker's riserless core for example is designed to have bends and twists in the combustion area to give the gasses enough time to mix and fully combust before sending & extracting the heat in whatever ways you choose. In your case a kiln.  Think of the kiln as sort of a bell or stratification chamber instead of a chimney and I think you'll be much better with achieving higher temperatures.
Secondly, all those kiln bricks are sucking up a lot of the initial heat prematurely before things start to really heat up.

OK.

thanks for the pointers.
I thought might get away with using the lid as a chimney being that it is very will insulated.
And I don't have any 150mm pipe.
I will try to arrange this for my next test.

and also the shape of the flue is now not round. more like a Rhombus, ( not a rhombus) but it's not round.

perhaps I will make something like a box on top and then a round opening for a pipe.
or a superwool riser

If you have purchased plans from Matt, he offers free consultation. He is very easy to talk with and is open to many ideas for expanding the uses for his stoves.

Look forward to seeing the results of your experiments

Can you post a quick sketch or diagram of the flow through the kiln? I'm not quite clear on how the combustion gases travel just by looking at the photos and I want to see if there's a potential restriction or counterflow that's working against you.

requested quick sketch

OK, no sign of restriction or bottlenecks. I'd say try a nice tall stack on it to encourage draft. Double-wall flue pipe, if possible.

Fraser,

Before you start modifying flues and design, please build the riseless core from insulating bricks. Some designs are more material sensitive than others. I have built this core over a weekend from old red bricks. I was not able to boil a small pot of water and what abut firing ceramics. All the heat was being absorbed by the walls and transferred outside through them faster than it was generated by combustion, so it would be good for heating a house, but not cooking or firing. Your bricks are denser than mine so I suspect even worse performance.

OK. I will try to source some insulated bricks.
But I have trouble finding these things in The Netherlands where I am based.
I used to build with CFB, the RMH I build in my ship is made from this. But it has not been available here for two years.
And the bricks you are referring to cost 12euro (13dollar) each. I have only seen them at specialist ceramic shops.

So would encasing the core with superwool be beneficial? This is readily available.

Wrapping the core in CFB will help - not as much as using insulating firebrick but at least once the core gets up to operating temperature it won't be shedding so much heat. That would be a lower cost interim solution and might even do the trick.

I think you would stand more chance with a 10” batchbox and a step ladder.
Vermiculite board might be available to you as it is widely  available in Europe, it would certainly last long enough to do some testing but might not last long term.
I am all up for experimenting and I really hope you find some success but  I think there are better ways.

Fox James wrote:I think you would stand more chance with a 10” batchbox and a step ladder.
Vermiculite board might be available to you as it is widely  available in Europe, it would certainly last long enough to do some testing but might not last long term.
I am all up for experimenting and I really hope you find some success but  I think there are better ways.

just curious what you do with the step ladder?
What are the "better way".
please share

Phil Stevens wrote:Wrapping the core in CFB will help - not as much as using insulating firebrick but at least once the core gets up to operating temperature it won't be shedding so much heat. That would be a lower cost interim solution and might even do the trick.

as I stated, cfb is not available here.
would ceramic fiber blanket suffice?

A step ladder to reach  the kiln as a 10-12” batch box is going to have a four foot tall riser.
I just dont think there are enough BTUs coming from a small core, you are only burning a small amount of wood.

You can also paint the interior of the bricks in the core with zirconium based coating, for example ITC 100 HT. It does miracles.
Let's calculate how much energy you need to fire to cone 06.
I will be using this page as the reference:

Propane kiln burner sizing

I will use imperial in calculations and will switch to metric.
Let's assume your kiln is 5 cubic feet, so for 6 hour firing (quite fast) to cone 06 (quite low) you need:

15000 BTU * 5 * 6 = 450000 BTU
450000 BTU/3500 = 129 kWh

It's a lot of energy. Matt's riserless core is equivalent of 150 mm batch rocket, so in theory with 2 firings can produce according to batchrocket.eu:
1.9 kW * 24 h = 45.6 kWh
It's 3 times too little, so in the period of 6 hours you would have to burn 6 full batches of wood.
This calculation assumes that you have NO LOSS of heat through the walls and the firebox opening.

If we switch to 15 h firing then you need:
5000 BTU * 5 * 15 = 375000 BTU, which is 107 kWh = 5 full firings. With such a long firing time any heat loss will have more time to work against you.

Per Fox James recommendation, with 250 mm batch box you will have in theory 4.5 times more power, but this power will also leave through the walls of the firebox, riser and the opening if not properly insulated and blocked. 250 mm or bigger batch box will need much more material and it would be more economical to build it from insulating boards, fabric, etc.

My bad, using an ambiguous acronym. Ceramic fibre blanket. The stuff you have is probably great.

so guys. I heard the advice given.
I know that the temperatures I am aiming for will be a challenge but I think I have the time and will power to try and perhaps fail. Or perhaps something comes of it. I will see.

Today I returned to the store where I purchased the bricks you see in the photos.
I asked if they had low density fire bricks. very light weight.

And they did. they also had a dented double insulated stainless pipe. which incould buy for 10euros. so I will be doing some testing and adjusting with this new material

Really interesting discussion.  Although this may be naive, would finding a large barrel that would fit around the exterior of the kiln and filling the space between the barrel and kiln with vermiculite/perlite provide for more insulation to reduce system heat loss?

Richard,

It would work and probably much better, because most of the heat would be contained. If the door was covered with insulative material then my calculations above could be applied to such a system.
The barrel would need to be at least 820 mm diameter (32") for the riserless core that is 575x575 mm.  Barrel of this size would be hard to get. It would be bigger than the interior of largest 3-phase round kilns. It would be easier to weld 6 pieces of sheet metal to make the housing for the core and then insulate the walls from the inside, but it would be off topic, because Fraser already has the kiln and holes drilled :)

Does the BTU increase if the firebox is extended out and longer pieces of wood could be added.

There are probably some huffs and puffs and shaking heads out there.

but needed to ask

this is my new insulated core.

update on chimney and firebox.

The port at the back of the firebox is suspiciously smaller than I expected. Is this correct or did I get something wrong

Cristobal - I was using the term "barrel", but on a bit of consideration, feel that a piece of culvert would be more appropriate and not as difficult to find in sufficient diameter.  Since that would not have a top or bottom, it would not require as much work to place over the kiln and could be as thick as wished to enhance heat retention.  I have noted short pieces of culvert lying around local town highway departments for several years.  Seemed appropriate to attempt to make use of something that was pretty much going to waste.

test of new core and chimney.

640c
1174F.

That's much better result, but still too low. You could try wrapping the core on the sides and the bottom with some insulating material, but I think it will not be enough. You already have IFB bricks so you could try to build a 25 cm batchbox and see what happens. If the temperature rises to much more than 640 C then you will know which route to take.

Cristobal Cristo wrote:That's much better result, but still too low. You could try wrapping the core on the sides and the bottom with some insulating material, but I think it will not be enough. You already have IFB bricks so you could try to build a 25 cm batchbox and see what happens. If the temperature rises to much more than 640 C then you will know which route to take.

do you mean increase firebox only and leave all the rest as a 150mm/6" system
do  you know the detentions for a 25cm firebox? or where I can find out..

So I am hoping someone in the community can wade into this and help me with understanding this. I am not sure of which step to take.
I'm not an engineer so please don't kick me down.

So reading on batchbox.eu (website from Peter van den berg) the 150mm has a 1.9kwh

the dimensions are calculated for the batchbox.
a base measure, (the diameter of the chimney). For example 150mm. From this 150mm, one is able to calculate the size of the box, Height Width Depth.

From talking with Matt Walker, increasing the size of the batch box, ( making it wider) will have a detrimental effect on the air flowing through the stove. based on these measurements. I'm sure that all the testing for this has already been explored.

My question is. Does extending the length of the firebox so that more wood is able to be burnt have an effect on the power output?
I.e does more wood in the firebox make more BTUs and raise the temperature higher?

Would multiple burns.  one after the other before the stove cools substantially be able to add more heat?
Or is it limited to the volume of space in the kiln.

The core could of course be scalled up but then I would need a large kiln so....


Do I need to make a Hybrid wood and gas to reach those temps.




O

You could try using two units back to back on along side each other, or possibly use a fan to supply more air into the fire box.

fraser stewart wrote:So I am hoping someone in the community can wade into this and help me with understanding this.  

My question is. Does extending the length of the firebox so that more wood is able to be burnt have an effect on the power output?
I.e does more wood in the firebox make more BTUs and raise the temperature higher?

Would multiple burns.  one after the other before the stove cools substantially be able to add more heat?
Or is it limited to the volume of space in the kiln.

The core could of course be scalled up but then I would need a large kiln so....


Do I need to make a Hybrid wood and gas to reach those temps.




O

Peter gives this variable on his page -- Depth of firebox is 4 to 5.5 times base.
His page (looks like you have found it, but for others-   https://batchrocket.eu/en/building#dimension

Dragon Tech on cold winter days, has done back to back burns and has often mentioned it.  (Thomas R)   Just do a search for Dragon Tech and you will find him.

I have posted the question "just how hot does the top section get under normal operation" and did not get an answer, so apparently this has not been documented other than the suggestions of needing fire brick from the  top of the riser on up.  But looks like your kiln would have that covered.

In your case, it looks like your trying to super heat a "space" vs a volume of mass.  If you find your going down a unproven avenue, I would listen closely to Peter, Fox, Dragon Tech, Matt (all with testing and proven designs behind them)  

No matter the size of your firebox, a pottery kiln will need to be fired without interruption from start to finish. Not just back to back firings, but reloading before the fire burns all the way down so heat input never falters.

You also need to be able to start the first fire slowly so the kiln temperature does not rise too fast and explode the pots. That is a matter for control rather than capacity, though the larger the firebox compared to the kiln the trickier it is to meter it. In my wood fired, cob-built kiln, I start the fire in front of the firebox and gradually over the course of an hour or so move it inside for gentle temperature rise. The firebox is about 4' long and 16" high and wide.

Glenn Herbert wrote:No matter the size of your firebox, a pottery kiln will need to be fired without interruption from start to finish. Not just back to back firings, but reloading before the fire burns all the way down so heat input never falters.

You also need to be able to start the first fire slowly so the kiln temperature does not rise too fast and explode the pots. That is a matter for control rather than capacity, though the larger the firebox compared to the kiln the trickier it is to meter it. In my wood fired, cob-built kiln, I start the fire in front of the firebox and gradually over the course of an hour or so move it inside for gentle temperature rise. The firebox is about 4' long and 16" high and wide.

Hey Glenn

I went to see if I could find more info on your kiln. But the website on your profile is not available. Is there info somewhere else?
These are questions I had aswell.
As to controlling the burn.

I had three ideas.
complex ideas

Idea 1
Imagine that you have two fireboxes which can be slid into position. you can Load one and then when it's doing slowly alternate to the other one and back and forth.

you can then step up the wood amount to reach desired temp. you would also have double the wood.

Idea 2

Double shoebox, twice.
with two double shoeboxes based on 150mm system.
would make 2x1.9kwh
3.8kwh
The original kiln was less so I am guessing that the temp could be reached.

Only I am almost certain that heading these into the kiln through the same entrance of 150mm would cause an issue.


Idea 3.
I found a vid from Uncle Mud.
A simple Jube design means you can add wood and raise the temperature manually. sort of.
In this video however he is working with bigger kiln and chimney so perhaps needs that size to reach the 2100F/1150c temperature mentioned in the film

perhaps simple is sometimes better.


what do you think?

Fraser,

Double core will be very impractical. I would try building a 25 cm batch box with shortened riser.
Is your core hot to the touch on the outside when reaching 640 C in the kiln?

Cristobal Cristo wrote:Fraser,

Double core will be very impractical. I would try building a 25 cm batch box with shortened riser.
Is your core hot to the touch on the outside when reaching 640 C in the kiln?

The core is warm. Comfortably warm. So there is some heat loss there which could be grabbed by insulating the core.

A 25cm batch box would out 8.6kwh, (according to batchrocket.eu)
This little kiln is a 3kw kiln when electric. So with that logic a 20cm (meaning 4.4kwh) would do it.  I dont know if its correct to think of it like that or not?

What would happen with a 20/25cm core, connected to a kiln with a 15cm hole and flue? That will choke the stove right? by making it 20/25 I would use almost the whole kiln as a flue and have no room left over.
The flue could come out the side of the kiln i guess?

does anyone know if a double shoebox follows the same power output. this could be a simple build at that size?
Are there any sketchup models that are made for large batchboxes than the regulare 150mm.