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Kiln Conversion Updraft Downdraft Chimney?


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#41 jrgpots

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Posted 16 October 2015 - 03:28 PM

As a trial firing, you may want to run a load of insulating bricks "pretending to be pots."  You can check out the ramp speed and figure out the chimney damper systems this way.  My conversion needed multiple firing "tweaking" to get it above 1800.  It will save some pots and the insulating bricks can act like a loaded kiln without ruining any ware.

 

Jed



#42 High Bridge Pottery

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Posted 17 October 2015 - 05:24 AM

I like the idea but a perfectly fired kiln of bricks would annoy me more than a terrible firing with pots. I hope that I have read enough and seen/done enough to have made a fairly successfully kiln, only time will tell when I fire the thing up  B) everything will be figured out on the fly.


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#43 High Bridge Pottery

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Posted 18 December 2015 - 02:43 PM

Little update on my gas kiln, hopefully going to sneak a firing in before Christmas. Had a dry run with it today to make sure everything was going well. Popped the burner on maybe 3-5 PSI and it got to 250degC in about 30 seconds. Plenty of heat making its way out the chimney but I won't really know if it has holes till I am up in reduction. 

 

All looks very promising. Had the stand built for the chimney through a friend, got some pots to make in exchange. Thing fits like a dream, just needs some wheels and bolts.

 

Some kind of burner holder is also in the pipeline  ^_^ Still working with the Raspberry Pi but spent £60 on a reader that can use any type as that is taking forever!

 

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#44 High Bridge Pottery

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Posted 22 December 2015 - 07:44 AM

The first kiln firing failed quite badly. First of all it seemed to be going great, 200C/h up to about 800 which then stalled out wavering between 820-850 although it got up to 900 when the wind was blowing well. Made me thing the stack is much too small. Quickly grabbed some other bricks and put them on the stack. It then climbed to 950 and sat there. I tried everything to get it to move higher but nothing would work, more gas, less gas, bung in the top out and every burner position. 

 

As it was getting hot the stack moved apart, or the heat just showed the gaps in the bricks and I think I lost even more of the pull.

 

Pots look like the have some good body reduction from me messing around with the gas too much at 900. 

 

Going to cement the stack and add a few more layers of brick. Seal it properly into the kiln and probably add a metal tube to that for even more stackage. There was a definite lack of oxygen for the gas. I would have liked to get away without cementing but looks like that is not going to happen.

 

Hopefully have it working by the new year.

 

 

 

 


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#45 Mark C.

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Posted 22 December 2015 - 11:24 AM

I think your stack needs to be double what your photo shows
How about a pipe extension
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#46 Diesel Clay

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Posted 22 December 2015 - 01:42 PM

+1 for pipe extension. It'll taper things slightly, which will increase your draft rate as well.

#47 High Bridge Pottery

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Posted 26 December 2015 - 01:49 PM

My dad has a friend who just finished installing a log burner so traded some engine oil for his cut off. Saved some money there. Spent a few hours today cementing layers and carving a hole for the tube.

Leaving it to set up over the next few days then I will finish it off. Need some inspiration for sealing the chimney into the kiln. Thinking cementing some bricks that would lock into the chimney. Have a think over the next few days.

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#48 RobS

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Posted 27 December 2015 - 09:44 AM

If you didn't want to cement it, you could make a couple of kaowool or fiber board gaskets then use a couple of long strap clamps to hold the stack to the kiln.  Since your frame is solid and one piece the stack shouln't move relative to the kiln so clamping it in place should be mechanically sound.  It would come apart quickly without busting up cement if you intend it to be portable.

 

Just a thought.  Good luck with whatever you devise.

 

BTW, on an off topic thread that you started.  Have you looked at something like an Omega CN7823 for your controller project?  It seemed like the Pi solution was extreme effort, but very interesting.  The Omega is a PID controller with a ramp/hold feature.  It has RS-485 communication built in, you'd just need a rs-485/usb converter or the like to talk to it with labview or something similar.  I have one that I use to run a couple of old manual kilns.  I don't have any comms enabled yet, but it's a great digital controller for the price.  I put it in a box with a SSR, and I can plug either kiln into it.  For the mechanically/electrically adept, it's a fairly low cost digital controller project.  I bet I don't have over $200 in the whole thing.



#49 High Bridge Pottery

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Posted 27 December 2015 - 01:58 PM

I have 20 metre of ceramic rope that could do the job. Probably going to use some to seal the metal tube to the stack. Been thinking about using that for some kind of seal. I might get away just strapping round the kiln and chimney to keep it together.

 

I will have a look into the PID. The Pi projects is going to be a slow burner anyway, bought a thermocouple reader so I can at least read what temperature my kiln is while I work with the Pi. Going to be a lot of effort but I feel it will be worth it in the long run.


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#50 High Bridge Pottery

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Posted 14 January 2016 - 06:06 PM

Cemented each layer together and added two more layers of brick. Going to strap each layer tomorrow and fire it. Hoping gravity will work at keeping them together up and down. Also added some rope and kiln cement to the exit from the kiln but forgot to take a snap. 

 

Drying out the cement a little. It now is 6 foot bottom to top. Will take better ones tomorrow.

 

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#51 High Bridge Pottery

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Posted 16 January 2016 - 09:09 AM

Ceramics always temps you into thinking you know what is going on. Tried firing the kiln with the new stack, still wouldn't go above 950.

 

Tank also froze up as it was emptying, started not going above 0.5psi. Luckily 2 min away I could buy a new tank. Still didn't help the kiln problems, whatever they are.

 

It looks good :D if only it would work. Maybe my exit flue is too small. Right now I have no idea. Probably the usual things, lots of small problems adding up to it not working.

 

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#52 neilestrick

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Posted 16 January 2016 - 10:19 AM

Does your burner have an air adjustment? My other thought is that there's not enough firebox space inside the kiln. Third thought is that you just don't have enough power to deal with the thin kiln walls. Part of the problem with these electric-to-gas conversions is that you have to have a crapload more power to deal with the thin walls, but you don't necessarily have enough firebox space to deal with that kind of power coming in. A single burner may be too much for that small space to deal with. Multiple small burners may work better. Do you have a bagwall? Is there a damper on the chimney? Just thoughts, no idea if they'll actually work.

 

I built one of these once. It was a conversion of an old square Amaco top loader. I used a pair of very small power burners on it, with an external downdraft chimney like yours. The chimney was not taller than the kiln, though, because power burners do not require the degree of secondary air that venturi's do. So using a power burner may be a good option. You can build a simple one for the price of a blower and some pipe, under $100 (without safety systems).


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#53 High Bridge Pottery

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Posted 16 January 2016 - 05:47 PM

No air adjustment although I am wondering if I could modify it somehow. I think the burner has the power but I am not using it right. Not much space for the burner to burn in or really a bag wall. Probably not stacked well either. My shelves are probably a little big.

 

It's just funny how doubling the stack did nada so there is obviously another problem stalling it out at 900. All seems to go well and then it just stops dead there going up and down 10 degrees.

 

Can I force air into the kiln not with the gas or is that a bad mix and idea?

 

I did read that 1inch square for every 8,000 max btu so I seem to be ok there. At 3 psi the burner output is 60,000 btu and the kiln is 0.6 cubic ft.

 

I actually did the maths wrong earlier so think my flue size is too small. I have a 1 inch radius if I remember right not 2...giving me 3 inch not 12. That could be the issue. I didn't actually post the maths, just double checked wrong in my head. DOH. Have to triple check when I am back at the kiln.


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#54 High Bridge Pottery

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Posted 11 February 2016 - 10:38 AM

After making the flue bigger and adding a 6 ft stack I am still not getting over 1000c. I did read that the stack should be about 9ft or bigger but I just don't feel safe making it that big the way I am set up. Made the flue 3 by 3 inch which should be enough for 60,000 btu which is my overestimate for amount of power.

 

Moved onto making my own forced air burner to try and navigate this issue. It is definitely (maybe) a lack of oxygen and I think whatever I do to the draft will never get me into an efficient firing.

 

Got the pipes, ordered a mig tip and tubes for the orifice and haven't figured out the forced air yet but once I have the orifice in and sealed that will come. Orifice will go in the top and turn 90 to be in same path as the air going in the back end.

 

I have 8 inch of mixing tube from where the orifice will be, hopefully that is a good amount of space. Can always extend the tube if needs must. 1.5 inch pipes.

 

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#55 High Bridge Pottery

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Posted 15 February 2016 - 10:22 AM

More burner shots, today the plug arrived so I drilled a 1.5mm orifice in, managed to snap the drill bit so carefully filed away the rest. Not exactly centre but I am happy. It looks good, let's hope it works. 

 

Also added a ball valve, need to get one of those flame failure device or take it off my old burner. Not sure what to do about the burner tip, just leave it as the threaded connection? I am not sure.

 

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#56 JBaymore

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Posted 15 February 2016 - 08:35 PM

You need a flame retention nozzle of some sort on the end.  Otherwise the turn-down ratio will be terrible and you'll constantly be dealing with back burning or fluffing out.

 

A pipe cap with multiple holes drilled in it will work as a 'poor man's alternative'.  You'll have to experiment with the pattern and the size of the holes.  Use a close nipple to mount it to the ell you have.

 

Better to just purchase one... they are more "engineered' than you realize.  Not expensive.

 

best,

 

.................john


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#57 Mark C.

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Posted 15 February 2016 - 08:51 PM

Johns suggestion is spot on when I used homemade burners I bought flame retention nozzles -your pipe size is the right size for them as well.

They are cheap.


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#58 jrgpots

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Posted 15 February 2016 - 11:16 PM

This is my poor man's power burner.

I bought a 3" turbo fan from an Auto parts dealer for $29.00. It is a dc 12 volt blower that produces 145 cf/min.
I attached an old 12volt DC adapter.
I fashioned it to 3" black pvc pipe.
I fitted a cd disc to act as a damper to the airflow.
I fitted a 3" to 2" reducer on the burner side of the fan.
I fitter a sheet metal tube to the T piece.

The burner nozzle is drilled to 3/32 and the burner is easily adjusted from 1psi to 5psi. The airflow damper places the burner easily into reduction.

Jed

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#59 Mark C.

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Posted 15 February 2016 - 11:40 PM

Jed one of these flame retention would really help you .

http://combustiondep...duct_list&c=395


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#60 jrgpots

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Posted 16 February 2016 - 09:32 AM

Thank you.




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