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High Bridge Pottery

Kiln Conversion Updraft Downdraft Chimney?

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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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neilestrick    1,381

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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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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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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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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JBaymore    1,432

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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Mark C.    1,807

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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jrgpots    231

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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Great, thanks for the tip about burner tips  ;) Hopefully as you say Marc it will be 'plug and play' into my end pipe. Doesn't seem to be a UK supplier I can find easily...

 

I am not in front of my other burner now but I am sure it has no kind of flame retention nozzle, will have to take a better look next time.

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After not being able to easily find the part and having little money I decided to start drilling holes. Had a few extra parts left over. Used the biggest drill bit I had but it was still too small. Added pilot flame holes kind of randomly, maybe I should have gone with less is more but it is what it is now.

 

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The square looked like it would probably cause issues so I lopped off the top and cracked out some files and started making the hole bigger. My files are tiny so I could do with a bigger one but I am happy with the progress. Who know if it will actually improve the flame  B)

 

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neilestrick    1,381

Lookin' good. With the power burner you can get rid of most of the chimney, down the the height of the kiln anyway. A kiln shelf across the top can then function as a damper, which will allow you to adjust pressure in the kiln. The more adjustment opportunities you have in these little conversions the better.

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The aeropress makes my favourite coffee :D although it is getting a bit old and can shoot boiling coffee out the plunger if you push too hard. Not a good experience.

 

For the air, if I wanted to burn 100,000 btu/h propane I would need 1,000 cubic feet of air through the burner in that hour for complete combustion? Trying to figure out what kind of fan I can use. I don't think I will need 100,000 but better to have that much air just incase.

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neilestrick    1,381

A little 50cfm blower will be more than powerful enough. They make smaller ones, but they tend to be too small, like 13 cfm. I recommend putting a rheostat on it to slow it down, otherwise you'll have way too much pressure.  THIS

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Mark C.    1,807

The blower in Neil's link is perfect and it has an air control on side

The rheostat is also perfect for better control

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JBaymore    1,432

10 cubic feet of air for every 1,000 BTUs of heat value in the fuel is the 'rule of thumb'.  If you want oxidations conditions at maximum output, then you need to add more capacity to the air supply.  10% excess is typically adequate.

 

Remember that blower CFM ratings are stated in either free air... or into some static pressure rating.  The free air rating gets de-valued when you attach that to pipes, and direct the nozzle into a kiln,  and such.  Static pressure calcs are a bit too difficult to get into here.  Very setup-specific.  Rule of thumb.... get a larger capacity blower than what the basic idea calls for.

 

Nice job on your first "retention nozzle".  Guessing that it will work OK.  Not as good as a commercial one... but probably functional.

 

best,

 

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

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Thanks John, I could remember you posting that before but couldn't find it. I thought it was 10 but was not sure.

 

Has anybody ever tried using a compressor? There is a guy on ebay who sells forced air burners with a compressor but he never replied to my email so I gave up on buying one. Reason is I could do with a compressor anyway for spraying glaze.

 

My dads neighbour has two fans and a compressor that I think he is probably happy to lend if they fit the bill. Going to pop over tomorrow morning and see what's there and find a bigger file to make the hole as big as possible.

 

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neilestrick    1,381

Personally, I would hate to listen to a compressor running all the time during a firing. Seems like a good way to wear out a piece of equipment when you could just buy a cheap blower. Plus compressors are made to run high pressure low volume, which is the opposite of what you need in a burner blower. I think it would be really easy to get too much pressure and blow out your flame. 

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Ok, some good reasons not to try and go with a compressor. I still haven't been able to find the right fan without taking two weeks to be delivered from USA or China... Very cheap ones from China if I want 1000 units.

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neilestrick    1,381

THIS-  54cfm, cheap. Only downside is that it's got a rectangular connection rather than round, but you should be able to bolt it to a floor flange connection and still get plenty of flow.

 

Just noticed the shipping price. I'd have him quote you a real price since you're not international.

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rayaldridge    276

Just a data point for consideration:  I ran my oil burner with a squirrel cage blower until it died, and then I started using a Shop-Vac.  You can find them pretty cheap at garage sales, and they aren't much new.

 

Another thought:  If you use a cheapo blower like a Shop-Vac, you can adjust the air pressure by putting a T into the delivery pipe, and a movable flap over the open end of the T.  By opening and closing this flap you can adjust the air flow pretty well.

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JBaymore    1,432

And they are running so much excess... that you are paying for all the electricity to run the thing blowing cold air out of a bypass.  And noisy.  Not a great solution.

 

best,

 

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

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