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help needed evening out my kiln temp differences


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#41 docweathers

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Posted 21 March 2013 - 11:13 AM

This relates to a project that I've been contemplating for my torchbearer.

I thought about building a heat exchanger around the exhaust port , then pumping the hot air back underneath the kiln so that it will be picked up by the burners. this would hopefully recycle some of the heat and feed warmer air into the bottom of the kiln. this might be particularly useful for me since where I fire the kiln it is often 30 to 40° in there. So it's getting very cold air coming in the bottom. Air few hundred degrees warmer might be helpful.

Has anyone tried anything like this?
Any thoughts about this strategy

Larry

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#42 shoshi

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Posted 27 March 2013 - 10:57 AM


Hello,
I have an Olympic torchbearer gas kiln model 2827G. It's a basic updraft with 4 venturi burners and I fire it manually using cones and a pyrometer with 2 leads to monitor the temperature. I've used it for bisque and oxidation glaze firing-both low and high up to cone 10. The problem has always been the temp difference between the bottom and the top shelves. There is usually around 100 degrees celsius difference (sometimes more) with the top being hotter. I've tried packing the top denser than the bottom with some success. I also tried moving my shelves to act as saggers with the hope it would redirect the flame. That made the bottom even cooler and I aborted that firing until I could rearrange the shelves back to usual configuration. The longer I fire it, the less difference there is but the longer the top shelf is at a mature temperature so it can end up over fired and the bottom under fired. Does anyone else have this problem with this kind of kiln? Any ideas on how to solve this?
Thanks


Hi,
I have been firing a 2827G for the past year with the same disappointing problem. I have tried the diverting flame on two burners, the self 1 1/2 inches from the top, packing more densely with staggered shelves - but to no avail.
I deduced that it was colder at the bottom because more cold air was being drawn in via the rather large burner ports in the bottom of the kiln. Which was also the reason that I couldn't reduce the bottom half of the kiln. What I tried was to take 4" standard insulating bricks and drill a 2" hole near one edge and mitre the edges to fit snugly into the angle so that the hole is centred over the burner. The 4 bricks now support my bottom shelf. The difference in temperature between top and bottom is negligible (the bottom being slightly hotter) and I get reduction throughout the kiln.



#43 shoshi

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Posted 27 March 2013 - 11:04 AM

Hi,I've been diverting the flame on two burners, shelf two inches from the top, and packing denser for the past three firings and it is better than ever before but still a variable difference between top and bottom. So I just want to double check-- your bottom shelf is resting on the insulating bricks and is 2 inches from the floor with the flames traveling up the sides of the kiln with no diversion?
Thanks

#44 R Fraser

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Posted 27 March 2013 - 03:15 PM

This relates to a project that I've been contemplating for my torchbearer.

I thought about building a heat exchanger around the exhaust port , then pumping the hot air back underneath the kiln so that it will be picked up by the burners. this would hopefully recycle some of the heat and feed warmer air into the bottom of the kiln. this might be particularly useful for me since where I fire the kiln it is often 30 to 40° in there. So it's getting very cold air coming in the bottom. Air few hundred degrees warmer might be helpful.

Has anyone tried anything like this?
Any thoughts about this strategy


This sounds like a recuperating (spelling?) type furnace I first read about when making my first blacksmith forge, I found the plans on the Sandia website (many years ago). It called for oval stainless steel pipe(s) running through the exhaust vent that was then collected and used to supply combustion air to the burner(s). These were atmospheric burners, and it was a small furnace < 2 cubic feet. In Nils Lou's book "The Art of Firing" he talks about a similar design for a ceramic kiln, but it is using a power burner with the blower first running through a pipe matrix in the exit flue to pick up heat before feeding the burner itself. I would say that everything from the flue to the burner would have to be stainless steel. I do not think this would be easily to make safe or simple using atmospheric burners.
Richard
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#45 docweathers

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Posted 27 March 2013 - 03:48 PM

Since I'm a welder I don't think it would be that difficult for me to build. What I'm not sure about is whether I would get enough recycling of heat to be worth the trouble.

Larry

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#46 R Fraser

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Posted 28 March 2013 - 02:14 PM

Since I'm a welder I don't think it would be that difficult for me to build. What I'm not sure about is whether I would get enough recycling of heat to be worth the trouble.


The Sandia Forge reported up to 30% improved efficiency if I remember corectly. Nils Lou suggested significantly increased efficiency with his recuperating power burner set up but I do not remember if he made any specific claims. I would be concerned that depending on the location of the recuperators and the temp of the exhaust gases a closed loop system relying on natural draft flow to feed the burners primary air the CFM flow of primary air may be low, possibly too low to offer any meaningfull cooling of the recuperators and thus the burner. This would also limit your ability to control the kiln atmosphere to regulating the secondary air flow. The more I think on it the more it seems that to use a recuperating design safely and effectively you are almost obligated to use a blower fed burner system.

Nils Lou's book "The Art of Firing" has a nice schematic outlining how to set up a recuperating kiln burner using a power burner system along with a ton of other great kiln construction info, probably the greatest information density per dollar of any kiln building books I bought second only to Olson's Kiln book. The plans and breif outline on design are at the end in an appendix if memory serves..

This is a link to the ABANA web site with the forge plans: ABANA Forge plans
Note that this is a very small volume chamber with very short primary air supply tubes to the atmospheric burners in more or less a closed loop design.

Richard
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#47 terryr

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Posted 01 January 2014 - 12:18 PM

I am firing the same kiln and having the same problems.  Thanks for all the ideas.  I have only fired this kiln twice with disappointing results top to bottom.

I am also thinking of another layer of insulation brick at the bottom of the kiln.  any updates would be appreciated. 

Thanks 

terry



#48 Rex Johnson

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Posted 17 August 2015 - 09:41 AM

tagging this thread.

I just bought a used 2827G (propane) in good shape

making notes from everything Diz suggested.

wish me luck


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#49 Rex Johnson

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Posted 17 August 2015 - 10:20 AM

Just read this blog, very interesting conclusion. This fellow removed the baffle plates entirely.

 

http://taikoearthpot...ed-firings.html

 

I'm going to contact Peter Addressi at Summit for info also.

I'd rather spend the time and $$$ on getting it reliable than spending fuel/ware/$$$ on testing.

 

http://www.summitkil.../Home_Page.html


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#50 Rex Johnson

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Posted 19 August 2015 - 09:31 AM

Got my new to me 2827G on Friday, new orifices on Saturday (planning!).

It's in good shape.

I'm doing much much reading on the problems people have with this unit attaining an even firing.

(Thanks Diz for your comments, I think I read them all.)

 

It seems like a good chamber all in all, considering it's neat 'square' dimensions.

I have to assume the problem is that the burners blow the heat straight up and out the flue.

Baffling and targeting the flame will be the challenge.

I've gotten some good feedback from Rob Addonzio ( www.taikoearth.com ) about stacking and shelf arrangement.

 

I'm trying to cover all the bases before I test it:

 

1.) All 3/4" gas line directly from the propane tank (200lbs) including a 7/8" diameter flex hose - Check

2.) Disassemble and cleaned all the burners, install new propane orifices - Check

3.) Set burner plates to <1/2" - Check

4.) Align burners to ports and measure distance of nozzles to kiln floor ports (1/2") - Check

5.) Make targets for two burners to re-direct flame under the bottom shelves (shelves 4" above floor) - Check

6.) Fab up a counterweight for the door - Check

7.) Drill out the peepholes so they are actually usable and make plugs to fit - Check

 

Today I'll light the burners and see how they work...

 

IMG_4424-XL.jpg

 

IMG_4420-XL.jpg

 

IMG_4435-XL.jpg

 

IMG_4434-XL.jpg

 

IMG_4431-XL.jpg


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#51 Rex Johnson

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Posted 24 August 2015 - 02:08 PM

First firing to cone 5 went well, 6+ hours from candle thru soak.

It does fire hotter on the bottom, about a cone. Bottom dropped about an hour before the top.

That said the cone 5 and cone 4-6 glazes should survive. I'll find out this eve...

 

I'm not understanding why people might be having reduction problems with this unit.

It's harder to actually get it not to reduce when it reaches temp and you want to hold it at soak.

 

More later...

 

IMG_4435-L.jpg

IMG_4438-L.jpg

 

IMG_4434-L.jpg

 

IMG_4441-L.jpg

 

IMG_4443-L.jpg


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#52 Rex Johnson

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Posted 24 August 2015 - 02:10 PM

IMG_4460-L.jpg

 

IMG_4461-L.jpg


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#53 Patat

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Posted 25 August 2015 - 12:19 AM

I suspect it's the evenness of the reduction people have trouble with. Mine reduces very well on the top 2/3's, but is a bit oxidised on the bottom. I think that's fixable if you wanted. I agree, oxidation is the harder one, even wide open there is still a lot of excess flame at the flue so...Other than bisque, I don't fire oxidation,so it doesn't really worry me.

 

I like that you're posting pics, thanks. Can never have too much info.

 

I had a bit of a breakthrough myself in the last firing, I used a couple old oversized shelves on the top layers. Though it was going to stall out, didn't need to damper at all. Took a bit longer to get to temp, but it was reduced on the top 5/6th of the kiln. I had heard that before, about putting an empty shelf below the flue...

There are pics of the loading here;

https://www.flickr.c...157655647221301

Sorry, haven't figured out how to paste photos here out of Flickr/Pinterest... Oh, also sorry, just looked at the photos and I forgot to upload the shot of my monitor tiles (I put a shino and a copper red test tile on every shelf to gauge the reduction). I'll try to find them and upload.



#54 Rex Johnson

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Posted Today, 02:07 PM

Let's try this. FLIKR doesn't have the easy right mouse  'copy image location' allowance.

I've done some HTML so I found it in the code...

Thanks for the input!

 

You load alot of shelves! I've got 5" posts on the bottom of mine at the moment. You seem to be getting good results though.

Cone 5 or ...?

 

19547006551_e0a86758f2_b.jpg

 

19356238269_28154d987e_b.jpg


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