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At Around What Cone Can Steel Not Be Used For Kiln Components?


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#1 GavJ

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Posted 05 July 2014 - 02:18 PM

I want to try making a kiln design where the air input (from a blower) circles around a spiral tube inside the chimney, thus using the waste heat to pre-heat the intake and massively increase fuel efficiency (which is going to be charcoal).

 

Simple diagram:

ZFumP2g.png

 

 

Problem is, pipes would be pretty damn hard to make out of ceramic, and probably quite prone to cracking even if I did pull it off.

 

But I don't want to fire porcelain or anything. So I'm wondering if I could do a low fire version of this using steel pipes, and if so, how hot could I fire it without them slumping OR oxidizing into dust?

 

In general, how long / up to what temperature do steel components like grills work in you guys' kilns?  Or cast iron or whatever other metal I can buy tubes in, if steel isn't the best option.

 

 

 

 

Also, any other issues to look out for? Like a need for expansion joints where the pipes meet the walls, or whatever? Or if I can get away with it not breaking, would I still have to support the spiral like every 3 inches or something to stop it from slumping into a useless pile?



#2 High Bridge Pottery

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Posted 05 July 2014 - 02:32 PM

Not sure about the steel but I did see an article relating to this a while back. Will see if I can find it.

Here it is
http://community.cer...n/?fromsearch=1

#3 GavJ

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Posted 05 July 2014 - 02:42 PM

Yeah that's one of the ones I read, I didn't just come up with it off the top of my head. But it doesn't have very good diagrams and the design is all weird because of the ceramic pipes, so I drew my own. Also, I can't afford making it like that.

 

Basically, if iron works, my plan was more along the lines of finding some long short skinny old radiator somebody is throwing out or selling for cheap, and calling it a day... (don't even have to put it upright. Since it is forced air, AND the exhaust isn't super hot to catch things on fire, the chimney doesn't have to be a chimney, it could go low along the ground)



#4 schmism

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Posted 06 July 2014 - 01:53 AM

16.jpg

 

what your looking at is the exhaust header glowing read from extreme temperature associated with the combustion inside the engine.  This normally occurs between about 1100 to 1200 deg F. 

 

That is likely 16g mild steel tubeing.   IT is also common to get 304 stainless in 16 ga for custom exhaust also.  while the stainless would take more heat, you can ballpark it to be only slightly above the mild steel tubeing.

 

Only suggestion I have is to build your setup then probe the chimney to get an idea of how far "down" (close to exit of the ware chamber) you could go before you exceed the above temp.  That would give you an idea of how far down you could spiral with "standard" tubing before having to transition to ceramic tube for high temp.   I have no advise on the transition between the ceramic and the steel tubing.

 

Personally i dont see how the cost of the above system would be worth it.  Especially if your going to fire with "wood"  it would seem you could buy a LOT of fire wood for the cost of the above system.

 

As to useing an old cast iron steam type radiator,  cast iron has a melting temp of ~2100F   



#5 Marcia Selsor

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Posted 06 July 2014 - 08:03 AM

I have seen this idea before. I think it was in an old Studio Potter magazine.
It is a good way to increase efficiency. The problems had been worked out. I hope you can find it.
It could be in the Studio Potter book. I will look.

Marcia

#6 JBaymore

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Posted 06 July 2014 - 08:52 AM

Yeah... I think it was in Studio Potter magazine..... and as I remember it was a bit after the last "energy crisis"... about 1977. Just post Carter era.  I think there was also recently a pice in Ceramics Techincal on the same subject.

 

Preheated primary air for combustion has been used in industry for a long time now.

 

For the studio potter it is all about calculating paybacks if one is looking at the investment in terms of economic sense.  The more you fire, and the more ciostly your fuel supply, the faster the payback of the investment.  Don't forget maintenence and replacement in figuring the potential payback... the heat exchanger does not last forever.

 

If you are thinking about making "environmental sense", then spending money to do that is a separate subject, and is based upon how much you can afford to spend to approach that ideal.  Personally... I'd fire normally and plant trees.

 

best,

 

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


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#7 GavJ

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Posted 06 July 2014 - 03:27 PM

Thanks everyone.

 

what your looking at is the exhaust header glowing read from extreme temperature associated with the combustion inside the engine.  This normally occurs between about 1100 to 1200 deg F. 

 

Yes, but are they about to take oxidative damage and/or slump into useless shapes if they go any amount beyond that? Or can they go ahead and get orange or yellow hot first, for a few hundred more degrees? That's the key question.

 

I suppose it might make more sense to ask at a metallurgy forum, though, if nobody knows for sure.



#8 Tyler Miller

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Posted 06 July 2014 - 05:44 PM

600F (blue oxidation)  max if you want it to have any kind of permanence.  Anything higher than that and it's a consumable.



#9 jrgpots

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Posted 06 July 2014 - 07:05 PM

I have seen a kiln stack that was filled with donut shaped saggars each connected to the saggar above and below it b small tubes. The stacked saggars acted like your steel coil to reclaim heat to preheat the intake air. It ended up being a big stack requiring a lot of brick. But it worked.

Jed

#10 CarlCravens

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Posted 07 July 2014 - 03:13 PM

Wikipedia says:

 

Feller kiln brought contemporary design to wood firing by re-using unburnt gas from the chimney to heat intake air before it enters the firebox. This leads to an even shorter firing cycle and less wood consumption. This design requires external ventilation to prevent the in-chimney radiator from melting, being typically in metal. The result is a very efficient wood kiln firing one cubic meter of ceramics with one cubic meter of wood.

 

You might try searching for "Feller kiln".


Carl (Wichita, KS)

#11 GavJ

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Posted 07 July 2014 - 04:35 PM

Okay. 600F is still way the hell more preheated than 80F air. By "consumable," just how "consumable" are we talking here? Would a 1200 degree pipe melt in one firing? Or do you just mean that it won't last a lifetime? Because a couple of 90 degree iron elbows and straight sections cost only a few dollars. Even if I have to replace it once every one or two firings, it seems cost efficient if it halves my fuel usage, for example.
 

Ideally what I'd want is some graph with "temperature exposed" on the X axis and "number of heating cycles until loss of integrity" on the Y axis for common iron pipe, or something like that. Then I could use the cost of the pipe versus the cost of wood versus that graph to pick a precise maximum efficiency point for me. Then test different lengths of pipe extending further into the chimney until the output temperature is measured at the desired level. Maybe no such thing exists due to it being more complex than that, though.

 

But anyway, yeah it doesn't have to be fully up to temperature of the kiln -- any amount closer = fuel saved. Just want to try and estimate how close I can push it before investing in all the other costs of the kiln.



#12 Tyler Miller

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Posted 07 July 2014 - 06:24 PM

Okay. 600F is still way the hell more preheated than 80F air. By "consumable," just how "consumable" are we talking here? Would a 1200 degree pipe melt in one firing? Or do you just mean that it won't last a lifetime? Because a couple of 90 degree iron elbows and straight sections cost only a few dollars. Even if I have to replace it once every one or two firings, it seems cost efficient if it halves my fuel usage, for example.
 

Ideally what I'd want is some graph with "temperature exposed" on the X axis and "number of heating cycles until loss of integrity" on the Y axis for common iron pipe, or something like that. Then I could use the cost of the pipe versus the cost of wood versus that graph to pick a precise maximum efficiency point for me. Then test different lengths of pipe extending further into the chimney until the output temperature is measured at the desired level. Maybe no such thing exists due to it being more complex than that, though.

 

But anyway, yeah it doesn't have to be fully up to temperature of the kiln -- any amount closer = fuel saved. Just want to try and estimate how close I can push it before investing in all the other costs of the kiln.

GavJ,

 

I think you may need to do some deciding about what's most important to you in this project.  It seems to me that you need to decide if making your design work is more important or making a fuel efficient or cost effective design is more important.   

 

Here's where I'm coming from:  600F is indeed much hotter than ambient air temp, but I think you'll find it difficult to make a draft work if you run your air intake only part way down the chimney.  There's the question of what you're going to do for the rest of the air intake.  If you run steel all they way down the chimney your steel/iron components will be very consumable indeed.  Not only is temperature a factor, but also the fact that corrosive gases like sulphur dioxide and hydrochloric acid will be off-gassed during firing, especially if your clay content has a high amount of organic material.  Based on your prior posts, it appears that it will.  Hot steel plus corrosive gases equals decay.  You may be able to get one firing out of them before your heat exchanger starts spitting iron oxides at your pots.  In all likelihood, if you're approaching cone 08-06 on your first firing, you'll be blowing FeO flakes into your ware right then and there--that's the temperature range where FeO begins to flake off on its own.  No good if you don't want little black/red stains on your bisque or FeO chips in your glaze.

 

If you're committed to the design, you will need to do quite a bit of R&D, which is expensive and time consuming.  There's likely something there, though, if you want to figure it out.  The X/Y graph data you seek, I don't think exists, and if it does, I don't know where to find it.  The materials science department at your local university might be able to help.  In all likelihood, it will be a part of the research you have to do yourself.  

 

If you're committed to keeping fuel costs low, trade wood out for any other source of heat.  Wood/charcoal is the most expensive, least effective way of getting your pots fired.  I think even those who fire with wood will agree to that.  Waste oil burners are easy to make, and the fuel can be had for a smile and a song.  You could certainly cobble together a waste oil burning kiln that would take you up to cone 10 very cheaply.  You can get used fire bricks for the cost of red clay pavers from some brick recycling places, if you're a good negotiator.  There's a place I know around my area that reclaims fire brick for the alumina, I got about 20 bricks from them for nearly nothing for a project I was working on.   Those with a few waste oil burners, some angle iron, and a little knowledge, would give you a kiln most potters would be envious of.  Would cost probably 5% of your wood/charcoal budget to run it, too.

 

I don't know, something to look into.  I know a guy who's very much like you, I think.  He's got a tremendous amount of talent and imagination, but gets hung up on reinventing the wheel.  His latest endeavours have been to bring serious drama back to puppetry and become music's next "musician's musician." I didn't have the heart to tell him about the existence of Jim Henson's creature shop and what they do.  Forgive me if this is a little too personal, impertinent, or isn't relevant, but this guy's been on my mind a lot lately--I'm more than a little worried about him.  I wouldn't want you to get hung up in the same mental traps.  Again, apologies for any perceived impertinence.

 

-Tyler



#13 JBaymore

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Posted 07 July 2014 - 08:29 PM

Wood/charcoal is the most expensive, least effective way of getting your pots fired. I think even those who fire with wood will agree to that.

 

Been woodfiring since 1969. The MOST absurd, labor intensive, expensive way to fire for sure. I love it. ;)

 

The one big thing wood firing has going for it is the carbon neutrality over about a 30 year cycle with new tree growth (as long as you re-populate the trees) and the renewable fuel aspects. The down side is the particulates.

 

As to the recuperative primary air systems.... don't expect to cut your fuel consumption by some magical HUGE percentage. The typical is about a max of 30%. And therre are all sorts of issues with metal exchangers... such as the tendency to corrode due to the presence of sulphur compounds in the clay bodies and the fuel....... so that speeds the deterioration of the exchanger and the capital and maintence costs.

 

best,

 

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


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Professor of Ceramics; New Hampshire Insitute of Art

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#14 Min

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Posted 08 July 2014 - 11:18 AM

Anybody use the ITC 213 for metals for an application like this? 

http://itccoatings.com/



#15 JBaymore

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Posted 08 July 2014 - 11:59 AM

Just like for coating the coils.... the protection is only as good as the integrity of the ENTIRE coating.

 

The underlying metal will fail at the ONE small pinhole that the ITC213 did not cover.  Or where in handling,...... you shipped off a piece.  And so on.

 

best,

 

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


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Professor of Ceramics; New Hampshire Insitute of Art

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#16 GavJ

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Posted 08 July 2014 - 02:45 PM

No, definitely thanks for your thoughts, Tyler. 

 

I'm aware it's super inefficient and that I could make a much better kiln quite easily using modern technology. It's simply a matter of me having more fun / being more motivated by:
* learning the various mechanics of the craft available
* building contraptions
* learning how to purify clay
* learning geology
* learning historical methods and ending up in awesome situations like gathering my own limestone from a local 19th century quarry site that was apparently 1 block from my house for years without me knowing about it. There are even still foundations of old possible lime kilns or outbuildings in the undergrowth. Just off to the side of this random park.

Actually making pottery itself is okay, I guess, but no more so than any of the above. So I'm not motivated to take modern shortcuts to just instantly get to that part of it, because I don't find that part of it terribly special or captivating, personally.

If, sometime in the future, I manage to make my own homemade kiln out of homemade local material firebricks, fired with a homemade bellows and charcoal/wood and using glaze from homemade potash and clay, then I'll probably call it a day after making a set of cool mugs or whatever and move on to some other hobby, honestly. Maybe come back to this later when I have a house and land to build legitimate tools on.



#17 Tyler Miller

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Posted 09 July 2014 - 09:44 AM

There's a passage in Plato's Symposium (I think, it's one with Alcibiades at least) where he talks about his involvement with philosophy as like being bitten by a snake.  Only those who have been bitten can truly communicate to each other the pain and madness the bite causes.  So it was for philosophy for Plato.

 

I admire your adventurous spirit, but I'll say that pottery's a venomous snake as well.  I suspect that if you end up making your mugs, by that point you'll have been bitten and driven mad for it.  And then you'll be like us--clay and fire crazed.

 

If it doesn't bite you, I hope you find the snake that does.  It's a wonderful thing.  :)



#18 Lockley

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Posted 09 July 2014 - 01:44 PM

The technique of heat recovery from exhaust gases has a long history.  In the days of open hearth steel making they created alternating exhaust paths called "Checkers". The checkers were stacks of pyro brick that heated up on the exhaust cycle and preheated the air on the intake cycle.

 

Counter current heat exchange  is used and any number of industrial processes  to improve heating cycles.  It is also used in the feet of migrating water fowl to keep from freezing in ice filled ponds. :)

 

In my own experience I have used Black Iron pipe ( not galvanized pipe) with propane in a blower system to increase the temperature I achieve.   Black iron is relatively inexpensive compared to stainless steel, and because it is thread-able by most suppliers it can be assembled  in manifolds without welding.  This makes replacement of parts a days work not a weeks.  I used straight pipes not coiled, and of a large diameter to slow the flow down with out reducing volume.  I didn't worry about the iron pipes because it is kind of like the "Mr. Wizard" trick of boiling water in a paper cup over an open flame. As long as air flowed through the pipe was ok despite the temperature would have melted steel.

 

For a wood fired system I have been toying with designs using two different  sizes of  fire place  flue tiles.  One outer and one inner.

 

 

 

 

 



#19 GavJ

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Posted 09 July 2014 - 03:42 PM

As long as air flowed through the pipe was ok despite the temperature would have melted steel.

 

Yeah that's what I was thinking. As long as the air is only preheating to 600F or 1000F or whatever before getting to the fuel, it should protect the pipe somewhat even in a hotter environment. Although relying on this prevents you from being able to fire the kiln in reduction, yes? Soon as you turn off the air, your chimney is full of slag. I guess you can still do so once per set of pipes...

 

Or maybe the air pipe could be set up to actually be removable during firing? That'd be kind of cool. And fairly dangerous sounding which makes it all the more fun!






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