A New Kiln Conversion Project: What Would You Do?

[Guest JBaymore]

The cheaper the burners... the less primary air they entrain and the less efficient the mixing activity they produce.  Industrial high velocity burners can be used without any bag walls or even most any consideration to the location of the burner on the chamber...... fire from one corner, top down, bottom up, whatever.  The typical potter level burners .....no so much.  Even forced air.

 

The bag wall will help to not only divert the flame / hot gas path to distriubute the heat energy approprioately to the circulation pattern of the particular design, but will also contribute ot assisting with the post burner mixing action (getting the air and gas in intimate combination to promote good combustion and an even atmosphere in the chamber).

 

Bottom up without a bag wall will result in a very uneven heating patern in that particular layout.

 

Plus one of the "de sign criteria" that was mentioned as "directionality" of flame path.  Firing into the stacking will help with this.

 

And all of the above recent comments are so true also on bottom up confirguatioons.  When I do kilns for clinets I NEVER deliberately use that configuration.

 

best,

 

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

[Mart]

neilestrick wrote: "don't particularly like having to lay on the floor to adjust my burners"

Here is picture for you, on our web site: "Holy moment" http://www.oostuudio.ee/wp-content/uploads/2013/08/IMG_7758.jpg (while my studiomate was studying in Helsiki)

I have crawled few circles around our gas kiln so I have to agree, it is not the most comfortable location but, it's something you do not have to do too often.

 

So, bag wall it is

 

All she has to do now, is come up with a design not to lose too many stetson hats worth of valuable kiln space.

[TJR]

neilestrick wrote: "don't particularly like having to lay on the floor to adjust my burners"

Here is picture for you, on our web site: "Holy moment" http://www.oostuudio.ee/wp-content/uploads/2013/08/IMG_7758.jpg (while my studiomate was studying in Helsiki)

I have crawled few circles around our gas kiln so I have to agree, it is not the most comfortable location but, it's something you do not have to do too often.

 

So, bag wall it is

 

All she has to do now, is come up with a design not to lose too many stetson hats worth of valuable kiln space.

Hilarious! A good laugh first thing in the morning when I am on my way to deal with those lazy Grade twelvers. That doesn',t even look posed.

[TJR]

Why do you like to spend energy (BTU, kWh) for heating up that bag-wall?

Will this work, if you send flames straight up?

This is a 3 min quick sketch, I hope it makes sense. What do you guys think, will this work? (I forgot the salt/soda opening)

 

CD_kiln.jpg

 

Now you will have a bit less than 29 stetson hats of space but still more, than on the drawing you had. I am not telling, your idea is wrong but it looks like something you want to use when building a wood fired kiln.

Every brick you place inside the kiln, needs to be heated up. There is no way around it. 

 

NB! Kristin, pay really close attention to page 21 in The Art of Firing

I agree with Neil on this one. We usually do agree. Not a fan of burners coming in from underneath the kiln.

1.Take a look at the sketch. Place the burner in through the wall horizontally.

2.To the left of the burner place three bricks along the floor.Otherwise, your flame will move under the shelves and out of the kiln. You will have a hot floor and a colder top.

Just sayin,

TJR.

[neilestrick]

neilestrick wrote: "don't particularly like having to lay on the floor to adjust my burners"

Here is picture for you, on our web site: "Holy moment" http://www.oostuudio.ee/wp-content/uploads/2013/08/IMG_7758.jpg (while my studiomate was studying in Helsiki)

I have crawled few circles around our gas kiln so I have to agree, it is not the most comfortable location but, it's something you do not have to do too often.

 

So, bag wall it is

 

All she has to do now, is come up with a design not to lose too many stetson hats worth of valuable kiln space.

 

That is HILARIOUS!

[Kristin_Gail]

Oh!  I feel so much better - as though I've actually learned a bit in the past few months of kiln-construction-information-cramming.  Because my reaction to your suggestion, Mart, was, "But don't I need a bag wall to even out temp?  If I were the flame in your drawing, I would just come in, turn left, and go straight out the flue - who needs to go all the way to the top?" and "I want to put wood / charcoal in this thing - I can't have the burners coming out holes in the bottom, getting all clogged up.  Also, I'm going to have a hard enough time securing the things horizontally sans welder; I have no idea how I'd stand them upright."

 

I'm glad to see the bag wall only need be one brick high.  And here I was going to go 13" high.

 

Another question:

 

...

Just allow plenty of room around and combustable roofing and use metal falshing as you stack will be hot.-You can use hard or soft brick up to the roof -then hard brick in the weather or a stainless steel salvage pipe??

...

 

Is there a magic height at which I can switch to stainless steel pipe?  (As I'm hoping it's less expensive than Canadian-price brick.)

[Mark C.]

Once you get above 5-7 feet you can switch to cheaper fireplace bricks (these are rated lower temp than a high fire brick) .

For me I put salvaged stainless steel pipe from a pulp mill on top of my 8 feet of brick.

Mark

[Stephen]

Hi Kristin,

 

There's a company here in WA that is selling firebrick on ebay by the pallet, may be worth taking a look:

 

http://www.ebay.com/itm/WHOLESALE-PALLET-OF-IFB-INSULATING-FIRE-BRICK-FIREBRICK-MIX-OF-K-23-ARCH-/330866185945?pt=LH_DefaultDomain_0&hash=item4d092956d9

[Kristin_Gail]

Hi Stephen - I'm East of Maine!  That, um, is a looooong way away from Washington.  Unfortunately.

[Biglou13]

Sometimes you can find soft brick for free.... Chat with local kiln repair guy. Guts from octagon kilns. Sure not as good as hard bricks but the cost is right.

[Mark C.]

BigLou 

Shes in either Nova Scotia or Iceland either way there is no local kiln repair guy-No local kiln anything around these parts as well.

Its a good idea if you live near lots of population as thats the onlyway you will have a kiln repair guy.

Free brick are also found at old mill sites-lumber mills (kiln dried wood)-pulp mills-some industrial sites as well.Or at least thats where I have in my younger days found them.

Mark

[Mart]

I must have missed something here.

Why are you building a brick chimney for your gas kiln?

 

This is how it's usually built.

 

Sheet metal pipe (duct) is the one that exits the building and if this kin is outdoor, in the open, you do not even need that.

Chimney is to generate draft. You do not need draft like you do in a wood fired kiln. Only draft you need, is the one in that ventilation duct. Make sure you have a dampener there too, if it starts sucking that air out too fast

 

Here is another example.

 

Burning gas, you shoot in to your kiln, will generate pressure inside the kiln and it starts to search its way out. When it finds the exit, it pushes out.

 

 

 

If I were the flame in your drawing, I would just come in, turn left, and go straight out the flue - who needs to go all the way to the top?"

Actually no. The speed at which the flame (burning gases) exit the burner and enter the kiln, will take them all the way up and go from there, searching for exit.

While your burners are going, there will be higher pressure in your kiln. You do not need traditional draft like you do for wood fired kilns - get air in and gasses out.

 

If you had a "passive" flame like candle or wood in a kiln - you need a chimney to generate draft or your fire will run out of air and die.

 

If you have a gas burner, that sucks in its own air (primary and secondary), you need an exit flue for the gases or the backpressure will rise too high and you will have a problem burning that gas and flames will try to exit from burner ports.

 

If you are planning to throw charcoal in to the kiln, just keep the burners going and they will take care of the gases and air. (I have actually never attempted this so do not take my word for it)

[neilestrick]

You do not need a tall chimney if you are using power burners. But for Venturi burners like she is using you will need the chimney height to create draw to bring in secondary air.

[oldlady]

mart, love the photo.  i realize that people put "gods" on their kilns, but worshipping them the way you guys are seems a little much!

[Mart]

mart, love the photo.  i realize that people put "gods" on their kilns, but worshipping them the way you guys are seems a little much!

 

 

You do not need a tall chimney if you are using power burners. But for Venturi burners like she is using you will need the chimney height to create draw to bring in secondary air.

(http://www.wardburner.com/draft.html)

I guess in this case, she needs 41.5+5+5=51.5 51.5/3=17.16 and 3*30=90 + 17.16 = 107.16" tall chimney. huh... over 2.7 meters! That sucks...

[Kristin_Gail]

Question:  The reason I planned to build up the kiln a few inches beneath the shelves is that nearly every photo/drawing I've seen has the firebox(es) lower than the stacking space.  The easiest way I could find to do this was to raise the stacking space instead of lowering the firebox.  As my books still haven't arrived, could someone explain why kilns are built this way?  Or maybe should I not be doing this?

 

Bricks:

I've been sniffing around for years - followed up on many leads, but haven't been able to find any used bricks.  I just contacted the refractory place that initially gave me a quote of $8.65/brick.  This time, once she knew it was just for a chimney, she recommended a much lower-rated brick, that's far cheaper (she's giving me a quote next week, but thinks it's $2-3/brick).  It's the "HI-HEAT" one on this site:  http://www.mtsavage.com/ProductInformation/ProductLines/FirebrickandOtherProducts/tabid/86/Default.aspx

 

She'll have the actual temp rating for me on Monday, but knows it's at the very least rated to 2800F.  Can you folks tell from the info on that site if they're the sort of bricks I could use?  

 

It sounds like I'd need to give her a yes on Monday in order to get them free freight from Pennsylvania, snuck in with a huge order that's coming our way.  Which means I should really hammer out the design of the thing, eh? 

 

Another chimney question:  Four bricks around, 9" square hole, is sufficient, right?  (I realize I'll be able to answer this on my own when the books arrive ...)

[Guest JBaymore]

Question:  The reason I planned to build up the kiln a few inches beneath the shelves is that nearly every photo/drawing I've seen has the firebox(es) lower than the stacking space.  The easiest way I could find to do this was to raise the stacking space instead of lowering the firebox.  As my books still haven't arrived, could someone explain why kilns are built this way?  Or maybe should I not be doing this?

 

Certain types of kilns utilize the "slope" of the kiln structure to assist in developing postive draft flow.  A kiln chamber can itself act as a "chimney"... as in most updraft designs.  Most (but not all) anagama do this "uphill slope" thing, all noborigama do this (hence the derivation of the name ....the verb "noborimasu" means "to go up (as in a set of stairs)", and some other single chamber designs of kiln do this (for actual functional reasons).  It is NOT at all necessary in designs such as yours.  You are simply losing interiror volume in the kiln. 

 

You will see a lot of stuff done in kiln designs that are not really necessary, or are even counterproductive...... just like you will see a lot of things done and said about clay and glaze chemsitry that are not accurate.  In general, a lot of such kilns are built by people who are artists and have studied the arts.... not the science side of life... where a huge oportion of glaze chemistry and kiln design tend to lie. 

 

 

Bricks:

I've been sniffing around for years - followed up on many leads, but haven't been able to find any used bricks. I just contacted the refractory place that initially gave me a quote of $8.65/brick. This time, once she knew it was just for a chimney, she recommended a much lower-rated brick, that's far cheaper (she's giving me a quote next week, but thinks it's $2-3/brick). It's the "HI-HEAT" one on this site: http://www.mtsavage.com/ProductInformation/ProductLines/FirebrickandOtherProducts/tabid/86/Default.aspx

 

 

$8.65 a brick apprears to be highway robbery to me.  But it is possible that it is a simply and demand issue if you live WAY out in the middle of nowhere.  Mt. Savage Hi-heats (the model) are serious overkill for most of the chimney on a gas fired kiln.  They are a high duty rated firebrick. .. and would be suitable for a cone 9 chamber lining usage in a non -slagging (serious wood kiln) environment unless you did not want a long life out of the lining.  In a gas kiln they could even be used in most firebox sitiations instead of super duty rating if REAL longevity was not a huge design constraint there.  Use them for a couple of feet at most (below the damper) and then switch to fireplace firebricks that you can get at a place like a Lowes or a Home Depot or a local construction/lumber yard.

 

 

Another chimney question: Four bricks around, 9" square hole, is sufficient, right? (I realize I'll be able to answer this on my own when the books arrive ...)

 

For that size kiln you do not need a 9" x 9" chimney cross section even with the inexpensive burners you are proposing.  (Most large gas kilns that have 9x9 chimneys don't need that size flue!)  But for ease of construction (minimal or no brick cutting) , you could use this configuration.  You'll then be dampering down that chimney a lot during firing.  Remember that to make a 9 x 9 chimney it takes six bricks per course (2 1/2" high), not four due to the overlap on the corners to make the walls 4 1/2" thick.

 

best,

 

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

[neilestrick]

You can cut hard brick with a masonry blade on a circular saw. It works fine for the small number of bricks you'd need to cut to make a chimney smaller than 9x9. I just built a soda kiln this past weekend, and we paid $2.39 for hard brick, $3.19 for K26 soft brick.

[Biglou13]

I must have missed something here. :)Why are you building a brick chimney for your gas kiln?This is how it's usually built.gas_kiln_ch01.jpgSheet metal pipe (duct) is the one that exits the building and if this kin is outdoor, in the open, you do not even need that.Chimney is to generate draft. You do not need draft like you do in a wood fired kiln. Only draft you need, is the one in that ventilation duct. Make sure you have a dampener there too, if it starts sucking that air out too fast ;)Here is another example.kiln_picture.jpgBurning gas, you shoot in to your kiln, will generate pressure inside the kiln and it starts to search its way out. When it finds the exit, it pushes out.

If I were the flame in your drawing, I would just come in, turn left, and go straight out the flue - who needs to go all the way to the top?"

Actually no. The speed at which the flame (burning gases) exit the burner and enter the kiln, will take them all the way up and go from there, searching for exit.While your burners are going, there will be higher pressure in your kiln. You do not need traditional draft like you do for wood fired kilns - get air in and gasses out.If you had a "passive" flame like candle or wood in a kiln - you need a chimney to generate draft or your fire will run out of air and die.If you have a gas burner, that sucks in its own air (primary and secondary), you need an exit flue for the gases or the backpressure will rise too high and you will have a problem burning that gas and flames will try to exit from burner ports.If you are planning to throw charcoal in to the kiln, just keep the burners going and they will take care of the gases and air. (I have actually never attempted this so do not take my word for it)Well I was hoping some one more learned would comment.

But I think every one jumped on the wood fire/possible wood fire with this kiln. Hence the flue chimney conversations.

I have seen videos of kiln you pictured.

I have seen kilns with four venturi burners, reduction fired gas only, that still had chimney.

 

So you post and my observations have me confused....

 

With gas only not forced air. When is a chimney necessary? When is it not?

 

So it is possible to fire this kiln with out a chimney if going with Venturi gas, reduction, soda/salt?

 

Which would solve shelter problem and chimney issue. If she added forced air wood firing no or very limited chimney also. Given she will need enough chimney to clear top if kiln. So some bricks are still necessary......

[JeffTimothy]

Hi there,  Just a heads up that I've sent you a private message regarding your kiln conversion.  It's not quite related to the topic hence the reason for not posting it here.  I don't want to hijack your thread.

Thanks!

Jeff.

[Kristin_Gail]

FWIW, Most consumer items cost 1.5x more here (New Brunswick - squarshed in between Maine and Nova Scotia) than in the U.S.  But that high-dollar one was overkill for me; they use it in their incinerators, etc.  At the time, she was just trying to give me a ballpark idea when I was thinking about building an entire kiln.  The price she gave me for soft bricks was $3.60/2300 and $6.50/2800.

 

Will be tackling this chimney-design/brick-number thing tonight - 100 lbs of produce needs to be canned first.

[Kristin_Gail]

Oh, my.  Holy helpful.  Thank you, John.

 

I realize now I also had the motive of making the space smaller inside, because: 1. I'm overwhelmed by the size and afraid I won't be able to fill it; and 2. Perhaps the burners won't be big enough.  If I were to put the exit hole/flue at the very bottom of the vertical wall (just above the actual floor), then I could later build up the floor higher if I needed to, putting a channel into these layers to bring the flame down to the exit hole - is my brain working on that one?

 

Because my brain clearly wasn't working on the 4 bricks/layer to get a 9" hole.  Right, Kristin.  That's a 4.5" hole.  Now, would that be enough? From Neil's suggestion of cutting the bricks, sounds like that's a no.  Somewhere in between, eh?

 

I'm so very thankful to see I can switch to cheaper bricks after a few feet.

 

I was going to put the damper - a slidable, vertical piece of kiln shelf - just outside the kiln, in a short (9" long) tunnel-like section between the kiln and the vertical section of the chimney.  Similar to this horribly out-of-scale representation:

 

|   |

|   |

|   |     ________

|   |     |               |

|   |_ _|               |

|___|_________|  

 

Sure as hell hope these books can help with my vocabulary.  Just because I don't know what I'm talking about doesn't mean I need to sound like I don't know what I'm talking about.

[Kristin_Gail]

By the highly sophisticated method of using my son's Lego bricks, I've decided I need 104 of the Hi-Fire bricks and 138 of ... I'll see what she can tell me about the medium-duty ones.  

 

And I only forgot about my boiling pickle jars twice.

 

I had no idea the chimney would be 1/3 of the cost of the entire thing.  Surprise, surprise.

[Mark C.]

Is there a reason you are thinking tunnel (sideways-damper) instead of going up and dampering on the horizontal?

Many fall short when it comes to chimneys-run out of bricks or funds and wing it with sideways results

Use good bricks at least to the damper then above that use the lesser bricks then mabey some pipe.

Mark

[Kristin_Gail]

I think it's just because the kilns I've visited have had their dampers set up this way, so I just assumed I'd do it that way, too.  Also, I looked around the Internet last night and found a few old Clayart discussions of people complaining about their horizontal one getting hard to slide after a while, and others agreeing it's best to go vertical.  But what the heck do I know?  If it's better for some reason to go horizontal, I can do that, too.

 

I was thinking of using the HI-FIRE bricks out the 9"-long tunnel and 3 feet up the 8-foot vertical chimney.  Then using other bricks for the remaining 5 feet.

 

Also, my Lego chimney design has the inside area of the chimney 4.5" x 9".   So, five bricks per layer.  Assuming I'll refine this once my books arrive ...