Electric-Propane kiln conversion advice

[BecMoore]

I’m a recent grad working on setting up a studio space on a really tight budget, and my current plan is to convert an old electric kiln I got for free into a propane-fueled gas kiln. My original plan was to fire it with a pair of propane weed burners, (like simon leach’s conversion) but it’s occurred to me that could be a safety issue during an overnight preheat. 

I’m planning to once-fire most of my work to cone 10 reduction, and I’m used to the university gas kilns, which use  Venturi burners with pilot lights and safety shut offs. 

My usual firing schedule is an 8-10 hour overnight preheat, bring it up to cone 06 slowly (4-5+ hours, reducing 012-09) and then up to 10 quickly(1-2+ hours) and letting it cool naturally. Obviously I’ll be monitoring the kiln while it’s firing, but I’m worried about the preheat. On the other hand, I don’t have a ton of money laying around until I can start firing work to sell, and proper kiln/forge/raku burners are prohibitively(for now)expensive. 

Does anyone have any advice for this? Maybe an inexpensive burner actually designed for long-term use? Or an alternative firing schedule that doesn’t call for me to be awake and alert for 16-24 hours?

[JohnnyK]

Is the overnight preheat actually necessary in your setup if you fire bone dry pieces? I just finished a Raku course at a local college and noted that they ran a lonnnggg preheat on their gas kilns, but that was because much of the work put into the kilns for bisque firing was not bone dry due to time considerations . Their bisque firings lasted a couple of days.

Another thing to think about is how you are going to control the preheat temp with the weed burners over your 8-10 hour stretch. I believe Leach's setup was for a Raku kiln designed for a fast firing to ^06, not ^10.

JohnnyK

[cabako]

I've been firing with a propane weed burner in a small home made kiln to cone 10 at about 8-9hrs. I find with the weed burners its harder to control a stable low temp at the de watering phase.  If you open the burner valve or turn up the psi just a bit too quickly you can break pieces.  I put a small fan behind the burner to move the air around and push the flame forward into the kiln rather than up the walls which helps.

Lately I've been using my kitchen oven  at 185-250 F for de watering. It has a convection fan so that helps.  Try to use  an oven if your piece size allows it.

[BecMoore]

One of my problems is my professor isn’t really experienced in single-fire, so we’ve been erring on the side of caution, I think. And there’s no real reason to conserve gas as it’s one of the few things the university studio has a near-unlimited supply of.  

I’m in Texas, so I guess waiting for really bone-dry work is less of an issue, but if not an overnight preheat, how long a preheat would be a reasonable amount of time for a bisque/first stage of a single-fire of very dry work? It’s a smaller kiln than I’m used to working in so I assume it’ll want to fire faster,  but I’m always wary of losing work. 

EDIT: I unfortunately don’t have an oven available to dry work in. I live with my family and they’re particular about non-food in the oven, regardless of how perfectly safe it is

[neilestrick]

The preheat isn't necessary if everything is totally dry and you can go slowly.

Weed burners are not good kiln burners, and no kiln should be fired without safety systems. At the bare minimum you need to have a Baso valve and pilot on the burners.

A lot of people have come to the forum in the past couple of years with questions about round gas kilns (converted electric kilns). They are generally difficult beasts. Electric kilns are designed for electricity, not gas. You can put a burner on just about any kiln shaped thing and get it to low fire temps for raku and such, but going to cone 10 with a controlled atmosphere, efficiently and with even temperature requires more engineering than a cylinder of bricks. Some folks manage to get them figured out to within a cone or so temperature difference top to bottom, some folks manage to get them to reduce evenly, but it seems to be rare that anyone is totally happy with their round gas kiln.

Those that seem to work best have an external downdraft flue added. Air flow is everything in a gas kiln. You will need smaller shelves than what the electric kiln uses, to allow for good air flow. Do some searching here on the forum and you'll find a lot of recommendations for placing shelves and target bricks and such to get it to work.

I'm not trying to be a downer here, I just want you to be aware of the reality of the situation. It will not be as simple as the kilns you used at school. Also take a look at the cost of firing with propane. Up here propane is really expensive, and it's cheaper to fire with natural gas (much cheaper with electricity). Also look at the glazes you work with and consider firing to cone 6 in reduction instead of cone 10. It will use half as much gas, and most glazes can be converted fairly easily. It will also be easier with your converted kiln.

[High Bridge Pottery]

I have no idea how he gets to cone10 on those weed burners, not that I have tried any but my venturi burner wouldn't get my kiln past 1000c (1800f) A forced air burner is the way to go for an evenish firing in small kilns.

 

If the weed burners do work but you are worried about them going out maybe a cheap science Bunsen burner would do the trick, hook that up over night for a slow preheat. Not that it has any safety systems if it does go out. Hmmmm. Safety systems and a small budget don't go hand in hand. My homemade burner has nothing but myself or the kiln when it's hot enough to auto-ignite.

 

 

[BecMoore]

@neilestrick - thanks, that’s a lot of good information and I appreciate it. Natural gas isn’t an option unfortunately; the city utility doesn’t reach our lot, the whole house runs on propane. I know it’s not going to be as easy to run as a professionally built kiln or one of the larger cone10 kilns we have at the university. The kiln I’m used to running is something of our red headed stepchild; a tiny student-designed test kiln. If I can’t get a good reduction or even temperature it’s nothing I’m not more than used to already.  One small advantage, my kiln is an old square paragon, so at least I have that. 

I’ve considered playing with some ^6 glazes, and might stick to the mid temps while I work the kinks out of my little frankenkiln. 

 

@High Bridge Pottery

You’re using a homemade venturi burner? Would you happen to have plans/advice for that? I’ve considered building one, but I’m leery of going that level of homebrew with fire and explosive gas, especially not without talking to someone with more experience in what I’m building. 

[neilestrick]

If it's one of those old top loading square kilns with a heavy frame, those are great for adding on a downdraft chimney. A dozen soft bricks and a few pieces of angle iron welded up and you've got a very functional gas kiln. I've built one of those before and they can work great- way better than a converted round kiln. The one I built had two small power burners, coming in from the front wall, one on the right one on the left, and a ware area in the middle. Basically you use 1 shelf instead of 2, with firebox area on each side of the shelf. You can get great results with a kiln like that. Another option is to have one power burner coming in at one corner at the bottom, and have a flue opening at the opposite corner at the top, like a cross draft. No added chimney needed there. I had a little salt kiln like that and it worked well, too.

[BecMoore]

That's great to hear! I might give the cross-draft method a try, anything that means fewer bricks to buy is a plus for me right now, and I'm not terribly confident in my welding abilities at the moment, being as I've used a mig welder all of once in my life.  also good to hear you've gotten good results using it as a salt kiln! my tentative plan was to use it as my primary gas kiln until I can afford to build something more practical, and then repurpose it for soda. It's my favorite firing technique and I'm heartbroken to lose access to the school's soda kilns. 

It's a tiny little thing, I don't expect to fit more than one or two layers of work in there once I've had to make room for a firebox and airflow, but it's better than no kiln at all, and I'm determined to keep on making and firing my work. 

[High Bridge Pottery]

I tried a mass produced venturi that didn't work then made a forced air burner (power burner)

There's a thread that follows most of the conversion - 

 

[neilestrick]

Here's a graphic of the little no-chimney cross draft design:

You could just cut a hole in the lid at the top corner for the flue opening, make it about the same size as the burner port or slightly larger, and you can cover it with a brick to control back pressure. A simple power burner is relatively cheap and easy to build from stock black pipe parts. The Baso valve and retention tips will be the most expensive parts.

[BecMoore]

@High Bridge Pottery I haven’t had a chance to read the whole thread but I’m always glad for more information. 

@neilestrick when you say a burner from black pipe do you mean the kind I’ve found on YouTube, usually for mini forges? Do you have a plan you can recommend for that?

[Rex Johnson]

Check out this kiln conversion from Simon Leach.

Fired with weedburner type burners. Modified as a downdraft.

Probably the way I would go.

 

 

 

[Rex Johnson]

On 12/15/2017 at 1:06 PM, BecMoore said:

@High Bridge Pottery

@neilestrick when you say a burner from black pipe do you mean the kind I’ve found on YouTube, usually for mini forges? Do you have a plan you can recommend for that?

Yes, he's talking about what's commonly known as a forced air burner. Easy to make.

Black pipe is in reference to common black gas pipe, not galvanized paipe.

My kiln uses the same made out of 2" pipe about a foot long. There's a 1/4" hole drilled through that pipe and a 1/4" pipe inserted with a propane specific venturi drilled. On the end is a pipe flange with a 'squirrel cage' blower bolted to it.

The tip of the burners have 'stiktite  tip to help the mix.

Looks kinda like this...

[neilestrick]

Sorry I didn't get to this sooner. Yes, the burners I was talking about are like the ones Rex posted. Here's a shot of the ones I built:

Basically the same thing as Rex's. It's all off-the-shelf pipe parts except for the retention tips. This has the bare minimum in safety systems I recommend- a Baso valve and gas solenoid. The solenoid will shut off the gas in the event that the power goes out and the blower shuts off. Otherwise it'll just be pumping pure gas into the kiln which is very dangerous. The solenoid could just be hooked up to the main power, or what I did was run all the electrical through a relay controlled by a high temp shutoff. It's nice in case you forget the kiln is running or get hit by a bus and can't get there to shut it off. On Rex's you can see the blower speed control right by the burner, but mine were mounted on the main control box where the shutoff was located.

[BecMoore]

@Rex Johnson @neilestrick Thanks for the responses guys, I know I have a lot of questions, but this is new for me, and not something I'm comfortable playing with blind. I understand the basics of kiln building and I can fire one fine, but you never really realize how complicated specific parts are until you have to get your own on a budget 

 

Baso Valve and Solenoid! That's what they're called! I couldn't for the life of me figure out what they were called. (at the university we just called them safety valves) That'll make it a lot easier to figure out what the heck I need to do with them.

Potentially stupid question: The kiln I'm used to was using passive-air burners, and the baso valve worked on temperature, when the pilot went out, the valve cut the gas, until the kiln got up to a temp where it would auto-reignite. what part senses the temperature/fire? is that a feature I could put on a home-built burner? is it something that can run without power or am I stuck running some kind of electrical to my studio?

Electricity based safety features might get complicated, my studio is away from the house by about 50-100 yards, and I wasn't planning to run electrical to it; my wheel is a kick wheel, and the kilns I intend to run off gas. that makes forced-air burners tricky too.  My professor suggested an inexpensive raku burner from Ward, but my professor has a yearly budget and a tenured teaching position, so I think our definitions of 'inexpensive' are different

Black pipe I'm at least familiar with. I've used it for a couple hipstery furniture builds, I honestly love working with it. That will probably be my go-to once I've worked out the kinks in all this,  but I'm probably gonna give it a shot with the weed burners first, the way simon leach did it. the burners are cheap, and there's not a huge amount of risk I'm thinking. definitely won't be walking away from the kiln while it's going but that's probably for the best. at least I'll have to get some work done while I'm firing!

 

[neilestrick]

The Baso valve is the safety system with the pilot. The solenoid is the valve on the gas line that shuts off the gas if the power goes out. Venturi burners work fine, and we had a home-made type on a kiln when I was in undergrad, but I don't think they were very efficient. Look at the Ward Burner website and see how many BTU's you'll need for your little kiln. Then you can start looking for used venturi burners on the web. You might just get lucky and find some. On a kiln that small it would be good to only need one or two. Also look at Baso valve prices.

[High Bridge Pottery]

1 hour ago, BecMoore said:

Potentially stupid question: The kiln I'm used to was using passive-air burners, and the baso valve worked on temperature, when the pilot went out, the valve cut the gas, until the kiln got up to a temp where it would auto-reignite. what part senses the temperature/fire? is that a feature I could put on a home-built burner? is it something that can run without power or am I stuck running some kind of electrical to my studio?

I don't think this is a feature, just something that happens because the kiln is hot enough to keep the burners lit so the flame never gets the chance to go out and have the sensor cut the gas supply.  There is no point the sensor decides it is hot enough to stop cutting off gas if I am understanding your question. 

 

I am pretty sure they work on that flames can conduct electricity so when it is lit an electrical signal can go down the copper rod thing. No flame means no electricity can flow so it shuts the valve, doesn't need external power.

[neilestrick]

16 hours ago, High Bridge Pottery said:

I don't think this is a feature, just something that happens because the kiln is hot enough to keep the burners lit so the flame never gets the chance to go out and have the sensor cut the gas supply.  There is no point the sensor decides it is hot enough to stop cutting off gas if I am understanding your question. 

 

I am pretty sure they work on that flames can conduct electricity so when it is lit an electrical signal can go down the copper rod thing. No flame means no electricity can flow so it shuts the valve, doesn't need external power.

The thermocouple produces a small electric current. The hotter it gets, the stronger the current. It must be very hot to produce enough current to activate the small electromagnet that opens the gas valve.

[Rex Johnson]

The burners that Simon is using are common to glass blowing studios and other shops.

I use a Red Dragon weed burner for my saggar kiln and it works fine for bisque and raku temps. But it's a 50 gallon drum lined with 1-2" of blanket.

It fires to bisque in about 3 hours including candleing.

They make different BTU torches. I'd assume that two of these would suffice. Maybe even one.

You could rig up some sort of semi-permanent rack/stand to hold them in place.

Your tank size and/or tanks will dictate how you go about plumbing them as they come with the rubber house and regulator inline for plugging directly into a propane valve just like a BBQ grille. On a conversion like yours you might use 10-20 gallons to get to cone 10...but that's only a guesstimate.

Lots of ideas here Raku Kiln images.

Looking into my saggar...

A similar set up to what I have VVV

common weedburner set up...

 

[High Bridge Pottery]

I never knew it was actually just a thermocouple. After a bit of searching it seems there are ones that work the way I described but they are powered with ac current and need a control board. Good to know.

[neilestrick]

The weed burner setup, while functional, is far from being acceptably safe. If you were to need to make any sort of homeowners insurance claim due to that setup, you'd never get your claim paid. Do everything right, do it safely, do it above board, get permits, check with your insurance company, etc. Peace of mind is worth the extra $$$ for a good, safe burner setup.

[BecMoore]

3 minutes ago, neilestrick said:

The weed burner setup, while functional, is far from being acceptably safe. If you were to need to make any sort of homeowners insurance claim due to that setup, you'd never get your claim paid. Do everything right, do it safely, do it above board, get permits, check with your insurance company, etc. Peace of mind is worth the extra $$$ for a good, safe burner setup.

I absolutely agree that it's worth the money to do it above-board and safely, but that's only the better option if you actually have the money to do that.  I'm trying to work a good burner setup into the budget, but as safety features go I'm thinking I might have to content myself with coffee and a fire extinguisher for the extremely near future. 

The home-built black iron burners look promising if I can work out how to do it properly with a baso. The problem is most videos I can find on them are quick-and-dirty no-safety backyard forge burners. I still have a little time to do more research in that area, I've just been a little swamped this week with moving out of my school studio (sad day) and holiday stuff. 

[C.Banks]

This conversation was begining to sound like something i had bookmarked so I figured i could add some information from an old clayart conversation stressing the importance of regulators in weed burner set-ups among a few other things.

http://www.potters.org/subject09775.htm

[High Bridge Pottery]

After thinking on this thread I decided to finally buy myself a valve and flame sense rod for my burner. After about 30 minutes ebaying trying to figure out the right search terms I ended up spending £25 ($34) on the lot so really not that much. Valve seems to have just about the right BTU throughput. Think they are both second hand.

After the burner arrived I noticed the 50mb (0.7PSI) rating and thought to myself oh crap, must be for natural gas only.... I had a look at the one on my bought venturi burner and now bought myself one of those. The thing is, this one has 25KPa (3.6PSI rating on it but also a sheet with it stating a maximum working pressure of 30PSI. What is this rating I can see as it doesn't seem to match anything. The bit that the thermocouple attaches to says 4PSI so that matches nothing.