Atmospheric injector setting

[inga239]

Hello,

This is my first posting and I hope I am in the right group.

I have 4 low pressure compound atmospheric injectors. Brand name: Eclipse TR 60 1 1/2" nozzle. They are installed (2 on each side) to fuel a 30 cu ft. ceramic car kiln that I fire to 2400 degrees F. The secondary (upstream) regulator is set at 30" WC with the burners on full bore. I would like to be able to set the flame on each burner with some type of measuring device. I have tried to "set" them both acoustically as well as visually which leaves me working mostly in the dark. The controls I have are ball valves on each injector to increase the flow of gas, primary air supply shutters, a damper and a Fluke dual digital thermometer. None of these control are very exacting with the exception of the Fluke meter. All of these controls can vary greatly depending on atmospheric pressure, ambient temperature wind etc.

I have searched the internet for test equipment that doesn't cost an arm and a leg to allow me to set each burner at each stage of the firing and reduce some of the variables attributed to firing "by the seat of my pants" so to speak. I haven't had much luck locating test equipment. Anyone have any suggestions?

I thank you for your time.

Inga239

 

[inga239]

Hello again,

I guess no one is interested in my question or has an answer. So I will sign off this list. Thanks

 

[MikeHalloran]

Not many of us have a car kiln to play with.

What do you mean by 'set' a flame?

The gas pressure at the regulator is what determines the maximum possible gas flow. The injector ball valves cannot possibly increase gas flow. They can reduce it in a fairly uncontrollable way, or shut it off. Why do you wish to change the gas flow?

In what way is the kiln not performing satisfactorily?

Did it ever work right?



Mike Halloran
Pembroke Pines, FL, USA

 

[inga239]

Hi Mike,

Thanks for your response. I understand most of you don't have a car kiln. I just thought since you are engineers you would have an engineering knowledge of how some of these things work and give me some help. I understand what you are saying but the problem is: There are so many variables involved. Atmospheric pressure, temperature, wind etc. Even how the wares are loaded and how the heat can flow inside the kiln. I would like to minimize some of the variables specifically the flame at each burner. Firing a ceramic kiln requires starting very slowly so as not to blow everything up. Then you slowly up the gas flow as the heat in the box increases. Too much gas flow can actually stall the kiln and drop the temperature. There is always this dance between the flow of gas, the heat rise and the temperature drop. It is impossible to really know how much heat each burner is pouring in at any given time. The valves are not sophisticated. I was hoping for a piece of equipment that can actually measure the heat at each burner as it is adjusted upward during the firing in order for me to chart each step and then be able to reproduce it each time I fire. The infrared heat guns I found on line don't go high enough for my application.

You ask Has the kiln ever worked properly...Absolutely, Many Many times. Conversely, many times it has not and trying to figure out why not is difficult. I keep extensive logs of how I fire in hopes of replicating a great firing. Some times it works and other times not. I think if I could understand exactly how much heat each burner is giving off at any given time so I can "set" them the same, it might solve the problem. I'm not sure. Maybe there is something I am missing that someone else can see not being close to the problem. The dual Fluke pyrometer gives me instant readouts with one probe installed in the top back portion and the other the bottom back wall. It tells me the heat rise or drop in temperature instantly. It tells me nothing about the burners or how they are adjusted.

You ask " in what way is the kiln not performing: I do one of a kind art pieces with a reduction firing. Reduction firing, reducing the oxygen in the Kiln. The reduced oxygen (if not over done) can give spectacular finishes to otherwise blah and ordinary wares. Reduction can change a copper based glaze to a spectacular red. Too much reduction can stall the kiln, drop temperature and produce unattractive glazes This is where the flame going into the kiln, the damper closure all come to play, good or bad.

Do you know of any equipment that is affordable for an individual that can measure the temperature of a flame at any given time? I think that might take a huge variable out of the equation.

Thanks.

Ingeborg

 

[MikeHalloran]

I can't believe somebody sold you a giant kiln without also providing complete controls and instrumentation.
... or maybe you built it yourself.
Regardless, I commend your persistence, and I think you are on the right track in first seeking consistency in operation.

The first thing I would suggest is replacing the Fluke with two chart recorders, or maybe one dual channel recorder, whether electronic, circular or linear, so that you have an archivable record of the complete continuous firing cycle for every batch. Maybe your manual records are complete and comprehensive enough; if so, I salute your patience and attention to detail.

Recognize that I know little about kilns, or furnaces. I hope someone will wander in with better suggestions than I can offer.

In the meantime, let's dream a little. I'd imagine that an automatic kiln equipped to do a firing cycle without human intervention would have:
- motor operated dampers, perhaps with position indicators.
- an individual electronically controllable fuel pressure regulator for each nozzle, perhaps with pressure transducers.
- a PLC with enough outputs to modulate the dampers and the gas regulators, and enough inputs to monitor the temperatures, the damper positions, and the nozzle gas pressures, and storage and output means to develop, record, and print a complete record of each firing cycle.

When you adjust the ball valves feeding the burner nozzles, you are adjusting the gas flow rate, which could as well or better be adjusted by controlling the pressure feeding the nozzles, i.e., the regulator output pressure.

It may be sufficient to get started by just using a cheap PLC to run a single electronically controlled regulator feeding all the burners. Look at the regulator you have; there may be a way to control it with compressed air, which can in turn be controlled electronically.

Of course you have to accumulate some data before you can program the PLC. Before you bother to mess with the regulator or add more, it might be instructive to tee in a small pressure sense line after the ball valves, so you can measure the actual pressure being fed to the gas nozzles. That sense line should of course be long enough to not conduct much heat to the pressure measurement device, which could be a water u-tube or a Dwyer Magnelic pressure gage of appropriate range.

I hope that helps a little.






Mike Halloran
Pembroke Pines, FL, USA

 

[btrueblood]

You don't mention what your fuel is, but presumably either natural gas or propane. One crude way to figure out whether you have a reducing flame with either fuel is by the luminance of the flame, i.e. a rich (reducing) flame will be a bright yellow, while a stoichiometric or lean (neutral to oxidizing) flame will be a pale blue. That may be what you mean by setting the flame "visually"?

In addition to Mike's (as usual) good advice, you may need a pressure sensor inside the kiln. It sounds like you are using an unpressurized air source (dampers) for the combustion, which makes control of the air-fuel mix a bit more tricky (rising pressure in the kiln may reduce the airflow too much). Maybe think about using compressed air to feed the combustors, it could make control of air/fuel mix independent of kiln back pressure.

You might look into (an) oxygen sensor(s) for the kiln, and feedback control of the dampers to keep the combustion fuel/air ratio where you want it.

http://www.axner.com/

http://www.cof.com.au/aos/products.asp?id=25

http://community.ceramicartsdaily.org/topic/5193-how-to-make-an-oxygen-sensor-for-your-kiln/

 

[MikeHalloran]

One extra cautionary note:

You know those tiny orifices that are used to meter fuel gas into range burners and such? You need one of those at the tee where you plumb any sense lines into the gas supply.

... to limit the size of the fire you get when the manometer/ pressure sensor develops a leak.

The actual orifice size is unimportant, and will not affect the pressure reading, since normally there's no flow, and no pressure drop.




Mike Halloran
Pembroke Pines, FL, USA

 

[inga239]

Hi Mike and BTrueblood,

I'm responding to you both in one post. First thanks very much for the thoughtful and insightful suggestions.

Mike, I did not build this dragon. Thought it would be cheaper in the long run to pay someone that knows how to do this.
Hired and engineer who does this type of thing all of the time. I was told to set the flames both visually and
acousticly which I have done to adnausium. Lots of green in flame, oxidizing, orange lazy flame too much reduction and of
course a perfect flame is a bushy blue flame. It's never that simple though in actuality.

The design is standard dry stacked bricks,
used in many college settings and private studios. It's pretty straightforward construction wise.
The kiln actually ran better when I was in the Pacific Northwest than here in SW Florida. Same kiln, different
climate and in the NW it was at an elevation of 400' not really huge in my mind. Everything is the same but it fires differently.

For this major move, I numbered all bricks boxed them and shipped them across the country to be reassembled. A huge endeavor and not inexpensive.
It has always run on propane. A long time ago I purchased an Oxi Probe. Used it until the Platinum wire broke. Had it fixed twice. the
last time decided it had questionable value so it is stored with a broken wire waiting for repairs. It gave perfect readings at the
location (back wall) However, the rest of the atmosphere was a guessing game. It's not practical to move it around which would of course help in getting better readings.
As for Dreaming and getting the perfect kiln. These days you can buy a fully automated kiln which would be lovely. I would have to knock
down a wall and or add on to the building to get it into the building. I think they run somewhere around $50K not counting shipping installation etc. None of that will happen in this life time or at
this location. You have both given me food for thought and things to research. The easiest would be to install something at the T or regulator. I can't recall what the tank regulator is set, want to say 10 lbs. Then the downstream secondary regulator is set at 10". I was not able to locate a low pressure propane regulator anywhere. The venturis simply won't run on high pressure. After inspection, I removed the 3 lb propane regulator and replaced it with a low pressure regulator designed for natural gas which is what the engineer installed originally.

Right now I am up to my eyeballs in alligators with a web site home page I deleted at 1:00 a.m obviously by mistake. Any changes to the kiln will have to be made during the summer when
tourist season is over. It will allow me time to research all of the potential changes I can make. In the mean time, I am ready for another firing. Wish me luck

Again, Thank You both

Ingeborg

 

[btrueblood]

Hmmm. Are your best or worst firings happening during summer (hurricane season) or winter? We get storms up here in the Pac NW, but I don't think the barometer swings as much as it might in Florida, but I'm also no meteorologist.

You might check the price of a standard automotive exhaust oxygen sensor, there are some blogs and whatnot online that talk about using them. They are likely cheaper than an "industrial" sensor, and perhaps you could afford a few more of them.

One last thing - can you jury rig a convection fan, to help keep your kiln atmosphere well-mixed?

Good luck.

 

[dgallup]

Let me say I have no experience using a kiln at all. So I goggled "dry stacked brick kiln" and looked at a couple of articles and lots of pictures. It seems to me that the entire kiln is one uncontrolled air leak. I do not find it surprising that such a thing would never repeat.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[btrueblood]

:/

If you read/learn about the Taguchi Method, you find that he had the same problem (ceramic products that would not fire the same each time due to kiln irregularities, etc.), and solved his quality control problems by fixing his input (makeup of the ceramics and glazes), using the aforementioned methods.

 

[inga239]

I have to confess I try not to fire during the summer as it is what hell must be like. Tourist season is over and anyone who has an order in will have to wait til fall. I make it very clear up front.

Atmospheric pressure is very much a factor during a firing with natural draft venturis. When it is very hot, it fires really different as to heat rise, Kind of like an airplane trying to take off in very hot air. It is hard to get heat rise and the firing just goes on and on.
We evacuated for Hurricane Charlie and I don't know exactly what happened but the kiln was soaking wet so I suspect the 3 foot over hang did little against winds and water flying sideways. After wards I called my kiln guy and he said to dry it out slowly with fans and it would be ok. My first firing after wards was unbelievable..Could not
control anything. I had NEVER experience anything like it. The kiln took off and just roared. It was frightening. Kept checking roof chimney to see if things was catching on fire. Closing damper lowering gas flow etc nothing made any difference it just fired itself. I figured everything would be ruined. Called my kiln guy again and he said I was making hydrogen. Results were typical.

I had at one point considered automotive sensors but thought they would not go high enough in temperature. Myabe I should check into it again, things change over the years. I think they are way less expensive than an oxi probe. A new probe now costs over one grand. I bought mine when it was 600 which was a lot of money at the time. To top it off, they only last for a limited number of firings when the platinum wire breaks and it is expensive to repair.

Ingeborg

 

[btrueblood]

The guts of an automotive probe are the same, I believe, but the support tube is probably stainless steel, which you are correct may not last at kiln temperatures. The blog I believe mentioned finding ceramic support tubes to hold the probe in position.