Need to know Olympic 2831 gas amount for fire

[MFP]

I have an Olympic SIX burner 2381 size propane fired kiln that I have never fired. Can anyone give me an estimate of how many gallons of propane would be required for a cone 6 or cone 10 fire please? This kiln only has a kiln sitter ....nothing fancy.  Thanks!  Also....any tips on how to load the darn thing?

[Mark C.]

I looked up that kiln number and could not find it.

I will say 6 burners is way better than  the 4 burner ones.

There has been much posted on these kilns so do  search from main page-they are hard to fire even but your 6 burner will work better than the smaller tw or 4 burner ones.

Are you sure on the 2381 model #s???

[MFP]

Sorry....being dylexic again....it's the 2831H type. It's so deep that even standing on a step I cannot reach the bottom without leaning on the edge of the kiln which can't be good. Also wondering what height the first stilts for the shelf should be. Yes...I am wondering how these new ones with the four burners are working....seems like they would create hot and cold spots? I also see on here that there are recommendations to put shorter shelves in the middle....do you agree with that?  How did our test go or have you opened the kiln yet? Olympic has said that the rest of the gas plumbing is the same. I have seen estimates from 40 to 100 gallons....not real helpful.  I also notice that most people are using tanks instead of having a propane service.....I understand why there would be advantages to that.

[TallerJMC]

Hi MFP... i just got an 2831 with four burners, propane. Yesterday I did my second firing and have not yet seen its results.  I fire at ^6 but am  in my way to ^8.  My objective is to develop and work mainly with natural glazes.  First firing was uneven. Bottom shelf did not reach temp, probably below ^5 since glazes did not mature;  top shelf reached ^6 and pieces were fine except one large vase that received direct flame and left a black spot on the side.  I contacted Olympic staff hoping to get some advice and received no answer at all. I began to look at this forum and here I am

I use 45 kg propane gas tank, conversion is about 12 gallons.  So far two firings and there is still gas in it (probably around 20 to 30%). In first firing I bent over to load it and was quite uncomfortable.  For this second one I took out the cover and first two rings, much better.  First shelf at the bottom is on 3” posts as recommended by Olympic.

On this second firing I did put cones all around to see cold/hot spots, also, changed the location of the shelves, used them as barriers to redirect flames and get an even burn. By the end of the week I should know how it went.  Also, did my first reduction firing, very excited about it.

[MFP]

I had wondered if their changing to four burners was going to be a problem. Mine has six burners.....it's 30 years old and has never been fired. I have lugged it around all these years.  I  previously was firing a sprung arch downdraft that I built.  I don't know much about updrafts, but that problem of being cold in the bottom does not surprise me. My instincts say to try shortening your flame until basic thermodynamics does the job for you. I had the same problem in my downdraft...it never seemed to draw like it should have, bringing the flame tip into the bottom....so my only recourse was shortening the flame---it was functioning like an updraft. It was counter intuitive because you would think that lengthening the flame would be the thing to do...but all that achieved was making the top even hotter.  I have also seen some discussion on here about short and tall shelf loading affecting the firing in these updraft kilns. What occurs to me is that if the bottom is too open the flame is just going to whiz through there. I am also wondering if you are bringing the temp up too fast?  There is always going to be a tendency for it to be hot in the top. I used to put my cone 9 glazes on the bottom and cone 10 on the top. You might also find more reduction effects in the top as well.   Thanks for the info on the gas consumption! 

[MFP]

On 6/26/2019 at 3:30 PM, TallerJMC said:

Hi MFP... i just got an 2831 with four burners, propane. Yesterday I did my second firing and have not yet seen its results.  I fire at ^6 but am  in my way to ^8.  My objective is to develop and work mainly with natural glazes.  First firing was uneven. Bottom shelf did not reach temp, probably below ^5 since glazes did not mature;  top shelf reached ^6 and pieces were fine except one large vase that received direct flame and left a black spot on the side.  I contacted Olympic staff hoping to get some advice and received no answer at all. I began to look at this forum and here I am

I use 45 kg propane gas tank, conversion is about 12 gallons.  So far two firings and there is still gas in it (probably around 20 to 30%). In first firing I bent over to load it and was quite uncomfortable.  For this second one I took out the cover and first two rings, much better.  First shelf at the bottom is on 3” posts as recommended by Olympic.

On this second firing I did put cones all around to see cold/hot spots, also, changed the location of the shelves, used them as barriers to redirect flames and get an even burn. By the end of the week I should know how it went.  Also, did my first reduction firing, very excited about it.

I forgot to ask if you are using a hood....that will also suck the flame into the top

[TallerJMC]

Hi MFP: no, no hood so far and am glad you mentioned it.  I´ve never fired a gas kiln before so everything is new to me.  By hood you mean adding bricks above the flue on top of the lid?  I did see some pictures in another post in this forum showing that possibility.  The thing is that in the second firing it happened the opposite: extremely hot at the bottom and not enough at the top.  This time I used the bottom shelves as barriers to slow the flames, against the wall, next level centered and top level of shelves against the wall again.  In the middle I got ^6 well bent, below must have reached ^10 and above ^5 or less. Reduction fired.  I am so amazed with the results, really happy although some pieces are worthless.  Also, I did put many small ^6 all around and was surprised to see temp differences in same shelf level.  In next firing I will detach shelves from the wall, slightly, and see if I can get an even temp around all levels.

Temp: yes, I increased temp too fast at the beginning.  The first and a half hour with pilot alone but once the burners got ignited temp rose super fast and I realized it when it was too late.  There was a lot of black smoke coming out the flue (I had burners in a very low mode) and the only way it stopped was when I increased the gas flow but then temp rose too fast.  Something I will pay close attention in next firing.

For the moment I continue using my regular glazes and expect to start developing new ones once I have a better understanding on how this kiln works.

Good luck with the installation of your kiln.

Regards,..

Juan A. Muller

TallerJMC

[MFP]

1 hour ago, TallerJMC said:

Hi MFP: no, no hood so far and am glad you mentioned it.  I´ve never fired a gas kiln before so everything is new to me.  By hood you mean adding bricks above the flue on top of the lid?  I did see some pictures in another post in this forum showing that possibility.  The thing is that in the second firing it happened the opposite: extremely hot at the bottom and not enough at the top.  This time I used the bottom shelves as barriers to slow the flames, against the wall, next level centered and top level of shelves against the wall again.  In the middle I got ^6 well bent, below must have reached ^10 and above ^5 or less. Reduction fired.  I am so amazed with the results, really happy although some pieces are worthless.  Also, I did put many small ^6 all around and was surprised to see temp differences in same shelf level.  In next firing I will detach shelves from the wall, slightly, and see if I can get an even temp around all levels.

Temp: yes, I increased temp too fast at the beginning.  The first and a half hour with pilot alone but once the burners got ignited temp rose super fast and I realized it when it was too late.  There was a lot of black smoke coming out the flue (I had burners in a very low mode) and the only way it stopped was when I increased the gas flow but then temp rose too fast.  Something I will pay close attention in next firing.

For the moment I continue using my regular glazes and expect to start developing new ones once I have a better understanding on how this kiln works.

Good luck with the installation of your kiln.

Regards,..

Juan A. Muller

TallerJMC

No....by hood, I mean a square sloping  sheet metal "roof" over the kiln with a stovepipe coming out of the center of "roof" usually venting through a roof. Depending on how close you get it it can increase the draw. If you are in a space where heat and fumes are not an issue....like outside....you don't need a hood. There are pictures of hoods on the Olympic website. They want $1500 for $100 worth of metal!  ( my husband did soffit.....so we have a 12 ft metal brake...making that is about an hour job...cutting the metal would take the longest time).

Usually reduction in those kilns is done just by putting a soft brick over the hole in the lid. These folks on here have all kinds of ideas about when and for how long to do reduction....probably dependent on clay bodies. In my day, very heavy reduction was the norm....I also shoved one inch cedar sticks into my ports....the wood ash made the colors more brilliant. But you cant's do that in a soft brick kiln like that. 

What you basically did was created a fire wall like there are in kilns of other types. You shouldn't have to have a fire wall in that design kiln.  That black smoke was carbon and means that the gas was not burning completely. I am assuming you put the regulator on the gas line at 11 water column inches? I am trying to think of why you would have unburnt fuel like that---it's very weird--like something was impeding the flow and combustion of gas....the fire walls perhaps . Yes...of course turning it up and letting it rip would take care of that but also cause many hot and cold spots with that fire wall you built.  Do you have the option of only starting out with two burners? If so you might try that. 

I am not going to fire mine for a while. I am returning to pottery after a 35 year hiatus...I was a production potter for about a decade. I have to catch up with all this new stuff...and oxidation. I also have a cone 10 electric Olympic.  Lots of glaze testing in my future....and I have to decide which clay bodies I am going to use ongoing.

Good luck!  If you figure it out--let me know!  I would be very interested in the solution.  If you get a chance to talk with Mark C.....he is a reduction potter from my era...he has more kilns than Carter has pills...and knows a LOT about reduction firing.  

Have a great 4th!

 

Marie

 

[TallerJMC]

Hi Marie: ok, yes I understand, no, no hood.  I have the kiln in a warehouse with plenty of air around.  The roof is about 5 ft above the kiln, could that be an issue? I suppose not.  I think I had the damper half closed probably that’s why there was black smoke; anyhow I still have a long way to go.  For the moment I have no gauges installed.  

Unfortunately it is not possible to turn off any burner because at low temp you do not have a choice to fire slower. I guess having the damper totally open would allow a slower increase in temp with unnecessary  gas consumption.

I am currently producing in order to have enough pots for a next firing, hopefully in a couple of weeks.  I will let you know how it went.

Thanks a lot for your patience.

Enjoy, be happy

Juan

[liambesaw]

It's not more gas consumption if there's black smoke coming out, that just means gas isnt burning completely, so you're technically wasting more gas with the damper closed down to the point it's smoking than you do with the damper open.  The damper helps maintain the correct gas to air ratio, when you close it off, the propane can't combust fully.  Also you don't want to run with an oxygen deficit in the beginning of a firing either, this is the time when you need to burn out as many organics as possible that that requires plenty of extra oxygen!  So don't worry about opening the damper up, you WANT air moving through, it doesnt even necessarily slow the heating, it usually speeds it up.

Adjust the burners for slowing down a firing and adjust the damper to control airflow and reduction

[MFP]

You didn't answer about the regulator. That's important. The Olympic site (great kilns) has a downloadable manual for all their kilns. They have a suggested firing schedule for the gas kilns. You might want to look at it. I would get rid of the fire wall.  As Liam indicated....sucking carbon into your clay body early in the firing is not a good idea. I think your point that the firewalls might have blocked the flow of gas leading to incomplete combustion is correct. 

Happy throwing!  

[neilestrick]

These round gas kilns are known to have a lot of issues with firing evenly, getting to temp, reducing evenly, etc. Based on what I've seen on the forum, the folks that have the best results are those that have modified the stacking configuration from what Olympic says, or have added in a baffle wall or flue channel. The biggest issue with these kilns is that they don't have enough room to breathe. Air flow is all-important in a gas kiln. If you load it like an electric kiln, there's not good air flow. 

[oldlady]

i do not use a gas kiln at all.   years ago, between 1975 and 1990, i did stack a round gas kiln for a friend with a broken arm.   she said she had never seen anyone stack that way and it was the best firing she had done in years.   wasn't to get me to do the next one, it was true that her work looked better.  

all i did was try to fit the odd shaped sculptures and other "normal" pots so air would flow around them.  some shelves were whole and some half.  some of the half shelves fit into the odd spaces left under the arms of the sculptures so nothing was stacked in a straight vertical line.   they almost spiralled up inside the kiln.  

maybe that kind of stack allows the air and flames to penetrate differently enough to make it work.

[MFP]

Hi Neil!

He has one of the new ones with four burners and I had suspected that was not going to turn out well. Mine is the old kind with six burners. These four burners are also larger...mine are smaller. That also means the ports are larger but also that the air flow is not uniform....(a really bad idea on their part as far as I am concerned).   I am thinking that I have a better chance of a more even fire. However, these kilns will  want to get hot in the top. When your only method for controlling the flame is sliding a brick over a hole or turning down the gas to shorten the flame,  your options for control are limited. I am still trying to find out how many gallons for a fire. He said he used 12 and that seems low to me--which makes me wonder if the temp is rising too fast which would also result in its being hot in the top. . I agree with "old lady"  that how you sack it is going to make a difference. He also said he got hot and cold spots throughout which also makes sense. I am thinking tight in the bottom, open in the middle and tight in the top. That will encourage the flame to the middle and hopefully through thermodynamics if you keep the flame short, the top and bottom should be about the same.  Now I might not know a lot about these new clays and glazes...but finicky kilns that don't fire the way they are supposed to is something I know a LOT about. 

[TallerJMC]

Thank you all for your comments.  I will have them in mind in my next firing and hope to report as best as I can.  I will try to answer your questions:

Marie: I do not use any gauges,  so no water column readings, I simply turn the gas valve to get more / less gas.  I do have Olympic manual but it is very vague.  In the first firing I followed exactly their instructions. 

Liam: agree with you. I made a few mistakes in second firing especially increasing temp too fast once the burners got ignited.  As it has been said, these kilns are very sensitive to minor changes and I need to get familiar with these changes.  I am using John Britt's book as a reference to get a proper curve temperature.  And am enjoying very much the ride, whatever happens is a good experience to learn and continue exploring.

Neil & Old Lady, thanks and yes, I believe the stacking has a lot to do with an even firing.  I always try to put pieces around that would contribute to gas flow.  What would you suggest regarding a taller piece?  is it better to place it at the beginning of the inflow of gas or behind with smaller pots in front?

Marie: the gas tank I use is about 12 gallons, maybe 15 gallons (I will check with more precision 45 kg equivalent, not sure if it includes the weight of the tank as well) .  I have two of them connected although so far I have not needed the second one.  I will send you a photo.   When I finished the second firing the bottom third of the tank showed freeze outside, I understand that it shows the gas content of the tank. Therefore, I can conclude that each firing consumes about 1/3 of the tank.  Hope this helps.

 Enjoy 4th July and happy firings 

[Babs]

If have two tanks and one in use shows freezing switch to other tank immediately. The emptier tank can be usdd up at start of firing next time.

[liambesaw]

You can put the tank in a basin half full of water to stop the freezing stuff, it can really impede the firing.

[MFP]

You are supposed to have a regulator on the gas line like the one you use for an RV. It adjusts the pressure of the gas to 11 water column inches. There should be a picture of one in the manual. If you are not using one.....that could be the source of your flame problems. 

[Bill Kielb]

@TallerJMC

Ok,

here is what I have. Your kiln assuming it is a torchbearer uses a #40 drill size orifice for propane and is designed for a maximum of 11” w.c. So you must have a regulator. As we increase the gas pressure the thermal output goes up exponentially which means 10% increase in pressure nets more than 30% output in thermal energy.

if you do not have a regulator, most propane tanks are charged to many PSI which is way higher than 11”. It takes about 28” of water column just to equal one PSI. So if this kiln needs a regulator and you do not have one it should have almost uncontrollable output which is very dirty. (Reducing) sounds like your symptoms actually. 

so, assuming the manual I excerpted is for your kiln, get a regulator, set your primary air as below and fire in stages as below as well. It’s Easy to go way too fast with this kiln as well as drive it into reduction even if unwanted. Generally safe speeds are in the 400 degree per hour range for glaze and 200 for bisque. (Generally)

 

 

 

[MFP]

Bill,

Do you have any information on my original question of how many gallons of propane  would be used in a cone 10 fire in the 2841 please? I apologize if it is in the manual....I couldn't seem to find it.  This whole other thread started with this other gentleman's problems with his fires. 

[Bill Kielb]

On 7/4/2019 at 1:17 AM, MFP said:

Bill,

Do you have any information on my original question of how many gallons of propane  would be used in a cone 10 fire in the 2841 please? I apologize if it is in the manual....I couldn't seem to find it.  This whole other thread started with this other gentleman's problems with his fires. 

Here is what I found - 15 gallons to cone ten if you believe the spec. below. I would guess that is an approximation and to just point out that propane cylinders are generally only filled to 75% capacity by weight and further restricted in the states here with an internal float assembly so it’s hard to get a tank filled with more than 75% capacity.

why bring this up? If we believe the 15 gallon spec to cone ten and a 20 pound cylinder is only filled to let’s say 15 pounds of propane and propane weighs 4.2 pounds per gallon we actually get 3-4 gallons in a freshly filled 20# cylinder. That is if we eek out all the propane when we use it. Cylinders are generally tare  weight stamped on their collar btw.

For me, I would weigh then fire and re-weigh the tanks to have a better idea of how much I consume. I would probably convert to BTU in the end just to have an idea how I treat Mother Earth and in the event I wanted to convert to natural gas at some point.

so if we believe the spec 15 gallons X 1.25 percent X 4.2 pounds per gallon = 78.75 # minimum with today’s cylinder fill practice to get to cone ten or lots of little 20# cylinders. Yikes! Seems high.

specs below and everything you wanted to know or not about propane as well

so what the heck, how much does it cost? Assuming propane at about 3.00 per gallon then 15x1.25x$3.00 = $56.00

and for electric? (15 gallons X 94500 btu per gallon / 3.41 btu per watt) / 1000 watts per kWh  x0.12 per kWh is about $50.00 bucks!

refill propane is actually $3.00 - $4.00 per gallon and electric rates here in the states vary by location so firing either way to cone ten  is probably in the  $50.00 - $100.00 range per firing.

 

 

 

 

[Babs]

12 hours ago, liambesaw said:

You can put the tank in a basin half full of water to stop the freezing stuff, it can really impede the firing.

Yeh but if have 2 the switch over at high end is less work.....been there, done that.

Iced tank going nowhere re finishing firing.

[liambesaw]

2 hours ago, Babs said:

Yeh but if have 2 the switch over at high end is less work.....been there, done that.

Iced tank going nowhere re finishing firing.

My tanks would freeze when they were half empty, maybe in a warmer area you get more out of them before they freeze, but if I switched over every time a tank froze I'd never get anywhere.  Keeping them in a pan of water stopped them from freezing at all and allowed me to use an entire tank before switching.

[MFP]

Thank you very much Bill. As always you have been very helpful. Costco has a 40 gallon tank that should do the job. I also have a tall rank that is probably 50 gallons. If we have both on hand we should be fine. The Costco tank is squat which would make putting it in a wash tub of water easier. The other tank is tall and would be harder to keep from icing up.  I also noted in the manual that they say that the tank should be 20 feet away from the kiln and have a hard line to the kiln. I get the 20 foot part but the hard line is a little mystifying. Yes..that firing schedule looks appropriate but I think keeping the middle somewhat open will help in not letting the top get too hot. If this thing fires like my old kiln, I will be ready for it....I had  cooler glazes for the bottom and hotter ones for the top. I just assumed it is going to be hot in the top. Thank you again Bill.

[Bill Kielb]

1 hour ago, MFP said:

Thank you very much Bill. As always you have been very helpful. Costco has a 40 gallon tank that should do the job. I also have a tall rank that is probably 50 gallons. If we have both on hand we should be fine. The Costco tank is squat which would make putting it in a wash tub of water easier. The other tank is tall and would be harder to keep from icing up.  I also noted in the manual that they say that the tank should be 20 feet away from the kiln and have a hard line to the kiln. I get the 20 foot part but the hard line is a little mystifying. Yes..that firing schedule looks appropriate but I think keeping the middle somewhat open will help in not letting the top get too hot. If this thing fires like my old kiln, I will be ready for it....I had  cooler glazes for the bottom and hotter ones for the top. I just assumed it is going to be hot in the top. Thank you again Bill.

Just a non intuitive note: early in the firing convection is useful and provides significant heating followed by conduction and radiation. Later well after red heat, radiation becomes the most prominent and then conduction followed minimally by convection. It turns out that at those temperatures the amount of energy that can be transferred by the very thin air is not very significant with respect to radiation and conduction. Pull a plug on an electric kiln at 2000 degrees and nothing comes out of the hole. The atmosphere is too thin.

whats the point? Line of sight is super important, total mass in a section and of course losses. Our old Alpine updraft are triangle shaped and always start off significantly hotter on the top than bottom. By the end of the firing, the bottom usually becomes hotter than the top by 20-50 degrees. Cools down that way also for many hours as the mass of the kiln and pots is highest in the bottom.

electric kilns  (later in the firing) are often cooler at the top due to the lid losses. Just a non intuitive thing that tends to confuse folks. If it’s hot or cold  in a spot, there is a reason, but it may be a non intuitive reason in the end.