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Troubleshooting This Converted Kiln O' Mine: Taller Chimney?


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#41 neilestrick

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Posted 26 February 2014 - 05:29 PM

Yes, Marc will probably solve this in 10 seconds. If it helps you can always refer him to this thread so he can see the videos.


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#42 Kristin_Gail

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Posted 26 February 2014 - 07:53 PM

I did give him a call this afternoon.  His knee-######## reaction was there is something plugging up the process in the kiln-chimney, but needed more info.  I did send him an e-mail with more photos and videos than a body would ever want or need.  Hopefully we will get this hammered out tomorrow.

 

I came here first because I figured it was a me problem and-or a chimney problem.  But now that we are talking burners so much ... My fingers are crossed he can help me easily.



#43 bmurphypots@gmail.com

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Posted 27 February 2014 - 08:21 AM

Neil, I'm amazed you made it through that ramble. I so appreciate your perseverance.

I never intended to make this a wood-burning kiln. I was just going to throw in a little stick or two when I added soda, because someone, somewhere, said it would make the flame longer and take the soda deeper into the kiln. When I wasn't able to get to temp, and the wood was just sitting there, I ended up throwing it in to get me over the hump. I'd rather fire the kiln as it was intended, for sure. But can't figure out how to do it.

I have made acquaintance with a very kind man who teaches pottery at a craft college a couple hours away. My next course of action is to do whatever sweet-talking I can to get him over to help (cookies help, right?). Because my constant messing with the burners, the pressure gauge, the damper, isn't getting me anywhere. Same flame, same stalling. Perhaps he'll have the magic touch.

And I'm definitely raising that bag wall!

Will playing with the burners and damper, with the kiln empty, teach me anything? Or do I need to do it with a full kiln, as I have been?

I'm still perplexed about all the cracked pots. Am I just firing too fast through a certain temp range? I loved the idea of blaming it on the accidental crash cool last time, but that obviously wasn't the case.

Forever thankful!



#44 bmurphypots@gmail.com

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Posted 27 February 2014 - 08:32 AM

You are having several issues with your kiln.  Firstly, your burners need to be adjusted to burn cleaner with a bluer flame that allows you to increase your temps at a good rate.  Cracking is probably happening because your pieces are subjected to different temps as the kiln heats unevenly.  You might start out with bisqued pots to avoid this obvious problem.  Take the brick out of your exit flue. It is the right size for the interior of your chimney.  The chimney is the engine of your kiln.  Add a pipe, don't worry about sealing it and see if that changes anything.  I do believe it will.  I had a small soda kiln and the chimney was 16 feet high.  The interior of the kiln was 15 cu ft.  Also, forget the sprayer.  What a pain they are.  Look up Gail Nicols from Austrailia, she uses a mixture of whiting and baking soda or soda ash in a paper burrito that you toss into the burner ports.  So much easier and less stressful than spraying and the soda coverage was much better.  Good luck.



#45 JBaymore

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Posted 27 February 2014 - 10:12 AM

His knee-######## reaction was there is something plugging up the process in the kiln-chimney, but needed more info.

 

This is why I was saying lose that "venturi" idea in the chimney earlier.  It is NOT helping you.

 

Is that REGULATOR supplied by Marc?  You listed the burners the hoses and the yoke...... but did not say the regulator.

 

best,

 

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


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#46 JBaymore

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Posted 27 February 2014 - 10:24 AM

The regulator is (theoretically) good for 195,000 BTU flow... so it is just OK for that installation.

 

Just by chance, did you touch the screw assembly that adjusts the outlet pressure via the diaphragm?  I expect not... but covering all bases here.

 

I still keep coming back to the video of the burners running by themselves.  The lack of a decent flame on the Ransome pilots and the VERY yellow and fluffy yellow and poorly directional quality of the MRs is really not looking correcet... even for the MRs. 

 

Another "grasping a straws" kind of thought trying to diagnose from afar.  How full are your tanks and how cold has it been when you've been firing and testing?  If the tanks get too low and it is very cold, the vaporization rate drops off greatly.  But to get that below the inlet pressure for the regulator is HIGHLY unlikely in this case.... but it COULD happen (looking at everything here). 

 

In fact... are you SURE that the valves on BOTH storage tanks have been fully open all the time?

 

best,

 

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


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#47 Marcia Selsor

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Posted 27 February 2014 - 10:34 AM

It is really difficult to understand all the complexities from all the bits of information and not being able to get the whole picture.

Marcia

#48 Kristin_Gail

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Posted 27 February 2014 - 12:03 PM

I know how difficult it is. I just wish I could whisk a few of you out here to figure it out!

 

I never touched anything on the regulator - in fact, I didn't even know you could. It was supplied by Marc. Everything but the tanks came from him.

 

The two 100-lb tanks were just filled to the top, and the valves on them were open all the way. It was about 40 degrees out on the day of the firing. (The first time I fired the kiln, it was cold enough out that the [full] tanks frosted on the outside, but not this time. No frost to be seen. Much warmer this time.)

 

I grasped at the "Maybe propane tanks are under a different amount of pressure in Canada!" straw last night. The husband laughed.

 

Marc did mention that it isn't right, that the dials on the burners only open up to 5.5". Will hopefully chat with him again soon.



#49 Kristin_Gail

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Posted 27 February 2014 - 02:01 PM

.... And the burner manufacturer's response:

 

#1. Fix the bag wall.

#2. Chimney needs at least one foot.

#3. Maybe also try to adjust the regulator - open up the black thing and screw closed completely whatever is inside there.

 

Every point of which everyone else is already saying - including me!

 

After these changes, I think I'll put everything back in that I just took out and light it up next week.  It was all headed to the shard pile, anyhow.  Might as well use it to test out all these theories.



#50 JBaymore

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Posted 27 February 2014 - 02:42 PM

Maybe the regulator got inadvertantly shipped to you without the discharge pressure setting set to the expected 11" W.C..  That kind of thing can happen...... no one is perfect.

 

With that "so-called" venturi business in the chimney.... I'm guessing it'll need more than an additional foot of height.  But maybe if the gas pressure is also increased,....... the two will combine to help you out.

 

Venturi operation (and engineering application) is SO misunderstood.  People somehow seem to ignore "science-y" things that apply like Reynold's Number and the Venturi Discharge Coefficent and what a venturi actualy does and how it is used.  Simply narrowing a duct/tube more typically creates what is known as an orifice plate or restrictor plate.  It does not increase flow...... it decreases flow.  Friction losses increase. 

 

The engineering of the necessary CURVES that keep the Discharge Coeffieint high is sophistiocated.  Jagged rectalinear brick changes are not going to do anything but induce turbulent flow and add friction losses, as well as thelosses induced by the change in relationship between cross section of the duct, and the wall contact surface area.

 

If you already have too much volume... it can apperar to help.... but not becasue of any action of a "venturi" impacting it.

 

The bagwall raising and tuning is a "no brainer".... HAS to be done.  Crossdraft circulation requires either a bagwall to distribute the heat energy evenly........ or using wares designed and stacked to do the same job (ala' an anagama kiln).

 

best,

 

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


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#51 Kristin_Gail

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Posted 27 February 2014 - 02:47 PM

Trust me - if I could go back in time, I'd have never put the thing in!

I plan to add 4' of height to the chimney, plus the bag wall and regulator tweaking. Giver 'er another whirl. And another and another. If it comes to it, I can rebuild the chimney. But I'm going to call that my very last resort.

#52 Mark C.

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Posted 27 February 2014 - 03:19 PM

Gail can you explain in detail how you built the chimney-Is the whole brick stack 9x9 inches inside or something else? and where is that something else located ?on the top or bottom of chimney? . Sorry if you have already explained this but so much has been covered.

 

Mark


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#53 Kristin_Gail

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Posted 27 February 2014 - 03:45 PM

Mark - I read Nils Lou's book "The Art of Firing" just before building the chimney, and he suggests putting one course of bricks in the stack, a few feet above the flue, that reduces the size of the inside, in order to create turbulence.  I was under the impression that my chimney was way over-sized at the time, and thought this layer would possibly help, and if it turned out the chimney was far too wide, I could slip a smaller pipe down to sit on this layer if need be.

 

I didn't measure the interior dimensions of the hole when I built it, but it appears from photos to be about 6" x 6" or maybe a tad bigger.  http://kgspottery.co...gAnthony/43.jpg  It's about 2' up from the base of the exit flue. The rest of the chimney, both below and above this one layer, has a 9" x 9" space.

 

p.s. The second half of my name sounds funny when applied to me.  "Gail" alone is my mum!



#54 Mark C.

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Posted 27 February 2014 - 07:18 PM

Ok I just reviewed both my Nils Lou books-I think its fine-You still may need more stack after you try again. I would not restrict it any more by putting a smaller pipe into it. 8 feet is just not very tall for a stack but you have burner/regualtor issues which need to be resolved 1st as well as the bag wall .

Mark


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#55 Marcia Selsor

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Posted 14 March 2014 - 07:25 AM

Did Marc made your set up for propane or natural gas?
Let us know what he says. He built my last two burner set-ups and I am happy with them..

Marcia

#56 schmism

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Posted 14 March 2014 - 11:02 AM

I'm thinking that unless you want to change out the orifices, that you should look more at a low pressure (11" Water Column) HIGH VOLUME regulator.  Regulators have two ratings...... delivery pressure and total gas volume that they can pass in a unit of time (minute / hour).  The issue here is likely volume... not pressure (see my comments above).

 

The issue is,  we are dealing with a gas so the 2, volume and pressure are directly related.   The listed "high pressure" regulator means it CAN put out a high pressure but doesn't have to. (it depends on how large an orifice you adjust the screw on the adjustable regulator to)     The reality is,  given a specific orifice size,  flow rate of a gas through it is going to be limited by the upstream pressure.   (if the upstream pressure its between 1.7-1.9 times higher, you can consider the orifice "choked")

 

If you want to saturate the downstream burner orifice, which is sized to put out ~100K btu/hr at 11" WC, then you HAVE to have a larger upstream pressure.   You want that adjustable regulator because the mass flow (flow rate) through the burner orifice WILL change with thins like gas temp, pressure,  air temp etc.  

 

FYI a larger flow rate regulator, is a regulator with a larger orifice,  there is simply no other way to do it.  (so you might as well go with the adjustable regulator listed above)

 

Now that last part, gas temp is an issue.   

 

Propane is a liquid in the tank, and that requires it to vaporize to a gas in the tank before you can use it.  This process (a phase change) requires heat,  (a considerable amount actually)  the tank draws that heat from the environment it sits in.  

In short, a given tank size is rated to put out only a certain number of BTU/hr based on surface area of the tank and the liquid inside.  exceed that btu/hr and the tank will freeze up (you'll actually form frost on the tank on the lower portion that holds the liquid propane. that frost then acts as an insulator so your vaporization rate drops even quicker)  once the tank starts to freeze up,  the output of the tank drops as the cold liquid propane cant vaporize enough gas to keep up with your demand. eg the mass flow drops (aka btu/hr)

 

For instance,  a 100lb tank (the kind you have)  are rated to put out ~80,000 btu/hr at 60deg.  that number drops off quickly as the outside temp drops.   at 30 deg that is down to 52K btu/hr.  

 

SO even if you did fix your regulator issue,  If you plan to fire in late fall when its cold,  you may have issue with the tanks freezeing up.  They sell heating blankets for propane tanks to offset this issue, but they are expensive.  Alternatively you could switch to a larger tank that has more surface area.  (such as a 150 gallon (not pound) tank will put out ~214,000 btu/hr @40F)

 

(and yes when we were living in a house with a 500 gal propane tank when the temp hit -20F we were outside with a heating blanket on our propane tank so the furnace would get enough gas)

 

 

FYI people firing on natural gas don't have to worry about the above problem because the supply always comes in gas form (not liquid as propane does)

 

<---- mechanical engineer for a living



#57 Kristin_Gail

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Posted 15 March 2014 - 07:54 AM

Hi Marcia -  He set it up for propane - he knows I'm running on two 100-lb tanks, etc.  A few posts above yours, I shared Marc's response ("And the burner manufacturer's response:").  

 

schmism - I unfortunately cannot run on any larger tank than 100-lb.  Bigger than that, and it would have to be delivered, and they cannot deliver to my system.   The tanks did freeze, the first time, when the outside temps were hovering just above freezing.  But they did not the second time.

 

I have called more people than I care to remember, looking for a damn piece of culvert pipe to extend the chimney.  Once I finally find one, I will be trying this again, with that change (4-5' added to chimney height); higher bag wall; turn that dial in the regulator; and oh yes, by that time it will be threatening Spring here, so the air temp will be higher.

 

I had hoped to have done all this by now, but unfortunately the rest of life (what, there's life beyond that kiln?) has gotten in the way.  



#58 jrgpots

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Posted 15 March 2014 - 11:59 AM

Just a thought about the gas... would a manifold between the tanks and burners help to prevent freezing of the tanks from too rapid depletion with associated drop in pressure. I built a forge using two venturi burners. The tanks were small and flow rate was high. Placing a large manifold between the tanks and burners helped to stabilize the tank temp, pressure, and flow rate.

Just a thought.

Jed

#59 Kristin_Gail

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Posted 15 March 2014 - 12:25 PM

I don't think there's an incredibly fast drop in the tanks?  In a 24-hour firing I only used a little over 1/4 of each tank.  (In addition, I have no idea what a manifold is!)



#60 JBaymore

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Posted 15 March 2014 - 02:42 PM

Kristen,

 

It is all about a combination of vaporization rate............ which is impacted by surface area of liquid gas exposed to evaporate from combined with the volume of liquid storage, and the availability of heat energy to replenish heat energy used in the evaporation process. You can certainly improve that "draw" situation by adding a third yoked tank (increase both storage volume and evaporative surface area)..... but I do NOT think this is your problem at all.

 

You can only burn the gasseous propane as fast as it will evaporate off the surface of the tanks. That evaporation rate is determined by the square area of the liquid surface exposed, the temperature at any given time in the firing of the liquid gas store, and (technically) the partial pressure of propane in the open space in the tank (whcih relates to the draw rate).

 

YOU don't need to know all the technical stuff....... your propane supplier has handy little charts of vaopriozation rates for given sizes of tanks with the tank in an environment at a specific temperature. As long as your kiln's burners needs are LESS than the numbers you have.......... you'll have the BTU output to the burners to fire the kiln.

 

That rate is a function of the surface area of the particular tank design, and the thermal mass of the gas storage. To evaporate, it requires heat energy to change from liquid to gas state. That energy flow comes (typically) from the outside environment that the storage tanks are placed in. They absorb heat energy from the surrounding environment. This keeps the temperature of the liquid storage up, and allows evaporization to continue. If the heat energy flow into the tank liquid is not equal to the energy uised to evaporate the liquid to gas, the store of liquid cools off. As it cools, the evaporization rate decreases.

 

Non of this speaks to WHAT the burners and the kiln system DO with that gas's potential heat energy. THAT is where the issues lie.

 

best,

 

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


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