Real-Time Kiln Advice (Kiln Curently Firing)

[Mark C.]

I just re-read the regulator section of that thread, and it sure seems as though it was a consensus to change to that specific regulator. But why didn't I? If I remember correctly, I thought someone said it wasn't the right one, as it says right on it "high pressure." But now I can't find this comment, so I was obviously confused. Also, in the middle of the discussion, I called Marc and he said just to turn up the regulator I already had.

 

Here's the suggested regulator: http://www.amazon.com/Bayou-Classic-5HPR-40-Adjustable-Regulator/dp/B0033JF0GE

 

I'm certainly more than happy to give this a go.

Yes thats the regulator that I use on a super high output stove I cook crab on and we bill our salted kiln water for salt kiln fires on as well.

It cranks up pressure and has high volume output

I would order that in a heart beat over your RV regulator.

Why you never changed this out after that talk I do not know-you do know yours is not doing the job.

Mark

 

PS forget about making chimney smaller do something that will make a difference and thats just counter productive

[Guest JBaymore]

First of all, propane (which you get delivered as LPG.... LIQUID propane gas) goes from the liquid to the gas state at       -44F  ......44 below zero F.  So unless you are getting down to that temp, you are not "freezing that tank". 

 

Water however freezes at 32F.  So if you have water freezing on the surface of the metal tank, that is telling you that the LIQUID gas temperature in the tank is then about at or below 32F.  THAT is telling you something very important.

 

Next point..... the core gas pressure in the tank itself will still be at a level higher than what you likely need to "run" a burner (particularly the ones you have) for a lot lower temperature than 32F.  At 50F the tank gasseous vapor pressure will be about 86 pounds per square inch (gas).  Down at 20 F it is still 47 PSIg.... and at even 0 F...... it is at 28 PSIg.  So unless you design the burner orfice sizing to require MORE than 28 PSIg to run, the GAS PRESSURE will be there to fire the kiln (and for the regulator to still do its job).  Every regulator has a minimum input level pressure that it has to see....... check the specs on yours.... but likely there is no danger of you going lower than that level.

 

A typical "100 pound" cylinder holds about 23.5 gallons of fuel when full.  That is 100 pounds of propane (tank weight is not counted in the "designation" of the tank.)   Note that when "full" the tank interior volume is actually only about 80% filled.  Above the liquid is space for the gas to evaporate into....from where you draw it out for use.  23.5 gallons of liquid propane has about 2,152,600 BTUs of potential heat energy available. So the total you have is "times two."  For that size kiln, you should not NEED anywhere near that total BTU capacity applied to the chamber to get it to cone 6.  However, you can't really GET all of that out of the tank for kiln use.... due to preactical vaporization problems.

 

Now let's look at the property called "vaporization rate".  You burn propane GAS.  Your storage is propane LIQUID.  To burn it, you need to convert the liquid to gas....... which is done by the process of evaporation.  Just like water evaporating from liquid to vapor.

 

IMPORTANT POINT:  This activity requires heat energy to happen.

 

As the liquid evaporates, it "uses" heat energy from the stor of liquid gas to do so.  You can think of this as the heat energy is "carried off" with the gas form as you burn it.  (Note this is not anything to do with the heat value of the fuel itself.)  Unless this heat energy is replaced into the store of liquid gas, the TEMPERATURE of the gas store decreases.  (Note that temperature and heat energy are not synonomous.) 

 

This replacement heat energy typically comes as the tank metal absorbs heat energy from the tank's environment (surrounding air, sunlight, etc.), and then passes it on to the liquid gas via conduction thrui the tank wall and convection in the liquid. 

 

Now there is another factor in all this.  That is the amount of surface area that the liquid store exposes for the gas to evaporatre off of.  The greater this is, the faster the gas CAN evaporate.  Double the surface area, and for any other given situation, you double the evaporation rate.  The 100 # cylinders, have a very small surface area relative to their liquid volume. This is why the larger higher draw tanks are laying sideways,........ to expose more surface area.  This is something you can't change on those 100# tanks. 

 

Bottom line, the colder the temperature of the gas liquid store, the less propane gas per hour will evaporate from it.  As you draw down the propane store, there is less and less heat energy to drive that evaporation.  So for any given size tank, as the store volume decreases, the vaporization rate steadily decreases.

 

When the necessary draw rate for your burners matches or even attempts to exceed the vaporization rate, you can't get any more BTU's per hour.  Stall........ as heat losses fr om the kiln equal or exceed heat input.

 

So now we look at your twin 100 lb. propane tanks.  Here is a chart of MAXIMUM draw rates for a single tank.  And we need to compare that (to START WITH) to your kiln's peak draw (maximum settings on the burners) of about 200,000 BTUs per hour.   I added red highlighting to this standard chart to highlight the facts.

 

Propane Vaporization Rate Chart

- 100 Lb. Propane Cylinders

(Approximate level for continuous draw)

 

Pounds

Of

Propane            0F                 20F               40F              60F            80F 

100              113,000          167,000       214,000       277,000      300,000

90                 104,000          152,000      200,000      247,000       277,000

80                   94,000           137,000      180,000     214,000       236,000

70                   83,000            122,000      160,000     199,000      214,000

60                   75,000            109,000       140,000     176,000     192,000

50                    64,000            94,000         125,000     154,000     167,000

40                    55,000            79,000          105,000      131,000    141,000

30                    45,000            66,000            85,000       107,000    118,000

 

This chart is saying that if your gas store is at 90% of full in both tanks, and the gas store is down at about zero degrees F,  you are getting into the "danger zone" of sustaining the draw.  By the time the gas store is at 60% you are in trouble up at 20F. 

 

Now we get into the "interesting" part here. 

 

We KNOW that you are getting frozen water on the outside of the tanks at some point ('cause you said so).  SO we then know that the liquid propane store is getting down to somewhere around 32F or less.  So we now look somewhere between the 40F column and the 20F column.  Somewhere in the 50% full range,..... FOR SURE, you simply cannot sustain the draw rate you need.  It might even slide up to the 60% full range. 

 

Likely right about the gas level where you are experienceing your stall out in every firing.  And I am assuming there that the gas store temp is not down to the 20F range.  If it is getting that low, then you are "right into the Danger Zone" (cue Top Gun music ) at as much as 65-70 percent full.

 

Sorry but a worse fact coming here now........ propane installation "standards" given to site workers for the use of 100 pound cylinders say that they should be calculated for a continuous draw of ONLY 50,000 BTU's per hour each, year round.  So with 2 cylinders, that says you are set up for only 100,000 BTUs per hour sustained draw.  By that yardstick, your kiln should have FOUR of those tanks, not two.

 

Most potters "push" the latter limits of that info. And sometimes they get away with it.  It looks like you might not be.  Get those tanks into the sun.  Some potters do spray WARM  water over the tanks to keep the liquid store temperature up (and sustaing the draw rate)....... but if you get that tank surface too hot, you can kick off the pressure relief valve on the tank... and get a lot of raw propane in the area around the firing kiln; NOT optimal. 

 

(Somewhere I saw pictures of a potter using a GAS BURNER!!!!!!! pointing at the propane tank to warm it up.        Darwin Award anyone.

 

You might want to think about changing from two 100 # cylinders to a bulk 250 gallon storage tank before going to 4 hundred pouunders.  While it will cost more to fill it, the price per gallon should be MUCH cheaper.  And you'll have more liqud gas store to sustain the liquid temperature under draw, plus larger evaporation surface area on those bigger tanks.

 

Note that in JAPAN, potters typically yoke together MANY (equivalents of) 100# cylinders together....... like 10-12 or more...... where here in the west we might use a 500 gallon or larger tank.

 

So there is some more info for you.  The regulator you have there is, as I alreay talked about, one potential issue here.  And the tank sizing is likely a second issue.

 

And I'll add a thrid factor ... and that is likely (sorry to say this) what is known as ...... "operator error".

 

This is a total GUESS... becasue I haven't seen you firing.... but I am GUESSING that you are firing with too much heat energy going up the chimney, and way too soon.  A very high initial BTU draw started very early, lots of gas consumption that is not really needed (due to high chiomney heat loss), and a stacking up "double whammy" hitting you as the tanks cool excessively early on in the firing and the gas store temp and volume both go down very fast.

 

My apologies if I am wrong in saying that there,...... but I bet that factor is in there also.

 

So like most things....... likely not one simple factor... but a set of circumstancees that are acting synergystically.

 

best,

 

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

 

PS:  As has been said.......  DON'T downsize the chimney.

[Kristin_Gail]

John - Just found this updated post; I'm digesting it post now.

Mark - I found now the post that made me decide not to buy that regulator way back in February:

 

 

Writing quickly from school...... students are working on a project .... triaxial blends.

 

The regulator listed above is a high pressure regulator.  Your burners (apparently and hopefully from Marc) have orifices drilled for low pressure gas. If you use high pressure gas thru a low pressure sized orifice, two things happen.  One is that the amount of gas that comes out of the orifice in a unit of time (per minute or hour) is significantly greater than at low pressure (remember the pressure conversion I listed above).  Second, the WAY that the gas will squirt out of that orifice is affected , so that it affects the flow at the throat of the venturi aspect of the burner...... DECREASING the percentage of primary air it will entrain. 

 

So while the BTUs per hour coming out of the burner will go up if you leave the orifices the same but increase the pressures, the ability of the burner to realize (combust) those additional BTUs will not go up.  So you are still gonna' be dependent on secondary air and the in-kiln mixing function to do that job. 

 

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).

 

That being said, one of the great advantages of having propane over having natural gas is the ability to easily run a high pressure system.  There ARE advantages to be had.  Most natural gas supplies, unless you live in an industrially supplied zone, max out at 11" WC.  Some places max at 4" WC.  Propane has a high tank pressure... so you have lots of available pressure to work with. 

 

High pressure gas does impart some kinetic energy to the flow of gas and air out of the burner nozzle, thereby acting to lessen (slightly) the impact of the kiln system's own draft characteristics.  Also, well designed venturi burners for high pressure operation can entrain more percentage of primary air than the low pressure versions can.  (Not much of an issue with the MRs....... low or high pressure, they are not all that great.)

 

So you would gain SOME advantage by changing to high pressure.  But you'll have to change the orifices, otherwise the burner gas output will be so high, that the burners will be VERY touchy to operate, and low settings will be very problematic.  Additionally, you'll have to run the "high pressure" set so low at the max, as to not gain any advantage of the higher pressure on the "driving forces" on the flow thru the kiln.

 

And we still are back at needing MORE AIR with those burners..... no matter what you do.  Kinetic energy from high pressure can help a bit.  As can more flow induced by the chimney (larger exit flue opening, taller stack, higher exit point temps). 

 

But the first place to go is finding out if the existing burners are getting the gas flow that they are supposed to get.  You should get the specs on the existing regulator, and make sure it is delivering what you THINK it is.  If it is wrong......... then you can ddecide where to go.

 

Don't treat the disease until the diagnosis is in based on the tests.

 

best,

 

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

 

[Guest JBaymore]

Kristin,

 

I have no idea how, out of reading that posting of mine (along with those of others), you decided not to do anything about looking into how the regulator might be impacting this problem?

 

CHECK the volume capacity of that existing regulator (research with the manufacturer).  If it is not able to run more than 200,000 BTUs per hour of throughput, then find an equivalent one that can handle that.  That means keeping the same low pressure output side for your existing burner setup.  If it is MARGINAL volume,........ upgrade it.

 

Figure out if the regulator you have is maybe OK manufacturer volume rating-wise, but actually is defective and THAT is an issue. You already know that as supplied to you from the vendor, even though it was supposed to be set up correctly for you to "plug-and-play", it wasn't.  You had to adjust the output pressure diaphram.  That is a little red flag.  Sometimes parts do come through defective (note the comments in that old Clayart thread I posted the link to a while ago about MR orifice drilling.).

 

If you want to take advantage of the potential capabilities that high pressure gas supply provides, get new orifices for the existing burners, sized for the maximum pressure you plan to use to provide 200,000 BTUs of gas output .  (You MIGHT have to check with the local authorities about doing so first...... some locations will limit you to 11" Water Column in a "home" / residential type situation).  Orifice spuds are easy to change on such burners: screw out, screw in.  Done.  Only t ools needed are a couple of appropriate sized wrenches.

 

This does not change anything that I said in the posting above about the propane tank vaporization rate or the other potential factors.

 

best,

 

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

[Lockley]

Wow, John Baymore  has provided a world of detailed information and analysis of this problem.  Wish,  I could make it to New Hampshire and sit at his feet.

 

I'd like to and something about regulators.  If you have not already, go to your local industrial gas, welding gas suppler, and purchase a high volume propane regulator.  They are relatively expensive but provide the capacity and volume needed in this application.  Propane fuel is used in an number of industrial application so they are usually available quickly on order.    There are, in most manufacturer catalogues, three size of each regulator bodies. You want the largest.   I like the suggestion of ganging together several 100# tanks.   However, If you decide to do that consult your supplier of welding supplies and purchase the equipment they supply to industry for assembling a Propane Supply manifold. 

You may not realize it but, even though you may see your self as a craftsman artist,  when you shift to firing in an independent  kiln your feet are on the first rung of the industrial ladder. Many aspects of Ceramics are best done by creative and  envelop stretching artists but running a kiln is a serious business and no place for cheaping  out.

 

Lockley

[potterbeth]

Regarding the stall in temperature rise: Are you sure the burners are properly sized for your kiln?

 

In my first painful experience with venturi burners, the burners were too small for the 40 cubic ft kiln. We were able to get to temperature after long grueling struggles by people with significant gas firing experience. Some firings took almost twice as long as they should have. Results were interesting. We spent most of a semester doing this before the size issue was identified. Smaller burners were replaced with larger ones, and VOILA the problem was solved.

 

Now, that kiln was being fired with industrial pressure piped natural gas. But, for years before, the same kiln was successfully fired with two tall bottles of liquid propane and forced air burners in all types of weather conditions including freezing during the winter.

 

Just a thought.

[Stephen]

I saw this on CL and it seems this guy has experienced what John B described and the 250 gallon tank was the solution:

 

10 cu.ft Aim propane fired updraft gas kiln available. Great for reduction and high firing. Depending on stacking, can reach cone 10 in 8 hours or less. I usually fired longer for effect. Three burners with control valve on each burner.

Important!!! This kiln needs a 250 gallon propane tank in order to get the right pressure. Gas pressure at kiln should be 11 water column inches. If you ignore this, you will be wasting much gas and never hit temp. You will also need to get a permit and dig a ditch 18 inches deep to bury the gas line to the kiln. If you already have a 250 gallon propane tank, never mind. If you need help with installation, call Calvin at Ag Supply. He's the go to man for gas kilns. He has the experience and the knowledge to get the gas pressure right.

 

here's the link to the ad:

http://wenatchee.craigslist.org/art/4432111315.html

[Mark C.]

Now we are getting somewhere-bigger tank new regulator-kabam presto it may do the job.

Mark

[bciskepottery]

Kristen --

 

Are you still having the issue with the flame inside the kiln looping over the bag wall and straight to the chimney? I remember that drawing and I think you said it was still occurring. I am relatively low on the experience in natural fuel kilns, but in thinking about the problems firing and suggestions being offered, I keep coming back to that drawing and wonder if the chimney is not pulling the heat out faster than you are able to build it up in the kiln. Will bigger/more tanks, better burners, better regulator also fix that problem -- if it is still occurring?

 

Bruce

[Guest JBaymore]

Bruce,

 

That is part of the potential "operator error" I am talking about above.

 

best,

 

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

[Kristin_Gail]

I get myself into trouble here when I try to put things in too simple of terms (or be silly), but here I go again:

1. I cannot buy a propane tank larger than 100 lb - any larger and I have to rent it, and they have to fill it. And the propane company will not deliver to my system. (I once called them out, two kilns ago. The fella held up his hands as he walked away, saying, "I was never here.") So I would be looking at adding more 100-lb tanks.

2. I was very confused about John's previous regulator comments - I thought you were saying I should not buy the one linked to at Amazon, as it was high pressure and I needed to find a low-pressure, high-volume one.

3. I'm certain user error is a huge factor. That's why I do not want to fire this kiln again until I rope in a real potter to come and sit with me for 12 hours or so. I cannot wait to find out what it is I'm doing wrong - because I can't for the life of me figure out what it is.

4. My current regulator is listed at 195,000 BTU/HR capacity.

5. Bruce, yes that's still what the flame is doing. I tried to post a video of it a page or two ago, but couldn't make it work. I can try to re-post it tomorrow.

[TJR]

Kristen;

I am still saying, and Mark agrees with me that you should open up the space [gap] between your pots and the bag wall on the right. In other words, move your bag wall an inch or two closer to the burners.

This may alleviate the problem of the flame jumping the bag wall.

Also,[John will love this, as you should not change more than one thing at a time], you should close your damper to one or two inches open. If it is wide open, you are sucking all the heat out of the chimney.

3. Crank those primaries down on the end of your burners.

Lets see some more pictures of that baby firing.

TJR.

[Kristin_Gail]

TJR - The damper, at its widest open, left an open space of 2.5" x 9". Anything more than that, and the temp drops dramatically. On this last attempt, the damper was between 1.75" and 2.5" open (of a 9" x 9" space).

[Kristin_Gail]

John recommended figuring out if the regulator is defective.  How can I do this?

[Guest JBaymore]

It is geting hard to remember 'all that came before' here.

 

I seem to remember some vague "can't have a large bulk tank" discussion now that you mention it again.  Sorry.  We'll go back to that a little later... I have questions in the "why" department.

 

We really need a link to every thread related to this kiln in this thread so that we can easily look back at all of the things that have been discussed.  And those who are posting ideas should be looking back at the prior discussions in this project before posting so that we don't keep "re-inventing the wheel".  Or re-adding in thoughts or appropaches that have aready been addressed and either adopted or rejected.

 

Figuring out if the regulator is defective.......... first and kinda' easy..... checking that the the maximum output pressure listed for the unit, when the unit is adjusted to the maximum output, matches that specified maximum output pressure (under full draw). If the regularot ios supposed to have a regulated output of 11" Water Column (under flow), then it should. 

 

(Hum......... writing that ....... I have an idea here.... have to go check it when I am done writing this.)  (just did  .... seer below!)

 

The second test is harder if you don't have the necessary tool.  You need a flowmeter.  It measures the VOLUME of gases flowing thru the regulator.  Hook it up, run the propane line into an output that can handle MORE than the reated flow, and see if it is passing the correct number of cubic feet per minuite/hour of gas.  Lacking that tool.......

 

Buy another regulator.  They are cheap.  Install it.  See if it makes a difference.

 

best,

 

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

[Kristin_Gail]

Literally as you were typing this, I was standing here at the computer, looking over my husband's shoulder as he read and re-read everything (again), saying to him, "How do you check a regulator?"  And he replied, "Just buy a new one!"  We really are comprehending all this information - it's just difficult to sort through it sometimes (children screaming, pots boiling over, etc.)

 

We are searching for a low-pressure, high-volume regulator.  We may have found on here:  http://gashosesandregulators.com/lowpressureregulators.html

 

 Low Pressure Propane Twin Stage Regulator Twin stage regulators combine first and second stage regulators into a single unit.  They are designed to reduce tank pressure to a preset 11" WC delivery pressure. Manually adjustable from 9" to 13" WC Equipped with 1/8" FNPT pressure gauge taps on inlet and outlet for easy system pressure checks.  Supplied with a 60" thermoplastic high pressure hose outfitted with a model 204051 Full Flow, POL tank connector.  Gas outlet is 3/4" FNPT.  Flexible 3/4" ID low pressure outlet gas hose may be found on our Natural Gas Hose webpage.  Supplied with GR-905 mounting bracket shown below.  Dimensions: 7.5"L x 5.5"W x 4.75"H  Weight 3# 15 oz.  Free shipping.

525,000 btu/hr maximum output  Perfect for small cabins using portable tanks

 

GR9412 132.50

 

Would this fit the bill?

 

I think that changing the regulator and moving the tanks into the sun (which isn't possible, but let's pretend it is) - this counts as a single change.

 

I will right now find links to various posts about this kiln and post them.

[Kristin_Gail]

Oh, my.  I ask an awful lot of questions.  Here are posts regarding this kiln:

 

When I first brought it home:  http://community.ceramicartsdaily.org/topic/4788-a-new-kiln-conversion-project-what-would-you-do/

 

How to add a chimney:  http://community.ceramicartsdaily.org/topic/5050-chimney-design-on-this-here-conversion-of-mine/

 

How to build the roof:  http://community.ceramicartsdaily.org/topic/4995-kiln-shed-roof-distance-from-kiln/

 

After I fired it once:  http://community.ceramicartsdaily.org/topic/5514-first-firing-of-this-here-electric-to-propanewoodsoda-converted-kiln/

 

After the second firing:  http://community.ceramicartsdaily.org/topic/5746-troubleshooting-this-converted-kiln-o-mine-taller-chimney/?do=findComment&comment=53295

 

And, of course, this thread started eight pages ago, during the third firing.

[Kristin_Gail]

We need to have some sort of incredible community party when I finally figure out how to make it work.

[Kristin_Gail]

This is the youtube video I intended to post, showing the flame coming through one shelf, down between the stacks of shelves, and out the chimney.  (Well, you can't see all of that, but you can at least see the type of flame it is).  

 

 

[Guest JBaymore]

WOAH!

 

I just went to the Ward Burner site...... and it looks like that regulator pictured there is a San Marco Model 290.  Is that what you have?

 

On his site Marc says it handles "6 times the volume of a gas grill regulator".  Great.... totally usless info...... means nothing.  I just went to the bother to look up that regulator from the supplier.... and found some interesting facts.

 

On the MANUFACTURERS product information sheet for that unit (if I am looking at the right one....and I am pretty sure I am) it says that it can pass only 160,000 BTUs per hour of propane.  Seems to me that is less than the theoretical rating of your burners output.  Right? 

 

So the regulator is the "engine governor" on the engine of your kiln.  No matter what the burners are set up to handle (their orifice sizes) the regulator will supply them with no more than 160,000 BTUs per hour.

 

Another key piece of information here......... but I can't verify this as is needed from here. 

 

On the MANUFACTURERS product information sheet for that unit, that regulator is supposed to output 11" water column.  You have mentioned that your guages are reading about 5" to 5 1/2" Water Column.  Now those guages are on the OUTPUT siode of the ball valve and between that and the orifices... so that would not be expected to show line pressure.  BUT......... a pressuure drop down to 5" if the line supply is 11" is very telling of the volume issue. 

 

As I remember.... (haven't looked back yet) your kiln is just over 20 cubic feet inside.  And also it is not all that greatly insulated.  For an IFB constructed kiln with a wall and roof and floor insulation rating that you could say was the insulating equivalent of a graded refractory 9" thick wall....... I use a "rule of thumb" figure of 10,000 BTU per hour per cubic foot of chamber.  Your kiln is slightly less well insuilated than that (don't know the precise matrerials so can't calculate it exactly) so for sure you need 200,000 BTUs/ hour of total input.

 

You need 200,000....... you likely HAVE 160,000........ hum.  What's wrong with this picture?

 

Unless Marc Ward is modifying those stock regulators...... or the specs have changed........ or the sheet I found is wrong........ I think that is a real concern here.

 

PM me your email address and I can send you the manuifacturer's .pdf file of the regulator product sheet if you want it.

 

best,

 

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

[Kristin_Gail]

No, that's not the regulator I have.  The one I have says "Gas-Flo Low Pressure Two Stage LP Gas Regulator" on it.  I don't see it on the Ward Burner site.  I'm having a difficult time finding a web site for the manufacturer, but various resellers list it as 195,000 BTU/HR capacity.

[Guest JBaymore]

Who supplied it? Marc?

 

What does it say on the housing?

 

best,

 

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

[Guest JBaymore]

Does it have Model # R-9950 or 9959 on the round part?

 

best,

 

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

[Kristin_Gail]

Marc supplied it, and it's model R-9950.

[Mark C.]

Heres a model that does 750,000 btu-output 3-35 psi

They have a few others as well.

Its a propane outlet shop-you could call them for the real specs.

Most of these cheap regulators have no specs about them-so calling a place for real specs may be worthwhile.

http://propanewarehouse.com/adjustableregulatordetail.asp?ID=2001

heres the spec sheet on these

http://www.documentation.emersonprocess.com/groups/public/documents/bulletins/d450130t012.pdf

Looks like forge folks use this regualtor a lot.

you still need another tank or two to gang together.

 

Mark