Grace Liu on sun 13 jul 97
------------------
I've just started testing a new gas kiln which measures 1 cubic meter
(interior). I'm high-firing to 1200degrees Centigrade (cone 6) for 4.5
hours. I'm using a 50kg gas tank. The problem is at about half the tank
(kiln temp approx. 1180degrees) the bottom half of the tank had ice
building up on it. I (=26 partners more experienced than I in using gas
kilns) quickly set the tank in a large shallow basin =26 poured cool water
over the tank.
I recall earlier discussions regarding warming gas tanks during firing
(usually by warm water soaking), especially during the cold winter months.
I also recall people on the Clayart forum strongly warning against soaking
gas tanks in warm water baths to increase the tank's pressure. So needless
to say, I am very concerned about this situation. My questions are:
1) Given my firing cycle (it's a rather fast firing), is having a frozen
gas tank a normal situation, or is something wrong? BTW, it's the middle
of the summer temp around (34degrees C). I'm afraid we'll have even bigger
problems in the middle of the winter when it's -10 degrees C outside (the
kiln is indoors). According to my partners, everyone else does the soaking
thing for every single firing all year round.
2) How does everyone else solve the problem of low pressure in gas tanks?
(Other than soaking in warm water.)
3) If warm water soaking is really the only viable method (I also need to
realistically weigh cost efficiency into the solution), what do I have to
be careful and vigilant about? We, of course, have pressure gauges along
the pipe line to the kiln (one right near the gas tank, the other on the
other side of a gauge which is used to reduce gas pressure to the kiln).
I am very concerned about this situation and words of advice and experience
would be greaty appreciated.
Thanks in advance.
Grace Liu
Talbott on mon 14 jul 97
Easy solution... use a much bigger tank and keep it above 40% full.. we
have a 500 gallon propane tank and it has never iced up on us (we have
never poured water over the tank..there is no reason to) ..even in the dead
of winter when it is really cold...but we try not to fire when it is less
than 10 fahrenheit...
>I've just started testing a new gas kiln which measures 1 cubic meter
>(interior). I'm high-firing to 1200degrees Centigrade (cone 6) for 4.5
>hours. I'm using a 50kg gas tank. The problem is at about half the tank
>(kiln temp approx. 1180degrees) the bottom half of the tank had ice
>building up on it. I (& partners more experienced than I in using gas
>kilns) quickly set the tank in a large shallow basin & poured cool water
>over the tank.
>
>I recall earlier discussions regarding warming gas tanks during firing
>(usually by warm water soaking), especially during the cold winter months.
>I also recall people on the Clayart forum strongly warning against soaking
>gas tanks in warm water baths to increase the tank's pressure. So needless
>to say, I am very concerned about this situation. My questions are:
>
>1) Given my firing cycle (it's a rather fast firing), is having a frozen
>gas tank a normal situation, or is something wrong? BTW, it's the middle
>of the summer temp around (34degrees C). I'm afraid we'll have even bigger
>problems in the middle of the winter when it's -10 degrees C outside (the
>kiln is indoors). According to my partners, everyone else does the soaking
>thing for every single firing all year round.
>
>2) How does everyone else solve the problem of low pressure in gas tanks?
> (Other than soaking in warm water.)
>
>3) If warm water soaking is really the only viable method (I also need to
>realistically weigh cost efficiency into the solution), what do I have to
>be careful and vigilant about? We, of course, have pressure gauges along
>the pipe line to the kiln (one right near the gas tank, the other on the
>other side of a gauge which is used to reduce gas pressure to the kiln).
>
>I am very concerned about this situation and words of advice and experience
>would be greaty appreciated.
>Thanks in advance.
>
>Grace Liu
1ST ANNUAL CLAYARTERS' GALLERY - NAPLES, MAINE (Summer 1997)
http://fmc.utm.edu/~dmcbeth/cag/naples.htm
Celia & Marshall Talbott, Pottery By Celia, Route 114, P O Box 4116,
Naples, Maine 04055-4116,(207)693-6100 voice and fax,(call first)
WBS Live Chat Room, Sat Nites 10 PM EDT, Private Room: Clayarters
E-MAIL: clupus@ime.net
Fay & Ralph Loewenthal on mon 14 jul 97
Dear Grace, it sounds as if you have far too little gas
bottles firstly. 1 cubic metre is equivalent to 36 cubic
feet. I use 4 X 48Kg gas bottles to fire a 10 cubic foot
kiln. What sort of burners do you have, and how much
gas do they burn an hour? My burners burn 4 Kg's an
hour at full blast. The 48 Kg gas bottles can each deliver
1 Kg an hour. I had no problems with 4 bottles and 2
burners going reasonably well. At the Natal University
they had a kiln the size of yours, which they were
running of 10 bottles. I would try at least 5 bottles if I
were you.
BTW there is a mad potter here in South Africa, who
uses a blow torch to warm his bottles up when they
freeze. This is IMHO the height of lunacy. He lives in a
beautiful mountain village and I know his neighbours are
very concerned about his behaviour. I just pray and hope
that the worst case scenario never happens.
Hope this helps Ralph in PE SA
Gavin Stairs on tue 15 jul 97
Hi Grace,
Permit me to drag you through the basic physics of what happens in a
propane tank when you fire. The propane in your tank is a gas at room
temperature and pressure. If you pour a pool of LPG (Liquified Petrolium
Gas) on the ground, it will boil away. It is a liquid in the tank because
it is under pressure. The higher the pressure, the higher the boiling
point. Conversely, the higher the temperature, the higher the pressure of
a contained volume of liquid/gas.
So, when you are about to begin firing, the tank of LPG is at some pressure
somewhat above atmospheric, and the temperature is just the ambient
temperature, or maybe a little above if the tank is in the sunshine. You
crack the valve, and what happens? The gas above the liquid escapes,
causing the pressure in the tank to fall. Lower pressure, lower boiling
point. So the liquid begins to boil, keeping the pressure more or less
constant.
If you put a pot of water on the stove, it just sits there. If you turn
the stove on, it heats up, and eventually it may boil (if you're not
watching it). While it is boiling, you must add heat to keep it boiling,
but the temperature doesn't change. In other words, boiling liquids absorb
heat. This is called the latent heat of vaporization/condensation (you get
the heat back when you condense the steam, which is how steam cooks, and
why steam burns so well). Now, where do you suppose the heat to boil the
LPG comes from?
The answer is that it comes from the liquid LPG, so the temperature begins
to fall. Soon enough, the temperature of the outside of the tank will
fall, and some heat will begin to leak in from the air, or, if you immerse
or flood the tank with water, from the water. Eventually, if not enough
heat can transfer through the tank wall, the temperature will fall enough
to frost up the tank. At this point, the frost begins to act like
insulation, and the temperature soon drops to the point that boiling almost
stops. Now, you can only boil as much LPG as there is heat being supplied
to the tank. As the LPG temperature falls, the tank pressure also falls.
What the water bath does is improve the heat transfer, and supply heat from
the water. If you use room temperature water, there is no danger of tank
overpressure, since the tank pressure only rises with the tank temperature.
It is when you use warm water or electrical heating that you need to be
concerned about overpressure. If you know the approved maximum temperature
of your tank, you can use water that warm or cooler without danger.
If you just stick the tank in a can of water, eventually the water will
freeze. Better is to flow water over the tank, particularly below the
liquid level (that's the level at which frost begins to accumulate). Or
stick it in a sizeable basin.
The other trick is to use a larger LPG tank, or more of them. This simply
increases the heat sources (LPG and tank area), so you have more heat to
evaporate LPG. It uses the same amount of LPG, but supplies it more
effectively.
Unless you have all of this down pat, and have appropriate safety measures
installed, you should not use heat sources hotter than the limit for your
tank. While the risks are relatively small, if care is taken, there are
risks, whereas if you stay below the safe pressures and temperatures, there
is no more risk than firing up your gas barbecue.
So the procedure you were following, of using cold water on the tank, is
perfectly safe. Fire away!
Gavin
=================================
Gavin Stairs
http://isis.physics.utoronto.ca/
Aaron DeBord on tue 15 jul 97
Well I only use 5 gallon tanks but I think you could some how do the same
as I do to youre big tank. What me and my dad do is just drop the tank in a
bucket of water and that for some reason works. We can fire the tank from
start to end without it freezing up. the tanks will build up ice on the
outside but other than that it is fine.
At 09:30 AM 7/14/97 EDT, you wrote:
>----------------------------Original message----------------------------
>Easy solution... use a much bigger tank and keep it above 40% full.. we
>have a 500 gallon propane tank and it has never iced up on us (we have
>never poured water over the tank..there is no reason to) ..even in the dead
>of winter when it is really cold...but we try not to fire when it is less
>than 10 fahrenheit...
>
>>I've just started testing a new gas kiln which measures 1 cubic meter
>>(interior). I'm high-firing to 1200degrees Centigrade (cone 6) for 4.5
>>hours. I'm using a 50kg gas tank. The problem is at about half the tank
>>(kiln temp approx. 1180degrees) the bottom half of the tank had ice
>>building up on it. I (& partners more experienced than I in using gas
>>kilns) quickly set the tank in a large shallow basin & poured cool water
>>over the tank.
>>
>>I recall earlier discussions regarding warming gas tanks during firing
>>(usually by warm water soaking), especially during the cold winter months.
>>I also recall people on the Clayart forum strongly warning against soaking
>>gas tanks in warm water baths to increase the tank's pressure. So needless
>>to say, I am very concerned about this situation. My questions are:
>>
>>1) Given my firing cycle (it's a rather fast firing), is having a frozen
>>gas tank a normal situation, or is something wrong? BTW, it's the middle
>>of the summer temp around (34degrees C). I'm afraid we'll have even bigger
>>problems in the middle of the winter when it's -10 degrees C outside (the
>>kiln is indoors). According to my partners, everyone else does the soaking
>>thing for every single firing all year round.
>>
>>2) How does everyone else solve the problem of low pressure in gas tanks?
>> (Other than soaking in warm water.)
>>
>>3) If warm water soaking is really the only viable method (I also need to
>>realistically weigh cost efficiency into the solution), what do I have to
>>be careful and vigilant about? We, of course, have pressure gauges along
>>the pipe line to the kiln (one right near the gas tank, the other on the
>>other side of a gauge which is used to reduce gas pressure to the kiln).
>>
>>I am very concerned about this situation and words of advice and experience
>>would be greaty appreciated.
>>Thanks in advance.
>>
>>Grace Liu
>
> 1ST ANNUAL CLAYARTERS' GALLERY - NAPLES, MAINE (Summer 1997)
> http://fmc.utm.edu/~dmcbeth/cag/naples.htm
>
> Celia & Marshall Talbott, Pottery By Celia, Route 114, P O Box 4116,
> Naples, Maine 04055-4116,(207)693-6100 voice and fax,(call first)
> WBS Live Chat Room, Sat Nites 10 PM EDT, Private Room: Clayarters
> E-MAIL: clupus@ime.net
>
>
Charles Williams on fri 18 jul 97
Grace,
The problem of icing relates to the rate of vaporization of the propane(?)
from liquid to gas. The higher the pressure required to fire the specific
type of burners you have the higher the vaporization rate must be. There are
tables, available at most gas/burner contractors, that reference the specific
pressure requirement to drive a burner at a specific BTU/hour output. Eg., I
wanted to fire a 90 square foot kiln using propane and burners that were
rated at 250,000 BTU/hour. The tables indicated I needed a 2500 gallon
propane tank, the size of a WWII submarine, to provide an adequate
vaporization rate. The belabored point is, you might try using 2 smaller
burners with separate tanks for each. This would give the same BTU/hour
output at a lower pressure/vaporization rate. I don't know if this will
eliminate the icing in the cold of winter.
As far as heating an icing tank, these tanks frequently sit in direct
sunlight and do not present a danger unless overfilled. I have experienced
this problem with my RAKU kiln and have used a hair dryer and hot water. Both
worked for me as a quick-fix. I have since approached the problem in a more
scientific manner by consulting the tables and arriving at the best
compromise between BTU/hour output and vaporization rate.
I hope this helps. Any questions, consult a local gas/burner contracting
company. They are usually very happy to provide help in hopes of selling you
a system.
C Willaims AKA Mississippi Mudcat Pottery
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