meadow on thu 16 jun 05
ok, i see EVERYBODY says a 500 gal tank.
i just bought my first kiln, propane, downdraft, 18 cuft setting space.
unfortunately (depending on how one looks at it) i live off the beaten path, and all they sell in
town here is the 100# (21 gal) tanks. no rentals. i got a lead on a used 100 gal tank. should i
chance it? otherwise, i have to order one and shipping charges will likely be quite high.
everyone says 500 gal, but they say it like a mantra.
i mean, shouldn't it be based on kiln size, construction, etc?????
also, what's the deal, why pounds AND gallons. it's confusing. in rhodes kiln book he says 500 gal
tank (of course) OR four or five 100 pound tanks hooked together in tandem. but that's not the
same thing!!!! five 100 pound tanks is only 105 gal. aaargh!
-meadow
Earl Brunner on fri 17 jun 05
You are dealing with the nature of the gas. It comes in a liquid and has to
evaporate to convert to the actual gas you burn in normal situations. If
the tank is too small, as you draw off the gas the tank chills and can
actually freeze up, but the lower the temperature of the liquid, the slower
it off gases. I, at different times had two different tanks, A 250 gal. and
a 350 gal. Both worked well for my soft brick kiln. Rhodes may be
factoring a hard brick kiln, I don't remember much in his book about soft
brick or fiber, but it's been a long time since I read it. My kiln was
about 14 cu ft if I remember.
What happens with the smaller tanks is by setting up a system where you try
to draw equally from several tanks at once you spread that temperature drop
out so that you don't freeze any one of the tanks up by itself. Can they
get a refill truck to your kiln location? If they can, I would try for at
least a 250 gal tank. If I remember rightly, I could get 4 or 5 firings out
of it to cone 10 before having to refill. My burners weren't very
efficient, and my stack door leaked heat like crazy, a nice tight kiln with
good burners might do better. In any case you don't want to try to fire
when you are low on gas. I tried to not get lower that a third full.
Earl Brunner
Las Vegas, NV
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of meadow
Sent: Thursday, June 16, 2005 5:27 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: propane kiln, tank size
ok, i see EVERYBODY says a 500 gal tank.
i just bought my first kiln, propane, downdraft, 18 cuft setting space.
unfortunately (depending on how one looks at it) i live off the beaten path,
and all they sell in
town here is the 100# (21 gal) tanks. no rentals. i got a lead on a used 100
gal tank. should i
chance it? otherwise, i have to order one and shipping charges will likely
be quite high.
everyone says 500 gal, but they say it like a mantra.
i mean, shouldn't it be based on kiln size, construction, etc?????
also, what's the deal, why pounds AND gallons. it's confusing. in rhodes
kiln book he says 500 gal
tank (of course) OR four or five 100 pound tanks hooked together in tandem.
but that's not the
same thing!!!! five 100 pound tanks is only 105 gal. aaargh!
-meadow
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Marvpots@AOL.COM on fri 17 jun 05
Your local bulk propane gas supplier would probably be willing to place their
tank at your location, run the gas line underground from the tank location to
your kiln, all at no charge to you. You will be obligated to have your tank
refilled by them (other suppliers would not "poach" on the original supplier.
You will probably have to provide a cement pad for the tank at your expense.
This is what I did and it has worked very well. You.just have to "lean" on
the propane supplier's price for each refill, reminding them you ar a potter,
etc. Propane gas prices vary enormously from place to place.
See if this works for you.
All the best.
Marvin Flowerman
marvpots@aol.com
Kenneth D. Westfall on fri 17 jun 05
The issue is not Gallons or lb but surface area for the propane to boil and
turn into gas. As liquid propane expands into gas it causes refrigeration
to happen. If you don't have a large enough tank or enough tanks with a
lot of surface area they freeze up in a solid block of ice and the liquid
stops turning into gas. No gas no firing! I wouldn't try the 100lbs
hooked together unless you have no other chooses. With the size kiln you
have you probable can run it on a 250 gal tank as long as it full when you
start firing every time and you don't try firing in the dead of winter if
you live in a cold climate. You can use the smaller tank if you add on a
heater or evaporator which is electric that adds heat to the propane to
boil it into gas. Your propane dealer would have to hook it up and they
may have never hear of one either and not want to help you out. I call
around more and even check farther away because you mite get someone to set
a larger tank say a 1000gal tank knowing that they only have to make a
delivery every year and that you mite be buying a lot more then the normal
house.
Kenneth D. Westfall
Pine Hill Pottery
R.D. #2 Box 6AA
Harrisville, WV 26362
kenneth@pinehillpottery.com
http://www.pinehillpottery.com
Tom at Hutchtel on sat 18 jun 05
OK, I found the LP Gas Serviceman's Manual that our Gas company service guy
gave me some years ago. To quote page 6
100 LB Cylinders:
Rule of Thumb for Installing 100 LB cylinders. For continuous draws where
temperatures may reach 0 degF. Assume the vaporization rate of a 100 lb
cylinder as approximately 50,000 BTU per hour. So, number of cylinders per
side = Total load in BTUH divided by 50,000. Example: Assume total load of
200,000 BTU/hr, divided by 50,000 equals 4 cylinders.
On page 7, rule of thumb for ASME storage containers:
D (diameter of tank) x L (length of tank) x a constant K which relates to
the % fill of the tank. The formula DxLxK equals the approximate BTU/hr
released at 0 degF. The constants (K) are
60%filled =100
50% filled = 90
40% filled = 80
30% filled = 70
20% filled = 60
10% filled = 45
To adjust for other air temps, this result should be multiplied by another
factor.
-15 degF 0.25
-10 degF 0.5
-5 degF 0.75
0 degF 1.00
+5 degF 1.25
+10 degF 1.5
+15 degF 1.75
+20 degF 2.00
To quote page 4
The heata lost due to the vaporization oof the liqquid is replaced by the
heat surrounding the container. this heat is transferred from the air
through the metal surface of the vessel into the liquid. The are of the
vessel in contact with vapor is not considered because the heat absorbe by
the vapor is negligible. The surface of the vesselthat is bathed in liquid
is known as the wetted surface. The greater this wetted surface, or in
other words the greater the amount of liquid in the vessel, the greater the
vaporization capacity of the system. A larger container would hae a larger
wetted surface area when filled and therrefore would have greater vaporizing
capacity.
Tom
Snail Scott on sat 18 jun 05
At 08:27 PM 6/16/2005 -0400, Meadow wrote:
>...i just bought my first kiln, propane, downdraft, 18 cuft setting space.
>unfortunately (depending on how one looks at it) i live off the beaten
path, and all they sell in
>town here is the 100# (21 gal) tanks. no rentals. i got a lead on a used
100 gal tank. should i
>chance it? otherwise, i have to order one and shipping charges will likely
be quite high.
>everyone says 500 gal, but they say it like a mantra.
I'm out of the way here, too (no natural gas) and so I
am installing propane for my kiln. (The house already
has propane, but it's far from the studio.) I called
the farm co-op propane outfit that supplies the house
and spoke with them. They will provide the tank for free;
I just pay to fill it. I wasn't sure I really needed a
500 gallon tank, either, but they said there was no
point at all in going smaller, and they've convinced me.
For one thing, the smaller sizes (200, 300) are scarce,
and I might have to wait a while for them to find one.
And, since it doesn't cost me any differently, why not
go for the one that needs less refilling? I might be able
to do all my fills in the summer when prices are lower,
instead of when I run out and haven't got a choice.
The bite of having to pay the whole cost of a 500 gallon
fill will require a bit of budget planning, is all.
Also, smaller tanks are more vulnerable to pressure drop
and freeze when the kiln is drawing fuel. A larger tank
won't be as affected by the same consumption rate.
Note that there is a limit on the size of portable tank
that you can legally transport in an ordinary vehicle,
never mind the difficulty of shifting a 100 pound tank
after refilling. And, it may not cost less to bring your
own tank for filling - prices vary a lot, so check.
Having a non-portable tank refilled on-site may be a
better deal, especially once you've figured what your
time and effort are worth.
And watch out for used tanks. They may be in fine shape,
but the US government is gradually requiring the new
safety valves. Right now, it's just the smaller sizes
that are affected, but that will eventually change, so
if it's got the old-style valve, add the conversion
cost to the price.
-Snail
Tom at Hutchtel on sat 18 jun 05
What counts in propane is the exterior surface area of the tank that is
covered by liquid propane. This is why you want to keep the tank more than
half full during winter months. What is of concern is the amount of heat
available to warm the liquid to produce gas. As has been noted, the liquid
temp lowers as gas is pulled off. You also lose pressure as the outside
temp lowers. Your propane supplier can show you a chart of available
pressure at various ambient temps. So at low outside temps, you're in a race
between not enough heat coming in to the tank and liquid, to overcome the
lowering of the temperature by boil off. We have 2 - 1000 gallon tanks and
at 10 below zero outside temp, can have problems keeping pressure high
enough to reduce at cone 10. (We're using 2 500,000 btu Ward burners on a
standard Minnesota flattop).
So you want to know how many btu's you'll need for your burners, and how
many lbs pressure you need. Then size the tank so it gives you enough tank
exterior surface area to give you the pressure you need at the lowest temp
at which you'll be firing. The gas company should be able to calculate
this for you.
As to gas prices, be aware that almost all gas companies "contract" prices
for anyone who uses say 500 gallons or more per year. If you fire a lot,
you may qualify for significant discounts. Some contracts require upfront
payment. Be sure to go through all the what-if's with them ahead of time
such as "what if I don't use all the gas I've contracted for" or "what if
the gas price falls below my contract price." Pricing and contract terms
will be pretty standard among companies in your area.
We tried tank heaters (automotive magnetic type) but they don't turn out
enough heat to make a difference for the 1,000,000 btus we're drawing. An
evaporator requires a liquid tap from the tank, and then uses heat
(typically a gas flame) to turn that into gas. We priced them recently and
for us they're about $1300....not installed.
NEVER< NEVER NEVER use a weed burner or torch to put heat under or on the
tank to try to get pressure. You can cause a change in the tank's metal
that can later cause it to rupture. They have a name for it, but I've
forgotten.
Tom
Dean Poole on sun 19 jun 05
My father and I went with a 1000 gallon tank which only holds 800 gallons
because of the head space needed. We receive a substantial price brake for
purchasing 800 gallons at a time. We live in Oklahoma so temperature isn=92t=
as big a problem during the winter months. Kiln size is approximately 20
cubic feet stacking and takes around 26 gallons to fire cone 10.I don=92t
think you would have to fill the 500 gallon tank completely to start with
this would probably cost more in the long run but would give you time to
arrange your budget for subsequent fillings.
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