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Raku Propane Tanks

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Hello everyone, I want to thank you for all your raku information. I have two more questions. I was looking at the zen or bracker(i think) raku kilns. I am wondering if anyone has any info on the size tank to use. This will be used as a hobby. I've heard something about 5 gallon tanks freezing up. I am not sure what that means. Would I be wrong in thinking I could use a 5 gallon tank? And do you know how many kiln loads I could do with the 5 gallon size. I really do not want to store a 100 gallon size. thanks

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Hi:

 

Freeze up refers to when the liquified petroleum gas in yuour bottle can not convert to a gas adn stays loquid. The amount of gas used is a direct function of the BTU output of your burner. There are a lot of complex issues but basicaly that is the way it works. You should be able to find out how many cubic feet there are in a 5 gallon tank and then you can determine how many BTUs you get out of a cubic foot of gas and that should tell you how long you can run the burner. Once you determin the BTUs of your burner your gas supplier shoujld be able to tell you if it will work.

 

Regards,

Charles

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After looking at both of those kilns, I would say that a five gallon tank will certainly work with either of them, but, as Charles mentioned, there are many factors which govern how many firingsyou will get/how long they take.

I built a 7 cubic foot fiber kiln, and I can get about four firings from a five gallon tank. I think you would get about that many from the zen kiln, it appears to be about that size. The bracker kiln appears to be about 3-4 cu. ft, and would probably give 6/7 firings? It depends on so many things : your burner size, efficiency, the ambient temperature, kiln load, etc.

The short answer is that the largest tank you can get would be the best and most convienient, in terms of firing, BUT as far as moving, filling that large tank, that's another question.

 

As far as freeze up is concerned :

http://www.wardburne...tankfreeze.html

 

Not to be a negative Nelly, but you could build your own fiber raku kiln out of parts from Home Depot, et al, and get a nice Ward burner for about a third to half of the price of the Zen kiln. ( Yeah I know : "I use a weed (not Ward) burner and it works just fine." Heh.)

Anyway, you'll have a great time with whatever you get, so try it and see.

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I had several portable homemade raku kilns I used for workshops. I had marc Ward custom make burner setup for me. The first set up was two burners for two kilns directly attached to three tanks. I now have a larger pulley kiln in my kiln shed plus I have made some portables for workshops after I moved to Texas. I had Marc Ward put a plumbing system of two tanks per burner.

My pulley kiln, shown in Kilns for the 21st Century, can be taller or shorter but the fiber box is 36 x 27 x 27 " . I used 1" fiber and made the frame from metal straps , nits and bolts and hardware fabric from home depot. I got the fiber from ebay. I sprayed the interior with ITC.

 

Marcia

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I had several portable homemade raku kilns I used for workshops. I had marc Ward custom make burner setup for me. The first set up was two burners for two kilns directly attached to three tanks. I now have a larger pulley kiln in my kiln shed plus I have made some portables for workshops after I moved to Texas. I had Marc Ward put a plumbing system of two tanks per burner.

My pulley kiln, shown in Kilns for the 21st Century, can be taller or shorter but the fiber box is 36 x 27 x 27 " . I used 1" fiber and made the frame from metal straps , nits and bolts and hardware fabric from home depot. I got the fiber from ebay. I sprayed the interior with ITC.

 

Marcia

 

 

Whoo, sounds nice, Marcia!

How is your propane usage, and what kind of tanks do you have? How big are the kilns?

"Centered" could use the five gallon tanks, no?

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Guest JBaymore

A little "technical gobbledy gook" for ya':

 

The maximum vaporization rate of propane gas from the normal storage liquid to the typical gas form that is burned in most all pottery type burners (industry often uses liquid withdrawal to eliminate the vaproization issues) is based upon the exact shape and material of the tank it is stored in (referred to as "wetted area"), the ambient air temperature surrounding the tank, the humidity of that surrounding air, and the amount of gas remaining in the tank, in gallons, at any given point in time. It is a dynamic number.

 

It is all about the thermal balance of the heat energy getting into the liquid mass of propane to drive the evaporation off of the exposed liquid surface area of the tank.

 

A topped-off FULL 20 pound cylinder will support a continuous draw of about 65,000 BTU/ hr. at an ambient air temp of about 40F and 70% relative humidity. If the air temp goes up to 70F that goes up to about 90,000 BTU/hr. and if the air goes down to about 20F it drops to about 48,000 BTU/hr. .

 

The instant you turn it on, that maximum withdrawal rate decreases!

 

A 20 pound cylinder holds about 430,000 BTUs of total heat potential energy, but you'll never get all of that energy out whan using the typical gas raku/kiln burner. This is because as the tank gets toward the empty point.....your withdrawal rate will exceed the ability of the tank to keep up with necessary vaporization. If you were to use the tank hooked to a different low withdrawal rate device of some sort.... you could then get that last part of the gas out. But not typically for kiln use.

 

Remember...... as that cylinder is used... the mass of gas in the tank is reduced... and that continually DECREASES the maximum draw rate all the time. It is a steadily dropping number as you use the tank. So what works at the beginning of a raku (or other) firing will not necessarily continue to work til the tank is empty.

 

If your burner is drawing more than 65,000 BTU/hr. on that full tank, then you not only have the steady decrease in the volume of liquid gas to account for, but also the steadily decreasing temperature of that mass of liquid fuel due to the fact that heat energy cannot get thru the tank walls from the air and into the liquid store at the rate it is being utilized to drive the evaporation. So that is a "double whammy" effect.

 

You always will need a storage amount of gas that allows appropriate withdrawal rate at a end point of the firing that will reuslt in the fact that threre is still gas left in the tank(s) when you shut down. Just a fact of life.

 

best,

 

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

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