3 Raku kilns, one 100pound tank?

[davidh4976]

If I wanted to simultaneously run three raku kilns off of one 100 pound tank, how would the plumbing work? A regulator at the tank to drop the pressure to something like 10psi and then an additional regulator for each kiln? Would I use a fixed 10 psi stage 1 regulator at the tank and a 'red-top' adjustable regulator for each individual kiln? Would I be concerned about tank/regulator freezing when feeding three raku kilns simultaneously from one 100 pound tank (assuming up to 6 psi for each kiln with a single MR750 burner for each kiln)? We are just brainstorming about whether to switch from three individual 20 pound tanks to a single 100 pound tank.

[Bill Kielb]

Most burners are rated in Btuh @ a specific pressure. If you are buying them from Ward then INCHES of pressure is what you need, not PSI. 1 PSI = 27.72 inches, ward burners are typically rated to 11” wc (propane) to get to peak output. Easier way to do this is figure how many btu you will use, know this number. Once known -  convert to gallons for an idea of how long the tank lasts. 

Normal propane design, 1st stage regulator reduces tank pressure down to 10 psi. Second stage regulation goes from 10 psi down to 11” water column. At 90 degrees tank temp you are approaching 200 psi. Running 200 psi line not the safest idea so reducing it to 10 psi improves safety and still allows a whole bunch of btu for a small diameter hose.

Best idea I have, sketch what you want to do and include realistic distances and btu required for all the legs. From there it’s pretty easy to pick stuff from a table if all that is known. Look at the ward burner spec below and decide if you are trying to follow that or run your burners at medium pressure.

The first stage tank regulator will need to be sized by the load on it (total btuh) Proper sizing is important.

A 100 pound  propane tank contains about 23 gallons. One gallon of propane contains about 91,400 btu. The MR750 will consume approximately 77,400 bru per hour full blast at 11” of water column.

Edited March 16 by Bill Kielb

[davidh4976]

Because we are doing raku, we run the MR750 burners at higher pressure. Starting at 1 psi and going up to 5 or 6 psi. (From Ward regarding raku: "With 1-8 PSI, the MR750 Single System is rated at 54,365 to 153,768 BTU's".)  The firings last from about an hour to about 40 minutes each depending on if it is the first firing or subsequent firings. I'm guessing we are averaging about 100,000 BTU per kiln per firing which tracks about right with our fuel usage. If we do three firings on each of three kilns, that should be about 10 gallons so a 100 pound tank  has enough fuel.

My bigger concern is tank freezing. My understanding is that using a 2 stage regulator system will help prevent freezing. I also think I understand that the tendency for a tank to freeze is related to the surface area of the liquid in the tank. A 100 pound tank has about 50% more liquid surface area than a 25 pound tank.  What I don't know is how all of this translates to real world experience! (We've had a 25 pound tank with single stage regulator freeze up in 40F weather, but the tank on the next kiln over did not freeze up.)

I'm seeing 1st stage regulators that handle from 1,500,000 to 2,250,000 BTU/hour depending on the model all at 10psi. They are all in the same price range, so  I assume that the higher the BTU/hour, the better.  So, my conceptual configuration is shaping up as: I'd use a 100 pound tank with a 1st stage regulator reducing the pressure to 10psi, then a manifold with individual valves for each kiln, with hoses leading to adjustable regulators (0-to-30psi) near each kiln, followed by the MR750 burners. I have to figure out my hose lengths and therefore sizes.

[Bill Kielb]

18 minutes ago, davidh4976 said:

'm seeing 1st stage regulators that handle from 1,500,000 to 2,250,000 BTU/hour depending on the model all at 10psi. They are all in the same price range, so  I assume that the higher the BTU/hour, the better.  So, my conceptual configuration is shaping up as: I'd use a 100 pound tank with a 1st stage regulator reducing the pressure to 10psi, then a manifold with individual valves for each kiln, with hoses leading to adjustable regulators (0-to-30psi) near each kiln, followed by the MR750 burners. I have to figure out my hose lengths and therefore sizes.

Interesting, so the MR70’s you are using will have medium pressure orifices. A larger 1st stage regulator will not respond as well as a smaller so probably not necessary to go to the 2.25 mil. Ten psi hose from the tank easily supplies 300 k - 500k btu and a single second stage from 10 psi down to your working pressure also easy at 300-500k btu. (Larger here is definitely not as accurate as one that matches the load best). So if the kilns are on a common manifold near each other  it sounds like one low pressure regulator can feed all three and just use a hand valve and pressure gauge to fire each.

Frost is complicated so as your tank empties it also has less thermal mass and tends to frost quicker. Trial and error here is almost a must. As to the primary regulator freezing, likely not much of a concern.

[neilestrick]

I think you'll just have to try it. My gut says 3 kiln is too many, though, and you'll get freezing.

How is your kiln constructed? 40 minutes to an hour seems a little long for a typical raku kiln.

[davidh4976]

6 hours ago, neilestrick said:

I think you'll just have to try it. My gut says 3 kiln is too many, though, and you'll get freezing.

How is your kiln constructed? 40 minutes to an hour seems a little long for a typical raku kiln.

We have a few different kinds. One is a 55 gallon drum lined with ceramic fiber; about 4 cu Ft. We are moving to only having this style. We are experimenting with ramp-up times will probably up faster in the future.

[Bill Kielb]

1 hour ago, davidh4976 said:

We have a few different kinds. One is a 55 gallon drum lined with ceramic fiber; about 4 cu Ft.

Do you know for sure how many btu your present burners are rated? If not you can sneak up on it with how many firings in a 20# new cylinder. Conservatively you will likely get down to 1/3 - 1/4 of full charge before it becomes difficult to use, especially at 40 degrees. There are about 4.6 gallons (440 kbtu) in a 20# tank so basically 5 times more in your 100# tank.

[davidh4976]

14 hours ago, Bill Kielb said:

Do you know for sure how many btu your present burners are rated? If not you can sneak up on it with how many firings in a 20# new cylinder. Conservatively you will likely get down to 1/3 - 1/4 of full charge before it becomes difficult to use, especially at 40 degrees. There are about 4.6 gallons (440 kbtu) in a 20# tank so basically 5 times more in your 100# tank.

They are Ward MR750 burners. We run them starting at 1 psi, going up to 5 or 6 psi. Ward says the MR750 is rated at 54,365 BTU at 1psi and up to 153,768 BTU at 8psi. That matches our fuel usage that we measure by weighing the tanks and confirming with the amount of fuel put in each tank when it is refilled.

[davidh4976]

22 hours ago, neilestrick said:

I think you'll just have to try it. My gut says 3 kiln is too many, though, and you'll get freezing.

My gut also says that freezing is possible.  Since no one is confidently saying that it's no prob running three raku kilns off one 100# tank, I think I will abandon the idea of using a single 100# tank. I would hate to invest in the 100# tank, regulator, and plumbing and then find out it freezes up!

Our alternative is to continue using the 20# tanks; one for each kiln, but we will put the tanks in tubs of water with an aquarium water heater in each.  I think this will work because we have only had the freeze ups in colder weather.

I do aquarium heaters with my personal gas kiln and I have never had freeze up. My configuration on my personal gas kiln is a TDI downdraft converted Skutt 1027 using two 20# tanks ganged together. Both tanks sit in a tub with an aquarium heater. I start at 0.5psi and run up to 3psi on a single Ward MR750 to get to cone 10 in 5 hours using less than 4 gallons of propane. No freeze ups.

[Bill Kielb]

1 hour ago, davidh4976 said:

Our alternative is to continue using the 20# tanks; one for each kiln, but we will put the tanks in tubs of water with an aquarium water heater in each.  I think this will work because we have only had the freeze ups in colder weather.

Presumably driven by cost, ease of use and not wanting to slug water around in the cold, locally I see self regulating heat tape for cold weather firings or a big box power blanket bucket heater.

[Mark C.]

My guess is freezing as well-one to many, but really trial and error is the only wat to know.

[Ben Eberle]

Hey David - love this premise...but you will 100% freeze the tank.

Also....these are fiber raku kilns or IFB? If they're IFB, you have no chance at firing those off on a single 100lb tank. Fiber...maaaaybe.

100lb tanks weigh around 160lbs full and can be lifted easily with two people into a pickup. I'd just get two of them and tee them together. I'd also forget the double regulator setup and simply go off an adjustable high pressure regulator. Put a gas cock at the back of each burner so you can fire one, two or all three on that regulator. There is literally zero need for two regulators. Done that setup a million times...on raku kilns and high fire gas reduction kilns. Marc Ward would tell you the same.

Just re-read your reply to Bill up top: You're burning HALF of the gas in 40min.....yep. There is zero chance you won't freeze up. It's not about the volume of liquid gas in the tank...it's about the RATE of evaporation. 10gal in 40 min is a heroic about of consumption on a 100lb tank....

 

Get two tanks!

[PeterH]

1 hour ago, Ben Eberle said:

Hey David - love this premise...but you will 100% freeze the tank.

Also....these are fiber raku kilns or IFB? If they're IFB, you have no chance at firing those off on a single 100lb tank. Fiber...maaaaybe.

100lb tanks weigh around 160lbs full and can be lifted easily with two people into a pickup. I'd just get two of them and tee them together. I'd also forget the double regulator setup and simply go off an adjustable high pressure regulator. Put a gas cock at the back of each burner so you can fire one, two or all three on that regulator. There is literally zero need for two regulators. Done that setup a million times...on raku kilns and high fire gas reduction kilns. Marc Ward would tell you the same.

Just re-read your reply to Bill up top: You're burning HALF of the gas in 40min.....yep. There is zero chance you won't freeze up. It's not about the volume of liquid gas in the tank...it's about the RATE of evaporation. 10gal in 40 min is a heroic about of consumption on a 100lb tank....

 

Get two tanks!

From: https://www.engineeringtoolbox.com/propane-d_1423.html
Propane's latent heat of evaporation is  184 Btu/lb = 0.054 KWh per lb.

... so 100lb is going to take 5.4KWh just to boil.

Edited April 4 by PeterH

[Bill Kielb]

It all really comes down to energy draw and the ambient temps. Charts can help and knowing your actual energy used really helpful

[davidh4976]

Everyone' comments have convinced me that a100 pound tank for all three is unlikely to work.

We are going to go with an individual 20 pound tank for each kiln with the tank placed in a tub of water warmed by an aquarium heater. In the past, we have run a good number of raku firings with 20 pound tanks and no heaters and we only had one freeze up on a day when the ambient temperature was in the low 40s. 

I successfully use an aquarium heater on a small downdraft kiln that I fire on a pair of 20 gallon tanks for 5-to-6 hours to get to cone 10. The heater does a good job of keeping the water in the tub in the 70s.

[Bill Kielb]

59 minutes ago, davidh4976 said:

The heater does a good job of keeping the water in the tub in the 70s.

I would only add the suggestion that all ought to be effectively protected by a gfi. Tank heaters without the third prong (ground) cannot really be effectively protected. Same for all devices without the third prong. Water, electricity, possibly lots of folks nearby, firing kilns, red hot wares - best to be as safe as practical.