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Old 03-10-2007, 07:25 PM   #1
Ryan_PA
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Default Too much propane!

At first, this may sound like a good thing, but alas, it is not.

In preperation for my last brew session, I picked up an additional tank for my Bayou Classic 150K BTU burner assuming my only tank was nearing empty. Well, I made it through the entire mash and boil for that session.

Flashforward to today. I pulled out the near empty tank again to see what miracles it had in store for me today... It made it through 80% of the mash, I was impressed. When I went to swith to the new full tank, I thought nothing of it. I did the swap, and tended to some of the brew day setup. Eventually I looked at the flane and it wast really acting funny, large plumes of orange flames, not the typical jet like action and blue, then I noticed the regulatore, hose and fittings were covered in frost. I know from my days as an LP forklift operator, that meant the liquid propane was coming in contact with these parts (this should not happen). I quickly disconnected the gas and pulled the regulator from the tank. Then hit google. Turns out, the never fail OPD (overfill protection device) in the tank failed and the company Home Depot uses to fill the tanks for the swap desk filled it to the brim.

Never had this happen in a home setting, actually I thought it was impossible, but I searched the forum and did not see a similar post, and figured this would help.
Q: My regulator has frost on it. Should I be concerned?

A: Frost on a regulator indicates that you may have an overfilled tank. Immediately close the LP tank valve and contact your local filling station for assistance. If the filling station is unable to assist you, contact your local fire department.

---------------------------------------------------------

Assume the tank is filled completely
full with no vapor space at all. When the valve is opened, the
liquid propane in the valve body will flash to gas and flow out,
entraining some liquid in the process. The regulator will receive
gas with a little liquid. This does it no harm and it will work
normally.

Now let's assume that somehow this absolutely full tank begins being
warmed as the valve is opened. Liquid propane will reach the
regulator. At first, the regulator will function normally.
However, since the propane is now being vaporized at the regulator
orifice instead of in the tank. the regulator is refrigerated.
Eventually it will begin to frost. Further down the line, the
diaphragm will become so cold that it stiffens. The regulator will
then lose control. The downstream pressure will rise until the aux
relief diaphragm (usually plastic and not affected by the cold)
lifts to vent the excess pressure to atmosphere. Because liquid is
in the regulator, some volume of gas and liquid will discharge from
the atmospheric vent until sufficient liquid is removed from the
tank to no longer feed from the valve. Since liquid propane
compresses very little and the steel tank expands very little, the
amount of liquid involved is small.

I know that this is the sequence of events because I've tried
operating a tank upside down trying to force more BTUs through a
small regulator than it was designed for. The (correct) logic was
that if the metering orifice is metering liquid propane instead of
gaseous propane, more volume would be available. It worked for
awhile until the regulator froze, whereupon liquid propane spewed
from the atmospheric vent. Had I supplied heat to the regulator, it
would have continued to work and would be functioning in a manner
almost identical to the fuel vaporizer used on propane-powered
vehicles.


Obviously if there were flame present, the escaping gas would
ignite. The chance of an explosion in this situation is slim. Big
fire maybe but not an explosion.


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