How Many Cubic Feet Of Propane Gas In A 500 Gallon Tank? (convert Liquid Propane To Cubic Feet Of Gas.)

There are 231 cubic inches per US gallon, or 0.134 cubic feet per US gallon, and 500 gallons x 0.134 cubic feet/gallon would be 66.8 cubic feet in the tank.  So if you release a pressurized gas from a 175 psi tank to 14.7 psi (sea-level), the gas will expand to 11.9 times more volume, or 786 cubic feet. Assuming there was negligible expansion under pressure, the volume of the tank remains 66.8 cubic feet (Was this a trick question?).

But if this is an Liquid Propane tank, then it's a different matter.  In addition to the pressure difference, there is a phase change from liquid to gas.  There are 36.41 cubic feet of propane gas in one gallon of propane liquid. That is measured with the gas at 60 degs F and 14.696 psia  (from the Natural Gas Processors Handbook).  That  works out to about 18,200 cubic feet.  

First of all a five hundred gallon tank of propane holds only 400 gallons. The propane company is only allowed to fill it to 80%. One gallon of propane = 36.39 cubic feet. 400 hundred gallons of propane = 14,556 cubic feet at a burn rate of 550 it should last 26 hours.

500 gallons = 66.8 cubic feet liquefied.  Natural gas, gasified versus liquid is roughly 600 to one in volume, this 66.8 cubic feet liquefied would be roughly 40,106.9 cubic feet gasified.  I suspect propane is pretty closely equivalent..

Of course, it depends on the temperature and pressure. Here is one estimate. Using those numbers, the consumption rate is about 15.1 gallons/hour. It looks like you might get about 30 hours with a little reserve.

It sounds very interesting

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