Propane Properties

Feb 05, 2019

I’m writing this newsletter article on January 31st. Last night it was so cold I had to chisel the dog off of a fire hydrant. It got down to 31 degrees below zero at my house and some of the customers I talked to were reporting temperatures even lower. That brings me to one of my subjects. The physical properties of propane. 
Propane is an odorless, clear liquid. They add a product called Mercaptan at the terminals where our transporters pick up the propane. Mercaptan is added so that you can smell the propane in case you have a small leak. It smells kind of like rotten eggs. 
Another characteristic of propane is that it is a very light fuel. It weighs 4.2 lbs per gallon. When we get extremely cold weather the percentage in the tanks can drop dramatically. This isn’t just a reflection of increased consumption. It’s also a reflection of the fact that a gallon of propane at 60 degrees F. shrinks as the temperature decreases. Let’s say you’ve got a propane tank that is 80% full at 60 degrees F. At -40 degrees F., the volume in the tank can drop at least 10%. 
So how can you be sure you are getting billed for the correct amount of propane at the time of delivery? Our propane delivery trucks have meters that measure the amount of propane pumped into consumer tanks. These meters have a volume correction device known as an automatic temperature compensator. The temperature compensator measures the temperature of the fuel and corrects it to 60 degrees F. We are required by the State of Wisconsin to have our meters checked annually to ensure their accuracy. The state may also make unannounced visits to test our meters. 
The final characteristic of propane I’d like to talk about is the boiling point. We’ve all been taught that the boiling point of water is 212 degrees. At 211 degrees the water stops boiling. The boiling point of propane is -43 degrees F. At -44 degrees F, propane stops boiling. The flow of propane to your house may stop before that point. Here’s why. 
The appliances in your house run on vapor. At the propane tank, there is a 10 PSI regulator. This regulator allows vapor at 10 PSI to flow toward the house. The regulator on the house adjusts the pressure to that required by the appliances. At 60 degrees F, the pressure in the tank is 102 PSI. At -30 degrees F, the pressure in the tank can be as low as 8 PSI. The first stage regulator needs to have 10 PSI in order to open. 
The night of January 30th, some of our customers were experiencing temperatures of -30 degrees F, their first stage regulator wasn’t opening because of low pressure and their appliances stopped working. After the propane warmed up a little in daylight, the pressure increased and the propane was flowing to the house again. What can you do to warm the propane in your tank up? One way is to make sure you keep the top and sides of the tank clear of snow and ice. The snow reflects the sun and it can’t warm the tank. If it gets this cold again (let’s hope not), placing an electric blanket on the tank may do the trick. Blocking the wind has no effect because inanimate objects are not affected by wind chill. If the ambient temperature is 20 degrees F and the wind chill is -5 degrees F, you’ll find that the propane in the tank is at 20 degrees F. 
I hope you’ve enjoyed this propane lesson. Now you know as much as I do. Thank you for your business. 

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