Propane tank question

[ning]

First, the size of tank has nothing to do with the internal pressure of the tank. The pressure is solely dependent on the ambient temperature and can be upwards of 200 psi. The pressure is controlled by a regulator and depending on the distances involved there may be more than one regulator. In my case the regulator at the tank steps it down to 10 psi (which is considered hi pressure - for propane) at the house is further stepped down to an 11 inch water column (somewhere around 1/2 psi) The size of distribution pipe matters as well on providing enough gas to meet the BTU requirements.

You will need to add up all your gas appliances to get a total BTU count - this is an important number! You will also need to know the coldest temperature you expect to see. You can then use the tank size you want to use with the ambient temperature to see if it will vaporize enough gas to meet that total BTU count. (Propane gas is in the form of a liquid in the tank with the propane gas above the liquid.)

Vaporization rate

There are charts for the different tanks. Vaporization depends on the surface area and temperature of the liquid propane, so a horizontal tank will have it's highest rate when half full because it has the greatest surface area at that point.

That's super useful!
Curious why the vaporization rate goes down as the amount of propane in the cylinder reduces - is it because there's less thermal mass and so the the entire mass cools down more rapidly from heat loss of vaporization?

 

[ponytug]

That's super useful!
Curious why the vaporization rate goes down as the amount of propane in the cylinder reduces - is it because there's less thermal mass and so the the entire mass cools down more rapidly from heat loss of vaporization?
View attachment 828871

It is because of several effects; the surface area of the liquid gets smaller (in a horizontal tank), so the evaporation rate at a constant temperature slows, but the temperature is dropping as the liquid propane evaporates, which means that the rate of evaporation slows further, and the area of the tank in contact with the liquid is getting smaller, which reduces the heat input into the liquid, causing the liquid propane to cool even faster, slowing the evaporation even more.

It is a vicious cycle, and why generators, and other high demand propane devices, don't do well on small, relatively empty, tanks in the wintertime.

All the best, Peter

 

[MAX-24-Dean]

Jotul 370 has a 61% efficiency rating. So the input btu's will be higher than the output btu's.

86 gal x 91,000 btu's per gallon = 7,826,000 total btu's.
7,826,000 / 24,000 btu stove output =326 approx. (326 units of 24,000 btu's)
326 / 4 hours per day = 81 approx. gal.

 

[MAX-24-Dean]

I live in MA and it was 60 degrees on the day of delivery and has averaged in the low 30's since the fill.
Is the gauge messed up? I didn't look at the gauge, right after they filled it.

Would I see that much contraction due to temp? Yes

Any thoughts? I am currently on endless hold with Amerigas.

Propane Volume correction factor is based on a 60° F standard. I believe the tank guage only reads the correct volume at 60° F
In general most liquids when warmed up causes the molecules to speed up and spread farther apart from each other, accupying a larger volume that results in a decreased density.
Conversely, when liquids are cooled (as in the 30 degree outside temp delta in your post) this causes the molecules to slow down and move closer together. Thus occupying a smaller volume and an increase in the density, so it has become more compact. It has the same amount of weight, so the usable amount of energy in the propane has not decreased.
A large Temperature drop does effect how the guage reads and will inidcate that there is less propane in your tank at a lower temperature.

Volume correction factor - Wikipedia

en.wikipedia.org

 

[2manyrocks]

My other problem is delivery. After snow falls propane truck can't get up to my long steep driveway. That's why i'd rather do it myself when I need it

If you could find a large enough tank to meet your entire seasonal needs, you could have it filled when prices are at their lowest and you wouldn't need delivery when snow is on the ground.

 

[jyoutz]

Look into purchasing a 250 gal above ground tank, probably $1200 - $1500, a 500 gallon would be a few hundred more. Shop around & fill when prices are lowest from whoever gives the best deal while a delivery is possible. Surplus capacity doesn't hurt, propane doesn't go bad.

Yep that’s the best solution.

 

[gasman1075]

a 100 gallon tank at 20' F and at 40% capacity will vaporize up to 235,000 btu/hour. A 100 lb tank has about 22 gallons in it and will vaporize about 79,000 btu when full but much less as the liquid level decreases. Owning your own tank means you can shop it when you need it. You can manifold 100 lb cylinders just like 100 gallon tanks and use the same regulators and POL fittings. If your tanks are next to the house but away from any windows below the top of the tank you probably have a twin stage regulator which takes it from tank pressure to 10psi then to 11-14" WC. Swapping out 100LB cylinders when they are empty and then transporting them to be filled and then reconnecting them is risky. By code a leak check has to be done and documented every time a tank is swapped out or run dry. Not far from here a blacksmith swapped out his own tank there was a fire and his insurance company still hasn't paid out on his claim.