Propane Tank Sizing

[PEDARRIN2]

I am trying to size a above ground liquid propane tank for use with an emergency generator.

I calculate required run times, convert from natural gas cfh to propane cfh, calculate wetted area of the tank based on % full, design temperature of the day, but what I am having trouble with is frost generation due to relative humidity.

I haven't found much engineering literature about doing this. The engineering books (and some propane literature) I have found say to consider frost. From them, for a 0 F design day, the usable temperature difference could vary from 2 F to 29 F, depending on the relative humidity

But the literature from the generator manufacturer, the engineering staff for the generator, and even an engineer for a large propane supplier do not seem to take frost into consideration.

I don't want to tell the equipment engineers who have been doing this a lot longer than I have that they are wrong, but I cannot discount that much of a variance in other engineering literature.

Has anybody designed these and am I missing something?

 

[Compositepro]

Most engines are designed to run on liquid propane so you do not have to worry about vaporizing the propane in the tank. Forklifts, for example. If you are drawing propane vapor, you do have to worry about freezing the tank.

 

[PEDARRIN2]

The application is a fire station in a seismic prone area so they want a propane tank as a back up for the natural gas.

The generator we have specified would be running on propane vapor.

 

[SteveWag]

Vaporizers are nice but cannot always be used. Attached (I hope) is a table from ONAN in the late 80’s. I have used it many, many times but end up with rather large tanks. Beware that the tank sizes are for horizontal, half-full tanks.
Steve

 

[PEDARRIN2]

The owner would not want a vaporizer so we have to use the tank shell as the heat transfer media.

Looking at the following information is what got me thinking there is more to it than temperature.

http://www.documentation.emersonprocess.com/groups/public/documents/bulletins/d4500147t012.pdf

The approach advised by Emerson would make it a very large tank. The math works, but it is one of those instances where actual experience is lacking to tell me that my numbers are suspect.

 

[chicopee]

It has been 12 days since the OP and perhaps it's not too late for my presentation on the way I would size a propane tank. Please see attachment.