Need help on sizing relief valves

[ruwl]

I am trying to size some PSV's that have properties (hydrocarbons) with MW < 40 and Relief Pressure above 2000 psig. The API curve has a minimum of MW = 40 and a max pressure at 1000 psig.

For Fire case, how do I obtain the Latent Heat of Vaporization and Relief Temperature at the conditions mentioned above?

Can I be conservative and use Latent Heat of 50 btu/# anf relief temperature = (oper. temp./op. press.) x relief pressure?

I would appreciate any suggestion. Thanks.

 

[Latexman]

It seems to me that when the PSV opens at 2000 psig the contents will be way above it's critical temperature. Therefore, the contents will be a gas and will have NO latent heat of vaporization. So, I'd say you cannot use 50 Btu/lb, because it will not be conservative. Furthermore, the temperature will probably be so high, 500 C or more using ethane as a rough model, you may need to worry about runaway decompostion reactions along with the fire.

Good luck,
Latexman

 

[Latexman]

Google "sizing relief valves for supercritical fluids". One hit. I recall that article. I think it was a pretty good one.

Good luck,
Latexman

 

[ruwl]

Thanks, Latexman.

 

[JimCasey]

A related thought: this product is probably relieving at above its autoignition temperature. Be sure to pipe the relief line accordingly, and don't aim it at anything that has legal representation or that you want to keep.