Trapped Liquid Propane Between Valves

[maddocks]

Here's a quirky one that's bothering me. We have a liquid propane receiver that is equipped with a normal level control valve on the liquid outlet line.

Due to the hazop - we're now installing an ESDV on the same line slightly downstream of the LCV. I've reviewed with my team and we believe that the system requires a thermal PSV in between the valves in the event that both valves are closed. Can we simply install a small (tubing sized) thermal PSV backwards around the LCV so the overpressure will relieve back to the receiver? My only concern with this is that if the overpressure occurs as a result of a fire then the pressure in the receiver will also be rising up to the set pressure of the PSV located on the receiver at the same time. Consequently there would be no differential to open the valve. Am I off-track here? Can I just install a small check valve backwards around the LCV?

How do most people solve these trapped liquid lines that can increase in pressure?

 

[Duwe6]

Typically, a small PRV is installed. Nothing wrong with venting it back to the vessel. In a Fire Case, the [large] vessel PRV will be relieving and the tiny ammount from the pipe will be insignificant -- but include it in the formal vessel relief calc's.