LPG pumping

[carletes]

Dear all!

I am facing a propane and butane bulk transfer system from horizontal bullets vessels towards rail tank wagons with no vapor return line. As far as I know in steady state the pressure inside the LPG vessels will depend only on their temperature and will be coincident with the LPG vapor pressure but during the bullet discharge there is a transient condition during which the pressure decreases below vapor pressure. Is it right? How can I calculate that transient pressure decrease?

Moreover if pressure decreases below vapor pressure we will have a problem with pump NPSH. Which are the usual solutions for this problem?

Thank you all for any help

 

[25362]

Probably a return of liquid from the pump to the bullet would induce the turbulence required for mixing and promote vertical convection currents to aid in "turn over" and minimize thermal gradients between the bottom outgoing stream and the liquid surface.