3 replies to this topic

[A mukherjee]

HI everyone,

We have a cryogenic reciprocating Liquid nitrogen pump that is used for transferring liquid nitrogen from low pressure to a high pressure tank. My boss is telling me to show a vapor return line from the pump to tank.

Can any one tell me why is this vapor return line required & how to size that line?

[fallah]

I think you mean "vapor return line including a PV or an orifice from the high pressure tank to a low pressure tank!" It is probably in order to keep constant delta P between two tanks during transfer operation. Am I right?

[Zauberberg]

I think he's referring to the pump casing vent but without P&ID or at least a sketch, it's not possible to give more detailed comment.

Pumps in cryogenic service need to be defrosted (dried), and cooled down prior to startup. The vent is used to release vapor flow from pump casing.

[raj.chengg]

Hi

I had done these steps while designing a liquefied gas transfer from LP tank to HP tank.

1) In addition to a liquid line there was a vapor line connection between the two tanks with appropriate CV and PRV.
2) The liquid volume flow rate was estimated for different liquid levels in HP (High Pressure ) and LP (Low Pressure) tanks based on system curve and the pump curve.
3) The equal volume flow rate was estimated to ensure that the pressure in the HP tank remained in the operational range that was required by the plant people
4) Based on the flow rates the expected pressure drop the pipe diameter was calculated.
5) The final design conditions were simulated to view conditions at min/max operational levels.

Kind regards

Raj