Vessel External Pressure Case

[MohdYaseen2010]

Dears;

We have the following case;

Plant having first stage separator delivering the crude to the second stage separator, the second stage separator is directly connected to the high pressure export pumps (no buffer tank).
In my view the second stage separator shall be designed for external pressure (full vacuum) as it connected to a suctioning source (export pumps) while the first stage separator not required to do so.
Our Contractor is urging that there is no possibility of negative pressure inside the second stage separator (even its happen will be for seconds as the vessel operating pressure is high so the liberated gaseous will fill the gap inside the separator wherever the pump is operating).

1st Stage Separator (DP/OP = 2.2MPag/1.2MPag) & (DT//OT 125/65-100°C)
2nd Stage Separator (DP/OP = 2.2MPag/1MPag) & (DT//OT 125/65-100°C)
Export Pumps Centrifugal 170m (two flowrate cases one with 135m3/hr & other with 300m3/h) design temperature 80C

What Do you think.

Mohd Yaseen

 

[JStephen]

At that design pressure, your vessels may be adequate for full vacuum without any additional cost- check into that first.

 

[waliq]

What is the dia, length (T/T) and thickness of this separator??

 

[MohdYaseen2010]

Dear JStephen;

I thought also the same & explained to our Contractor that just they need to do the FV calculation for verification purpose and abiding to the procedure.

Dear waliq;
T/T = 30m
Dia = 4m

Mohd Yaseen

 

[MortenA]

The lowest pressure will be equal to the NPSH. At this pressure the pump will cavitate and cant deliver a lower pressure. Remember to correct for elevation difference! You need to consider if thisis foroil (one vapor pressure) or if just water can be present in the vessel (another vaporpressure). The pump cant make absolute vacuum on its own although elevation difference may help. But then the vessel must be water filled (with cold water to boot)