TWO-PHASE FLOW IN A FEED LINE

[ChemE2912]

HI FOLKS,

We are dealing with the following problem:

The line that feeds a Crude Unit, coming from a heating train,which is 100 m away from the tower, handles a mixed phase product (vapor/liquid).

The product leaving the heater is at 453 °F, and the tower pressure is 15 psig. The pipe that interconnects the heater with the tower is 42".

Is there any limitation and criteria (velocity, density x (velocity^2), location of the heater with respect to the tower, etc...)for this line to handle two phase flow? We have the understanding that it should not exceed 80% of the sonic flow, but have no other means to determine whether the line is sized correctly or not.

Any help is appreciated.

Regards,

ChemE2912

 

[MortenA]

Hopefully you have a slope towards the tower inlet with no "water locks". You tower inlet pressure is quite low - how much dP do you have?

I dont think that you can use 80% of sonic velocity for a 2 phase flow in a 42" line in a plant for anyting - you should be much lower.

This seems like complicated work. If you dont have sufficient inhouse knowledge try to look for a consultant. Dont expect to get more that "good advice" here (even though its often quite good - you dont get any liability ;-) )

Best regards

Morten

 

[SeanB]

From my limited experience, for 2 phase flow, we design the pipe to not exceed 70% of the erosional velocity.

 

[MortenA]

SeanB

Propably also what ChemE2912 meant (i mean erosinal - not sonic allthough i didnt see that at first.

Best regards

 

[aikmeam]

Sizing of two phase flow lines has to be such that the following is met:
1. Pressure drop is acceptable.
2. Flow regime should be in the stable phase, avoid slug flow where possible. Generally, this is related to velocity, the higher the velocity, the better you can avoid slug flow. Check the flow map. And this is also another reason why you would not want a liquid pocket along the line. It doesn't necessarily needs to be sloping, just no pocket will do.
3. Lower than erosinal velocity (but this is primarily for material integrity protection, and where solids or erosive material is present)

 

[ChemE2912]

Thank you AIKMEAM, we indeed verified what you said, checking the flow regime in the line, and also ensured that we were not near the erosional velocity.

Regards,

ChemE2912