Pump minimum flow recycle control 1

[liberoSimulation]

I need to hear from you about controlling the min flow of a centrifugal pump by pressure differential control (Pressure discharge minus suction pressure of the pump).
What I have seen in such application is that flow controller is used with a predetermined flow set point from the pump performance curve by the manufacture.
Some cases a RO is used in the recycle line where pump is designed with small flow quantity.
I am not sure if having PDC is a cold pump service is commonly used.
Any help is appreciated

Regards

 

[sshep]

liberoSimulation,

check out thread408-53164

Until about 5years ago, I would have been reluctant to use ARC valves. While working on a few plant start-ups in other locations I got lots of experience with these, and I think they work great.

best wishes,
sshep

 

[25362]

W.C. Driedger's article Controlling centrifugal pumps in the Hyrocarbon Processing issue of July 1995, under the general heading Fluid Flow, covers all the situations, and in particular the pros and cons of ARC valves.

 

[liberoSimulation]

25362: I could not find the article
sshep: thanks for the reference
But still I am not clear if using PDC "pressure differential control" for min flow recycle is a good proposal for cryogenic pumps and non-cryogenic pumps(operating temperature below -100 C) or using conventional FC valve is the preferred choice.
Actually I don't have an experience with ARC and its applications, so I would rather know more about the right choice either FC or PDC for cryogenic pumps or non-cryogenic.

Thank you anyway,
Still looking..

Regards

 

[rzrbk]

I am not familiar enough with cold service pumps to know how that might affect the choice, but...

For pumps in general, I have seen pressure control used successfully in cases where the pump curve was steep enough to give a significant pressure control range. On pumps with relatively flat curves, a tiny change in pressure causes a wild swing in flow, and can cause constant control valve fluctuations. I don't have a rule of thumb on a breakpoint between 'steep' and 'flat' curves.

A flow control measuring total flow from the pump discharge is probably the preferred method, but it will likely be more expensive and harder to retrofit. This option will tend to operate more smoothly, and be less susceptible to any specific gravity changes caused by temperature swings or other.

 

[liberoSimulation]

Thank you rzrbk for the information you provided for my subject.
You told S.G. changing with temperature and that causes not proper control. I agree with you and think FC is the best choice regardless of the cost.
Another point that it might not be clear for such application is how to know the DPC set point from the performance curve of the pump whereas Head vs Q curve is the commonly used and understandable.

Regards

 

[bimr]

driedger article

http://www.driedger.ca/ce1_cp/CE1_CP.html