PSV in pump suction line ??

[Armen75]

On a centrifugal compressor.
assume normally operating at a suction of 10 bar (constant, very large volume tank) and a discharge of 100 bar. Flowrate of 100m3/h.
Recirculation line for full flow, going from high pressure to low pressure rated piping (note, NOT back to source tank).
There is a cooler on the low pressure suction side (low design pressure) and the spec-break to higher rated piping at the block valve just upstream of the pump.

If I have a blocked outlet and the recirculation line opens, what will be the pressure at the suction of the pump?

With minimal Delta Pressure in the system, we have figured that the pump will eventually go off its curve (on the right) and hopefully shut itself off prior to shaking itself to peices.... but what happens before that occurs...

I am trying to determine if a heat exchanger in the suction side needs overpressure protection, and if so, how do you determine the relieving rate required.

 

[Chance17]

In theory, you can not overpressure the suction at 100% internal circulation.
In practice there are usually external source of pressure outside the circulation loop.
1) Back flow depressure from discharge side equipment
2) liquid injection suction cooling
3) Continued suction gas input from an upstream source
My advise is to look for the pressure sources outside the internal loop. This will lead to the answer.

 

[BenThayer]

pump or compressor? you state both.

basically, the pressure at the inlet will be what it was before the event unless the case of "no flow" causes high pressure in your large inlet tank.

assuming compressor, your recirculation line, if it is there for anti-surge protection, should keep the compressor on its curve and not cause it to shake itself apart.

does the heat exchanger in the suction see the flow for the recirculation? can it remove the heat of compression of the compressor?

i would be more worried about heating up the recirculated gas causing issues.

 

[Armen75]

sorry, it is a pump,
actually, it is 2 pumps in series with a cooler in the middle.
The first pump (small) normally discharges at 5 bar and has a shut-off of 10.
the second pump (big) goes to 90 and has a shut-off of 100.
The recycle of the second pump returns upstream of the cooler (designed for 10 bar) before going back to the pump. Although considered, thermal not an issue due to heat sink.
we are wondering if the big pump recirculating around (due to being blocked-in) can overpressure the cooler in it's suction side.