Use of compressor Inlet Guide Vanes to control pressure of the upstream HP Separator

[Sesquipedalianist]

I would love to know your views on the efficiency to control vessel pressure (HP Separator) using compressor IGV. My view is a response from the pressure of the vessel may be too slow leading to a surge in the compressor. What is your view? Do you an alternative to such a control routine.

 

[georgeverghese]

Can we see a process control scheme for this compressor - Presume this machine is running on fixed speed with capacity control by IGV and/ or by recycle ?

 

[Sesquipedalianist]

I'm currently reviewing a set of P&IDs for a CPF and was surprised as to why such a routine would be considered especially vessel pressure control (HP separator) using IGV since as I stated the slow response may surge trip the compressor. The vapor line from the separator heads to gas compression unit hence i would imagine the thought system was depending on the pressure in the vessel, the rate into the unit would be varied however in my view the response would still be too slow in the even of overpressurisation which would probably require flaring but by the time the response is sent to the compression unit, a surge would be eminent.

 

[LittleInch]

Well surge is a low flow or blocked outlet issue usually. The compressor will need to have anti surge fitted for that anyway, but I don't think you really mean surge??

90% of the time a CPF will run pretty much the same flow, with only gradual changes as wells change or the occasional one trips or is shut in for some reason.

So use of IGV to fine tune the flow I assume and hence maintain pressure or vice versa seems like it could work.

You will also need additional controls for shut down and start up and to deal with sudden large changes of flow or pressure, but these should be rare enough that the main IGV way of adjusting flow is a good way of dealing with it.

Difficult to say much more without the full PFD and H&M balance to see what is going on.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

IGV is normally used only for operations optimisation; it is usually not intended as a first line of response to operating variations. As you say, its action does not allow it to respond over as wide a range as speed or recycle controls. Its response is also kept deliberately slower than SIC or recycle controls to prevent it from destabilising the overall operations. Take a look at the controls in the compressor unit itself: you may find SIC or recycle controls details there.