Dry gas seal flow control system

[protons]

Good day!
Work with Dresser Rand back to back centrifugal compressor (pumping natural Gas).
From data sheets, Dry gas seal flow control system (see attach) is desing for normaly work when discharge pressure after compressor is 90 bar. Just now we want to work with discharge pressure 65bar, in this mode the control comand what is being passed to FCV-1611(flow control regulator) all time varying from 23% - 27% and also PDIT_1611, PDIT_1612(pressure diff on orifice) values varyate of course. If we increase the discharge pressure above 89 bar the seal system start work stable, control comand what is being passed to FCV-1611 stay stable at 23%.

Flow control valve is - emerson model 24000 with positionner DVC6010.
my question is:
1) I need to re-tuned the DVC6010 or change the flow orifices FE_1611, FE_1612.
attach -

http://files.engineering.com/getfil...4ef8-8ff4-7508de2c2740&file=flow_system_1.bmp

Thanks,

 

[pmover]

is the problem a fluctuating or pulsating fcv-1611 control valve at the lower inlet pressure of 65-bar? please clarify your question so fellow forum participants can assist you.

is there a reason you do not forward your query to DR?

with lower inlet pressures to FCV-1611, this control valve will need to open more to meet the required flow rates at FE-1611 & FE-1612. insufficient detail on fcv-1611 is given as there are various trims available. suggest you forward your criteria to your local emerson rep and ask them. you may need to change valve trim
at the lower inlet pressures.

hope this helps.
-pmover

 

[protons]

Thanks,
"change valve trim" - This mean i need to recalibrate positionner DVC6010, change valve respons time, open time.
i add also flow rate at FE-1611 & FE-1612.
straight line is when we increis pressure.

 

[jbattershell]

my advice is to re-tune the PID loop which is controlling the Bauman 24000 valve. that valve is likely receiving information on flow from the flow element. it should be able to control to a steady flow even if the inlet pressure is reduced down to 65BarG. however, it was likely tuned with an input pressure of 90barG and according to your report, is now acting unstable at the lower input pressure. so, the controls need to be tuned for the new conditions. you should not need to change any hardware on the seal support system. especially, do not change the orifices at the FE-1611 and 1612. those are sized for the system.

also, when it was suggested to change the trim, that means to modify the internal parts of the bauman 24000 valve. there could be different internals to the valve which would change the flow range of the valve for different conditions. you should not need to do that and should be able to provide enough flow with the existing hardware. As you described, "acting unstable" is definitely requiring a re-tune.