3 replies to this topic

[vnpetroleum]

Dear All,

I have a question relating to Anti-surge control valve (ASCV) operation needs your help.
Our compressors was designed to handle maximum capacity of 12 MMSCMD. It is a centrifugal compressor. Due to the low gas demand, it is required to run the compressor at very low gas rate which is lower than minimum capacity of compressor.

Based on the reservoir pressure (suction pressure) & back pressure from shippers/pipeline, the minimum compressor capacity now is defined at 5 MMSCMD (as per compressor performanc curve).

To prevent the compressor surge, ASCV must be openned to bring the operating point be away from surge line.
Because we dont have Recycle Valve for our platform, we must sometimes use ASCV as a capacity control. It is not recommended to use a protection equipment as control equipment.

I think about installing a new recylce valve for control capacity but it is very high cost.

Has anyone experienced about using ASCV as control capacity? Is there any integrity effect on compressor system/ ASCV integrity/ Noise Vibration?

Please share with me. I need some information to see the PROS&CONS b/w high cost of new recylce valve & safety of using ASCV

Many thanks

vnpetroleum

[ankur2061]

vnpetroleum,

A safety or protection device has a higher SIL (Safety Integrity Level) than a control device. If you start using a safety or protection device as a control device you are downgrading its SIL level due to the continuous operation (operating cycles per unit time). This is the reason that most operating companies demand that the safety or protection function be completely separated from a control function.

Thus IMHO a safety or protection instrument should never be used as a control instrument.

My suggestion would be to install a separate capacity control system for your centrifugal compressor whether it involves providing a separate recycle control valve, providing inlet guide vanes or a variable speed drive.

But do remember that providing a recycle-control valve is a tremendous wastage of energy for a fixed-speed machine. I would recommend to critically evaluate inlet guide vanes or a variable speed drive considering that your capacity reduction is less than half (i.e. from 12 MMSCMD to 5 MMSCMD). It might prove to be more economical than using a recycle-control valve. Do consult your compressor vendor regarding this.

Hope this helps.

Regards,
Ankur.

[Bobby Strain]

I don't see any problem with continuing to use the antisurge valve for capacity control. But I would operate it through the antisurge controller. If you want a bit more margin than usual, then raise the minimum flow setpoint. You will likely need to do this by reprogramming. But it's a lot cheaper than installing another valve. If this low capacity will continue forever more, you might want to conside rewheeling the machine to save energy.

Bobby

[RoyenG]

Hi,

installing control valve for ASCV and capacity control depend on the company's spec requirements.
Some company accept to install one CV for both purpose but others doesn't.

safety is the pros for installing separate valves whilst cost will be the cons.

cost will be the pros for installing one valve for both purpose whilst valve reliability (one valve should work (open/close) for two conditions) will be the cons.

Regards,
Royen