3 replies to this topic

[BJMAC]

Dear All,

I need to size an anti-surge line of a gas compression system with 550 bar of discharge pressure and Molecular weight from 20 to 40. Regarding only fluid velocity, the only criteria I know for maximum velocity is the Norsok P-001e5, where the following equation is applied: v = (200 or 175)/(density^0,43).

Question: Is there any other criteria I could use?

Thanks in advance,

BJMAC

[ankur2061]

BJMAC,

As per the "Compressor Handbook" by Paul C. Hanlon, the sizing of the anti-surge valve should be at 105% of the compressor design flow rate.

Mobil and JGC standards recommend that the anti-surge control valve be sized for 100% of the design flow rate of the compressor.

Compressor anti-surge control is still a very specialized field and I would advise you to get a reputed compressor manufacturer's opinion on this rather than trying to do a specialist design and sizing which you are probably not familiar with. The reason why I am saying this that it is not just a matter of flow rate as mentioned above according to the standards I have mentioned, which give no further explanation regarding sizing. Other factors such as differential pressure rise at surge conditions, gas temperature at surge conditions all play an important role in determining the sizing of the anti-surge control loop along with its associated piping. If you are buying a new compressor ask the manufacturer to provide the anti-surge control system rather than trying to do your own engineering and sizing.

Regards,
Ankur.

[Himanshu Sharma]

Just to add my two cents !

I can safely assume that compressor under discussion is a centrifugal compressor since 'Surge' is a process witnessed only in Centrifugal compressors as Kinetic Energy of the fluid is converted into the Pressure energy

As a process engineer , in order to have capacity control of the centrifugal compressor we normally size a spill back line equipped with a control valve to cater to process requirements.

Anitsurge lines and control valves are provided so that centrifugal machine suction flow does not drop beyond a certain point after which a surge can occur.

Logically Antisurge control lines and spillback lines can coincide because both normally recirculate flow from compressor discharge to compressor suction,however some compressor vendor insists to provide a separate anti surge control line for machine safety point of view.(the reasons may become clear while referring to suggested link)

As a process engineer you have to typically specify spillback line and control valve ,the sizing comes from understanding of process requirements of minimum flow (typically at turndown conditions),designing spillback valve for 100% flow is the safest bet in case you are not very sure of the process.

Designing of an Antisurge control valve is more art than science in the sense that design should be more effective than being accurate,i could never design the same as the same involves a lot of instrumentation fundamentals coupled with a deep understanding of compressor dynamic behavior.

I would suggest you to seek vendor's help because what you are asking is a specialized field ,in case you still need some directional guidance look at http://www.kcicms.co...f?resourceId=77

Edited by Himanshu Sharma, 07 July 2012 - 01:48 PM.

[BJMAC]

Ankur and Himanshu,

thanks for the notifications. I will look for the compressor supplier opinion.

Rgds,

BJMAC