Booster Compressor added to exisitng unit Anti Surge Desigb

[HamzaNossair]

Hello,

I'm adding a booster compressor to an exisitng cracked gas compressor, which one is the best?

1- Have 1 common Antisurge valve from last stage of exisitng Compressors to the first stage of the booster added, with one pressure controller for the perfromance at the inlet of the new compressor?

2- Have 2 Antisurge valve across each compressor but all is returning the flow to the new added Booster, this will be with 1 Pressure controller?

 

[TD2K]

There's not a lot of details in your current post. I'm assuming you currently have an antisurge valve on your existing compressor and you are asking how to modify that system with the addition of the booster compressor. You refer to cracked gas, is this an ethylene plant? Those are multistage centrifugal compressors and I'm going to assume that is what you have.

Your booster compressor simply adds additional stages to your existing cracked gas compressor which if it is anything what I'm familar with is already a multistage machine. To keep things simple, I would likely try to keep that philosophy and tie the antisurge piping to the suction of the new booster compressor. You'll need to analyze the surge line(s) of the two compressors' stages to see if a single antisurge line/setpoint will protect both machines without excessive recycling to one of the two compressors (it likely will work as your existing antisurge valve has a set point such that all of the stages in the cracked gas compressor operate above their surge line). If a single surge valve doesn't look feasible and you need more than one antisurge valve, you'll need to review the compressor curves and operating envelope to identify the best control strategy and set-points.

 

[HamzaNossair]

Right- Sire, I will need to expand my reply so I can get your / and any one want to share with an advise. Thanks

Option 1: Basis of the current Design (2 separate Recycle valves on each Chare Gas and CGBooster)
Discussion
1- Minimum flow thru CG booster compressor occasion will reach (affect) existing CG compressor with time delay.
2- Each compressor has dedicated suction pressure controller. CG compressor Min flow would satisfy the CG booster minimum flow without any delay.
3- CG booster interlock include a feature to lower existing CG compressor suction pressure controller set point to allow for quick opening of CG booster bypass.

Advantages:-
It appears that, CGB min flow scenario will not reach CG immediately; CG min flow (when happen) will satisfy CGB min flow as both of them based on dedicated PC.

Concerns:- You will need to achieve a logic to reduce the CG suction set point, means of interlock, to facilities opening the CGB min flow and Engineers who will support the design, engineering and commissioning of both compressors control systems will have a tough job to configure two compressors control systems, two performance controllers, two Anti surge systems, who's overriding what with the Current CG control system DCS and new proposed CGB system from Elliott.

Option 2: Basis of the predicted Design (Common Recycle Valve for both CG and CGB)
Single and common Pressure controller located at the suction of the CGB with a single Min Flow valve from last CG combined train, still CG 4th stage, to the new 1st stage of CGB across the quench tower.

How that option will be more likly to occur than option 1?