Process Surge Control Decoupling Block

We have triconex PLC for Our ITCC System. We Have a manual about How Process and Surge Decoupling Block Works in Performance Control Application. But It is having Very Limited Explanation and does not Have Detailed Explanation about working of this Block. I want to know how this works in real-time applications.
Regardless of control system you have decoupling for surge control should always have the same meaning. You run you compressor which somehow connected to process or pipeline or part of refrigeration (I simple don't see details in your message).

In any case you normally have some downstream volume (like pipes or columns etc.) where you can have all kind of problems which can knock down compressor to surge. Like sudden shutdown of downstream equipment lead to rapid rise of pressure or some temporary changes in process which put compressor to surge or to surge direction.
Another factor can be that your driver need to lower speed (say to unload machine quickly).

In any disturbance you do not want to wait until you go surge or to that direction and you want to act as soon as possible to have smooth control. Here is when you need decoupling. Say you have pressure sensor 1km downstream of you compressor and if it sense a sudden increase of pressure you can react immediately and open a little recycle and not wait until this pressure rise will reach your compressor. This is what decoupling is for, you simply add change to your PID or whatever control(or combination) you use for ITCC control output. Say you were recycling 10% and with decoupling it will go up to 15%). It's also called feed forward. As as any other control you need to tune that, apply gains , may be even make calculations of it from more than one measurement.

For speed. If you decrease quickly speed setpoint you already know that compressor will go toward surge (depends where you operate close to surge line) so to not wait you connect speed SP change to surge control to open recycle partially to avoid surging to stalling.
As any control you need to be careful and use feed forward only when it makes sense as you can affect process.