Why do we need to keep antisurge valve open 20%to30% open in RGC and why have they given margin for antisurge controller PID?
Peter Marsh, XBP Refining Consultants Ltd, email@example.com
A small, continuous flow of recycle gas is normally maintained through the anti-surge control valve to prevent condensation, freeze-up and dead leg corrosion. The anti-surge controller must be capable of fast response but with no overshoot into the surge region. The controller's speed of response is a function of proportional band width and integral action time (derivative action not required), but these parameters also affect the stability of the system. For example, under certain conditions, decreasing proportional band width or integral action time will increase the controller's speed of response but control may become increasingly oscillatory. The margin between the controller set point and the surge line typically equates to approximately 10% of full scale on the surge parameter.