PetroStreet

Usually Anti surge controllers manipulate Flow (By recycling / throttling) and discharge pressure of any compressor (by recycling / venting) to keep it out of surging zone.
It can also manipulate the speed of machine to perform the same operation.

My queries are,
1) What are limitation we can face, if turbine speed is manipulated to keep compressor out of surging zone?
2) What are the benefits of manipulating compressor speed for anti surge control?
3) Where such configuration can be used?
3) Can any body quote any example where anti surge is manipulating compressor speed?

Thanks in advance.

imran, I don't think that would save my machine. Anti-surge control valves are designed to operate in seconds (typically time would be 2 sec, or maximum 10 sec in a very rare case, from full closure to full opening). Machine ramp down and up to manipulate accordingly, especially in case of discharge valve full closure, will itself create a catastrophe. OEM has to install some breaks for getting an equivalent effect of ASCV full opening. In addition, machine health will also sacrifice due to sudden ramp down or up.
But anyhow, if you have any such experience, that would be worth sharing.

Salam Dear Imran,

I agree with Tosif. We may not be able to save your machine by manipulating turbine speed rather anti-surge controllers. In general, anti-surge valves, recycle or vent process gas maintaining a defined +ve flow across the compressor. if we try to manipulate it using our ramped controllers of speed regulation, then the action may be very sluggish [except ESV's which totally shut turbine driving fluid] and the machine may fall in the surge zone, during speed manipulation, in no time. The efficient control is that you maintain flow across the compressor, either by vent or recycling.

I am unable to quote any example for speed manipulating anti-surge controllers as they are not in my knowledge yet.

Reducing speed of the centrifugal compressor train is helpful during surge conditions. Most common anti surge control systems reduce speed after manipulating the control valve beyond 50~70 % opening, to avoid possible threat to machine still going to surge.