Anti surge system for fixed speed compressors

[rotw]

Hello

Consider a centrifugal compressor driven by fixed speed driver.
I was wondering if the anti surge controller gets the compressor map with all the speeds ranging from 0 or so to the 100% speed.

The question is do we have a surge control line programmed into the surge controller or it is just a surge set point assuming there is only one characteristic curve at fixed speed and that's it. Is it correct to refer to surge control "line" for fixed speed compressors ?

My opinion is that we need anyway the whole mapping (all speed curves) so that the compressor remains protected during start-up and trip (acceleration/deceleration).

Anyone can share some experience please ?

thanks

 

[rakuday]

Rotaryworld,

When centrifugal compressors are started, there will be very minimal flow at the inlet. It is not possible for the machine to surge for these low flows. Once the machine reaches 100% speed, the IGV or inlet valve will be gradually opened. When the machine is built and tested for the first time, it will be operated with different IGV openings (starting from 10% to 100%) and it will be taken to surge for all valve openings. This data is used to plot the performance map of the compressor at different openings and a surge line is plotted. This data is used to program the controller for surge protection. Further, a ~5% offset (safety margin) is provided from the actual surge values, so that when the machine approaches surge, the controller can take the necessary action.

Unlike the theoretical data where the surge line is a straight line, actual data reveals that the surge line is curved and is not linear.

Please note that these are my experience with integrally geared AIR compressors. For gas and barrel compressors, it might be different.

 

[rotw]

Thanks but I don't want IGV. Yes surge line is not a line, but its a matter of terminology.
With IGV you get a map with a surge/control line so that is not my case.
Basically I refer to the case where there is a single characteristic curve with fixed speed driver on a typical anti-surge control implementation approach.
I simply want to know if the surge controller get anyways the complete mapping for the whole speed range to the 100% speed.

I expect it gets that because during a trip, at any speed the controller should be triggered when the capacity falls below surge and I guess it could make sense that surge control/surge line are relevant concept.

 

[Midan]

Why do you bother yourself about starting and shut down? Anti surge valve shall be fully opened during both cases and hence your machine is protected !
It's a typical procedure for both fixed and variable speed drives.