3 replies to this topic

[Lyne]

Hello everyone,

I’m working on a dynamic centrifugal compressor simulation where the capacity is controlled by inlet guide vanes (IGVs). I’d like to clarify how the IGVs should behave during different shutdown scenarios:

Emergency Shutdown (ESD): My understanding is that IGV position doesn’t change during an ESD, so the simulation should be run with the normal operating IGV position.

Normal Shutdown: In this case, the IGVs can be driven to their minimum position as part of the turndown sequence.


Since I’m new to this type of control, I’d really appreciate any insights or confirmation from those who have dealt with IGV-controlled compressors.

Thanks in advance!

[breizh]

Hi,

This link may help you.

UnderstandingCentrifugalCompressorCapacityControls.pdf

 

Breizh

[Lyne]

Many thanks breizh

[astro]

Hello everyone,

I’m working on a dynamic centrifugal compressor simulation where the capacity is controlled by inlet guide vanes (IGVs). I’d like to clarify how the IGVs should behave during different shutdown scenarios:

Emergency Shutdown (ESD): My understanding is that IGV position doesn’t change during an ESD, so the simulation should be run with the normal operating IGV position.

Normal Shutdown: In this case, the IGVs can be driven to their minimum position as part of the turndown sequence.


Since I’m new to this type of control, I’d really appreciate any insights or confirmation from those who have dealt with IGV-controlled compressors.

Thanks in advance!

 

Working to the fundamental premise of avoiding surge in any situation plus providing for economic design of right sizing equipment in preference to unnecessary oversizing, I'd say for any shutdown of a centrifugal compressor (as a basic principle), the objective is to unload the machine.

 

For an IGV controlled compressor, that would be returning operation to the minimum flow setting for the IGV.

 

Refer here:

https://www.cagi.org...encyMay2023.pdf

and specifically the section marked "Adjustable Blades Rather Than a Butterfly Valve" that states:

When fully-closed, the blades overlap to block all air flow except that through a small centre hole that is required for stable compressor operation (see Figure 2). 

 

That stable minimum flow needs to be set to a rate at some margin above surge for safety and economy.

 

So for a controlled shutdown, ramp the load down to its minimum (as per the IGV in its closed position) with mechanical sympathy in mind.

 

As a general principle for an ESD, I'd specify the IGV to fail shut and the anti-surge valve to fail open.

 

Speaking from the perspective of experience, there's always value in validating the shut down regime using dynamic simulation for bespoke designs because the influence of system volumes and cooler operation will shape the trajectory of an ESD trip as the machine spins down to a stop. Good practice ensures that the final design avoids crossing the anti-surge line during the transient.

 

You can see from the attached that the cases reviewed were short-listed from datasheet points in closest proximity to the surge line. The trajectories demonstrates that the design that was assessed, provides satisfactory protection of the machine from surge during an ESD.

 

 

Competent development of this sort of work should be undertaken by practitioners with the requisite expertise. Dynamic simulation is hungry for a lot of detail to feed into a model, so that it's sufficiently representative of real-world behaviour. When the time frames that need to be assessed work to a millisecond basis, it's crucial to be clear on the assumptions applied to avoid wasting the many hours to build a working model that delivers value (as per the garbage-in/garbage-out rule).

 

Note that my comments are based on a detailed working experience (including dynamic simulation) with speed control centrifugal compressors. However, I've managed process plant involving IGV compressors so know my way around the different presentations of their performance maps to be confident to assert that the same basic principles apply. The suggestions noted above, should be relevant and hopefully assist your thinking.

Edited by astro, 01 October 2025 - 08:48 PM.