Capacity Control Methods

[HamzaNossair]

Hello Gents & ladies:

Can anyone advise over the selection of Inelt Guide Vanes Vrs. Inelct suction Throtlling for the Cent. Compressor? how to choose either of them and based on which certain values or aspects you can go either this or this, as our process guys are open on the selection?

 

[jbattershell]

inlet throttling using a pressure reduction device like a butterfly valve will of course throttle the compressor effectively. however, it gives up efficiency for cost. an inlet guide vane will first throttle the compressor by pre-swirling the air/gas to the first stage. this effectively reduces the capacity of the compressor and throttles the compressor with less loss in efficiency than using a butterfly valve.

so, if long term operating costs are important, then choose the IGV. if up front costs rule the day, then the butterfly valve will likely be less expensive option on the OEM's price sheet.

 

[rakuday]

IGV's reduces the power consumption of the compressor. As already mentioned by jbattershell, the selection will depend on the initial investment and you can reap its benefit in the reduced operating costs of the compressor during its lifetime.

 

[rotw]

are we talking about an integrally geared centrifugal compressor or single shaft?
On an integrally geared compressor you could envisage variable IGV at the inlet of each stage, therefore you benefit of a wider flexibility.
On a multistage barrel type, typically you impact the 1st stage inlet only with pre rotation, next stages individual operating ranges could lock your overall range limiting/attenuating the overall benefit. Still for this type of compressor it is an option over variable speed or suction throttling. However for heavy/dirty gas it is not always recommendable to use variable IGVs. In general mechanical reliability should be extensively probed through references.
Also and as advised above, throttling would be an energy consuming option, potentially higher motor sizing, but eventually more robust solution - again a case by case evaluation would apply. The best way in my view for your specific application is to ask quotation to manufacturers for both options IGVs and suction throttling and compare the performance figures.

 

[CaracasEC]

If this is an integrally geared compressor, consider also the driver. If the driver is a steam turbine you could use the butterfly valve (higher friction loss). if you are using a motor (fixed speed), using igv is better. On the maintenance point of view, igv maintenance needs more skilll....cheers...