2 replies to this topic

[asade abiodun]

Hi,

I have been studying on the design of a centrifugal compressor. I need information on the control aspects such as the:
1) Capacity control
2) Anti-surge control {am studying that at present)
3) Load sharing (How do one share the load on compressor?)

In depth understanding to the above questions is highly appreciated for enlightenment.


Regards.

[BLL]

Hi,

I have been studying on the design of a centrifugal compressor. I need information on the control aspects such as the:
1) Capacity control
2) Anti-surge control {am studying that at present)
3) Load sharing (How do one share the load on compressor?)

In depth understanding to the above questions is highly appreciated for enlightenment.


Regards.

1. This can be by speed control of the driver or by recycle or a combination of the two.
2. This is achieved by recycle control.
3. Are you wanting to share the load with another machine or with another stage of the same machine? This is achieved by linking the stage controls of an individual machine through a common controller or the linking of separate machine controls.


In all cases the supplier of a new machine(s) will advise on options. For existing installations seek advice from the original supplier/manufacturer

[Steve McGahey]

Hi,

I have been studying on the design of a centrifugal compressor. I need information on the control aspects such as the:
1) Capacity control
2) Anti-surge control {am studying that at present)
3) Load sharing (How do one share the load on compressor?)

In depth understanding to the above questions is highly appreciated for enlightenment.


Regards.

Off the top of my head, so your mileage may vary with these answers...

(1) You can manipulate the speed of the compressor, or the suction or discharge pressures to affect the flowrate through the compressor.

(2a) If the compressor in a compressor drops below a certain critical limit, the gas stream passing through the compressor can... err... slip. It's a sudden change in operation, and one that is upsetting for the poor chap operating the compressor. What you end up with then, is all of this high pressure gas trying to push backwards through the compressor. The gas goes from the discharge side of the compressor, pushes through to the suction (backwards through all those rotating blades). Then, when the compressor finds it has all this gas at it's suction, it compresses it, and sends it forward again. This leads to a lot of stress on the blades in the compressor. Thing of newton's laws and action/reaction. First it's pushing the gas one way, so the blades are being distorted in one direction, and then the gas is rushing another way, so the blades are pushed in another direction, and so on. This all happens on a timescale of milliseconds, and it can destroy the insides of the compressor.

(2b) Stonewall is also a problem, but you'll find different people have different ideas on how much of a problem. For the proof of the pudding, just look at the bit on your guarantee that says the warranty is going to be void if you're going to be operating in stonewall.

(3) Imagine three compressors with common suction and discharge manifolds. The suction and discharge manifolds are fed and bled from only one side, so each compressor gets a different "availability" of gas, and a different resistance to flow downstream. If you're setting all the compressors to run at the same speed, you'll find the one closest to the inlet of the header passes the most gas, and the one closest to the dead-end of the header passes the least gas. If you mess around with load sharing, you can tell the compressors to speed up or slow down according to how much power they are using, and these sorts of things.

Hope this gives some insight.

- Steve.