No replies to this topic

[umeshr]

We are having a four compressors in series(centrifugal compressor) out of which comp-1 & comp-2 are working on same shaft, comp-3 & comp-4 are working on same shaft. These are fixed speed machines. Comp-4's suction KOD is having two inlet stream. The main stream (80% of the total flow) is from comp-3 discharge. The side stream (20% total flow) is from a separator system. There is a throttling valve on this side stream (ie.20%flow stream). Compressor-3 outlet is having no pressure control. This is floating with the suction KOD of comp-4.

Discharge of comp-4 is connected to a constant pressure system. Hence always comp 4 discharge will see a back pressure of 100 bar. Compressor was designed for a suction pressure of 53 bar discharge pressure of 103 and flow rate of 36 kg/sec. My compressor is having a side stream suction throttling controller whcih will throttle the side stream if the discharge pressure is 108 bar, Anti surge is set at a discharge pressure of 112bar

Now my doubts are the following.

1. Currently the back pressure at compressor 4 discharge is recalculated 100 bar. That means my compressor will deliver a pressure of 100 bar and hence the operating point will shift to right side of the curve compared to its design operating point and the flow rate will increase to that corresponding to 100 bar? the suction pressure will be same as my design suction pressure?? comp 3 will work on pressure which is near to its design operating point (as comp 4 suction pr and comp discharge pressure are floating)

or

Since the pressure in the comp 4 discharge is less, this will result in a lower suction pressure (considering constant pressure ratio) for comp 4..and this lower suction pressure of the booster 4 will act as a back pressure for comp-3 (ie. lower discharge pressure for comp 3) which inturn will reduce compr 3 suction pressure and thus backword towards the comp 1. ??


2. My side stream throttling valve upstream pressure is 58bara and rated discharge pressure of the comp 3 is approx. 53.4 bar(discharge do not have any pr control). if the operating point moves to 108bar (ie. throttling set pre) due to some reason whether it is possible to reduce the discharge pressure using side stream throttling?? Will it be effective??


thanks
Umesh.R