Why are the monitoring points for anti-surge control different between centrifugal compressors and axial flow compressors?
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In the four-in-one unit of our factory (tail turbine – axial flow fan – gearbox – centrifugal compressor – steam turbine), the centrifugal compressor draws air from its outlet and divides it into two streams: one stream goes to a buffer tank before reaching the differential pressure gauge, while the other stream goes directly to the pressure differential sensor; this pressure differential is used as an indicator parameter for detecting surge； And does axial flow use the pressure difference at the inlet throat as the parameter for anti-stall control? Why are the reference values for the two options different?
It is not clear what the specific configuration of the owner’s unit is; this is merely a perspective offered for reference: 1. The horizontal axis of the anti-surge curve represents flow rate, while the vertical axis represents pressure ratio. The flow rate at the operating point is corrected for pressure and temperature. As the flow rate decreases, the operating point approaches the surge line. 2. To obtain a flow rate, it is necessary to have a flow channel cross-section that is sensitive to changes in flow rate. 3. A throat with a variable cross-section is often designed at the inlet of an axial flow compressor to measure the inlet flow rate ； The centrifugal compressor, on the other hand, is derived from the flow orifice plate. It is guessed that the centrifugal compressor used by the poster relies on the flow-pressure difference relationship established between the compressor outlet pipe and the buffer tank to reflect the flow rate.
Yes, I’m thinking about whether it would be feasible for both compressors to use the pressure difference at the throat, or both to use a buffer tank as a basis for making decisions.
1. If my above assumptions are correct (based on the compressor configurations I have encountered), and it is not important where the flow rate is measured as long as it can be obtained, then it is feasible to use the same method for both types of compressors. 2. However, to establish a relationship between flow rate and pressure difference for compressors with variable cross-sections, there needs to be a certain pattern, such as linear or quadratic relationships, that can be calculated numerically; such patterns are taken into account during compressor design, and tests have shown that they can accurately reflect the flow rate corresponding to different pressure differences. 3. Therefore, if the sampling method is to be changed, a large amount of experimental data is required as support