Anti Surge Control System

Centrifugal compressor has three operating parameters are: Speed, Head, and Flow. Speed is the rotational speed compressor, the Head is the energy or force or capacity compressor (units feet or meters of unit length, so confused: p) to raise the pressure of the inlet pressure (Pin) to the outlet pressure (Pout), Flow is the flow of fluid being transferred by the compressor. "Centrifugal compressor can reach the maximum condition headnya at a certain speed, these conditions will be passed on the fluid flow is also certain." The above statement is called the boundary conditions peak of the compressor stable. Well, when Headnya rising (meaning larger Pout) then the flowrate to be dropped following the Performance Curve of the compressor. Pout increases could be due to the discharge pipe that is streamed by the compressor there is blockage, the filter is dirty, no clothes left in the pipe (ahh this is not possible), etc.. Sample Performance Curve of the compressor as follows: 






Performance Curve on the link Isentropic Head vs. Flowrate. Anyway since the word "isentropic" is a sacred word and hard to understand by ordinary people rich, then I have to use other performance curve that is similar but uses the relationship Compression Ratio vs. Flowrate. Compression Ratio and Isentropic Head "flavor-taste" associated in a linear fashion but is better discussed elsewhere. So let's use the Performance Curve, Compressor as below:



Abscissa is the Q1 (Flowrate) and the ordinate is Rho = Pout / Pin. While the N1 and N2 is the rotational speed of the compressor (rpm). Now the line is curved upwards Surge Limit. The graph above can be read when the compressor is running with the speed N1 and Rho increases (eg due to enlarged Pout) then Q1 will shrink following the N1 graphs. Once the chart until the surge-line is the stability of the compressor will be disrupted. If the stability of the compressor disrupted what mechanical impact to the compressor? Let's give it to mechanical engineer, mechanical engineer, took the point just did not want kompressornya surging into the area. The duty of the instrument engineer is the plot point to Ensure Against Rho Q1 is not in the surge area. It means

    * Q1 Should not be allowed to drop
    Rho * Should not be allowed to raise
Flow Q1 do not fall, meaning that suction and discharge should be able to drain the fluid on the amount that is on the right side of his line of surge. Flow Q1 suctionnya could fall due to lack of fluid flowrate or can also be because the compressor in the line downstream dischargenya anyone nyumbat. Or why else huh?. Her Rho (Pout / Pin) not to increase the pressure line and the line will be similar though not with flowrate. I bayanginnya if flowrate in the discharge became disturbed to near-pet clogged the pressure will rise and Rho to enlarge and enter and cross the surge line. Mode presented by Robert C. White and Rainer Kurz in an article for Compressor Surge Avoidance System is a schematic follows:

Additional by-pass pipe at the compressor discharge after cooler and is fed back to the compressor suction before the scrubber and the speed is governed by the anti-surge control valve is introduced the concept of surge control.
But this novel is somewhat hampered a bit because the solution Robert C. White and Rainer Kurz does not measure the pressure at the compressor discharge only other reference while measuring the suction pressure at compressor discharge