Methods of rotating stall and surge detection in centrifugal compressors

Abstract

Systems for prevention of surging of centrifugal compressors and methods of rotating stall detection and early surge diagnosis using statistical processing of sensor signals of various parameters, i.e., the method of calculation of the correlation function of the signal and the method of calculation of signal dispersion, are discussed. The results of routine tests of air and high-speed air centrifugal compressors and their detachable flow parts are adduced.The presently available systems for prevention of surging of centrifugal compressors (CC) can be divided roughly into two groups.1. Systems preventing surge, which are often called antisurge control systems. In this case, the surge boundary is plotted on the gas-dynamic curve of the compressor and to its right (10-15% toward the flow rate increase) is drawn the antisurge control line. If the working point of the compressor curve lies to the left of the control line, the bypass (or dump) valve slightly opens up, which prevents surging of the compressor. The surge boundary is determined experimentally in the course of surge tests or by calculation. As an example, in Fig. 1 are shown the surge boundary line for the supercharger N133-21-01 (curve 1) determined in the course of the surge tests and the antisurge control line (curve 2).2. Systems responding to incipient surge (surge signal indicators). In these systems, use is made of the distinguishing features of the behavior of the signals from the sensor, which characterize the compressor operation conditions (flow rate, supercharging pressure, current strength of the main electric drive, etc.), and a discrete signal is generated for forced opening of the bypass valve and/or for stopping of the compressor.A surge signal indicator can be installed in addition to the antisurge control system, and if this system fails either due to variation in the parameters of the gas being compressed or due to inadmissible increase in the thickness of the deposit layer in the flow part, the surge signal indicator prevents operation of the compressor in inadmissible surge conditions. Let us examine the second group of surge prevention systems. Research carried out by developers of surge prevention systems for centrifugal compressors was focused on detection of distinguishing features of incipient surge, which is characterized by fluctuations of the (discharge) pressure and the rate of gas flow through the compressor, the delivery temperature, the current strength of the electric drive, etc. Many patents have been granted on this subject in Russia and abroad. For example, an antisurge device based on fixing of the moment of concurrent drop in the delivery pressure and the rate of gas flow through the compressor has been patented [1].In a series of experiments performed in the 1960s [2, 3], it was found that rotating stall appears in the centrifugal compressor in the region of the working points of the compressor characteristics (curve) near the surge boundary. Theoretical and experimental studies of rotating stall that precedes surg...

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