Four Quadrant Centrifugal Compressor Performance

Abstract

Lecture 16: The characterization of the compressor behavior in all quadrants of performance map has acquired, in the last years, growing attention. Two dedicated experimental campaigns have been performed to characterize fourth quadrant and second quadrant operation in terms of performance, pressure fluctuations and mechanical vibrations. Experimental campaigns allowed the acquisition of performance curves of a centrifugal compressor in deep choke up to reverse pressure and indicated a large region of safe operating conditions at low peripheral Mach number. In stable reverse flow, the trends of work coefficient and pressure ratio were acquired for a large range of flow rates together with the evolution of vibration and pressure fluctuation along the speed lines. Pressure ratio and absorbed power for the different modes of operation can be very important to simulate dynamic scenarios far from the steady state operation and size accordingly compressor protection equipment and predict accurately compressor startup torque from pressurized condition (Fourth Quadrant Operations). The main frequency content and amplitude of pressure variations within the flow field or the radial/axial vibrations at the bearings are important to estimate blade loading and possible presence of excitation frequencies in the system. In the reported experience the operating points characterized by stable reverse flow rates close to the nominal one in direct flow did not show features much more critical than in standard conditions (Second quadrant operation) . This result may be hopefully used to reduce BOP in early design phase of system layout.