Evaluation of Centrifugal Compressor Stability Margin and Investigation of Antiswirl Mechanism

Stringent stability screening criteria by the American Petroleum Institute (API) result in higher level rotor stability analyses to be performed on more intermediate-pressure compressor rotors and in more detail. These high-level stability analyses include predictions of impeller and seal rotordynamic forces and even extra effort on design and analysis of special damping devices as a backup, such as damper bearings and seals. Several moderate-pressure compressors were selected here to discuss the use of stability screening diagrams and the proposed API screening criteria. These compressors are operating successfully with or without a deswirl mechanism. However, most of them fail to pass the proposed new API screening. Furthermore, rotor aerodynamic logarithmic-decrements (log-decrements or log-dec) were predicted by implementing equivalent aerodynamic destabilizing forces that were calculated using Wachel’s equation, the API proposed equation, and the original equipment manufacturer’s (OEMs) empirical method, 49 EVALUATION OF CENTRIFUGAL COMPRESSOR STABILITY MARGIN AND INVESTIGATION OF ANTISWIRL MECHANISM