Improving the Design of a High Pressure Casing With the Help of Finite Element Analysis to Ensure the Rotor Dynamic Stability of a High Pressure Centrifugal Compressor Equipped With a Hole Pattern Seal

This paper focuses on the casing geometry of high pressure compressors. It is common practice to use damper seals, typically the hole pattern type, at the balance piston to ensure the stability of the compressor when compressing fluids with high density levels. Special attention must be paid to the clearance of the hole pattern seal, which must be kept convergent at all operating conditions because a clearance divergence can lead to a rotor dynamic instability of the compressor. Furthermore, the clearance must be kept as low as possible to reduce the leakage losses through the balance piston. Therefore, extensive fine element analyses are performed to determine the mechanical casing deflections in operation and hence, the correct clearance behavior of such damper seals. This paper discusses the history of the casing design during the last 10 years and compares the configurations with respect to the clearance distribution along the damper seal length. To validate the analytical predictions, leakage and stability measurements (using a magnetic shaker) are performed for these high pressure compressors during the full-load, full-pressure testing. This paper presents the stability measurements carried out on two compressors (390 bars and 655 bars discharge pressure) and compares the results.