Rotor Dynamics Modification Of An Eight Stage Compressor For Safety/Reliability Improvement.

LecturePg. 81-96The catastrophic failure of a high pressure centrifugal air compressor utilizing air-pressurized bearing housings dictated the redesign of its sister compressor. The modification of this early 1950's compressor involved elements of both practical and analytical design. The project included the design of new bearings and seals and the alteration of various support systems to permit operation with non-pressurized bearing housings. The project was undertaken as risk minimization, with all performance and reliability improvements being additional benefits. The matching of the computer model with the field data of the existing system was the key to its successful evaluation. It was found that a case seal was acting as an additional bearing during certain operating conditions. This third bearing caused the compressor to behave differently than had been predicted with the initial two-bearing models. With the system properly modeled, changes were proposed to optimize the rotor dynamics. The main objectives were to achieve reliable rotor dynamic characteristics and to maintain the integrity of the process labyrinth seals. The changes were made in April, 1982, with the normal hardware fitting considerations. The subsequent start-up and operation were without incident. The modified compressor has performed well through a number of emergency trips and subsequent restarts, exhibiting exceptional rotor stability and overall reliability