The Offshore Application of a Dual-Mode Injection Centrifugal Compressor and Improvements to Rotating Stall

Abstract

This paper covers the experience from the retrofit of a new dual-mode injection compressor into the existing gas compression facilities on an offshore platform. The implementation of this new and innovative compressor technology made it possible to fulfil new requirements to higher throughput, different kind of service, improved safety level and economical operation. But then the compressor exhibited gas dynamic instability — determined as rotating stall in the impeller — a phenomenon not well understood. The literature on this topic is scare. The rotating stall phenomenon caused a significant reduction in useful operational area of the compressor. An improvement program was carried out. Changes in the impeller geometry led to restoration of the expected operational range. The magnitude of the phenomenon has diminished partially also. Rotating stall criteria proved to be useful in order to improve or avoid rotating stall problems in a centrifugal compressor. The dual-mode injection compressor allowed decommissioning of a whole equipment module, which represents a very useful experience factor in the design of new offshore platforms. The compressor has been in operation since November 1994, and it has been able to fulfil all specified operating requirements.