Development and Application of Very High Flow Covered Stages for Process Centrifugal Compressors

Abstract

For process centrifugal compressor applications, achieving higher flow rates through a given sized compressor can reduce capital cost while still meeting process requirements. Key technologies for enabling such higher flow rates are high flow coefficient (design ϕ > 0.12) and very high flow coefficient (design ϕ > 0.20) aerodynamic staging featuring covered impellers. Since the 1990s the prevalence of high flow coefficient stages has only increased in LNG, Ethylene, and some other compression services. The overall trend has been towards higher flow coefficient stages that push beyond existing experience limits. Applications involving what can be termed as very high flow (VHF) coefficient staging have only first been applied since around 2010. The present work describes the development and application of a family of very high flow (VHF) stages with nominal design flow coefficient of 0.24 and moderate to high Machine Mach Number (Mu) of 0.88. The design is essentially a constrained optimization where the stage aerodynamic performance (range and efficiency) is optimized while still meeting targets related to mechanical robustness and rotor dynamic usability. The first part of the paper describes the aerodynamic design focusing on the features that help address the aerodynamic performance requirements. As the design flow coefficient increases, both the efficiency and the available stable operating range become further challenged, especially as the inlet relative Mach number increases. The presented aerodynamic stage design solution consists of an impeller with both full and splitter blades having unique features and a return channel system that also features three-dimensional Copyright© 2021 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station 2 blading, which extends into the cross-over section. Subsequent parts of the paper discuss the mechanical design, single stage aerodynamic rig testing, selection examples, and a case study involving results from a tested shop order.