AN IMPROVED THRUST PREDICTION MODEL FOR HIGH PRESSURE MULTI-STAGE CENTRIFUGAL COMPRESSORS

Abstract

Axial thrust load predictions are an important aspect when it comes to predicting the performance of centrifugal compressors. The accurate prediction of axial thrust forces is necessary to size the appropriate balance piston and the thrust bearing dimensions for the operating limits of the compressor. Inline centrifugal compressors utilized for pipeline compression (and multistage upstream & midstream applications) often have a range of operating conditions, varying in flow, speed and discharge pressure (in addition to other variables such as gas composition and ambient conditions). The ability to accurately predict thrust loads over these ranges is thus important, especially at discharge pressures exceeding 3,000 psia [207 bar]. The key to predicting axial thrust forces lies in estimating the swirl ratio in the front and rear cavities of a shrouded impeller. This paper presents the modeling techniques for the prediction of swirl ratios in cavities as validated with scaled testing at the original equipment manufacturer’s (OEM) facility. The extension of this proposed model for full-scale compressor models, along with test results on high pressure compressors operating at 4,285 psia [295 bar] has also been presented. The ability to validate thrust modeling procedures in the absence of load cell measurements from thrust bearings is detailed in this paper.