Optimizing Peak Efficiency & Flow Range in Pipeline Centrifugal Stages
Most pipeline compression systems today must operate effectively over a wide range of flow conditions. End users cannot accept a significant reduction in performance for so-called off-design operation. This demand for increased flexibility in pipeline compressor operation has forced turbomachinery suppliers to focus on attaining high efficiency over a wider flow range. This has resulted in the increased use of advanced design, analysis, and test methods in the development of pipeline stages. The paper will describe the approach taken to develop a new line of high efficiency centrifugal stages that also provide wide flow range, i.e., from surge/stall to choke. The paper will begin with a brief review of the key parameters used to assess compressor performance, such as efficiency, rise-to-surge, surge/stall margin, overload capacity, and range ratio. This discussion will then move to the various design and analysis tools applied in the development of the new stages, i.e., 1-D, 2-D, and 3-D analysis software. Analytical results for the new stages will be presented and observations will be offered regarding the typical assessment parameters applied to insure optimal efficiency and range. Next, test data gathered on the new stages will be presented and comments will be offered regarding the agreement (or lack thereof) between the analytical and test results. Of particular interest, 5-hole probes were used during the testing of the new stages allowing direct measurement of flow angles at key locations in the stage, i.e., impeller exit, return channel entrance. This permitted a direct comparison against the flow angles predicted by the analytical results. Such comparisons are atypical for production testing and represent a major step forward in the validation of new stage designs. Finally, conclusions will be drawn with respect to the success of the new stages at meeting the design objectives: increased range and efficiency. Comments will also be offered regarding the desi
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