Experimental Analysis of Surge-Detection System Based on Pressure Derivatives at Part-Speed Operation

Abstract

This paper presents tests of an antisurge system based on pressure derivatives. The control algorithm was proven to work on different machines and with different unstable flow phenomena. Compressors are known to be affected by unstable flow conditions appearing at low mass flowrate conditions. The best known and most dangerous phenomenon is surge, which is a global instability affecting the entire impeller and regions upstream and downstream from it. A list of identified local phenomena includes among others: impeller rotating stall, diffuser rotating stall, and inlet recirculation. All have a specific pressure signature that is used for early identification. The method presented in this paper is based on a control parameter named the rate of derivative fluctuation (RDF). This approach involves a simple measure of flow instability that is universal and reacts to flow disturbances. RDF has been already confirmed to identify inlet recirculation and surge. The aim of this study is to conduct real-time tests of an antisurge system, implementing the RDF algorithm triggering the safety valve opening. The study confirmed the optimal position of the monitoring point. The results showed that the RDF is indeed sensitive to different types of flow instabilities appearing in different impellers, and that it provides efficient flow stability monitoring.