MODELING OF PRESSURE DYNAMICS DURING SURGE AND ESD
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Centrifugal compressors operability at low flow is normally limited by the onset of surge that occurs when operating near maximum achievable pressure rise. Surge is characterized by large amplitude and periodic pressure oscillations in which the compressor can also experience a series of flow reversal and recovery. Surge may happen when compressors are subjected to rapid transients. Examples are represented by the emergency shutdown (ESD) or a power failure. To prevent this from occurring, compressor stations are equipped with single or dual recycle systems using valves, which are required to quickly open in presence of ESD. For the proper sizing of recycles valves and whole system 3rd Middle East Turbomachinery Symposium (METS III) 15-18 February 2015 | Doha, Qatar | mets.tamu.edu Page 2 layout in general the estimation of surge inception and frequency during transients are key parameters especially for high-pressure centrifugal compressors and usually require the characterization of compressor pressure ratio curve including the reverse flow region. Spool dynamics is important to simulate ESD transients so also the torque law for the compressor needs to be provided and extended in the negative flow region. Usually pressure ratio and torque law are not available from experiments. A quite simple approach based on considerations about velocity triangles is analyzed in this paper and compared with experimental data. The approach is firstly assessed in the analysis of simple systems (one model test and a full scale compressor), both modeled according to the classical plenum-pipe description suggested by Greitzer. Computed pressure and speed trends are compared with experimental data from the dynamic pressure probes during surge and ESD. Kulite probes were installed in addition to the standard instrumentation in the test loops of the model test as also of the full scale string test. The curve extension model based on velocity triangles proved good accuracy in the simulation of dynamic behavior of those systems. The same method was also applied for the analysis of a more complex compression train equipped with four machines and modelled with a commercial tool for dynamic simulation of fluid systems. The results obtained showed good agreement with pressure and speed trends coming from site acquisition devices.
Belardini, Elisabetta; Tapinassi, Libero; Rubino, Dante Tommaso; Pelella, Marco (2015). MODELING OF PRESSURE DYNAMICS DURING SURGE AND ESD. Turbomachinery Laboratory, Texas A&M Engineering Experiment Station. Available electronically from