Development of High-Pressure Ratio and Wide-Operation Range 700bar Compressor

Abstract

Pre-Salt development projects continue to expand offshore Brazil into ever deeper waters year after year. Consequently, the required Discharge Pressures for Re-Injection Compressors aboard FPSO’s are likely to exceed current 550 bar levels, and requirements for design of higher pressure compressors becomes more severe. This paper presents development of super high pressure compressor and the results of verification tests. Super high pressure compressor can be used as re-injection compressor or injection compressor such as in the CCS plant and FPSO. Rotor stability is the most considerable requirement for super high pressure operation because of the high density flow destabilization force in the compressor. From the point of view of rotor dynamics, the short bearing span and high shaft diameter are desirable for the stability of the rotor. On the other hand, from the point of view of aerodynamics performance, that rotor arrangement may decrease the performance. Some parametric study was conducted to optimize the boss ratio of compressor stage to get both high rotor dynamic stability and high aerodynamic performance. Rotating stall can be the cause of sub-synchronous vibrations in super high pressure operation condition and it induces narrow operation range. To prevent such situation, vaned diffuser was applied for developed compressor stage and it can also help to reduce the diffuser radius space. Seal leakage flow have large effects on the rotor stability and aerodynamic performance. For this item, the hybrid construction of hole pattern seal and step labyrinth seal was proposed. Hole pattern seal is well known as damping seal for high pressure compressor. CFD dynamic analysis and dynamic characteristics test for this hybrid hole pattern seal are introduced under the condition of high density by using hydraulic shaker device. The extensive verification test of developed super high pressure compressor were conducted with impeller of optimized boss ratio, vaned diffuser and hybrid honeycomb seal, and has demonstrated the robustness for all field operation condition including Molecular weight variation with high aerodynamic performance and small vibration.