Benefits of the Virtual Orifice: Pulsations & Vibrations Reduced, Performance Improved
Controlling cylinder nozzle resonant pulsations while maintaining acceptable compressor performance has been an issue in reciprocating compressors for the last 50 years or more. The common solution to reduce vibrations and pulsations in the cylinder nozzle was the installation of an orifice plate at the compressor cylinder nozzle flange or welded into the nozzle near the nozzle-to-bottle acoustic junction. Lower efficiencies and higher pulsations are more evident for high speed, high horsepower machines due in part to the higher mean flows and coincidence of the cylinder nozzle acoustic response with lower compressor orders. The GMRC Pulsation Research Program at Southwest Research Institute has developed a pulsation control device as a replacement and improvement upon the commonly installed cylinder nozzle orifice plate solution. The new device is termed the Virtual Orifice. The Virtual Orifice (VO) has recently been installed at El Pasos Baxter compressor station. Measured field data has shown that the installation of the VO resulted in a significant reduction in pulsations and vibrations related to the cylinder nozzle resonance while noticeably improving the compressor efficiency. This paper will discuss the fundamental issues that the virtual orifice is designed to address. It includes data (vibration, pulsation, and performance) from a field compressor before and after virtual orifices were installed. The paper will explain and demonstrate the results from the field test of the installation of a virtual orifice on each cylinder of a high speed reciprocating compressor. The field test results will include summaries of the data that describe the vibration, pulsation, and performance improvements that were observed. This paper demonstrates the benefits of properly applied virtual orifices.