Screw Compressor Acoustic Issues and Silencer Design
Screw compressors are becoming more common due to the increased compression needs for multi-phase liquid and gas applications, seen in shale gas production, gas processing and refinery applications. They are particularly well suited to low suction pressures and high pressure ratios. The simplicity and durability for well-engineered screw compressor designs makes the technology a preferred choice, provided that the compressors suction and discharge silencer design protects the related piping from high pulsations and vibrations. The high frequency content found in the dynamic velocity and pressure content is caused by the increased rotational speeds and the screw compressor lobe cancellation, placing the fundamental excitation at high frequencies (200-600 Hz). This combination of high frequency and high amounts of energy can create undesirable system resonances, both acoustically and mechanically, if the pulsation levels are not controlled with a good silencer design. Often, one badly designed silencer can underscore the importance of a reliable design and the need for a complete system acoustic / mechanical evaluation. The following paper will contrast two silencer designs in order to highlight some of the primary acoustic issues. These issues are similar to reciprocating compressor filter bottle designs (well known and easily modeled in one-dimension). The paper will also point out differences between screw compressor and reciprocating compressor filter designs due to the higher frequencies of excitation and the reliance on 3D acoustic modeling for screw compressors. Case study data will be used to illustrate various 3D acoustic modes within the silencer.