Acoustic simulation, pulsation and vibration
1. What are the differences between the API 618 design approaches 1,2 or 3 (DA1,DA2 or DA3) ?
DA1: Pulsation damper is requested to be designed using analytical technique to meet line side pulsation level and pressure drop allowable.
However, SIM Engineering is always designing the pulsation damper with an acoustical simulation instead of analytical technique.
DA2: An acoustical simulation of the compressor, pulsation dampers as well as the customer’s piping lines is requested. A review of the supporting is requested but only using analytical technique and experience.
DA3: Like as DA2 an acoustical simulation is requested. Additionally, a mechanical response study is requested using a modal analysis software.
2. Are the vibrations induces, by the reciprocating compressor, or by the pulsations ?
The vibrations directly induced by the reciprocating compressor are typically:
- The periodic forces induced by the unbalanced mass in motion.
- The periodic torques generated by cylinders offset.
- The vertical force at the crosshead.
- The cylinder stretch induced by the gas compression loads inside the cylinders.
- Particularly for high speed compressor, the rotating parts misalignment.
The vibrations induced by the pulsations are typically:
- The pulsation induced shaking forces across the vessel
- The pulsation induced shaking forces across the piping runs, between elbows, between elbow and closed-end, between tee and closed-end….
- The effect of pulsations on the PV diagram and compressor vibrations.
3. I was believing that a screw compressor is pulsation and vibratrion free ?
A screw compressor (wet or dry) is not compressing the gas continuously, but in a series of flow pulses cadenced by the number of lobes on the male screw. The pulsations are much higher at discharge side compared to suction side, particularly when the compressor is working in Over-compression or in Under-compression (means that the max internal pressure reached within the screw is respectively higher or lower than process discharge pressure).