Screw Compressors

In screw compressor systems, the cyclical compression and expansion of fluid during the rotation of the helical lobes generate fluctuating flow and pressure pulsations. These pulsations are transmitted into the inlet and exhaust piping at frequencies that are integer multiples of the pocket passing frequency (PPF).

The acoustical pulsation analysis involves calculating the pressure pulsations, pulsation-induced shaking forces, and pressure drops resulting from specified pulsation attenuation measures. This analysis is used to adjust pulsation control designs, including the implementation of pulsation suppressors, silencers, and pressure drop elements, to ensure system compliance with the latest API 619 guidelines.

An example of acoustical pulsation analysis for a screw compressor package with the following specifications is illustrated below. The analysis was performed using Bentley PULS XM Option 3 software in accordance with the API 619 Standard.

The calculated acoustical pulsations, represented by the maximum pulsation violation ratio, for the suction system, both before and after design modifications, are shown in the following figures. Specific operating speeds were restricted to mitigate excessive pulsations and shaking forces.