Forced Responce of Cylinder Manifold for Reciprocating Compressor Applications

Abstract

The system consisting of the reciprocating compressor and associated bottles, known as the “Cylinder manifold” may potentially be the source and location of high vibration problems. Consequently special attention must be paid to the complete simulation of the system to assure smooth and safe operation. Applicable standards specify the items to be included in the study (crosshead guides, distance pieces, cylinder flanges, joints, supports, etc.). However only a model built using manufacturing drawings and validated by site measurements can provide a sufficient accurate description of the characteristics of these critical components and therefore realistic results. Knowledge of the frequencies and amplitudes of pulsation induced shaking forces defined by acoustical simulation, internal gas forces in the cylinder, and unbalanced mechanical forces and moments allows a proper forced response analysis of the cylinder manifold system to be performed. These forces are applied to the finite element model to calculate the relevant vibrations and stress amplitudes by performing a harmonic analysis. When the dynamic stresses are out of the limits it is necessary to go back to the cylinder manifold system analysis or to the acoustical study to find a solution using different supports, with lower shaking forces, or by modifying the volume bottle design. This enables an iterative analysis of the system until all requirements have been satisfied. Additional results of a forced response analysis are the reaction forces on the cylinder and discharge volume bottle supports. When the application requires a large and heavy acoustic damping system with consequently a low mechanical natural frequency, or the compressor speed is significantly high, the possibility of mechanical resonance in the first design is very high. Therefore the execution of these studies at a very early stage of the project is fundamental. The proper solution can be found only by close cooperation between the compressor manufacturer, end user, engineering contractor and vibration specialist.

Compressor General Arrangement Dynamic Design Guided by Preliminary Cylinder Manifold Forced Response

“…Pressure pulsation analysis recommendations can protect plant operations by limiting their effect through a proper damping/ filtering system. This study aims to determine a method that limits pulsation amplitude and consequently reduces the relevant induced forces in the compression system, connected piping, and equipment [3,4,5].…”

Preliminary Piping Sizing and Pressure Pulsation Evaluation

“…The unsteady gas flow of reciprocating compressors generates pressure pulsations that might be increased by acoustical resonance. Depending on plant configuration and fluid characteristics, this can cause high vibrations, high noise levels and reduced performance [6,7,8]. Therefore, it is necessary to make very detailed analyses -particularly for high-pressure piping -to prevent failures from cyclic stresses that result from: The studies to be performed are:…”