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Stepless capacity regulation through delayed closure of suction valves plays an important role in energy conservation for reciprocating compressors. Serious gas pulsation usually occurs with a suction valve unloader, and its analysis and suppression is a challenge owing to the varied components of the pulsation excitation under different conditions. In this study, a fast algorithm was proposed to calculate the gas pulsation of a compressor system with stepless capacity regulation and was further incorporated into the frequency-domain modeling of the gas pulsation. A test rig was constructed, and the model was experimentally verified. The dynamic pressure at positions in the suction and discharge valve chambers was measured, as the compressor capacity was varied by changing the closing time of the suction valves. The experimental data were compared with the simulated results and indicated a good agreement. The results showed that the suction valve unloader had a negative impact on the gas pulsation in the suction pipeline system. The pressure pulsation of the main excitation frequency increased in the suction pipeline system and decreased in the discharge pipeline, as the opening time of the suction valve increased. [ABSTRACT FROM AUTHOR]

This paper presents the root cause analysis and solving process of the torsional vibration problem in a reciprocating compressor shaft system. The field measured data showed that the fifth-order torsional resonance occurred in the shaft system. The lumped-mass method was adopted to calculate the torsional natural frequencies (TNFs) and mode shapes of the shaft system. A sensitivity study was conducted to investigate the effect of each inertia and stiffness in the calculation model on the first TNF of the shaft system. The uncertainties of the primary data of the calculation model were discussed, and the mass-elastic model was modified by adjusting the stiffness of the flexible disc coupling. After adding an inertia of 4.68 kg·m2, torsional resonance was avoided, and the speed fluctuation of the shaft system was significantly reduced. The compressor package has been operating normally for nearly one year after modification. The analysis methods and conclusions given here can provide guidance for trouble-shooting torsional vibration problems. [ABSTRACT FROM AUTHOR]

The severe vibration of a screw compressor outlet piping system caused the premature failures of some thermowells and the unplanned shut down of the compressor system. The root causes of the vibration problem were investigated by numerical simulations. An acoustic model was established to predict the pressure pulsation of the gas inside the pipelines, and two finite element models were built to study the vibration characteristics of the overall piping system and of the thermowells. The numerical results indicated that the vibration problem may be attributed to the excessive pressure nonuniformity of the gas inside the pipelines, low overall stiffness of the piping system and the first-order structural resonance occurred on the thermowells. A pulsation attenuator was added and the pipelines were rearranged to reduce the pressure pulsation, some pipe supports were added to improve the overall stiffness of the piping system, and the thermowells were reinforced to avoid the first-order structural resonance. After the modifications, the field measurement data showed that the vibration of the piping system decreased significantly, and the modified piping system has been operating normally for nearly two years. [ABSTRACT FROM AUTHOR]

The film flow behavior in an oil–gas cyclone separator was experimentally studied to improve the separation efficiency in terms of the effect of the oil film on the cylinder wall. The oil film flow pattern was captured using a high-speed camera, and the cylinder wall was divided into seven regions to analyze according to the different oil film flow patterns. Along the cyclone cylinder height, the central part of the cylinder was the main flow area, in which droplet–wall collisions and oil film splashing were severe. Additionally, the oil film’s distribution characteristics under inlet velocities of 14.0, 16.0, and 18.0 m/s were compared, and the results showed that more splashing oil droplets were generated under higher inlet velocity. Moreover, changing the structure of the central channel and outer cylinder slightly changed the oil film’s area and flow pattern but exhibited a weak effect on the oil film thickness and re-entrainment. Then, an improved structure was proposed by adding a porous cylinder to the outer cyclone to avoid the generation of small splashing droplets from the oil film. The performance of the modified separator was measured in a real oil-injected compressor system, which demonstrated higher separation efficiency with no increase in static pressure loss. The separation efficiency increased by up to 2.7%, while the pressure loss decreased by up to 10%. Thus, the improved structure can improve the performance of oil–gas separators by changing the distribution and thickness of the oil film on the cylinder wall. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the influence of the orifice plate parameters and installation positions on the attenuation of gas pulsation in a reciprocating compressor piping system. The acoustic wave theory and transfer matrix approach were applied to establish the simulation model, in which the valve chamber was assumed to be the pipe–volume–pipe element. Based on the model, the effects of the size and installation positions of the orifice plate on the gas column natural frequencies and pressure pulsation amplitudes were analyzed for the discharge piping system of a two-stage reciprocating air compressor. A test rig was built to validate the simulation results. The gas column natural frequencies and pressure pulsation amplitudes at different locations of the piping system were measured to verify the model. A favorable agreement was noted, with a maximum error of 2.1% for the natural frequencies and 6.3% for the pulsating amplitudes. The influence of the orifice plate on the gas column natural frequency varied according to its position and parameters. The results showed that all orders of natural frequencies decreased slightly as the inner diameter of the orifice plate decreased when the orifice plate was installed downstream of the vessel. However, the distribution of the gas column natural frequency changed when the orifice plate was installed upstream of the vessel. The pressure fluctuations in the piping system could be attenuated substantially by placing an orifice plate of reasonable parameter downstream of the vessel, within a distance of 0.4 m. The degree to which the orifice plate could attenuate the gas pulsation varied under different operating conditions. However, its attenuation effect was more sensitive to the compressor speed than to the discharge pressure. [ABSTRACT FROM PUBLISHER]

This article presents a numerical simulation of the thermodynamic process in the cylinder and dynamics of the self-acting valves for an air reciprocating compressor. The finite-volume method was employed to solve the compressible turbulent flow in the cylinder and through the valves. A single degree-of-freedom model was adopted to simulate the valve dynamics. The piston’s motion was defined by a user’s preset function, and the fluid-structure interaction between the gas flow and the valve dynamics was solved in a strictly coupled fashion. The technique of non-conformal interfaces was adopted to allow fluxes between adjacent zones with different mesh node locations. Based on the analysis of the characteristics of the flow through valves and the valve movement, sensitivity analysis on the valve impact velocity and the angle of inclination indicates that the valve impact velocity was more sensitive to the variation of the rotational speed and the valve lift while severe inclining motion occurs when the valves are installed in the radial direction. Instantaneous gas flow and force coefficients with the variation of valve displacement are also obtained according to the mass-flow rate across the valve and the gas force acting on the ring plate. [ABSTRACT FROM PUBLISHER]