Experimental Investigation Of A Horizontal Hermetic Scroll Compressor With Novel Oil Circuit Design

Owing to its reliable operation and low maintenance requirement, the scroll compressor has a potential application for oil and gas industry, e.g. the natural gas production for gas wells with low production and boil-off-gas recovery for gasoline filling stations. Though millions of scroll compressors are put into the refrigeration and air conditioning market each year, a much smaller number of such equipments have been used in the field of oil and gas production. This should be attributed to much larger quantity of compression heat for the natural gas compressor due to higher pressure ratio and larger isentropic exponent, which can not be taken way from oil circulation with traditional oil circuit design typical of refrigeration application. This paper presents an experimental investigation of a horizontal hermetic scorll compressor with novel oil circuit design. The oil was not injected but carried into the compression chamber by the suction gas to remove the compression heat. The oil circuit was so designed that the high pressure oil from the oil-gas separator was cooled, throttled into low pressure, and then stored in the horizontal motor casing, where the oil together with the suction gas entered the compression chamber. Owing to self-balancing, the oil level in the casing was kept constant whatever the operating conditions could be. Based on the novel oil circuit design, a vertical scroll compressor for commercial refrigeration was modified into a horizontal prototype compressor for natural gas compression. The prototype compressor was validated under a wide range of operating conditions in the closed loop test system. Its thermodynamic performances including flow rate and power consumption were tested under various working conditions. The results showed that the compressor could work reliably as the suction pressure ranged from 0 MPa(Gauge) to 0.25 MPa, and with one stage compression the maximal discharge pressure reached 3 MPa as the suction pressure was kept at 0 MPa

Effects of Low Suction Temperature on the Boil-off Gas compressor

The Boil-off Gas (BOG) compressor is used as a key facility in the liquefied natural gas (LNG) terminal, to recycle the excessive boiled gas for re-liquefaction or direct application. The low suction temperature down to -162? brings about big challenges in design of the BOG compressor. In this paper, the three-dimensional finite element model was used to simulate both the static and periodic transient temperature distribution in the cylinder of a BOG compressor, and a computational fluid dynamics (CFD) model was established to calculate the flow and heat transfer inside the compression chamber and suction/discharge pockets. A test rig was built up to validate the simulated results. The results showed that, the average temperatures in the suction and discharge pockets were about -109? and -60?, respectively, and the temperature of the compression chamber was in-between. The maximum temperature difference between outer and inner surface of the compressor cylinder reached up to 84? during start-up of the compressor, which yielded a thermal strain and stress in the cylinder much larger than those during steady operation of the compressor with only 31? of temperature difference. A variety of pre-cooling temperatures ranging from -20? to -60? were examined, and the results showed pre-cooling down to -20? before start-up was good enough. The amplitude of temperature fluctuation due to the periodic movement of the piston was less than 0.1? in the cylinder wall. The temperature coefficient tended to decrease at lower suction temperature. As the suction temperature decreased from -54.2?to -142.2?, the suction coefficient dropped drastically by 24.4%

Investigation On Premature Failure Of the Self-lubricated Piston Rings in Oil-free Compressor

Abstract: This paper presents the numerical simulation and experimental investigation on impact factors on premature failure of the self-lubricated piston rings in oil-free compressor. In this paper, the finite element method (FEM) was applied to study the non-uniform pressure distributions among the piston rings and the friction process between the self-lubricating piston rings and the cylinder wall, which influence the failure of the self-lubricated piston rings most. In order to verify the mathematic model, a test rig was built to measure the dynamic pressure distributions and temperature field between the piston rings. Both the theoretical and experimental results showed that the first piston ring afford more than 75% of the total pressure difference which was the main reason for the non-uniform wear and thus lead to early invalidation. The friction heat produced between the first piston ring and the cylinder was far more than the rest, which cannot be diffused rapidly through the low conductivity self-lubricating plastics and led to thermal failure of the self-lubricating piston rings. The results provide the theoretical basis to determine the design parameters and the thermal performance of piston rings reasonably

Design And Validation Of An Adjustable Dynamic Vibration Absorber For Piping Vibration Suppression In Skid Mounted Compressor Unit

The vibration control for a reciprocating compressor as well as piping has always been a challenge. Because of compact installation and limited space for the skid mounted compressor unit, it is difficult to arrange a piping support freely or change the piping layout. A new type of adjustable dynamic vibration absorber (DVA), consisting of an annular clamp and several discrete spring-mass systems (DVA subsystem), was proposed to solve this problem. The spring-mass system of this new DVA used the electromagnet and leaf spring equipped with linear slideway, which permitted continuous adjustment of the DVA’s natural frequency by means of variation of the mass and change of the electromagnet’s position. The finite element models of the piping with DVA was established to analyze the harmonic responses in the case of pre- and post- installation of DVA so as to validate the DVA performance of vibration suppression. The results showed that this DVA could suppress vibration effectively at original resonance frequency. Compared with the traditional DVA, multiple distributed units of DVA subsystems in an annular clamp could obtain a much wider frequency band, which overcame the defect that two resonance peaks appeared after installing the traditional DVA. The results also showed that this DVA, equipped with multiple sets of DVA subsystems with different natural frequencies, had an effective vibration suppression for the piping vibration simultaneously excited by multiple resonant frequencies. The study indicates that this novel adjustable DVA can effectively damp the piping vibration of the skid mounted compressor unit

Study on the Effects of Vane Parameters on Separation Performance in an Axial Flow Cyclone Separator

The oil-gas cyclone separator is a key component to an oil injection compressor system for its advantages of small volume, simple structure, high separation efficiency and low pressure loss. This paper presents the investigation on new type axial flow cyclone separator performance under different structural parameters, including the angle of vanes, the number of vanes, the rotation angle of single vane, by numerical simulation and verification experiments. A numerical model of two-phase flow in the cyclone separator was established and the separation efficiency and pressure loss of cyclone separators were simulated. A test rig was built and the diameter distributions of droplets at the inlet and outlet of separator were measured by a Malvern laser particle size analyzer to verify the simulation model. The results showed that the separation efficiency and pressure loss can be improved with the increase of the rotation angle of vanes. With the decrease of the outlet angle of the first stage vane and the increase of the number of vanes, the critical separated droplet diameter of separator can be lowered effectively. The results showed that the optimum outlet angle of vanes is 22°~25° considering the separation efficiency and the pressure loss of separators

Analysis And Control Of Severe Vibration Of A Screw Compressor Outlet Piping System

The severe vibration of a screw compressor outlet piping system caused the fatigue failure of some thermowells and the unscheduled shut down of the system. The main reasons of the abnormal vibration in the outlet piping system were investigated by developing an acoustic model to simulate the gas pulsation and establishing two finite element models to conduct the mechanical vibration analyses. The acoustic analysis results showed that the pulsation amplitudes of most nodes in the outlet piping system exceeded the allowable values. The results of mechanical vibration analyses indicated that the insufficient stiffness of the outlet piping system and the first-order structure resonance occurred on thermowells were also the key factors inducing vibration. Several methods were put forward to attenuate vibration amplitude of the outlet piping system as well as the thermowells. A new pulsation attenuator was installed and the piping layout was rearranged to reduce pulsation amplitudes and shaking forces of all nodes in the outlet piping system. Several reasonable supports were added to improve the stiffness of the outlet piping system. After reinforcing the thermowells, the first-order natural frequency of the thermowells increased from 207.4Hz to 280.7Hz, away from the excitation frequency of 196.67Hz. The field measurement results showed that vibration amplitude and the vibration velocity decreased significantly after modifications