Oil Flooded Screw Compressors Research Articles

Performance prediction and Bayesian optimization of screw compressors using Gaussian Process Regression

Optimizing the performance of screw compressors is critical for achieving high efficiency and reducing costs in various industrial and engineering applications. Often, the design and optimization processes are time-consuming owing to the underlying iterative complex analyses. In this context, the present research investigates the potential of Gaussian Process Regression (GPR) and Bayesian optimization for the prediction and optimization of the performance of an oil-flooded screw compressor. Specifically, the GPR-based surrogate model is developed to predict the compressor performance characteristics based on its four main geometrical design parameters such as wrap angle, relative length, tip speed of the male rotor and built-in volume ratio. The model is trained using a dataset comprising 19,200 data points relating the input design parameters with the compressor performance, obtained using physics-based multi-chamber thermodynamic models. While four different learning algorithms such as Support Vector Machine (SVM), Artificial Neural Network (ANN), Polynomial regression and GPR are explored, the GPR performed the best resulting in an R2 value of 0.99 for the test dataset after hyperparameter tuning. Further, the model is also experimentally validated on a completely unseen dataset, showing very good predictions with a maximum error of 5%. The resulting surrogate model is then used to optimize the compressor design parameters using Bayesian optimization. The results are compared with optimization using Genetic Algorithm (GA) and physics-based multi-chamber thermodynamic model. It was shown the proposed approach results in similar optimal design parameters but with a significantly less optimization time by a factor of 7. The study highlight the potential of machine learning-based prediction and optimization of screw compressors in engineering applications.

Computational Fluid Dynamics Evaluation of an Oil-flooded Screw Compressor

The cost of energy is directly influenced by geopolitical, economic, and environmental factors. There is an international trend towards renewable resources, although the implementation pace and legislation in force have issues. Complete abolishment of fossil fuels is practically impossible. Evolution is only possible with the use of these fuels but with modern, efficient equipment to reduce the pollution resulting from the process of extracting, processing, and using fossil fuels. In this paper, a screw compressor with oil injection, used in oil extraction stations, is analyzed numerically. This analysis is useful in the process of modernizing and improving the efficiency of this type of compressor, which is capable of operating in extreme working regimes, highly contaminated with impurities. The numerical analysis presented certain challenges related to biphasic flow in extremely small spaces at high compression ratios. The results include the absolute pressure variation and the flow rate variation. Regarding future research, test series will be carried out to validate the numerical results on the test bench with a 1:1 scale prototype.

Commissioning of the Warm Compressor System for the ESS Accelerator Cryoplant

The accelerator cryoplant (ACCP) providing the cooling for the cryomodules and the cryogenic distribution system for the cold part of the ESS proton linac is being built and commissioned at the European Spallation Source (ESS) in Lund, Sweden. The ACCP warm compressor system (WCS) consists of several compression stages. The sub-atmospheric pressure stage (SP) is used to compress helium coming from the cold compressors directly to middle pressure (MP) level. The low pressure stage (LP) compresses the helium from LP level to the same MP level, being merged with additional flow from the cold box and the flow from the SP stage. The total flow is compressed in a single compression stage (HP) from MP to HP. The oil-flooded screw compressors are chosen in a way that the flow in each stage SP, LP and MP is compressed by a single screw compressor. Both, SP and LP compressors are equipped with a variable frequency drive (VFD) to adapt the compressor capacities to the various load cases. The ACCP had been contracted to Linde Kryotechnik AG in 2015 and all compressors are made by the Aerzener Maschinenfabrik GmbH, Germany. Following successful installation and commissioning in 2018, the final 100 hours test run at maximum nominal design condition and the part load tests under various ACCP operation modes were carried out at the beginning of 2019. The key parameters, including mass flow, power consumption, isothermal and volumetric efficiencies, are well fulfilled with the design data. The paper describes the system features, project challenges, lessons learned and acceptance test results.

Analysis of a high-pressure screw compressor performances

Oil flooded screw compressors with discharge pressures of up to 26 bar have been available, commercially for some years. However, demands for higher pressure operation led to the design, construction and testing of a compressor operating with discharge pressures of up to 45 bar. To maximize the compressor efficiency, extensive performance simulations were carried out. Since 1980 oil flooded screw compressors have been used in many process gas compression applications and in the last year the higher pressure and larger capacity was realized. From 2010 to 2015 INCDT COMOTI manufactured screw compressors under GHH-Rand license (CU type, with max. delivery pressure 26 bar). Experience gain in this process gives us the power to develop the new type of screw compressors - based on license - with high delivery pressure - max. 45 bar. This paper will present details about the tests with a new high pressure screw compressor test in a closed loop test configuration. The machine was then tested in a closed loop test rig and, as is shown, the measured performance agrees well with that predicted by the numerical model. The parameters will be analysed starting from CFD modelling of the process and finally comparative analysis with actual parameters. The demonstrated advantages of this type of compressor, like high reliability, simple foundations, low operational cost, low initial cost, suitability for process fluctuation - gas pressure, gas composition - led to a significant demand for such compressors.

Development and Design of Energy Efficient Oil-Flooded Screw Compressors

It is estimated that about 17% of the world’s generated power is used for compression. Thus all, even minor improvement of the efficiency of compressors will substantially reduce CO2 emission. This paper presents development of family of energy efficient oil-flooded screw compressors for Kirloskar Pneumatic Company Ltd. The developmental techniques adopted to improve efficiency such as introduction of superior ‘N’ rotor profile, rotor clearance management, performance calculation using 3D CCM (Computational Continuum Mechanics), direct parametric interface to CAD (Computer Aided Design), which contains bearing selection for complete 3D solid modelling. Also, contemporary prototyping and experimental investigation is supported by the fully computerised data acquisition and processing. The cumulative improvement of all these elements of the design process resulted in a very efficient machine which guarantees the competitive position of Kirloskar Pneumatic Company Limited in the screw compressor market.

Determining Changes in the Engagement of Screw Rotors Due to Transmission Error

As a rule, the structural analysis of screw compressors during their design comes down to determining the geometric dimensions of the screws, the position of their window edges, as well as the gas forces acting on the compressor rotors. The latter determine the loads on the compressor bearings and affect vibration of the rotors and the compressor as a whole. Their effect plays the dominant role but not the only one. To create a mathematical model describing the vibration state of rotors, determining all additional forces acting on the compressor rotors that arise in the course of its operation under normal operating conditions is also required. These include the manufacturing inaccuracies causing skewing and bending of the rotor axles, as well as contact forces caused by the interaction of rotors due to their deviation from the nominal position. The latter are the least studied and, as a rule, are typical only for oil-flooded screw compressors with no rotor synchronisation mechanism. This article is devoted to the determination of rotor dynamics and the forces caused by rotor teeth engagement. In future, its results will serve as a basis for developing a rotor vibration state model. Meanwhile, the analysis of results obtained already at the current research stage allows to decrease their impact and effect.

An integrated mixed refrigeration cycle for pre-cooling of refrigeration below 25 K

Two trends can be found in current large-scale cryogenic projects. The first is the ever-increasing capacity requirements, while also a shift towards cooling demands at higher temperatures is observed. Conventional helium cycles require the use of oil flooded screw compressors, which are limited in efficiency, capacity, and reliability. Reverse-Brayton cycles with neon-helium mixtures deliver efficient refrigeration at a temperature above the dew point of neon, but cannot be applied to the cooling of conventional superconductors. This paper describes an approach where oxygen as a heavier gas allows the use of turbo-compressors viable. The oxygen is separated and used for providing refrigeration at higher temperature levels.

Experimental study of the processes of aerosol production for technical oil cleanup

From the experimental study of mechanism of fine mist formation in oil-flooded screw compressor it has been drawn the conclusion on evaporation of fine aerosol of mineral oil that has been obtained in two ways: on the basis of oil spray with mechanical burner and on the basis of volume condensation of oil vapour in air. The given paper presents experimental facility for the production of mineral oil aerosol and also comparison of the experimentation results with calculations.

Neon helium mixtures as a refrigerant for the FCC beam screen cooling: comparison of cycle design options

In the course of the studies for the next generation particle accelerators, in this case the Future Circular Collider for hadron-hadron interaction (FCC-hh), different aspects are being investigated. One of these is the heat load on the beam screen, which results mainly from the synchrotron radiation. In case of the FCC-hh, a heat load of 6 MW is expected. The heat has to be absorbed at 40 to 60 K due to vacuum restrictions. In this range, refrigeration is possible with both helium and neon. Our investigations are focused on a mixed refrigerant of these two components, which combines the advantages of both. Especially promising is the possible substitution of the oil flooded screw compressors by more efficient turbo compressors. This paper investigates different flow schemes and mixture compositions with respect to complexity and efficiency. Furthermore, thermodynamic aspects, e.g. whether to use cold or warm secondary cycle compressors are discussed. Additionally, parameters of the main compressor are established.

Economics of water injected air screw compressor systems

There is a growing need for compressed air free of entrained oil to be used in industry. In many cases it can be supplied by oil flooded screw compressors with multi stage filtration systems, or by oil free screw compressors. However, if water injected screw compressors can be made to operate reliably, they could be more efficient and therefore cheaper to operate. Unfortunately, to date, such machines have proved to be insufficiently reliable and not cost effective. This paper describes an investigation carried out to determine the current limitations of water injected screw compressor systems and how these could be overcome in the 15-315 kW power range and delivery pressures of 6-10 bar. Modern rotor profiles and approach to sealing and cooling allow reasonably inexpensive air end design. The prototype of the water injected screw compressor air system was built and tested for performance and reliability. The water injected compressor system was compared with the oil injected and oil free compressor systems of the equivalent size including the economic analysis based on the lifecycle costs. Based on the obtained results, it was concluded that water injected screw compressor systems could be designed to deliver clean air free of oil contamination with a better user value proposition than the oil injected or oil free screw compressor systems over the considered range of operations.

Modern oil-flooded screw compressors for new unconventional gas developments

Technical and commercial advantages of API-619 oil-flooded screw compressors (using fixed-speed electric motors) have made them the compressor of choice for unconventional gas gathering applications. The lubricant oil provides screw rotor separating, internal cooling, noise damping, corrosion protection and a considerably higher compression ratio capability. The minimum number of compressor trains in a single station is recommended. It is recommended to design nodal compressors with a low suction pressure capability in a way that compressors can facilitate gas collection even for a low well pressure. The compressor speed is an important parameter in compressor sizing, selection and optimisation. Critical areas for performance and reliability including component design/manufacturing, seals, pulsation, noise, and auxiliary systems are outlined. Best methods of capacity control and condition monitoring are also described. Case studies are presented.

The Twin Spool Efficiency Control

The development and implementation of the energy-saving technologies is one of the challenges facing the domestic industrial enterprises; when it comes to the compressor equipment, a large-scale implementation of the variable capacity screw compressors into the manufacturing processes has become the first proper step concerning the solution of energy-saving questions. Nowadays the spool efficiency controlled oil-flooded screw compressors are widely used for the fuel gas supply into the gas turbine unit (GTU). This paper presents the existing types of the spool configurations whereby the screw compressors control is realized as well as the new spool design construction that allows to implement the gas bypass from the higher pressure paired chamber to the low pressure one is offered. Gas is not bypassed into the suction chamber, that in turn saves the supplied power.

On heat transfer in screw compressors

Heat transfer between the working fluid and machine parts within a screw compressor does not affect its performance significantly because the thermal energy dissipation is usually less than 1% of the compressor power input. However, it can be detrimental to the machine reliability because the fluid compression creates a non-uniform three dimensional temperature field leading to local distortions, which may be larger than the clearances between the machine parts. This phenomenon is widely known and special control procedures are required to allow for start-up and shut down, as well as for steady running operation. These measures are usually derived only from test-bench data and may result in larger clearances than necessary, thereby reducing the optimum performance.This paper gives an outline of two methods of computing heat transfer in a screw compressor; namely: by means of a quasi-one dimensional differential model and by three dimensional computational fluid dynamics (CFD). Both methods enable the clearance size for start-up and steady running conditions to be determined. The 3D CFD procedure is more accurate but requires a far longer running time. Two cases are considered: heat transfer in a dry screw compressor where fluid temperatures are high, and an oil-flooded screw compressor where fluid temperatures are relatively low but the convective heat transfer coefficient is substantially higher.

The Study of Vibration Processes in Oil Flooded Screw Compressors

The Study of Vibration Processes in Oil Flooded Screw Compressors

Анализ целесообразности применения рекуперации тепла в компрессорных установках с маслозаполненными винтовыми компрессорами

Анализ целесообразности применения рекуперации тепла в компрессорных установках с маслозаполненными винтовыми компрессорами

Oil-flooded screw compressor for coal seam gas applications

The technical and cost advantages of oil-flooded screw compressors have made them the compressor of choice for coal seam gas field compression. The optimum arrangement for this compressor is presented. Lubricant oil provides rotor separating, internal cooling, noise damping, corrosion protection, and considerably higher compression ratio capability. The machine is simple, reliable, efficient, and compact. Critical areas for performance and reliability, including component design and manufacturing, journal and thrust bearing, seals, pulsation, noise, and auxiliary systems are outlined. The best methods of capacity control and condition monitoring are also described. A case study is presented.

Dynamic modeling of compressors illustrated by an oil-flooded twin helical screw compressor

Compressed air is a basic energy source in several industrial areas. The energy of pressurized air is used during manufacturing processes, commonly as driving force for actuating pneumatic cylinders and in power tools such as pneumatic screwdrivers. The widespread use of this energy source justifies efforts to reduce losses within the compressed air infrastructure. One of the main energy consumers in the network is the production of compressed air. Thus, one problem area is generation with compressors of different kinds and sizes. Another problem affects the transmission through piping networks with non-negligible leakage effects adding to energy losses within the pneumatic infrastructure. This paper focuses on the process of compressing air and describes a dynamic simulation model of an oil-flooded screw compressor. A single compressor block, part of an overall compressor station, is split into four subsystems which are presented as mathematical models. Simulation results are compared to physical measurements and studied with respect to energy losses. The presented model is detailed enough to account for dynamic effects in real machines. But it is also abstract enough to be integrated in further simulations with more components. Future work will be done on optimizing compressor station design with respect to the reduction of energy losses.

Opportunities for innovation with screw compressors

It is falsely considered, but widely accepted, that little can now be done to improve the screw compressor process and design. Screw compressors are indeed a mature product today and they form a highly competitive market, especially the oil-flooded air compressor. However, the simultaneous efforts of a large number of manufacturers have resulted in a compact and efficient oil-flooded screw compressor machine. Even small design details now tell the achievement of better compressor efficiency, and there is still some place left for implementation of new methods and procedures that will undoubtedly result in a better final product. New rotor generation procedures, rotor and compressor design optimization for a specified compressor duty and specialized compressor design are innovation elements that are continually improving and developing screw compressors and opening up hitherto unknown ways to produce compressors with better features. Also, the development of a combined compression and expansion machine is reported which could further increase the useful range of application of such machines, especially in refrigeration systems. A review of recent results of computational fluid dynamics (CFD) in screw machines is also given in the paper.

Analysis of the working process in an oil-flooded screw compressor by means of an indicator diagram

This paper presents the results of an experimental investigation of the thermodynamic processes in an oil-flooded screw compressor. The pressure within the working chamber is measured with a small pressure sensor, embedded in the female rotor on the discharge side. The results so obtained were transformed into an indicator diagram. Based on the indicator diagrams at various operating conditions, the working process is analysed. Owing to oil restricting back-flow of the gas through the discharge port, constant-volume compression is not evident even at substantial under-compression conditions, thus making the compressor maintain a high efficiency over a wide range of pressure ratios. However, the additional power consumption resulting from over-compression is comparatively large at pressure ratios lower than that for which the compressor was designed. So a compressor with fixed volume ratio should be designed with the built-in volume ratio low enough to avoid this effect. At the end of the discharge process, the pressure rises steeply due to increased resistance to oil flow, and therefore, the design of a flow-guiding slot to assist oil discharge is recommended. Higher rotating speeds increase the pressure slightly, but the losses associated with this are compensated by the increased volumetric efficiency. Thus a screw compressor maintains its isentropic efficiency over a wide range of speeds. Larger oil:gas ratio presents a higher pressure level in the indicator diagram, offsetting the improved sealing effect, and test results show that the appropriate oil:gas mass ratio range is between 8:1 and 20:1.

Impact Vibration Analysis of Screw Compressor Rotor System. 3rd Report. Analysis in consideration of Inertia of both rotors.

The oil flooded screw compressor rotates with contact between the corresponding male and female rotors. As gas pressure rises in the grooves of the rotor, a periodically fluctuating torque occurs. An impact vibration between the male and female rotors is induced by the torque. In this report, impact vibration analysis is carried out considering movement of both rotors. The stable region of the periodical impact vibration, which causes a noise of compressor, is calculated. Except this region, the impact damped vibration only occurs, where the compressor is driven quietly.