Investigating the effect of the impeller blade gradient angle on the compressor reliability

Studies show that operating stress and natural frequency of the turbocharger impeller are two key parameters that affect the service life of the turbocharger. In this regard, NREC and ANSYS software are utilized in the present study to design impellers and calculate the impeller stress, natural frequency, and the inertia moment of the impeller for each baseline impeller and their modifications. Furthermore, modal tests are carried out to verify the simulation results. Finally, the compressor characteristic maps before and after the blade gradient angle optimization are compared. Obtained results show that compared with the cantilever length, the blade thickness has a remarkable influence on the blade gradient angle. Moreover, it is found that the correlation between the blade gradient angle and the first-order frequency multiplication ratio is linear. As the blade gradient angle increases, the maximum stress at the blade root of the compressor initially decreases and then increases. The value of the blade gradient angle varies within the range of 2.288°–3.955°. Moreover, the closer the gradient angle to 3.26°, the smaller the maximum equivalent stress of the impeller, and the higher the impeller strength. The greater the thickness of the blade, the longer the cantilever length of the impeller, and the greater the inertia moment. Optimizing the blade gradient angle can improve the efficiency of the compressor without changing the pressure ratio and flow rate. It should be indicated that error between the results from the simulation and the experiment is within the range 1.736%–1.254%. Therefore, the calculation results are reliable. It is concluded that the regular pattern of the blade gradient angle affects the compressor impeller stress and its natural frequency. The present article is expected to provide a helpful theoretical basis for designing an optimized compressor impeller.

STUDY OF DESIGN FEATURES AND MAIN CAUSES OF VALVE FAILURES IN RECIPROCATING COMPRESSORS

At present, the compressor industry of the oil sector of Azerbaijan is one of its leading links. If by the end of the 20th century the number of wells using the gas-lift method of production was about 42-46%, then by the end of 2019 it exceeded the 50% level. Compressors are an integral part of this technological process and require a strict improvement in the technical level of their safe operation. Therefore, improving the technical and economic performance of the compressor unit is an important task. This work is devoted to the study of design features and the main causes of valve failures in reciprocating compressors, as well as an assessment of their safe operation. Keywords: reciprocating compressor, reliability, valve, safety, gas-lift extraction method.

Performance of a Two-Phase Injection Heat Pump with the Variation of Injection Quality and Pressure

Heat pumps are becoming more commonly and widely used due to their advantages in efficiency and versatile applications in both cooling and heating. However, the reliability of its compressor is being compromised due to high discharge temperatures caused by harsh operating conditions. Among the numerous studies conducted in improving the discharge temperature and performance of the heat pump, two-phase injection is receiving great interest. In this study, the performance of the two-phase injection heat pump was measured with a variation of operating parameters. The experiment results were used to study the performance change according to the operating parameter such as injection quality and pressure. It was found that the performance of the heat pump using the two-phase injection was better in terms of COP by up to 5.8% compared to that using the vapor injection. Furthermore, the two-phase injection was effective in reducing the discharge temperature to improve the compressor reliability. Two types of optimum injection qualities were suggested through this study: discharge temperature optimum injection quality (TIQ), and performance optimum injection quality (PIQ). It was found that in most conditions PIQ was sufficient in satisfying the compressor reliability, but in harsh operating conditions, where the compression ratio was high, TIQ was required in order to maintain the compressor reliability.

Numerical Simulation and Experimental Study on Temperature Distribution of Self-Lubricating Packing Rings in Reciprocating Compressors

The nonuniform abrasion failure and high-temperature thermal failure of packing rings have a significant influence on compressor reliability, particularly that of oil-free compressors. In this study, a test rig was constructed to measure the dynamic temperature of packing rings under different operational conditions in an oil-free reciprocating compressor. The dynamic axial and radial temperature distributions of the packing rings were obtained using an innovative internal temperature testing device that kept the thermocouples and packing box relatively static during compressor operation. A three-dimensional heat transfer model was also developed to analyze the temperature distribution of the packing boxes, piston rod, and cylinder during such operation. Good agreement was observed between the simulation results and experimental data, which showed an average relative error of less than 2.35%. The results indicate that the pressure ratio exerts a significant effect on the axial temperature distribution and determines which packing ring reaches the maximum temperature. They also show the average temperature to rise with an increase in the rotational speed and to fall with an improvement in the external cooling conditions. Finally, the material of the packing rings was found to affect the temperature gradient from their inner to outer surface.

Development of Gas Compressor Diagnostic Program Using Knowledge Based Management Concept

Gas compressor reliability is vital in oil and gas industry because of the equipment criticality which requires continuously operations. Currently, plant operators often face difficulties in predicting appropriate time for maintenance and would usually rely on time-based predictive maintenance intervals as recommended by Original Equipment Manufacturer. Delayed decision on compressor maintenance intervention has caused prolonged downtime due to poor readiness of spare parts and resources. The paper discussed on development of a software-based tool which is able to assist machinery engineers to quantify performance deterioration of gas compressor and predict optimum time for maintenance activities. Maintenance history data is collected and analysed regularly and maintenance advices are subsequently produced based on the input parameters. Natural gas compressors of an oil producing offshore platform at Peninsular Malaysia are used as a case study of this project. It was found that isentropic efficiency and head decrease, but gas power increases parabolically with time for the low pressure compressors, suspected due to heavy component fouling. From these information, Compressor Performance Monitoring Program is developed which able to compute the fouling level of the compressor in terms of performance indicators deviations. The results are then being utilized to estimate future maintenance requirements based on historical data. In general, this software provides a powerful tool for gas compressor operators to realize predictive maintenance approach in their operations.

Identification and Quantification of Start Up Process in Oil Flooded Screw Compressors

Oil injected screw compressors, used for air compression, refrigeration and air conditioning, are usually installed in simple packages which often do not include an oil pump to supply oil to the bearings and the working chamber, since the oil is pressurised, together with the gas being compressed, in the working chamber. Consequently, normal lubrication will only start when the back pressure reaches the chamber pressure,. Due to the lack of lubrication in this start up period, the rotors will be in direct contact with insufficient or no oil film between them, while the pressure in the compression chamber will increase causing the temperature to rise. The period of un-lubricated operation then depends on the size of the oil system and the length of the discharge piping. Also, during this time, due to the lack of oil in the working chamber, the leakage flow will be higher than normal. This will increase the overall temperature in the compression chamber. It is expected that some surface damage may occur on the rotors. When the compressor operates intermittently, with frequent starts and –stops, mode, this may result in rapid wear and decrease in the compressor performance. This paper addresses such issues through experimental investigation and simulation and defines the scope of work required to understand the oil flooded compressor process in transient operation mode. This will allow prediction of wear in such compressors and give some insight to the modifications required to increase the compressor reliability.