Research On The Effect Of Centrifugal Compression Performance By The Inlet Parameters Of Mixed-refrigerant

The mixed-refrigerant centrifugal compressor is the core motive equipment in the LNG plant and it is also the main equipment in the large-scale cryogenic mixed-refrigerant refrigeration system.However,it is difficult to determine the physical properties of the mixed-refrigerant during the compression because it involves multi-stage centrifugal impeller with high pressure ratio mixed-refrigerant in the centrifugal compressor.In addition,the designment of multi-stage centrifugal compressor is complex,so the mixed-refrigerant centrifugal compressor has not achieved localization manufacture for a long time.In order to reveal the change law of various physical parameters and the mechanism of multi-stage centrifugal compression for the different mixed-refrigerant ratio in the LNG liquefaction system,firstly,the six-stage centrifugal impeller are designed based on the multi-component mixed-refrigerant of N₂,CH₄,C₂H₄,C₃H₈,C₄H₁₀ and i-C₄H₁₀ in the centrifugal compressor.The paper focuses on the compression mechanism of mixed-refrigerant in the multi-stage centrifugal compression,the change law of mixed-refrigerant parameters,and the optimal structure of the centrifugal impeller.The parameters of model such as meridional flow passage is corrected.The distribution and variation of mixed-refrigerant parameters in multi-stage and high pressure ratio compression are researched.And the effects of mixed-refrigerant on the centrifugal compression performance parameters are also studied under different working conditions.The impeller loss model is established based on the actual flow in the centrifugal compression after determining the structural parameters and aerodynamic parameters of the compressor.Computer Integration are used to build mathematical loss model by MATLAB.Completing the performance prediction program under different working conditions and predicting changes of compressor performance such as pressure-ratio and polytropic efficiency caused by changing the inlet parameters of mixed-refrigerant.The reliability and accuracy of the performance prediction program for centrifugal impeller are verified.Then,the three-dimensional model of centrifugal compressor impeller is established and imported to ANSYS-CFX.The internal flow field of centrifugal impeller is numerically simulated based on SST turbulence model,analyzing the change trend of flow field of centrifugal impeller under different working conditions.Finally,by comparing the numerical simulation results with the programming calculation results,the accuracy of impeller loss model under different working conditions is verified,the design method of mixed-refrigerant centrifugal impeller is optimized,and the change law of mixed-refrigerant during compression is obtained.Also,the mixed-refrigerant ratio and inlet temperature and pressure are analyzed as a single variable in the two softwares,and the variation trend of centrifugal compressor performance parameters are obtained and researched by two methods.The optimal design method for the centrifugal impeller of mixed-refrigerant is given.The results show that by comparing methods of numerical simulation and programming calculation,the change law of performance parameters such as polytropic efficiency and the physical properties of mixed-refrigerant during compression under different mixed-refrigerant ratios and different inlet parameters can be obtained.The internal relationship between the physical parameters of the multi-component refrigerant and the structural parameters of the centrifugal impeller can be revealed.It can provide theoretical reference for the performance research of multi-stage centrifugal compression and optimization designment of centrifugal compressor.