Study On Supercritical Carbon Dioxide Centrifugal Compressor

The supercritical carbon dioxide Brayton cycle power generation system itself has the characteristics of small equipment size,compact structure,and strong environmental adaptability.Compared with the commonly used steam Rankine cycle,it has the advantage of high power generation efficiency in the medium and high temperature zone.Compressors are the "heart" equipment of various power cycles.Supercritical carbon dioxide compressors are also the key to improving cycle efficiency and operational stability in supercritical carbon dioxide(CO2)Brayton cycle power generation systems.At the same time,due to the particularity of the working medium,The design and operation of supercritical carbon dioxide compressors are significantly different from traditional compressors,and in-depth research is needed.At this stage,the supercritical carbon dioxide Brayton power generation cycle technology is mainly MWe level,and it is more suitable to use supercritical carbon dioxide centrifugal compressors.At present,most domestic and foreign researches on supercritical carbon dioxide centrifugal compressors focus on numerical simulation,and systematic and in-depth research has not been carried out yet.Based on the numerical simulation analysis and taking the impeller of Sandia main compressor as an example,this paper explores the influence of different grid division,physical property table division and turbulence model on the numerical simulation calculation,verifies with the experimental results,and obtains the numerical simulation calculation method suitable for supercritical CO2 centrifugal compressor;on this basis,the supercritical CO2 centrifugal compression is carried out.The internal flow of the compressor was studied in detail.Details of secondary flow in supercritical CO2 compressor were analyzed.Severe meridian reverse secondary flow was found in the tip clearance.The influence of leading edge condensation,surface roughness,tip clearance and diffuser type on the flow field was analyzed in detail.Further,based on the one-dimensional design theory of traditional compressor and the results of numerical simulation of flow field,the one-dimensional design theory for supercritical CO2 centrifugal compressor was explored,the influence of tangential secondary flow of tip clearance on slip factor was corrected,and the performance loss prediction model was put forward from the aspects of blade leading edge impact,surface roughness,secondary flow of tip clearance,etc.Accurate labyrinth seal calculation theory is required for accurate calculation of secondary flow at the top of blade and design calculation of seal at each position of compressor.Sealing characteristics of supercritical CO2 working fluid,especially two-phase critical flow,are quite different from ideal gas working fluid.In this paper,a one-dimensional iteration calculation method of labyrinth seal based on physical property model of actual gas is introduced and a suitable one-dimensional iteration method for supercritical gas is given.Experimental correlations of the two key coefficients(flow coefficient and energy residue coefficient)calculated for CO2 labyrinth seals.In order to test and verify the design theory of supercritical CO2 centrifugal compressor,an experimental prototype of single-stage supercritical CO2 centrifugal compressor is designed based on MW supercritical CO2 Brayton power generation cycle,with emphasis on the optimization of compressor impeller pneumatic design.In order to solve the problem of high-pressure supercritical CO2 seal,a supercritical CO2 stepped staggered labyrinth seal is put forward and carried out.Structural design;Supercritical CO2 single-stage centrifugal compressor is confronted with serious axial force balance problem.Back vane structure is adopted and the starting working rule of single-stage compressor is optimized to control the axial force within a reasonable range.The first MW supercritical CO2 compressor experimental platform in China was built,the key parameters of supercritical CO2 compressor were measured,tested and calculated,and the self-covered single-stage supercritical CO2 centrifugal compressor was tested.The experimental results of single-stage supercritical CO2 centrifugal compressor with different inlet conditionss were summarized and analyzed,and the experimental data were compared with the theoretical model.The key correction factors in the one-dimensional calculation model are verified.In addition,the stepped staggered labyrinth seal proposed in this paper is tested experimentally and verified by comparison with the one-dimensional calculation results.Finally,based on the design and experimental experience of single-stage supercritical CO2 centrifugal compressor,two-stage back-to-back arrangement is attempted to solve the axial force balance problem,and the pneumatic design characteristics of two-stage supercritical CO2 centrifugal compressor are analyzed.In view of the shortcomings of the experimental measurement of single-stage supercritical CO2 centrifugal compressor,the experimental measurement scheme was optimized.