Key Technology Research On Rotor Stability And Axial Displacement Fault Prevention Of Centrifugal Compressor

Centrifugal compressor is the core equipment of industrial sectors such as metal smelting,pressure supply,gas transportation and separation.The rotor stability and axial displacement fault are related to the reliable operation of the whole unit and the economic benefits of the production.The journal bearing burning or wear is one of the most direct manifestations of rotor instability and axial displacement fault for the centrifugal compressor,and most of the high-end journal bearings are faced with severe conditions such as heavy load,high speed and extreme temperature.The surface contact,friction,wear and lubrication of the friction pair are complicated.Meanwhile,the dynamic problem of the integrally geared compressor with the advantages of high efficiency and compact structure has become increasingly prominent,which has restricted the development and progress of the domestic geared centrifugal compressor,and it is imminent to solve the design problem of high-speed and heavy-load bearing and to solve the dynamic problem of the bearing-rotor-gear coupling complex system.Study on rotor stability and axial displacement fault prevention of centrifugal compressor has a strong engineering background.This paper mainly focuses on the performance of journal bearing and rotor dynamic behavior involved in radial and axial vibration.Through the combination of theoretical analysis and experimental test,it aims to reveal the effect of key parameters such as static and dynamic characteristics of journal bearing on the unit operation and rotor vibration,to diagnose the corresponding rotor instability and axial displacement fault,and to provide theoretical basis and test verification for the prevention and control of rotor instability and axial displacement fault.The specific research contents are listed as below:First,in order to improve the prediction accuracy of heavy-load thrust bearing performance,a thermal-elasto-hydro-dynamic(TEHD)coupling theoretical model for calculating the dynamic lubrication performance of thrust bearing with considering the oil viscosity temperature effect,turbulence model and centrifugal inertia item,is established,and the simulation analysis program is written to obtain the flowrate,oil film thickness,pressure,temperature and pad temperature and deformation of thrust bearing under the coupling of multiple physical fields.It is found that the elastic deformation of thrust pad not only affects the temperature prediction,but also affects the calculation of Reynolds number.If the elastic deformation is not considered,the Reynolds number will be smaller so that the turbulence flow can not be predicted in time.Second,aiming at the problem of axial displacement fault prevention in centrifugal compressor,a method is proposed to identify the static and dynamic parameters of thrust bearing by using the hydraulic excitation system combined with instrumental variable filter(IVF)algorithm,and static and dynamic axial load are applied to thrust bearing by the electromagnetic proportional overflow valve in the electric oil pump system.The maximum static load is 20000N.The influence of rotation speed and axial load on the bearing temperature is tested,while the effect of axial excitation amplitude and excitation frequency on axial and radial vibration is studied.The coupling relationship between axial and radial vibration is revealed,and the axial displacement vibration mechanism caused by surge is also revealed.The results show that bearing pad temperature,axial stiffness and damping coefficient all increase with the static axial load.The increase of excitation amplitude will reduce the axial stiffness and damping coefficient,thus affect thrust bearing capacity.Meanwhile,a self-recovery control device for axial displacement fault of centrifugal compressor is invented,which can regulate the axial displacement intelligently,increase the thrust bearing capacity and reduce the pad temperature.Third,in order to test the high speed and heavy load journal bearing performance in the design stage,a test method of radial journal bearing performance based on the active electromagnetic actuator loading is developed.The electromagnetic actuator is used to simulate the change of radial bearing load caused by gear meshing in the gear coupling-bearing complex system for the first time,the maximum speed of the designed radial journal bearing performance test-rig is up to 12000 r/min,the whole bearing load applied by electromagnetic actuator is 20000N.By applying different bearing load amplitude and direction,the journal bearing performance under different bearing clearance is tested.The changes of pad temperature and power loss with the rotation speed and bearing load are mainly studied under the high-speed and heavy-load condition.The research shows that besides the rotation speed and bearing load amplitude,the bearing load angle also has significant influence on bearing pad temperature.Compared with the effect of rotation speed on power loss,the influence of bearing load on power loss is relatively small.Fourth,aiming at the rotor stability problem of integrally geared centrifugal compressor,the changes of stiffness and damping coefficient of radial journal bearing are analyzed under different load amplitude and load direction.On this basis,the finite element model of four parallel shafting bearing-rotor-gear coupling system is established to study the dynamic behavior and the unbalance response law of the complex system under different loads,as well as the influence of different bearing structure,bearing load and cross coupling stiffness on the rotor stability.It is pointed out that during the operation of integrally geared compressor,bearing is required to have wide and stable operation range,which ensures that the rotor system will not be unstable with different rotation speeds and bearing loads.Under the influence of the same cross coupling stiffness,the high speed rotor of the geared compressor is easier and faster to become instability than the low speed rotor and the middle speed rotor.Overall,key technology research on rotor stability and axial displacement fault prevention of centrifugal compressor is helpful to analyze the dynamic behavior of the gear shafting-bearing coupling complex system,especially the theoretical analysis and experimental test of static and dynamic bearing characteristics,which is very important to the design,manufacture and fault prevention of high-end bearing.It can overcome the key technical difficulties,improve the simulation precision of journal bearing,ensure the bearing machining quality,prevent the occurrence of rotor instability and bearing fault,and then avoid the abnormal rotor vibration and bearing failure.