Research And Analysis Of The Reverse Rotation Dynamics Characteristics Of Centrifugal Compression System

With the development of design and manufacturing technology, under the requirements of energy saving and emission reduction, the centrifugal compressor with large scale and high pressure ratio is developing. Meanwhile, new operating problems will appear in the product, which are related with system control, rotor dynamics, flow component matching, control of start-up and shutdown. In large flow system with multi flow pipeline, large container and large system inertia, it is hardly to regulate the flow parameters in short time.Owing to the technology requirements, a large amount of process gas is stored in the flow system during the production process. Centrifugal compressor unit will shut down with the loss of driving force once power failure occurs in the operation process. The pressure of process gas in outlet section is far greater than the pressure of process gas in outlet section at this moment, high pressure process gas may go from the outlet section to the inlet section through the inside of the centrifugal compressor at this moment, reverse flow may emerge in the system. Reverse rotation torque generated by the reverse flow may cause the rapidly decreasing of rotation speed of centrifugal compressor, more seriously, reverse rotation of rotor may appear when the reverse rotation torque overcome the inertia moment of rotor and resistance pneumatic moment. Serious damage of inter-stage seals and bearings are caused by the reverse rotation of rotor which will seriously affect the normal production order in enterprises. Thus it is necessary to study on the reverse rotation of centrifugal compressor unit, so as to put forward relevant measurements to restrain reverse rotation.According to the actual reverse rotation accident happened in enterprises, in this paper, centrifugal compression system is simplified, flow compression system of centrifugal fan with single impeller. The system is consist of pipeline, inlet and outlet valve, outlet gas tank. Real time multi-channel data acquisition was established based on LABVIEW, pneumatic parameters and rotation speed variation of the centrifugal fan system were obtained. The influence of pneumatic and friction resistance on rotation speed in idling process of centrifugal rotor was studied, the theoretical model of rotating speed was determined with pneumatic moment and friction torque of the rotor, the accuracy of theoretical model was verified by the comparison between the testing data and the calculated data. The structure of centrifugal impeller was simplified step by step to determine the expression of moment of inertia, the influence of regulating of reverse-flow valve on the reverse flow characteristics was analyzed. Torque and power endured by the rotor under forward rotation and reverse rotation in the same rotation speed variation range were compared to verify the destruction of centrifugal rotor which may be caused by reverse rotation.The flow parameters in each stage of a set of cracked gas centrifugal compressor of ethylene plant in a petrochemical enterprise was analyzed based on the results of theory analysis and experiment in centrifugal fan with single rotor. Combined with flow compression system model, the theoretical model of rotating speed driven by reverse flow was set up with moment inertia of multi stage centrifugal impeller, initial rotation speed, opening of anti-reverse valve. The model can be applied in the reverse rotation dynamics analysis of actual multi stage centrifugal compressor, so that we can obtain relevant parameters to restrain reverse rotation.The models derived in the paper were verified by the experiment results and the operation data. They can be used to get the strategy for the large centrifugal compressors to avoid anti-reverse rotation.