Analysis Of Factors On Fluidization And Separation For FCCU Catalyst Loss

The catalyst loss occurred in FCC unit is the excessive discharge of catalyst,which is one of the main factors affecting the long-term operation of FCC unit.There are many factors cause catalyst loss,which are related to process operation,equipment performance and properties of catalyst.Catalyst loss usually comes from the abnormal fluidization operation and the abnormal catalyst separation from flue gas or oil gas.Therefore,this work analyzes the mechanism of catalyst loss during start-up stage and fault stage based on the data of loss particle spectrum from the fluidized bed experiment and cyclone separator experiment.Firstly,the faults of catalyst loss in the industrial catalytic cracking unit were systematically summarized,and the characteristics of catalyst loss caused by various factors were analyzed,focusing on the performance of fluidized bed and the cyclone separator.The relationship between these factors and the catalyst loss type including the catalyst physical properties and flow parameters was also discussed.Then,experiments of the catalyst loss during start-up stage were carried out on a two-dimensional fluidized bed and a (?)300mm cyclone separator.The experimental results showed that:(1)during the continuous operation of the fluidized bed,the particles in the dilute phase space gradually coarsened with the loss of fine particles,and the particle diameter size decreased with the increase of height in axial direction.Both the median particle diameter size and kurtosis of dilute phase particle size distribution were gradually increasing,while the change of particle size distribution tended to be stable after a period of operation time.Therefore,a time-varying model of particle size distribution in dilute phase space in the start-up and running stage was established.(2)The physical properties of separated particles and the effects of inlet concentration and inlet velocity on the separation efficiency were investigated on the cyclone separator device.The cycle test of cyclone separator showed that the variation of separation efficiency with time at different inlet velocity were similar.When the cycle test reached a certain time,the separation efficiency tends to a stable value,indicating that the particle loss tends to be stable.Therefore,the separation efficiency model on catalyst loss in the start-up stage was also established.At last,three kinds of experiments,including bias fluidized velocity on twodimensional fluidized bed,low inlet velocity and air leakage on (?)300mm cyclone separator,were carried out.The experimental results showed that:(1)when the bias fluidized flow occurred in the fluidized bed,t catalyst particles with size less than 40μm were increased significantly on the height above TDH compared with the cases of normal working conditions.(2)The separation efficiency of cyclone separator decreased with the increase of the air leakage rate.When the air leakage rate exceeded a certain value,the separation efficiency decreased sharply.(3)When the inlet velocity of the cyclone separator was relatively low,the separation efficiency decreased largely and the particle loss increased.This work was focused on the analysis of the catalyst loss factors of catalytic cracking unit based on the experimental analysis and theoretical modeling.The relationship between catalyst loss and fluidization parameters,separation parameters and the change of catalyst particle size distribution were studied.The results are helpful to accurately locate and diagnose the catalyst loss fault of FCC unit,and provide support for fault treatment and elimination,as well as corresponding preventive measures.