Strength Failure Analysis And Improvement Research On Central Cylinder Of FCC In High Temperature

A three-spin central cylinder of a FCC is operated in temperature from 630℃to 680℃with ten large-opening nozzles connecting with five cyclone collectors and failure problems of leakage occur near the reinforcement circle for openings due to the crack, which seriously affects the continuous and stable operation of the FCC. It is very important to study the failure mechanism of the multi-opening reinforcement of cylinder shell because of the inadequacy of relevant existing standard. The following researches have been carried out:The complex FE model reflecting the actual mechanical conditions of the three-spin central cylinder of the FCC is established in ANSYS. The boundary conditions of thermal analysis are obtained by interpolating the measured temperature values and the steady temperature field is simulated using the 3-D isoparametric element SOLID90. The analysis of the heat-transfer character of the reinforcement circle under heat conduction and heat insulation is compared showing that the dead air gap between the circle and the shell is similar to the insulation blanket, which has impact on the local temperature distribution and thermal stress concentration.The thermal stress of failure cylinder shell is analyzed and compared under different working conditions. The multi-opening of cylinder shell is verified using the equal-area method of reinforcement and the limitation and unsafety of this method are pointed out. Then the relevant analysis is made in four different working conditions, that is, free sliding and constrained of the bottom board、previous cold drawing、improved cold drawing. The drawbacks of the previous design and maintenance problems are found. All of these provide reference for the improvement design.The improvement design of the three-spin cylinder shell is made using integral reinforcement due to the limitation of the reinforcement circle in high temperature. The cylinder shell is thickened and its FE model is established and evaluated. The bottom board in free sliding and constrained conditions is considered and the optimum cold drawing of the revised pipeline is obtained using free expansion. In addition, the analysis of the original model and the revised model have been made proving that the improvement of the cold drawing can reduce the thermal deformation and stress greatly. Finally, the improvement design scheme is determined based on this and site operation is carried out according to this.