Numerical Simulation Of Wall Temperature Change For Coke Drum In Unsteady-State Process

The axial symmetry unsteady-state temperature field model was established for special working condition of coke drum which boundary is located in inner steel wall and outer insulating layer, the upside and underside section. Based on the basic heat transfer theory, the governing differential equation was derived from the law of conservation of energy and the Fourier thermal conductivity theory. The discrete equation for different nodes was rigorously derived from Finite Volume Method. Finally, the numerical solution of wall temperature was obtained in vapour and oil gas preheating.The vapour driving air process in coke drum was simulated with ANSYS-CFX11.0. Besides, the total time that vapour driving remaining air in coke drum was examined and the velocity and vapour concentration distribution in different section at different times was investigated. It was found that the wall temperature had no influence on the time that vapour driving air. The time needed for the 6m diameter coke drum was 18min, as well as 15min was needed for the 9.4m diameter coke drum. The operating time needed in the field was 10~20min. In order to ensure remaining air was completely replaced with vapour, 20min was the best operating time.The integrative specific heat capacity and the heat transfer coefficient of oil gas were regressed according with the actual wall temperature. Besides, the software of simulation of wall temperature change for coke drum in unsteady-state process was developed with Visual Basic 6.0 and Finite Volume Method. During temperature-rise period, the numerical solut??of wall temperature for coke drum was obtained at different heights for different times. The wall temperature results provided basis data for structure and stress analysis of coke drum. It was showed that the heat transfer condition between the vapour and the inner steel wall and the thermal insulating layer were the main reason that affected the radial temperature, as well as the preheating time was the main reason that affected the axial temperature. The radial temperature difference in vapour preheating was less than 3℃, as well as that was less than 20℃in oil gas preheating, and the radial temperature drop was centered on the 0~50mm in thermal insulating layer. The distribution of the axial temperature in vapour preheating was consistent with that in oil gas preheating. Meanwhile, the wall temperature decreased as its height increasing, and the axial temperature difference between the underside section and the underneath thermocouple was the largest.