Numerical Simulation Of Gas Distributor Used In FCC Regenerator

The gas distributor with dendritic tube structure is the most widely used in the catalytic cracking regenerator at present,but it has some problems such as uneven gas distribution,wear and bias flow,which directly reduces the fluidization quality and regeneration efficiency of the catalyst.Therefore,the research on the flow field in the internal space and external bed space of the gas distributor has important reference for the structural optimization and performance of the gas distributor.The study was conduct by simulating the gas phase flow field in the full-scale gas distributor by the standard K-ε turbulence model under the condition of normal operation and fault operation.Then,the structural changes of the gas distributor and its internal flow field under fault conditions such as wear and perforation are investigated;Finally,the Euler Euler two fluid model is used to simulate the gas-solid two-phase flow field in the outer bed of the branch pipe area,and the causes of nozzle and branch pipe wall wear are analyzed from the perspective of flow field.The main conclusions of this study are as follows:(1)The velocity distribution along the branch pipe and branch pipe in the dendritic gas distributor shows a downward trend as a whole,and the outlet velocity of the nozzle along the branch pipe shows an increasing trend as a whole;The static pressure distribution on the branch pipe is "Hump type",and the static pressure distribution along the branch pipe is related to the length of the branch pipe;The flow in the branch pipe meets the variable mass flow,in which the flow in the long branch pipe belongs to the friction resistance control type and the flow in the short branch pipe belongs to the momentum exchange type.(2)When the tube hole area ratio of the branch pipe is 1.5～3,the gas distributor has better distribution effect.At this time,the average outlet velocity set of the nozzle is closer to the design outlet velocity of the nozzle;In a certain range,the non-uniformity of gas distribution can be reduced by changing the diameter of branch pipe and nozzle inlet;For the long branch pipe,when the nozzle interpolation depth is large,the gas flow in the branch pipe has the characteristics of variable mass flow controlled by friction resistance.When the nozzle interpolation depth is small,the gas flow in the branch pipe has the characteristics of variable mass flow controlled by momentum recovery.(3)When the gas distributor works under low load,the average outlet velocity of the nozzle of each branch pipe is lower than the design outlet velocity;When the branch pipe is worn or broken,the velocity along the corresponding branch pipe will increase and the static pressure along the branch pipe will decrease;When the nozzle is blocked,the outlet velocity of other nozzles will increase,while when the nozzle falls off,the outlet velocity of other nozzles will decrease.Among them,the influence of nozzle falling off on the outlet velocity distribution of nozzle along the branch pipe is more obvious.(4)Euler Euler two fluid model and syamlal-o’brien drag model can effectively predict the flow field characteristics of two-dimensional gas-solid two phases in the regeneration bed;The incidence angle and velocity of the nozzle have obvious effects on the gas-solid two-phase flow field near the branch pipe;The main reasons for the wear of the branch pipe and nozzle include: the high-speed air flow from the nozzle drives the particles to cut the outer pipe wall;The wear of the inner tube wall caused by the catalyst particles entering the distributor by back suction.