Study On Removing Flue Gas Entrained By Regenerated Catalyst

Study on Removing Flue Gas Entrainedby Regenerated CatalystAbstractCatalytic Pyrolysis Process is a novel method to produce ethylene and propylene. With higher catalyst/oil ratio, more flue gas is entrained into reactor by regenerated catalyst in the process, and interferes with the operation of compressing, separating and depurating for its gas products, even more could cause explode. So, developing a method and apparatus to reduce the carryover of flue gas is evidently necessary.The adsorption experiment and molecular simulation results show that the adsorbed amount of flue gas within the pores of the catalyst particles themselves is a little, more than 90% of entrained flue gas is contained in voids between catalyst particles. Degassing and steam stripping is a better solution to remove entrained flue gas. Unfortunately, steam is known to cause catalyst deactivation. Higher temperature and longer contact of catalyst with steam accelerate the deactivating effects of steam. In present efforts, the method of multi-stage, crossover-flow and short-contact stripping (short for MCSS) was developed to reduce hydrothermal degradation, which entrained flue gas is rapidly degassed and stripped in staged degassing tower with degassing tube and stripping baffles, so that steam and stripped flue gas have short contact with catalyst particles when flow upward through the catalyst bed.The cold model experimental results indicated that the MCSS degassing tower keeps the contact between catalyst and steam within two stages. Accordingto this data, the time of the deactivation caused by steam stripping would less than the lifetime of catalyst in commercial apparatus if the activity remains 73%, so the deactivation could be disregarded. Under the conditions of solid mass flux ranging from 10 to 50 kgm~s' and stripping gas velocity from 0.1 to 0.2m~s1, the stripping efficiency for three-stage proposed structure could reach 90%, while 50~60% for non-internals and 70-~S0% for ordinary baffles. Based on the behaviors of gas-solid flows in MCSS degassing tower, a calculating method was established for the bed voidage, the gas flow rate entering the degassing tube and the concentration profile of entrained gas.Taken into account of dense gas-solid flow in degassing tower, a computational fluid dynamics model based on a two-fluid model including the kinetic theory of granular flow was implemented in the commercial code CFX to describe solid viscosity and solid pressure caused by the collisions between the particles. The model was applied to study the behaviors of gas-solid flow in a two-dimensional MCSS degassing tower.On the basis of the experimental and simulating results, the design method of commercial MCSS degassing tower was established. The blue prints of MCSS degassing tower for two different commercial applications were put forward.