Systematic Comparison Of Hydrodynamics And Stripping Efficiency In Catalyst Strippers With Different Internals

An fluidized catalytic cracking?FCC?unit is one of the most important secondary crude oil processing unit in a petroleum refinery.The catalyst stripper is an indispensable device in an FCC unit,whose main purpose is to use water vapor to replace the oil gases entrained in the catalyst particles and adsorbed in their pores.Efficient stripping can not only improve the yields of gasoline,diesel oil and other light products,but also reduce the burning load of the regenerator.In addition,in recent years with a number of new fluidized bed chemical reaction process developed,the stripper is essential equipment.Such as methanol to olefins?MTO?technology,which is the process of converting coal through the intermediate product methanol to ethylene and propylene.Stripper separates N₂,CO₂,CO and other non-condensable gas from the regeneration catalyst.In catalytic cracking?CPP?technology,the strippers also play a role in separating non-hydrocarbon gases.On the other hand,the previous scholars on the stripper research often lack of systematic comparison of flow hydrodynamics and stripping effect of different structure strippers under different conditions.Moreover,the previous studies are based on the gas-solid flow hydrodynamics in the stripper is circumferentially symmetrical,and this article through a certain preliminary investigation finds that the stripper in the gas-solid distribution there is a certain degree of circumferential heterogeneity,which may occur?gas streaming?phenomenon.In this paper,the gas-solid flow hydrodynamics and stripping efficiency of the strippers are studied by means of differential pressure gauges,optical fiber probes and gas tracing on a large-scale cold-mold device.Empty cylinder type,disc-donut baffle,perforated disc-donut baffle and a Crosser grid stripper developed by China University of Petroleum?Beijing?were studied.In the experiment,the flow hydrodynamics of different types of stripper were compared with the optical fiber probe from the circumferential direction,radial direction and axial direction respectively and the gas stripping efficiency was compared by using the gas tracer method.So we can get the reason of the different stripping efficiency of the different structures by analyzing the circumferential and radial uniformity of the gas-solid distribution in the bed.It is found that there is a phenomenon of back-mixing and the stripping efficiency is low at the same time in the empty cylinder type stripper.The circulation cross section of the disc-donut baffle is the smallest,and there is"air cushion",reducing the gas-solid two-phase effective contact space and residence time.Perforated disc-donut baffle can effectively increase the stripping time of the particles so that stripping efficiency has been significantly improved,but there is always more serious non-uniform radial,circumferential distribution.Crosser grid stripper achieves uniform distribution of the bubble in radial and circumference direction in the entire circulation space;and has the highest stripping efficiency.In this paper,we also study the phenomenon of?flooding?in the disc-donut stripper.When the phenomenon of?flooding?occurs,the fluctuation of the pressure signal periodically occurs with the occurrence of the"bridge"phenomenon.The experiment also found that in the catalyst mass flow rate range of this paper,Crosser grille-type stripper has no?flooding?phenomenon,indicating that it has a better operational flexibility.