Gas-Solid Hydrodynamics Of A Novel Flexi-Coking Reactor

The efficient processing and conversion of heavy oil is a key issue in the world’s refining industry,and the main solutions are divided into two routes:decarbonization and hydrogenation.The coking process,as an important component of decarbonization schemes,has advantages of low plant investment and is less influenced by the quality of the feedstock.The flexi-coking process,as an important coking technology,has a wide range of feedstock adaptability,is environmentally friendly,and has good prospects for development globally.Flow problem in the jet-influenced zone of flexi-coking reactor threaten to the operation,which can lead to fouling,agglomeration and loss of bed fluidity in the unit.In order to cope with the flow problem in the jet-influenced zone,a new baffled coker with inclined downward jets is proposed from the perspective of regulating the meso-scale flow structure（jets,bubbles and particle agglomerates）in the fluidized bed.In order to investigate the effect of the novel coker on the flow problem in the jet-influenced zone,the interaction of the jet,bubbles and particle agglomerates are investigated in a two-dimensional（2D）and a three-dimensional（3D）experimental apparatus.Firstly,this paper investigates the characteristics of inclined jets in the 2D fluidized bed with FCC catalyst 1,FCC catalyst 2 and quartz sand using high-speed camera technology.An image recognition method based on the adaptive algorithm for image segmentation was established to achieve the extraction of jet characteristics from all images of the sampled video.By analyzing the width(b_max),expansion angle（θ）and penetration depth（L）of the inclined jets with five angles（α=0°,±30°and±60°）,the effect of the incident angles and the properties of the bed materials are investigated and a penetration model of the inclined jet is established.The results show that the L,b_max andθof the jet gradually increase as the angle of incident increases from-60°to 60°.This paper then analyses the interaction of inclined jets（α=0°,60°and-60°）with tracer bubbles at l/L=0.15,0.5 and 0.85 positions in the 2D fluidized bed using image processing.The results show that when the jet is introduced,it has an effect on the bubble diameter,velocity and trajectory.As the jet velocity increases,there is a tendency for the bubble diameter to decrease.As the jet velocity increases,the velocity of the tracer bubble at l/L=0.15 increases and then decreases,while the velocity of the tracer bubble at l/L=0.5and 0.85 decreases.The trajectory of the bubbles is related to the location of the jet and the bubble coalescence.The coalescence locations where the inclined jet and bubbles are:A)the nozzle exit;B)the end of the jet cavity;and C)above the jet cavity where the initial bubbles are about to break away.Based on the experimental results,it is found that the tracer bubbles were attracted to the nozzle side,whereα=-60°has the strongest ability of entrain bubbles.The effect of bubbles on the jet characteristics is predicated on the coalescence of the two.In this paper,the minimum distance between the bubble and the jet at the critical condition is used as a criterion for coalescence to occur,and it is found that the jet and the bubble are most likely to merge atα=-60°.Using the depth of jet penetration and the initial bubble equivalent diameter generated as indicators,the characteristics of the jet were examined.It was found that the changes in the jet characteristics were mainly dependent on where the bubble and jet coalescence occurred.The penetration of jets increased significantly only when the coalescence occurred during the expansion phase of the jet cavity.The larger the diameter of the tracer bubble,the larger the equivalent diameter of the initial bubble.The initial bubble equivalent diameter obtained at the end of the jet and after the tracer bubbles have merged is greater than the merging at the remaining locations.Next,the effect of jet incident angles（α=0°,60°and-60°）on the characteristics of bubbles and particle agglomerates in the 2D fluidized bed with FCC catalyst 1 and FCC catalyst 2 using optical fiber probe.The h/H=0.6 cross section is found to be the most significant affected.When the inclined jets are introduced,the average solid holdup and residence time of the bubbles decrease and the frequency,velocity and chord length of bubbles increase on the side of the bed close to the jet（l/L=0.1,0.3 and 0.5）;the bubble characteristics on the side of the bed far from the jet（l/L=0.7 and 0.9）showed the opposite pattern.The higher the jet velocity,the lower the frequency,residence time and chord length of the particle agglomerates and the higher the agglomeration velocity in the jet influence zone,while the characteristics of particle agglomerates on the bed away from the jet show the opposite pattern.From the perspective of the coker,the initial bubbles formed by the inclined jet have stronger shearing effect on the particle agglomerates,and accelerates the renewal frequency of the bubbles,which is beneficial for reducing the survival rate of particle agglomerates and alleviating coke particle agglomeration.Next,this paper investigates the hydrodynamic of the fluidized bed with double layerα=-60°jets using optical fiber probe techniques when FCC catalyst1 and FCC catalyst 2as bed material.The hydrodynamic characteristics of bubbles and particle agglomerates were obtained by decoupling the pulsation signals of solid holdup in the fluidized bed using the statistical moment consistency principle.The hydrodynamic characteristics of the bubbles were analyzed,revealing an increase in initial bubble size,a decrease in solid holdup of bubble,and an increase in frequency,chord length,and rise velocity of bubble as the jet velocity increased.The analysis of the hydrodynamic characteristics of particle agglomerates indicates that the higher the jet velocity,the higher the velocity of the particle agglomerates.Furthermore,this relationship results in a reduced frequency,chord length,and residence time of the particle agglomerates,aiding in alleviating flow problems in the jet-influenced zone.Finally,this paper presents an exploratory experiment on the hydrodynamic characteristics of the baffled fluidized bed with inclined jets using fiber probe techniques.The study uses FCC catalyst 1 as the bed material.The hydrodynamic characteristics of bubbles were analyzed,and the results showed that the installation of the double layer baffles decreased the bubble chord length and rise velocity while increasing the bubble residence time when the jet velocity was 0 m/s.As the jet velocity increases,the bubble chord length and velocity in the bed increase and the average residence time decreases.The analysis of hydrodynamic characteristics shows that,after setting the double baffle,the frequency,chord length and residence time of particle agglomerates were further reduced,and the renewal frequency was accelerated.Thus,the baffled fluidized bed with inclined jets is highly beneficial for alleviating agglomeration problems in the fluid coker.