Heat transfer between FCC catalyst and an electrically heated horizontal cylinder in a circulating fluidized bed

Abstract

The heat transfer coefficient between a suspension of FCC particles and a horizontal cylindrical heat transfer probe inserted into the riser or the standpipe of a CFB has been quantified. With the heat transfer probe located in the riser 4.75 meters above the L-valve, and solids mass flux varied between 0 to 100 kg/(m2.s), the heat transfer coefficient ranged from 70 W/(m2.K) to 475 W/(m2.K). On a plot of heat transfer coefficient versus solids mass flux, three zones have been identified, which correspond to the difference in the flow structure of the solids around the heat transfer probe as the solids mass flux increases. Also, measurements were taken of the radial solids flux in two orthogonal directions using an isokinetic sampling system. The data shows the asymmetry due to the perturbations introduced by the heat transfer probe. Finally, the heat transfer in the downcomer was investigated. It has been found that the magnitude of the heat transfer coefficient in the downcomer is dominated by the solids flux; variation in gas bypassing in the standpipe has little effect. Results obtained by traversing the heat transfer probe across the diameter of the standpipe suggest that the heat transfer coefficient is nearly independent of radial position within the standpipe.On a quantifie le coefficient de transfert de matiere entre une suspension de particules de FCC et une sonde de transfert de chaleur cylindrique horizontale inseree dans la colonne montante d'un CFB. Avec une sonde de transfert de chaleur situee dans la colonne montante a 4,75 metres au dessus de la vanne en L et un flux massique de solides variant entre 0 et 100 kg/(m2.s), le coefficient de transfert de chaleur varie de 70 W/(m2.K) et 475 W/(m2.K). Sur un graphique du coefficient de transfert de chaleur par rapport au flux massique de solides, trois zones ont ete identifiees, qui correspondent a la difference dans la structure d'koulement des solides autour de la sonde de transfert de chaleur lorsque le flux massique de solides augmente. En outre, des mesures du flux radial de solides ont et6 prises dans deux directions orthogonales a I'aide d'un systbme d'echantillonnage isocinetique. Les donnees montrent I'asymetrie due aux perturbations introduites par la sonde de transfert de chaleur. Enfin, on a etudie le transfert de chaleur dans le dkversoir. On a trouve que la grandeur du coefficient de transfert de chaleur dans le deversoir etait domine par le flux de solides; la variation de la deviation du gaz dans la colonne montante a peu d'effet. Les resultats obtenus en faisant passer la sonde de transfert de chaleur a travers le diametre de la colonne montante suggerent que le coefficient de transfert de chaleur est presque independant de la position radiale a l'interieur de la colonne montante. circulating fluidized bed (CFB) is a type of gassolid A contactor in which the solids are transported upward by a high velocity gas stream. The first, and still main application of circulating fluidized bed technology, is the cracking of petroleum products in...