Multiscale Study of Reactive Dense Fluidized Bed for FCC Regenerator

Abstract

Re´sume´-É tude multi-e´chelle d'un lit fluidise´dense re´actif de type re´ge´ne´rateur FCC -Ce travail porte sur les e´coulements re´actifs gaz-particules tels que ceux que l'on rencontre dans la combustion du coke pour la re´ge´ne´ration des particules de catalyseurs de FCC. Les e´tudes re´alise´es pour de tels e´coulements montrent qu'en ge´ne´ral le taux de re´action global au cours du temps est mal pre´dit. La raison peut eˆtre lie´e a`la cine´tique chimique utilise´e qui est en ge´ne´ral base´e sur des expe´riences macroscopiques. Le lien entre des releve´s macroscopiques et une cine´tique chimique de re´action he´te´roge`ne locale qui a lieu a`l'interface meˆme entre la surface de la particule et le gaz environnant n'est pas imme´diat. Nous avons utilise´des re´sultats cine´tiques issus d'expe´riences afin d'identifier les proble`mes qui apparaissent lorsque l'on utilise cette meˆme cine´tique pour des e´chelles diffe´rentes. Une analyse multi-e´chelle est donc effectue´e. Nous montrons alors que la fraction volumique de particules a une influence sur le taux de re´action. Par ailleurs, nous montrons la ne´cessite´de de´velopper un mode`le de sous-maille pour le taux de re´action lie´a`la pre´sence de clustering dans les e´coulements gazparticules. Dans les calculs effectue´s couramment, le taux de re´action est calcule´en conside´rant une re´partition homoge`ne des particules a`l'inte´rieur de la maille de calcul. En effet l'analyse microscopique montre que lorsque les particules sont regroupe´es en nuages denses, la fraction massique de dioxyge`ne a`l'inte´rieur de ce nuage est rapidement nulle et donc le dioxyge`ne est en de´faut. La re´action he´te´roge`ne est donc limite´e.Abstract -Multiscale Study of Reactive Dense Fluidized Bed for FCC Regenerator -This study deals with reactive gas particle flows like the coke combustion during the regeneration of FCC particles. In this kind of reactive flow, the global reaction rate is usually bad predicted. In a first approximation, the chemical scheme can be the reason because of the limitation of its modeling. It is usually based on macroscopic experimental results. The link between these macroscopic measurements and a local kinetics of the heterogeneous reaction occuring at the gas-particle interface is not confirmed. Results of kinetics coming from experimental measurements are used and we try to highlight the problems that appear when the same kinetics are used at different scales. In common industrial computations, coarse meshes are used to solve continuity equations. Averaged or filtered Navier-Stokes and species continuity equations have to be solved in which additional correlation terms appear because of non-linear terms in the original equations, including reaction rate correlation. Therefore a multiscale analysis is performed in order to improve the modeling of this terms. This paper, shows that the eulerian formulation of kinetics has to be improved due to the impact Oil & Gas Science and Technology -Rev. IFP Energies nouvelles, Vol. 68 (2013), No. ...

CFD Applied to Process Development in the Oil and Gas Industry – A Review

“…However, and as can be seen in Figure 15b, CFD offers the opportunity to study some 3D effects which can be important, for example, for predicting local hot spots whose occurrences depend on some injection configurations that can be optimised. Note that, even if CFD simulations are mostly focused on risers, some deal with regenerators with a focus on coke combustion modeling (Moula et al, 2013). Such developments are important since the regenerator is of high capital cost and its optimisation could be addressed by CFD simulations in terms of catalyst and air injection systems and associated mixing.…”