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UBC Theses and Dissertations

CFD modeling of wet agglomerate growth in gas-fluidized beds Maturi, Anish


Oil and gas companies which often face excessive agglomeration when operating Fluidized Bed Reactors (FBRs). In Syncrude Canada’s fluid cokers, agglomeration is highly undesirable because it reduces the product yield and causes significant problems including partial defluidization. In Syncrude Canada’s process, the non-volatiles in bitumen are deposited on the particles and contribute towards agglomeration. There is significant practical knowledge and methods regarding agglomeration. A mathematical model of the agglomeration could contribute significantly to a better understanding and limit the agglomeration problem. This thesis presents a mathematical model of fluidized beds with liquid injection, with emphasis on the agglomeration process. Agglomeration takes place via particle coalescence in the presence of a liquid in industrial FBRs. Industrial FBRs are maintained well above the liquid boiling point, and there is significant vaporization. Therefore, the model should account for vaporization. Hence, this work presents a vaporization model followed by an agglomeration model. The model is based on the Kinetic theory of Granular Flows (KTGF) and uses the Population Balance Method (PBM) to solve momentum, heat, and mass transport equations. The simulations were performed using ANSYS Fluent, supplemented by User Defined Functions coded in C Language. Vaporization was modeled, and the influence of temperature and droplet size investigated. The results confirm that boiling is more important than evaporation. Parametric studies on the droplet diameter concluded that, in the absence of agglomeration, vaporization does not vary much with changes in the droplet diameter. They also predicted that agglomeration has a significant impact on the extent of vaporization. The rate of agglomeration calculated by this model was very high, high enough to cause defluidization of the bed. The over-estimation of agglomeration is due to the neglect of agglomerate breakage that is accounted for in this thesis by imposing an artificial limit on the agglomerate diameter. The limit was chosen because less than 1% (wt%) was above 4000 microns.

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