Modeling of Carbochlorination of Zircon in Fluidized Bed Reactor
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THE fluidized bed reactor has received considerable attention for its zirconium tetrachloride production—an intermediate in zirconium metal production, which is produced by zircon carbochlorination according to the following reaction: ZrSiO4 ðs) þ 4C(s) þ 4Cl2 ðg) ! ZrCl4 ðg) þ SiCl4 ðg) þ 4CO(g)
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The fluidized bed technique has many inherent advantages that include temperature uniformity, favorable heat transfer, ease of solid handling, low pressure drop, and operational flexibility. Modeling the fluidized bed is necessary for design and scale. Among the models employed, the hydrodynamic flow models are the most satisfactory for describing the performance of a bubbling fluidized bed.[1] This model describes and characterizes the parameters that influence the hydrodynamics of fluidized beds. Hydrodynamic models are divided into three categories (i.e., single-, two-, and three-phase models). Many of these models are based on the two-phase concept of fluidization. In this model category, the fluidized bed is divided into two sections—bubble phase (rich in gas) and emulsion phase (rich in solids). Based on this model, the Davidson– Harrison model,[2] Partridge–Row model,[3] Kunii– Levenspiel model,[4] Kato–Wen bubble assemblage model,[5] Chiba–Kobayashi bubble flow model,[6] and shell model[7] have all been developed in accordance with different bubble dynamics.
Some investigations report on the chlorination of zirconium-bearing materials.[8–11] Several mathematical models have been developed to simulate the fluid dynamics and reaction phenomena in the fluid bed. Few et al.[12] introduced the bubble assemblage model to interpret the selective chlorination of oxidized Ilmenite ore in the batch-type fluidized bed. Rhee and Sohn[13] developed a more detailed model that incorporated the solid mixing. Youn and Park[14] developed a model to simulate the chlorination of rutile with coke in a fluidized bed. The main objective of this work was to develop a hydrodynamic two-phase model to simulate the fluidized bed reactor applied in zircon carbochlorination reaction. Furthermore, the validated model was used to investigate the important operating parameters that affect the reactor performance. Therefore, it is possible, through the application of the obtained model, to pinpoint the appropriate conditions for reactor operation without any additional time-consuming and expensive experiments. In this model, a particle size reaction rate expression, which takes into account the solid particle size distribution, was incorporated to calculate the concentration profile of chlorine in the bed. The particle size distribution in bed was determined by a population balance. The model assumed that solid particles were mixed well (continuous stirred tank reactor, CSTR) throughout the bed, but gas concentrations varied with the bed height (plug).
II. M.H. JAZINI, PhD Student, S.M. GHOREISHI, Associate Professor, and A.A. DADKHAH, Assistant Professor, are with the Department of Chemical Engineering, Isfahan University of Technology, Isfahan 84156
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