Graduate Thesis Or Dissertation
 

Fluidized bed granulator for an autocausticization recovery process of sodium in black liquor : experiment and theory

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/kw52jb45b

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  • Production of dry particles made of titanium dioxide powder and black liquor is the first step in a newly proposed black liquor treatment process (Frederick et. al., 1992). This work investigates the granulation processes in a fluidized bed granulator of titanium dioxide and black liquor. Experiments are performed in a batch-solid operated fluidized bed granulator with batch-fed addition of black liquor. Two separate sub processes are identified in the granulation process: agglomeration of particles and attrition of formed agglomerates. Two independent transients determine the dynamics of the agglomeration process: time and liquid load. The agglomeration process is kept in the nucleation regime. The agglomeration of particles is here caused by liquid droplets being loaded with dry particles as they enter the bed. The agglomeration process is very fast due to the vigorous motion of particles in a fluidized bed. One can assume that the time transient behavior of the agglomeration process is completed shortly after the droplet enters the bed. This enables modeling of the agglomeration as a liquid transient process alone. The time scale for the attrition process is determined by the drying operation of the agglomerates. This is a slow process compared to the formation of agglomerates, and the attrition is modeled as a time transient process. The difference in the time scales of the two processes enables us to observe the effect of the attrition process independently, and thus model the two processes separately. Each of the two sub processes is modeled as first order processes. The obtained rate constants are valid only within the range of experimental conditions used in this study. However, the work contains several examples, that show the method of combining the results of the model of the two sub processes and their conversion/extension to different experimental conditions (different bed loads and liquid flow rates), and different process configurations (continuous feed of solids, selective removal of solids etc.). Three new dimensionless criteria, that describe the mass and energy relations in a fluidized bed granulator, are introduced. Each of these criteria must be satisfied to obtain stable operation of the fluidized bed granulator.
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