TOWARD A GENERAL DESCRIPTION OF GAS-SOLID REACTIONS IN A FLUIDIZED BED REACTOR
Abstract
Fluidized bed reactors have become attractive process alternatives for carrying out solid-gas reactions. Predicting the performance of a noncatalytic reactor often requires accounting for the changing characteristics of the solid reactant as reaction progresses. Past modelling efforts have been restricted to monosized feeds and been computationally cumbersome. The method described in Part I permits the description of a reacting particle according to any of several limiting case models. The solution of the balance equations by orthogonal collocation allows both monodispersed and polydispersed feed distributions to be treated with equal ease. Extensions to a wider range of applications including several options for particle attrition are also discussed. Part II presents a series of examples that demonstrate the flexibility of the model discussed in Part I. A fluidized bed combustor model is compared with experimental results of Babcock and Wilcox. The behavior near the distributor is a key to the composition profiles. The combustion (fixed carbon) efficiency was found to be most strongly related to single particle elutriation and reaction rates--effects well represented by the more detailed description of solid behavior. Parametric studies for a steam fed gasifier reveal that here too grid effects may overshadow bubble behavior. A model of a steam fed gasifier with external char recycle showed that a significant reduction in conversion resulted from heating the recirculating char. Finally, an examination of a steam-oxygen-char gasifer indicated that the behavior of the ash, whether or not it attrites, may be as important a factor as the manner in which the particle reacts.
Degree
Ph.D.
Subject Area
Chemical engineering|Energy
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