Catalytic reactions are carried out in reactors with a fixed, fluidized, or moving bed of catalyst. Although the chemical kinetics of the reaction obviously remains the same for all these reactors, the hydrodynamic features vary considerably. Because no complete description of these features is possible, it is convenient to postulate different situations and develop mathematical models to represent these situations for each type of reactor. It is also important to note that wherever solid catalysts are used, the question of catalyst deactivation cannot be ignored. Several books and reviews covering a variety of situations have been written, including those marked with an asterisk in the list of references. They are recommended for general reading. Our intention in this chapter is limited, however: formulate approaches to the design of two main classes of catalytic reactors, fixed and fluidized bed; briefly describe selected procedures along with a few numerical (or methodological) examples to illustrate their use; and outline a procedure for incorporating the effects of catalyst deactivation in reactor design and operation. There are basically two types of fixed-bed reactors: (1) multitubular, in which tubes of approximately 1.5 to 4.0 cm in diameter are placed as a bundle within a shell through which a heat exchange fluid is circulated to control the temperature profile within the reactor; and (2) adiabatic, in which the catalyst is placed directly inside a reactor (with no a priori limitation to the diameter), and heat removal is accomplished by multistaging the bed and removing the heat of reaction by heat exchange between stages. Four major models have been proposed for describing the behavior of a packed tubular reactor (see Doraiswamy and Sharma, 1984). Of these, the most extensively used is the quasi-continuum model in which the fluid-solid system is assumed to act as a single pseudohomogeneous phase with effective properties of its own (as for any true single phase). Thus the procedures developed in Chapters 4 and 10 for the homogeneous model can be used to determine the axial profiles of concentration and temperature. One can also allow for radial transport gradients within each tube [two-dimensional (2-D) models], as opposed to the simpler models in which these gradients are neglected—the one-dimensional (1-D) models.
Influence of Fin Length on Magneto-Combined Convection Heat Transfer Performance in a Lid-Driven Wavy Cavity