REACTORS FOR FLUID-SOLID NONCATALYTIC REACTIONS

In this chapter, we develop matters relating to the process design or analysis of reactors for fluid-solid noncatalytic reactions that is, for reactions in which the solid is a reactant. To construct reactor models, we make use of  

We restrict attention to relatively simple models involving solid particles in fixed-bed or ideal-flow situations. More-complex flow situations are considered in Chapter 23, for both catalytic and noncatalytic reactions. 

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Chapter 22 Reactors for Fluid-Solid (Noncatalytic) Reactions... 

One of the most common catalytic reactors is the fixed-bed type, in which the reaction mixture flows continuously through a tube filled with a stationary bed of catalyst pellets. Because of its importance, and because considerable information is available on its performance, most attention will be given to this reactor type. Fluidized-bed and slurry reactors are also considered later in the chapter. Some of the design methods given are applicable also to fluid-solid noncatalytic reactions. The global rate and integrated conversion-time relationships for noncatalytic gas-solid reactions will be considered in Chap. 14. 

Laboratory reactors for fluid-solid and fluid-fluid reactions were described in Sections 3.1.6 and 3.3.2, respectively. The discussion in these sections is also useful for gas-liquid-solid reactions. A combination of the Carberry reactor (Eigure 11.7) and a stirred cell (Figure 11.14A) is useful for noncatalytic and catalytic reactions. Some discussion of these issues is presented in Case Studies CS8 and CSll as well as by Joshi et al. (1985) and Joglekar et al. (1991). 

This chapter is devoted to fixed-bed catalytic reactors (FBCR), and is the first of four chapters on reactors for multiphase reactions. The importance of catalytic reactors in general stems from the fact that, in the chemical industry, catalysis is the rule rather than the exception. Subsequent chapters deal with reactors for noncatalytic fluid-solid reactions, fluidized- and other moving-particle reactors (both catalytic and noncatalytic), and reactors for fluid-fluid reactions. 

A chemical reactor is a vessel in which reactants are converted to products through chemical reactions. This vessel takes many shapes and sizes depending upon the nature of the chemical reaction. The choice of a suitable laboratory reactor depends upon the nature of the reaction system (fluid-solid catalytic, fluid-solid noncatalytic, fluid-fluid, etc.), the nature of the required kinetic or thermodynamic data, or the feasibility of operation. The important parameters for a successful reactor design are the following ... 

Our objective here is to study quantitatively how these external physical processes affect the rate. Such processes are designated as external to signify that they are completely separated from, and in series with, the chemical reaction on the catalyst surface. For porous catalysts both reaction and heat and mass transfer occur at the same internal location within the catalyst pellet. The quantitative analysis in this case requires simultaneous treatment of the physical and chemical steps. The effect of these internal physical processes will be considered in Chap, 11. It should be noted that such internal effects significantly affect the global rate only for comparatively large catalyst pellets. Hence they may be important only for fixed-bed catalytic reactors or gas-solid noncatalytic reactors (see Chap. 14), where large solid particles are employed. In contrast, external physical processes may be important for all types of fluid-solid heterogeneous reactions. In this chapter we shall consider first the gas-solid fixed-bed reactor, then the fluidized-bed case, and finally the slurry reactor. 

A glib generalization is that the design equations for noncatalytic fluid-solid reactors can be obtained by combining the intrinsic kinetics with the appropriate transport equations. The experienced reader knows that this is not always possible even for the solid-catalyzed reactions considered in Chapter 10 and is much more difficult when the solid participates in the reaction. The solid surface is undergoing change. See Table 11.6. Measurements usually require transient experiments. As a practical matter, the measurements will normally include mass transfer effects and are often made in pilot-scale equipment intended to simulate a full-scale reactor. Consider a gas-solid reaction of the general form... 

Flow of Two Fluids. The major applications are in absorption, extraction, and distillation, with and without reaction. Other applications, also quite important, are for shell-and-tube or double-pipe heat exchangers, and noncatalytic fluid-solid reactors (blast furnace and ore-reduction processes). 

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