Modeling of fixed-bed reactors

In this chapter it is not possible to concentrate on specific cases and processes. Instead, we discuss general models and principles involved in the design and analysis of any type of fixed bed reactor, no matter what the process. 

The development in recent years of chemical reaction engineering as a recognized discipline and the increasing possibilities of computers have led to extensive exploration of reactor design and performance, both in the steady and nonsteady state. Models now range from the very simple ones that could be handled before 1960, to some very sophisticated ones presented in the last two or three years. 

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This equation may be used as an appropriate form of the law of energy conservation in various pseudo homogeneous models of fixed bed reactors. Radial transport by effective thermal conduction is an essential element of two-dimensional reactor models but, for one-dimensional models, the last term must be replaced by one involving heat losses to the walls. 

Pseudo homogeneous models of fixed bed reactors are widely employed in reactor design calculations. Such models assume that the fluid within the volume element associated with a single catalyst pellet or group of pellets can be characterized by a given bulk temperature, pressure, and composition and that these quantities vary continuously with position in the reactor. In most industrial scale equipment, the reactor volume is so large compared to the volume of an individual pellet and the fraction of the void volume associated therewith that the assumption of continuity is reasonable. 

The One-Dimensional Pseudo Homogeneous Model of Fixed Bed Reactors. The design of tubular fixed bed catalytic reactors has generally been based on a one-dimensional model that assumes that species concentrations and fluid temperature vary only in the axial direction. Heat transfer between the reacting fluid and the reactor walls is considered by presuming that all of the resistance is contained within a very thin boundary layer next to the wall and by using a heat transfer coefficient based on the temperature difference between the fluid and the wall. Per unit area of the tube... 

For more details see Shah (Gas-Liquid-Solid Reactor Design, McGraw-Hill, 1979) and Hofmann [Hydrodynamics and Hydrodynamic Models of Fixed Bed Reactors, in Gianetto and Silveston (eds.), Multiphase Chemical Reactors, Hemisphere 1986]. 

One- and two-dimensional models of fixed-bed reactors are compared for a numerical case in G. F. Froment, Current Design Status, Fixed-bed Catalytic Reactors, Ind. Eng. Chem., 59, 18 (1967). 

Pseudo homogeneous models of fixed bed reactors are widely employed in reactor design calculations. Such... 

The One Dimensional Pseudo Homogeneous Model of Fixed Bed Reactors... 

Schuurman, Y. (2008), Aspects of kinetic modeling of fixed bed reactors, Catalysis Today, 138(1-2) 15-20. 

Advanced learners should then also study the more complex aspects of reactor design and modeling (dispersion model, Section 4.10.6) and the modeling of fixed bed reactors (Section 4.10.7). Novel developments in catalytic reactor technology are discussed in Section 4.10.8. 

Aspects to be dealt with in the modeling of fixed bed reactors. 

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