Reactors selection and design

A number of industrial reactors involve contact between a fluid (either a gas or a liquid) and solids. In these reactors, the fluid phase contacts the solid catalyst which may be either stationary (in a fixed bed) or in motion (particles in a fluidized bed, moving bed, or a slurry). The solids may be a catalyst or a reactant (product). Catalyst and reactor selection and design largely depend upon issues related to heat transfer, pressure drop and contacting of the phases. In many cases, continuous regeneration or periodic replacement of deteriorated or deactivated catalyst may be needed. 

The case studies presented in this chapter illustrate reactor design procedures for a carefully selected set of reacting systems wherein the physical dimensions of the reactor (diameter, height) and fixed and operating parameters (catalyst loading, superficial velocity, impeller speed, and other) were calculated. As a postscript to these studies, we would like to consolidate and emphasize certain fundamental and practical considerations in reactor selection and design. 

Rational reactor selection and design requires information on thermodynamics, chemical kinetics, heat and mass transport, and reactor hydrodynamics. In practice, a quantitative analysis is based on reactor models and engineering correlations. In this chapter we limit ourselves to a qualitative discussion, emphasizing principles rather than quantitative calculations. 

Many successful types of reactors are illustrated throughout this section. Additional sketches may be found in other books on this topic, particularly in Walas Chemical Process Equipment Selection and Design, Butterworths, 1990) and Ullmann Encyclopedia of Chemical Technology (in German), vol. 3, Verlag Chemie, 1973, pp. 321-518). 

It is more difficult to develop general guidelines regarding the selection and design of a reactor for a series-parallel reaction network than for a parallel-reaction or a series-reaction network separately. It is still necessary to take into account the relative... 

Dr. Walas has several decades of varied experience in industry and academia and is an active industrial consultant for the process design of chemical reactors and chemical and petroleum plants. He has written four related books on reaction kinetics, phase equilibria, process equipment selection and design, and mathematical modeling of chemical engineering processes, as well as the sections Reaction Kinetics and Chemical Reactors in the seventh edition of Chemical Engineers Handbook. He is a Fellow of the AlChE and a registered professional engineer. 

G. J. Eye, J. M. Woodley, (Advances in the selection and design of two liquid phase biocatalytic reactors), in Multiphase Bioreactor Design, J. M. S. Cabral, M. Mota, J. Tramper (eds.), Taylor Francis, Fondon, pp. 115-134, 2001. 

Figure S.4. Residence time distributions of pilot and commercial catalyst packed reactors CWalas, Chemical Process EQuipment Selection and Design, 19903.

Walas, S. M. Chemical Process Equipment Selection and Design. Chapter 17—Chemical Reactors (Butterworths, 1988). 

Figure 8-38. Residence time distributions of some commercial and fixed bed reactors. The variance, equivalent number of CSTR stages, and Peclet number are given for each reactor. (Source Walas, S. M., Chemical Process Equipment—Selection and Design, Butterworths, 1990.)...

Figure 8. Designs of ammonia synthesis converters (a) Principle of the autothermal ammonia synthesis reactor (b) Radial flow converter with capacities of 1,800 tpd (c) Horizontal three-bed converter and detail of the catalyst cartridge. (Source Walas, M. S., Chemical Process Equipment, Selection and Design, Butterworth Series in Chemical Engineering, 1988.)...

In industrial practice, the laboratory equipment used in chemical synthesis can influence reaction selection. As issues relating to kinetics, mass transfer, heat transfer, and thermodynamics are addressed, reactor design evolves to commercially viable equipment. Often, more than one type of reactor may be suitable for a given reaction. For example, in the partial oxidation of butane to maleic anhydride over a vanadium pyrophosphate catalyst, heat-transfer considerations dictate reactor selection and choices may include fluidized beds or multitubular reactors. Both types of reactors have been commercialized. Often, experience with a particular type of reactor within the organization can play an important part in selection. 

Design Alternative with Partial Conversion of Phenol In this section we demonstrate the advantage of performing reactor analysis and design in a recycle structure. As explained in Chapter 2, in contrast with a standalone viewpoint this approach allows the designer to examine systemic issues, the most important being the flexibility with respect to production rate and target selectivity, before... 

The selection and design of a reactor for bench-scale kinetic experiments should be considered case by case. It is important to stress, however, that one should not try to build a bench-scale replica of what is believed to be or is the industrial reactor. Industrial reactors are designed to operate a process in a profitable way, which is not the case for experimental reactors. In industrial reactors heat, mass and momentum transport has to occur in an economically justifiable way, leading in general to temperature, concentration and/or pressure gradients inside the reactor. Also, the hydrodynamics can be rather complicated. Fluidized beds, bubble columns and trickle-flow reactors require model equations that involve several physical parameters, besides the intrinsic kinetic parameters. Empirical... 

Inherently, the selection and design of a chemical reactor are made iteratively because, in many instances, the global reaction rates are not known a priori. In... 

At the end of each case study, general remarks are given that bring out the lessons learned. Furthermore, at the end of the case studies we give our recommendations (morphology) for the selection and design of reactors. 

Insoluble brown reaction products (presumably phenolic tars) were deposited on the surfaces of the reactor vessel and lamp well. This expected phenomenon plus the high solvent absorbence demanded a careful reactor selection and photolysis system design. 

Optimal reactor operation and design are two methods to maximize sulfur removal. In addition, considerable research effort is focused on finding new. cata,lysts to improve activity, selectivity and durability. 

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