Industrial reactor

Be sure to view the actual photographs of industrial reactors on the DVD-ROM and on the Web site. There are also links to view reactors on different Web sites. The DVD-ROM also includes a portion of the Visual Encyclopedia of Equipment— Chemical Reactors developed by Dr. Susan Montgomery and her students at the University of Michigan. Also see Professional Reference Shelf on the DVD-ROM for Reactors for Liquid Phase and Gas Phase Reactions.  

In this chapter, and on the DVD-ROM, we ve introduced each of the major types of industrial reactors batch, stirred tank, tubular, and fixed bed (packed bed). Many variations and modifications of these commercial reactors (e.g., semibatch, fluidized bed) are in current use for further elaboratiem. refer to the detailed discussion of industrial reactors given by Walas.  

The DVD-ROM describes industrial reactors, along with typical feed and operating conditions. In addition, two solved example problems for Chapter I can be found on the DVD-ROM. 

Closure. The goal of this text is to weave the fundamentals of chemical reaction engineering into a structure or algorithm that is easy to use and apply to a variety of problems. We have just finished the first building block of this algorithm mole balances 

This algorithm and its corresponding building blocks will be develt ted and discussed in the following chapters  

In the remainder of this chapter we look at slightly more detailed drawings of some typical industrial reactors and point out a few of the advantages and disadvantages of each.- 

When is a batch Be sure 10 view actual photographs of industrial reactors on the CD-ROM and reactor used on [he Web site. There are also links to view reactors on different web sites. 

The CD-ROM also includes a ponion of the Vistuil Encyclopedia of Equip-we /—Chemical Reactors developed by Dr. Su.san Montgomery and her students at University of Michigan. 

Fijrure l-15fal Somibatch reactor. [Excerpted by special permission from Cliem. Eng.. 211 (Ocl. [95fil. 

TA ui 1-1 Representative Pfal dler CSTR/Batch Reactor 

The ammonia synthesis reaction is an exothermic reversible reaction that is carried out in a packed-bed of catalytic pellets. The removal of the heat generated by the reaction is the dominating factor in the design of the reactor. Since the 

The objective of this chapter was to describe the diversity and complexity of chemical reactor operations and to provide an overview of the phenomena encountered. 

The difficulty in obtaining a global reaction rate expression—an expression that accounts for both intrinsic kinetics and transport effects. 

The inherent difficulty in designing chemical reactors, which is due to two factors (i) Global reaction rates depend on the local flow conditions, which are not known a priori, and (ii) even when the global reaction rate expressions are known, solving the reactor design equations is a formidable task that rarely can be performed in the design exercise. 

Approximate engineering approaches are successfully employed (using ideal reactor models) to estimate the reactor operations and guesstimate the limits of its performance. 

---

Multiphase Reactors. The overwhelming majority of industrial reactors are multiphase reactors. Some important reactor configurations are illustrated in Figures 3 and 4. The names presented are often employed, but are not the only ones used. The presence of more than one phase, whether or not it is flowing, confounds analyses of reactors and increases the multiplicity of reactor configurations. Gases, Hquids, and soHds each flow in characteristic fashions, either dispersed in other phases or separately. Flow patterns in these reactors are complex and phases rarely exhibit idealized plug-flow or weU-stirred flow behavior. 

Bosch and co-workers devised laboratory reactors to operate at high pressure and temperature in a recycle mode. These test reactors had the essential characteristics of potential industrial reactors and were used by Mittasch and co-workers to screen some 20,000 samples as candidate catalysts. The results led to the identification of an iron-containing mineral that is similar to today s industrial catalysts. The researchers recognized the need for porous catalytic materials and materials with more than one component, today identified as the support, the catalyticaHy active component, and the promoter. Today s technology for catalyst testing has become more efficient because much of the test equipment is automated, and the analysis of products and catalysts is much faster and more accurate. 

Press, 1973. Lee, Y. Y. and G. T. Tsao, Engineering Problems of Immobilized Enzymes, ]. Food Technol, 39, 667 (1974). Messing, R. A., Immobilized Enzymes for Industrial Reactors, Academic Press, 1975. Torry, S., Enzyme Technology, Noyes DataCorp., Park Ridge, New Jersey, 1983. 

Data from die results of an industrial reactor study produced the result a — 0.606 + 0.012 ... 

Industrial reactors for iron ore reduction to solid iron... 

The simple form of time derivative of concentration was used in classical experiments in physical chemistry to express the rate of reaction. This must be changed to satisfy the condition in industrial reactors in which many other physical changes, such as flow and diffusion occur and for which conditions are frequently in a transient state. These forms are reviewed here. 

In previous studies, the main tool for process improvement was the tubular reactor. This small version of an industrial reactor tube had to be operated at less severe conditions than the industrial-size reactor. Even then, isothermal conditions could never be achieved and kinetic interpretation was ambiguous. Obviously, better tools and techniques were needed for every part of the project. In particular, a better experimental reactor had to be developed that could produce more precise results at well defined conditions. By that time many home-built recycle reactors (RRs), spinning basket reactors and other laboratory continuous stirred tank reactors (CSTRs) were in use and the subject of publications. Most of these served the original author and his reaction well but few could generate the mass velocities used in actual production units. 

Industrial reactors operate in the steady state with the volume, concentration, and temperature of the reaction mixture being constant... 

The success of designing industrial reactors greatly depends on accurate and reliable laboratory data. These data are derived from the... 

Most chemical reactions are greatly affected by temperature. The previous chapters discussed reactions at isothermal condition, however, industrial reactors often operate under non-isothermal condition. This is because chemical reactions strongly depend on temperature, either absorbing (i.e., endothermic) or generating (i.e., exothermic) a large amount of heat. 

Figure 12-6. Causes of runaways in industrial reactors. (Source Internal Ciba-Geigy Publication, 1984.)...

Mixing times in mechanically agitated vessels typically range from a few seconds in laboratory glassware to a few minutes in large industrial reactors. The classic correlation by Norwood and Metzner for turbine impellers in baffled vessels can be used for order of magnitude estimates of... 

Many industrial reactors operate in the fed-batch mode. It is also called the semibatch mode. In this mode of operation, reactants are charged to the system at various times, and products are removed at various times. Occasionally, a heel of material from a previous batch is retained to start the new batch. 

Since the power of transmitted light drops off as the square of the distance from the light, for efficient reaction and energy usage the reactants must be as close as possible to the light source. This has practical implications for the design of industrial reactors. 

Increased computational resources allow the widespread application of fundamental kinetic models. Relumped single-event microkinetics constitute a subtle methodology matching present day s analytical techniques with the computational resources. The singleevent kinetic parameters are feedstock invariant. Current efforts are aimed at mapping catal) t properties such as acidity and shape selectivity. The use of fundamental kinetic models increases the reliability of extrapolations from laboratory or pilot plant data to industrial reactor simulation. 

C04-0074. Ammonia is produced industrially using the Haber process N2 + 3 H2 2 NH3 Suppose that an industrial reactor is charged with 75.0 kg each of N2 and H2. Use a table of amounts to determine what mass of ammonia could be produced if the reaction went to completion. 

As an indispensable source of fertilizer, the Haber process is one of the most important reactions in industrial chemistry. Nevertheless, even under optimal conditions the yield of the ammonia synthesis in industrial reactors is only about 13%. This Is because the Haber process does not go to completion the net rate of producing ammonia reaches zero when substantial amounts of N2 and H2 are still present. At balance, the concentrations no longer change even though some of each starting material is still present. This balance point represents dynamic chemical equilibrium. 

A change in the amount of any substance that appears in the reaction quotient displaces the system from its equilibrium position. As an example, consider an industrial reactor containing a mixture of methane, hydrogen, steam, and carbon monoxide at equilibrium ... 

Figure 1.8. Relevant length scales in catalysis range from the subnanometre domain of the atomic and molecular level to the macroscopic domain of an industrial reactor.

The next level is that of shaped catalysts, in the form of extrudates, spheres, or monoliths on length scales varying from millimeters to centimeters, and occasionally even larger. Such matters are to a large extent the province of materials science. Typical issues of interest are porosity, strength, and attrition resistance such that catalysts are able to survive the conditions inside industrial reactors. This area of catalysis is mainly (though not exclusively) dealt with by industry, in particular by catalyst manufacturers. Consequently, much of the knowledge is covered by patents. 

Hence one could say that kinetics in the 20 century widened its scope from a purely empirical description of reaction rates to a discipline which encompasses the description of reactions on all scales of relevance from interactions between molecules at the level of electrons and atoms in chemical bonds, to reactions of large quantities of matter in industrial reactors. 

Arguing from an industrial point of view, Worz et al. list three basic tasks which an industrial reactor has to fulfil [110-112]. 

Table 1.7 Numerical example illustrating the increased heat transfer on miniaturization of industrial reactors [110].

Industrial reactors work below or above the explosion regime, hence operahon cannot be carried out at any ethylene-to-oxygen raho (see original citations in [43]). 

---