Other Industrial Chemical Reactors

There are a host of other chemical reactors that are employed in industry that do not comfortably fit into the rather narrow window of three classes of reactors addressed in the previous section. Other reactors include (there are, of course, many more)  

A brief description of these units is presented below. Other chemical reactors not covered include  

Chemical reactions are often conducted at elevated temperatures in order to ensure high chemical reaction rates. To achieve this temperature, it is necessary to preheat the feed stream with auxiliary energy. This type of reactor is popularly referred to by some as an afterburner. Along with the feed stream, air and fuel may be continuously delivered to the reactor where the fuel is combusted with air in a firing unit (burner). 

This reactor will have an entire chapter devoted to it in Part IV. Catalytic reactors are occassionally an alternative to thermal reactors. If a solid catalyst is added to the reactor, the reaction is said to be heterogeneous. For simple reactions, the effect of the presence of a catalyst is to  

Permit the reaction to occur at a more favorable pressure. 

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At Sandia National Laboratories, experiments in an SCWO flow reactor provided data on a number of organics, including methanol, phenol, and other industrial chemicals, as well as military munitions (Rice, 1994). Commercial SCWO processes are designed to operate at temperatures typically less than 700°C. The development of SCWO technology depends on understanding the reaction kinetics of a wide variety of compounds at SCWO conditions. Predictive chemistry models, as they become available, will play an important role in finding answers to such design problems as ... 

Some real unit operations can find direct correspondence with the blocks used in flowsheeting, as flashes, distillation columns, heat exchangers, etc. However, the equivalence could be difficult for many others. This is typical the case of the industrial chemical reactors and a number of separators. In some cases, a simple model may be satisfactory for a quite complex unit from mechanical point of view. Consequently, the modelling of real units can follow one of the following possibilities ... 

The above brief discussion gives an elementary idea about the economic benefits of using rigorous high-fidelity, steady-state models in the design and operation of industrial catalytic reactors. The same principle applies to other industrial chemical and biochemical units also. 

Material and Energy Balances in the Design of Industrial Reactors. The analysis of chemical reactors in terms of material and energy balances differs from the analysis of other process equipment in that one must take into account the rate at which molecular species are converted from one chemical form to another and the rate at which energy is transformed by the process. When combined with material and... 

This chapter contains a discussion of two intermediate level problems in chemical reactor design that indicate how the principles developed in previous chapters are applied in making preliminary design calculations for industrial scale units. The problems considered are the thermal cracking of propane in a tubular reactor and the production of phthalic anhydride in a fixed bed catalytic reactor. Space limitations preclude detailed case studies of these problems. In such studies one would systematically vary all relevant process parameters to arrive at an optimum reactor design. However, sufficient detail is provided within the illustrative problems to indicate the basic principles involved and to make it easy to extend the analysis to studies of other process variables. The conditions employed in these problems are not necessarily those used in current industrial practice, since the data are based on literature values that date back some years. 

This first industrial device has been designed by MES company [65] for drying. It could be used for solid state reactions with powder reactants. Consequently, the reactor cannot be a classical chemical vessel or a classical chemical reactor with stirrer and others associated technical devices but a container able to enclose a reactant powder layer. The geometrical shape of the microwave applicator is parallelepiped box and the reactants are supported by a dielectric conveyor belt with edges as described by the Fig. 1.18. 

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. 

As many other industries, the fine chemical industry is characterized by strong pressures to decrease the time-to-market. New methods for the early screening of chemical reaction kinetics are needed (Heinzle and Hungerbiihler, 1997). Based on the data elaborated, the digital simulation of the chemical reactors is possible. The design of optimal feeding profiles to maximize predefined profit functions and the related assessment of critical reactor behavior is thus possible, as seen in the simulation examples RUN and SELCONT. 

There are many chemically reacting flow situations in which a reactive stream flows interior to a channel or duct. Two such examples are illustrated in Figs. 1.4 and 1.6, which consider flow in a catalytic-combustion monolith [28,156,168,259,322] and in the channels of a solid-oxide fuel cell. Other examples include the catalytic converters in automobiles. Certainly there are many industrial chemical processes that involve reactive flow tubular reactors. Innovative new short-contact-time processes use flow in catalytic monoliths to convert raw hydrocarbons to higher-value chemical feedstocks [37,99,100,173,184,436, 447]. Certain types of chemical-vapor-deposition reactors use a channel to direct flow over a wafer where a thin film is grown or deposited [219]. Flow reactors used in the laboratory to study gas-phase chemical kinetics usually strive to achieve plug-flow conditions and to minimize wall-chemistry effects. Nevertheless, boundary-layer simulations can be used to verify the flow condition or to account for non-ideal behavior [147]. 

The 7th international symposium on Chemical Reaction Engineering represents another milestone in the advancement of the art and science of the chemical reactor. Forty-six contributed papers are presented here nineteen from Western Europe, five from Asia and Australia, one from Canada, and twenty-one from the United States. The Symposium continues to be dominated by university professors—only six papers have one or more coauthors from industry. If chemical reaction engineering is to serve industry, strong messages from industry are needed in the future. A bridge cannot give good service if there is a massive pier on one shore and a flimsy one on the other. 

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