Choice of reactor types

Figure 2.3 Choice of reactor type for mixed parallel and series reactions when the parallel reaction has a higher order than the primary reaction.

In the preceding section, the choice of reactor type was made on the basis of which gave the most appropriate concentration profile as the reaction progressed in order to minimize volume for single reactions or maximize selectivity for multiple reactions for a given conversion. However, after making the decision to choose one type of reactor or another, there are still important concentration effects to be considered. 

Having discussed the choice of reactor type and operating conditions at length, let us try two examples. 

The need to satisfy these interrelated and often contradictory factors makes reactor design a complex and difficult task. However, in many instances one of the factors predominates, hence determining the choice of reactor type and the design method. 

Choice of reactor type, process stability, optimization. 

Having made a choice of the reaction path, a choice of reactor type must be made, together with some assessment of the conditions in the reactor. This allows assessment of the reactor performance for the chosen reaction path in order for the design to proceed. 

Reactor conversion. Earlier in Chapters 5 to 7, the initial choice of reactor type, operating conditions and conversion was discussed. The initial assumption for the conversion varies according to whether there are single reactions or multiple reactions producing byproducts and whether reactions are reversible. Consider the simple reaction ... 

The possibility of a species reacting by parallel paths to yield geometric isomers or entirely different products is often responsible for low yields of a desired product. If circumstances are such that the orders of the desired and unwanted reactions are different with respect to one or more species, it is possible to promote the desired reaction by an appropriate choice of reactor type and reaction conditions. 

The relative product yields in this case are insensitive to the type of reactor used, so reactor volume considerations will govern the choice of reactor type. 

In this section, we combine discussion of choice of reactor type and of experimental methods so as to develop the basis for the methodology of experimentation. We focus... 

The choice of reactor type and its design for a particular reaction netw ork may require examination of trade-offs involving reactor size and mode of operation, product distribution (selectivity), and production rate. If, as is often the case, selectivity is... 

The scope of this book includes several aspects of safe process design and operation, such as the choice of reactor type, safe operating conditions, and the selection of protective systems, primarily related to chemical reactivity. However, even in a process plant where these aspects have been carefully considered and thoroughly applied, there are still numerous events that can occur and can lead to hazardous incidents. Examples of such events are ... 

When products of low molecular weight are obtained from a chemical reaction process, it is often possible to separate these products after they have left the reactor. Thus, the choice of reactor conditions can be taken from a wide range of options. With polymerisation processes, the results of reaction selectivity (i.e. the molecular weight distribution of polymer molecules) cannot be changed easily once the material has left the reactor. Since polymer properties depend on the molecular weight distribution, the relative yields of polymers with particular sizes must be matched to a required specification. Therefore, the choice of reactor type is very important. 

In practice, most industrial processes are staged with multiple reaction processes and separation units as sketched in Figure 4-15. A is the key raw material and is the key product, it is clear that many factors must be included in designing the process to maximize the yield of E. The effectiveness of the separations are obviously critical as well as the kinetics of the reactions and the choice of reactor type and conversion in each reactor. If separations are perfect, then the yields are equal to the selectivities, so that the overall... 

Since it is impractical to fractionate the products and reformulate them into desirable ranges of molecular weights, immediate attainment of desired properties must be achieved through the correct choice of reactor type and operating conditions, notably of distributions of residence time and temperature. Reactor selection may be made on rational grounds, for historical reasons, or to obtain a proprietary position. 

Points 2 and 4 are the main ones governing the choice of reactor type. The high gas/liquid ratio restricts the choice to types d, e, i, and k in Fig. 19-26. Due to the high rate of heat transfer needed, the choice is a falling film or tubular reactor. 

Of primary interest for the industrial application of monolith reactors is to compare them with other conventional three-phase reactors. Two main categories of three-phase reactors are slurry reactors, in which the solid catalyst is suspended, and packed-bed reactors, where the solid catalyst is fixed. Generally, the overall rate of reactions is often limited by mass transfer steps. Hence, these steps are usually considered in the choice of reactor type. Furthermore, the heat transfer characteristics of chemical reactors are of essential importance, not only due to energy costs but also due to the control mode of the reactor. In addition, the ease of handling and maintenance of the reactor have a major role in the choice of the reactor type. More extensive treatment of conventional reactors can be found in the works by Gianetto and Silveston [11], Ramachandran and Chaudhari [12], Shah [13,14], Shah and Sharma [15], and Trambouze et al. [16], among others. 

The choice of reactor type is usually dictated by the liquid residence time required to attain the desired degree of reactant conversion and... 

Choice of reactor type and batch or continuous mode of operation... 

Nuclear reactors are designed for production of heat, mechanical and electric power, radioactive nuclides, weapons material, research in nuclear physics and chemistry, etc. The design depends on the purposes, e.g. in the case of electric power production the design is chosen to provide the cheapest electricity taking long term reliability in consideration. This may be modified by the availability and economy of national resources such as raw material, manpower and skill, safety reasons, etc. Also the risk for proliferation of reactor materials for weapons use may influence the choice of reactor type. Many dozois of varying reactor concepts have been formulated, so we must limit the discussion in this chapter to a summary of the main variables, and the most common research and power reactors. Fast reactors and some other designs are discussed in Chapter 20. 

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