The Structure of Reactor Design

Before e take up quantifative aspects of hefefogene ous reactor design in Chap. 13, let us survey the problem. It is appropriate to present an overview here because of the interaction between laboratory and large-scale reactors i.e., the purpose of the laboratory study is to obtain a rate equation useful for designing the large reactor. 

Suppose a new chemical reaction, or new example of a known type of reaction, has been discovered. The product has promising economic possibilities. Samples of product have been made and tested, and a preliminary economic analysis has been completed. It is decided to proceed with calculations and experimental work necessary to design a large reactor to produce the product. The overall structure of the problem is represented schematically in Fig. 12-4. The items at the right indicate the scientific dis- 

After the intrinsic rate equation has been established, it is used to develop a mathematical model of the large-scale reactor. The first step is to obtain the global rate at any point in the reactor, as illustrated in Example 12-2. To complete the model, equations are derived to give the conversion and selectivities in the product stream in terms of the proposed operating conditions. These equations and their solution are the subject of Chapter 13. 

In homogeneous reactors that are not isothermal, scale-up is dangerous because it is difficult to allow for the differences in heat-transfer conditions in laboratory and large-scale units. When precautions are taken to obtain the same global rate and the same heat-transfer conditions (for example, 

It is a simple matter to demonstrate that it is the interaction of reaction, geometric, and heat-transfer requirements that limits the value of scale-up. Consider a fixed-bed catalytic reactor. Suppose that the pressure drop has no effect on the rate and that plug flow exists. The mass balance for reactant is given by Eq. (12-2) as 

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