Scaleup of nonisothermal reactors

Thermal effects are often the key concern in reactor scaleup. The generation of heat is proportional to the volume of the reactor. Note the factor of V in Equation 5.31. For a scaleup that maintains geomedic similarity, the surface area increases only as Sooner or later, temperature can no longer be controlled by external heat transfer, and the reactor will approach adiabatic operation. There are relatively few reactions where the full adiabatic temperature change can be tolerated. Endothermic reactions will have poor yields. Exothermic reactions will have thermal runaways giving undesired byproducts. It is the reactor designer s job to avoid limitations of scale or at least to understand them so that a desired product will result. There are many options. The best process and the best equipment at the laboratory scale are rarely the best for scaleup. Put another way, a process that is less than perfect at a small scale may be better for scaleup precisely because it is scaleable. 

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We begin a discussion of scaleup relationships and strategies for tubular reactors. Results are restricted to tubes with a constant cross-sectional area. Chapter 3 discusses only isothermal or adiabatic reactors, but the relationships in Tables 3.1-3.3 include scaleup factors for the nonisothermal reactors that are discussed in Chapter 5. These results assume constant density, but Tables 3.4 and 3.5 give some specialized results for ideal gases when the pressure drop down the tube is significant. 

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