The influence of enthalpy management and temperature control

In the preceeding sections it was indicated briefly how to arrive at the appropiate reactor configuration and mode of operation. From these two requirements the reactor type follows automatically, even if it turns out that such a desired reactor type has never been constructed before. 

The importance of enthalpy management , or how to cope with large amounts of heat of reaction, has been indicated in Chapter 8. The importance of this aspect increases with the scale of the reactor, for obviuous reasons. The consequence is, that requirements for heat transfer may be more decisive factors in reactor design, the larger the scale of operation. So it may be that the selection of a reactor type has to be revised completely when heat transfer is considered. Yet the indicated order of decision mal g may be the most effective. 

When one has decided on a well mixed reactor, possibly with one or several dispersed phases, the solution of the heat transfer problem is relatively simple. It may be merely a question of installing sufficient heat transfer area, either inside or outside the reactor. Vigorous mixing will increase the heat transfer to the wall or to submerged tube bundles. For rapid exothermic reactions, the volume of the reactor may be determined by heat transfer, not by reaction kinetics or mass transfer. The use of a boiling solvent for effective heat removal and temperature has been indicated in section 8.3.3. It can often be applied on large scales. 

When a narrow residence time distribution is desired, good heat transfer will usually require high flow rates, which in combination with a given residence time would result in long or tall reactors. Occasionally very long coaxial tubes are used for single liquid phase processes. For processes wiUi a liquid as the continuous phase, a cascade of stirred tanks (sections 3.3.3 and 7,2,1,3) or a pulsed pack column (section 45,15) may then be interesting alternatives. 

For gas/solid processes the fluidiz bed is the best alternative when large amounts of heat have to be supplied or removed (sections 45,1,4, 5.4.4 and 7,22.4), 

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