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Scale-up of chemical reactors. It was shown by Damkohler as long ago as 1936 that full similarity can not be achieved in the scale-up of chemical reactors. The scale-up process must therefore either be undertaken by trial and error or it must be based on calculation, i.e. on a mathematical model. The computation requires kinetic data as input, which can only be obtained from experimental observations. The very fact that only reactor behaviour can be observed in the laboratory requires that the physical model and its mathematical formalization must be used twice: Once for „back calculation” of kinetic data (coefficients) from the observed behaviour of the laboratory reactor and then again to predict the behaviour of a full scale reactor on the basis of these data. This procedure is of limited reliability due to the interaction of transfer processes (like heat transfer) at the boundaries of the system and relaxation processes in the bulk (like chemical reaction). These interactions may influence the kinetics in a way that cannot be predicted from theory or experiment. Damkohler's dilemma cannot be resolved through computation. |
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