Modelling of a series of continuously stirred tank reactors for thermal processing of liquid foods

A series of stirred tanks for the thermal treatment of liquid foods is easy to model and operate. Good modelling leads to accurate predictions and small uncertainties in the lethality, giving a safe food product because of a small chance of underprocessing. Mathematical proof is presented that the minimum overall reactor volume for a given degree of thermal destruction of cells or spores is obtained when the stirred tanks are of equal size. Analytical techniques based on theoretical residence time distributions are employed to find the optimum number of tanks in the series using capital and operation costs in the definition of the objective function. If typical scaling factors are used, these optima depend only on the degree of reduction of viable cells/spores sought and a dimensionless economic parameter relating operating and capital costs if a single stirred tank were employed.