Fundamental Bioengineering

11Mixing and Mass Transfer in Industrial Bioreactors

John Villadsen

Summary

Design of a real reactor for a real process in industrial scale requires much more than the design of the “ideal” reactors, the subject of Chapter 10. Mass balances and mathematical solution of mass balances must be supplemented by insight derived from construction of and operation of different reactor types in many scales and for many different purposes. This insight is formulated in empirical relations between key process parameters, such as mass and heat transfer coefficients, and the power input to the process. Mixing becomes an important issue, and from mixing time as a function of the geometry of the reactor and the power input, one derives expressions for the transfer parameters. With the new types of reactor that were briefly introduced in Chapter 10, new design expressions have to be developed since the present experimental background is mostly derived from the use of mixing aggregates that have become standard through industrial application for many decades. This chapter collects the most important empirical knowledge about design of mixers to achieve a particular goal. The resulting design formulas are not in any way quantitatively correct, but based on dimensional analysis one is able to extrapolate from small- to large-scale operation, and it is shown that linear scale-up may not give the smallest power input for a given mixing objective. The introduction given here is the basis for the ...