Mass transfer characteristics of multiple-impeller fermenters for their design and scale-up

Mechanically agitated gas–liquid contactors are frequently used in the chemical, food and biochemical industries as fermenters and as hydrogenation or chlorination reactors. However wide the usage of such vessels is, their design is not based on chemical engineering data, but is still rather empirical. Thus, it is highly desirable to have a tool for the rational design of agitated gas–liquid contactors that is based on fundamental chemical engineering parameters that are transferable to other systems and operating conditions. Focusing on liquid film-controlled processes and using the data from fermenters of different scales, we develop kLa correlations that are suitable for scale-up.First, we discuss the way how to determine the proper experimental kLa values, which are not distorted by other equipment parameters as the gas residence time is. We demonstrate the possible kLa distortion on the pilot-plant experimental data by the comparison of the results obtained by two different experimental techniques. Further, we present physically correct kLa data for coalescent (pure water) and fully non-coalescent (sodium sulphate solution) batches. The data are presented both for laboratory and for pilot-plant fermenters. We identify the process parameters, the values of which are dependent on the vessel scale when operated under the same power input per unit volume, and, using these parameters, we develop common kLa correlations suitable to describe the data for various scales of the vessel.The correlations developed reduce the uncertainty in predicting the volume of industrial scale fermenters from almost 1/2 to 1/4 of their total volume, thereby enabling significant reductions in both the initial costs and operating costs.

► Fermenters scale-up based on volumetric mass transfer coefficient, kLa, is presented.
► Experimental kLa data for pilot-plant fermenter are presented.
► Process parameters are identified, the value of which depends on the fermenter size.
► The kLa correlations suitable for scaling-up are developed.
► The uncertainty is significantly reduced in the volume of the designed industrial fermenter.