Mathematical simulation of the performance of the solid liquid extractors—I: Diffusion batteries

Abstract

The extraction in purely countercurrent solid liquid extractors is extensively discussed in literature. In practice, the local mode of phase-contact often deviates from the overall counter-currence as is the case in e.g. belt type extractors and diffusion batteries. In the diffusion battery the local phase contact in each of the columns is, in essence, an instationary column process. However, from an overall point of view the extraction approaches a purely contercurrent process, dependent on the choice of the number of columns in the system and the cycle time. The differential equations describing mass transfer in this extractor were solved by numerical methods. The exit concentrations in cyclic steady state are averaged over one time cycle to obtain the extraction efficiency. Results of the calculations are presented as a correlation between the number of “plug flow” and “true” transfer units. It is shown that deviations from pure countercurrent are small when 4 or more columns are used under normal operating conditions.