The design of extraction columns based on information from lab experiments and appropriate simulation tools allows reduction of time and costs compared to conventional design methods using pilot-plant experiments. For this purpose, the behavior of drops and drop swarms is investigated in lab-scale experiments in order to create mathematical models containing system-specific parameters that have to be fitted to those experiments. These models are implemented in a simulation program that solves drop-population balances in extraction columns. At AVT-Thermal Process Engineering of the RWTH Aachen University this concept was implemented in the program ReDrop. ReDrop can predict the separation performance and flooding point of pulsed sieve tray and structured as well as random-packing extraction columns for standard and technical systems. The program has successfully been extended to columns with rotating internals.