A distributed parameter model for simulation of SCP-production processes in tower reactors with an outer loop was developed by considering substrate, cell, and CO(2) balances in the liquid phase, and O(2) and CO(3) balances in the ges phase and taking into account variations of dissolved oxygen concentration, pressure, and k(L)a along the column, as well as double substrate Monod kinetics. This model was used to describe the cultivation of Hansenula polymorpha in a tower-loop reactor (height 275 cm, diameter 15 cm). Parameter identification and process simulation were carried out by a hybrid computer. The variation of identified mass transfer parameters with fermentation time and operation mode is considered employing ethanol and glucose substrate, respectively. Relationships among k(L)a, substrate concentration, and superficial gas velocity were developed to facilitate the layout and simulation of pilot-plant reactors.