Continuous steady state and fed-batch dynamic simulation of fermentation process in an ethanol distillery

Most of the unit operations in an ethanol distillery are carried out in continuous mode. The fermentation unit may be designed to work either continuously or semi-continuously with cell recycle. After the process start up, the steady state continuous operation may be easily coupled to other unit operations of the process. In the semi-continuous configuration, however, it is necessary to use a set of vats in order to integrate the fermentation unit to the continuous steps. In this work both configurations were implemented in EMSO software: six parallel fed-batch vats and four continuous steady state vats in series. The process was modelled at macroscopic level based on material balances for cells, substrate, and product. Kinetic models accounting for product and substrate inhibition were used. Both configurations were integrated to a previously built model of a complete ethanol distillery, replacing a previous stoichiometric conversion fermentation model. The simulated distillery processes 500 t/h of sugarcane with varying levels of sucrose. Stoichiometric models may reproduce the results obtained by more complete kinetic models as long as the fermenter operates properly or the if the juice sugar concentration is controlled. However, these models cannot represent the effects of unusual conditions of operation. Hence, it is important to use more complex models in design activities and to check the operation range in which simplified models, such as the stoichiometric conversion ones, are valid.

Acknowledgments: FAPESP.