Optimum Design of a Continuous Fermentation Unit of an Industrial Plant for Alcohol Production

The aim of this work was the optimum design of the fermentation unit of an industrial plant for alcohol production from sugar cane by Saccharomyces cerevisiae. The kinetics was represented by a mathematical model having the growth rate as a function of the total reducing sugars, cell and alcohol concentrations and temperature. By means of computer simulations it was possible to obtain the best design for a fermentation plant under common Brazilian operational conditions. The result was a series of four CSTR’s with medium feeding in the first reactor. The volume of each reactor was not necessarily the same. In fact, there was an optimal profile that gave the highest productivity. The optimum volume of each stage was obtained using the simulation results and the SIMPLEX method of optimization. The volume profile leading to the highest productivity was: 21% of total volume for the first reactor, 27% for the second reactor, 31% for the third one, and 21% for the last one. The equations used in the simulations were obtained from the mass and energy balances of the system and kinetic equations based on parameters taken from industrial data. The final result was implemented in an ethanol factory and the so far collected operational data showed good agreement with the theoretical results.