Optimization of ethanol fermentation process design

The ethanol fermentation process using molasses as the feedstock has been studied. The process alternatives, compared to the original fermentation process described in the literature, have been modeled using single and double distillation columns. Short-cut and rigorous models for the distillation column were compared and their influence on the process economics indicate the rigorous model to be more exact, the short-cut model to be faster and more convenient for comparative analysis of finding the optimal process structure. The process with the single distillation column was shown to be the optimal variant requiring the lowest equipment and utilities cost. Estimated net present worth value for the single column was 29.6 MUSD and for the double columns 27.1 MUSD. A heat pump use was found to be a possible option for heat integration. The span of temperatures in distillation columns was confirmed to be the decisive factor for the economy of heat pump use. The pay back time was more than 5 years. Thermal integration reduced the total annual costs by 27% as compared to the basic process scheme. (C) 2000 Elsevier Science Ltd. All rights reserved.