Converting Sweet Sorghum to Ethanol - An Alternative Feedstock for Renewable Fuels

Abstract

The goal of this project was to design an ethanol production process from sweet sorghum for use as a renewable fuel. Sorghum stalks are first harvested and sent through a series of 2 three-roller extractors (70% total efficiency). Extracted juice is pumped to the reactor for preservation and fermentation. Sodium metabisulfite preserves the juice. Ethanol Red (Saccharomyces cerevisiae) is the fermentation yeast. Following fermentation, the juice (8% ethanol by mass) is distilled to achieve 90% ethanol. A molecular sieve extracts excess water, resulting in 100% ethanol. Plant wastes accumulate during the process. These wastes are collected, dried, and sold as animal feed for profit. The project economics indicate that the overall process is not currently economically feasible. The net present value (NPV) for the optimum economic situation, assuming a 15 year plant lifetime and 15% interest rate, is -$125 M. Under these circumstances, the ethanol would need to be sold at $44.37 per gallon to break even. To improve this process, further development of methods for increasing juice extraction efficiency should be explored. Additionally, the distillation process could be enhanced with a second distillation column to achieve 95% ethanol prior to using the molecular sieve.