Evaluation of Scenarios for the Industrial Use of Sweet Sorghum

Grant # :05-02
Principal Investigator: Robert P. Anex
Organization: Iowa State University
Technical Area: Renewable Energy

Public Abstract
Over the past thirty years there has been considerable interest in using sweet sorghum as a feedstock for fuel and chemical production. A number of studies have examined the yields of different sorghum varieties, examined the possible production of ethanol from sorghum, and considered technical issues at different stages of the production process, such as fermentation, harvest systems or juice separation processes.

The goal of this study is to evaluate the economic and technical viability of a range of scenarios for converting sweet sorghum into valuable products. Likely scenarios include ethanol production using technologies similar to sugarcane, including combustion of residues to generate electrical energy and provide process heat. This study focused on comparing traditional forage harvest systems with a prototype mobile juice harvest system, along with considering the possibility of storing sweet sorghum as ensilage and using it as a supplemental feedstock for existing corn-ethanol facilities.

Findings
Results of the study indicate that traditional forage harvest systems combined with existing sugar extraction technologies common to the sugarcane industry (up to 97) are far more cost effective than mobile juice harvest systems which are only able to extract approximately 50 of fermentable carbohydrates (FC). It has also been found that fresh processed sweet sorghum can produce FC at costs competitive with corn grain. In contrast, ensilage of high moisture sweet sorghum in bunker silos can lead to significant losses of FC (in excess of 20) and result in net FC costs that are well above corn derived FC.