A systems analysis of sweet sorghum harvest for a Piedmont ethanol industr

The Piedmont System is a collection of equipment for efficiently removing the juice from sweet sorghum stalks for the production of ethanol. The concept is to separate the whole stalks into pith and rind-leaf fractions, pass only the pith fraction through a screw press, and thus achieve an improvement in juice expression efficiency and press capacity. The operation of three alternative harvesting/processing systems were modeled and compared using computer simulation to determine which system could produce sweet sorghum juice and deliver it to a central plant at the lowest cost per liter of potential ethanol produced. In addition, an energy analysis was done to determine the net energy gain.;System A cut the sorghum stalks and hauled them to a crossroads site where they could be stored up to 30 days before juice expression. System B separated the pith and rind-leaf fractions in the field, and juice expression was accomplished at a nearby site. No storage was possible for System B. System C cut the stalks like System A, but then a mobile processor moved through the field to separate the pith and rind-leaf fractions.;It was found that the cost of producing feedstock with System C ($0.87/L) was significantly higher than either System A ($0.56/L) or System B ($0.63/L). While the System A cost was slightly lower than that of System B, it is recommended that both Systems A and B should be studied further since small adjustments to the model could eliminate the advantage of System A over System B. Increase in whole-stalk yield and juice sugar level would lower the cost of all three systems by as much as 43%.;As the price of energy rises, sweet sorghum is expected to gain an economic advantage over corn as a feedstock for ethanol, because of its higher energy ratio. If the by-products are used to produce ethanol through cellulose conversion, the overall energy ratio for sweet sorghum was calculated to be 1.1 compared to 0.8 for corn. The energy ratio if only liquid fuels are considered was 7.9 for sweet sorghum compared to 4.5 for corn.