Assessment of Sweet Sorghum as a Feedstock for a Dual Fuel Biorefinery Concept

Abstract

In the field of sustainable biorefinery concepts, sorghum receives increasing attention as a raw material. Main advantages of various sorghum types are fast growth as well as efficient nutrient and water utilization. When considering the competition between food and energy crop production, sorghum could be part of a sustainable solution. Through a convenient integration in a crop rotation system, sorghum could be grown as an alternative crop with good harvest results within a short vegetation period. In cooperation with a biogas plant in lower Austria, the potential of sorghum as a resource for fuel and energy production was evaluated. Field tests were carried out, and for a certain period of time, a sweet sorghum variant was incorporated into the substrate mixture of a biogas plant to monitor the process. Three concepts for grain and sweet sorghum variants were simulated in ASPEN Plus® to assess the coproduction of bioethanol and biogas in one facility and compared to the crops ethanol potential and conventional biofuel processes. The future growing conditions for this crop were evaluated on a climatologic basis for the Lower Austrian region in question. The highest harvest yields were achieved in the first year of testing, highlighting the dependency on cultivar and weather conditions. The sorghum processes could compete against the established processes, reaching up to 92 % ethanol, 107 % DDGS, 80 % methane and up to 202 % of their total energy output. Climatologic evaluation shows, that more regions in Austria will become available for sorghum cultivation due to climate change.