AbstractsBiology & Animal Science

Research in biomass production and utilization: systems simulation and analysis

by Albert S. Bennett

Institution: Iowa State University
Year: 2009
Keywords: Bioenergy; Biomass; Combined heat and power; double crop; simulation; Sweet Sorghum; Bioresource and Agricultural Engineering
Record ID: 1854410
Full text PDF: http://lib.dr.iastate.edu/etd/10562



There is considerable public interest in developing a sustainable biobased economy that favors support of family farms and rural communities and also promotes the development of biorenewable energy resources. This study focuses on a number of questions related to the development and exploration of new pathways that can potentially move us toward a more sustainable biobased economy. These include issues related to biomass fuels for drying grain, economies-of-scale, new biomass harvest systems, sugar-to-ethanol crop alternatives for the Upper Midwest U.S., biomass transportation, post-harvest biomass processing and double cropping production scenarios designed to maximize biomass feedstock production. For each question of interest, specific examples were identified and detailed models developed in MS Excel<®>. Techno-economic analysis and Monte Carlo simulation techniques were used to challenge each model and evaluate viability. The first section of this study considers post-harvest drying of shelled corn grain both at farm-scale and at larger community-scaled installations. Currently, drying of shelled corn requires large amounts of fossil fuel energy. To address future energy concerns, this study evaluates the potential use of combined heat and power systems that use the combustion of corn stover to produce steam for drying and to generate electricity for fans, augers, and control components. Techno-economic analysis suggests that there are significant economies of scale with community-based dryers, e.g. grain elevators, which show a much faster return on investment over farm-scaled systems. Because of the large capital requirements for solid fuel boilers and steam turbines/engines, both farm-scale and larger grain elevator-scaled systems benefit by sharing boiler and power infrastructure with other processes. The second and third sections evaluate sweet sorghum as a possible "sugarcane-like" crop that can be grown in the Upper Midwest. Various harvest systems are considered including a prototype mobile juice harvester, a hypothetical one-pass unit that separates grain heads from chopped stalks and traditional forage/silage harvesters. Also evaluated were post-harvest transportation, storage and processing costs and their influence on the possible use of sweet sorghum as a supplemental feedstock for existing dry-grind ethanol plants located in the Upper Midwest. Results show that the concept of a mobile juice harvester is not economically viable due to low sugar recovery. However, traditional forage/silage harvest systems provide an economically viable harvest solution as long as chopped forage can be quickly processed in a nearby, centralized facility. The transportation of low bulk density, fresh harvested or ensiled sweet sorghum was found to significantly contribute to overall costs. However, at the scales evaluated in this study, those costs did not adversely affect the viability of sweet sorghum as a supplemental feed for existing dry-grind ethanol plant. The addition of front-end stalk processing/pressing…