Date of Award
Doctor of Philosophy
Agricultural and Biosystems Engineering
Robert P. Anex
Robert C. Brown
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 equipment into existing ethanol facilities was also found to be economically viable when combined with the plants' use of residuals as a natural gas fuel replacement. Because of high loss of fermentable carbohydrates during ensilage, storage of sweet sorghum in bunkers was not found to be economically viable.
The forth section looks at double cropping winter triticale with late-planted summer corn and compares these scenarios to traditional single cropped corn. Double cropping systems show particular promise for co-production of grain and biomass feedstocks and potentially can allow for greater utilization of grain crop residues. However, additional costs and risks associated with producing two crops instead of one could make biomass-double crops less attractive for producers despite productivity advantages. Detailed evaluation and comparisons show double cropped triticale-corn to be at a significant economic disadvantage relative to single crop corn. The cost benefits associated with using less equipment combined with availability of risk mitigating crop insurance and government subsidies will likely limit farmer interest and clearly indicate that traditional single-crop corn will provide greater financial returns to management.
To evaluate the various sweet sorghum, single crop corn and double cropped triticale-corn production scenarios, a detailed but generic model was developed. The primary goal of this generic approach was to develop a modeling foundation that can be rapidly adapted, by an experienced user, to describe new and existing biomass and crop production scenarios that may be of interest to researchers. To facilitate ease-of-use, the techno-economic model was developed in MS Excel<®>. It also incorporates the Excel add-on, Crystal Ball<®>, which provides Monte Carlo simulation and sensitivity analysis capabilities. The foundation model allows input of management practices, crop production characteristics and utilizes standardized machinery performance and cost information, including farm-owned machinery and implements, and machinery and farm production operations provided by custom operators. Several of the studies reported in this dissertation take advantage of the flexibility of the foundation model. Many specific models of unique production scenarios (in excess of 100) were developed and tested. Twenty of these models are actually presented in this work. More important to the success and value of this modeling approach is the now readily available Monte Carlo simulation tools, which allows researchers to describe uncertainty around key model variable in a more realistic manner. It is opinion of the author that all future crop related techno-economic studies should incorporate Monte Carlo simulations as standard practice.
Albert S. Bennett
Bennett, Albert S., "Research in biomass production and utilization: systems simulation and analysis" (2009). Graduate Theses and Dissertations. 10562.