Analysis of post-harvest handling of corn stover and corn

摘要

Fuel and food are two major global issues. Interestingly, both of them have a close relationship with corn, a staple crop around the world. Bioethanol, which is the most popular gasoline alternative, is mostly produced from corn in the US. Since corn grain is for human food or livestock feed, the production of corn ethanol has caused some controversies. However, ethanol produced from corn stover is less controversial since corn stover is agricultural waste. On the other hand, more food needs to be produced globally to meet the fast-growing world population. Despite that, a stunning portion of food is being wasted every year, among which a lot of corn is being lost due to storage insect maize weevil (Sitophilus zeamais) in sub-Saharan Africa and around the world. One of the objectives of this project was to find an energy-efficient operation for corn stover size reduction processing, which is an unavoidable and energy-intensive process for lignocellulosic ethanol production. The other objective was to test the effectiveness of a new method to separate maize weevil, the most common corn storage insect, from corn kernels, to reduce the storage loss of corn grain.Chapter 1 of this thesis is the general introduction and literature review. Chapter 2, 3, 4 are three individual chapters for the three studies in this project. Chapter 5 is the summary, conclusions, and suggestions for future work.Chapter 2 and chapter 3 of this thesis are focused on corn stover size reduction process. Specifically, chapter 2 talks about a bench-scale experiment of grinding corn stover of different initial sizes and different moisture contents with a knife mill using different screens, looking for the most energy-efficient settings. The results showed that initial size of corn stover had no effect on grinding energy consumption. However, both moisture content of corn stover and the screen size affected the grinding energy consumption. As higher moisture content and smaller screen size, the grinding energy consumption would increase. In Chapter 3, a TEA and an LCA of the grinding experiment were conducted. CO2 emissions and cost of 6 different grinding scenarios were compared on the basis of producing the same amount of fermentable sugars after the size reduction process. The results showed that grinding the corn stover at the moisture content of 5% W.B. with 2mm screen had both the lowest CO2 emission and the lowest cost.Chapter 4 is about a new method to control the population of maize weevils in corn. An aspiration devices were used to separate the bugs from the corn. The results showed that the separation rate can be as high as 100% when the air flow rate reaches 15m/s.