Semester

Fall

Date of Graduation

2011

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committtee Chair

Bruce Kang

Committee Co-Chair

Eric Johnson

Committee Member

Dirk Van Essendelft

Abstract

Motivated by the transition to a more sustainable society, biomass, currently the largest renewable energy source in the world, could therefore in principle become a key energy source in the future. Co-combustion of these materials and coal can lead to a significant reduction in carbon dioxide net emissions in new and existing power plants while potentially reducing capture costs as well. However, many challenges remain to be solved before biomass can be used on a much larger scale as a sustainable energy source. Some of these challenges are related to biomass production, land management, and competition with food production; but challenges also exist in the handling of biomass as a fuel. The relatively low-energy density of biomass, in combination with its high moisture content, makes transport of biomass from production sites to power stations or future bio-refineries costly. Due to this reason, torrefaction is required, where in the raw biomass is thermally treated in the absence of oxygen at relatively low temperature ranging from 200-300°C. This mild treatment both increases the energy density and facilitates grindability by weakening the fibrous structure and tenacity of biomass. During the process the biomass also decreases in mass, but will maintain the majority of its initial energy.;Historically, the Hardgrove Grindability Index (HGI) has been used to assess fuel grinding energy, and yet this parameter is incapable of categorizing raw or torrefied biomass materials. The objective of this research is to conduct material mechanical property evaluation of torrefied biomass and identify the correlation related to grindability as well as grinding energy assessment.;This work involves the influence of torrefaction temperature and residence time, flow rate of inert gas, size reduction via ball-milling (energy consumption for grinding), and mechanical property evaluation (hardness, elastic modulus, fracture toughness). Torrefaction leads to a very substantial improvement of the grindability. It therefore provides a solution to the problems concerned with biomass gasification and co-firing with coal where size reduction of biomass materials is required.

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