Date of Award

2017

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Ezra Bar-Ziv

Advisor 2

Jordan Klinger

Committee Member 1

David Shonnard

Committee Member 2

Jeffrey Naber

Abstract

Biomass is considered a renewable source of energy with minimum carbon foot print if managed sustainably. The majority of the worlds energy is spend on transportation, and fast pyrolysis of biomass could be a potential route for production of a sustainable liquid transportation fuel. However, there are several hurdles in the conversion process. This work addresses these hurdles by investigating the impact of several pretreatment methods on fast pyrolysis including thermal pretreatment (torrefaction), comminution/grinding, mineral reduction. The impact of important parameters like heat transfer medium, conversion temperature and particle size were also investigated.

A mild thermal pretreatment of biomass (~10-15% dry solids loss) had been proven to provide multiple benefits which include, reduction of grinding energy (~85% reduction), narrower particle distribution and production of bio-oils that have lower water and acid content, thus increasing stability. Comminution followed by mechanical sifting reduced the insoluble minerals (primarily silicon), which can cause damage to bio-refineries by increasing the equipment wear. More than 80% of the inorganics (both soluble and insoluble) were removed through aqueous high-shear mineral reduction technique when paired with mild thermal pretreatment. Removal of these soluble, structural minerals has decreased the amount of aqueous-fraction bio oils, and produced a higher quality oil.

Arundo Donax is a fast growing cane which is considered a low cost energy crop. However, its high mineral content made it less attractive for alternative bio-fuel production. The high potential of the feedstock was the primary reason why this feedstock has been extensively studied in this work, and an effective pretreatment method to enable efficient conversion was sought. It was concluded that the particle size of the feedstock has minimal effect on the bio-oil yield within the studied range (<2 >mm), whereas the conversion/reaction temperature had shown predominant effect. The optimal bio-oil yields for raw Arundo Donax were approximately 50-52% observed for feedstock with particle size in range of 0.425-0.850 mm at temperatures of 470-500 ºC. The high shear mineral reduction technique with multi stage fast pyrolysis was also investigated with up to approximately 40% dry solids loss in first stage (torrefaction). It was found that the mineral reduction increased the liquid product yield (up to 62%), approaching that of clean woody feedstocks. This work indicated that the liquid yield can be effectively fractionated through sequential degradation stages without losing the product yield.

In conclusion, the presented work in this dissertation indicates that integration of pretreatment methods like mineral reduction, comminution and thermal treatments with fast pyrolysis enables the use of low cost biomass feedstocks to be able to produce stable bio-oils with optimal yields. Further, this work demonstrates, in part, that the presented (relatively) simple and low-cost conversion reactor can produce a high yield of liquid pyrolysis oil from a range of woody, herbaceous, and agricultural residues and wastes. Sequential staging of these reactors can produce a thermally fractionated product.

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