Date of Award

2021

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 L. Klinger

Committee Member 1

David R. Shonnard

Committee Member 2

George W. Huber

Committee Member 3

Armando G McDonald

Abstract

The world is witnessing unprecedented accumulation of solid wastes in the environment and landfills with well-documented ecological, environmental, health, and economic consequences. With population growth and rise in living standards, solid wastes generation will increase, making the issue more pressing. In addition, current practices of solid waste disposal are creating an immediate challenge and a long-term disaster-scale problem. The solid wastes comprises two main groups of materials: (i) fiber wastes (paper, food, wood, trimming, 61% of U.S. municipal solid waste) and (ii)uniquely challenging subset of plastic wastes (13%) that become a threat to global sustainability including dangers to marine and terrestrial wildlife. Thermal treatment can turn these high calorific value wastes into fuels that can be used in small-to-large power plants. However, there exist several hurdles: (i) huge heterogeneity of the wastes that would produce ununiform products; (ii) high chlorine content that is corrosive and its emission is strictly controlled; (iii) requires binder for compaction.

This work focused on two main aspects: (i) studying the properties of waste blends after torrefaction at various conditions; (ii) researching the dechlorination of wastes through torrefaction. The work started by studying the effect of torrefaction on different types of wastes and comparing the properties of the product to coal. It was found that the grinding characteristics and size distribution after grinding were similar to coal, with the heat content increased as the mass loss increased. And with the help of extrusion, the product has significantly higher uniformity, durability and water resistance. The results showed that torrefied wastes can be a drop-in-fuel in coal power generation facilities. During the study of torrefaction of wastes, it was observed that there existed synergistic effects between fiber and plastic wastes. In order to understand this interaction, synergy within the fiber wastes and between fiber and plastic wastes were further studied. A multi-consecutive reaction mechanism that focuses on solid products was developed for fiber waste thermal degradation. And further insights between fiber and plastic wastes during torrefaction were also investigated.

The study then focused on the dechlorination of wastes through torrefaction. A multi-consecutive reaction mechanism that focuses on gaseous products were developed for PVC thermal degradation. The kinetic parameters provided unique insight into the thermal degradation mechanism. The model was then validated by applying to different reactor design and sample sizes. The study of chlorine removal through torrefaction from waste with different chlorine levels was also carried out. It was found that despite of different chlorine levels, the torrefaction behaviors the materials were comparable, and their heat contents and chlorine removal efficiencies were also similarly correlated to torrefaction. The chlorine removal efficiency increased as mass loss increased, reaching an asymptotic value of ~80% at ~ 40% mass loss, while the remaining 20% of chlorine can be attributed to inorganic sources. The above studies could greatly help with the process design for treating wastes and turn them into fuels.

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