Date of Award

2019

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

Jeffrey D. Naber

Committee Member 2

David R. Shonnard

Committee Member 3

Armando G. McDonald

Committee Member 4

Robert M. Baldwin

Abstract

This work is focused on the fundamental understanding and the development of paddle mixer reactors (or modified screw augers). This work will contribute to the effort of the thermal conversion of biomass and wastes. We developed and studied two paddle systems (i) 25-mm lab-scale (up to 1 kg/hr) and (ii) 101-mm pilot-scale (up to 100 kg/hr). Thermal behavior of the two systems was studied and it was estimated that the lab-scale system has a high heating rate of up to 530 °C/s. Residence times were thoroughly measured and were determined as a function of rotation frequency and volume fraction. We also determined the specific process energy requirements and the specific heat of the material. Extensive pyrolysis experiments were carried out with many types of biomass. It was found that solid/liquid yields were comparable to those measured in circulating fluidized bed at NREL. Modification of the pilot-scale system is required to enhance the mass flow rates and the heating rate.

Fiber and plastic waste blends were thoroughly investigated in a mixture of 40% plastic and 60% fiber. Extensive torrefaction experiments were carried out and thermal and mechanical properties of the torrefied material were measured and correlated with mass loss. Degradation reaction of waste blends was modeled using a first-order reaction. Excellent fit between the experimental and modeling results was obtained. Activation energy and pre-exponential factors were determined. One major finding was that the paddle mixer significantly increased the homogeneity of the waste blend and it is further increased as the size of the material reduces. Density was measured and found that at a density of ~1200 kg/m3, the water intake was 0.7% after 30 days of immersion in water. Extensive grinding study was carried out with these torrefied waste blends and the grinding energy behavior was found similar to that of PRB coal. Heat content was measured, and it was shown that the initial heat content is ~30 MJ/kg and as the torrefaction process proceeds the value increases to ~35 MJ/kg at ~51% mass loss. Combustion experiments were carried out and showed that with the reduction of volatile matter (due to thermal degradation) the combustion time has increased.

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