Date of Award

12-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering and Sciences

First Advisor

M. Toufiq Reza

Second Advisor

Pavithra Pathirathna

Third Advisor

Jonathan Whitlow

Fourth Advisor

Manolis Tomadakis

Abstract

Waste corn stover is one of the most abundant agronomic resources in U.S., however, those are either incinerated or unprocessed in the field to avoid high logistical cost, economic forfeiture, and environmental complications. Hydrothermal carbonization (HTC) is a promising thermochemical process that transforms wet biomass like waste corn stover into a solid fuel called hydrochar, process liquid, and process gas. The recycle of process liquid is warranted as the HTC process liquid contains organic acid that would increase the mass yield and fuel quality of the hydrochar by catalyzing the HTC reactions. HTC also promotes the fuel quality by densifying mass and energy in hydrochar while augmenting hydrophobicity. The hydrochar, due to having approaching fuel quality as coal, i.e., coalification degree towards coal with increasing HTC temperature, poses an alternative to the coal for combustion. Therefore, the objectives of this dissertation are (1) to study the process liquid recycle effect on the hydrochar’s chemical properties, (2) to densify hydrochar in order to enhance the energy density of the fuel, and (3) to evaluate combustion properties of the hydrochar by cone calorimeter. HTC of waste corn stover was collected from Idaho National Laboratory, where air classification (AC) was applied to separate clean corn stover from waste corn stover. Waste corn stover is often considered as waste that is destined to landfill. In this study, the effect of HTC temperatures on hydrochar’s fuel quality was investigated. The effect of process liquid recyclability on the material properties was evaluated by recirculating multiple times. The hydrochar was characterized by several analytical techniques such as CHNS, TGA, SEM, FT-IR, and fiber analysis etc. The hydrochar was blended with clean corn stover and pelletized in a single press-pellet press. The blend pellet was characterized by proximate and ultimate analysis, mass and energy density, and hydrophobicity etc. The combustion properties of the hydrochar was investigated in cone calorimeter and a combustion kinetic model was proposed based on proximate analysis and combustion thermogram of the hydrochar. Finally, a comprehensive technoeconomic analysis was performed to evaluate the economic viability of the integrated AC-HTC-pelletization process.

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