Date of Award

6-7-2024

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Systems Engineering

First Advisor

Ashokkumar Sharma

Abstract

The need to maximize current energy sources and create new ones has increased due to the world's growing energy demand and the depletion of major energy sources. Biomass and solid waste, such as wood, sawdust, plant wastes, paper, cardboard, and plastics, present promising carbon-neutral alternatives, collectively accounting for over 10% of global energy generation. The concept of integrating fixed and fluidized bed reactors in industrial applications needs additional research to ascertain the optimal configuration and interplay between these reactor types. Hence this research focuses on the utilization of a unique hybrid modular gasification system that combines fixed and fluidized bed configurations to build a waste-to-energy system at the UA Little Rock campus. The present study assesses the performance of a unique hybrid modular gasification system to produce bioenergy. The studied gasification system can be operated in fixed bed or dual bed (i.e. fixed bed + fluidized bed) configuration. Wood pellets are utilized as fuel for the reactor. Each experiment's performance characteristics are monitored and recorded using detailed instrumentation on the gasification system. The performance of the system in terms of temperature, pressure, gas composition and yield, and gasification efficiency was evaluated. Compared to a fixed bed gasification mode, the dual bed (fixed bed + fluidized bed) configurations offered a higher flow resistance thus, longer residence time due to the presence of the sand in the fluidized bed. The dual bed configuration with charcoal bed resulted in a combustible gas mixture consisting of 2.09% H2, 2.70% CH4, 15.08% CO, 0.33% C2H2, and 1.92% C2H6. The higher heating value (HHV) of biomass-generated gas was found to be 4.77 MJ/Nm3. The average gas yield, energy efficiency, and carbon conversion efficiency (CCE) were found to be 2.77±0.17 Nm3/kg, 58.78±0.34%, and 106.71±0.71%, respectively. The dual bed configuration without charcoal bed showed a gas mixture consisting of 4.97% H2, 2.65% CH4, 14.28% CO, 0.00% C2H2, and 1.13% C2H6. The gas HHV was 4.28 MJ/Nm3. The average gas yield, energy efficiency, and CCE were recorded to be 2.66±0.03 Nm3/kg, 50.08±5.63%, and 88.37±1.48%, respectively. In the fixed bed configuration, a flammable gas composition of 6.40% H2, 2.42% CH4, 20.38% CO, 0.00% C2H2, 0.19% C2H4, and 1.47% C2H6 was observed. The HHV of the combustible was 5.50 MJ/Nm3. The gas yield, energy efficiency, and CCE were found to be 2.37±0.12 Nm3/kg, 51.22±5.39%, and 83.78±5.78%, respectively. Tar was observed in semisolid form for the fixed bed and liquid form for the dual bed. The gas conditioning system (cyclones + cooling unit) further improves the overall process by reducing emissions of particulates and tar, contributing to environmental friendliness. Flaring the gas generated during test runs highlights its potential use in energy applications such as fuel cells, turbines, and combustion engines for electricity generation. While more research is needed to understand gasifier behavior using other gasifying agents (oxygen, steam) and testing with other biomass types generated on UA Little Rock campus, gasification presents a viable approach to generating clean energy from waste materials, supporting environmental sustainability initiatives and reducing negative environmental effects.

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