Graduation Year

2024

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Chemical, Biological and Materials Engineering

Major Professor

John Kuhn, Ph.D.

Co-Major Professor

Babu Joseph, Ph.D.

Committee Member

Norma Alcantar, Ph.D.

Committee Member

George Philippidis, Ph.D.

Committee Member

Qiong Zhang, Ph.D.

Keywords

Siloxanes, Biogas, Landfill Gas, Waste-to-Energy, Gas to Liquid

Abstract

This dissertation aims to enhance the cost competitiveness and minimize the environmental footprint of technologies that convert biogas to energy, contributing to global climate change mitigation efforts. Biogas, a by-product of the anaerobic decomposition of organic waste from various sources, is a renewable energy source with the potential to reduce carbon emissions and meet local energy needs. However, widespread adoption requires the development of economically viable and environmentally friendly technologies.The central hypothesis of this dissertation suggests that by adopting a holistic strategy that combines cutting-edge techniques to purify biogas and improve its conversion into valuable liquid fuels, we can substantially elevate the cost-effectiveness and environmental sustainability of biogas-to-energy systems. This, in turn, will foster the widespread adoption of these technologies and play a pivotal role in advancing a cleaner and more sustainable energy landscape. Three specific objectives were defined to test this hypothesis: • Evaluate low-cost adsorbents for siloxane removal from biogas. • Conduct a technoeconomic and sustainability analysis of contaminant removal from landfill gas. • Perform process modeling, techno-economic analysis (TEA), and life cycle assessment (LCA) of the intensified biogas-to-liquid (IBGTL) process. To achieve these objectives, a combination of methods was employed, including experimental procedures for characterization and adsorption testing, process modeling using Aspen Plus software, technoeconomic analysis using CAPCOST, life cycle assessment with Simapro software, and sensitivity analysis. The findings from the initial objectives revealed that low-cost adsorbents like clinoptilolite are economically comparable to the current state-of-the-art technology, activated carbon, for biogas purification. Clinoptilolite also emits significantly fewer carbon emissions on a life cycle basis compared to activated carbon. Additionally, installing a siloxane removal unit proves to be economically beneficial for biogas-to-electricity plants with flow rates greater than 2000 m3/h, highlighting the importance of contaminant removal for efficient energy generation. Building upon these achievements, the subsequent investigation focused on the IBGTL process, exploring avenues for reduced input requirements and lowered capital investments. Four scenarios were evaluated: (1) a once-through process with no recycle, (2) a process with material recycling, (3) a process with liquefied petroleum gas (LPG) co-product recovery, and (4) a process with electricity generation from the fuel gas produced. The process modeling and techno-economic analysis results indicate varying C5+ mass yields and energy recovery percentages across these scenarios. Among them, Scenario 2, characterized by material recycling, emerged as the most cost-effective option, achieving a Minimum Fuel Selling Price (MFSP) of $4.59 per gallon. This MFSP is cost-competitive with the current national diesel price of $4.7 per gallon, affirming the potential economic viability of the IBGTL process. However, comparing the IBGTL process with a conventional two-reactor system scenario highlights the need for catalyst performance improvements to ensure cost competitiveness with this process. The sensitivity analysis conducted emphasizes the significance of key factors such as cost of manufacturing, liquid fuel yield, and biogas flow rate in determining the overall economic performance of the IBGTL process. The comparative life cycle assessment (LCA) conducted reveals substantial reductions in greenhouse gas emissions for the IBGTL process compared to fossil-based liquid fuels. The LCA results demonstrate that the IBGTL diesel offers significant environmental benefits, with emissions savings ranging from 55.7 to 221 gCO2eq/MJ across different pathways evaluated. In conclusion, this dissertation provides practical insights into improving the economic viability, reducing the environmental impact, and optimizing the performance of biogas-to-energy technologies. The findings contribute to waste management and transportation sector decarbonization, emphasizing the IBGTL process's promise as a sustainable solution. By enhancing the cost-effectiveness and environmental sustainability of biogas-to-energy technologies, this dissertation contributes to the development of a more resilient and sustainable energy future.

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