Life cycle assessment and techno-economic analysis of sustainable ethanol production from industrial tail gas

Abstract

Conversion of low-value tail gas from industries into ethanol (TG-ethanol) is a promising cutting-edge route for value-added utilisation of tail gas. However, a systematic and objective understanding of the environmental impact and economic benefits is still lacking, and a comparison with traditional ethanol production technologies is urgently needed to justify its future competence. This thesis performed a life cycle assessment (LCA) and techno-economic analysis (TEA) of this “waste-to-value” technology and its upgraded process, as well as the upstream and downstream industries. First, the life cycle environmental impacts of Linz-Donawitz Gas from the steel industry into ethanol (LDG-ethanol) were evaluated and compared with other ethanol pathways. LDG-ethanol exhibited 22–25% lower comprehensive environmental impact than Corn-ethanol and Coal-ethanol. Sensitivity analysis highlighted electricity as a key factor, reducing electricity consumption and introducing green power can mitigate the environmental impact by 15–68%. While some technologies have been demonstrated for commercial deployment, new technological concepts keep emerging to improve the life cycle and techno-economic performance. In this investigation, a novel ethanol production technology integrating TG-ethanol with electro-catalytic CO2 reduction (TGEE-ethanol) was first proposed. Different integration scenarios using steel, iron alloy, and calcium carbide tail gas were modularly modelled, followed by LCA and TEA via Monte Carlo simulation. Results suggested TGEE-ethanol could increase ethanol capacity 1.3–2.9 times with a carbon efficiency of 36–82%, and carbon footprint of 1.77–3.93 t CO2eq/t ethanol, with 32–63% higher carbon reduction potential than TG-ethanol. Minimum ethanol selling price is estimated at 428–962 $/t ethanol, lower than the ethanol market price (900–1080 $/t). In addition, the upstream and downstream should be investigated to identify the environmental and economic benefits of such low-carbon technologies. The results show that upstream (steeling-LDG-ethanol) industries showed potential carbon reductions of 5.3–5.6 MtCO2 and economic benefits of $2.97–3.49 billion by 2060. Downstream (TGEE-ethanol-jet fuel) industries exhibited lower carbon footprints for TGEE-ethanol from iron alloy (IEJ, 65 g CO2eq/MJ) and calcium carbide (CEJ, 74 g CO2eq/MJ) than fossil jet fuel (90 g CO2eq/MJ), while costs are higher. Carbon taxes of $10, $50, and $100 could reduce costs by 3–32%, achieving cost parity with fossil fuels 2–10 years earlier than previously estimated around 2050. Therefore, a comprehensive analysis suggests that the TGEE process is a more economically and environmentally benign next-generation technology for producing ethanol from industrial tail gas. Overall, this study could provide guidance for future planning and strategies for the ethanol industry and may be inspiring to help heavy industries seek new technologies to reuse CO/CO2-containing waste gases.

Date of Award	Nov 2024
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Cheng Heng Pang (Supervisor), Kien Woh Kow (Supervisor), Wei Wei (Supervisor) & Edward Lester (Supervisor)