A feasibility study on integrating electric buses with waste gasification for a green public transport system and solid waste management

Lui, Jade Victoria (2023) A feasibility study on integrating electric buses with waste gasification for a green public transport system and solid waste management. PhD thesis, University of Glasgow.

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Waste management and public transport are two major issues requiring decarbonisation in the face of climate change and environmental concerns related to global warming. Green transport systems are classified as zero or low carbon alternatives to the fossil fuel-based approach and vehicles. These systems rely on zero emission fuels such as hydrogen. Thermochemical processes (e.g., gasification) and biochemical technologies (e.g., fermentation) can convert carbon-based feedstock such as waste to produce desirable products like hydrogen. Waste-to Hydrogen is proposed as a potential solution to provide both sustainable waste management and hydrogen production.

Waste-to-Hydrogen (WtH) is a hybrid solution that simultaneously combines sustainable waste management and non-fossil-fuel based hydrogen production. The concept of distributed WtH systems, based on gasification and fermentation, is to support hydrogen fuel cell buses in Glasgow is considered as a potential solution zero emission transport development. Hydrogen has potential to replace petrol and diesel fuels and consequently become part the zero-carbon measures to aid the transition to cleaner energy sources. When hydrogen is produced from renewable or sustainable energy sources it can help decarbonise the energy and transport sector. To be attractive to policymakers and investors it is necessary for the hydrogen from a WtH system to demonstrate its carbon footprint is lower than conventional methods. By supporting the effort to reach carbon emission reduction targets, hydrogen is part of the solution to limit climate change, a global emergency. Providing research to support the roadmap of hydrogen-powered public transport to shape the direction of future technological improvement and policy formulation.

As well as the potential to provide a clean versatile fuel through hydrogen, WtH can offer an alternative waste management practice that diverts waste away from landfill and incineration. By utilising and transforming waste into a useful energy resource, a value is applied which can encourage the development of sustainable disposal methods such as WtH conversion processes.

Glasgow was chosen as the location for the study due to the large population which would supply regular amounts of waste to be used as feedstock. The city council is also actively trying to decarbonise local industries including transport, this is seen by the strategies and targets in place such as Net Zero by 2045. An aim of this study is to demonstrate how low carbon hydrogen production technologies could fit into the city’s transport and energy plan and support the hydrogen strategy, thereby benefitting the people of Glasgow. Whilst Glasgow does not currently use fuel cell electric buses (FCEB) for public transport, an intention to run a fleet has been presented through the publication of the Scottish Governments Hydrogen Policy Statement (2020) and Hydrogen Action Plan (2022). FCEB fleets in other parts of the UK notably London and Birmingham, have shown the environmental benefit through the annual carbon savings made. FCEBs are classified as zero emissions buses (ZEB) which the UK Department of Transport has stated can reduce carbon emissions by 46 tonnes per year and nitrogen oxide (NOx) by 23kg when compared to a diesel bus (UK Government Department for Transport, 2021).

This study contributes to the growing evidence of the benefits of using hydrogen as a transport fuel in terms of the carbon savings as an alternative to conventional fossil fuels. Whilst the main concerns of the underdeveloped industrial status, relatively immature technology and high costs are explored. In practice WtH is currently limited to laboratory and pilot scale systems and requires further investment and policy support for advancements to be made. These bottlenecks and limitations are considered in the discussion section of this study.

The research question centres around the economic and environmental feasibility of WtH within Glasgow. A feasible project would show the carbon savings compared to conventional methods in both aspects of waste management and hydrogen production. The feasibility is also a measurement of positive returns on economic investment where total project costs do not outweigh the environmental benefits associated with low carbon technologies. This study critically assesses the current situation for WtH development in terms of the environmental impact and potential carbon savings, economic implications, and cost benefits, plus transport and climate policy. The novelty of the study establishes a procedure for defining how WtH could support the growing hydrogen industry as a low carbon hydrogen production technique. The results from the environmental impact analysis and economic assessment add data sets to existing research in academia and energy industry. Life cycle assessment (LCA), cost benefit analysis (CBA) and multi-bjective optimization (MOO) have been conducted to determine the feasibility of WtH projects to support green transport systems and sustainable waste management schemes. A variety of WtH scenarios were designed based on biomass waste feedstock, hydrogen production reactors, and upstream and downstream system components. The WtH systems selected use thermochemical and biochemical technologies to convert the different waste feedstocks available in Glasgow with suitable operational conditions according to the waste characteristics. The waste considered in this study is biodegradable, carbon based and organic including household, plastics, waste wood products, as well as the wet fraction of waste such as food and sewage sludge.

Five scenarios, four WtH technologies and one conventional hydrogen production technology of steam methane reforming (SMR), were designed to allow for comparison of environmental and economic results. The scenarios differ in waste feedstock type and technology leading to differences in hydrogen production rates, hydrogen yields, and process carbon emissions. Waste that is less suitable for thermochemical conversion processes can be utilised by biochemical technology to ensure the most efficient and least energy intensive method is applied.

The environmental approach for this work focuses on the LCA method to evaluate environmental performance through the carbon saving potential using global warming potential (GWP) as the impact indicator for the WtH technologies. It was shown that WtH technologies could reduce <55% of CO2-eq emissions per kg H2 compared to SMR. Gasification treating municipal solid waste and waste wood had global warming potentials of 4.99 and 4.11 kg CO2-eq/kg H2 respectively, which were lower than dark fermentation treating wet waste at 6.6 kg CO2-eq/kg H2 and combined dark and photo fermentation at 6.4 kg CO2-eq/kg H2. The distance emissions of WtH-based electric fuel cell bus scenarios were 0.33-0.44 kg CO2-eq/km as compared to 0.89 kg CO2-eq/km for the SMR-based scenario.

The economic assessment in this study uses cost benefit analysis to determine whether the carbon savings outweigh the expected cost of a WtH system. The CBA was conducted to compare the economic feasibility of the different WtH systems with the conventional SMR. A database was that includes, direct cost data on construction, maintenance, operations, infrastructure, and storage, along with indirect cost data comprising environmental impacts and externalities, cost of pollution, carbon taxes and subsidies was collated. The results are in the form of economic indicators Net present value (NPV), Internal rate of return (IRR), Benefit cost ratio (BCR) and Levelized cost of hydrogen (LCoH). The LCoH was calculated as 0.49 GBP/kg for the gasification systems using MSW feedstock and 0.52 GBP/kg for waste wood gasification. The LCoH for dark fermentation was calculated to be 0.52 GBP/kg and 0.59 GBP/kg for combined dark and photo fermentation systems. Sensitivity analysis was conducted to identify the most significant influential factors of distributed WtH systems. The results indicate that the conversion efficiency and the energy density of the waste had the largest impact for biochemical technology and thermochemical technologies, respectively. It is concluded that WtH could be economically feasible for hydrogen production in Glasgow. However, limitations including high capital expenditure will require cost reduction through technical advancements and carbon tax on conventional hydrogen production methods to improve the outlook for WtH. The multi-objective optimisation results suggest that optimisation is possible with the best solution calculated to minimise both total cost and GWP for the four Scenarios assessed in this work.

The results from the three analysis types in this work, indicate the feasibility of WtH in Glasgow. The results suggest there is potential to utilise the waste generated within Glasgow to produce hydrogen, reduce the environmental impact of waste management practices, and provide economic benefit to both the energy and transport industry.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Supported by funding from the Engineering and Physical Sciences Research Council (EPSRC).
Subjects: T Technology > T Technology (General)
Colleges/Schools: College of Science and Engineering > School of Engineering > Systems Power and Energy
Supervisor's Name: You, Dr. Siming
Date of Award: 2023
Depositing User: Theses Team
Unique ID: glathesis:2023-83773
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 24 Aug 2023 10:40
Last Modified: 24 Aug 2023 10:43
Thesis DOI: 10.5525/gla.thesis.83773
URI: https://theses.gla.ac.uk/id/eprint/83773
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