| 1. |
- Mohseni, Farzad, 1981-
(författare)
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Power to gas : Bridging renewable electricity to the transport sector
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Globally, transport accounts for a significant part of the total energy utilization and is heavily dominated by fossil fuels. The main challenge is how the greenhouse gas emissions in road transport can be addressed. Moreover, the use of fossil fuels in road transport makes most countries or regions dependent on those with oil and/or gas assets. With that said, the question arises of what can be done to reduce the levels of greenhouse gas emissions and furthermore reduce dependency on oil? One angle is to study what source of energy is used.Biomass is considered to be an important energy contributor in future transport and has been a reliable energy source for a long time. However, it is commonly known that biomass alone cannot sustain the energy needs in the transport sector by far.This work presents an alternative where renewable electricity could play a significant role in road transport within a relatively short time period. Today the amount of electricity used in road transport is negligible but has a potential to contribute substantially. It is suggested that the electricity should be stored, or “packaged” in a chemical manner, as a way of conserving the electrical energy. One way of doing so is to chemically synthesize fuels. It has been investigated how a fossil free transport system could be designed, to reach high levels of self-sufficiency. According to the studies, renewable electricity could have the single most important role in such a system. Among the synthetic fuels, synthetic methane (also called synthetic biogas) is the main focus of the thesis. Hydrogen is obtained through water electrolysis, driven by electricity (preferable renewable), and reacted with carbon dioxide to produce synthetic methane. The concept of the mentioned process goes under the name Power to Gas. The electricity to fuel efficiency of such a process reaches about 50 %, but if utilizing excess heat produced during the electrolysis and the reaction, the total process efficiency can reach much higher levels.The economics of the process is as important as the technology itself in terms of large scale implementation. The price of electricity and biogas are the most important influences on the economic viability. The minimum “spread” between purchase and selling price can be determined to obtain a general perception of the economic feasibility. In this case biogas must be sold about 2.6 times higher than purchased electricity per kWh.
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| 2. |
- Tingelöf, Thomas, 1979-
(författare)
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Polymer Electrolyte Fuel Cells in Reformate Power Generators
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The topic of this thesis is the generation of electricity from hydrocarbon fuels via polymer electrolyte fuel cells (PEFC). The aim has been to develop methods and hardware for experimental evaluation of process parameters and design variables in PEFC reformate cells and stacks. Reformate fuel cell systems have the potential to offer a way for utilizing fuels efficiently with low global and local emissions. Reforming of hydrocarbon fuels may also provide a way around the famous “chicken or egg” dilemma of hydrogen vehicles and infrastructure. In this thesis current distribution measurements are introduced as a tool for investigating the current distribution in a PEFC with Pt/C or PtRu/C anode catalyst as function of reformate fuel gas composition. It is shown that CO may induce a strong transient behavior, with respect to current density, on both Pt/C and PtRu/C catalysts, depending on mode of operation. Analysis of the exhaust fuel gas showed that the oxygen in the air bleed most likely reacts close to the anode inlet, but this is not visible in the measured current density plots. The time dependence of the CO poisoning reactions is studied more closely in a commercial fuel cell stack. The development of a test fuel cell system, called multisinglecell, that can multiply the capacity of a conventional test station is reported. The setup is successfully demonstrated with initial screening of the corrosion resistance of different stainless steel grades and coatings. Most of the iron originating from a stainless steel sample accumulates in the MEA and GDLs. These results were validated with a similar measurement in a commercial fuel cell stack. The experimental validation of a 3D FEM computer endplate model, which can accurately predict pressure distribution within any type of fuel cell at any temperature, is described. The model could reliably predict trends in changes in the compression pressure distribution. The PBI fuel cell competes with the PEFC in small-scale power applications. A high temperature break-in procedure for PBI fuel cells is developed, which can rapidly and reproducibly ensure stable cell behavior.
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| 3. |
- Hedström, Lars
(författare)
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Fuel Cells and Biogas
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns biogas-operated fuel cells. Fuel cell technology may contribute to more efficient energy use, reduce emissions and also perhaps revolutionize current energy systems. The technology is, however, still immature and has not yet been implemented as dominant in any application or niche market. Research and development is currently being carried out to investigate whether fuel cells can live up to their full potential and to further advance the technology. The research of thesis contributes by exploring the potential of using fuel cells as energy converters of biogas to electricity. The work includes results from four different experimental test facilities and concerns experiments performed at cell, stack and fuel cell system levels. The studies on cell and stack level have focused on the influence of CO, CO2 and air bleed on the current distribution during transient operation. The dynamic response has been evaluated on a single cell, a segmented cell and at stack level. Two fuel cell systems, a 4 kW PEFC system and a 5 kW SOFC system have been operated on upgraded biogas. A significant outcome is that the possibility of operating both PEFCs and SOFCs on biogas has been established. No interruptions or rapid performance loss could be associated with the upgraded biogas during operation. From the studies at cell and stack level, it is clear that CO causes significant changes in the current distribution in a PEFC; air bleed may recover the uneven current distribution and also the drop in cell voltage due to CO and CO2 poisoning. The recovery of cell performance during air bleed occurs evenly over the electrode surface even when the O2 partial pressure is far too low to fully recover the CO poisoning. The O2 supplied to the anode reacts on the anode catalyst and no O2 was measured at the cell outlet for air bleed levels up to 5 %. Reformed biogas and other gases with high CO2 content are thus, from dilution and CO-poisoning perspectives, suitable for PEFC systems. The present work has enhanced our understanding of biogas-operated fuel cells and will serve as basis for future studies.
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| 4. |
- Magnusson, Mimmi, 1980-
(författare)
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Energy systems studied of biogas : Generation aspects of renewable vehicle fuels in the transport system
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The transport sector is seen as particularly problematic when concerns about climate change and dependency on fossil energy are discussed. Because of this, bioenergy is strongly promoted for use in the transport sector, both on a European level and nationally in Sweden. Even though bioenergy is considered one of the key solutions, it is generally agreed that both supply- and demand-side measures will be needed to achieve a change to a more sustainable transport system. One of the reasons for this is the limited availability of biomass, especially agricultural feedstocks competing with food or feed production. Woody biomass, however more abundant, is also exposed to tough competition from other sectors. In this thesis, the role of biogas as a vehicle fuel in a future sustainable transport system is discussed together with the prerequisites needed to realise such a transport system. Biogas is a biofuel that could be produced in several different ways: by anaerobic digestion, which is a first-generation production route, by gasification, which is a second-generation process, and by catalytic reduction of carbon dioxide, a third-generation technology. The main focus in this thesis is on biogas produced by anaerobic digestion and the results show that there is a significant potential for an increase compared to today’s production. Biogas from anaerobic digestion, however, will only be able to cover a minor part of the demand in the Swedish transport sector. Considering biogas of the second and third generations, the potential for production is more uncertain in a mid-term future, mainly due to competition for feedstock, the possibility to produce other fuels by these processes, and the present immaturity of the technology. The limited potential for replacing fossil vehicle fuels, either by biogas or other renewable fuels, clearly shows the need for demand-side measures in the transport system as well. This thesis shows the importance of technical and non-technical means to decrease the demand for transport and to make the transport as efficient as possible. The results show that both energy-efficient vehicles and behavioural and infrastructural changes will be required. Policies and economic incentives set by governments and decision-making bodies have a prominent role to play, in order to bring about a shift to a more sustainable transport system, however, measures taken on individual level will also have a great impact to contribute to a more sustainable transport system.
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| 5. |
- Sadegh-Vaziri, Ramiar, 1987-
(författare)
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Biomass to Biofuel : Syngas Cleaning and Biomass Feedstock
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis builds around the idea of a biofuel production process that is comprised of biomass production, biomass gasification, gas cleaning, and fuel production. In this work, we specifically looked into H2S removal as a part of cleaning the producer gas and flocculation of microalgae which is involved in the harvesting of microalgae after biomass production. One of the impurities to remove from the producer gas is hydrogen sulfide which can be removed by using a packed bed of zinc oxide. Despite the regular use, it was only recently shown that during reaction with H2S, nano-size particles of ZnO exhibit void formation and outward growth. In this work, a micro-scale model was introduced to describe the void formation and outward growth. On the macro-scale, the simulations captured pore clogging of pellets due to the outward growth. The pore clogging prevents the full conversion of pellets and consequently leads to shorter breakthrough times of beds. The second problem investigated here deals with the flocculation of microalgae. Microalgae is produced in relatively low concentrations in the incubator liquid medium and during the harvesting, the concentration is increased to an acceptable level. The harvesting process includes a flocculation followed by a filtration or centrifuge unit. During flocculation, microalgae are stimulated to aggregate and form clusters. The experiments showed that the mean size of clusters formed during flocculation increases with time to a maximum and then starts decreasing, resulting in an overshoot in the mean size profile. The size of clusters influence the efficiency of the afterward filtration or centrifuge, thus it is of interest to carefully track the size evolution of clusters, making the studying of overshoot a crucial research topic. In this work, the possible mechanisms behind this overshoot were investigated.
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| 6. |
- Svens, Pontus, 1970-
(författare)
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Development of a Novel Method for Lithium-Ion Battery Testing on Heavy-Duty Vehicles
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing demands for lower environmental impact from vehicles, including heavy-duty vehicles, have driven several vehicle manufacturers to consider adding hybrid electrical vehicles (HEV’s) to the product portfolio. Present research on batteries for HEV’s is mainly focused on lithium-ion battery chemistries, since lithium-ion batteries has the most promising technical potential compared to other types of batteries. However, the uncertainty regarding battery lifetime combined with a high battery cost can have a negative impact on large scale commercialisation of heavy-duty hybrid vehicles in the near future. A large part of present lithium-ion battery research is focused on new materials, but there is also research focusing on ageing of already established lithium-ion battery chemistries. Cycle ageing of batteries often includes complete charging and discharging of batteries or the use of standardized test cycles. Battery cycling in real HEV applications is however quite different compared to this kind of laboratory testing, and real life testing on vehicles is a way of verifying the soundness of laboratory ageing. The aim of this study was to develop a test method suitable for real life testing of lithium-ion batteries for heavy-duty HEV-usage, with the purpose of investigating the correlation of battery ageing and usage in real life applications. This concept study includes both cell level battery cycling and performance testing on board vehicles. The performance tests consist of discharge capacity measurements and hybrid pulse power characterization (HPPC) tests. The main feature of this test equipment is that it is designed to be used on conventional vehicles, emulating an HEV environment for the tested battery. The functionality of the equipment was verified on a heavy-duty HEV with satisfying results. Results from real life testing of 8 batteries using the developed test equipment on four conventional heavy-duty trucks shows that the concept of comparing battery ageing with battery usage has a most promising potential to be used as a tool when optimizing battery usage vs. lifetime. Initial results from this real life study shows significant differences in state of charge (SOC) and power distributions between cycled batteries, but so far only small differences in ageing. Lithium-ion batteries of the type lithium manganese spinel/lithium titanate (LMO/LTO) were used in this study.
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| 7. |
- Zhang, Chi
(författare)
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Sustainable Business Innovation of Photovoltaic Water Pumping Systems
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of renewable energy technology provides an effective approach to replace fossil fuels for greenhouse gas (GHG) emission. Technological innovation and transfer are the main driving forces in promoting renewable energy usage, because of the better efficiency and economic payback under an emission reduction target. With three of the mechanisms of emission trading originating from the Kyoto Protocol, the most wildly accepted and important mechanism between developed and developing countries is the Clean Development Mechanism (CDM). The CDM has been implemented contributing the most of the trading carbon credits. In this study, by extracting and building an exclusive database of issued Chinese CDM projects, a modified multivariable logistic regression model for technology transfer’s correlation test with 11 extended indicators was investigated for the first time. Renewable energy projects were analyzed with certified emission reduction (CER) sizes, economic development, and geographic scopes.In addition, technological innovation should also be enhanced with new business developments to demonstrate and scale up technologies for better economic and environmental performances. This doctoral thesis studied photovoltaic water pumping (PVWP) technology as a technological solution for integration with the new business model for development and co-benefits. The integration of PVWP with water saving irrigation techniques and sustainable management of water resources, leads to technical innovations, economic benefits, and climate benefits. Field measurements at a pilot PVWP system in Inner Mongolia were conducted with detailed economic performance analyses. Different scenarios for PVWP systems considering variant market incentives were proposed with internal rate of return (IRR), and discounted payback period analyses to develop a new business model approach for implementing PVWP systems with multi-value propositions. The environmental externalities were successfully addressed by evaluating the CO2 emission reduction credits. The economic assessment of feasible and optimal production processes for implementing PVWP systems in dairy milk production was conducted with self-supplied energy and forage assumptions. In comparison with other financing mechanisms, discrete choice model analyses were employed with interviews and costumer behavior surveys to explore the willingness to purchase through crowd funding mechanisms in financing integrated PVWP systems.The results showed that emission reduction mechanisms, such as CDM, have promoted the renewable energy development in China with the national incentives at an entrance level. Yet, the limited sizes and lower income from CERs of renewable energy projects than other projects, required renewable energy projects to develop more advanced technological innovations and business model innovations. The PVWP systems represent the better technical and economic solutions under a feasible innovated business model in comparison with traditional photovoltaic (PV) systems and current PV business models. The dairy farms with integrated PVWP systems and self-sufficient feeds could improve their investment performance through extra energy saving and CO2 emission reductions. The semi-structured interviews and customer surveys’ results showed that customers can tolerate high prices, and are willing to crowd-fund nutritious and secure cow milk with environmental compensation characters. The results from the PVWP technology integration in China as a specific PV application study can be further applied for the business model of innovation of renewable energy systems in other regions of the world under emission reduction targets leading to economic and environmental benefits.
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| 8. |
- Guan, Tingting
(författare)
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Biomass-fuelled PEM FuelCell systems for small andmedium-sized enterprises
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomass-fuelled proton exchange membrane fuel cells (PEMFCs) offer asolution for replacing fossil fuel for hydrogen production. Through using thebiomass-derived hydrogen as fuel, PEMFCs may become an efficient andsustainable energy system for small and medium-sized enterprises. The aim ofthis thesis is to evaluate the performance and potential applications of biomassfuelledPEMFC systems which are designed to convert biomass to electricity andheat. Biomass-fuelled PEMFC systems are simulated by Aspen plus based ondata collected from experiments and literature.The impact of the quality of the hydrogen-rich gas, anode stoichiometry, CH4content in the biogas and CH4 conversion rate on the performance of the PEMFCis investigated. Also, pinch technology is used to optimize the heat exchangernetwork to improve the power generation and thermal efficiency.For liquid and solid biomass, anaerobic digestion (AD) and gasification (GF),respectively, are relatively viable and developed conversion technologies. ForAD-PEMFC, a steam reformer is also needed to convert biogas to hydrogen-richgas. For 100 kWe generation, the GF-PEMFC system yields a good technicalperformance with 20 % electrical efficiency and 57 % thermal efficiency,whereas the AD-PEMFC system only has 9 % electrical efficiency and 13 %thermal efficiency. This low efficiency is due to the low efficiency of theanaerobic digester (AD) and the high internal heat consumption of the AD andthe steam reformer (SR). For the environmental aspects, the GF-PEMFC systemhas a high CO2 emissions offset factor and the AD-PEMFC system has anefficient land-use.The applications of the biomass-fuelled PEMFC systems are investigated on adairy farm and an olive oil plant. For the dairy farm, manure is used as feedstockto generate biogas through anaerobic digestion. A PEMFC qualified for 40 %electrical efficiency may generate 360 MWh electricity and 680 MWh heat peryear to make a dairy farm with 300 milked cows self-sufficient in a sustainableway. A PEMFC-CHP system designed for an olive oil plant generating annual 50000 m3 solid olive mill waste (SOMW) and 9 000 m3 olive mill waste water(OMW) is simulated based on experimental data from the Biogas2PEM-FCproject1. After the optimization of the heat exchanger network, the PEMFC-CHP system can generate 194 kW electricity which corresponds to 62 % of the totalelectricity demand of the olive oil plant.The economic performance of the PEMFC and biogas-fuelled PEMFC areassessed roughly including capital, operation & maintenance (O&M) costs of thebiogas plant and the PEMFC-CHP, the cost of heat and electricity, and the valueof the digestate as fertilizer.
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| 9. |
- Larsson, Mårten
(författare)
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The role of methane and hydrogen in a fossil-free Swedish transport sector
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Drastic reductions of greenhouse gas emissions are required to limit the severe risks associated with a changing climate. One measure is to disrupt the fossil-fuel dependency in the transport sector, but it appears difficult and costly in comparison to other measures.Vehicles and fuels are available, but no single alternative can replace petrol and diesel in all parts of the transport system. None of them are ideal regarding all of the following aspects: vehicle performance, fuel production potential, sustainability, infrastructure, technology development and economy. Instead, several fuels are needed.In this thesis, the aim is to investigate the role of methane and hydrogen in a fossil- free vehicle fleet in Sweden, and compare them with other fuels in terms of well-to-wheel energy efficiency and economy. Processes for producing methane from biomass, waste streams from pulp mills and electricity are studied with techno-economic methods. Furthermore, well-to-wheel studies and scenarios are used to investigate the fuel chains and the interaction with the energy and transport systems.Effects of policy instruments on the development of biogas in the Swedish transport sector are also analysed and policy instruments are suggested to increase the use of methane and to introduce hydrogen and fuel cell electric vehicles. The results reveal that tax exemptions and investment support have been and will continue to be important policy instruments, but that effective policy instruments are needed to develop fuelling infrastructure and to support alternative vehicles.Electricity will be an important transport fuel for several reasons; the electric powertrain enables high energy efficiency and electricity can be produced from various renewable energy sources. Nevertheless, other fuels will be needed as complements to electricity. The results reveal that methane and hydrogen and associated vehicles may be necessary to reach a fossil-free vehicle fleet in Sweden. These fuels have several advantages:- The function of the vehicles resembles conventional vehicles but with lower local and global emissions.- Methane is a well proven as a transport fuel and hydrogen infrastructure and FCEVs, are commercial or close to commercialisation.- They enable high well-to-wheel energy efficiency.- They can be produced from renewable electricity and act as energy storage.
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| 10. |
- Tan, Yuting, 1989-
(författare)
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Thermo-physical properties of CO2 mixtures and their impacts on cryogenic carbon capture processes
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Carbon capture and storage (CCS) is one of the most promising technologies that may significantly reduce CO2 emissions. A better understanding of the thermo-physical properties of CO2 mixtures is required for the design and operation of different CCS processes. Before the knowledge gaps of the property models are being filled, it is important to identify the properties that can significantly influence the processes and find the proper property models. In this thesis, the status and progress of property impacts on CCS processes were reviewed by a literature survey. The studied CCS processes in this thesis include CO2 conditioning, transport, and storage. The results show that heat capacity and density are most important for the pumping process in CO2 conditioning systems, while heat capacity and compressibility have greater impacts on compression processes. In addition, density is the most important in CO2 pipeline transport and CO2 storage.To follow up the knowledge gaps of the property impacts identified in the literature survey, quantitative impacts of the related properties on design and operation of key components including the multi-stream plate-fin heat exchanger and the centrifugal compressor, as well as the cryogenic process performance, were investigated by a sensitivity analysis. The results show that thermal conductivity has the most significant impact on heat exchanger sizing. Density and enthalpy have the most significant impact on the compressor impeller diameter and on the isentropic efficiency. In addition, thermal conductivity has the most significant impact on the capture rate of CO2, CO2 purity, and the operation cost of the cryogenic separation process. Hence, developing a more accurate thermal conductivity model should be prioritized for process design and operation of the cryogenic separation.The performances of the thermal conductivity and viscosity models were evaluated for CO2 mixtures with non-condensable impurities. The results show that the KRW (Kestin-Ro-Wakeham) model is recommended for predicting the viscosity. For estimating thermal conductivity, the GERG (Groupe Européen de Recherches Gazières) model is the most accurate.
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