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The depletion of fossil fuels together with growing environmental concerns have created incitement for developing a more energy-efficient and environmentally-friendly vehicle fleet. The development towards cleaner heavy-duty vehicles started already in the 80’s with the introduction of emission legislations. Initially, engine optimization was enough for reaching the legislated levels of emissions. However, at present engine optimization is not enough but exhaust aftertreatment has become an essential part of heavy-duty vehicles, in order to meet the emission standards. Today, the total emissions are targeted which means that there is an interest in decreasing the idling emissions as well as the emissions during operation. To reduce the overall emissions several states in the USA have introduced idling legislations. Due to the limitations in idling time alternative solutions for power generation during rests are requested. A possible alternative is a fuel cell auxiliary power unit, combining a fuel cell with a fuel reformer (FC-APU).  The focus of this thesis is the development of the fuel reformer for an FC-APU, in which the hydrogen to the fuel cell is generated from diesel in a high-temperature catalytic process. The produced hydrogen can also be used in other heavy-duty vehicle applications i.e. selective catalytic reduction of NOx (HC-SCR), where addition of hydrogen is essential for reaching high conversion at low temperatures. The effect of using hydrogen from a fuel reformer in HC-SCR is included in this work. The catalytic material development is focused on developing promoted materials with lower rhodium content but with catalytic activity comparable to that of materials with higher rhodium content. This includes evaluation and extensive characterization of both fresh and aged promoted materials. The work also includes reactor design where a micro reactor with multiple air inlets is evaluated. This work has contributed to increased knowledge of catalytic materials suitable for reforming of diesel. By changing the support material from the traditionally used alumina to ceria-zirconia, increased H2 yield was achieved. In addition, the ceria-zirconia supported material was less prone to coke. By promoting the material with cobalt or lanthanum it was possible to decrease the rhodium content by 2/3 with enhanced catalytic performance. It was also discovered that promotion with lanthanum decreased the tendency for coking even further. Additionally, the lanthanum-promoted material had higher thermal stability as well as a stable highly dispersed rhodium phase. Furthermore, the work has contributed to an increased knowledge concerning the fuel reformer’s effect on HC-SCR. The work displays clear evidence of benefits with using hydrogen-rich gas from a fuel reformer instead of pure hydrogen. The benefits are derived from the content of low molecular weight hydrocarbons present in the hydrogen-rich gas, which are strong reducing agents increasing the NOx reduction. This finding proves that fuel reforming in combination with HC-SCR is a viable option for NOx abatement. / <p>QC 20150202</p>

Syngas, a combustible gaseous mixture of hydrogen, carbon monoxide, and other species, is a promising fuel for efficient energy conversion technologies. Syngas is produced by breaking down a primary fuel into a hydrogen-rich mixture in a process called fuel reforming. The motivation for the utilization of syngas rather than the primary fuel is that syngas can be used in energy conversion technologies that offer higher conversion efficiencies, e.g. gas turbines and fuel cells. One approach for syngas production is partial oxidation, which is an oxygen starved combustion process that does not require a catalyst. Efficient conversion to syngas occurs at high levels of oxygen depletion, resulting in mixtures that are not flammable in conventional combustion applications. In non-catalytic partial oxidation, internal heat recirculation is used to increase the local reaction temperatures by transferring heat from the product stream to pre-heat the fuel/air mixture before reactions occur, thus increasing reaction rates and allowing for combustion outside the conventional flammability limits. As peak temperatures lie above the adiabatic equilibrium temperature predicted by thermodynamic calculations, the combustion regime used for non-catalytic fuel reforming is referred to as 'superadiabatic'. Counter-flow heat exchange is an effective way to transfer heat between adjacent channels and is used for a novel, heat-recirculating fuel reformer design. An analytical study predicts that combustion zone locations inside adjacent flow channels adjust to operating conditions, thus stabilizing the process for independent variations of flow velocities and mixture compositions. In experiments, a reactor prototype with four channels with alternating flow directions is developed and investigated. Tests with methane/air and propane/air mixtures validate the operating principle, and measurements of the resulting syngas compositions verify the feasibility of the concept for practical fuel-reformer applications. Results from a two-dimensional numerical study with detailed reaction chemistry are consistent with experimental observations. Details of the reaction zone reveal that reactions are initiated in the vicinity of the channel walls, resulting in "tulip"-shaped reaction layers. Overall, results confirm the viability of the non-catalytic reactor design for fuel reforming applications. / text

In the effort to introduce fuel cell technology in the field of decentralized and mobile power generators, a hydrocarbon reformer to syngas seems to be the way for the market uptake. In this thesis, a potential technology is developed and investigated, in order to convert commercial liquid fuel (diesel, kerosene and biodiesel) to syngas. The fundamental concept is to oxidise the fuel in a oxygen depleted environment, obtaining hydrogen and carbon monoxide as main products of the reaction. In order to extend the flammability limit of hydrocarbon/air mixtures, the rich combustion experiments have been carried out in a two-layer porous medium combustor, which stabilises a flame at the matrix interface and recirculates the enthalpy of the hot products in order to enhance the reaction rates at ultra-rich equivalence ratio. This thesis demonstrates the feasibility of the concept, by exploring characteristic parameters for a compact, reliable and cost effective device. Specifically, a range of equivalence ratios, thermal loads and porous materials have been examined. n-heptane was successfully reformed up to an equivalence ratio of 3, reaching a conversion efficiency (based on the lower heating value of H2 and CO over the fuel input) up to 75% for a packed bed of alumina beads. Thermal loads from P=2 to 12 kW at phi=2.0 demonstrated that heat losses can be reduced to 10%.Similarly, diesel, kerosene and bio-diesel were reformed to syngas in a Zirconia foam burner with conversion efficiency over 60%. The effect of different burners, thermal loads and equivalence ratios have also been assessed for these commercial fuels, leading to equivalent conclusions. A preliminary attempt to reduce the content of CO and hydrocarbons in the reformate has been also performed using commercial steam reforming and water-gas shift reaction catalysts, obtaining encouraging results. Finally, soot emission has been assessed, demonstrating particle formation for all the fuels above phi=2.0, with biodiesel showingthe lowest soot formation tendency among all the fuels tested.

Distributed hydrogen generation from liquid hydrocarbon fuels to supply portable fuel cells presents an attractive, high energy density alternative to current battery technology. Traditional unit operation reactor design for hydrogen generation becomes inadequate with decrease in scale because of the unique challenges of size and weight minimization. To address the challenge of reactor scale-down, the concept of multifunctional reactors has emerged, in which synergistic combination of different unit operations is explored to achieve improved performance. The direct droplet impingement reactor (DDIR) studied here is based on this approach in which the liquid feed is atomized using a regularly spaced array of droplet generators with unparalleled control over droplet characteristics, followed by vaporization and reaction directly on the catalyst surface. Considering each droplet generator in the array as a unit cell, a comprehensive, first-principles model of the DDIR has been developed by considering the intimately coupled processes of 1) droplet transport, heating, evaporation, and impingement on the catalyst surface, 2) liquid reagent film formation, capillary penetration, and vaporization within the catalyst layer, and 3) gas phase heat and mass transfer and catalytic reactions. Simulations are performed to investigate the effect of reactor operating parameters on performance. Experimental validation of the model is carried out by visualizing droplet impingement and liquid film accumulation while simultaneously monitoring reaction product composition over a range of operating conditions. Results suggest an optimal unit cell shape for reaction selectivity based on a balance between reagent back diffusion and catalyst bed thermal resistance. Further, achieving a target throughput is best accomplished by adding together a larger number unit cells with optimized geometry and lower throughput (per unit cell) to more effectively spread heat and avoid hotspots at the catalyst interface. At the same time, conditions must be satisfied for ensuring droplet impingement on the catalyst surface, which become more stringent as unit cell throughput is decreased.

The member states of European Union aim to promote the reduction of harmful emissions. Emissions from combustion processes cause effects on human health and pose environmental issues, for example by increasing greenhouse effect. There are two ways to reduce emissions; one is to promote renewable energy sources and the other to utilize more effectively the available fossil fuels until a long-term solution is available. Hence, it is necessary to strive for CO2 mitigation technologies applied to fossil fuels. Low natural gas prices together with high energy efficiency have made gas turbines popular in the energy market. But, gas turbine fired with natural gas come along with emissions of CO2, NOx and CO. However, these disadvantages can be eliminated by using gas turbine with precombustion CO2 capture, separating carbon from the fuel by using fuel reforming process and feeding pure hydrogen as a fuel. Hydrogen fired gas turbines are used in two applications such as a gas turbine with pre-combustion CO2 capture and for renewable power plants where hydrogen is stored in case as a backup plan. Although the CO2 emissions are reduced in a hydrogen fired gas turbine with a pre-combustion CO2 capture, there are still several challenges such as high flame temperatures resulting in production of thermal NOx. This project suggests a method for application of hydrogen fired gas turbine, using exhaust gas recirculation to reduce flame temperature and thus reducing thermal NOx. A NOx emission model for a hydrogen-fired gas turbine was built from literature data and used to select the best operating conditions for the plant. In addition, the economic benefits of switching from natural gas to pure hydrogen are reported. For the techno-economic analysis, investment costs and operating costs were taken from the literature, and an economic model was developed. To provide sensitivity analysis for the techno-economic calculation, three cases were studied. Literature review was carried out on several journal articles and websites to gain understanding on hydrogen and natural gas fired gas turbines. Results showed that, in the current state, pure hydrogen has high delivery cost both in the US and Europe. While it’s easy to access natural gas at low cost, therefore in the current state gas turbine fired with natural gas are more profitable than hydrogen fired gas turbine. But, if targeted hydrogen prices are reached while fuel reforming process technology are developed in the coming future the hydrogen fired gas turbine will compete seriously with natural gas.

abstract: As world energy demands increase, research into more efficient energy production methods has become imperative. Heterogeneous catalysis and nanoscience are used to promote chemical transformations important for energy production. These concepts are important in solid oxide fuel cells (SOFCs) which have attracted attention because of their potential to provide an efficient and environmentally favorable power generation system. The SOFC is also fuel-flexible with the ability to run directly on many fuels other than hydrogen. Internal fuel reforming directly in the anode of the SOFC would greatly reduce the cost and complexity of the device. Methane is the simplest hydrocarbon and a main component in natural gas, making it useful when testing catalysts on the laboratory scale. Nickel (Ni) and gadolinium (Gd) doped ceria (CeO2) catalysts for potential use in the SOFC anode were synthesized with a spray drying method and tested for catalytic performance using partial oxidation of methane and steam reforming. The relationships between catalytic performance and structure were then investigated using X-ray diffraction, transmission electron microscopy, and environmental transmission electron microscopy. The possibility of solid solutions, segregated phases, and surface layers of Ni were explored. Results for a 10 at.% Ni in CeO2 catalyst reveal a poor catalytic behavior while a 20 at.% Ni in CeO2 catalyst is shown to have superior activity. The inclusion of both 10 at.% Gd and 10 at.% Ni in CeO2 enhances the catalytic performance. Analysis of the presence of Ni in all 3 samples reveals Ni heterogeneity and little evidence for extensive solid solution doping. Ni is found in small domains throughout CeO2 particles. In the 20 at.% Ni sample a segregated, catalytically active NiO phase is observed. Overall, it is found that significant interaction between Ni and CeO2 occurs that could affect the synthesis and functionality of the SOFC anode. / Dissertation/Thesis / M.S. Materials Science and Engineering 2012

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17555号 / 工博第3714号 / 新制||工||1566(附属図書館) / 30321 / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 中部 主敬, 教授 牧野 俊郎, 教授 小森 悟 / 学位規則第4条第1項該当