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Hydrogen fuel cell applications are set to ameliorate the world's energy woes, yet there still exists problems that need to be overcome in terms oftheir fuelling. While compressed storage, cryogenic storage, chemical storage, and adsorptive storage solutions exist, none meet the requirements that are needed to facilitate a replacement for the gasoline powered automobile. Metal hydrides have been long studied as an alternative method for storing hydrogen safely and efficiently, with significant developments being made in advanced alloys. While this research is beneficial, it was theorized that an externally applied magnetic field might augment the storage properties of existing magnetically susceptible metal hydrides, without trial and error alloy development. Constant volume hydrogen absorption experiments were conducted using LaNi5 in order to test this theory. A known amount of LaNi5 was exposed to hydrogen, with the absorption equilibrium data collected over a period of 6 hours. An equal sample was then exposed to hydrogen with a 0.7 Tesla applied field applied to the sample. There was a distinct difference between the absorption curves of the two equal samples, with the sample under the influence of the magnetic field achieving an absorption of only 0.60% wt. in comparison with the unmodified sample which absorbed 0.88% wt. It was concluded that the presence of an externally applied magnetic field has a negative effect on the overall capacity of LaNis through the prevention of a shift in the inner lattice structure of LaNis that would otherwise permit an increased hydrogen capacity. This effect while negative in terms of overall storage capacity could have a possible benefit in terms of the desorption of the stored hydrogen, as the magnetic field could be used in lieu of an increase in temperature in order to drive the hydrogen from the fully filled structure. / Thesis / Master of Applied Science (MASc)

Hydrogen use in a gas turbine engine has many benefits. Chief among these is the elimination of carbon based emissions. The only products and emissions from the combustion process are water vapor and oxides of nitrogen (NOx). However due to the lower flammability limit of hydrogen, it can be burned at much lower equivalence ratios that typical hydrocarbon fuels, and thus reducing the emissions of NOx. Multiple efforts have been made for the design of premixing injectors for gaseous hydrocarbon fuels, but very few attempts have been made for hydrogen. To this end a premixing hydrogen injector was designed for the cruise engine condition for a PT6-20 turboprop engine. Swirl generated by tangential entry was utilized as a means to enhance mixing and as a convenient means to stabilize the flame. A prototype was designed to prevent flashback and promote a high degree of mixing, as well as a test combustor to evaluate the performance of the injector at scaled engine conditions. Numerical simulations were also performed to analyze the flowfield at the engine conditions. Performance and emissions data are used to draw conclusions about the feasibility of the injectors in the PT6 engine. / Master of Science

The overall performance of a hydrogen storage system can be affected by various parameters, such as operation and design parameters, but also by the state of the hydrogen contained inside the storage tanks. In this work, a methodology is developed to evaluate the state of the hydrogen during the filling process and its impact on the overall system performance under variable operation conditions and design parameters. To approach as close as possible hydrogen as real gas, the thermodynamic properties of it are obtained from experimental thermodynamic tables. Based on those thermodynamic tables, a discrete database for each thermodynamic property is constructed. To minimize the error and achieve acceptable execution time, a searching method based on curve fitting techniques is developed to derive the thermodynamic properties from the discretized data. The evaluation of the hydrogen state is done based on a developed method that derives the pressure and temperature based on calculated thermodynamic properties during the filling process. The interaction between the contained hydrogen and tank during the filling process is taken into account during the methodology development. Furthermore, energy requirements for the compression system of the hydrogen storage system, including the cooling demand, are also included in the methodology. Based on the developed methodology, a transient model that can evaluate the hydrogen state condition, storage tank wall temperature condition, and energy requirement of the storage system is developed. Validation against experimental and simulation results for an actual filling event of a hydrogen storage tank is done, showing good agreement in the results. The model was used to simulate the performance of a hydrogen storage system, inspired in terms of layout by a real-world HRS storage system. The results showed that the total amount of filled hydrogen and the filling duration of the charging process are greatly affected by the compression and heat transfer phenomena occurring inside the tank. The storage tanks with lower volumes and higher operation pressure tend to be more affected by compression and heat transfer phenomena. Operation parameters such as inlet mass flow and inlet temperature, can have an impact on the system, both in terms of energy consumption and filling performance. Furthermore, based on the investigation of compression stages, the results showed that the number of stages can affect the compression ratio of each stage, resulting in lower or higher efficiency, which directly affects the energy consumption of the compression system. A parametric investigation of the upper operation pressures of the hydrogen tanks showed that the total amount of stored hydrogen is affected when the respective upper pressures vary. Last, it was shown that there is an optimal upper pressure level for each bank that can result in lower specific compression energy, indicating that the model could be used for optimization purposes.

There is a well-established market for hydrogen, mainly for refining purposes, producing chemicals, and producing fertilizers. Today, almost all hydrogen is sourced from fossil fuels, with less than 1% of hydrogen sourced from renewable sources. Alternative solutions for fossil-free hydrogen are necessary to ensure that the demand for hydrogen can be met in a sustainable fashion. The objective of this study is to analyse the feasibility and cost-effectiveness of combining hydrogen production through electrolysis with electricity production from an array of wave energy converters to supply the hydrogen market with fossil-free hydrogen. A techno-economic analysis is performed for 16 cases of offshore hydrogen production and storage in eastern Japan, using three storage mediums; Compressed hydrogen, liquid hydrogen and ammonia. Technical and economical specifications of all components required for the production systems are modelled for each case to find the most beneficial system through the Levelized Cost Of Hydrogen (LCOH), which is compared to other available renewable and fossil hydrogen sources today. The production systems evaluated in this study reach an LCOH of $5.5-7.1 /kgH2 depending on the hydrogen storage medium, where compressed hydrogen is the cheapest. This can be considered competitive with other renewable hydrogen sources, but not with fossil counterparts. / Det finns en väletablerad marknad för vätgas, främst för raffinering och framställning av kemikalier samt gödningsmedel. Idag produceras nästan all vätgas av fossila bränslen, med mindre än 1% från förnybara källor. Alternativa lösningar för förnybar vätgas är nödvändiga för att möta efterfrågan på ett hållbart sätt. Syftet med denna studie är att analysera om det är ekonomiskt försvarbart att producera vätgas offshore genom elektrolys av el från vågkraftverk för att förse vätgasmarknaden med fossilfri vätgas. Detta utförs genom en tekno-ekonomisk analys av 16 fall av havsbaserad vätgasproduktion och lagring i östra Japan. Fallen behandlar tre lagringsmedium; komprimerad vätgas, flytande vätgas och ammoniak. Tekniska och ekonomiska specifikationer för alla komponenter som krävs för produktionssystemet modelleras för varje fall. Det mest fördelaktiga systemet beräknas genom Levelized Cost of Hydrogen (LCOH), som jämförs med andra tillgängliga förnybara och fossila produktionssystem för att avgöra systemets konkurrenskraft på marknaden. Produktionssystemen som utvärderas i denna studie har en LCOH från $5.5-7.1 /kgH2 beroende på lagringsmedium, där komprimerad vätgas är det billigaste. Detta resultat kan betraktas som konkurrenskraftigt med andra förnybara vätgaskällor, men inte med fossila motsvarigheter.

Positronium-hydrogen (Ps-H) scattering is of interest, as it is a fundamental four-body Coulomb problem. We have investigated low-energy Ps-H scattering below the Ps(n=2) excitation threshold using the Kohn variational method and variants of the method with a trial wavefunction that includes highly correlated Hylleraas-type short-range terms. We give an elegant formalism that combines all Kohn-type variational methods into a single form. Along with this, we have also developed a general formalism for Kohn-type matrix elements that allows us to evaluate arbitrary partial waves with a single codebase. Computational strategies we have developed and use in this work will also be discussed.With these methods, we have computed phase shifts for the first six partial waves for both the singlet and triplet states. The 1S and 1P phase shifts are highly accurate results and could potentially be viewed as benchmark results. Resonance positions and widths for the 1S-, 1P-, 1D-, and 1F-waves have been calculated.We present elastic integrated, elastic differential, and momentum transfer cross sections using all six partial waves and note interesting features of each. We use multiple effective range theories, including several that explicitly take into account the long-range van der Waals interaction, to investigate scattering lengths for the 1,3S and 1,3P partial waves and effective ranges for the 1,3S-wave.

The process of purifying hydrogen gas using pressure swing adsorption columns heavily relies on highly efficient adsorbents. Such materials must be able to selectively adsorb a large amount of impurities, and must also be regenerated with ease. The work presented in this thesis focuses on a novel class of porous solids, metal-organic frameworks (MOFs), and their potential for use as adsorbents in hydrogen purification processes. MOFs are tuneable structures, a property that can be exploited in order to achieve the desired characteristics that are beneficial for a specific application. The design or selection of MOFs for any separation process however, relies on a thorough understanding of the relationship between a framework’s characteristics and its adsorption and selective properties. In order to identify favourable MOF characteristics for the separation of hydrogen from typical impurities a systematic molecular simulation study is performed on a large group of MOFs. Features such as the presence of short linkers, amine groups and additional aromatic rings, and a high density of linker groups are found to increase the adsorbate - framework interaction strength, and reduce the free volume available inside the pores. Both of these effects are shown to enhance MOF selectivity for impurities. Two promising materials, exhibiting desirable features, Mn MIL-53 and MIL-47, are studied further through a variety of approaches. A combination of experimental work and molecular simulations are employed in order to assess the level of flexibility in Mn MIL-53 on uptake of CO2 and CH4. An investigation of the experimental and simulation adsorption and characterization data indicates that the framework undergoes structural changes, in order to accommodate CO2 molecules, but not CH4. The form of the framework during CO2 uptake is also shown to be strongly influenced by temperature. In the case of MIL-47, adsorption isotherms simulated for a wide range of gases overpredict experimental adsorption data, leading to an in-depth investigation of non-porous effects, force field suitability, and framework rigidity. Ab initio molecular dynamics studies of MIL-47 indicate that the benzene dicarboxylate linkers rotate about their symmetry axis to reach more energetically favourable configurations, an effect responsible for the discrepancies between simulated and experimental isotherms. The effect of MOF flexibility on adsorption is further highlighted in a study of Sc2BDC3, a material able to undergo structural changes in order to accommodate a variety of adsorbates. Molecular simulations show that structural changes in the framework are responsible for the creation of additional CO2 adsorption sites as pressure is increased, whereas methanol adsorption sites occupied at extreme pressure are stabilized by the formation of hydrogen bonds. Finally, the exceptionally robust UiO-66(Zr) and UiO-67(Zr) families of MOFs are analysed using a multi-scale simulation study combining molecular level and process-scale computational work, seeking to compare the materials to commercial adsorbents, and assess whether they are suitable for H2 purification through pressure swing adsorption (PSA). Of the four MOFs studied, UiO-66(Zr)-Br is the most promising, as it significantly outperforms commercial zeolites and activated carbons in H2 purification from steam methane reformer offgas.

Ph.D., Faculty of Science, University of the Wiwatersrand, 2011 / Biological production of hydrogen gas has received increasing interest from the international community during the last decade. Most studies on biological fermentative hydrogen production from carbohydrates using mixed cultures have been conducted in conventional continuous stirred tank reactors (CSTR) under mesophilic conditions. Investigations on hydrogen production in reactor systems with attached or self-immobilized microbial growth have also appeared recently in the literature. These investigations on attached or self-immobilised bacteria involve hydrogen production in the mesophilic and thermophilic temperature range. The present study investigated the design and operational features of anaerobic fluidized granular bed bioreactor (AFGB) system which would facilitate the simultaneous achievement of high productivities (HPs) and high hydrogen yields (HYs).Where high HPs is greater than 120 mmol H2 /(L.h) and HYs greater than 4 mol H2/mol glucose. Theoretical maximum yield for an exponentially growing non-granulated bacterial monoculture will always be less than the thermodynamic maximum of 4 mol H2 /mol glucose: C6H12O6 +4H2O → 2CH3COO- + 4H2 + 4H+ + 2HCO3. The design features included reducing the total non-working or dead volume of bioreactor system. The operational improvements included application of thermophilic temperatures and high rates of de-gassed effluent recycling through the fluidized granular bed. An example of an optimal ratio of effluent recycle rate (R) to bioreactor working volume (V) was (3.0 L/min)/(3.2 L/min) = 0.94 minutes. Under conditions where temperatures were maximised and V/R were minimized the HPs increased to 21.58 L H2 /h. Also under these conditions the HYs increased above 3.0 mol H2/mol glucose. Specific hydrogen productivity for the fluidized granular bed increased from 0.25 L H2 / (g BM.h) or 8.83 mmol H2 / (g BM.h) at 45 oC to 0.525 L H2 / (g BM.h) or 18.03 mmol H2 / ( g BM.h) at 70 oC. A 3.64 fold increase in hydrogen yield occurred with an increase in temperature from 45 oC to 70 oC. XX When expressed in terms of glucose, this represents an increase from 1.34 mol H2 /mol glucose to 4.65 mol H2 /mol glucose. Finally, an evaluation of the net energy production by the AFGB system revealed a positive energy balance, making thermophilic biohydrogen production energetically viable from a commercial perspective.

Hydrogen is likely to be an important energy carrier in the future. It can be produced by the steam reforming of natural gas, coal gasification and water electrolysis among other processes. However current processes are not sustainable because they use fossil fuels or electricity from non-renewable resources. In this context, this thesis focuses on biomass based-hydrogen production and considers three plants intended for sustainable producing hydrogen using. These three systems are analyzed thermodynamically using Aspen Plus and their performances are examined and compared in regards to hydrogen yield. Therefore, comparisons of the systems are made based on several factors, including energy and exergy efficiencies. In addition, an economic analysis is performed in order to determine the minimum hydrogen production cost for these three systems. The results are expected to be useful to efforts for the design, optimization and modification of hydrogen production and other related processes. In the three system considered, the gasifiers are modelled using the Gibbs free energy minimization approach and chemical equilibrium considerations. Gasification, which is characterized by partial oxidation, is a vital component of several clean energy technologies including the ones considered here. Parametric analyses are carried out of several factors influencing the thermodynamic efficiency of biomass gasification. The energy efficiencies were found to be between 22-33% for all systems. However the exergy efficiencies range from around 22 to 25%. It was also found that gasifier produces the greatest quantity of entropy, due to its high irreversibility, and merits attention from those seeking to improve efficiencies. It was found that the hydrogen production cost range varies between 1.28 and 1.84 $/kg for the three systems; this is higher than the cost for that produced from conventional oil. / UOIT

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