Naoko Ellis

Sorption-enhanced chemical looping reforming is a process with the potential to produce synthesis gas (syngas), mostly a mixture of CO and H₂, from hydrocarbon fuels, without having to separate O₂ from air. In this system, particle attrition is an important consideration due to the high gas velocity and chemical reactions, affecting reactor performance, operating conditions and material loss by entrainment and elutriation.Fundamental studies on jet attrition with iron as oxygen carrier and limestone as CO₂ sorbent were carried out with varying temperature, jet velocity, duration, solid species weight fraction and the presence of chemical reactions to understand how these various factors affect attrition. Experimental investigation included comparing SEM images and PSD data before and after attrition, and particle size changes with different operating conditions. Furthermore, crushing strength and breakage energy tests were determined with a compression unit to understand how material properties affect particle attrition. In addition, for in-depth fundamental attrition studies on material properties, porosity, specific surface area and pore size distributions were measured to investigate the effects of chemical reaction on attrition.Based on the experimental findings, a mechanistic jet attrition model (JAM) was developed to improve the understanding of jet attrition and predict the particle size distribution in fluidized systems, considering that particle attrition was affected by changes in various operating conditions, such as time, temperature, gas phase species concentrations, reactions and particle composition. Material property changes were considered, as well as how both fragmentation and abrasion affect fluidized bed systems. A novel mechanistic model for attrition was suggested, allowing for variations of material properties, chemical reactions, and mechanical attrition by fragmentation and abrasion. With the aid of three fitted constants, the model fitted the experimental results well.

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Greenhouse gas emissions (mostly CO₂) have resulted from massive fuel consumption over recent decades, with devastating effects on humans, climate, and wildlife. Cost-effective environmentally-friendly energy sources and carbon capture are required to diminish the destructive effects of CO₂ emissions. Calcium-looping, a process based on reversible solid-gas carbonation and calcination, utilizing lime-based sorbents to capture CO₂ at elevated temperatures, is an emerging carbon capture technology, also applicable for enhanced hydrogen production. A key challenge in this continuous process is the high temperature needed for cyclical sorbent regeneration (via limestone calcination). This adversely affects the thermal/energy efficiency of the process, while also leading to sorbent deactivation during first calcination-carbonation cycles. Investigations are required to enhance current knowledge on limestone calcination conditions in calcium-looping, while also identifying alternative low-temperature technologies for sorbent regeneration.This thesis proposes a novel methane-concentrated oxy-fuel calciner, combining methane combustion, reforming and limestone calcination in a single reactor. The process is shown to be capable of autothermal syngas-producing sorbent regeneration with in situ CO₂ utilization, reducing the CO₂ concentration within the reactor, thereby decreasing the calcination temperature. The thermodynamic and kinetic performances of the process are evaluated by means of reactor simulations. Appropriate ranges of conditions are determined for autothermal, coke-free and complete limestone calcination. Increasing temperature and nitrogen concentration in air are shown to enhance limestone calcination, whereas elevating pressure and CaCO₃/gas feed ratio hinder sorbent conversion. A design methodology is suggested to determine appropriate operating conditions and/or reactor dimensions for this sorbent regeneration technology. Potential practical constraints of the process (e.g. safe operation and catalyst instability) are also briefly discussed. The thesis examines three potential applications of the process: sorbent-enhanced steam methane reforming, ammonia production without air separation, and Ca(OH)₂/CaCO₃ co-calcination. Thermogravimetric analysis is employed to assess the effect of sorbent regeneration conditions (especially partial calcination) on the cyclic CO2 capture capability of lime-based sorbents. Increasing calcination temperature is shown to reduce sorbent reactivity, while extending calcination duration and exposing limestone to high temperature without reaction did not appreciably change sorbent performance. Partially calcined sorbents are found to offer smoother CO₂ uptake over extended calcination-carbonation cycles.

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This thesis evaluates K₃PO₄, clinoptilolite, bentonite and their combinations as potential additives for enhancing microwave absorption, catalyzing pyrolysis of biomass and improving bio-oil and biochar qualities. Catalyst load ratio, pyrolysis temperature, liquid and solid product yields, bio-oil and biochar properties are examined to screen selected catalysts in terms of their effectiveness in increasing microwave absorption and improving bio-oil and biochar qualities. Thermogravimetric analysis (TGA) was also used to study the catalytic behaviour of those catalysts to interpret its performance in microwave-assisted catalytic pyrolysis and to study the catalytic pyrolysis kinetics for each of the three major biomass components, i.e., hemicellulose, cellulose and lignin, using the lumped three parallel reactions model. The performance of the produced biochars is evaluated in terms of their ability to improve soil water holding capacity (WHC), cation exchange capacity (CEC) and fertility of loamy sand soil. The capacity of those biochars in reducing bioavailability, phytotoxicity and uptake of heavy metals by wheat plants and the efficacy of those biochars in increasing soil fertility and plant growth in contaminated soil were also investigated.K₃PO₄, clinoptilolite and bentonite all showed good catalytic activities in microwave-assisted pyrolysis, resulting in reduced acidity, viscosity and water content of bio-oil product and catalyst loading and combination of different catalysts are controlling parameters on heating rate and product quality. The synergistic effects were observed in the combination of K₃PO₄ and clinoptilolite or bentonite, resulting in higher-than-expected microwave heating rate, in conjunction with improved bio-oil and biochar quality. Biochar produced from mixing K₃PO₄ and clinoptilolite or bentonite with biomass showed better performance in reducing toxicity and uptake of heavy metals than biochars produced from single catalyst. Catalytic microwave-assisted pyrolysis could be one potential approach for tailoring biochar quality to improve soil physiochemical properties. High microwave absorption, high water and nutrient affinity, desirable plant nutrients and high catalytic performance are the four key features of an effective additive for microwave-assisted biomass pyrolysis for making high quality bio-oil and biochars.

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A novel travelling fluidized bed, designed to facilitate deployment at different research centres, was used to compare advanced measurement techniques for the study of key hydrodynamic properties of gas-fluidized beds. Fast X-ray imaging was employed to visualize the internal flow structures of the bubbling and turbulent fluidization flow regimes. Transition between flow regimes based on X-ray system images were compared with results from pressure fluctuations. Average Shannon entropy reached a maximum plateau at superficial gas velocities close to Uc derived from pressure fluctuations, whereas average kurtosis and skewness leveled off at lower Ug’s. The degree of interference of a 4-mm intrusive probe inserted in the fluidized bed was found to be small by comparing the time-average voidage in a region with and without the probe present. Voidage data obtained by different measurement techniques in a previous study were extended by new data based on fast X-ray imaging and borescopy. Fair, but imperfect agreement among voidage results from alternate techniques was observed and quantified in terms of deviations from the overall average results of all measurement techniques at each gas velocity. Radial profiles of time-average particle velocity in FCC (a Geldart A powder) and sand (a Geldart B powder) fluidized beds at different operating conditions, obtained by radioactive particle tracking (RPT – non-invasive, Ecole Polytechnique), positron emission particle tracking (PEPT – non-invasive, University of Birmingham), optical fibre probe (invasive, UBC) and borescopic high-speed particle image velocimetry (invasive, PSRI) were directly compared. For FCC, each of these techniques provided similar trends with respect to profiles of time-average particle velocity, but with significant differences in some cases. For sand, there were significant quantitative differences among the profiles in many cases. The reasons for the discrepancies included lack of matching of tracer particles, probe intrusiveness, unmatched sensitivities to the direction of motion and different analysis procedures. The RPT, PEPT and borescopy data were further analyzed to obtain solid mass and momentum flux for identical operating conditions. All three techniques provided broadly similar time-average flux profiles. The experimental results obtained in this study provide a unique hydrodynamic benchmark database for validation of CFD codes and other models.

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Biochar, a by-product of biomass pyrolysis, was investigated as a carbon-based electrode material for a water treatment method based on electrostatic adsorption/desorption of ions in electric double layers (EDLs) formed on the charged electrodes (capacitive deionization, CDI). Surface area, porous structure, and functional groups of biochar were developed, and corresponding effects on EDL capacitive performance were studied. A novel method was explored to tailor the micro- and meso-porous structures of activated biochar by exploiting the interaction between pre-carbonization drying conditions and carbonization temperature (475–1000 C) in a thermo-chemical process (KOH chemical activation). The mechanism of porosity development was investigated; results suggest that the conversion of KOH to K₂CO₃ under different drying conditions has a major role in tailoring the structure. The resultant surface area, micro- and meso-pore volumes were: 488–2670 m² g-¹, 0.04–0.72 cm³ g-¹, and 0.05–1.70 cm³ g-¹, respectively. Tailored biochar samples were investigated using physico-chemical surface characterization and electrochemical methods. For electrochemical testing, activated biochar was sprayed onto Ni mesh current collectors using Nafion® as binder. The majorly microporous activated biochar showed promising capacitances between 220 and 245 F g-¹ when 0.1 mol L-¹ NaCl/NaOH was used as the electrolyte. Addition of mesoporous structure resulted in significantly reduced electrode resistance (up to 80%) and improved capacitive behaviour due to enhanced ion transport within the pores. CDI of NaCl and ZnCl₂ solutions was investigated in a batch-mode unit through the use of tailored biochar electrodes. For NaCl removal, all samples showed promising capacity (up to 5.13 mg NaCl g-¹) and durability through four consecutive cycles. In contrast, in the case of ZnCl₂, the microporous sample showed a considerable drop in removal capacity (>75%) from cycle 1 to 4, whereas the combined micro- and mesoporous sample exhibited relatively small electrosorption capacity. Interestingly, the sample with mostly mesoporous structure has shown the highest removal capacity (1.15 mg ZnCl₂ g-¹) and durability for Zn²⁺ removal. These results emphasize the importance of tailoring the porous structure of biochar as a function of the specific size of adsorbate ions to improve the CDI performance.

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Biodiesel is a promising alternative to petroleum diesel with the potential to reduce overall net CO₂ emissions. However, the high cloud point of biodiesel must be reduced when used in cold climates. Cloud point is the temperature at which solid crystals first start to appear. Skeletal isomerization of biodiesel and/or its feedstocks was investigated to reduce the high cloud point. Catalytic isomerization and hydroisomerization reactions were carried out on pure unsaturated fatty acid (UFA) and saturated fatty acid (SFA) samples, respectively. The catalyst used for the experiments was a beta zeolite and 0.5 wt% Pt-doped beta zeolite for the isomerization and hydroisomerization reactions, respectively. Reaction conditions of temperature, pressure, co-catalyst and time were varied to find an optimal reduction in the cloud point of the products. It was concluded that isomerization was unsuccessful at reducing the cloud point; in contrast, hydroisomerization was successful at reducing cloud point. A 10 degree Celsius reduction was achieved at 285 degrees Celsius and 4.0 MPa H₂ pressure. The next stage of the research studied the combined effects of isomerization and hydroisomerization on a mixture of UFAs and SFAs, namely oleic and palmitic acids. It was shown that the combination of the reaction gave a cloud point reduction of 7.5 degrees Celsius on a 55/45 mass ratio of oleic to palmitic acids. These results led to the conclusion that SFAs and UFAs through skeletal isomerization can reduce the cloud point of a mixture of fatty acids. Thus, vegetable oil feedstocks can be improved for their biodiesel cloud point. A study of ten different oils was conducted with varying contents of fatty acids. Results have shown that high unsaturated fatty acid biodiesels increased in cloud point, due to the hydrogenation side reaction. In contrast, low unsaturated fatty acid biodiesels yielded cloud point reductions, and overall improvement in the flow properties. A maximum cloud point reduction of 16.5 degrees Celsius was observed with coconut oil as the starting material. These results led to the design of an optimal cloud point improvement process of for vegetable oil biodiesel of: hydrolysis (of vegetable oil → hydroisomerization (300 degrees Celsius, 4.0 MPa H₂ pressure → and esterification.

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The issues of energy security, climate change, and environmental protection attract the use of biodiesel as an alternative fuel worldwide despite several potential setbacks such as deforestation and escalating food prices. A better biodiesel production scheme is needed to reduce the setbacks, to increase the economical value, and to have a safer production process. The use of waste oil and fat as feedstock, and conversion of glycerol into fuel oxygenates are the key solutions in this scheme. Motivated by the high activity of the sugar catalyst, a low surface area and non-porous carbon-based catalyst, this study investigates the synthesis of mesoporous, high surface area and acidity carbon-based catalysts that are active for the conversion of oleic acid and glycerol into biodiesel and fuel oxygenates, respectively. The results showed that a silica templating technique, prepared via confined activation process, was effective for synthesizing mesoporous and high surface area catalyst, but low in total acidity. The technique of catalyst functionalization in liquid fuming sulfuric acid was effective, but destroyed the internal pores of the char. The activity of the mesoporous catalyst was lower than the sugar catalyst in esterification of oleic acid. The catalyst activity was dependant on the total acidity, but independent of surface area and porosity. Further investigation showed that multiple vapour phase sulfonation was effective in synthesizing higher acidity catalyst while maintaining the mesoporous and high surface area structure. Vapour phase sulfonation caused less pore destruction in the char compared with liquid phase sulfonation. Repeated vapour phase sulfonation was effective in loading increased functional groups on the catalyst at the expense of its surface area. Evaluation of the activities of carbon-based catalysts on esterification of oleic acid showed that it depended on density and accessibility of active sites, and catalyst deactivation. Evaluation of etherification of glycerol showed that all catalysts, despite having huge differences in surface area, had comparable activity per unit mass. The carbon-based catalysts had a high selectivity to di- and tri- glyceryl ethers. In conclusion, the carbon-based catalysts synthesized through multiple vapour phase sulfonation processes are promising catalysts for a better biodiesel production process.

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A novel interconnected fluidized bed (IFB) reactor with a bypass line for chemical looping combustion (CLC) has been developed to overcome the problem of short residence time of oxygen carrier in the air reactor. A comprehensive hydrodynamic study was carried out on the cold-flow model of the proposed reactor. Detailed mapping of the operating conditions for the reactor system was studied. Pressure transducers were applied to investigate the pressure loops and the cross-sectional average solids hold-up along the air reactor. Solids circulation flux between the two reactors was measured using butterfly valves by estimating the time interval for collecting a given volume of solids. Helium was used as gas tracer for gas leakage measurement. The experiments examined the gas leakage from air reactor to fuel reactor, from fuel reactor to air reactor, from loop-seals to fuel reactor and from fuel reactor to the cyclone. For scaling consideration, the cold-flow reactor was operated with fluidizing gas mixture of helium and air to simulate the hydrodynamics of the hot unit. The effect of density ratio of solids to gas on the solids circulation flux, pressure loops and voidage distribution along the air reactor was investigated. The connection between cold unit and hot unit is achieved by applying a scaling law. It can be stated that the cold-flow model operated with fluidizing gas mixture of 96 vol% helium and 4 vol% air can be used to simulate the hydrodynamics of an atmospheric CLC hot unit. A comprehensive model for the investigation of the reactor is introduced by combining fluidization properties and a particle population balance for calculation of the bed particle conversion, considering the chemical reaction of a single particle. The dimensionless parameters, Mrfuel and Mrair, which represent the mass ratio of input oxidized-particles to the input fuel in unit time for the fuel reactor and the mass ratio of reduced-particles to the input oxygen in unit time for the air reactor, respectively, are introduced. The model shows that Mrfuel should be more than 50 for achieving fuel conversion of 90% in the fuel reactor and Mrair should be more than 60 for achieving oxygen conversion of 85% in the air reactor. A procedure for optimizing the performance of the atmospheric CLC reactor is developed. The modeling analysis indicated that the optimum operating condition of an atmospheric CLC reactor hot unit should be chosen as follows: fuel capacity is 80 kW, Ua0=6.6 m/s, Uf0= 0.076 m/s, UA1=4Umf, UA2=1Umf, and the temperature in air reactor is 1223 K and in fuel reactor is 1173 K.

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Economic utilization of biomass as a fuel has been limited by transportation cost. One suggested remedy to address the problems of processing biomass on a large scale is to pyrolyze solid biomass at numerous local sites and transport the resulting liquid or liquid/char slurry to a large centralized conversion plant. This research involves the gasification of biomass fast pyrolysis oil, so called bio-oil, and a slurry mixture of bio-oil and fast pyrolysis char into synthesis gas.Kinetics of the reaction of steam with chars was studied using a thermo-gravimetric analyzer. Slurry Char was produced by pyrolysis of an 80 wt% bio-oil/20 wt% char mixture at nominal heating rates of 100–10,000°C/s. The resulting Slurry Char was subjected to steam gasification with 10–50 mol% steam at 800–1200°C. Reactivity of the Slurry Chars increased with the pyrolysis heating rate, but was lower than that of Original Chars. Kinetic parameters were established for a power-law rate model. Some measurements were initially done of gasification in CO₂.A fluidized bed reactor, equipped with an atomization system, was constructed for gasification of bio-oil and slurry. The reactor contained either sand, or Ni-based catalyst. Experiments included gasification with pure steam and air. Effects of bed temperatures in the range 720–850°C, steam-to-carbon molar ratios of 2.0–7.5, and air ratios of 0–0.5 on gas composition and yields were tested. The carbon conversion of bio-oil to gas was found to be greater than that of slurry. The product gas composition was affected significantly by catalysis of the water-gas shift and the steam gasification. Greater yields of hydrogen and lesser yields of CO and hydrocarbons were found when catalyst was used. On a dry, inert-free basis, gases of up to 61% H₂ were obtained. The data were compared with a thermodynamic equilibrium model. The product gas yield was reasonably predictable by the model.A mass and energy balance model of steam gasification in a dual-bed gasifier-combustor revealed that energy requirements are sensitive to the steam/carbon ratio and to the recovery of latent heat in the produced gas.

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