Doctoral theses

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Pulsed electron deposition and characterization of nanocrystalline diamond thin films
(Laurentian University of Sudbury, 2013-10-07) Alshekhli, Omar
Diamond is widely known for its extraordinary properties, such as high hardness, thermal conductivity, electron mobility, energy bandgap and durability making it a very attractive material for many applications. Synthetic diamonds retain most of the attractive properties of natural diamond. Among the types of synthetic diamonds, nanocrystalline diamond (NCD) is being developed for electrical, tribological, optical, and biomedical applications. In this research work, NCD films were grown by the pulsed electron beam ablation (PEBA) method at different process conditions such as accelerating voltage, pulse repetition rate, substrate material and temperature. PEBA is a relatively novel deposition technique, which has been developed to provide researchers with a new means of producing films of equal or better quality than more conventional methods such as Pulsed Laser Deposition, Sputtering, and Cathodic Vacuum Arc. The deposition process parameters have been defined by estimating the temperature and pressure of the plasma particles upon impact with the substrates, and comparing the data with the carbon phase diagram. Film thickness was measured by visible reflectance spectroscopy technique and was in the range of 40 – 230 nm. The nature of chemical bonding, namely, the ratio (sp3/sp3+sp2) and nanocrystallinity percentage were estimated using visible Raman spectroscopy technique. The films prepared from the ablation of a highly ordered pyrolytic graphite (HOPG) target on different substrates consisted mainly of nanocrystalline diamond material in association with a diamond-like carbon phase. The micro-structural properties and surface morphology of the films were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The mechanical properties of the NCD films were evaluated by nano-indentation.
Model based fault detection for two-dimensional systems
(Laurentian University of Sudbury, 2014-05-05) Wang, Zhenheng
Fault detection and isolation (FDI) are essential in ensuring safe and reliable operations in industrial systems. Extensive research has been carried out on FDI for one dimensional (1-D) systems, where variables vary only with time. The existing FDI strategies are mainly focussed on 1-D systems and can generally be classified as model based and process history data based methods. In many industrial systems, the state variables change with space and time (e.g., sheet forming, fixed bed reactors, and furnaces). These systems are termed as distributed parameter systems (DPS) or two dimensional (2-D) systems. 2-D systems have been commonly represented by the Roesser Model and the F-M model. Fault detection and isolation for 2-D systems represent a great challenge in both theoretical development and applications and only limited research results are available. In this thesis, model based fault detection strategies for 2-D systems have been investigated based on the F-M and the Roesser models. A dead-beat observer based fault detection has been available for the F-M model. In this work, an observer based fault detection strategy is investigated for systems modelled by the Roesser model. Using the 2-D polynomial matrix technique, a dead-beat observer is developed and the state estimate from the observer is then input to a residual generator to monitor occurrence of faults. An enhanced realization technique is combined to achieve efficient fault detection with reduced computations. Simulation results indicate that the proposed method is effective in detecting faults for systems without disturbances as well as those affected by unknown disturbances.The dead-beat observer based fault detection has been shown to be effective for 2-D systems but strict conditions are required in order for an observer and a residual generator to exist. These strict conditions may not be satisfied for some systems. The effect of process noises are also not considered in the observer based fault detection approaches for 2-D systems. To overcome the disadvantages, 2-D Kalman filter based fault detection algorithms are proposed in the thesis. A recursive 2-D Kalman filter is applied to obtain state estimate minimizing the estimation error variances. Based on the state estimate from the Kalman filter, a residual is generated reflecting fault information. A model is formulated for the relation of the residual with faults over a moving evaluation window. Simulations are performed on two F-M models and results indicate that faults can be detected effectively and efficiently using the Kalman filter based fault detection. In the observer based and Kalman filter based fault detection approaches, the residual signals are used to determine whether a fault occurs. For systems with complicated fault information and/or noises, it is necessary to evaluate the residual signals using statistical techniques. Fault detection of 2-D systems is proposed with the residuals evaluated using dynamic principal component analysis (DPCA). Based on historical data, the reference residuals are first generated using either the observer or the Kalman filter based approach. Based on the residual time-lagged data matrices for the reference data, the principal components are calculated and the threshold value obtained. In online applications, the T2 value of the residual signals are compared with the threshold value to determine fault occurrence. Simulation results show that applying DPCA to evaluation of 2-D residuals is effective.
Flexible floating thin film photovoltaic (PV) array concept for marine and lacustrine environments
(Laurentian University of Sudbury, 2014-05-16) Trapani, Kim
The focus of the research is on the development of the concept of floating flexible thin film arrays for renewable electricity generation, in marine and lacustrine application areas. This research was motivated by reliability issues from wave energy converters which are prone to large loads due to the environment which they are exposed in; a flexible system would not need to withstand these loads but simply yield to them. The solid state power take off is an advantage of photovoltaic (PV) technology which removes failure risks associated with mechanical machinery, and also potential environmental hazards such as hydraulic oil spillage. The novelty of this technology requires some development before it could even be considered feasible for large scale installation. Techno-economics are a big issue in electricity developments and need to be scoped in order to ensure that they would be cost-competitive in the market and with other technologies. Other more technical issues relate to the change in expected electrical yield due to the modulation of the PV array according to the waves and the electrical performance of the PVs when in wet conditions. Results from numerical modelling of the modulating arrays show that there is not expected variation in electrical yield at central latitudes (slightly positive), although at higher latitudes there could be considerable depreciation. With regards to the electrical performance a notable improvement was measured due to the cooling effect, slight decrease in performance was also estimated due to water absorption (of ~ 1.4%) within the panels. Overall results from both economic and technical analysis show the feasibility of the concept and that it is a possibility for future commercialisation.
A novel method of detecting galling and other forms of catastrophic adhesion in tribotests
(Laurentian University of Sudbury, 2014-10-01) Dalton, Gregory Michael
Tribotests are used to evaluate the performance of lubricants and surface treatments intended for use in industrial applications. They are invaluable tools for lubricant development since many lubricant parameters can be screened in the laboratory with only the best going on to production trials. Friction force or coefficient of friction is often used as an indicator of lubricant performance with sudden increases in friction coefficient indicating failure through catastrophic adhesion. Under some conditions the identification of the point of failure can be a subjective process. This raises the question: Are there better methods for identifying lubricant failure due to catastrophic adhesion that would be beneficial in the evaluation of lubricants? The hypothesis of this research states that a combination of data from various sensors measuring the real-time response of a tribotest provides better detection of adhesive wear than the coefficient of friction alone. In this investigation an industrial tribotester (the Twist Compression Test) was instrumented with a variety of sensors to record: vibrations along two axes, acoustic emissions, electrical resistance, as well as transmitted torsional force and normal force. The signals were collected at 10 kHz for the duration of the tests. In the main study D2 tool steel annular specimens were tested on coldrolled sheet steel at 100 MPa contact pressure in flat sliding at 0.01 m/s. The effects of lubricant viscosity and lubricant chemistry on the adhesive properties of the surface were examined. Tests results were analyzed to establish the apparent point of failure based on the traditional friction criteria. Extended tests of one condition were run to various points up to and after this point and the results analyzed to correlate sensor data with the test specimen surfaces. Sensor data features were used to identify adhesive wear as a continuous process. In particular an increase “friction amplitude” related to a form of stick-slip was used as a key indicator of the occurrence of galling. The findings of this research forms a knowledge base for the development of a decision support system (DSS) to identify lubricant failure based on industrial application requirements.
The use of packed sphere modelling for airflow and heat exchange analysis in broken or fragmented rock
(Laurentian University of Sudbury, 2015-01-26) Schafrik, Sidney
Airflow and heat exchange characterizations through large bodies of fragmented rock in mines, such as those at Creighton and Kidd Creek Mines, reveal them to be still fundamentally only empirical in nature. Analysis of the accepted methods for the design and understanding of geometric properties such as the heat exchange area or the length or shape of airflow passages known to affect heat transfer in, for example, heat exchanger design do not appear in the ‘design’ equations for those bodies of broken rock. This thesis couples a method of discontinuum porous media modelling (referred to as a packed sphere model, abbreviated PSM) with a computational fluid dynamics (CFD) code to develop a proxy methodology for analysis of porous media that incorporates variables of airflow, heat transfer, and geometry (including porosity and tortuosity). Material property values for equivalent continuum fluid dynamics models are established and are found to follow formulations for airflow branches used in mine ventilation network analysis. Laboratory experiments of airflow and heat transfer with the PSMs were compared to CFD results for the same models on a 1:1 scale, to verify the approach and CFD results. Three separate approaches were investigated for the scaling of the results of the PSMs for use in large scale (~1km3) CFD simulations of industrial situations. The result of the work presented in this thesis is a verified methodology for establishing CFD airflow and heat transfer parameters for large bodies of broken and fragmented rock from knowledge of the particle size distribution parameters or the body porosity. The application of the methodology is illustrated with reference to the so-called Natural Heat Exchange Area at Creighton Mine, Sudbury, Ontario.
Application of neuroergonomics in the industrial design of mining equipment.
(2015-06-26) Mach, Quoc Hao
Neuroergonomics is an interdisciplinary field merging neuroscience and ergonomics to optimize performance. In order to design an optimal user interface, we must understand the cognitive processing involved. Traditional methodology incorporates self-assessment from the user. This dissertation examines the use of neurophysiological techniques in quantifying the cognitive processing involved in allocating cognitive resources. Attentional resources, cognitive processing, memory and visual scanning are examined to test the ecological validity of theoretical laboratory settings and how they translate to real life settings. By incorporating a non-invasive measurement technique, such as the quantitative electroencephalogram (QEEG), we are able to examine connectivity patterns in the brain during operation and discern whether or not a user has obtained expert status. Understanding the activation patterns during each phase of design will allow us to gauge whether our design has balanced the cognitive requirements of the user.
Estimation of confined peak strength for highly interlocked jointed rockmasses
(Laurentian University of Sudbury, 2015-07-20) Bahrani, Navid
The determination of rockmass strength for mining has become critically important in recent years due to the increase in the number of projects at depths exceeding 1500 m. The commonly used empirical approaches for the estimation of rockmass strength are primarily based on experiences at shallow depths (< 1500 m) and from observations of rockmass behaviours at low confinement (e.g., tunnel wall failure). Therefore, the application of these techniques for estimating the strength of rockmasses when highly interlocked and confined (e.g., pillar cores) is hypothesized to be flawed. The goal of this research is to develop reliable means of estimating the confined strength of highly interlocked jointed rockmasses. A two-dimensional code based on the Distinct Element Method (DEM) and its embedded Grainbased Model (GBM) is used to simulate the behaviour of a highly interlocked jointed rockmass to better understand its Strength Degradation (SD) from intact rock with increasing confinement. The GBM is first calibrated to the laboratory response of intact and granulated marble. The term "granulated" refers to a heat-treated marble where the cohesion at grain boundaries has been destroyed. The granulated marble represents an analogue for a highly interlocked jointed rockmass. The calibrated GBMs are then used to simulate micro-defected and defected rocks and jointed rockmasses. The results of triaxial test simulations on the calibrated synthetic rockmass specimens are used to develop two semi-empirical approaches. In the first approach, called the SD approach, equations that relate the strength degradation of a jointed rockmass from intact rock to the confinement are developed. The second approach is based on adjusting the strength parameters of the Hoek-Brown failure criterion to extend its applicability to highly interlocked jointed rockmassess. It is demonstrated that these two approaches can be used to estimate the confined strength of such rockmasses in a situation where the unconfined and confined strengths of the intact rock and the unconfined strength of the rockmass are known. The findings of this research provides the foundation for a better characterization of the strength for highly interlocked jointed rockmasses, and increases our understanding of the influence of confinement on rockmass strength.
An improved energy management methodology for the mining industry.
(2015-09-10) Levesque, Michelle
The focus for this work was the development of an improved energy management methodology tailored for the mining sector. Motivation for this research was driven by perception of slow progress in adoption of energy management practices to improve energy performance within the mining sector. Energy audits conducted for an underground mine, a mineral processing facility, and a pyrometallurgical process were reviewed and recommendations for improved data gathering, reporting and interpretation were identified. An obstacle for conducting energy audits in mines without extensive sub-metering is a lack of disaggregated data indicating end use. Thus a novel method was developed using signal processing techniques to disaggregate the end-use electricity consumption, exemplified through isolation of a mine hoist signal from the main electricity meter data. Further refinements to the method may lead to its widespread adoption, which may lower energy auditing costs via a reduced number of meters and infrastructure, as well as lower data storage requirements. Mine ventilation systems correspond to the largest energy demand center for underground mines. Thus a detailed analysis ensued with the development of a techno-economic model that could be used to assess various fan and duct options. Furthermore, the need for a standardized methodology for determination of duct friction factors from ventilation surveys was proposed, which included a method to verify the validity of the resulting value from asperity height measurements. A method was also suggested for determination of leakage and duct friction factor values from ventilation survey data. Dissemination of best practice is a strategy that could be employed to improve energy performance throughout the mining sector, thus a Best Practice database was developed to iv improve communication and provide a standardized reporting framework for sharing of energy conservation initiatives. Demonstration of continuous improvement is an underpinning element of the ISO 50001 energy management standard but as mines extract ore from deeper levels energy use increases. Thus ensued the development of a benchmarking metric, with the use of appropriate support variables that included mine depth, production, and climate data, that demonstrated the benefit of implemented energy conservation measures for an underground mine. The development of an ultimate energy management methodology for all stages of mineral processing from ‘Mine to Bullion’ is beyond the scope of this work. However, this research has resulted in several recommendations for improvement and identified areas for further improvements.
Numerical modeling of seismic wave propagation in underground mines.
(2015-11-04) Wang, Xin
The phenomenon of rockburst damage localization, which is not well understood, has been observed in deep underground mines. Analysis of seismic wave propagation in underground mines is of great interest for improved understanding of the dynamic rock failure problem. This thesis aims at making a contribution for improving understanding of the seismic wave propagation in deep underground mines. Advanced numerical modeling tools are used and new modeling techniques are developed to attain this goal. In this thesis, research is emphasized on the ground motion around excavations due to seismic wave propagation that results from a fault-slip seismic event in the far-field and the near-field. It is found that moment tensor point source model seems to be suitable for the source representation in the far-field and the non-point source model (such as kinematic rupture source model) seems to be suitable for the source representation in the near-field. The modeling results confirm that ground motion is influenced by many factors such as target-source distance, slip direction, spatial location, and geometrical and geological conditions. Influence of wavelength-to-excavation span (/D) ratio on the wavefield is investigated to gain insights of ground motion behavior under both quasi-static and dynamic loading conditions. It is revealed that PPV (peak particle velocity) values increase as the /D ratio increases and the amplification effect increases as the /D ratio decreases. The loading condition maybe changed from the dynamic loading to the quasi-static condition when the /D is larger than 30. Strong dynamic loading should be considered when the /D ratio is small (less than 10, with a shear wavelength less than 50 m and an excavation span greater than 5 m) for most underground excavations. A method is proposed to estimate the quality factor (a measure of energy loss per oscillation cycle) for shear waves propagating in underground hard rocks so as to gain insight into the influence of internal attenuation on seismic wave propagation. A proper shear wave quality factor can be obtained by comparing modeling results with that from a scaling law, even if there are no high quality data for quality factor back analysis. Furthermore, the influence of different geological structures on seismic wave propagation is studied. It is shown that wave propagation patterns around an excavation can be altered and PPV amplification and shielding effect can occur near the excavation boundaries amongst other reasons due to heterogeneities such as tunnels, open and backfilled stopes, and dykes in underground mines. Finally, a coupled numerical procedure, which couples FLAC and SPECFEM2D, is developed to consider the excavation effect on ground motion. The FLAC model considers the excavationinduced stress change and rock mass failure, and passes the input data to SPECFEM2D by invoking FISH scripts. In addition, a new nonlinear velocity model that considers the influence of confinement and rock mass failure on wave velocity is presented. This nonlinear velocity model and the coupled numerical technique are used to model a simple stope excavation problem. It is found that there is a large difference in the wavefields and ground motions between the results from the uniform and non-uniform velocity models. A relatively stronger amplification is observed in the low confinement zones and on the excavation surface in the non-uniform velocity models. Because stress redistribution and rock mass failure around an excavation are considered, a realistic non-uniform velocity field can be obtained. The proposed coupled numerical procedure offers a method to improve the understanding of the site amplification effect and ground motion near excavation boundaries. This thesis presents some insights with regard to seismic wave propagation due to fault-slip seismic events in underground mines. If seismic wave propagation in underground mines can be modeled properly using techniques such as these presented in this thesis, then it is possible to conduct forensic analysis after a large seismic event so as to explain one of many factors that caused rockburst damage localization. Alternatively, the modeling approach may provide valuable inputs for decision-making with regard to strengthening high risk areas to prevent rockburst, thus improving mine safety.
Optimal design and control of mine site energy supply systems.
(2016-08-26) Romero, Alberto
The mining sector has seen an increase in costs associated with the use of energy in recent decades. Due to lower ore grade, deeper mineralization, or more remote location new mines generally require more energy to produce the same amount of mineral. Mining operations require reliable and cost-effective energy supply, without which extraction becomes economically risky, as well as unsafe for miners. Commercial software and research-oriented computer models are now available to assist in the decision making process regarding the optimal selection of Energy Supply Systems (ESS) and associated costs. However, software and models present limitations: some are designed to minimize the cost of supplying only heat and electricity, while others are custom applications for the residential and commercial sectors. Most computer tools assume invariable operating conditions, e.g. energy supply and demand profiles that do not change throughout the lifetime of the mine, or conditions whose variations can be perfectly predicted. As a result, the optimization of ESS can yield designs that lack robustness to deal with real life, changing environments. Under the same approach, the Optimal Mine Site Energy Supply (OMSES) concept was originally developed as a deterministic mathematical programming tool to find the optimal combination of energy technologies and sources that could meet final energy demands. The solution also included the optimal operation strategy based on typical energy demands of a specific mine site. This thesis expands OMSES to address the robustness of the solution, by considering the uncertainty and variability of real operating conditions. A method is proposed herein, based on the optimal solution obtained by OMSES and utilizing Model Predictive Control (MPC). The MPC-based simulation under changing environmental conditions ensures that energy demands are met at all times, taking into account energy demands and supply forecast, as well as their inherent variability. Results show that near optimal, more robust design solutions are obtained when the system is simulated under uncertain, more realistic operational conditions, leaving MPC in charge of exploring under-capacity events and of redesigning the system to ensure feasibility with minimum cost increase. This new method has been termed MPC-OMSES dynamic redesign. This thesis also reports on research work to adapt OMSES formulation to account for varying demands throughout the life of the mine, as a consequence of the natural process of mine development and extraction, which means deeper operations over time. This process entails a progressive increase in energy demands, and therefore the energy supply system must be planned accordingly. The proposed Long Term OMSES (LTOMSES) shows the advantages of considering an investment plan for the ESS, especially in the case of capital-intensive renewable energy technologies. Other concepts that have been integrated in OMSES and are covered in this thesis include: (i) material flows with considerable impact in the energy consumption have been included in the mathematical formulation, in combination with the corresponding technologies, such as pumps, fans and mobile equipment; (ii) energy and material storage have been also included, along with complex utility tariff structures, and grid and pipeline extensions. More innovative and integrated solutions can be considered by expanding the feasibility region of the optimization problem, as shown in a case study covering the integration of battery-powered electric underground mobile equipment. Overall, this thesis provides insight and tools to assist engineers in the important task of designing comprehensive and cost-effective energy supply systems for underground mines. Future work suggested includes: the development of a methodology to design fully adaptive ESS (not considering a pre-existing optimal or sub-optimal design); the simultaneous optimization of the production plan (ore extracted per day) and the design and operation of the ESS; and a dynamic approach to review the investment plan in the face of long-term environmental operating conditions.
Numerical modeling of unstable rock failure.
(2016-09-23) Manouchehrian, Seyed Mohammad Amin
Rockburst is an unstable and violent rock failure and it is a hazardous problem in deep underground mines and civil tunnels; it imposes a great danger to safety of workers and investment. Many factors that influence rockburst damage have been identified. In many rockburst case histories, the presence of geological structures such as faults, shear zones, joints, and dykes has been observed near excavation boundaries but their role in rockburst occurrence is still not fully understood. A good understanding of the role of geological structures on rockburst damage is important to anticipate and control rockbursts and constitutes the focus of this thesis. In this research an explicit finite element tool (Abaqus-Explicit) is employed to study unstable rock failure and rockburst processes. First, uniaxial compression tests were simulated to confirm the suitability of the adopted numerical tool for simulating unstable rock failures. Two indicators namely Loading System Reaction Intensity (LSRI) and the maximum unit kinetic energy (KEmax) were proposed to distinguish between stable and unstable failures in laboratory testing conditions. Unstable rock failures under polyaxial unloading conditions were also simulated. The influences of loading system stiffness, specimen‘s height to width ratio, and intermediate principal stress on rock failure were investigated. Next, material heterogeneity (in terms of strength and deformability) was introduced into the models using Python scripting to enhance the efficiency of Abaqus for modeling geomaterials. Numerical simulation results showed that heterogeneous models resulted in more realistic failure modes than homogeneous models. The effect of material heterogeneity on rock failure intensity in unconfined and confined compression tests was investigated. It was observed that when two materials have the same peak strength, the heterogeneous model had more released energy than the homogeneous model due to differences in the failure mode. The tensile splitting failure mode of the heterogeneous model released more energy than the shear failure mode of the homogeneous model. Then, the role of geological weak planes on rockburst occurrence and damage near the boundary of tunnels was studied using 2D models. Initially, a tunnel without any adjacent weak plane was modeled. Then a fault with different lengths, inclinations, and distances to the tunnel was added to the models and its effect on rock failure was simulated. The velocity and the released kinetic energy of failed rocks, the failure zone around the tunnel, and the deformed mesh were studied to identify stable and unstable rock failures. The simulation results showed that the presence of a fault near a tunnel could induce rockburst if the fault is positioned and oriented in such a way that it promotes high stress and low local loading system stiffness. Finally, a rockburst that occurred in the Jinping II drainage tunnel in China with an observed nearby fault was simulated. The modeling results captured the field observation of rockburst damage and confirmed that the presence of weak planes in the vicinity of deep tunnels is a necessary condition for the occurrence of rockburst. The finding from this research constitutes a better understanding of unstable rock failures in both laboratory and in situ. The insights gained from this research can be useful for rockburst anticipation and control during mining and tunneling in highly stressed grounds.
Utilization of industrial waste heat for the cultivation and harvesting of microalgae
(2017-03-17) Laamanen, Corey Alfred
Microalgae sourced lipids that can be transesterified into biodiesel are a promising source of biofuels that can be produced while mitigating industrial carbon dioxide (CO2) in offgasses. There are many advantages to microalgae compared to other bio-feedstocks, including their rapid growth rate, their ability to accumulate significant amounts of lipid, and the possibility of year-round production. However, there are significant limitations to achieving wide spread and economic microalgae mass cultivation and two of these are addressed in this research program. Microalgae cultivation is currently generally limited to climatic zones where temperatures remain above 15°C, which effectively restricts mass cultivation to tropical or sub-tropical regions thereby eliminating the use of a number of worldwide industrial CO2 sources. However, many of these sources also produce significant amounts of waste heat. The capture and repurposing of waste heat to maintain culture temperature and provide an alterative method for harvesting was explored. A dynamic model was developed to determine the potential of waste streams from a nickel smelter to maintain year-round growth in a cold climate. From this model, it was determined that there is more than enough heat to maintain cultivation temperatures even when the ambient temperature drops well below freezing. Harvesting of microalgae prior to lipid extraction is, with current approaches, often cited as an area where costs need to be significantly reduced. As a wholly novel approach, the capture of this waste heat was also explored for the use as a pretreatment for harvesting by flotation. It was determined to be highly effective and crucially avoids the addition and costs of chemical coagulants, which contaminate and restrict the use of the remaining biomass after lipid extraction.
Design and optimization of a novel top-lit gas-lift bioreactor for industrial CO2 mitigation and microalgae-sourced biodiesel production
(2017-03-24) Seyed Hosseini, Nekoo
Mitigation of CO2 in industrial off-gasses by sparging the gas through photosynthetic microalgae bioreactors is an attractive concept. The goal is for the CO2 to be consumed by the microalgae as a nutrient, which in turn produces lipids suitable for conversion into biodiesel, as well as other value-added bioproducts such as Omega-3 fatty acids and antioxidants. Open systems are considered the most economic outdoor, large-scale cultivation option but have large land space requirements due to their shallow depths (15-35 cm). Consequently, finding sufficient space to locate them close to off-gas sources on industrial sites can be a significant challenge. Shallow depths are also likely to result in low uptake of CO2 and consequently reduced biomass productivity due to short gas residence times in the culture medium. In order to obtain longer gas/liquid transfer times, as well as greater per area productivity, the tanks through which the off-gas is sparged must be as deep as possible. However, to make the tanks deeper and avoid the costs associated with sub-surface artificial lighting, the issue is how to ensure the microalgae receive adequate light exposure. We have, therefore, looked for a novel method for increasing the depth of the tanks through which the off-gas is sparged. To achieve this, we have investigated the use of a gas-lift circulating system in a deep top-lit open bioreactor. In addition to providing CO2, the sparged gas also provides continual vertical circulation of the microalgae to ensure good mixing and an adequate light/dark cycle. Compared to existing shallow open systems, the results obtained showed comparable biomass productivity per unit volume, but importantly around three-times higher biomass productivity per unit area occupied by the bioreactor. The lipid productivity was also increased due to light and hydrodynamic stresses. In order to enhance further light utilization efficiency in the deep cultivation bioreactor, the use of a novel non-energy-consuming light column was also evaluated. The results of using the light column showed a 33% increase in areal biomass productivity and a 16% increase in areal lipid production. The proposed design and developed models can be easily translated into larger scale, onsite production facilities in industrial sectors emitting off-gas. The carbon capturing properties of microalgae can, therefore, help reduce industrial carbon dioxide emissions, whilst at the same time producing biodiesel from the resulting lipids.
Influence of test conditions on post-peak deformation behavior of rock
(2017-04-10) Xu, Yuhang
Understanding the post-peak deformation behavior of rock is important for underground rock engineering. Laboratory property testing is commonly employed to investigate the post-peak deformation behavior. However, the test conditions of laboratory testing, especially the Loading System Stiffness (LSS) of stiff test machines, are usually varied and the influence of this variation on the test results has not been fully elucidated. In addition, studying the influence of test conditions on the post-peak deformation behavior of rock is crucial for interpreting test results and subsequently applying the results to rock engineering design. The goal of this dissertation is to identify how the post-peak deformation behavior of a rock specimen is affected by three major aspects of test conditions––the specimen geometry, the contact conditions, and the LSS. To achieve this goal, an FEM/Explicit tool was employed to carry out numerical experiments, in which the same material property was assumed for the rock specimens and each wanted test condition was isolated for analysis. The well-observed slenderness effect and the recently-observed cross-sectional shape effect on the Uniaxial Compressive Strength (UCS) of rocks were studied. The modeling results suggest that the numerical tool and models are suitable for investigating the problem and the hoop tension theory could be flawed. Next, the cross-sectional shape effect on the post-peak deformation behavior was investigated. The modeling results reveal that although the influence of the cross-sectional shape on the UCS of rocks is small, the cross-sectional shape affects the post-peak deformation behavior considerably. The actual contact condition and the end effect in true triaxial compression tests were simulated while the legitimate intermediate principal stress (2) effect was excluded from the rock material contacts are frictional and the specimen in the 2 loading direction is squat. Thus, existing 3D empirical failure criteria based on previous true triaxial compression test results may overestimate the rock strength. The influence of LSS on the post-peak stress–strain relations of stable rock failure was examined. Key loading components of stiff test machines were considered in the numerical model. The modeling results clarify that LSS affects the post-peak stress–strain curves of rocks even when the failure process is stable. Unless LSS is either perfectly rigid or equivalent to the critical LSS (), the post-peak stress–strain curves obtained under various LSS (with LSS >  ) are varied and all steeper than the one under an ideal loading condition. This dissertation demonstrates the cross-sectional shape effect in the post-peak deformation stage, the long overlooked 2 effect caused by the end effect, and the variation of post-peak stress– strain curves due to the LSS. This dissertation also makes a contribution to examining the hoop tension theory and recognizing the correct choice of cross-sectional shape for test specimens, offers insights into improving 3D empirical failure criteria and true triaxial test settings, and suggests new requirements for developing stiff test machines in the future.
Modeling of plasma dynamics during pulsed electron beam ablation of graphite.
(2017-07-26) Ali, Muddassir
Recent advances in the field of plasma nanofabrication suggest that plasma-based technologies may replace many of the conventional chemical and thermal routes in the synthesis of nanomaterials (with at least one dimension below 100 nm) and thin films. In contrast to the conventional processing routes, where only neutral species are involved, a plasma is made up of energetic species including ions, electrons, and excited molecules in addition to neutrals. Due to the highly energetic nature of interactions among these species and with other surfaces (substrates), a plasma allows for the formation of materials at higher rates even though their concentrations might be low as compared with those of neutral species in non-plasma based methods. While the mechanisms of the various interactions in a plasma are undoubtedly complex and require a fundamental understanding, they offer new opportunities for material nanofabrication. Pulsed electron beam ablation (PEBA) has recently emerged as a novel and promising technique for high quality thin films growth. Pulsed electron beam film deposition consists of many physical processes including target material heating, target ablation, plasma plume expansion, and film growth on a substrate. Electron beam ablation is a complex process, which comprises heating, phase change, and removal of a fine fraction from the target surface. Ablation strongly affects the space distribution, composition, mass transfer processes, which in turn has a critical bearing on the structure, stoichiometry and properties of thin films. Plasma plume expansion into an ambient gas is a fundamental issue in PEBA as the quality of thin films deposited onto the substrate depends on the composition, energy and density of particles ejected from the target. A one-dimensional heat conduction model is presented to investigate the heating and ablation of a graphite target upon interaction with a polyenergetic electron beam. The effect of electron beam efficiency, power density, accelerating voltage, and Knudsen layer just above the target surface during ablation are taken into account in the model. Phase transition induced during ablation is considered through the temperature dependent thermodynamic properties of graphite. The temperature distribution, surface receding velocity, melting depth, ablation depth, and ablated mass per unit area are numerically simulated. Upon ablation, plasma expansion, induced by interaction of a nanosecond electron beam pulse (~100 ns) with a graphite target in an argon atmosphere at reduced pressure, was investigated by solving gas-dynamics equations. The spatiotemporal profiles of the temperature, pressure, velocity, and density of the plasma plume are numerically simulated for a beam efficiency of 0.6 and accelerating voltage of 15 kV. Each model is validated by comparing some of the obtained simulation results with experimental data available in the literature.
Production of cryogens using wind energy for use in deep mine cooling and ventilation.
(2017-09-05) Kunwar, Saruna
This research work, named as ‘CryoVent’, was focused on determining the feasibility of using wind energy, to produce liquefied gases (cryogens) continuously in a safe approach that can be used for the cooling and ventilation of underground mines. The experimental work performed suggested that the continuous production of liquefied gases with variable input work is practical. The average specific power consumption for liquefaction of nitrogen in this work was 7.86 kWh/kg using the refrigeration produced by helium. This is ~20 times higher than that consumed by industrial scale gas liquefaction systems, but is practical for a small scale system. This specific power consumption could probably be lowered if the working fluid itself is liquefied. Analysis on wind speed variability and wind speed data synthesis were also performed which suggested presence of multi-fractal nature in wind speed data that represent the temporal variation. A new method developed to generate high sampling frequency wind speed data from available low sampling frequency wind speed data can have contribution in all sectors when there is a need of higher sampling frequency time series data for simulation/study purposes. The liquid nitrogen mass flow rate (kg/s) increased with increase in compressor motor frequency and also when operating at variable motor input frequency. However, the average compressor power consumption also increased compared to average power consumption during operation at standard motor frequency of 60 Hz. This was in a laboratory scale liquefaction system and needs to be tested in the large scale system experimentally. With 1 kg/s of liquefied nitrogen supplied, ~459 kWr of cooling power is available to cool the deep mine air which is at 30-400C. A volumetric flow rate of 0.062 m3/s of liquefied air can provide a cooling power equivalent to that provided by a volumetric flow rate of 4000 m3/s of atmospheric air, which is the requirement of some of the biggest mines in the world. The hydraulic wind turbine as proposed in this work can eliminate the system start-up issues following the calm period, which are typical concerns with the wind energy integrations. This research work has provided the required modeling and simulation results that are crucial in development of the full scale ‘CryoVent’.
Production and characterization of polystyrene resins containing fine activated carbon particles
(2017-11-20) Hmidi, Nuri
The development of high capacity adsorbent using engineered activated carbon fines technology, and their ability to extract gold from solution is presented. The unique feature of these adsorbents is their ability to adsorb gold ions from low concentration solutions like mine effluent as well as from leached solutions in gold mills. Production of polystyrene ion exchange resins containing fine activated carbon particles denoted, PSAC, (Polystyrene Activated Carbon) and their gold stripping kinetics were studied. Polystyrene beads were prepared by simple suspension polymerization. However, addition of fine activated carbon (AC) during suspension polymerization was not successful in producing small beads, but rather a conglomerated mass, which was then broken up and shaped into smaller beads. PSAC beads were also produced by co-extrusion of polystyrene with activated carbon and by physical adsorption of activated carbon onto raw polystyrene beads in an autoclave at a temperature above the glass transition temperature of polystyrene. Stripping tests were performed which identified the latter bead type as being the most promising form of PSAC bead for future research. The work was aimed at optimizing the production of the beads in terms of their physical and chemical properties. This work led to the development of a new polystyrene/activated carbon ion exchange bead as an alternative to pure activated carbon. A mini-elution column was also designed to carry out the test work to study the performance of beads and loaded fine carbon stripping parameters under typical industrial conditions. Further development of this research may lead to a new method of stripping loaded fine carbon on mine sites as part of the existing gold milling and extracting circuits.
Cobalt-doped zinc oxide thin films as model Fischer-Tropsch nano-catalysts grown by pulsed electron beam ablation
(2017-12-05) Ali, Asghar
The production of materials in thin film form with unique properties is of growing scientific and technological interest. Zinc oxide is a low cost, and environmentally benign wide band gap semiconductor, which makes it an excellent supporting material for nanoparticles with a plethora of potential applications. Upon doping with Co and other transition metals, ZnO exhibits room temperature ferromagnetic properties with enhanced performance and new functionalities when used in thin film devices. Zinc oxide-supported cobalt nano-composites are promising materials with desirable catalytic properties making it an interesting material for use as an efficient nano-catalyst in many important reactive processes such as Fischer-Tropsch synthesis (FTS), photocatalysis, hydrogen production and steam reforming. Pulsed electron beam ablation (PEBA) has recently emerged as a potential technique for the fabrication of superior quality thin films. The production of well controlled nano-sized particulates is a characteristic feature of PEBA, which has a strong bearing on the surface morphology of the deposited films. In the current work, the potential of PEBA in the deposition of Co-doped ZnO thin films has been assessed and the critical process conditions that affect the growth of the thin films on different substrates have been thoroughly investigated. The main objective of the current work is to deposit Co-doped ZnO thin films via PEBA, and assess the potential of the deposited films as model nano-structured catalysts for the synthesis of green liquid fuels from syngas. PEBA has several advantages including modest requirements for vacuum, control of film thickness, easy set-up, low capital cost, reduced operation and maintenance costs, small footprint, enhanced efficiency, and relative safety (no toxic gases as in pulsed laser ablation or potential noxious by-products as in solvo-thermal routes) over other film preparation techniques. In this project, Co:ZnO thin films have been synthesized from a single target on various substrates. Numerous process parameters have been assessed such as substrate material, deposition temperature, electron beam voltage, beam pulse frequency. Targets of varying cobalt loads viz., 5 w%, 10 w%, and 20 w% have been investigated as well. The effects of pre and post annealing on the physico-chemical properties of the thin films have also been studied. The deposited films have been characterized using complementary analytical techniques such as xray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive x-ray (EDX), visible reflectance spectroscopy (VRS), and atomic force microscopy (AFM). Such comprehensive analyses have helped in assessing the quality of the films and in guiding the experimental strategy in the quest to find the optimal process conditions. Finally, the films have been evaluated for their potential as model nano-catalysts for FischerTropsch synthesis in a 3-phase continuously-stirred tank slurry reactor (3-φ-CSTSR) using a Robinson-Mahoney stationary basket (RMSB). The results have been described in terms of activity and selectivity of the thin film nano-catalysts.
Dynamic modelling of catalytic SO2 converter in a sulfuric acid plant of an industrial smelter
(2018-04-16) He, Jianjun
In industrial nickel and copper production, sulfur dioxide (SO2) is generated from the combustion of sulfide ores. With increasingly tightened regulations on SO2 emissions, a sulfuric acid plant has become a crucial part of industrial smelters. It converts environmentally harmful SO2, which is generated in smelter furnaces, roasters, and Cu-reactors, into commercially beneficial sulfuric acid. This method is recognized as one of the most effective ways to ensure that smelters are able to satisfy the SO2 emission regulations. A sulfuric acid plant is primarily comprised of a central catalytic SO2 converter, SO3 (sulfur trioxide) absorption towers and a series of interconnected heat exchangers. The catalytic SO2 converter is the key component and the focus of this research. Both steady-state and dynamic models of the converter are developed in this thesis. A steady-state model of the converter is established in accordance with steady-state mass and energy balances. The developed model provides an explicit relation between SO2 conversion ratio and gas temperature, which is denoted as the heat-up path of the converter. By combining the heat-up path with the equilibrium curve of the SO2 oxidation reaction, an equilibrium state for every converter stage can be obtained. Using the developed steady-state model, simulations are performed to investigate the effect of inlet SO2 molar fraction and gas temperature on the equilibrium conversion ratio. In an industrial SO2 converter, the SO2 concentration and conversion ratio out of each bed are important variables but are not measured in real time. To monitor these unmeasured variables in industrial operations, a soft sensor is proposed by combining the derived steadystate model with dynamic data analysis. The obtained soft sensor provides a real-time estimation of outlet SO2 concentration and the conversion ratio from measured temperatures. For synchronization between the inlet SO2 concentration and outlet temperature, a first-order exponential data filter is applied to the feed SO2 data. With the filtered signal being used, the proposed soft sensors give a satisfactory estimation of both outlet SO2 concentration and conversion ratio in the converter stages. Dynamic modelling is carried out using two different model forms: ordinary differential equation (ODE) and partial differential equation (PDE) models. The ODE model is obtained by applying dynamic mass and energy conservation to the SO2 converter. The resulting model can be used in industrial applications and describes the converter performance even if information of reaction kinetics is not available. A good fit with collected industrial data verifies the validity of the developed ODE model. The effect of process input variables is studied using simulations with the ODE model. Dynamic modelling is performed by implementing mass and energy balances on both fluid and solid-phase gas flows. The proposed two-phase dynamic model, which takes the PDE form, is able to generate detailed profiles of the SO2 converter within time and space. With the estimated parameters, this two-phase dynamic model generates a good fit between the simulated and measured outlet temperatures. Based on the PDE model, simulations are run to investigate the detailed mechanistic performance of the converter. The detailed PDE model provides useful explanation of, and prediction for the converter behaviour.
Characterization of seismic sources using sequential spatial clustering and fractal dimension
(2018-07-30) Cortolezzis, Donna Marie
Despite years of research, unexpected seismic events in mines continue to cause damage and loss to people, equipment, infrastructure, and reserves. This research uses novel approaches to characterize the locations, times, and intensity of seismic events for four known seismic sources. The seismic source case studies are the development of a ramp, the abutments around a zone of stopes, a failing stope pillar, and a shear zone adjacent to an orebody. Each seismic source is characterized by sequential spatial clustering, and the fractal dimension of the seismic source parameters of location, time and intensity. The novel application of sequential spatial clustering preserves the sequence of events within a cluster. The method can be used at any point in time which means as a rock mass changes the seismic response is expressed and identified very early on. Once identified, it allows the opportunity for investigation and decision making to take place as the rock mass changes in an unexpected manner. The application of fractal dimension to seismic source parameters revealed that the fractal nature of a parameter is not infinite but exists within a range. The fractal range reflects the character of a seismic source. If some events occur outside the fractal range they also provide important information about the history of the seismic source that occur less often than the fractal range but are still possible. This research has expanded the knowledge of when, where, and how intense seismic events can be expected for four seismic sources using a new sequential spatial clustering method and fractal dimension characterization.

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