Recent Submissions

  • Fabrication, characterization, and hydrogen permeation in [BaCe_x Zr_(0.9-x) Y_0.1 O_(3-[delta])] prepared by solid-state reactive sintering

    Sullivan, Neal P.; O'Hayre, Ryan P.; Manerbino, Anthony R.; Kee, R. J.; Gorman, Brian P.; Coors, Grover; Kaufman, Michael J. (Colorado School of Mines. Arthur Lakes Library, 2013)
    This dissertation focuses on the fabrication and characterization of BCZY for hydrogen-separation applications. The structural and hydrogen-permeation properties of a series of proton-conducting oxides based on the solid solution of BaZrO3-BaCeO3 as an emerging class of ceramic hydrogen-separation membranes were investigated. Yttrium was used as the specific dopant; the ceria and zirconia contents were varied from 0 [less than or equal to] x [less than or equal to] 0.4 BaCe_x Zr_(0.9-x) Y_0.1 O_(3-[delta]). Materials were prepared by solid-state reactive sintering from both BaCO3 and BaSO4 barium precursors. The cubic phase was observed over all ranges of the differing ceria to zirconia ratios. In an effort to decrease the thickness and increase the flux of hydrogen through these membranes, two-phase membrane-support tubes were fabricated from 65 wt-% NiO / 35 wt-% BCZY27, and then spray coated with BCZY27 membranes; the active area of these thin BCZY27 membranes approached 75 cm[superscript 2]. Hydrogen-permeation measurements were executed utilizing two different measurement techniques. The first technique used mass spectroscopy to measure the flux of hydrogen through the membrane under a hydrogen partial-pressure difference. The second technique used a method of titration to indirectly calculate hydrogen flux across the membrane. Results from both techniques reveal that BCZY27 had thermally activated hydrogen transport at temperatures above 700 °C. This phenomenon is attributed to ambipolar diffusion of protons and electrons. A simple computational model and Arrhenius analysis were used to compare and understand the observed results. These thin BCZY27 membranes on tubular porous Ni-BCZY27 supports demonstrated in this dissertation are the first realization of this architecture in high-temperature proton-conducting ceramics.
  • Density functional theory investigations of graphene-based heterostructures

    Ciobanu, Cristian V.; Ebnonnasir, Abbas; Agarwal, Sumit; Kappes, Branden Bernard; Olson, D. L. (David LeRoy); Richards, Ryan (Colorado School of Mines. Arthur Lakes Library, 2013)
    Graphene, a two-dimensional single crystal of carbon atoms arranged in a honeycomb lattice, is attractive for applications in nanoelectromechanical devices; in high-performance, low-power electronics, and as transparent electrodes. The present study employs Density Functional Theory (DFT) to identify the atomic and electronic structure of graphene (Gr) on three different types of substrates: transition metals (nickel, palladium), insulators (hBN) and semiconductors (MoS2). Our DFT calculations show that graphene layer on Ni(111) and Ni(110) becomes metallic owing to large binding energies and strong hybridization between nickel and carbon bands. Furthermore, in Gr/Gr/palladium systems, we find that the electrostatic dipoles at the Gr/palladium and Gr/Gr interfaces are oppositely oriented. This leads to a work function of bilayer graphene domains on palladium (111) higher than that of monolayer graphene; the strengths of these dipoles are sensitive to the relative orientation between the two graphene layers and between the graphene and palladium (111). Additionally, the binding energy of graphene on palladium (111) depends on its orientation. We elucidate the physical origin of the effect of growing graphene on hBN/Ni(111) on the binding of hBN to a Ni(111) substrate, and on the electronic properties of hBN. We find that hBN/Ni has two configurational minima, one chemisorbed and one physisorbed, whose properties are not altered when graphene is placed atop hBN. However, a switch from chemisorbed to physisorbed hBN on Ni can occur due to the processing conditions during graphene growth; this switch is solely responsible for changing the hBN layer from metallic to insulating, and not the interactions with graphene. Finally, we find that the relative orientation between graphene and MoS2 layers affects the value and the nature of the bandgap of MoS2, while keeping the electronic structure of graphene unaltered. This relative orientation does not affect the binding energy or the distance between graphene and MoS2 layers. However, it changes the registry between the two layers, which strongly influences the value and type of the bandgap in MoS2.
  • Ignition Quality Tester: an alternative for characterizing the combustion kinetics of low volatility fuels, The

    Dean, Anthony M.; Osecky, Eric; Bogin, Gregory E.; Ratcliff, Matt; Zigler, Brad; Maupin, C. Mark (Colorado School of Mines. Arthur Lakes Library, 2013)
    The objective of this thesis is to demonstrate that the Ignition Quality Tester (IQT) can be used to validate the kinetic mechanisms of both high and low volatility fuels. Such validated mechanisms are an essential component for engine models used to improve efficiency and determine the impact of alternative fuels. There are other approaches to measure the ignition kinetics of high volatility fuels, but only very limited data are available for low volatility fuels. The IQT was modified by increasing the range of temperatures it could access and by implementing a purge program so that the accuracy and repeatability of experiments at low pressures could be increased. Experiments were performed to characterize the effect of varying parameters (temperature, pressure, oxygen concentration, equivalence ratio, mass of fuel injected, choice of diluent, fuel physical properties, and fuel structure) on the ignition delay, and whether these effects were due to the chemical kinetics or spray physics. CFD modeling, run without chemistry, was used to show that at long times (>20ms) the IQT becomes pseudo-homogeneous in both temperature and equivalence ratio. This suggested that a 0-D homogeneous batch reactor model could be used to predict the ignition delay at the longer times. Experiments were performed for five heptane isomers where accurate mechanisms are available, and the 0-D model ignition time predictions were consistent with the measurements. Similar favorable comparisons were found for iso-octane, another well studied high volatility fuel. Attention then shifted to validate chemical mechanisms for low volatility fuels. Model predictions for n-hexadecane were a factor of sim 2.5 longer then the observed ignition delays at long times (> 20 ms). This difference could be due to the older rate rules used in the mechanism. Experiments were done with 2,2,4,4,6,8,8-heptamethylnonane (HMN) since the inherently lower reactivity of this fuel allows NTC behavior to be observed without needing to go to the lower pressures (thus allowing experiments more relevant to diesel combustion). The 0-D model significantly underpredicted the ignition delay. This provided an opportunity to develop an improved HMN mechanism. It was discovered that the highly branched structure of HMN meant that additional terms needed to be considered when computing the thermodynamic properties. This updated thermo, in combination with updated estimates for various reaction types, greatly improved the HMN mechanism.
  • Computational analysis of cellobiohydrolase Cel7b from Melanocarpus albomyces

    Maupin, C. Mark; Granum, David; Neeves, Keith B.; Sum, Amadeu K. (Colorado School of Mines. Arthur Lakes Library, 2013)
    Cellulases are a broad class of enzymes responsible for decomposing lignocellulosic biomass. These enzymes have several industrial applications, most notably in the production of 2nd generation biofuels from cellulosic feedstock. However, current degradation technologies involving cellulase cocktails are not sufficiently optimized for economical biofuel production on an industrial scale. Thus, there is significant incentive to further understand and improve the enzymatic degradation of cellulose by cellulase enzymes. In this thesis, constant pH molecular dynamics simulations (CpHMD), classical molecular dynamics (MD), docking calculations and kinetic modeling were utilized to evaluate the fundamental interactions impacting cellulose degradation by the cellobiohydrolase Cel7B from Melanocarpus albomyces (Ma). Presented in this thesis is an extensive evaluation of the ionizable residues in [alpha]-Conotoxin by both CpHMD and [superscript 1]H NMR, which serves as a validation of the computational pKa prediction procedures used in the subsequent thesis chapters. The procedures established in the study of [alpha]-Conotoxin were then utilized in the simulations of active site residues in Ma Cel7B. The pKa values of active site residues predicted by the simulations support the role of Glu217 as the catalytic acid-base and Glu212 as the catalytic nucleophile. In addition to predicting pKa values, the simulations identified significant charge correlations and hydrogen bonding networks that are critical to hydrolysis of the glycosidic bond. The results from the CpHMD simulations were then incorporated into a kinetic model, which further supports the hypothesis that hydrogen bonding and charge coupling are needed to achieve an optimal activity near the experimental active pH of Ma Cel7B. Beyond residue pKa values and their influence on the observed enzymatic rate, standard MD and CpHMD simulations were used to evaluation protein dynamics and loop flexibility. Investigation of peripheral loops enclosing the active site revealed structural fluctuations that are likely crucial to the binding and threading of the cellulose polymer substrate, as well as contributing to the pH and temperature tolerance of Ma Cel7B. It was found that the protonation of several residues on adjacent peripheral loops are responsible for the observed loop fluctuations and overall conformation in the free enzyme. Simulations with substrate bound in the active site reveal significant changes in the conformation and fluctuation patterns of several peripheral loop regions. The substrate induced response of the loop regions secures the cellulose polymer in the catalytic tunnel, creating an environment that is conducive for hydrolysis of the glycosidic bond. Similar loop fluctuations and dynamics are also observed when a free enzyme resides on a cellulose microfibril, indicating the role of the peripheral loops in guiding substrate into the catalytic tunnel. To further probe enzyme-substrate interactions on the hydrolysis of cellulose, the confirmation of the sugar ring at the catalytic site was investigated under different residue protonation environments. In general, the results indicate the highly charge coupled active site effectively modulates the formation of the catalytically active skewed-boat confirmation, and clearly identifies the protonation states of active site residues as the major contributing factor to the formation of the skewed boat configuration. The results presented in this thesis provide insights into molecular-level interactions that lead to the observed enzyme characteristics of Ma Cel7B, and indicate computational methods can be used to gain valuable insights into the protonation environment and specific residue pKa values that are crucial to the hydrolysis reaction performed by family 7 cellulase enzymes.
  • Analysis of engineered nanomaterials in the environment

    Ranville, James F.; Reed, Robert Bruce; Higgins, Christopher P.; Voelker, Bettina M.; Richards, Ryan; Williams, S. Kim R. (Colorado School of Mines. Arthur Lakes Library, 2013)
    With increasing incorporation of engineered nanoparticles (NPs) into consumer products, there is concern that these materials will be released to the environment with unknown ecological effects. Methods for detection and characterization of these materials at environmentally relevant concentrations are crucial to understanding this potential risk. A relatively new method, single particle inductively coupled plasma mass spectrometry (spICPMS), was applied to analysis of metal oxide NPs such as ZnO, CeO2, and TiO2, as well as silver nanowires and carbon nanotubes. A lack of nanoparticulate "pulses" in spICPMS analysis of nano-ZnO led to a study on ZnO NP solubility in a variety of matrices. Dissolution of nano-ZnO was observed in nanopure water (7.18 - 7.40 mg/L dissolved Zn, as measured by filtration) and Roswell Park Memorial Institute medium (RPMI-1640) (~5 mg/L), but much more dissolution was observed in Dulbecco's Modified Eagle's Medium (DMEM), where the dissolved Zn concentration exceeded 34 mg/L. These results suggest that solution chemistry exerts a strong influence on ZnO NP dissolution and can result in limits on zinc solubility due to precipitation of less soluble solid phases. Detection and sizing of metal-containing NPs was achieved at concentrations predicted for environmental samples (part-per trillion levels) using spICPMS. Sizing of silver nanowires, titanium dioxide and cerium oxide NPs was done by correlating ICP-MS response (pulses) from NPs entering the plasma to mass of metal in dissolved standards. The ratio of NP pulse detections to the total number of readings during analysis was optimized at 2.5% or less to minimize coincident pulses while still allowing definition of a size distribution. Detection of single walled carbon nanotubes (CNTs) was performed using spICPMS. This study focuses on using trace catalytic metal nanoparticles intercalated in the CNT structure as proxies for the nanotubes. The small, variable, amount of trace metal in each CNT makes separation from instrumental background challenging, and multiple approaches to this problem were attempted. To highlight the potential of spICPMS in environmental studies the release of CNTs from polymer nanocomposites into solution was monitored, showcasing the technique's ability to detect changes in released CNT concentrations as a function of CNT loading.
  • Techno-economic analysis of wastewater sludge gasification: a decentralized urban perspective

    Porter, Jason M.; Lumley, Nicholas P. G.; Braun, Robert J.; Bogin, Gregory E. (Colorado School of Mines. Arthur Lakes Library, 2013)
    Wastewater sludge management is a significant challenge for small-scale, urban wastewater treatment plants (WWTPs). Common management strategies stabilize sludge for land disposal by microbial action or heat. Such approaches require large footprint processing facilities or high energy costs. A new approach considers sludge to be a fuel which can be used on-site to produce electricity. Electrical power generation fueled by sludge may serve to reduce the volume of hazardous waste requiring land disposal and create economic value for WWTP operators. To date, no detailed system designs or techno-economic analyses have been found for small scale sludge fueled power plants. Fortunately, a literature base exists describing the fundamentals of applying thermochemical conversion (TCC) technologies to sewage sludge. Thermochemical conversion of sludge is established for large WWTPs, however large system design techniques may not be applicable to small systems. To determine the feasibility of small scale power generation fueled by sludge, this work evaluates several thermochemical conversion technologies from the perspective of small urban WWTPs. Literature review suggests wet oxidation, direct combustion, pyrolysis, and gasification as candidate front-end TCC technologies for on-site generation. Air and steam blown gasification are found to be the only TCC technologies appropriate for sludge. Electrical power generation processes based on both air and steam blown gasification are designed around effective waste heat recovery for sludge drying. The systems are optimized and simulated for net electrical output in ASPEN Plus[Registered Trademark]. Air blown gasification is found to be superior. Sensitivity analyses are conducted to determine the effect of fuel chemical composition on net electrical output. A technical analysis follows which determines that such a system can be built using currently available technologies. Finally, an economic analysis concludes that a gasification based power system can be economically viable for WWTPs with raw sewage flows of 0.115 m[superscript 3]/s, or about 2.2 million gallons per day.
  • Detecting changing geologic conditions with tunnel boring machines by using passive vibration measurements

    Steele, John P. H.; Mooney, Michael A.; Walter, Bryan W.; Delborne, Jason; Henn, Raymond W.; Schowalter, Jeffrey; Wakin, Michael B. (Colorado School of Mines. Arthur Lakes Library, 2013)
    This research explores the detection of changing geological conditions with a Tunnel Boring Machine (TBM) by using passive vibration measurements. In this investigation, three iterations of an acquisition system were deployed at two different field sites. In these deployments, the TBMs were instrumented with accelerometers, and the response of the transducers was paired with the machine's operating data to seek correlations associated with changing geological conditions. To better understand the system's response, both contributions from specific machine components and the dynamic response of the TBM's structure were considered. Additionally, an advanced filtering method was tested to more completely explore the complicated relationship between vibration and geology. Results from this study yield a number of interesting findings. First, that the passive vibration measurements can be used to detect events in successive revolutions of the TBM's cutting head. Second, the structural modes, of the TBM, are not well characterized in the response spectra, because the system's inputs (Torque, Thrust, Advance Rate, etc.) are non-stationary in nature. As a result of the non-stationary inputs, traditional techniques such as operational modal analysis (OMA) were of limited use. Finally, an advanced filtering technique, called principal motion analysis, shows promise as a method for detecting and analyzing whole machine motion and overcoming the limitations of OMA.
  • Optimization-based decomposition heuristic for solving complex underground mine scheduling problems, An

    Newman, Alexandra M.; O'Sullivan, Donal; Eggert, Roderick G.; Kaffine, Daniel; Kuchta, Mark (Colorado School of Mines. Arthur Lakes Library, 2013)
    Underground mine production scheduling possesses mathematical structure similar to and yields many of the same challenges as general scheduling problems. That is, binary variables represent the time at which various activities are scheduled. Typical objectives seek to minimize costs or some measure of production time, or to maximize net present value; two principal types of constraints exist: (i) resource constraints, which limit the number of activities committed to a time period based on the availability of a given supply and on the amount of that supply required to perform the activity, and (ii) precedence constraints, which dictate the order in which activities must be completed. In our setting, we maximize "discounted metal production" for the remaining life of an underground lead and zinc mine that uses three different underground methods to extract the ore. Resource constraints limit the grade, tonnage, and backfill paste (used for structural stability) in each time period, while precedence constraints enforce the sequence in which extraction (and backfill) is performed in accordance with the underground mining methods used. We tailor existing exact and heuristic approaches to reduce model size, and develop an optimization-based decomposition heuristic; both of these methods transform a computationally intractable problem to one for which we obtain solutions in seconds, or, at most, hours for problem instances based on data sets from the Lisheen mine near Thurles, Ireland. Our solution adds value to the Lisheen mining operation by: (i) shifting metal production forward in the schedule; (ii) reducing waste mining and backfilling delays; (iii) avoiding expensive mill-halting drops in ore production; and (iv) enabling smoother workforce management. Our modeling approach could be applied to other mines, especially to operations with flat lying deposits that practice retreat, i.e., room-and-pillar, mining, such as coal mines, and to mines that are approaching the end of their operational life.
  • Creation of "bonding structures" on nanoparticles

    Liang, Hongjun; Zheng, Wan; Liberatore, Matthew W.; Richards, Ryan (Colorado School of Mines. Arthur Lakes Library, 2013)
    Nanoparticles can be used as a new type of fundamental building blocks to construct macroscopic materials, and hierarchically organized nanoparticles often show enhanced properties originated from the collective interactions among these individual nanoscale building blocks. Taking one step further, colloidal molecules with well-defined architectures made by directed assembly of nanoparticles could serve as the basic structural units of more complex functional materials. This is highly desirable but challenging due to the lack of "bonding structures" on nanoparticles. In this thesis, we aim to create "bonding structures" on nanoparticles by modifying them with heterogeneously functionalized polymers bearing "click" moieties. We hypothesize that by controlling the location of "click" recognition pairs on nanoparticles, well-defined polymer linkers, nanoparticle geometry and reaction stoichiometry, the "directionality", "bonding length", and "valency" characteristics of real chemical bonds could be introduced on as-synthesized nanoparticles, which will help organize nanoparticles into colloidal molecules via highly specific and efficient "click" reactions. Using gold nanoparticles as models, we show here that well-defined, heterogeneously functionalized polymer chains bearing "click" recognition pairs can be prepared, and subsequently used to modify gold nanoparticles at controlled locations. Our future work is to study the broad utility of this strategy on creating "bonding structures" on nanoparticles to transform them into "artificial atoms", as well as the system design to assemble these nanoparticles into well-defined colloidal molecules.
  • EOS modeling and reservoir simulation study of Bakken gas injection improved oil recovery in the Elm Coulee field, Montana

    Hoffman, B. Todd; Pu, Wanli; Wu, Yu-Shu; Meckel, Lawrence D. (Colorado School of Mines. Arthur Lakes Library, 2013)
    The Bakken Formation in the Williston Basin is one of the most productive liquid-rich unconventional plays. The Bakken Formation is divided into three members, and the Middle Bakken Member is the primary target for horizontal wellbore landing and hydraulic fracturing because of its better rock properties. Even with this new technology, the primary recovery factor is believed to be only around 10%. This study is to evaluate various gas injection EOR methods to try to improve on that low recovery factor of 10%. In this study, the Elm Coulee Oil Field in the Williston Basin was selected as the area of interest. Static reservoir models featuring the rock property heterogeneity of the Middle Bakken Member were built, and fluid property models were built based on Bakken reservoir fluid sample PVT data. By employing both compositional model simulation and Todd-Longstaff solvent model simulation methods, miscible gas injections were simulated and the simulations speculated that oil recovery increased by 10% to 20% of OOIP in 30 years. The compositional simulations yielded lower oil recovery compared to the solvent model simulations. Compared to the homogeneous model, the reservoir model featuring rock property heterogeneity in the vertical direction resulted in slightly better oil recovery, but with earlier CO2 break-through and larger CO2 production, suggesting that rock property heterogeneity is an important property for modeling because it has a big effect on the simulation results. Long hydraulic fractures shortened CO2 break-through time greatly and increased CO2 production. Water-alternating-gas injection schemes and injection-alternating-shut-in schemes can provide more options for gas injection EOR projects, especially for gas production management. Compared to CO2 injection, separator gas injection yielded slightly better oil recovery, meaning separator gas could be a good candidate for gas injection EOR; lean gas generated the worst results. Reservoir simulations also indicate that original rock properties are the dominant factor for the ultimate oil recovery for both primary recovery and gas injection EOR. Because reservoir simulations provide critical inputs for project planning and management, more effort needs to be invested into reservoir modeling and simulation, including building enhanced geologic models, fracture characterization and modeling, and history matching with field data. Gas injection EOR projects are integrated projects, and the viability of a project also depends on different economic conditions.
  • Integrated reservoir characterization and modeling in support of enhanced oil recovery for Bakken

    Kazemi, Hossein; Kurtoglu, Basak; Scoggins, Myles; Graves, Ramona M.; Sonnenberg, Stephen A.; Heeley, Michael B.; Hoffman, B. Todd; Chen, Hung-Lung (Colorado School of Mines. Arthur Lakes Library, 2013)
    This research presents an integrated reservoir characterization study of the Bakken fields in North Dakota. First, the Bakken petroleum geology is studied to evaluate the flow-related properties of the hydrocarbon-bearing formations from core scale to field scale. This part of the research focuses on the Middle Bakken formation which has been the target for horizontal drilling in Williston Basin. Second, the fluid flow hierarchy in the Middle Bakken formation is determined by comparing the differences between permeability measured from laboratory core experiments and field tests. Effective permeability measurements from well tests infer the reservoir contains both micro and macro fractures. Core permeability measurement alone does not provide the fluid flow characterization. In addition, laboratory flow experiments to determine basic core properties such as porosity, permeability, wettability, pore size, mineralogy, and fluid saturations and specific laboratory tests with low salinity brine and CO2 are conducted. Third, geological and petrophysical properties are integrated into a compositional dual-porosity reservoir model to simulate production performance. Time analysis of flow and pressure over the history of a well, supplemented by the pressure and rate transient analysis of shorter-duration well tests, provides the most important flow characterization data for reservoir modeling. The reservoir model has a flow hierarchy focusing on the stimulated reservoir region with the nanometer-scale matrix pores connected to a network of interconnected micro-fractures and macro-fractures and eventually connecting to the wellbore via hydraulic fractures. Reservoir heterogeneity is addressed using a heterogeneous matrix and fracture petrophysical model which combines the core analyses and well log data. The integrated modeling approach is used for planning of production options and evaluating enhanced oil recovery strategies. Finally, the technical feasibility of producing more oil from Bakken reservoir by waterflooding and CO2 injection is investigated. Several simulation scenarios are presented to provide insight about the injected fluid, injection scheme, well pattern, injector well completion, and well spacing. In summary it is concluded that: (1) the difference in the magnitude of core-measured permeability (10[superscript -3]-10[superscript -5] md) and field-measured permeability (10[superscript -1]-10[superscript -2] md) and the presence of a micro-fracture network in Bakken are the main reasons for facilitating oil production from Bakken. Furthermore, for enhanced oil production, the micro-fracture network is the main pathway for delivering water or CO2 to the tight matrix of the Bakken formation. (2) Dual-porosity modeling is the prudent approach for simulating primary production and improved oil recovery from Bakken because of the flow hierarchy; that is, flow from matrix to microfracture and microfracture network, then to the multi-stage hydraulic fractures, and eventually to the horizontal wellbore. (3) CO2 injection, via injector-producer well pattern, can enhance oil production but, for economic viability, recycling of the produced CO2 is absolutely necessary. (4) Oil production by CO2 injection is higher than by waterflooding, but field pilot tests are needed before any major field project is implemented.
  • Infrared thermographic defect detection in fuel cell gas diffusion electrodes

    Porter, Jason M.; Bittinat, Daniel C.; Braun, Robert J.; Sullivan, Neal P. (Colorado School of Mines. Arthur Lakes Library, 2013)
    Polymer Electrolyte Membrane fuel cells (PEMFCs) are energy conversion devices that offer high power densities and high efficiencies for mobile and other applications. Successful introduction into the marketplace requires addressing cost barriers such as production volumes and platinum content. The platinum-catalyst employed in PEMFC electrodes is a primary cost driver for manufacturing. For cost reduction, it is vital to minimize waste during large-scale production of electrodes, including gas diffusion electrodes (GDEs), by developing quality control (QC) diagnostics suitable for a continuous manufacturing environment. In this work, the development of an infrared thermography QC diagnostic for a GDE manufacturing web-line is conducted. A non-flammable H2/O2 gas mixture in N2 was passed through the GDE, reacting exothermically with the platinum catalyst, causing the GDE temperature to rise. Infrared imaging of the variations in the GDE's thermal profile revealed manufacturing defects and nonuniformities in the catalyst loading. Experiments with a moving substrate were conducted to demonstrate the applicability of the diagnostic for real-time web-line inspection. Initial experiments used a stationary enclosed testing manifold made of brass to quantify the thermal response caused by the gas-catalyst reaction. This manifold allowed for a controlled environment and to force all gas through the GDE. Experiments with the stationary manifold demonstrated successful detection of GDE defects. The GDE was then suspended above the manifold to simulate open-air testing. Although the thermal response decreased with increased offset distance, successful defect detection was demonstrated. Next, a perforated-tube gas knife was fabricated to deliver a uniform gas flow across the GDE surface in a line pattern. The gas knife uniformity was tested by microscope inspection of the gas knife holes and a hot plate cooling experiment. Finally, the diagnostic was demonstrated on a moving GDE by constructing a bench top roller system with a height and angle-adjustable gas knife holder. The GDE thermal response was tested under varying gas knife height, angle, flow-rate, and hydrogen concentrations. The optimized QC diagnostic was then demonstrated under conditions typical of a manufacturing environment, resulting in the successful detection of a 2 mm square defect on a GDE moving at 30 feet per minute. These results indicate that this QC diagnostic for detecting defects on GDEs is effective.
  • Establishment and characterization of a bioenergy-focused microalgal culture collection using high-throughput methodologies, The

    Posewitz, Matthew C.; Spear, John R.; Elliott, Lee Garrett; Cohen, Ronald R. H.; Dorgan, John R.; Darzins, Al; Donohoe, Bryon S. (Colorado School of Mines. Arthur Lakes Library, 2013)
    A promising renewable energy scenario involves utilizing microalgae as biological solar cells to capture the energy in sunlight and then harvesting the biomass for renewable energy production. Through photosynthesis photons are captured by light-sensitive pigment molecules and used to create a cellular chemical energy gradient. Microalgae ultimately use this energy gradient to drive their metabolism by reducing inorganic carbon into renewable, energy-rich organic hydrocarbon stores such as triacylglycerols (TAGs). These valuable molecules act as a cellular energy reserve, readily drawn from when required, often forming large oil-bodies within microalgal cells that can be abundant in certain oleaginous species. This is important for biofuel production because lipids can be extracted from biomass and then converted into a variety of biofuels such as renewable diesel and jet fuel. Thus, from a biofuels perspective, maximizing lipid productivity in selected microalgal feedstock strains is considered essential to the development of an economically viable algal biofuels industry. To achieve this, many current research and development efforts are directed towards genetically engineering well-characterized microalgae to optimize TAG production; however, this approach is a time-consuming, costly prospect and the number of well-characterized strains is relatively few, especially when compared to the number of known extant species. Alternatively, microalgal feedstock optimization could be more readily accomplished by taking advantage of the prodigious natural diversity of microalgae in the environment and identifying native strains of microalgae that, through natural selection, already possess key metabolic traits necessary for commercial feedstock development. Formulated on this premise, a collaborative project between the National Renewable Energy Laboratory (NREL) and the Colorado School of Mines (CSM) recently established and cryopreserved a clonal microalgal culture collection containing 360 unique strains with preliminary data regarding lipid accumulation and the growth potential of select isolates. The goal of this work has been to 1) perform a far more detailed characterization of the algal culture collection by developing high throughput screening procedures and tools for identifying fast-growing, oleaginous strains; and 2) gather further insight into the microalgal diversity found in the southwestern United States. Herein is described in detail the rationale, methods, results and conclusions of these efforts.
  • Advanced ICP-MS methods for examining the stability of silver nanoparticles in natural waters

    Ranville, James F.; Higgins, Christopher P.; Gately, Thomas Joseph; Braley, Jenifer C. (Colorado School of Mines. Arthur Lakes Library, 2013)
    The rapid growth of nanotechnology, specifically the incorporation of engineered nanoparticles (ENP's) into various products, will almost certainly lead to their release into the environment. Silver nanoparticles (nano-Ag) have seen widespread use in consumer products as a result of their antimicrobial properties. Silver ion (Ag+), is known to be toxic to a large variety of organisms, especially aquatic species. The release of Ag+ from nano-Ag under relevant environmental conditions is not currently well understood, as many studies use unrealistically high concentrations. This is in part due to limitations in the techniques used to detect and characterize ENP's. Using Single Particle Inductively Coupled Plasma Mass Spectrometry (SP-ICP-MS), a newly developed method to examine ENPs we are able to detect and quantify both nano-Ag and Ag+ at part per trillion concentrations, considered a realistic environmental level. In a collaborative study with the Trent University, PVP-coated 50 nm nano-Ag particles were introduced into several mesocosms within a lake. Their fate (particle number, dissolution) was monitored by a number of methods including SP-ICP-MS, FFF-ICPMS, and total Ag analysis. Before the experiment could proceed a preservation method was needed to allow sample transport from the Ontario Lake to the lab in Colorado. Flash freezing using liquid nitrogen was found to be an effective method for preserving the particles that there was minimal change to the particle size and number. The samples were stored at -80 degrees C until the time of analysis. 60 nm PVP capped particles were initially found to be 58.3 ± 5.3 nm and the flash frozen particles were found to be 58.4± 5.2 nm. A series of lab experiments were also performed using lake water in which the stability of nano-Ag particles was examined. The particles were found to decrease in diameter from 50 nm to 36 nm over the course of seven days. Particle number also decreased over the course of the experiment illustrating that further work on methodology is required. Typical decreases in particle number were on the order of 60% over the course of a week. The rate of particle loss/transformation was significantly slower when lake waters were filtered suggesting a role for other suspended sediments or biota in the process. Sterilization using autoclaving provided further evidence for the role of biota but results showed complex behavior depending on the methods used (e.g. filtration and autoclaving). This study further demonstrates the utility of SP-ICP-MS to detect, quantify and characterize ENPs, but further work is needed to fully understand the processes controlling nano-Ag stability in aquatic environments.
  • Statistical identification of local and regional wind regimes

    Hering, Amanda S.; Kazor, Karen E.; Navidi, William Cyrus; Tenorio, Luis (Colorado School of Mines. Arthur Lakes Library, 2013)
    Distinct wind conditions driven by prevailing weather patterns exist in every region around the globe. Knowledge of these conditions can be used to select and place turbines within a wind project, design controls, and build space-time models for wind forecasting. Identifying regimes quantitatively and comparing the performance of different regime identification methods are the goals of this research. The ability of statistical clustering techniques to correctly assign hourly observations to a particular regime and to select the correct number of regimes is studied through simulation. Pressure and the horizontal and vertical wind components are simulated under different regimes with a first-order Markov-switching vector autoregressive model, and the following five clustering algorithms are applied: (1) classification based on wind direction, (2) k-means, (3) a nonparametric mixture model, and (4,5) a Gaussian mixture model (GMM) with one of two covariance structures. The GMM with an unconstrained covariance matrix has the lowest misclassification rate and the highest proportion of instances in which the correct number of regimes are selected. This method is applied to one year of averaged hourly wind data observed at twenty meteorological stations. The lagged wind speed correlations between neighboring sites under upwind and downwind regimes are shown to differ substantially.
  • Investigation of unstable failure in underground coal mining using the discrete element method

    Ozbay, M. Ugur; Kias, Evan M. C.; Nakagawa, Masami; Mustoe, Graham G. W.; Berger, John R.; Higgins, Jerry D. (Colorado School of Mines. Arthur Lakes Library, 2013)
    Unstable failure in underground coal mining is the sudden and violent ejection of coal from mine walls and pillars into the mine opening. This thesis demonstrates the use of the discrete element method to simulate stable and unstable modes of compressive failure of a western U.S. coal. Two discrete element models are evaluated for their ability to simulate unstable and stable compressive failure using the discrete element program Particle Flow Code in Two Dimensions (PFC2D): the bonded particle model and the displacement softening model. Compressive strength tests show that the displacement softening model is better suited for unstable failure studies based on consistent behavior in stable and unstable modes of failure and a post-peak softening characteristic that is independent of the loading rate. A set of model behaviors, called indicators, are analyzed on their ability to distinguish the stability of failure in a series of unconfined compression tests and then a series slender pillar compressive strength tests. Generally, the indicators show consistent values for stable failures and increasing magnitude with increasing levels of instability. A grid based measurement technique is used to observe indicator behavior and model damage spatially. The work by the damping mechanism, kinetic energy, and the mean unbalanced force are used to analyze pillar edge failure in a model with excavation induced loading conditions. The indicators reveal unstable failure events, and a comparison between stable and unstable mining steps show that the indicators can be used to detect local instabilities on, such as pillar rib failure. Grid based measurements show that the unstable failure is initiated due to a single mining step and that failure occurred along a diagonal failure plane originating from the mine face similar to that seen in practice. Unstable failures show highly localized planes of failure while stable pillar failure is more dispersed. Future application of the techniques developed in this thesis include more in depth study of factors influencing unstable failures in coal mines including the mine/coal seam contact condition and depth.
  • LIDAR-assisted feedforward and feedback control design for wind turbine tower load mitigation and power capture enhancement

    Johnson, Kathryn E.; Wang, Na; Moore, Kevin L., 1960-; Steele, John P. H.; Vincent, Tyrone; Wright, Alan (Colorado School of Mines. Arthur Lakes Library, 2013)
    In the wind industry, research needs exist in the areas of reduction of wind turbine structural loads and maximization of wind energy capture in order to reduce the cost of wind energy. For modern large scale variable-speed variable-pitch wind turbines, these goals can be achieved via the use of modern controllers. Current commercial wind turbine control algorithms are typically feedback only and operate on a feedback signal such as the error in rotor speed or power out of the turbine. Recent advances in light detection and ranging (LIDAR) systems, which can provide realtime upcoming wind speed or direction measurements in front of the turbine using lasers, open a new area of research in feedforward wind turbine control. Feedforward controllers that use preview wind measurements can compensate for the effect of wind disturbances on rotor speed and turbine structural components (blades, tower, shaft, etc.). Feedback controllers can be augmented with these feedforward control strategies to improve turbine performance compared to feedback only controllers. In the dissertation, a number of combined feedforward and feedback control designs are proposed and developed for use with the Alstom ECO-100 3 MW turbine and the 600 kW controls advanced research turbine (CART3) at the National Renewable Energy Laboratory's (NREL) National Wind Technology Center (NWTC). Two research directions of wind turbine performance are pursued using LIDAR-enabled feedforward and feedback control designs: mitigating each turbine's fatigue loads and improving each turbine's energy production. For mitigating fatigue loads, an adaptive feedforward controller based on a filtered-x recursive least squares (FX-RLS) algorithm has been designed to augment a predesigned collective pitch feedback controller for the CART3. Adaptive control has the potential to overcome some of the drawbacks of linear time-invariant (LTI) control, because the control law in this case can be updated at every time step according to the wind input conditions. For the Alstom ECO-100, a collective pitch LQ-based preview control scheme that augments the existing feedback controller has been designed with a Kalman filter in the control loop as the observer. The LQ-based preview control strategy is a scheme to synthesize closed-loop controllers including both a feedforward term and a feedback term for LTI systems during tracking of previewed wind inputs by minimizing a defined output error. This design results in two feedback control loops: one is the baseline pitch control loop for speed regulation; the other is solved from the optimal preview control strategy for tower fore-aft fatigue load mitigation. Regarding maximizing energy production, two advanced LIDAR-enabled torque controllers have been developed for the CART3: 1) disturbance tracking control (DTC) augmented with LIDAR, where the wind speed estimator is replaced with the LIDAR measurement in the hopes of improving accuracy, but the feedback gain is kept at the same value as when the wind speed is estimated, and 2) optimally tracking rotor (OTR) control augmented with LIDAR, where we use a LIDAR preview measurement to provide the potential aerodynamic torque to give the rotor additional acceleration and deceleration. For the Alstom ECO-100, a nonlinear and a linear below rated feedforward torque controllers are designed to alleviate the effect from wind disturbance on rotor speed. The nonlinear feedforward torque term is designed according to the wind measurement that can predict the required future torque command to regulate rotor speed and the linear feedforward torque controller according to disturbance accommodating control (DAC) has one benefit over the nonlinear strategy of not requiring the feedback signal. Also, a tower fore-aft feedback damping pitch controller combined with a feedforward pitch controller designed through the method of Lagrange multipliers optimization has been developed in this research. Below rated feedforward pitch control strategy could assist the turbine to regain the optimal power coefficient values without increasing the thrust coefficient. The proposed LIDAR-enabled controllers are evaluated in simulation with the full nonlinear turbine models and numerous stochastic turbulent wind conditions. The control effectiveness is evaluated by comparing to a feedback only controller for tower fore-aft and side-to-side bending moments, blade flapwise and edgewise bending moments, low speed shaft torsional load, averaged power, rotor speed regulation and required control authority.
  • GIS procedure for assessing abandoned coal mine subsidence hazard, Boulder-Weld counties, Colorado, A

    Higgins, Jerry D.; Marsters, Ryan; Santi, Paul M. (Paul Michael), 1964-; Zhou, Wendy (Colorado School of Mines. Arthur Lakes Library, 2013)
    The objective of this research is to explore a new GIS-based procedure for predicting coal mine subsidence hazard by geographically relating data from past subsidence investigations. A coal mine subsidence susceptibility map was created using the procedure for the Tri-Towns communities, Weld County, Colorado, much of which is underlain by abandoned coal mines. The literature from past mine subsidence investigations was evaluated for causative indicators and their applicability to the project. The primary indicators utilized were extent of mining, depth of mined interval, percentage of claystone in the overburden, estimated condition of mine workings, groundwater withdrawal, and subsidence event history. The elapsed time since a mine was closed is another traditional subsidence factor; however, it was ruled out as a predictive factor since the last mine closed in 1979 and the primary failure period of 15 years has passed. A drilling program helped to assess the factors in some locations. Past site investigation data used in the project, primarily an extensive borehole data compilation, were available at the Mine Subsidence Investigation Center, a component of the Colorado Geological Survey (study sponsors). A few different GIS techniques were explored for combining the data and the selected procedure was developed to reduce bias resulting from incomplete, unknown, or unreliable data. The technique combines depth to workings and percent claystone borehole extrapolations using the Fuzzy Overlay toolset. The overlay is then factored on a mine-by-mine basis incorporating groundwater withdrawal and mine void presence. The resulting mosaic is then reclassified into an interpretive map displaying the severity of abandoned mine subsidence hazard. The model was calibrated based on observed mine condition and validated through an analysis of past subsidence events. A map of subsidence hazard was constructed that may aid in city planning and future subsidence studies
  • Experimental investigation of recycling rare earth elements from waste fluorescent lamp phosphors

    Mishra, Brajendra; Eduafo, Patrick Max; Taylor, Patrick R.; Anderson, Corby G. (Colorado School of Mines. Arthur Lakes Library, 2013)
    Characterization techniques and experimental measurements were used to evaluate a process for recycling rare earth elements (REEs) from spent fluorescent lamp phosphors. QEMSCAN analysis revealed that 70% of the rare earth bearing minerals was less than 10 µm in size. Feeds of varying characteristic were received throughout the course of the experimental analysis. A representative sample of the as-received feed contained 5.8% total rare earth elements (TREE) and upon sieving to below 44 µm, the grade increased to 16.5% TREE. By sieving further to below 10 µm, the grade increased to 19.8% TREE. Hydrochloric acid was used as lixiviant in batch leach experiments on the phosphor powder. The maximum extraction obtained was 90% for europium and yttrium at the following conditions: 1.5 M HCl, 70 degrees C, 1 hr, 30 g/L and 200 rpm. However, the solubility of cerium, lanthanum and terbium remained low under these conditions. Multistage leaching and calcination followed by leaching processes also resulted in poor extraction of cerium, lanthanum and terbium. Based on experimental results a new process for extracting the chief REEs from end of life fluorescent lamps has been developed. The proposed process employs a multistage acid leach using HCl under both mild and strong leaching conditions in addition to thermal treatment of the powder. Using this process, about 90% of the europium and yttrium is extracted in the first stage leach and over 90% of lanthanum in the second stage leach. There is also over 80% of cerium and terbium extracted which marks a significant improvement. Precipitation using oxalic acid as precipitant and sodium hydroxide for pH adjustment was able to recover 100% of the REE from the leach liquor. However, the purity of the mixed rare earth oxides produced is very low because of co-precipitation of impurities from the leach liquor. The process needs to be optimized for potential industrial application.
  • Fourth-order finite difference scheme for Poisson's equation in polar coordinates on the unit disc, A

    Bialecki, Bernard; Wright, Lyndsey; Ganesh, Mahadevan; Collis, Jon M. (Colorado School of Mines. Arthur Lakes Library, 2013)
    We solve Poisson's Equation on the unit disc in polar coordinates using a fourth-order finite difference method. We use a half-point shift in the r direction, in order to avoid approximating the solution at r = 0. We derive a new fourth-order accurate finite difference method from analysis of the truncation error of the well-known second-order scheme. The resulting linear system is solved very efficiently (with cost almost proportional to the number of unknowns) using a combination of a Matrix Diagonalization Algorithm and Fast Fourier Transforms.

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