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A research report submitted in partial fulfilment of the requirements for the degree of Master of Science in Engineering, to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, 2019 / A dynamic simulation study is a critical deliverable of a mine project feasibility study. Mining houses rely on simulation to confirm that complex, integrated systems can achieve design capacity before investment decisions are made. Dynamic simulations are powerful tools, but only if they are developed using the right methodology, and with information that has been verified. The importance of work in the field of mine dynamic simulation validation was made clear during the early stages of this research report when it was identified that there is limited information available on the subject. Work conducted in the realm of validation can make an invaluable contribution to the success of future projects undertaken around the world. The last few years have been difficult for employees of some mining companies because of looming job cuts due to high production costs, high overheads, and decreasing product demand. For many mining companies, it was a case of survival which gave rise to the development of new strategies and innovative thinking. Coal Mine A Life of Mine (LOM) extension project is a prime example of innovative thinking. In this case, the project was approved for implementation when export coal prices were on the low end of the price cycle. The dynamic simulation of the full materials handling value chain conducted during the project was of utmost importance, and provided assurance to the project review team that annual production targets can be achieved. The simulation development methodology was based on a unique approach that reduced time spent on the simulation through the integration of different, independent models that represented sub-systems in the materials handling value chain. There was, therefore, a strong need to validate the simulation, which could lead to the adoption of this approach on future projects. In this research report, the LOM extension project scope and the mining activities conducted by Coal Mine A are explained, and a brief, but interesting history of Modelling and Simulation (M&S) is provided. The subject of M&S is vast and has evolved into its own separate discipline. M&S is an invaluable tool, and the importance of verification, validation and credibility is elaborated on. The development of the simulation and the inputs and outputs of the simulation are discussed before the validation effort. The work conducted on the validation aimed to confirm the accuracy of the simulation unequivocally. Although the production target was not achieved as predicted by the dynamic simulation during the period of validation, there was an indication that the materials handling value chain could perform as predicted as each of the individual sub-systems had achieved the design capacity. Problem areas were identified which could be attributed to the poor performance, and if these areas are addressed, the system could perform as predicted by the simulation. This confirms that dynamic simulation can add value to predictions about mining system performance such that informed decisions can be made. / TL (2020)

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This investigation details the effects of fuel constituents on ash deposition through systematic experimental and theoretical analyses of fundamental particle experiments and a suite of fuels with widely varying inorganic contents and compositions. The experiments were carried out in the Multifuel Flow Reactor (MFR) at Brigham Young University. Fuels included several biomass fuels (straw, sawdust and mixtures of straw-sawdust with other additives such as Al(OH)3, CaCO3, etc.) and four commercially-used coals (Illinois#6, Powder River Basin – Caballo and Cordero, Blind Canyon, and Lignite – Beulah Zap). The data from the series of experiments quantitatively illustrate the effects of fuel properties, physical and/or chemical, on ash deposition rate mechanisms. In deposition investigation, the most significant deposition mechanisms in a general ash deposition model – inertial impaction, condensation and eddy impaction – were selected. In this PhD work, these three mechanisms are analyzed using simulation techniques such as Fluent and programming languages such as C++. The experimental data was collected for deposition rate measurements to provide a data set for the model validations except for eddy impaction. In this model analyses, the impaction efficiency model predictions from this work indicated lower impaction efficiencies than the traditional potential flow model presented by others (Israel 1983). The experimental data by others (Lokare 2003) and the data collected in this work support these predictions and present a new impaction efficiency correlation as a function of Stokes number. Similarly, the capture and condensation models perform well and are supported by the respective experimental data. The comprehensive ash deposition model predicts ash deposition rates within 10% of experimental data and is able to distinguish the role of various additives in recipe fuels combustion. As an additional results, NOX behavior of Illinois#6 and PRB (Caballo) in oxyfuel combustion show evidence of inherent NOX reducing feature of oxyfuel combustion.

A major problem associated with any power generation process in which coal is burned is the formation of ash and slag from the inorganic constituents of the coal. Ash deposition on heat transfer surfaces in coal-fired reactors is unavoidable and can have a significant effect on the performance and maintenance of boilers and gasifiers. A greater understanding of the thermal properties of coal ash deposits is important in reducing their negative impact. This work presents the development of an experimental method for making in situ measurements of the spectral emittance of coal ash deposits. It also provides measured emittances for two coals under oxidizing and reducing conditions. The experimental procedure consisted of burning coal in a down-fired entrained-flow reactor and collecting ash deposits on a circular probe under controlled conditions. Spectra collected from a Fourier transform infrared (FTIR) spectrometer were combined with an instrument response function to measure the spectral emissive power from the surface of the ash deposit. The spectral emissive power was used to infer the deposit surface temperature. These two measurements were used to calculate the spectral emittance of the deposit. This experimental method was validated by measuring the known temperature and spectral emittance of a blackbody radiator. The experimental method was used to find the spectral emittance of bituminous and subbituminous coals under both oxidizing and reducing conditions. The bituminous coal analyzed was Illinois #6 coal from the Crown III mine and the subbituminous coal analyzed was Wyoming coal from the Corederro mine. The spectral emittance of the subbituminous coal was lower than that of the bituminous coal under both oxidizing and reducing conditions. The emittances of both coals under reducing conditions were greater than those found under oxidizing conditions. A total band emittance was defined and calculated for each coal. The total band emittance as well as theoretical upper and lower total emittance limits were calculated as functions of temperature. There was little temperature dependence in the total emittance estimates.

The cleaning and dewatering of ultrafine (minus 44 micron) coal slurries is one of the biggest challenges faced by coal industry. Existing commercial technologies cannot produce sellable products from these ultrafine streams; therefore, the industry is forced to discard this potential energy resource to waste impoundments. This practice also has the potential to create an environmental hazard associated with blackwater pollution. To address these issues, researchers at Virginia Tech have worked over the past decade to develop a novel separation process that simultaneously removes both mineral matter and surface moisture from fine coal particles. The first stage of the process uses immiscible non-polar liquids, such as straight chain hydrocarbons, to selectively agglomerate fine coal particles in an aqueous medium. The agglomerates are then passed second stage of processing where mild agitation is used to disperse and fully engulf hydrophobic coal particles into the non-polar liquid and to simultaneously reject any residual water and associated hydrophillic minerals entrapped in the agglomerates. The non-polar liquid, which has a low heat of evaporation, is then recovered by evaporation/condensation and recycled back through the process. The research work described in this document focused on the engineering development of this innovative process using batch laboratory and continuous bench-scale systems. The resulting data was used to design a proof-of-concept (POC) pilot-scale plant that was constructed and successfully demonstrated using a variety of fine coal feedstocks. / Ph. D.

It has been found that naturally hydrophobic carbonaceous materials such as coal and graphite can be selectively coagulated and separated from hydrophilic impurities without the use of oily agglomerants, flocculants or electrolytes. The coagulation occurs at ζ-potentials significantly higher than those predicted by the classical DLVO theory, suggesting that it is driven by a hydrophobic interaction energy. Thus, the process is referred to as the selective hydrophobic coagulation (SHe) process. The fundamental development of this process is the focus of this study. In this study, the energy barriers for the coagulation of two different coal samples and a graphite sample have been calculated using the extended DLVO theory, which incorporates the hydrophobic interaction energy in addition to the dispersion and the electrostatic energies. Stability diagrams have been developed from the data, which show that the maximum ζ-potential at which a given coal can coagulate decreases as surface hydrophobicity decreases. For the coagulation of minerals present in coal, the classical DLVO theory has been used for the energy barrier calculations. The results of these calculations provide an excellent correlation with the results from a series of SHC tests conducted with run-of-mine coal. The strength of the coal aggregates have also been investigated by measuring the coagula size distributions under different hydrodynamic conditions. The coagula size distributions were measured using an in-situ particle size analyzer. These results have been used along with models for coagulation rate and breakage rate to determine strength characteristics of the aggregates and to verify the primary parameters controlling the aggregate size. The study found that the coal and graphite aggregates incurred a substantial reduction in size when a small amount of mechanical agitation was applied. Based on this outcome, quiescent continuous processes have been successfully designed and developed to separate the coagulated hydrophobic particles from the dispersed hydrophilic particles. / Ph. D.

In today's energy constrained world, carbon capture and sequestration can play an essential role in mitigating greenhouse gas emissions, while simultaneously maintaining a robust and affordable energy supply. This technology is an end-of-pipe solution that does not contribute to a decrease of the production of greenhouse gases, but is very useful as a transition solution on the way towards other sustainable energy production mechanisms. This research involves the development of a comprehensive decision making framework for assessing the techno-economic feasibility of CO2 sequestration in unmineable coal seams, with the Central Appalachian Basin chosen for analysis due to the availability of empirical data generated through recent characterization and field validation studies. The studies were conducted in order to assess the sequestration capacity of coal seams in the Central Appalachian Basin and their potential for enhanced coal bed methane recovery. The first stage of this research involves assessment of three major sequestration performance parameters: capacity, injectivity, and containment. The assessment is focused on different attributes and reservoir properties, characteristic of deep unmineable coal seams in the Central Appalachian Basin. Quantitative and qualitative conclusions obtained through this review process are used later in the identification of the minimum set of technical information necessary for effective design and development of CO2 storage operations. The second section of this dissertation analyzes economic aspects of CO2 sequestration. This segment of the research uses a real options analysis to evaluate the impact of major sources of uncertainty on the total cost of developing and operating a CCS project in a regulatory environment that expects implementation of carbon taxes, but with uncertainty about the timing of this penalty. Finally, all quantitative and qualitative information generated in the first two stages of this research were used for development of a decision making framework/matrix that summarizes the interactions between major technical and economic parameters and constraints, on the other hand, and their impact on overall feasibility of CO2 sequestration in unmineable coal seams. This framework will provide user with capability to address complex problems in a more systematic way and to analyze the most efficient way to utilize available resources. / Ph. D.

The maximum von Mises stress is calculated for solid finite element models of splined shafts with straight-sided teeth. One spline shaft is stepped with larger diameter section containing spline teeth and the smaller diameter section circular and cylindrical with no spline teeth. A second shaft is not stepped, but contains incomplete spline teeth. Finite element analyses are performed for the cases of a stepped shaft of three different step size ratios (d/D). The second set of models consists of a solid cylindrical shaft with incomplete spline teeth. The incomplete regions of the spline teeth are modeled in three radii (R). Bending, torsion, and combined loads are applied to each model, including several combinations of bending and torsion between pure bending and pure torsion. Finite element stress results are converged to within 2% for verification. The stresses in the stepped splined shafts are up to 50% greater than nominal stresses in the non-splined section and up to 88% greater than nominal stresses splined section. Stresses in the partially splined shaft showed little or no correlation between the hob radius and the magnitude of the peak von Mises stress, but show a strong correlation between the peak stress and the proportion of bending to torsion. The peak von Mises stress occurs when the applied load consists of greater proportions of torsion as opposed to bending. Stresses in the partially splined shaft are up to 42% greater than the well-developed nominal stress in the non-splined section of the shaft, and up to 7% greater than the nominal stresses in the splined section. / Master of Science