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Thesis--University of Missouri, School of Mines and Metallurgy, 1908. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed November 18, 2008)

The overall heat-transfer mechanism within a direct-fired rotary kiln has been examined theoretically. To accomplish this task, the work has been divided into three parts: (1) the characterization of radiative heat transfer within the freeboard area; (2) the overall heat transfer mechanism in the absence of freeboard flames; and, (3) the overall heat transfer mechanism in the presence of freeboard flames. The radiative heat transfer between a nongray freeboard gas and the interior surface of a rotary kiln has been studied by evaluating the fundamental radiative exchange integrals using numerical methods. Direct gas-to-surface exchange, reflection of the gas radiation by the kiln wall, and kiln wall-to-solids exchange have been considered. Graphical representations of the results have been developed which facilitate the determination of the gas mean beamlength and the total heat flux to the wall and to the solids. These charts can be used to account for both kiln size and solids fill ratio as well as composition and temperature of the gas. Calculations using these charts and an equimolal CO₂-h₂O mixture at 1110 K indicate that gas-to-surface exchange is a very localized phenomenon. Radiation to a surface element from gas more than half a kiln in diameter away is quite small and, as a result, even large axial gas temperature gradients have a negligible effect on total heat flux. Results are also presented which show that the radiant energy either reflected or emitted by a surface element is limited to regions less than 0.75 kiln diameters away. The radiative exchange integrals have been used, together with a modified reflection method, to develop a model for the net heat flux to the solids and to the kiln wall from a nongray gas. This model is compared to a simple resistive network/gray-gas model and it is shown that substantial errors may be incurred by the use of the simple models. To examine the overall heat-transfer mechanism in the absence of freeboard flames a mathematical model has been developed to determine the temperature distribution in the wall of a rotary kiln. The model, which incorporates a detailed formulation of the radiative and convective heat-transfer coefficients in a kiln, has been employed to examine the effect of different kiln variables on both the regenerative and the overall heat transfer to the solids. The variables include rotational speed, per cent loading, temperature of gas and solids, emissivity of wall and solids, convective heat-transfer coefficients at the exposed and covered wall, and thermal diffusivity of the wall. The model shows that the regenerative heat flow is most important in the cold end of a rotary kiln, but that generally the temperature distribution and heat flows are largely independent of these variables. Owing to this insensitivity it has been possible to simplify the model with the aid of a resistive analog. Calculations are presented indicating that both the shell loss and total heat flow to the bed may be estimated within 5 per cent using this simplified model. Finally, to examine the overall heat-transfer mechanism in the presence of freeboard flames a mathematical model has been developed to determine both the temperature and heat flux distributions within the flame zone of a rotary kiln. The model, which is based on the one-dimensional furnace approximation, has been employed to examine the effects of fuel type, firing rate, primary air, oxygen enrichment and secondary air temperature on the flame temperature, solids heat flux shell losses, and overall flame length. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Convective heat transfer in a rotary kiln was studied as a function of operating parameters. The experiments were carried out in a steel kiln of 0.19 m in diameter and 2.44 m in length. The operating parameters covered included gas flow rate, solid throughput, rotational speed, degree of solid holdup, inclination angle, particle size and temperature. To minimize radiation effects, air was used as the heating medium and maximum inlet air temperatures were limited to 650 K. Ottawa sand was used in all the runs except in the study of the effect of particle size where limestone was employed. The experiments were conducted under conditions where the bed height along the kiln was maintained constant and the bed was in the rolling mode. Both the heat transfer coefficients from the gas to the solids bed and the gas to the rotating wall were found to be significantly influenced by gas flow rate. Increasing rotation al speed increases the gas to bed heat transfer, but decreases the gas to wall heat transfer. The former effect is relatively small. The effect of degree of fill was slightly negative in the gas to solids bed heat transfer, and insignificant in the heat transfer from the gas to wall. The effects of inclination angle, solid throughput, particle size and temperature were found negligible over the range tested. One of the major findings in this study is that contrary to suggestions in the literature, the coefficients for gas to bed heat transfer are about an order of magnitude higher than those for gas to wall. The higher coefficients for gas to solids bed are attributed to two factors, the underestimation of the true area by basing coefficients on the plane chord area and the effect on the gas film resistance of the rapid particle velocity on the bed surface. The experimental data were correlated in a form suitable for design purposes, and the results compared with meager data available in the literature. A mathematical model was developed for convective heat transfer from the gas to a rolling solids bed. The model requires the knowledge of the gas to particle heat transfer coefficient and the rolling velocity of the aerated particles. The model gives a reasonable prediction of the gas to bed coefficient in a rotary kiln using values of the gas to particle coefficient taken from the literature. The required data on the surface velocity of particles was obtained in a lucite kiln of the same size. Residence time distribution of particles was also studied briefly to verify that solids were nearly in axial plug flow. A simple mathematical model of a rotary kiln heat exchanger is presented. This model predicts gas, solids and wall-temperatures in a kiln as a function of the kiln design and operating parameters using the heat transfer correlations developed in this work. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

A project report submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering. / The flushing flow rate required to maximise penetration rate of holes drilled by rotary percussion is dependant on drilling parameters and chip size. Experimental work to determine the optimal flushing water flow rate for two common drilling situations was undertaken. It consisted of drilling, analysis of chip samples and flow visualization. A computer modal to predict flow rate was developed. Its output and the experimental results Were combined to explain the relationship between penetration rate and flow rate. All chips should be fiushed from the gap between the bit and the end of the hole in the time between hammer blows (ie. - within the duration of a percussion cycle). As flow rate increases, flushing improves and therefore penetration rate increases. Once flushing is adequate there is no mechanism for further increases in penetration rate, thus it remains constant and independent of further increases in flow. / Andrew Chakane 2018

viii, 197 leaves : illustrations.

Thesis (M.S.)--Rochester Institute of Technology, 2009. / Typescript. Includes bibliographical references (leaves 119-124).

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The objective of this research is to analyze and develop controller to minimize vibrations of the drill string in rotary drilling rigs. The rotary drilling process is affected by many vibrations which adversely affect the drilling efficiency. The vibrations are mainly classified into three: lateral, tosional and axial. Among the vibrations, lateral vibrations are the most destructive. The research conducted a detailed analysis on lateral vibrations. Bent drill string and unbalanced drill bit was found to be its major causes; and the resultant phenomenon was known as drill bit whirl. Practical demonstration and analysis of the bit whirl phenomenon was done by conducting experiments using an unbalanced drill bit model. Their controllability issues were also discussed and practical solutions suggested. Black box identification methods were applied to develop mathematical models for the system. Box Jenkins structure model was identified and validated by a twofold procedure. Accurate simulations results were obtained with a mere 0.05% residual. Studies revealed that the vibrations in rotary drilling were aggravated by two major causes: borehole friction and critical operation speeds. This research developed a self tuning adaptive controller which could effectively mitigate the vibration aggravating causes and improve overall drilling efficiency. On practical implementation, the controller automatically detected vibrations, mitigated the vibration aggravating causes, and resumed normal drilling operation in less than 10 seconds. The controller action was proven experimentally in two cases: (1) when affected by borehole friction and (2) in presence of an unbalanced drill bit. All the experiments and control techniques applied in this research are validated by experimental data. The prototype used in this research is also distinguished from the rest due to a universal joint, providing an additional two degrees of freedom. Thus, the laboratory set-up provided better dynamic analysis.