Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Engineering and the Built Environment, School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, 2017 / Three medium rank C coals and a discard coal from different coalfields within the Karoo Basin were investigated. In this study, physico-chemical properties, ash fusion tests, quantitative single particle -electron probe X-ray microanalysis (SPAEPXMA), petrography, X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), and micro-Raman spectroscopy (mRs) were used as analytical techniques of choice to investigate the heterogeneous nature of coals, including mineralogical structure, mode of occurrence, and association of mineral matter in coals. The aim of the work was to highlight the significance of understanding the heterogeneous nature of coals, and to develop comprehensive and reliable approaches of characterising coals, coal ashes, and predict the behaviour of coals in coal conversion processes. The FTIR technique identified a well ordered kaolinite of authigenetic origin, characterised by inner hydroxyl group with H2O vibration at 3618 cm-1 absorption bands as the major mineral. Smectite and muscovite were identified at peaks 797 cm-1 and 799 cm-1 respectively, with quartz confirmed by the υ (Si-O-Si) and δ (Si-O) bands. The SPA-EPXMA data, modelled using principal component analysis (PCA) and chemical boundary classification (CBC), identified a diverse range of minerals such as alunite, chlorite, fayalite, almandine, anatase, ilmenite, brushite, goyazite, gypsum, dolomite, calcite, sodalite, rhodochrocite, and halite in raw coal samples. The mRs technique showed that in addition to bassinite, other oxidation products that formed at low temperature included lepidocrite and coquimbite. The technique proved to be ideal for the characterisation of high temperature ashes. High spatial resolution of mRs confirmed the presence of mixtures of anatase, brookite, and rutile, hematite, nephaline, apatite, crednerite and apatite in high temperature ashes. The SPA-EPMXA and mRs technique probed minerals on a micro-scale and their application could be extended to prediction of slagging and fouling behaviour in coals. The multiple technique approach revealed the importance of using a combination of techniques to characterise coals, and provided useful information that can help understand and relate the mineralogical and elemental composition of coals. This knowledge could be useful in designing conversion processes, and necessary downstream manipulations. / XL2018

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Bibliography: pages 116-119. / In South Africa, ever increasing quantities of fine (-0,5 mm) coal are being produced as a result of the increased use of mechanised mining methods. Very few mines beneficiate the fines; in most cases they are discarded. However the fine size of this material suggests that it should be well liberated, with the potential to produce a low ash product. This thesis forms part of an ongoing research program examining the use of flotation to beneficiate coal fines to produce a low ash product. Coal is a highly heterogeneous material, consisting of a number of both organic (maceral) and inorganic (mineral) components with different physical and technological properties. Therefore in order to evaluate and interpret flotation results, an understanding of the liberation characterist ics of both the organic and inoganic components is required. This thesis presents a liberation study on fine coal from the Greenside Colliery, a typical colliery in the Witbank Coalfield which is the most important source of South African low ash coal. The study was performed by mining a run of mine coal sample to varying degrees of fineness (from 30 % finer than 150 micron to 90 % finer than 150 micron), screening, and assessing the liberation of each size fraction. These results were compared to those obtained from a sample of naturally arising fines (thickener underflow). Liberation was assessed by float and sink analysis, and for this purpose a new technique was developed that enables rapid and accurate float and sink analysis of coal down to a few micron in size. Petrographic analyses were performed to determine the liberation of the organic coal components.

In recent years, a great deal of interest has been shown in developing methods for preparing super—clean coal containing less than 2% ash and 0.5% sulfur. New techniques for recovering fine coal, such as micro—bubble flotation, can achieve the desired result provided mineral matter is sufficiently liberated. To achieve sufficient liberation, however, it is often necessary to grind to a mean particle size finer than 10 microns. Since conventional ball mills are highly inefficient in this fine size range, the stirred ball mill has been proposed as a more suitable means for ultrafine grinding. / Master of Science

Both active and residual mine subsidence resulting from underground coal mining have caused surface damage to land and structures. A method of subsidence mitigation successfully used abroad, and to a much lesser extent in U.S. coal mines, is backfilling. In addition to the possible benefits of subsidence mitigation, backfilling has the potential to increase coal recovery, enhance ventilation control, and to minimize mine fires. Backfilling can also be used as a means of mine refuse disposal, provided the refuse is a suitable fill material. A Iiterature review has been made of the various backfilling practices and stowing materials that have been used in both underground hardrock and coal mines. The mechanics of fill support were also reviewed, as well as how the physical properties of a stowing material affect its ability to provide ground support. Based on this review, a testing program was conducted to examine properties of coal refuse which are pertinent to its placement and its ability to act as a ground support material. The testing program consisted of the slake durability test, plasticity test (Atterberg's Limits), grain-size analysis, standard Proctor compaction test, falling-head permeability test, and triaxial compression test. Based on the geotechnical properties of the refuse which was sampled, it was determined to be inadequate as a backfill material. / Master of Science

This study was conducted at the Virginia Tech Power Plant to measure and compare stack emissions while firing coal alone and coal mixed with shredded tires. The coal-tire mixtures consisted of 10 and 20 percent tire chips. Modified EPA method 5 sampling train was used to determine particulate emissions. CO emissions were determined with an ENERAC 2000 gas analyzer. Supelco XAD-2 resin was used in the modified method 5 sampling train to adsorb nonpolar, vapor phase hydrocarbons. The XAD-2 resin was extracted and the wash concentrated before High Performance Liquid Chromatography (HPLC) was used to quantify the presence of benzene, chrysene, phenol, and benzo(a)pyrene. Particulate emissions resulting from the combustion of 0, 10 and 20 percent tire mixtures with coal were 0.88, 2.32, and 2.13 lb/10⁶ Btu, respectively. For carbon monoxide, the emissions were 0.17,0.22, and 0.33 1b/10⁶ BTU for 0, 10, and 20 percent tire mixtures, respectively. Large variations in polynuclear aromatic hydrocarbon (PAH) emissions were observed. Therefore, only trends in the PAH data can be discussed. Phenol emissions appeared to increase with the addition of shredded tires to the combustion process. Benzene and benzo(a)pyrene emissions appeared to decrease with the addition of shredded tires to the combustion process. An increase in chrysene emissions for 20% addition of shredded tires was observed. A larger data base is needed in order to develop stronger conclusions regarding PAH emissions resulting from coal/tire shred combustion in a conventional spreader stroker. / Master of Science