PhD, Faculty of Engineering, University of the Witwatersrand

Coal supplies over 90% of South Africa’s electrical energy power requirements. The coal mainly comes from the Witbank and Highveld coalfields, which together account for about 75% of South Africa’s production. However, the Witbank and Highveld coalfields will be depleted in the next 15 to 25 years. This poses an energy risk for the country unless replacements coalfields are fully developed in time. Of the country’s total of 19 known coalfields, the Waterberg coalfield despite its small geographical footprint is a suitable replacement for the Witbank and Highveld coalfields because it contains the largest known coal reserves. However, exploitation of the Waterberg coalfield faces challenges of mining deep-seated multiple coal seams that are intercalated with mudstone and shale in the top 50-60 m and occurring over a coal thickness in excess of 110m. For example, east of the Daarby fault, coal seams are at a depth in excess of 250m. This challenge is further amplified by the fact that South Africa currently does not have experience in mining deep, multi-seam coal formations. While the shallow reserves in the western portion of the Waterberg are currently mined by an open-pit, the deep eastern part will need to be exploited by multi-seam underground mining on a scale never before attempted in South Africa. This dissertation has reviewed international practice and concludes that United States experience is the most applicable to the underground mining of the Waterberg reserves. It is probable that total extraction using longwall will be the correct choice of mining method. Finally, this dissertation has illustrated the essential need for fundamental research if the industry is to successfully transition to the Waterberg. While a horizon of 20-25 years appears far- off to those concerned with day to day production issues, the mining, infrastructure, environmental and social issues are of such magnitude that co-ordinated research will need to be initiated well ahead of mining activities and preferably in the next few years.

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Ph.D., Faculty of Engineering, University of the Witwatersrand, 1985.

Thesis (M.Sc.), Faculty of Engineering (Metallurgy and Materials Engineering), 1996

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

by Wong Woon-chung Jonathan. / Bibliography: leaves 232-260 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1984

Photocopy of typescript. / Digitized by Kansas Correctional Industries

High-intensity pyrolysis, rapid heating in an inert gas atmosphere at up to 20 atm pressure, of 6 Australian coals was examined to gain further insight into high-intensity processes such as Integrated Gasification Combined Cycles (IGCC). Experiments focussed on pyrolysis in a specially developed Wire Mesh Reactor (WMR). The particle temperature lagged that of the mesh by 0.2 seconds at a heating rate of 100??~C s -1 and was predicted by modelling. This is part of the reason the volatile yield (VY) results for 10 s hold-time at ???b1.7 wt% daf of coal, is much more reproducible than 1 s hold-time experiments at ???b4.2 wt% daf of coal. Four coals of the same rank did not behave identically when heated. Three of the coals had a pyrolysis VY the same as the proximate VM when heated to 100??~C at 1 atm but the fourth, higher inertinite coal had a 1 atm pyrolysis VY 90% of its proximate VM. All four coals of similar rank had a significant decrease in VY, between 10 and 20 wt% daf of coal, with pressure increasing from 1 to 20 atm. The two lower rank coals showed less decrease in VY with increasing pressure than the higher rank and higher inertinite coals. The lower decrease in VY with increased pressure was mostly attributed to the lower inertinite levels for both the coals of similar rank and VM, and the coals of lower rank. Char characteristics examined focussed on pore Surface Area (SA). For high intensity WMR and Drop Tube Furnace (DTF) pyrolysis experiments CO2 SA for char from a particular coal was similar but the BET SA different. This was due to the char in the WMR experiments having longer to form larger pores determined by BET N2 SA. Both the N2 and CO2 SA was more than an order of magnitude greater than for low intensity pyrolysis char. This highlights that the WMR can be used to attain char with similar CO2 SA characteristics as other high intensity pyrolysis experiments and to provide a more meaningful insight into char reactivity than low intensity chars do.

Cleats are natural fractures in coal that serve as permeability avenues for darcy flow of gas and water to the well bore during production. Theoretically, the development of cleat and coal-seam permeability is related to the rank, type and grade of the coal concerned. The permeability of a coal seam, moreover, may change during gas production, due to either matrix shrinkage, cleat closure or both. Matrix shrinkage and cleat closure are also affected by numerous geological factors, including coal rank, desorption character and geological setting. A method integrating geochemical and petrographic analysis, reservoir engineering diagnosis, geophysical data and production characteristics has been developed, and used to determine the initial permeability of coal seam on a metre by metre scale. This overcomes the constraint of conventional well test by refining the test intervals. The effect of coal rank, grade and type on the initial permeability of coal seams was also investigated, with the special reference to the coals of the Galilee Basin. The permeability was estimated using analytical equations based on the permeability data obtained from well tests and from cleat descriptions within the seam section. This aspect of the study showed that the coal type, rank and grade strongly influence the initial permeability of individual coal seams. Increase in ash content has negative effect on cleat development and permeability. On contrast, increasing coal rank and proportion of bright coal lead to reduction in cleat spacing and increase in permeability. Twenty three core samples collected from the Qinshui Basin in China were evaluated in the laboratory to investigate the effects of coal grade, rank and type on the change in permeability during pressure depletion. The experimental factors included the coal's geochemical properties, the permeability against changing pressure, and strain with pore pressure depletion. This part of the study fund that permeability changes with pore pressure depletion in relation to coal rank, grade and type. The strain values determined by the experiments with pressure depletion were used to identify the mechanical principles associated with changes in permeability during pressure depletion in relation to the rank, grade and type of the coal concerned. A reservoir simulation study was used to investigate the effects of desorption pressure, geological setting and coal rank on the variation in permeability under in-situ conditions during coalbed methane production, based on a study in the Hedong area, Ordos Basin, China. The simulations allowed history matching of gas and water production from 12 wells with the actual well conditions specified as the model pressure. Good agreement was achieved between the model yields and the actual production data, suggesting that the changing permeability interpreted from the simulation is a realistic representation of the in-situ reservoir properties. The reservoir simulation study found that the decreases in permeability with production exceeded the increase in permeability caused by matrix shrinkage for nearly all wells in the Hedong area. The magnitude of the decrease in permeability increases as the gap between initial pressure and desorption pressure increases. The decrease in permeability is slower in the zone closest to the fault. The reservoir simulation has demonstrated that coal rank influences significantly the change in permeability during coalbed methane production.