Numerical simulations of coal gasification process inside a generic 2-stage entrainedflow gasifier are carried out using the commercial CFD solver ANSYS/FLUENT. The 3-D Navier-Stokes equations and eight species transport equations are solved with three heterogeneous global reactions, three homogeneous reactions, and one thermal cracking equation of volatiles. Finite rates are used for the heterogeneous solid-gas reactions. Both finite rate and eddy-breakup combustion models are calculated for each homogeneous gas-gas reaction, and the smaller of the two rates is used. Lagrangian-Eulerian method is employed. The Eulerian method calculates the continuous phase while the Lagrangian method tracks each coal particle. Fundamental study is carried out to investigate effects of five turbulence models (standard k-ε, k-ω, RSM, k-ω SST, and k-ε RNG) and four devolatilization models (Kobayashi, single rate, constant rate, and CPD) on gasification simulation. A study is also conducted to investigate the effects of different operation parameters on gasification process including coal mixture (dry vs. slurry), oxidant (oxygen-blown vs. air-blown), and different coal distributions between two stages. Finite-rate model and instantaneous gasification model are compared. It is revealed that the instantaneous gasification approach can provide an overall evaluation of relative changes of gasifier performance in terms of temperature, heating value, and gasification efficiency corresponding to parametric variations, but not adequately capture the local gasification process predicted by the finite rate model in most part of the gasifier. Simulations are performed to help with design modifications of a small industrial demonstration entrained-flow gasifier. It is discovered that the benefit of opening the slag tap on the quench-type gasifier wider by allowing slag to move successfully without clogging is compromised by increased heat losses, reduced gasification performance, downgraded syngas heating value, and increased unburned volatiles. The investigation of heat transfer on fuel injectors shows that blunt tip fuel injector is less likely to fail compared to conical tip fuel injector because the maximum high temperature on the injector is scattered. Two concentric fuel/oxidant injections provide better fuel-oxidant mixing and higher syngas heating value than four separate fuel and oxidant injections.

Amostras de cinzas geradas na combustão do carvão e de cinzas provenientes da queima dos resíduos da cana-de açúcar foram usadas como fonte de silício e alumínio para sintetizar zeólita 4A pelos métodos IZA e fusão alcalina seguida de tratamento hidrotérmico. A razão molar de Si/Al para a formação da zeólita foi ajustada pela adição de resíduo de alumínio da indústria terciária como fonte alternativa de alumínio. Os efeitos da temperatura, do tempo de fusão e o tempo da reação hidrotérmica foram investigados. Os resíduos e os produtos sintetizados foram caracterizados por diferentes técnicas, tais como: fluorescência de Raio X, difração de Raio X, capacidade de troca catiônica, entre outros. A zeólita sintetizada a partir de cinzas leves de carvão foi usada para a remoção de Cd2+ e Zn2+ de solução aquosa em sistema de batelada. Os dados de equilíbrio de adsorção foram avaliados usando-se equações não lineares dos modelos de Langmuir, Freundlich, Temkin e Dubinin-Radushkevich (D-R). Os modelos de D-R e Freundlich foram os que melhor se ajustaram aos dados experimentais do Cd2+ e Zn2+, respectivamente. A capacidade máxima de adsorção foi de 78,0 mg.g-1 para o Cd2+ e 35,8 mg.g-1 para o Zn2+. Os resultados mostraram que o resíduo de alumínio e as cinzas de carvão e de biomassa podem ser usados como matéria prima para obtenção de zeólita 4A, considerado um material de valor agregado e com promissoras propriedades de adsorção. / Ash samples generated in the combustion of coal and ash from the burning of sugarcane residues were used as a source of silicon and aluminum to synthesize zeolite 4A by IZA and alkaline fusion followed by hydrothermal treatment. The Si/Al molar ratio for zeolite formation was adjusted by the addition of aluminum residue from the tertiary industry as an alternative source of aluminum. The effects of temperature, melting time and hydrothermal reaction time were investigated. The residues and the synthesized products were characterized by different techniques, such as: X-ray fluorescence, X-ray diffraction, cation exchange capacity, among others. The zeolite synthesized from fly ash was used to remove Cd2+ and Zn2+ from aqueous solution in a batch system. The adsorption equilibrium data were evaluated using non-linear equations of the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) models. The D-R and Freundlich models were the best fit for the experimental data of Cd2+ and Zn2+, respectively. The maximum adsorption capacity was 78.0 mg.g-1 for Cd2+ and 35.8 mg.g-1 for Zn2+. The results showed that the coal and biomass ashes mixed with aluminium residues can be used as feedstock to obtain 4A zeolite, considered a value-added material with promising adsorption properties.

This thesis analyses the formation of haze by taking the case of severer haze in Beijing in the winter of 2015, which was caused by the collective effect of human activities, topography and meteorological. Among these causes, anthropogenic emissions contributed most, such as coal-fired emissions and vehicle emissions. The haze not only brings direct harm to health, but also slowly changes the way people live in the haze. Beijing has issued the Clean Air Action Plan to mitigate haze. Additionally, a series of stringent control measures were adopted during Beijing Olympics and APEC summit. These measures, such as vehicle emissions reduction and coal-free programme effectively reduced the PM concentration but failed to reduce GHG emissions. Hence, the causes for the lack of sustainability of air pollution control measures are included in thesis.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, .tohannesburg, ill fulfilment of the requirements for the degree or Mester of Science in Engineering Johannesburg, 1992 / Pillar extraction using 'handgot' methods has been practised in South African collieries fOJ' many years. During the late Sixties pillar extraction with mechanized conventional equipment commenced, and approximately a decade later, continuous miners were introduced into pillar and rib pillar extraction panels. During the years that these mining methods were practised, a vast amount of experience was gained on the various collieries. Problems were experienced by various mines and the management of these mines made numerous alterations to the mining methods with varied degrees of success, Research was 0.150 conducted by COMRO and by V,\ri01l5 mines and mining house". Apart from the recommendations of Salamon and Oravecz (1976) on pillar design in stooping sections, little information has been published and, thus, little is generally available to mine managers, planners and operators to assist them in the layout and design for plllar and rib pillar extraction. A survey of all the pillar and rib pillar practises, past and present, has been conducted for collieries in South Africa and abroad and the successes, failures, problems experienced, changes made to the mining methods and the results of these changes have been documented. The problems and successes experienced, t~ similarities and difference between mines and mining methods, and the research flndlngs have been assessed and evaluated. Design guidelines relevant to the various methods of pillar and rib pillar extraction have been established to improve the safety and performance of pillar extraction operations. These guldellnea ate not intended to be prescriptive but are designed more to bring to the attention of the mine manager, planner and operator those fllctors which should be taken into consideration during the planning and operation \)f a pillar Ot rib pillar extraction panel. In addition to the strata related factors, the economics of the mining method is important to determine if it is beneficial to do secondary ext-action, and also to assist in optimlsing the secondary extraction. The design prlnclplns were therefore appUed to diffcrtmt panel layouts, pillar sizes and extraction sequences to determine the effect on the production costs.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2016 / The blind headings created in room and pillar mining are known to be the high risk areas of the coal mine, since this is where the coal production is actually taking place and hence the liberation of maximum quantity of methane. The ventilation of this region called the localized ventilation is carried out using auxiliary ventilation devices. This ventilation may be planned and be the subject of mine standards, but it is not very well understood and implementation on a day to day basis is usually left to the first level of supervisory staff. Majority of the methane explosions have been found to occur in these working areas and blind headings. The correct use of auxiliary ventilation devices can only be carried out once the effect of the system variables associated with each device is very well understood and can be calculated mathematically. Presently, no mathematical models or empirical formulas exist to estimate the effect of the associated system variables on the flow rates close to the face of the heading. The extent of ventilation of a heading ventilated without the use of any auxiliary device is not clear. Furthermore, to design additional engineering solutions, the flow patterns inside these heading ventilated with the auxiliary ventilation devices needs to be understood. The study of the face ventilation systems and the effect of the system variables associated system with each auxiliary ventilation device can be carried out experimentally, but doing a large number of experiments underground is very difficult as it disturbs the mine production cycles. Furthermore, studying the flow patterns experimentally is even more cumbersome, and can only be done to some extent using smoke or tracer gas. Therefore, Computational Fluid Dynamic‟s (CFD) advanced numerical code ANSYS Fluent was used to study the effect of a number of system variables associated with the face ventilation systems used in blind headings. As part of the procedure, the CFD model used was validated using four validation studies, in which the numerical results were compared with the actual experimental results. The numerical results differed to a maximum of 10% for all the experimental results. The system variables associated with ventilation of a heading, without the use of any auxiliary device, with the use of Line Brattice (LB) and fan with duct were selected. A range of values was chosen for each variable, and scenarios were created using every possible combination of these variables. All the scenarios were simulated in Ansys Fluent, the air flow rates, air velocities, velocity vectors, and velocity contours were calculated and drawn at different locations inside the heading. The effect of each system variable was found using a comparative analysis. The results were represented in simple user-friendly form and can be used to estimate the air flows at the exit of the LB and face of the heading for various settings of the LB and fan and duct face ventilation systems. The analysis of the ventilation of a heading without the use of LB shows that a maximum penetration depth is found with the Last Through Road (LTR) velocity of 1.35m/s. The flow rates and the maximum axial velocities increase with the increase in the LTR velocity up to a depth of 10m (maximum air flowing into a heading of 1.26m3/s and 1.58m3/s is found for the 3m and 4m high heading using 2m/s LTR velocity). For the LB ventilation system the LTR velocities, heading height, length of the LB in the LTR and heading, angle of the LB in LTR, and distance of the LB to the wall of the heading (side wall) were varied to identify clearly the effect of these control variables, on the flow rate at the exit of the LB, and close to the face of the heading. The flow rate at the exit of the LB is found to be proportional to the product of the distance of the LB to the wall in the LTR and heading. The flow rate at the exit of the LB, face of the heading, and inside the heading is found proportional to the LTR velocity and height of the heading. It is found that a minimum length of LB is associated with each distance of the LB to the wall in the heading, to maximize the delivery of air close to the face of the heading. This length is found to be equal to 15m for 1m LB to wall distance, and 10m for 0.5m LB to wall distance. Mathematical models were developed to estimate the effect of each studied system variables on the flow rates at the exit of the LB and close to face of the heading. For the fan and duct systems the length, diameter, and the fan design flow rates were varied. It is found that for a force fan duct system only a maximum of 50% of the total air that reaches the face is fresh and the remaining 50% is recirculated air. The flow rate with the exhaust fan system is found to be much lower than the force fan duct system. It increases with the reduction in duct mouth to heading face distance, and increase in duct diameter. Mathematical models are developed to calculate the flow rates at the face of the heading using the effect of each studied system variable. The research reveals that the ANSYS numerical code is an appropriate tool to evaluate the face ventilation of a heading in a three dimensional environment using full scale models. The South African coal mining industry can benefit from the outcomes of this study, specially the mathematical models, in a number of ways. Ventilation engineers can now estimate the flow rates close to the face of the heading for different practical mining scenarios and ensure sufficient ventilation by using the appropriate auxiliary ventilation settings. The results can easily be developed into training aids using easy to use excel spread sheets to ensure that mineworkers at the coal face have a better understanding of the working of the auxiliary ventilation devices. It can also serve Academia as part of the curriculum to teach the future mining engineers how the different variables associated with the auxiliary ventilation system affect the ventilation in a heading. The research therefore, has the potential to provide a significant step toward, understanding airflow rates delivered by the auxiliary devices close to the face of the heading and the air flow patterns inside the heading as a basis for improving the working environment for underground mineworkers. / MT2017

Thesis (M.Sc. (Engineering))--University of the Witwatersrand, Faculty of Engineering, 1987.

Master of Science in Engineering by advanced coursework and research: A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 2016 / The mining sector plays a significant role in the economy of Zimbabwe. The mining sector is the second largest contributor to the country’s GDP at over 20%. Zimbabwe as a country is endowed with abundant mineral resources. The top three commodities in terms of estimated resources are iron ore, coal and platinum with resources of 30 billion tonnes, 26 billion tonnes and 2.8 billion tonnes respectively. Zimbabwe’s vast mineral resources and reserves are of strategic importance to the Zimbabwe economy. Coal mining is one of the major economic contributors to the mining industry in Zimbabwe. The purpose of the study is to determine the optimal operational model for Makomo Resources from a mining and processing point of view. The study is based on a coal-mining project in the Zimbabwean mining industry. Makomo Resources is the largest privately owned coal mining company in the country, which has a mining licence to perform coal-mining activities in the north-west part of the Bulawayo Mining District of Zimbabwe. Makomo Resources applies a conventional strip mining method by means of truck and shovel to extract the coal reserves. Makomo Resources is supplying over 200,000 tonnes of coal per month to the local and export market. The mine has invested in USD20 million capital to commission a wash plant. The study investigates how to optimise the plant throughput by comparing two mining options: Mining Option 1 - crush and screen 2m power coal, crush & screen and wash a full 7m low ash coal seam and wash 2m of coking coal. Mining Option 2 – crush and screen 2m power coal, crush & screen a 3m low sulphur coal seam and wash low ash coal and coking coal of 4m and 2m respectively. The study investigated all the marketing, geology, mining and financial parameters in the Zimbabwean coal mining context. The study determines the appropriate mining methodology and explore to optimise the coal processing. Two financial models were developed to evaluate and compare the two proposed mining options, determine their feasibility and conclude the optimal mining model. Financial techniques were used to analyse and evaluate the two mining options. The financial models were used to analyse and evaluate the following:  The cashflow over the 10-year period.  The Net Present Value (NPV) and Internal Rate of Return (IRR) of each mining option.  The payback period of the washing plant.  Profitability Index per mining option. The NPV of a project determines the economic value of the mining project. The decision on a mining investment is mostly related to the NPV and IRR of the project. Discounted Cash flow (DCF) models were developed for both mining options that shows project cash in and out flows and calculates economic indicators, such as IRR and NPV. The NPV and IRR were the main methods for the evaluation of the two mining options. The resulting DCF models were developed in an Excel spreadsheet format designed for a 10-year Life of Mine (LOM) period. Mining Option 1 has a higher NPV of USD38.2 million in comparison to USD9.7 million for Mining Option 2. The IRR for Mining Option 1 was calculated at 48%, which is bigger than the IRR for Mining Option 2 of 26%. Mining Option 1 has a simple payback period and discounted payback period of 2.7 years and 4.9 years respectively. Mining Option 2 has a simple payback period and discounted payback period of 3.9 years and 11.9 years respectively. Mining Option 1 has a shorter payback period than Mining Option 2. Both mining options have a Profitability Index (PI bigger than one with Mining Option 1 and Mining Option 2 recording values of 1.87 and 1.18 respectively. Mining Option 1 has the better PI value and is therefore more profitable. Based on the economic evaluation, Mining Options 1 is by far more attractive than Mining Option 2, which results in a better return on the investment and profitability, therefore the preferred option. / MT2017

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, 2017 / Productivity is an important topic within the mining industry and advances in productivity open up opportunities to make the best possible use of South Africa’s mineral wealth. The report uses publicly available data to assess trends in productivity in the SA coal mining industry since the 1980s and to compare SA’s performance with that of the US and Australia. It is found that between 1980 and 2003, productivity growth in the SA coal mining sector was primarily driven by capital deepening. However, productivity growth has been negative from 2004 onwards, despite continued capital deepening. Possible explanations include resource depletion, investment lags, deteriorating worker quality, increased complexity, more stringent safety regulations and adverse labour market conditions. The report highlights skills development and investment in innovation as possible ways of addressing declining productivity performance in the SA coal mining sector and recommends improvements to the availability of data for productivity research purposes. / CK2018

A study was conducted in 2006 to investigate the long-term effects of air pollution on soil properties in the vicinity of the Arnot power station, Mpumalanga, South Africa. Fifteen sites were re-sampled and the soil chemical properties compared to baseline data gathered in 1996, resulting in a ten year period after which changes in soil properties were investigated. A spatial gradient was incorporated into the study in order to better understand the deposition of pollutants with increasing distance from the power station. The study indicates that long-term acidic deposition has led to detectable changes in soil chemical properties. Three chemical properties, namely the concentrations of calcium and magnesium in both the topsoils and the subsoils, as well as the effective cation exchange capacity in the subsoils showed a significant increase since 1996. However, five soil chemical properties, namely soil pH (K2SO4), the concentration of hydrogen and aluminium and total sulphur in both the topsoils and the subsoils, as well as extractable sulphate in the topsoils and soluble sulphate in the subsoils, all show that the soils have become more acidic over the ten years. The acidic components in the soil override the basic components, as shown by the ratio of basic cations to acidic cations in the soils. The spatial gradient generally indicates that at approximately 8 km from the power station, there is a decrease in the concentration of acidic soil properties and one explanation for this may be a reduction in the acidic components of atmospheric deposition at this site. However, this needs further investigation. Two significant relationships with distance were found, namely a significant negative relationship with soluble sulphate and a significant positive relationship with acid neutralising capacity. This research will form part of a database for other long-term monitoring programmes and will allow data to be compared to other data from this area of research. It will also provide information to important industry leaders such as Eskom.

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the Degree of Master of Science in Engineering, 2016 / Previously undermined areas pose a significant challenge to mining by opencast due to the risk of sinkhole occurrence. In order to optimise reserve utilisation as well as safeguard personnel and equipment there was need to develop a “Sinkhole Prediction Model” to assist in the prediction of areas prone to sinkhole formation. The aim of this research therefore was to develop a “Sinkhole prediction tool” with a view to pre-identifying areas of potential sinkhole hazard to inform better controls to assist in mining these areas safely. This was done utilising the current Hill (1996) caving height method culminating in the development of a hazard index model dividing the mining zones into high and low hazard. These areas were colour coded Red (High hazard) and Green (Low Hazard). The “Sinkhole Prediction Model” evolved to include over hundred sinkhole incidences that were statistically analysed to firm up on the robustness of the Prediction Model capabilities. The Hill (1996) caving height formula was discounted after the statistical analysis indicated that a good prediction model lies in the interrogation of site specific data. The outcome of the work conducted in this research report indicated a 97% correlation between the refined “Sinkhole Prediction Model” and the actual sinkhole occurrence at the Anglo American case study area (Mine X). Various refinements inclusive of lithological assessments, blast and drilling reconciliations as well as the implementation of the roughening up quality audits led to the implementation of a robust sinkhole management process that has managed to consistently assist in safeguarding equipment and personnel thus allowing for coal extraction optimisation in areas that could have been written off due to the sinkhole hazard. This risk can only be eliminated by mining the areas with the sinkhole risk. Currently the method is being impacted by significant roughening up cost incurred in a drive to make the areas safe to allow for coal extraction. The roughening up process on average costs R3.5 million per sinkhole and is a function of the number of sinkholes found, which translates to an equivalent cost of R7 / sales tonne. The current sinkhole prediction model being employed in deficient in that it cannot pinpoint the actual location of the void in the area previously undermined by bord and pillar and this is a great limitation of this report. Various geophysical techniques were pursued to assist in the precise identification of the actual sinkhole spatially. This process was aimed to reduce the roughening up cost (entire block stabilisation) as opposed to targeted sinkhole excavation and stabilisation. This process proved futile as the void identification systems are highly incapable of identifying the voids / iv sinkholes spatially (x, y and z coordinates) to assist targeted sinkhole treatment as a result of the following:  System inability to penetrate areas comprised of highly conductive strata such as clays.  Inability to distinguish between the underground voids and geological anomalies such as dykes.  Not suitable for penetrating wet strata.  Impacted by noise interference from mining machinery. The major result of this research is the establishment of a site specific “Sinkhole Prediction Model” that can generate hazard plans in real time thus informing the management on areas associated with a potential sinkhole hazard. The hazard plans can be generated timely and decisions made to facilitate safe coal extraction in areas of high sinkhole hazard. This has culminated in a robust sinkhole management process within the group that has managed to eliminate the risk of personnel and equipment exposure at Mine X. The roughening up process is accepted as the primary sinkhole mitigation or rehabilitation process with the need to work towards reducing the roughening up costs through development of the tool capable of precisely identifying the voids routinely to facilitate targeted rehabilitation. Significant research is required in this area as the mining environment is comprised of strata that currently cannot support the use of real time void identification to facilitate targeted void identification and rehabilitation. There is also merit in the future to formulate the database capable of assisting in the prediction of sinkholes in the Witbank coalfield as well as assist in robust management of mining boundaries across the different mining houses. The system implemented at Mine X is currently being deployed to other operations in the group where modification will be made to match the site specific conditions. Future research into understanding the sinkhole occurrence dynamics is quite crucial if targeted rehabilitation is to be achieved for cost reduction and mining sustainability. A combination of the understanding of the sinkhole occurrence driving mechanisms in conjunction with use of modelling packages such as ELFEN (a hybrid Modelling) tool will go a long way in enhancing the development of precise sinkhole prediction point in space.