3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item An investigation into the use of borates to improve coke CSR/CRI when blending metallurgical coal to make blast furnace coke(2018) Musiiwa, AdmireThe availability of prime metallurgical coking coals is limited in Africa. This lack of good coking coals results in steel manufacturers (ArcelorMittal in particular) incurring high costs when importing the necessary prime coking coals from abroad. Such products are then mixed with local partially-coking “blend” coals. The need therefore is to find alternative methods to obtain substitutes for imported costly coking coals or to blend local coals in a manner that would achieve the same technical properties of products comprising prime coking coals in a blend. If achievable, this would have the added benefit of reducing expensive imported prime coking coals (mainly from Australia) and would ensure a more cost-effective product for use in the vital iron and steelmaking process in South Africa. Most imported coals from Australia are three times more expensive compared to local blend coking coals. ArcelorMittal has been using blends that contain prime coking coals from Mozambique, North America and Australia and have so far only been able to incorporate up to a maximum of 30% of the local South African “blend” coking coals, these arising primarily from Grootegeluk Colliery, Lephalale in the Waterberg region of the country. Such low proportions of local content with high proportions of imported products have led to everincreasing high costs in recent years, prompting research into blend optimisation to enable the incorporation of higher percentages of local coals to produce cheaper and more cost-effective blends. The current research, in attempting to address this issue, focused on the evaluation of coke qualities from blends that contained increased proportions of Grootegeluk blend coking coal (GG), ranging from 31% and incrementally up to 40 %. In each case, samples of the resultant coke products were split into separate sub-samples with one sub-sample quenched using normal water while another sub-sample was quenched by water containing a solution of sodium tetraborate. A similar process was used successfully in China and Russia and this yielded very positive coke CSR/CRI results. Results showed that, for each blend with an incrementally increased proportion of GG coal, the coke strength properties improved by 17% when the sub-sample was quenched by the borate solution. There was no change in coke strength properties in the sub-samples quenched by water. The ultimate cut-off point at which the blend coke quality properties would still be usable in a blast-furnace process was achieved when the proportion of GG coal in the blend was 37% after quenching by the borate solution. The 7% increase of GGcoal in the blend from 30% is likely to lead to considerable saving in blend coking production due to the reduction of imported coking coal in the mix.Item The technical evaluation of non-coking coals in the production of semi-coke(2018) Brijball, Jayshree KalyanchadGrootegeluk Coal Mine produces a metallurgical non-coking coal that is used in the production of semi-coke. Semi-coke is a new product that is used as a reductant in ferrochrome furnaces. The Exxaro semi-coke is of a high quality and is able to substitute the locally produced market coke due to its comparable (and better) strength and reactivity indexes. This research was started to better understand the Exxaro semi-coke and the competitive advantage that comes from the single coal source in the production of semi-coke. In addition, it is important to understand if there are any other non-coking coals available in the Witbank and Highveld coalfields that can produce a similar product and replace Exxaro as a market leader. Coals were selected from the Waterberg, Witbank and Highveld coalfields. These coals were then subjected to proximate testing and full petrographic analysis before being “charred” mimicking actual production parameters. The “charred” coals were then evaluated using petrographic analysis to better understand their inherent structures and their role in CSR and CRI. It was found that the vitrinite reflectance of the selected coals were in a very close range of 0.67 - 0.69. It could be found that a suitable semi-coke with comparable CSR and CRI indexes could be produced from 6 of the 8 samples sourced from the Waterberg, Witbank and Highveld coalfields. However, the requirement for a substantial low phosphorus coal source will remain a barrier to entry for other potential producers of semi-coke as only minimal amounts remain. In addition, it could be seen that semi-coke has a higher CSR than market coke due to the formation of anisotropic structures as compared to locally produced market coke that is predominantly isotropic. This ensures superior performance in the furnace It is recommended that further work be completed to better understand the reasons for anisotropic structures in coals sourced from Exxaro. Further investigation should also be considered in utilizing coals of varying ranks in similar testing in the production of semicoke.Item Estimation of surface moisture in a composite coal stockpile(2018) Enslin, KyleThis dissertation, through a literature survey, investigated the different types of moisture in coal, what parameters affect coal moisture content as well as technologies and methods for drying coal. It was found that the parameter that affects surface moisture the greatest was particle size and in particular, the -500µm size fraction. Based on this knowledge a hypothesis was developed. The hypothesis states that each size fraction contributes to the total surface moisture content relative to the size fractions equilibrium surface moisture content and weighting within the overall size distribution. The total surface moisture content is then the sum of these individual contributions. Where SMi = relationship (equation) between the equilibrium surface moisture content and the geometric mean of the individual size fraction (%) fi= weighting of size fraction in particle size distribution (%) In order to test this hypothesis the relationship between equilibrium surface moisture and size fraction had to be established first. This was done by performing drainage tests on nine different size fractions and determining the equilibrium surface moisture content for each. Tests were then done in two stages on composite coal samples to determine the equilibrium surface moisture content. The size distribution for stage one (PSD1) was different to stage two (PSD2). The samples had a fixed +500µm size distribution while the fines fraction (-500µm) increased by 1% for each test from 0% to 10%. Increasing the fines content resulted in a direct linear relationship between the fines fraction and surface moisture content. This was found to be true for the test data as well as the estimated data. Both the test and estimated data showed that for every 1% increase in fines content there was about 0.25% increase in equilibrium surface moisture content. This was true for both size distributions. Although the relationship was consistent, the size distribution did make a difference to the overall result. The finer size distribution resulted in a higher overall surface moisture content. Finally the model (equation 1.1) was used to estimate the surface moistures of 90 Eskom mill feed samples from five different power stations. Between the 25L drum, drainage pipe tests and Eskom data, the model estimated the Eskom data the best. The Eskom data also showed that in order to reach a minimum surface moisture of 6% the fines content should be kept below 9%.Item Shared-use of railway infrastructure in South Africa: the case of coal and citrus production in Mpumalanga(2015-02-03) Dube, Mishack SiyafundaEconomic activities such as mining extraction and farming have in the past been supported by railway infrastructure, which continues to provide a cheap transportation option for the movement of freight. This research paper looks at the apparent bias that exists in the shared-use of railway infrastructure in South Africa between coal miners and citrus growers in Mpumalanga. The study is specifically concerned with the regulatory regime governing access and the extent to which it enables or hinders the shared-use of rail infrastructure, which is critical in the movement of freight for different sectors of the economy. The paper uses literature on regulatory practices and a case study of Mpumalanga’s coal miners and citrus growers, to investigate South Africa’s regulatory regime and its role in creating particular biases in the use of rail infrastructure.Item Development of a dust exposure level index (Deli) for South African underground coal mine workers(2006-11-17T11:18:12Z) Belle, Bharath KumarInhaling excessive amounts of respirable coal dust will lead to work-related lung disease commonly known as Coal Worker’s Pneumoconiosis (CWP) or black lung. Prevention and control of CWP requires accurate knowledge of the dose-response relationship to set-up and review occupational exposure limits (OELs), which do not exist in SA. Due to historical reasons, poor emphasis of occupational health on the mines resulted in inadequate exposure data in SA. The new Mine Health and Safety Act (1996) overcame the deficiencies of the past and require quantifying the dust exposure and efficiency of dust control measures, and continuous risk assessments for dust exposure. The current method of exposure assessment is expressed using an Air Quality Index (AQI) which is the ratio of the measured dust level and OEL of coal dust. The difficulties with the usage of AQI are poor descriptions of dust problem areas and its magnitude, poor quality of the data leading to “no dust problem situation” and failure to extract information on ‘dose in milligram’ to relate them to the disease rate. Gravimetric size-selective dust sampling was introduced for the first time in 1990 in SA. Due to the lack of critically important coal dust exposure data available, this thesis has set out to examine several critical exposure related parameters and determine dust levels underground. This research study had the objective of the development of a pragmatic diagnostic tool (method) called the Dust Exposure Level Index (DELI) to evaluate the exposure of workers. The DELI incorporates a set of controllable parameters and influential areas and prioritises them to manage and reduce the worker exposure. The DELI model was to provide critical information as an index, i.e., to show whether the environment is dusty, border line or relatively free of dust and effectiveness of administrative and engineering dust control measures. The research work in this thesis has led to very explicit conclusions, which were based on extensive dust measurements in various coal mines over a five year period. Conclusions obtained for the various sets of controllable parameters used in the DELI model are as follows: 1. A previous analysis of the dust data during 1990 indicated that the dust levels have increased with mechanisation. The contamination of coal dust samples due to stone dusting can result in high dust levels giving a “false” indication of the efficiencies of the dust-control systems. 2. The dust exposure levels during coal cutting indicated that a worker positioned inside the cabin of a CM during the cutting of a 24 m coal block is at a higher dust exposure risk than the worker when cutting a 12 m coal block. Also, the miner who is operating in a heading is exposed to higher dust exposure risk than in a split. 3. The analyses of measured real-time dust data showed a clear relationship between the average dust levels and the frequency of occurrence of “peak” dust levels. The study demonstrated a clear method of using real-time dust data for assessing exposure. 4. The average measured section intake dust level was 0.80 mg/m3 and 60 % of the collected data exceeded the 0.5 mg/m3 limit indicating that this is a base dust level to which the worker is exposed without carrying out any additional work in the section. 5. The average measured section return dust level was greater than 2.0 mg/m3 indicating the high exposure levels of workers, and ineffectiveness of the ventilation and dustcontrol systems. 6. The results of this research study indicated that there is no conclusive relationship between the rate of coal production and respirable dust levels. Also, the type of dust control system used has pronounced effect on dust levels in the sections. The capture efficiency of any dust control system is not one hundred percent at any given time. During any cutting process for a given time and dust control type, part of the escaped respirable dust is added to the coal face atmosphere through air re-circulation. Therefore, respirable dust levels can be expected to increase with time during the shift, even at constant production levels. 7. A limited number of particle size analyses have indicated that there is no clear relationship between the dust concentration in mg/m3 and total surface area (m2) of the respirable dust sample. 8. For the first time, a clear delineation of coal types (semi-bituminous and semianthracite) that possess the most inherent respirable dust generation potential (IRDGP) was possible (p = 0.000). Also, there was no conclusive relationship (p = 0.373) between different semi-bituminous coal seams (1, 2, 4 and 5) and IRDGP. 9. The laboratory roll-crusher test results of South African coal types indicated that average inherent silica for the test coals was 3.54 %. The DELI model took into account, the merits of personal exposure data in exposure assessment, but the limitations and quality of data one obtains in the South African situation overweighed use of the fixed-point sampling. The “limits of acceptability” used in DELI are based upon acceptable guidelines prescribed by the authorities such as National Institute of Occupational Safety and Health (NIOSH), Mine Safety and Health Administration (MSHA), South African Department of Minerals and Energy Affairs (DME) and latest information on epidemiological studies. The DELI model gives the visual “colour” coding and descriptive categories for easy interpretation and understanding of exposed dust level to uneducated workforce. This type of DELI index representation gives a clear and concise picture of the mine or various section dust conditions. The DELI model exposure assessment technique gives accurate feedback because it was based on latest recommended size-selective sampling methods and instrument and vast amount of measured data, which was not previously available. The application of the developed DELI model for exposure assessment and its comparison with AQI were evaluated for coal mine dust data. The study demonstrated that the DELI model is a practical diagnostic tool that gives a fair reflection and information on dust levels and is an exposure assessment tool for the coal mining industry that will assist in reduction of CWP in South Africa.