Electronic Theses and Dissertations (Masters)
Permanent URI for this collectionhttps://hdl.handle.net/10539/37963
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Item Assessment of in-service durability performance of natural draft cooling towers in a petrochemical environment(University of the Witwatersrand, Johannesburg, 2024) Shaw, Kyle Lloyd; Otieno, MikeEffective temperature control is an important operation requirement in petrochemical processes, where Cooling Towers (CT) play a key role in efficiently lowering water temperature for reuse in various chemical processes. Natural draft cooling towers function as heat extraction systems, dissipating thermal energy from hot water into the atmosphere through cold air. However, many reinforced concrete cooling towers have exhibited signs of deterioration over time, such as cracking, corrosion, and structural misalignment, posing the risk of structural failure. To address these issues, structural condition assessment programs, aiming to inspect, repair, and monitor cooling towers to prevent structural collapse are of significant importance. The focus of this study investigates the durability of natural draft cooling towers in an aggressive petrochemical environment. With a focus on Sasol Secunda Natural Draft Cooling Towers, the research aims to identify and characterize the various concrete deterioration mechanisms, quantify durability parameters, and explore mitigation measures for both new and existing cooling towers. Concrete deterioration is a significant concern in structures exposed to harsh environments, affecting their global stability and service life. The study examines the role of cover concrete quality in resisting corrosive agents and assesses durability using South Africa's three durability index (DI) tests, including water sorptivity, chloride conductivity, and oxygen permeability. The study comprised of on-site assessments and laboratory testing methods to determine the durability performance of cooling towers. The approach includes the three durability index tests. On-site assessments include visual inspections and non-destructive testing (NDT) near areas displaying signs of deterioration. The significance of this research relies on the operational efficiency of cooling towers in petrochemical plants, their vulnerability to harsh conditions, and the need for durability design considerations at Front End Loading (FEL) engineering and planning. It aims to shift from prescriptive to performance-based design approaches and provide insights for maintenance and mitigation strategies. This study contributes to the knowledge of concrete durability in challenging environments, aiming to enhance the longevity and performance of critical industrial infrastructure, particularly natural draft cooling towers.Item A linear vibration isolator integrating a non-linear energy sink (nes)(University of the Witwatersrand, Johannesburg, 2024) Waite, Clinton; Li, KuinianThis report investigates the integration of traditional linear vibration isolators with non-linear energy sinks (NES) to enhance vibration control in structures subjected to dynamic loading. Structures often respond to dynamic loads—such as machinery vibrations, seismic activity, and environmental factors—by vibrating at their natural frequencies, potentially leading to resonance and structural failure. Vibration isolation and damping systems, such as linear isolators and NES, mitigate these effects. Linear isolators are effective at higher frequencies but have limited performance at lower frequencies, while NES systems offer broader frequency- range effectiveness. This study explores the effectiveness of combining these systems to optimize vibration control. Through simulation of both simple and complex setups, the research compares the vibration response of traditional linear isolators, NES-integrated isolators, and NES systems combined with additional damping elements. Key findings demonstrate that integrating NES with linear isolators significantly reduces peak transmissibility and improves vibration reduction under harmonic and seismic loading. However, the integration's effectiveness varies depending on system configuration and specific loading conditions, highlighting the need for further optimization. The study also presents a parametric analysis for designing vibration control systems tailored to diverse applications, offering valuable insights for engineering practice in reducing structural vibrations.Item Heavy metal contamination and its spatial distribution from mining wastesin receiving environments of Mazowe District, Zimbabwe(University of the Witwatersrand, Johannesburg, 2024) Charema, Josiah; Taigbenu, Akpofure; Newete, SolomonThe purpose of this study was to investigate heavy metal contamination and its spatial distribution from mining wastes (especially artisanal/informal mining) and the impact of agriculture on heavy metal pollution in receiving environments of the Mazowe district, Zimbabwe. Agriculture and mining have considerably contributed to heavy metal and nutrient concentration into the world’s freshwater systems. This study aimed to improve the understanding of the contribution of agriculture and informal mining to heavy metal and nutrients pollution of Mazowe River. Also, the research aimed to establish the contribution of sulphates and phosphorous on heavy metal mobility in agricultural and mining areas. The research was conducted in Mazowe District in Mashonaland Central Province of Zimbabwe. Collection of the samples was carried out at five locations along Mazowe River, from its outlet at Mazowe dam to about 25 km downstream. The samples were preserved using WHO approved preservation methods and transported to a licensed laboratory in Harare for testing and analysis of heavy metals (Hg, Pb, Cr and Cd), extractable sulphates and phosphorus at Zim Labs laboratory, in Harare - Zimbabwe. Heavy metal analysis was done using the flame Atomic Absorption Spectrometer after wet digestion. The results indicated an average concentration of heavy metals in the river sediments ranging from 0.01mg/kg (Hg) to 26.68 mg/kg (Pb) during the wet season. During the dry season the levels of Hg, Pb, Cr and Cd were less than 0.01mg/kg. There were low detectable levels of heavy metals in the water samples for both wet and dry seasons. Significant differences in mean levels of phosphates and extractable sulphate pollutants were observed in the wet and dry season. The average phosphorus levels detected in the sediment samples during the wet season was 14.93mg/kg which was 93.7% higher than that of water samples which was at an average of 0.94 mg/l. The sampling points were small due to budget constraints and limited access to some areas because of property rights’ issues and national key points along Mazowe River. Thus, it would imperatively be unjustified to generalise the effects of the research outcome to other locations within Mazowe River Catchment or locations along Mazowe River downstream from the study area, without considering other land use patterns. The results showed that the presence of heavy metals in the sediment samples of Mazowe River could be highly attributed to informal mining along the river while extractable sulphates and phosphorous in both water and sediment samples could be attributed to agricultural activities. These findings may assist the environmental management and mining authorities to regulate the activities of artisanal mining to combat heavy metal contamination of rivers from mining activities