A dissertation 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. Johannesburg 2016 / Stringent worldwide emissions legislation, the drive to lower carbon emissions, together with the ever increasing demand to preserve the environment has led to a considerable demand for cleaner and more efficient coal combustion technologies. A primary technology for the reduction of emissions of oxides of nitrogen (NOx) is the installation of low NOx coal combustion burners. Extensive research into various burner characteristics and, in particular, the aerodynamic characteristics required to improve combustion performance of low NOx coal burners has been extensively undertaken and is ongoing. In this work the aerodynamic behaviour of a full-scale, aerodynamically staged, single low-NOx coal burner was numerically investigated. The objective of the study was to develop a single low NOx burner CFD model in Ansys Fluent, to better characterize and understand the flame shape in terms of the temperature profile achieved. CFD serve as an additional tool to assist with plant optimization, design proposals and occurrence investigations. To have confidence in the single burner coal combustion CFD model, the results of the model were compared to data obtained from an existing operational low NOx burner on site during a pre-defined load condition. To further improve on the theoretical CFD combustion model, drop tube furnace (DTF) experiments have been done to calculate the single rate Arrhenius kinetic parameters (pre-exponential factor and activation energy) for coal devolatilization and char combustion of the specific South African coal used. The combustion CFD simulations showed with a lower than design air flow through the burner, a reduced amount of swirl was achieved. This reduced amount of swirl produces a jet like flame and influences the way in which the combustion species are brought together. Under these operating conditions the flame distance from the burner mouth was predicted to be 1.2 (m). A very promising result was obtained through CFD and compared well with the in-flame temperature measurement obtained through the burner centre-line of approximately 1.4 (m). In an attempt to improve the aerodynamic profile of the burner under the same operating conditions the swirl angle on the tertiary air (TA) inlet was increased. The increased swirl on the TA inlet of the burner showed an improvement on the aerodynamic profile and had a significant impact on the temperature distribution within the flame. The increased swirl resulted in an improved flame distance of approximately 0.5 (m) from the burner mouth. The effect of increased swirl on the temperature profile of the flame displayed the aerodynamic dependence of the low NOx burner on combustion performance. / MT2017

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science June 2015 / Lephalale is the home of Matimba, one of Eskom’s coal-fired power stations. Matimba is the biggest power station with a dry cooling system in the world. There are other industries (including coal mines) currently in operation in close proximity to the station. This industrial area is expected to grow as more industrial activities are planned for the following years. These activities will aggravate the levels of air pollution and possibly result in it being a “hot spot” for air pollution. The impact of air quality on health is covered by the National Ambient Air Quality Standards (NAAQS), but the impact of air quality on the terrestrial and aquatic ecosystem is not known. Therefore, this study focuses on the deposition of nitrogen oxides (NOx) (as nitrogen dioxide (NO2)) and sulphur dioxide (SO2) within Lephalale in the Waterberg-Bojanala Priority Area. Additionally, inter-annual variability of NOx and SO2 ambient concentrations and back trajectories of air masses were analysed. The study obtained ambient air quality data and meteorological data from Eskom for the period 2008–2012, while additional meteorological data were obtained from the Agricultural Research Council (ARC) and the South African Weather Service (SAWS). An inferential model was used to estimate the dry deposition flux of SO2 and NOx (as NO2), and the Hybrid Single Particle Langrangian Integrated Trajectory (Hysplit) Model was used to cluster back trajectories of air masses. The results of the seasonal dry deposition velocities of SO2 (0.17 to 0.23 cm/s) and NOx (0.10 to 0.15 cm/s) (as NO2) were higher in summer and lower in winter. They were also within the magnitude of the deposition velocities found in previous studies in the Highveld. The high deposition velocities in summer were attributed to photosynthetically active vegetation, turbulence and solar radiation. However, seasonal dry deposition fluxes of SO2 and NOx were higher in winter across the years. The higher flux values in winter were attributed to higher ambient concentrations of the trace gases. Additionally, the annual dry deposition flux of SO2 ranged between 0.43 and 0.67 kg S ha-1 yr-1, while NOx (as NO2) ranged between 0.84 and 1.05 kg N ha-1 yr-1 over the period studied. The annual deposition flux values found in the current study are lower than those found in previous studies in the Highveld. This difference could be because of the lower ambient concentrations of SO2 and NOx observed in this study. There is an inter-annual variability of the ambient concentrations of SO2 and NOx during the period 2008–2012. However, the difference is not large or statistically significant. The dominant direction of the back trajectories of air masses is east and southeast across all seasons for the entire period of 2008–2012. This lack of seasonal pattern in back trajectories and source regions cannot explain the seasonal changes in ambient concentrations (SO2 and NOx). Hence, climatic factors (e.g. change in weather) or seasonal changes in combustion source intensity must be responsible.

This report describes a 3 year study carried out to determine the effects of modern coal power generation technologies on the properties of fly ash and how these may affect the use of the material in concrete. A total of 18 fly ashes, from 11 different sources, produced under a range of conditions and technologies were investigated. These primarily included co-combustion, low NOx, supercritical and oxy-fuel technologies, although other available materials (run-of-station, air-classified, processed and stockpiled fly ashes) were included for comparison. The initial experimental work involved physical and chemical characterization of the fly ash samples. Thereafter, tests covering fresh properties, strength development and durability were carried out on selected concretes. A fly ash level of 30% was used with w/c ratios covering the practical range considered (0.35 to 0.65). Equal strength comparisons were also made where appropriate. Finally, granular (unbound fly ash) and monolithic (fly ash concrete) leaching tests were carried out to assess the environmental implications of using the fly ashes. The results from the physical and chemical characterization tests suggest that modern technologies used for coal fired power generation can have an influence on the properties of fly ash produced. The co-combustion, oxy-fuel and in-combustion low NOx fly ashes had reduced fineness and greater LOI, which had a negative effect on foam index and water requirement of the materials. However reactivity was largely unaffected. The post-combustion low NOx and supercritical fly ashes appeared to be unaffected by their production methods compared to that produced by conventional/establish means. Tests on fresh concrete properties showed that fly ashes with high LOI and low fineness required higher SP doses than the reference PC concrete. However, fly ashes with high fineness and low surface area were found to require a lower SP dose than the PC concrete. The concrete compressive strength tests indicate that, in general, finer fly ash concretes tended to have higher strengths than those containing coarser material. However, there did not appear to be any significant difference in performance between fly ash concretes, which suggests that, although modern technologies can have an impact on fly ash properties, if account is taken of these they should not have any significant influence on strength development. Comparison with an earlier study from the 1990s considering BS EN 450-1 fly ashes showed general agreement between the data. The durability study showed that finer, low LOI fly ashes had higher chloride resistance and at equal strength fly ash concretes performed better than those with PC. Equal strength fly ash concretes covering the modern technologies were found to have similar levels of durability for sulfate attack, abrasion and carbonation. High alkali concrete (following the BS 812-123 method) gave similar expansion levels and good resistance with respect to AAR. With air-entrainment, it was found that the fly ash concretes required high doses of AEA (relative to the PC concrete), with high LOI/BET fly ashes requiring greatest quantities. At equal strength, the fly ash concretes had poorer freeze-thaw scaling resistance than PC concrete. However, the majority of the fly ashes did manage to achieve acceptable scaling resistance according to the Swedish criteria. In general, the findings of the durability study are in agreement with the earlier study from the 1990s. Overall, no effect of production technology on the durability of concrete was observed. The leaching studies showed that, in general, in both granular and concrete form, modern fly ashes met the non-hazardous waste requirements in the WAC for all components tested except chromium. For the granular test, there were instances where elevated chromium levels were observed. Similarly, the fly ash concretes failed to meet the non-hazardous limit for chromium. However, chromium from the cement may have contributed to this, since the PC reference also failed to meet this requirement. Based on the results, there is no effect of production technology on the leaching characteristics of fly ash or concrete and the materials do not appear to pose a significant environmental risk. The practical implications of the study have been considered and overall, it has been shown that modern fly ashes behave in much the same way as traditional materials, and therefore, if these materials meet the requirements of BS EN 450-1, and their properties are taken into account in the proportioning of concrete, they should give satisfactory performance.

In this study, flue gas emissions and combustion efficiencies during combustion and co-combustion of olive cake and coal are investigated in a bubbling fluidized bed with an inside diameter of 102 mm and a height of 900 mm and 1900 mm. Tun&ccedil / bilek lignite coal and Edremit olive cake were used in the experiments as fuels. Temperature distributions along the combustion column were continuously measured. Flue gas concentrations of O2, CO, SO2 and NOx were measured during combustion experiments. Four sets of experiments were performed in order to examine the effect of fuel composition, excess air ratio, freeboard extension and limestone addition on flue gas emissions and combustion efficiency. The olive cake addition to coal were 25, 50, 75 % by wt. The bed temperature on the average was 850 oC. The results of the experiments showed that coal combustion occurs at lower parts of the combustion column whereas olive cake combustion takes place more in the freeboard region. As olive cake percentage in the fuel mixture increased, CO emissions increased, SO2 and NOx emissions decreased. The reason for the decrease of NOx emissions with increasing percentage of olive cake in the fuel mixture was due to a reducing atmosphere created in the combustion column. Mostly combustion losses resulted mainly from the unburnt carbon in the fly ash. With the freeboard extension, noticeable decrease in CO emissions and slight increase in combustion efficiencies were observed. Among the limestones tested, &Ccedil / an limestone gave the best result with Ca/S = 3 at an optimum bed temperature of 850 oC. The SO2 reduction was 87% at this Ca/S ratio. For co-combustion experiments, it was observed that SO2 adsorption efficiency of limestone increased with the addition of olive cake to the fuel mixture.

Coal is likely to remain an important energy source for the next several hundred years and hence advances in coal combustion technologies have major practical impact. Detonation combustion of coal initiated by a plasma cartridge driven detonation wave holds promise for improving both system and combustion efficiencies. Both fragmentation and chemical kinetic pathways are qualitatively different in comparison to conventional coal combustion. The present work is a theoretical investigation of fragmentation due to detonation wave. The theoretical simulation starts with simple model and progressively incorporates more realistic analysis such as combined convective and radiative boundary condition. It studies the passing of detonation wave on coal particles suspended in air. Concepts of solid mechanics are used in analysing fragmentation of coal particles. A numerical model is developed which includes stress developed due to both thermal and volatilization effects. Weibull statistical analysis is used to predict the fracture time and fracture location resulting from principal stress induced. It is observed that coal particles fragment within microseconds. Radiation does not have much effect on developed stress. Volatilization does not have much effect on fragmentation for the particle size considered in this work and stress due to thermal effect dominated the fragmentation. Coal size distribution statistics is considered to obtain real regime. Coal is used as mixture of different sized particles in real combustors. Hence it is important to analyse the effect of detonation wave on mixture of coal particles. Results presented in this work from simulation run suggest that plasma assisted detonation initiated technology can fragment coal particles faster. Average fracture time of mixture of coal particles is far less than detonation travel time for the detonation tube considered here. Simulation results suggest that almost 90% of coal particles fragment early. Average fracture time reduces as Mach number increases. Same phenomena can be observed for volatile matter generated at fracture and ow of volatile matter at fracture. Hence it can be concluded that plasma assisted detonation combustion leads to different volatilization and fragmentation pathways.

>Magister Scientiae - MSc / The aim of this study was to produce useful composite materials from fly ash, a major waste product of coal combustion from power plants. Polyaniline-fly ash (PANI-FA) composites were prepared by in situ polymerisation of aniline in the presence of Fly Ash (FA) by two slightly different methods. In one case polystyrene sulphonic acid (PSSA) was used as a stabilizer and in another case the starting materials (aniline and FA) were aged before oxidation. The aging procedure formed nanotubes that have cross-sectional diameters of 50-110 nm. The other procedure produced nanotubes with a diameter of 100-500 nm and the length of up to 10μm. The presence of metal oxides and silica in FA were responsible for the formation of nanorods in PANI-PSSA-FA.. The formation of the composites was confirmed by UV-Vis and FTIR. The UV-Vis showed maximum absorbance at 330-360 nm ( due to π-π* transition of benzoid rings) and 600-650 nm(due to charge transfer excitons of quinoid rings), which are characteristics of emaraldine base. The electrochemical analysis of the composites showed that the composites were conductive and electroactive. The Cyclic Voltammetry of PANI-PSSA-FA showed three redox couples which are characteristics of sulphonated PANI. The morphology of the composites was studied by Scanning Electron Microscopy (SEM) and showed that our methods gave composites with improved homogeneity as compared to other reported methods. Thermo Gravimetric analysis (TGA) showed that the presence of FA in the composites improves the thermal stability of the composites by up to 100 0C.

Orientador: Arai Augusta Bernardez Pecora / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-13T23:51:53Z (GMT). No. of bitstreams: 1 Morita_EugeniodeSouza_M.pdf: 4021816 bytes, checksum: da9670c797e58d9f79ea109135e7df7d (MD5) Previous issue date: 2009 / Resumo: O objetivo deste trabalho é avaliar as emissões de óxidos de nitrogênio (NO + NO2) durante a combustão de carvão mineral com adição de calcário dolomítico como adsorvente em leito fluidizado circulante (LFC). As variáveis de influência estudadas foram o excesso de ar, que variou entre 18 e 32 %, e a relação molar cálcio enxofre (Ca/S) que variou entre 0 e 2. A quantificação das emissões de NOx foi realizada em condições de regime estacionário através da técnica de detecção por infravermelho não dispersivo (NDIR). Perfis de temperatura e pressão foram medidos durante a realização dos experimentos. A combustão foi mantida a uma temperatura média do riser de 840 ºC e velocidade superficial do gás próxima de 9 m.s-1. Utilizou-se um Delineamento Composto Central Rotacional (DCCR) para o planejamento dos experimentos mediante determinação das variáveis de influência e seus limites de operação. Um total de treze experimentos foram realizados, sendo onze deles relativos ao planejamento experimental. A influência do parâmetro relação molar Ca/S foi mais significativa quando comparada à influência do excesso de ar. O aumento da razão Ca/S provocou acréscimo nas emissões de NOx, enquanto a redução do excesso de ar provocou a diminuição das emissões. Os resultados obtidos nesta pesquisa apontam para uma região de otimização, buscando-se a minimização das emissões de NOx que pode ser alcançada pela utilização de valores baixos de excesso de ar (18 %) e relação Ca/S de 0,6, uma vez que para relações maiores, a emissão de SO2 foi praticamente nula, destacando o elevado poder de remoção do enxofre por este calcário. / Abstract: This work reports an experimental study concerning NOx emissions from brazilian coal combustion with limestone addition in circulating fluidized bed as a function of operational parameters excess air (18 to 32 %) and Ca/S molar ratio (0 to 2). The NOx concentration was achieved at steady state operation through a non-dispersive infrared (NDIR) detection technique. Profiles of temperature and pressure were measured. Bed temperature around 840 ºC and superficial gas velocity around 9 m.s-1 were conditions maintained at the experiments. Central Composite Rotational Design has been used for planning the experiments according to the knowledge of influence variables on combustion process and its operational limits. A total of thirteen experiments were carried out. The influence of Ca/S molar ratio on NOx emissions was greater than air excess influence. Increasing Ca/S molar ratio it was observed tha NOx emissions also rise, meanwhile decreasing air excess factor leds a reduction on NOx emissions. Results pointed to a optimizing area, seeking to minimize NOx concentrations that can be achieved with low air excess (18 %) and Ca/S molar ratio of 0.6, since for larger ratios, the SOx emissions was insignificant, highlighting the limestone's high efficiency to sulfur capture. / Mestrado / Termica e Fluidos / Mestre em Engenharia Mecânica

No description available.

Physical activation of oil-sands fluid coke, a dense carbonaceous material, using sulfur dioxide (SO2) was investigated as a means of utilizing a plentiful and inexpensive waste for elemental mercury (Hg) removal. A new model was developed to elucidate physical activation of dense carbonaceous materials. Experiments and model simulations revealed that, during activation with SO2, a sulfur-rich porous layer is formed around the periphery of the coke particles; this porous layer reaches a maximum thickness as a result of diffusion limitations; the maximum porous layer thickness is controlled by activation conditions and determines the maximum achievable specific surface area (SSA). Pre-oxidation in air prior to activation, acid washing after activation and smaller coke particle size all result in higher SSA. The highest SSA achieved was 530 m2/g, the highest yet found for oil-sands fluid coke with physical activation. If present, oxygen out-competed SO2 for carbon during activation. SO2 activation and porous layer formation did not occur until oxygen was depleted. Sulfur added to coke through SO2 activation is mainly in reduced forms which are more thermally stable than elemental sulfur in commercial sulfur-impregnated activated carbons (SIACs). TGA and elemental analyses revealed that only 17% of sulfur was removed at 800°C from SO2-activated coke under inert conditions, compared with 100% from a commercial SIAC. The role of sulfuric acid (H2SO4) in vapor Hg capture by activated carbon (AC) was studied due to conflicting findings in the recent literature. In the absence of other oxidizing species, it was found that Hg could be oxidized by oxygen which enhanced vapor Hg adsorption by AC and Hg absorption in H2SO4 solution at room and elevated temperatures. At 200°C, AC treated with 20% H2SO4 reached a Hg loading of more than 500 mg/g, which is among the highest Hg capacities yet reported. When oxygen was not present, S6+ in H2SO4 was found to act as an oxidizer of Hg, thus enabling Hg uptake by H2SO4-treated AC at 200°C. Treating the AC with SO2 at 700°C improved the initial rate of Hg uptake, with and without subsequent H2SO4 treatment.

Physical activation of oil-sands fluid coke, a dense carbonaceous material, using sulfur dioxide (SO2) was investigated as a means of utilizing a plentiful and inexpensive waste for elemental mercury (Hg) removal. A new model was developed to elucidate physical activation of dense carbonaceous materials. Experiments and model simulations revealed that, during activation with SO2, a sulfur-rich porous layer is formed around the periphery of the coke particles; this porous layer reaches a maximum thickness as a result of diffusion limitations; the maximum porous layer thickness is controlled by activation conditions and determines the maximum achievable specific surface area (SSA). Pre-oxidation in air prior to activation, acid washing after activation and smaller coke particle size all result in higher SSA. The highest SSA achieved was 530 m2/g, the highest yet found for oil-sands fluid coke with physical activation. If present, oxygen out-competed SO2 for carbon during activation. SO2 activation and porous layer formation did not occur until oxygen was depleted. Sulfur added to coke through SO2 activation is mainly in reduced forms which are more thermally stable than elemental sulfur in commercial sulfur-impregnated activated carbons (SIACs). TGA and elemental analyses revealed that only 17% of sulfur was removed at 800°C from SO2-activated coke under inert conditions, compared with 100% from a commercial SIAC. The role of sulfuric acid (H2SO4) in vapor Hg capture by activated carbon (AC) was studied due to conflicting findings in the recent literature. In the absence of other oxidizing species, it was found that Hg could be oxidized by oxygen which enhanced vapor Hg adsorption by AC and Hg absorption in H2SO4 solution at room and elevated temperatures. At 200°C, AC treated with 20% H2SO4 reached a Hg loading of more than 500 mg/g, which is among the highest Hg capacities yet reported. When oxygen was not present, S6+ in H2SO4 was found to act as an oxidizer of Hg, thus enabling Hg uptake by H2SO4-treated AC at 200°C. Treating the AC with SO2 at 700°C improved the initial rate of Hg uptake, with and without subsequent H2SO4 treatment.