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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. Johannesburg, 2015. / Fly ash is a by-product generated during the combustion of coal for electricity gen- eration. Previous studies have shown that various waste fly-ashes (Japanese, Saudi Arabian, and Australian) contain trace quantities of transition metal elements which can be used in the synthesis of shaped carbon nanomaterials. A survey of the litera- ture has shown that no attempts to correlate the composition of a particular coal fly ash and the type or quantity of carbon nanomaterials (CNMs) that can be synthesized has been made. Neither has the effect of leached fly ash been tested for the synthesis of CNMs. Hence a study on the effect of the chemical composition of South African fly ash (collected from ESKOM’s Duvha power station in Mpumalanga) upon the chemical vapour deposition (CVD) synthesis of carbon nanostructures is justified. Untreated and chemically treated fly ash samples were used as catalysts in the CVD method to synthesize CNMs. In the latter case selective leaching experiments were conducted on the fly ash samples under acidic, basic and neutral conditions. Op- timal CNM synthetic conditions were achieved by initially flowing H2 gas to re- duce the metal oxides within the fly ash catalyst followed by the introduction of the carbon source (C2H2) at a temperature range of 600 - 800 ◦C. All samples were quantitatively and/or qualitatively characterized. Inductively coupled plasma optical emission spectrometry (ICP-OES) and X-ray fluorescence (XRF) techniques were used to quantify the metal ions which were removed from the fly ash samples. Fur- thermore, qualitative studies were conducted with (PXRD, and laser Raman spec- troscopy), morphological and surface area characterization techniques (SEM, TEM and BET) were used to investigate the synthesis of CNMs from the untreated and chemically treated fly ash samples. Results have shown that carbon nanofibers (CNFs) of different geometric morpholo- gies were synthesized at an optimal yield temperature of 700◦C. A combination of smooth, thin, wide, spiral platelet-like, stacked cup, and fishbone morphologies were reported when the untreated fly ash catalyst was used. Fly ash catalysts under acidic, basic and neutral treatments showed CNFs of varying sizes and specific morpholo- gies. Smooth graphitic platelet-like, stacked cup and platelet-like CNFs were re- ported when the fly ash catalyst was leached with neutral, basic and acidic solutions. Carbon nanofibre sizes with the IG ID ratios were reported as follows 115 nm (1.092), 52 nm (0.799), and 200 nm (0.960) under neutral, basic and acidic mediums respec- tively. Surface areas (41, 14 and 7) m2/g for the CNFs that were synthesised from the neutral, basic and acidic treated fly ash catalysts were related to the selective leaching of metals. The quality and quantity of CNFs obtained under acidic medium were associated with the leaching of iron (5.6%), cobalt (1.7%), calcium (20.4%), copper (12.5%), chromium (4.6%), magnesium (23.3%), manganese (15.2%) and nickel (2%) from the fly ash catalyst. Under a basic medium only chromium (0.2%), calcium (0.3%) and copper (7.4%) were removed. Significantly the best quality of CNFs was ob- tained when fly ash was treated under neutral conditions. Metal ions such as: cal- cium (3.7%), copper (3.8%), chromium (0.1%), and magnesium (1.3%) were mod- erately removed from the ash matrix. Therefore, composition and quantity of the fly ash catalyst had an effect on the synthesis of CNFs.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 246-250. / by Matthew Neville. / Sc.D.

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Pulverized coal injection (PCI) technology is widely practised in blast furnace ironmaking due to economic, operational and environmental benefits. High burnout of pulverized coal in the tuyere and raceway is required for high PCI rate operation. A comprehensive review reveals that although there have been a variety of PCI models, there is still an evident need for a more realistic model for PCI operation in blast furnace. Aiming to build a comprehensive PCI model of a full-scale blast furnace, this thesis presents a series of three-dimensional mathematical models, in terms of model development, validation and application, in a sequence from a pilot-scale to a full-scale, from a simple to complicated geometry, from a coal only system to a coupled coal/coke system. Firstly a three-dimensional model of pulverized coal combustion is developed and applied to a pilot-scale PCI test rig. This model is validated against the measurements from two pilot-scale test rigs in terms of gas species composition and coal burnout. The gas-solid flow and coal combustion are simulated and analysed. The results indicate that the model is able to describe the evolutions of coal particles and provide detailed gas species distributions. It is also sensitive to various parameters and hence robust in examining various blast furnace operations. This model is then extended to examine the combustion of coal blends. The coal blend model is also validated against the experimental results for a range of coal blends conditions. The overall performance of a coal blend and the individual behaviours of its component coals are analysed. More importantly, the synergistic effect of coal blending on overall burnout is examined and the underlying mechanisms are explored. It is indicated that such synergistic effect can be optimized by adjusting the blending fraction, so as to compensate for the decreased burnout under high coal rate operation. The model provides an effective tool for the optimum design of coal blends. As a scale-up phase, the coal combustion model is applied to the blowpipe-tuyereraceway region of a full-scale blast furnace, where the raceway is simplified as a tube with a slight expansion. The in-furnace phenomena are simulated and analysed, focusing on the main coal plume. The effect of cooling gas conditions on combustion behaviours is investigated. Among the three types of cooling gas (methane, air, and oxygen), oxygen gives the highest coal burnout. Finally, a three-dimensional integrated mathematical model of pulverized coaVcoke combustion is developed. The model is applied to the blowpipe-tuyere-raceway-coke bed region of a full-scale blast furnace, which features a complicated raceway geometry and coke bed properties. The model is validated against the measurements in terms of coal burnout from a test rig and gas composition from a blast furnace, respectively. The model gives a comprehensive full-scale picture of the flow and thermo-chemical characteristics of PCI process. The typical operational parameters are then examined in terms of coal burnout and gas composition. It is indicated that the final burnout along the tuyere axis is insensitive to some operational parameters. The average burnout over the raceway surface can better represent the amount of unburnt coal particles entering the surrounding coke bed and it is also found to be more sensitive to the changes of most parameters. In addition, the underlying mechanisms of coal combustion are obtained. The coal burnout strongly depends on both oxygen availability and residence time. The existence of recirculation region gives a more realistic coal particle residence time and burnout. Compared with the fore-mentioned two models, this model is considered as a more comprehensive model of PCI operation for understanding the infurnace behaviours and provides more reliable information for the design of operational parameters.

This thesis is concerned with the implementation of Artificial Neural Networks (ANNs) to monitor and control chain grate stoker-fired coal boilers with a view to improving the combustion efficiency whilst minimising pollutant emissions. A novel Neural Network Based Controller (NNBC) was developed following a comprehensive set of experiments carried out on a stoker test facility at the Coal Research Establishment (CRE) Ltd., before being evaluated on an industrial chain grate stoker at Her Majesty's Prison Garth, Leyland. The NNBC mimicked the actions of an expert boiler operator, by providing 'near optimum' settings of coal feed and air flow, as well as taking into account the correct 'staging' sequence of these parameters during load following conditions, before subsequently fine tuning the combustion air under quasi steady- state conditions. Test results from the on-line implementation of the NNBC on both chain grate stoker plants have demonstrated that improved transient and steady state combustion conditions were attained without having any adverse effect on the pollutant emissions nor the integrity of the appliances. A novel combustion monitoring system was also developed during the course of the work that can be used to infer the stability of combustion on the fire bed, following a pilot study of the 'flame front' movement during boiler load changes on the stoker test facility at CRE. This novel low-cost flame front monitor was rigorously tested on the industrial stoker plant, and long hours of successful on-line operation were achieved. It was also demonstrated with the use of ANNs, that the data gathered from the novel flame front monitor can be processed to yield evidence concerning movement of the ignition plane over a short period of time (several minutes). The prototype controller and flame front monitor would thus provide both stoker manufacturers and users with a means of meeting future legislative limits on pollutant emissions as indicated by the European Commission, as well as improving the combustion efficiency of this type of coal firing equipment Finally, ANNs were also used as a simplistic means to represent the complex coal combustion process on the bed of the stoker test facility whilst burning a particular type of coal. The resultant 'black-box' models of the combustion derivatives were able to represent the dynamics of the process and delivered accurate one-step ahead predictions over a wide range of unseen data. The work demonstrated the complex functional mapping capability of ANNs and also addressed the deficiencies in mathematical modelling of the coal combustion process on fixed grate, as indicated in the literature.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / A utilizaÃÃo de resÃduos como materiais alternativos tem se mostrado uma soluÃÃo satisfatÃria de acordo com vÃrias pesquisas realizadas. Os produtos da combustÃo do carvÃo mineral (PCCs) sÃo resÃduos que causam impacto ambiental, mas apresentam grande potencial de utilizaÃÃo no setor da construÃÃo civil na produÃÃo de argamassas e concretos. Apresentam elevado teor de sÃlica (SiO2), podendo ser utilizados como pozolanas. Esta pesquisa objetivou verificar a viabilidade da utilizaÃÃo dos produtos da combustÃo do carvÃo mineral em argamassas de assentamento e revestimento. As matÃrias-primas foram caracterizadas quanto aos aspectos fÃsicos, quÃmicos e para os PCCs tambÃm foi avaliada sua pozolanicidade. Foram confeccionadas argamassas de referÃncia e com adiÃÃo de PCCs nos teores de 10, 20, 30, 40 e 50% como substituto parcial do cimento. ApÃs tempos de cura de 7 e 28 dias, foram feitos teste de resistÃncia à traÃÃo na flexÃo e resistÃncia à compressÃo. AlÃm disso, as argamassas foram sujeitas a anÃlises de difraÃÃo de Raios â X, Microscopia EletrÃnica de Varredura, absorÃÃo de Ãgua, determinaÃÃo de Ãndice de vazios e massa especÃfica aparente. Os resultados obtidos mostraram-se compatÃveis quando comparados com os dados da literatura, demonstrando ser viÃvel a aplicaÃÃo dos produtos da combustÃo do carvÃo mineral na indÃstria da construÃÃo civil. / The use of residues as alternative materials has proven successful according to several investigations. Coal combustion products (CCPs) is a residue that causes environmental impact, but it has a great potential for use in civil engineering construction in the production of mortars and concrete. It posesses a high content of silica (SiO2) and so it can be used as pozzolan. This research aimed to verify the viability of adding coal combustion products to mortars for bricklaying and covering. The raw materials were submitted to physical, and chemical characterization. CCPs were also rated according to their pozzolanicity. Reference mortars were prepared, as well as mortars containing 10, 20, 30, 40 and 50% amounts of CCPs as a partial replacement for cement. After curing time of 7 and 28 days, prismatic samples were tested to determine their tensile strength in bending and their compression strength. Moreover, the mortars were subjected to X-ray diffraction, scanning electron microscopy and determination of water absorption, voids and apparent density. The results obtained were consistent with literature data, showing that application of coal combustion products in the construction industry is a viable alternative.

In this work the combustion characteristics of coal, charcoal, microalgae biomass and blends between these three components were evaluated by means of non-isothermal thermogravimetry. Blends between coal, charcoal and microalgae biomass were made according to the specifications of a D-optimal mixture design so as to be able to model interactions between the three components with maximum precision despite multiple constraints built into the design. These constraints specified that coal can have a minimum value of 70 mass percent in any blend, while microalgae can have a maximum value of 20 mass percent. While coal and charcoal were blended by mixing the two respective dry components, microalgae biomass was incorporated into the blends by first absorbing microalgae onto fine coal from concentrated slurry of the microalgae in water. The microalgae in these blends were therefore intimately associated with the coal. This approach differed substantially from the normal practice of preparing coal – biomass blends (which are usually dry-mixed as for coal – charcoal blends). Proximate analyses of the starting materials showed that the microalgae biomass has a significantly higher volatile matter: fixed carbon content than both coal and charcoal, which should improve the combustion of these materials by providing a more stable combustion flame. Analyses of the thermogravimetric data obtained showed that coal and charcoal have much simpler combustion profiles than microalgae biomass for which five different thermal events could be observed in the DTG combustion profile. Qualitative kinetic analyses showed that the combustion of coal and charcoal follows first-order kinetics, but for microalgae biomass combustion, the first two combustion stages appear to follow first-order kinetics. The TG and DTG profiles for coal, charcoal, microalgae and blends of these three components were used to derive values for the so-called comprehensive combustion property index (S-value), which provides a combined measure of the ease of ignition, rate of combustion, and burn-out temperature. The S-values so obtained were used as response variable for the construction of a response surface model in the experimental domain investigated. Following statistical validation of the response surface model, the model was used to predict an optimum S-value or a blend that would display optimum combustion behaviour. Two optimum blends were obtained from the optimisation process, one in which only charcoal is added to coal, and one in which only microalgae is added to coal. Adding both charcoal and microalgae produced an antagonistic effect compared to when only one of these are used. Qualitative kinetic analyses of the combustion data of blends indicate that blends of coal and charcoal combust in a manner similar to the individual components (hence following first-order kinetics), but blends of coal and microalgae follow more complex kinetics despite the fact that the combustion profile is visibly more simple compared to the combustion profile for microalgae alone.