No description available.

No description available.

The size distribution and strength of metallurgical coke are factors vital for the steady and high-efficiency operation of a blast furnace, since these factors govern stack penneability. Coke strength influences the size of lump coke not only because of size degradation by impact and abrasion during transfer to and descent in the blast furnace, but also because of its influence on the fracture which takes place in the coke layer during carbonisation and the effect this has on the initial mean size and size distribution of the feed coke. Therefore, the elucidation of the relationship between coke strength and the fissure fonnation phenomena is significant. In this study, therefore, the coke strength development during carbonisation has been examined in conjunction with various parameters, such as the degree of carbonisation of the coal, namely the extent or fraction of pyrolytic reaction, and the degree of graphitisation of the coke, as well as carbonisation temperature and heating regime. The porous structure of coke has also been examined with a view to establishing a relation between the porous structure and the coking properties of the coal carbonised. The quality of coke porous structure was evaluated by parameters introduced in this study, i.e., the pore size distribution and pore rugosity factors. A poor porous structure is shown to be associated with high proportion of small pores and pores with a rough surface. These features are considered to stem from poor coking properties and the consequent poor adhesion between coal particles. An attempt has also been made to establish a mathematical model capable of predicting the degree of fissuring of coke during carbonisation by utilising the understandings obtained in this study of the coke strength development during carbonisation and the effect of coal properties on coke strength. Coke samples large enough to facilitate the observation of the degree of fissuring in relation to various coal properties and heating conditions, were made to evaluate the mathematical model and introduce the concept. The concept that fissuring takes place when developing thennal stress exceeds the developing coke strength is demonstrated to be capable to evaluate the effects of coal properties and heating conditions on the degree of fissuring observed.

No description available.

Thèse de doctorat : Spectrochimie, molécules, solides, réactivité : Lille 1 : 2001. / Résumé en français et en anglais. Bibliogr. en fin de chapitres.

Refcoal is a carbon precursor obtained by alkali-mediated extraction of coal with aprotic solvents such as DMF. Refcoal can be converted into a graphitic material through appropriate heat treatment. Graphitisable materials require the development of an intermediate liquid crystalline mesophase. Thus formation of a mesophase during the carbonisation of Refcoal is essential for obtaining highly graphitisable anisotropic cokes suitable for nuclear graphite applications. Anisotropic carbons are even more important in other commercial and industrial application because of their distinctive properties. The formation of anisotropic carbon depends on the nature of the parent precursor, temperature and carbonisation conditions, especially the molecular mobility during the mesophase stage. High-temperature extraction of coal produces Refcoal that yield cokes with a low level of anisotropy. Good control of the mesophase stage during carbonisation may lead to the development of anisotropic cokes. Hydrogen donor additives increase the molecular mobility in the liquid phase by stabilising the free radicals formed by thermal decomposition of coal. Hydrogen donor additives also increase the temperature range over which fluidity occurs, thereby allowing the formation of large sized mosaic structures. Mittal pitches (CTP) and tetralin were examined for their effectiveness as hydrogen donor additives. Refcoal blends containing 10 to 50% by mass additive were prepared by mixing and carbonisation conducted at temperatures ranging form 400 to 1000 °C. Samples were analysed using thermogravimetric analysis (TGA), diffuse reflectance infrared Fourier transform (DRIFT), optical microscope techniques, scanning electron microscopy (SEM), Raman spectroscopy and X-ray diffraction (XRD). It was found that addition of at least 10% tetralin improves the optical texture of Refcoal cokes and also increases the carbon yield. In both tetralin and pitch addition, 20% additive gave coarse circular anisotropic cokes after carbonisation at 650°C. However the carbon yield was reduced for the Refcoal coke treated with Mittal pitch. In fact the yield roughly decreases with an increase in pitch content. Although the cokes from pitch treated Refcoals showed a low ratio of d/g (where d indicates the degree of disordering and g the degree of ordering), Raman and XRD results indicate little further improvement in crystallinity but SEM showed development of a smooth morphology with increasing pitch content. Previous literature results suggest that this indicates that the material must have passed through a mesophase stage. Surprisingly, the addition of tetralin yielded cokes with high ratio of d/g, but improved the carbon yield and optical anisotropy. Increasing tetralin content in the carbonising system increased the size of anisotropic textures but the SEM micrographs show rough morphology with compounds that appear to inhibit mesophase spheres coalescence. / Dissertation (MSc)--University of Pretoria, 2009. / Chemistry / unrestricted

La croissance démographique mondiale, associée à une augmentation générale du niveau de vie, se traduit par l'explosion des besoins en matières premières et énergie. Afin de relever ce défi, une attention accrue est accordée aux énergies et ressources naturelles renouvelables. Parmi elles, la biomasse est particulièrement prometteuse. Elle présente des avantages certains (abondance, répartition homogène) mais aussi plusieurs inconvénients (faible densité énergétique, humidité élevée,…). Pour surmonter ces difficultés, la torréfaction est la méthode la plus connue, mais elle induit une augmentation des taux de cendres et une perte de matière. La carbonisation hydrothermale (HTC) est une alternative possible. L'objet de cette thèse est l'étude de la HTC comme moyen de bonifier la biomasse lignocellulosique. Trois axes principaux ont été considérés: augmentation de la densité énergétique, récupération de molécules, et minéraux d'intérêt. L'étude porte d'abord sur la HTC de systèmes moléculaires représentatifs de ceux présents dans le bois. Le hêtre a été étudié comme biomasse modèle, permettant de déterminer des conditions expérimentales optimales, appliquées ensuite à diverses biomasses. Enfin d'autres méthodes d'activation ont été testées telles que les micro-ondes et les fluides supercritiques. Les hydrochars obtenus après HTC présentent une diminution concomitante des ratios atomiques H/C et O/C. La phase liquide contient différentes molécules d'intérêt (furfural,…). Enfin, les teneurs en cendres diminuent après HTC du fait d'une lixiviation partielle de certains éléments (alcalins et alcalino-terreux). En conclusion, la HTC semble être une alternative intéressante à la torréfaction ; elle permet la production d'hydrochars avec des teneurs élémentaires adaptées à une utilisation en gazéification et la récupération de molécules et minéraux. L'intérêt et la faisabilité technique ont été démontrés en particulier sur des biomasses humides (plantes agricoles) ou polluées (broyats de déchetterie). / Population growth, coupled with a general increase in standard of living, result in a booming demand for raw material and energy. To face this challenge, an increased attention is paid to the use of renewable energies and natural resources. Among them, biomass is especially promising. Its advantages (abundance, distribution all over the Earth) are balanced by several drawbacks (low energy density, high moisture content,…). To overcome these problems, torrefaction is the most traditional way, but it has some inconveniences (increased ash content, loss of material). Hydrothermal carbonisation (HTC) is a possible alternative. The purpose of this thesis is the study of HTC a means to beneficiate the lignocellulosic biomass. Three main aims were identified: increase of the energy density, recover molecules and minerals of interest. The study initially focused on HTC of molecular model systems present in wood. Beech wood was also studied, as a model biomass. This study allowed determining optimal experimental conditions for treatment of further biomasses. Finally, other activation methods have been tested, such as microwaves, and supercritical fluids. Hydrochars obtained after HTC feature a concomitant decrease of the atomic H/C and O/C ratios. Liquid phase contains different molecules of interest (furfural,…). Finally, ash content decreases after HTC owing to a partial leaching of some elements (alkali and alkaline earth metals). In conclusion, HTC seems to be an interesting alternative to torrefaction as it allows for the production of hydrochars suitable for gasification, and the recovery of molecules and minerals of interest. The interest and technical feasibility have been demonstrated in particular for biomasses with high moisture (agricultural crops) or with high pollutant contents (grounds of waste disposal).

Thèse de doctorat : Sciences du Bois : Nancy 1 : 2009. / Titre provenant de l'écran-titre.

Reproduction de : Thèse de doctorat : Spectrochimie, molécules, solides, réactivité : Lille 1 : 2001. / Label européen. Résumé en français et en anglais. Titre provenant de la page de titre du document numérisé. Bibliogr. en fin de chapitres.

Synthetic graphite is an important industrial material, used in nuclear reactors, electrodes and many other applications. Graphitisation of coke is the solid-state transformation of the disordered carbon atoms into a well-ordered hexagonal graphite structure, requiring temperatures as high as 2 600 ºC. Catalytic graphitisation using metals or metal compounds allows the rearrangement of atoms to occur at lower temperatures. The extent of catalytic graphitisation is markedly dependent on the structural ordering of the parent coke, the catalyst concentration and the reaction conditions. Solvent extraction of coal using dimethylformamide (DMF) as a solvent yields a refined coal solution referred to as Refcoal solution. Cokes of solvent-refined Tshikondeni coal derivatives have been found to be graphitisable. The activity of acetylacetonate and hydroxyquinolinate complexes of Al, Ca, Cu, Fe and Zr for catalysing the graphitisation of Refcoal cokes at 1 600 and 2 000 ºC was investigated. The effect of residence time on the catalytic graphitisation of Refcoal cokes was investigated by heat-treating cokes for two and six hours at 1 600 °C. For iron(III)acetylacetonate, the effect of metal concentrations was studied. Samples were analysed using thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and optical microscope techniques. The results show that calcium(II)acetylacetonate catalyses the graphitisation of Refcoal cokes. The degree of graphitisation increases with an increase in the iron concentration. However, iron promotes localised graphitisation, probably in the vicinity of the catalyst particles. / Dissertation (MSc (Chemistry))--University of Pretoria, 2008. / Chemistry / unrestricted