Metallurgical coke is used primarily as a reducing agent for the reduction of iron in the blast furnace. Due to the high cost, high demand and reduced availability of high quality coking coals used in the production of metallurgical coke, alternative resources are being sought. One possible alternative is to use petroleum coke. Petroleum coke has the advantage of having a higher calorific value than traditional coke, at relatively low cost with a low ash content and ready availability. However the drawback to petroleum coke relates to its poor mechanical strength and reactivity. The main focus of this study was therefore to develop a process for producing petroleum coke with the required qualities for blast furnace application. In an initial series of experiments tests including proximate analysis, ultimate analysis, intrinsic reactivity test, DSC, direct tensile strength, calorific value, X-ray computed tomography, X-ray diffraction and scanning electron microscopy were used to characterise a wide range of petroleum coke and compare it with metallurgical coke properties. X-ray computed tomography methodology was also used to provide 3D information on coke lumps. Results show that none of the petroleum coke samples met the full requirements needed for use as a good blast furnace coke.

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Metallurgical coke for blast furnace and foundry use, and for some domestic boiler cokes are produced by carbonising coals in slot-type ovens. The coal is heated by heat transferred from the hot oven walls (usually 1250°C) so that a temperature gradient is set up within the oven charge. A layer of plastic coal is formed (350-500°C) which moves progressively towards the oven centre as carbonisation proceeds. Immediately after re-solidification, and again near 700°C, the semi-coke suffers shrinkage as the carbon structure reorganises The post re-solidification shrinkage is the more severe and results in large, horizontal and vertical primary fissures being formed which allow breakage of the charge into lumps as it is pushed from the oven. A large central fissure, formed when the two plastic layers meet, divides the charge into two. Further breakage occurs at primary fissures on handling the coke after pushing. Smaller secondary fissures present in the resultant coke lump are believed to be a result of the shrinkage near 700°C. Coke has three roles in the blast furnace: as a source of heat, a source of reducing agents and as a support for the burden. The latter function is particularly important at the bottom of the stack when coke is the only solid material present. The blast furnace output is dependent on the quantity of air that can be pushed up the stack. This depends on the permeability of the coke bed in the lower reaches of the stack. To maintain permeability, the coke should not suffer size degradation as it progresses down the stack; a mixture of large and small coke particles is disastrous. Thus coke quality tends to be assessed in terms of resistance to size degradation in a drum test. Size degradation occurs as a result of volumetric breakage at fissures and abrasion of surfaces. Brittle fracture theory suggests that volumetric breakage should occur as a result of the propagation of secondary fissures in coke lumps.

Le craquage du méthylcyclohexane (MCH) à 450 °C et la conversion de l'éthanol (EtOH) en hydrocarbures à 350 °C sous 30 bar sont effectués sur zéolithes HZSM-5 (de taille de cristallite micrométrique et nanométrique) hiérarchisées. Ces deux réactions modèles mais complexes conduisent à la formation du coke, qui est toxique en MCH et potentiellement actif en EtOH. La toxicité (Tox) et la réactivité du coke dépendent fortement des propriétés texturales des catalyseurs. Dans ce travail, il est démontré que quelle que soit la réaction, le coke dans le cas des zéolithes taille micrométriques est « lourd », il est principalement constitué d'alkylphénanthrènes et alkylpyrènes et est localisé dans les micropores. Dans les zéolithes de taille nanométriques et hiérarchisées (méso-microporeux), le coke est plutôt « léger », formé majoritairement d'alkylbenzènes et alkylnaphtalènes ; ce coke qualifié de léger, est localisé en surface externe. Le coke situé dans les canaux et intersection de la zéolithe HZSM-5 est plus toxique (Tox ≥ 1) que celui situé en surface externe (Tox < 1). La diminution du chemin de diffusion offre également un avantage certain lors de la régénération des catalyseurs en abaissant les températures d'élimination totale de ces cokes. Les effets des propriétés texturales sur les performances catalytiques et la désactivation sont nettement plus marqués dans le cas de EtOH (réaction plus sensible) que MCH. / The Methylcyclohexane (MCH) cracking at 450 °C and the ethanol (EtOH) conversion into hydrocarbons at 350 °C under 30 bar are performed over Hierarchical HZSM-5 zeolites (with micro- and nanometer crystal size). These two model but complex reactions lead to the formation of coke which is toxic with MCH and active with EtOH. The toxicity (Tox) and the reactivity of coke depend strongly on the catalysts textural properties. In this work, it's shown that whatever the reaction, coke in the case of micrometric zeolites is "heavy" and consists mainly of alkylphenanthrenes and alkylpyrenes located into the micropores. In nano-sized and hierarchical (meso-microporous) zeolites, coke is rather "light" and consisting mostly of alkyl benzenes and naphthalenes located on the external surface. The coke located into the channels and at the channels intersections of HZSM-5 zeolite is more toxic (Tox ≥ 1) than that located on the external surface (Tox <1). The decrease in the diffusion path also offers a clear advantage in the catalysts regeneration by lowering the temperature of total coke removal. The effect of textural properties on the catalytic performances and the deactivation are more pronounced in the case of EtOH (more sensitive reaction) than MCH.