Identification of preferential pathways in the pore microstructure of metallurgical coke and links to anisotropic strength properties

• Published in: Fuel (Guildford) Vol. 296; p. 120688
• Main Authors: Steel, Karen M., Jenkins, David R., Balucan, Reydick D., Mahoney, Merrick R.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15.07.2021; Elsevier BV
• Subjects: Anisotropy; Blast furnaces; Carbon dioxide; Coal carbonisation; Coal fluidity; Coke; Coke strength; Computed tomography; Connected pore network; Digitization; Mechanical properties; Membrane permeability; Metallurgical coke; Micro-CT; Microstructure; Modelling; Modulus of elasticity; Permeability; Pore microstructure; Shearing; Stiffness; Tortuosity; Micro-CT; Coal fluidity; Connected pore network; Pore microstructure; Coke strength; Coal carbonisation
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2021.120688

•X-ray micro-CT analysis on coke with known orientation in oven has revealed anisotropy.•Preferred pathways in the pore structure of coke was found to be parallel to the oven wall.•Tortuosity doubled when direction changed from parallel to perpendicular with oven wall.•Young’s modulus decreased by 25% going from perpendicular to parallel with oven wall.•Applied load caused by internal gas pressure may cause anisotropy in pathways and strength. This paper has examined whether there are preferred pathways in the pore microstructure of coke. By modelling permeability and tortuosity in the digitised 3D structure obtained from 3D X-ray micro CT analysis of coke samples, preferred pathways were found to be perpendicular to the direction of applied force, i.e. parallel to the oven walls. The tortuosity was approximately doubled when moving from a direction of parallel to perpendicular with the oven wall and the permeability halved. It is hypothesised that applied force could squeeze the pore structure cutting off the openings in the direction toward the wall. Furthermore, by modelling mechanical properties of the digitised 3D structure it was also found that the Young’s modulus decreased by almost 25% going from the parallel to perpendicular direction (with respect to the oven wall). This result indicates that anisotropy in coke’s mechanical properties can occur. This anisotropy could have implications for coke strength. The coke might be more prone to breaking/shearing along particular planes when in the blast furnace. Furthermore, anisotropic permeability suggests that reactivity toward CO2 may also be anisotropic, and this could also have implications for strength deterioration behaviour in the blast furnace. The findings here are at a preliminary stage and it is recommended that the approaches developed here be applied to more coke samples to examine whether the findings here occur universally, and also the extent that anisotropic permeability and stiffness have implications for strength anisotropy during utilisation.