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Coke samples, produced from coals having a range of rank and vitrinite content, were subjected to uniaxial loading in a universal tester. Cokes were also imaged at high resolution using micro-CT. The aim was to understand the relationship between the internal microstructure of the coke and coke strength under load. The loading was done in two separate ways, being either compression to failure or progressive loading. The results showed that the coke samples underwent a form of stiffening at low loads, potentially due to closing of fine-scale pores and/or re-alignment of graphitic layers in the RMDC. Measurements of plastic strain indicated that these changes were permanent. At higher loads, small load-bearing components of the microstructure were found to break, leading to a softening of the coke samples. Evidence of the breaking was observed using micro-CT images before and after loading of samples. The work has relevance to the understanding of the fundamentals of coke strength, as well as to issues relating to handling and preparation of coke for standard testing. [ABSTRACT FROM AUTHOR]

Micro-CT imaging of samples of metallurgical coke was achieved at high resolution (~ 10 μm), using the Imaging and Medical Beamline of the Australian Synchrotron. The coke samples were then stressed to breaking point and imaged again. The result is that we can examine, in fine detail in 3D, the locations of the fracture surfaces in the coke, and their relationship to the different aspects of the microstructure. In addition, we have performed 3D finite element linear elasticity analysis, using the microstructure of the cokes as input to the calculations. The result is a 3D map of the von Mises stress in the structure, which provides information about the likely locations of fracture. Finally, we have performed a fractographic analysis of the fracture surfaces, in order to characterise the nature of the fracture mechanisms. The imaging and analysis has been performed for both compressive and mixed-mode loading of the coke samples. The work provides the opportunity to identify the key mechanisms for fracturing of coke due to the aspects of their microstructure, and has the potential to aid in the production of stronger metallurgical coke, by means of blending coals to produce coke with improved strength properties. [ABSTRACT FROM AUTHOR]

Metallurgical coke is a complex brittle heterogeneous material consisting of carbon derived from fusible, semi-fusible and inert coal particles that forms a porous composite matrix. This paper presents a novel approach to assess and quantify the breakage behaviour and microstructural weaknesses in a pilot oven metallurgical coke. The approach uses fractography, a method commonly applied to determine the fracture behaviour and origin(s) in homogeneous materials, such as metals and ceramics. Determination of the fracture origin(s), paths of crack propagation and microstructural weaknesses in such a complex heterogeneous material as metallurgical coke represents a significant advance in both the application of fractography and the assessment of coke strength and breakage behaviour. Identification of the key features that contribute to the coke’s failure will facilitate better prediction of coke strength from coal properties and ultimately optimisation of the coal blending process. Key features and markings have been clearly identified on fracture surfaces that can either be traced back to the fracture origin or give an indication of the type of fracture or stresses to which the coke has been subjected, including the directionality and strength of those stresses. These markings include hackle, hackle twist and wallner lines, as well as markings generated by conchoidal and overload fractures. A three-step approach was applied to determine the breakage behaviour in stabilized lumps of the pilot oven coke, in which fractured coke surfaces were analysed at the macro, micro and submicron levels. The observed mechanisms of failure were quantified and summarised using a radar diagram. [ABSTRACT FROM AUTHOR]

Metallurgical coke samples across the tuyere level of an operating blast furnace were analysed using a fractographic approach to identify and quantify various coke failure mechanisms. Tuyere level cokes displayed different failure mechanisms compared to the feed coke, implying a strong influence of the blast furnace reaction environment on the modification of coke failure mechanisms. The conchoidal and brittle overload type failures were noted to have an effect on the propagation of transgranular and intergranular crack growth in the coke microstructure. Feed coke breakage behaviour was strongly influenced by existing fissures and conchoidal fracture, while the breakage of the deadman coke lumps was dominated by pore wall collapse through intergranular crack growth in combination with erosive wear. The porosity at the IMDC–RMDC interface in coke has been identified as a critical parameter contributing to coke failure at tuyere regions. This fractographic study demonstrates that the fracture faces show evidence of the varying failure mechanisms presented in the preceding manuscripts (Part 1 and Part 2), in addition to the erosive wear resulting from the blast furnace exposure. However, further studies are required to establish the association between the identified coke failure mechanisms and coke texture, which has implications for improving coke performance in a blast furnace. [ABSTRACT FROM AUTHOR]

Metallurgical coke used in blast furnaces is the result of blending coals to achieve the optimum coke strength properties. Prediction of coke strength from coal properties relies primarily on statistical methods. Improvement of these models is desirable. We believe a better understanding of the fundamental factors controlling coke strength is required to achieve this. In this second of a series of three papers, we apply our recently developed fractographic approach to examine and quantify the breakage behaviour and microstructural weaknesses in pilot oven metallurgical cokes from two series of single coals and binary blends of the coals. We have successfully applied fractography to perform an effective failure analysis of the complex, heterogeneous coke material. Summaries of the factors contributing to the failure of each coke studied have been presented as radar graphs. These graphs demonstrate that the failure profile of the cokes from blends is not simply a weighted average of the fracture behaviour of the cokes from the constituent single coals. Instead, non-additive effects are observed, and this may have implications for the mathematical models widely used to predict coke behaviour and strength in the blast furnace. Trends between the various fractographic parameters have been identified, and preliminary relation of these to both the maximum compressive strength of each coke and basic properties of the original coals, has been completed. Enhanced understanding of how the fracture behaviour of each coke relates to the properties of the coal blend used will help facilitate better prediction of coke strength from coal properties and ultimately optimisation of the coal blending process. [ABSTRACT FROM AUTHOR]

The steel industry is one of the largest industrial carbon dioxide emitters, accounting for up to 7% of global emissions. Increasingly stringent global carbon emission regulations are prompting the steel and coal industries to explore and implement carbon abatement strategies through both the incremental development of current technologies and the incorporation of new, innovative ones. This paper reviews the current status and future development of sustainable cokemaking, aiming to identify suitable carbonaceous materials for partial coal displacement in metallurgical coking blends and the desirable properties of coals which facilitate such displacements. Results from works pertaining to the influence of renewable and waste additions on the thermoplastic properties of coal blends and the quality of resulting cokes are included. This includes the mechanism of interaction between various additives and metallurgical coal and the influence on the coking behavior, microstructural and microtextural transformation, and ash chemistry during cokemaking. The sustainability of incorporating certain carbonaceous additives in blends on a commercial scale has also been evaluated. Efforts were made to draw correlations from literature data regarding the impact of coal property parameters on the carrying capacity of coal in blends with renewable biomass feedstocks and other waste additives. The review has identified the knowledge gaps and future research needs in sustainable cokemaking. • Influences of renewable additives for cokemaking are reviewed. • Promising carbonaceous materials for partial coal displacement in coking blends were analysed. • The significance of coal properties on coal carrying capacity was explored. • The knowledge gaps and future research needs in sustainable cokemaking were identified. [ABSTRACT FROM AUTHOR]

• Measures for reducing the carbon intensity of blast furnace ironmaking were introduced. • Influences of low-carbon ironmaking processes on fuel requirements are reviewed. • The introduction of alternative reductants cannot eliminate the need for metallurgical coke. • Sustainability of blast furnace ironmaking depends on improving the H/C replacement ratio. • Introduction of hydrogen promotes the solution loss and structural degradation of coke. The blast furnace technology is still the main ironmaking route with a current global share of 70%. Reduction of fossil carbon consumption and CO 2 emissions in blast furnace operations are essential for the decarbonization of steelmaking. Potential solutions such as introducing renewable carbon-based materials (torrefied biomass, charcoal), using hydrogen-enriched reducing gases (i.e., hydrogen gas, coke oven gas, reformed coke oven gas, green methane), oxygen enrichment with top gas recycling, and carbon capture and storage/utilization have been considered to decrease emissions. The enhanced sustainability of blast furnace operations depends primarily on improving the hydrogen-to-carbon replacement ratio. Hydrogen is an effective reducing agent, producing steam during the reduction of ferrous burden. The replacement of coke and PCI with hydrogen leads to reduced fuel rates and CO 2 emissions. Although implementing the innovative ironmaking solutions reduces coke and coal consumption, coke cannot be replaced entirely as it plays an irreplaceable role as a mechanical support network and the permeable layer for gas movement in the blast furnace. The injection of alternative reducing agents into the blast furnace alters the reaction environment by changing gas composition and temperature. Therefore, understanding the impacts of new reaction conditions on coke rate and quality requirements is important to both coal producers and steel manufacturers. This paper reviews the current understanding of how the introduction of alternative reducing agents into the blast furnace influences the gasification behavior, degradation mechanism, and consumption rate of coke. The review also identifies the knowledge gaps and future research opportunities in the field. [ABSTRACT FROM AUTHOR]