Dr Hannah Lomas

The blast furnace technology is still the main ironmaking route with a current global share of 70%. Reduction of fossil carbon consumption and CO2 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 CO2 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.

A coke produced using a custom-built sole-heated oven and a coke prepared in a pilot-scale oven from a matched coal, were compared using a range of analytical techniques. The aim of this comparison was to assess to what extent the small-scale sole-heated oven can successfully replicate the production of pilot-scale oven cokes, and thus be used to rapidly prepare and screen a wide range of cokes for particular characteristics, e.g. abrasion resistance. The techniques applied included conventional methods and novel methods developed by our research team. These included microstructural and microtextural analyses of samples of each coke, and tribological, scratch test and fractographic analyses, each of which elucidates different strength attributes. These include microstructural weaknesses, abrasion resistance, and the strength of microtextural interfaces. The level of replication achieved indicates that the sole-heated oven, used in combination with an annealing step in a muffle furnace, can be beneficially used to model the pilot-scale oven.

Acoustic emission profiles generated during scratch testing of a range of metallurgical coke samples were recorded and linked to the concurrent energy release, dispersal or absorption on coke fracture or damage. Three different signatures were identified, which were based on the simultaneous measurement of acoustic and total energy release profiles, and these signatures could be correlated with both the microstructure and microtexture of the coke being traversed at the time. The acoustic emission signature for fracture or damage to the coke reactive maceral derived constituents (RMDC) was correlated to the rank of the parent coal or coal blend, with the signature number generally increasing with increasing rank. Conversely, the signature numbers did not vary with parent coal rank for fracture or damage to the inertinite maceral derived constituents (IMDC), with the majority of IMDC fractures associated with a release of mechanical energy. The incidence of the signature associated with a release of mechanical energy (type 1) became increasingly dominant from RMDC to RMDC-IMDC interfaces to IMDC. Conversely, signature types associated with a dispersal (type 2) or absorption (type 3) of mechanical energy become increasingly dominant from IMDC to RMDC-IMDC interfaces to RMDC. The findings suggest acoustic emissions recorded during scratch testing and their subsequent characterisation can be used to indicate the fracture toughness of a given coke. This study contributes towards a broader program of research to improve understanding of the factors which influence the strength of coke and its microtextural constituents and interfaces, and how this relates to the properties of the parent coals.

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.

© 2016 Elsevier Ltd. All rights reserved.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.