Associate Professor Tom Honeyands

Hydrogen-enriched blast furnace (BF) operation is currently being assessed to mitigate greenhouse gas emissions while the steelmaking industry transitions to low carbon emission technologies. Increasing the usage of lump ore in the BF also presents opportunity to decrease carbon emissions, as it can be directly charged to the furnace without agglomeration. Use of lump ore in modern blast furnace operations is facilitated by high temperature interactions with sinter. With more emphasis on hydrogen enrichment in BF operations, the behaviour of lump and sinter mixed burdens must be characterised under new conditions. In this study, 15% hydrogen is added to the standard gas conditions of a Softening and Melting (S&M) apparatus (replacing nitrogen). Analysis of auxiliary reactions such as the Boudouard Reaction and the Water-Gas Shift Reaction is presented and their impact on burden reduction and performance assessed. Results indicate that with the inclusion of hydrogen, the performance of sinter burden deteriorates, while lump burden shows significant improvement. Interaction between sinter and lump still occurred with the inclusion of hydrogen in the gas, and the mixed burden behaviour of 20% lump and 80% sinter fell between that of the individual burdens. From interrupted experiments, it is noted at high degrees of reduction, the lump burden forms a solid metallic layer which maintains its interparticle voidage at high temperatures, supressing exudation of liquid slag.

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.

The iron ore sintering process needs to be optimised to decrease its energy intensity and emissions of carbon and atmospheric pollutants, while continuing to produce sinter of sufficient quality for current and future low carbon blast furnace operations. Ideally, the sinter structure and mineralogy should be related back to the particle-level structure of the iron ore types mixed from different mine sources. This particle-level detail can be visually obtained by 3D X-ray micro-Computed Tomography (micro-CT), but requires subsequent algorithms to individually identify and classify particles and identify the relationship between ore sources and sinter quality. In this study, individual particles in sinter green ¿ beds comprising a mixture of coking coal, fluxes, return fines and 5 iron ore samples from different mine sources are identified and classified in high resolution micro-CT images using a machine learning algorithm and associated data processing workflow. Coking coal, fluxes, and return fines are first segmented from iron ores based on their X-ray attenuation and texture. By imaging individual samples from each iron ore source, reliable training data is readily obtained from particle isolation with Convolutional Neural Networks (CNNs) guided by Trainable Weka Segmentation (TWS). Supervised machine learning is then applied to the datasets of isolated particles to produce a per-particle segmented digital sinter green bed image. A collection of geometric, texture, and greyscale features are computed for the particles and used to train a gradient boosting classifier. Tests are then performed on unseen subsets of the single ore source data, on a stratified mixture, and on a random mixture. An accuracy over 90% is achieved for iron ores that are morphologically domain-distinct in their feature space, while lower accuracy in the order of 40%¿80% is achieved between iron ore particles that derive from different mine sources, but are domain-similar, suggesting similar mineralogy. The effect of limited training domain, the visual/morphological/feature space similarities and the resulting domain shift in data between training and testing are carefully analysed to identify major sources of similarity. This per-particle multilabel classification of sinter green bed mixtures distinguishes both similar and distinct ores from different mines, and provides a high resolution, accurately characterised digital twin analogue of mixed iron ore sinter green beds. This allows for future detailed analysis of sinter quality, energy intensity, and carbon emissions during the metallurgical process, all of which could be optimised to produce cleaner, higher quality iron.

Analogue sinter tablets were produced at temperatures between 1250°C and 1320°C, with a range of hold times and cooling rates. Platy silico-ferrite of calcium and aluminum (SFCA) morphology was identified in samples produced at 1250°C using reflected light microscopy; however, quantitative x-ray diffraction (XRD) identified the presence of the SFCA phase, with no SFCA-I detected. This proves that the platy SFCA morphology common in analysis by reflected light microscopy cannot be attributed to the SFCA-I mineral without further analysis. Micro-XRD and electron probe micro-analysis (EPMA) were carried out on an area of platy SFCA confirming this result. The sinter analogue tablets were reduced in a 30% CO, 70% N2 gas mixture at 900°C in a tube furnace thermo-gravimetric analyzer. The degree of reduction of the tablets in this study was found to be controlled by the porosity of the samples, rather than by the morphology or mineralogy of the bonding phase.

In the iron ore sintering process, the resistance to air flow is a major factor in deciding the flame front speed, which influences the sinter productivity and quality. In this work, pressure drop during sintering and the resistance to air flow was investigated in milli-pot sintering for different coke rates. The sintering experiments were conducted in a milli-pot (diameter 53 mm, height 400 mm) and pressure and temperature were measured at the same locations in the bed by four taps located equidistant to each other. The yield of sinter product was measured following a modified drop test and the mineralogy of the sinter product was analysed. The results from milli-pot sintering were then compared to the reported results from standard pilot-scale sintering, and it was found that the lower half of the milli-pot bed gave a reasonable representation of the pilot-scale sintering process. The results of sinter mineralogy, yield and productivity of the lower half of milli-pot at 5.5-8.0% coke rate were found to be similar to pilot-scale sintering tests at a corresponding coke rate from 3.5 to 5.5%. The maximum resistance to air flow in the bed was found to be in the region between the leading edge of the flame front at ~100°C and the trailing edge of the flame front at ~1 200°C. This suggests that the maximum resistance to air flow includes the effect of de-humidification and combustion in addition to the high temperature "flame front" region usually defined at temperatures above 1 100°C or 1 200°C.

Slags are a co-product produced by the steel manufacturing industry and have mainly been utilised for aggregates in concreting and road construction. The increased utilisation of slag can increase economic growth and sustainability for future generations by creating a closed-loop system, circular economy within the metallurgical industries. Slags can be used as a soil amendment, and slag characteristics may reduce leachate potential of heavy metals, reduce greenhouse gas emissions, as well as contain essential nutrients required for agricultural use and environmental remediation. This review aims to examine various slag generation processes in steel plants, their physicochemical characteristics in relation to beneficial utilisation as a soil amendment, and environmental implications and risk assessment of their utilisation in agricultural soils. In relation to enhancing recycling of these resources, current and emerging techniques to separate iron and phosphorus slag compositions are also outlined in this review. Although there are no known immediate direct threats posed by slag on human health, the associated risks include potential heavy metal contamination, leachate contamination, and bioaccumulation of heavy metals in plants, thereby reaching the food chain. Further research in this area is required to assess the long-term effects of slag in agricultural soils on animal and human health.

Sinter quality is a key element for stable blast furnace operation. Sinter strength and reducibility depend considerably on the mineral composition and associated textural features. During sinter optical image analysis (OIA), it is important to distinguish different morphologies of the same mineral such as primary/secondary hematite, and types of silico-ferrite of calcium and aluminum (SFCA). Standard red, green and blue (RGB) thresholding cannot effectively segment such morphologies one from another. The Commonwealth Scientific Industrial Research Organization¿s (CSIRO) OIA software Mineral4/Recognition4 incorporates a unique textural identification module allowing various textures/morphologies of the same mineral to be discriminated. Together with other capabilities of the software, this feature was used for the examination of iron ore sinters where the ability to segment different types of hematite (primary versus secondary), different morphological sub-types of SFCA (platy and prismatic), and other common sinter phases such as magnetite, larnite, glass and remnant aluminosilicates is crucial for quantifying sinter petrology. Three different sinter samples were examined. Visual comparison showed very high correlation between manual and automated phase identification. The OIA results also gave high correlations with manual point counting, X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) analysis results. Sinter textural classification performed by Recognition4 showed a high potential for deep understanding of sinter properties and the changes of such properties under different sintering conditions.

Several sinter plants in China are still using significant proportions of local magnetite concentrate in the sinter blend based on supply proximity. However the overall trend is that concentrates are being replaced by more cost effective sinter fines. The fine size of concentrates results in additional challenges for sintering. In this study, granulation and packing experiments were conducted to investigate the influence of concentrate addition level on granule structure and green bed properties under a wide range of moisture and hydrated lime dosage levels. Provided sufficient water is added during granulation, the existence of micro-particles including concentrate and hydrated lime favours granule growth and increases the mass ratio of adhering layer to nuclei. However, at the same moisture and hydrated lime content, the introduction of more concentrate decreases the bed voidage remarkably since the thicker and weaker adhering layer deforms during dynamic packing. Compared to the 100% sinter fines base blend, introducing concentrate has a negative effect on bed permeability and therefore sinter productivity. For the 10% and 30% concentrate blends tested, increasing hydrated lime from 0 wt% to 4 wt% could improve the green bed permeability in JPU from 53.0 to 65.8 and 39.4 to 60.8 respectively. Based on the experimental results, a semi-empirical green bed voidage model was improved in two aspects. One is applying a one dimensional packing algorithm to get the ideal porosity of dry coarse particles utilising size distribution data rather than the simple log-normal deviation parameter. The other is to add a probability term considering the deformation of granules only happens to the adhering layer. Combined with the widely accepted population balance granulation model developed by Litster, the improved model can give more accurate predicted voidage values for modeling the sintering process and optimizing actual production from the properties of raw materials and moisture content.

An experimental and modelling program has been conducted by BHP Billiton to study the rate and mechanism of melting of hot briquetted iron (HBI) during steelmaking. Single briquettes melt quickly relative to scrap, due to vigorous stirring from CO evolution caused by internal reaction of C and residual iron oxides. The melting rate is determined by the bath carbon level, with briquette carbon only important in a low carbon bath (< 0.1 wt%). This information can be used to optimise the HBI continuous feeding rate for steelmaking, or the batch addition profile.

The conditions necessary for the optimal use of Hot Briquetted Iron (HBI) in scrap pre-heating systems have been determined by experiment on a laboratory and pilot scale. The development of a process model has allowed prediction of the pre-heat temperature that is achievable in shaft type systems, and the consequent electrical energy savings and productivity improvements possible for an electric arc furnace (EAF). The behaviour of HBI during pre-heating involves a complex series of chemical reactions, as shown in Figure 5. Single briquette experiments have demonstrated that gains in HBI metallisation can be realised during pre-heating. HBI was successfully heated to 1000°C in an atmosphere containing <5% oxygen in pilot scale studies (2 tonne batches). Metallisation gains of approximately 0.5 to 1% were measured for batches of FIOR/FINMET HBI, confirming the laboratory scale work. Models have been developed for an EAF and a generalised pre-heating system. The EAF model is a versatile heat and mass balance model for heating, melting and chemical reactions. Key operating parameters such as electrical energy, oxygen and flux consumption, off-gas temperature and composition canbe calculated. The off-gas conditions are used as an input to the pre-heater model, which calculates the gas and HBI temperature distributions and HBI metallisation along the pre-heat system. Model predictions for a shaft pre-heater suggest that a charge of scrap and HBI has a heat capture efficiency up to 25% higher than an all-scrap charge. Optimum conditions for pre-heating require the HBI to be in a layer near the bottom of the charge or uniformly dispersed with scrap throughout the charge. Continuous charging and discharge of the pre-heat shaft would improve the overall performance. The challenge that remains is to confirm the model predictions at full scale and to develop operating practices, such as the optimum layering strategy for a mixed charge.

Hot briquetting reduces the porosity and surfaces to volume ratio of direct reduced iron (DRI). The usual air oxidation of iron is slow at ambient temperatures and becomes prominent only at temperatures above 500 °C. Briquettes passivated in air have a much slower corrosion rate in air at room temperature than unpassivated hot briquetted iron (HBI). Briquettes exhibit surface cracking, suggesting oxidation is not limited to the surface of the briquettes, but occurs also within the interior.

At present we are witnessing large investments in the iron ore industry, fuelled by demand from Asia. At the same time, there is a changing landscape in pricing of iron ores, with the recent demise of the benchmark system and the evolution of market based index pricing systems. From a customer perspective, it is the behaviour of iron ores in downstream processing that gives them their value; their impact on the sintering or pelletising process and subsequently blast furnace ironmaking. It is therefore important to consider this value when developing projects, making mine planning/cut-off grade decisions, and in setting quality price differentials. This paper describes the use of the Marx value in use (VIU) model to quantify the downstream value of iron ores. The Marx model consists of heat and mass balance modules for sintering, pelletising and a rigorous two-stage heat and mass balance model of blast furnace ironmaking. Mass balance and cost models are applied for steelmaking, casting and rolling. The use of a heat and mass balance allows accurate comparison of the impact of raw material properties on blast furnace operation. The impact of minor elements, such as alumina, silica and phosphorus, and metallurgical properties on ironmaking is described, and examples given for the relative value of haematite, Marra Mamba, and channel iron deposit (CID) ores.

The experiments conducted and the techniques used to analyze the melting rate before discussing the implications on the briquette melting rate were described. The experimental results show that the cylinders of hot briquetted iron (HBI) melt much faster than steel cylinders, due to the higher C and FeO content of the briquettes. It was observed that the higher C content tended to increase the driving force for melting, could lead to grains of DRI detaching from the bulk of the briquette during melting, and led to greatly enhanced heat transfer due to formation of CO gas. The inverse heat transfer analysis had been completed and had shown that the bath carbon content was important in determining the overall melting time.