Dr Apsara Jayasekara

Molten slag, which is primarily generated in the blast furnace (BF) cohesive zone, trickles down through the coke packed bed in the form of films, rivulets, or droplets in the lower zone of the BF. During its downward flow, there are significant interactions occurring between slag and other phases such as gas, coke particles, hot metal, and fine powders. In terms of these interactions, slag flow behavior can greatly affect BF productivity and be associated with furnace irregularities such as channeling, hanging, and slipping. Hence, understanding the interactions between phases is useful to maximizing BF efficiency in terms of operating cost, reliability, and production capacity. In the current study, a Volume of Fluid (VOF) modeling technique was applied to track the movement of individual slag droplets in the packed bed at a mesoscopic level, considering various bed permeabilities, more wide-ranging slag properties, and different wettability between slag and packing particles. Results demonstrate the significant role of modeling at a mesoscopic level in understanding macroscopic slag flow behavior. Modeling work helps to visualize the trickling behavior of slag droplets in more realistic and complex conditions representing a BF, and clarify the mechanisms of the different flow patterns generated for variations in operating conditions. Transient flow characteristics such as localized slag accumulation and droplet morphology were identified and analyzed in relation to complex condition changes. The current modeling proved to be a valuable tool to provide a foundation for better understanding the slag flow behavior and its interactions with other phases in the BF lower zone.

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.

Slag flow behaviour is critically important in the lower zone of the ironmaking blast furnace, and is closely related to the selection of charged raw materials, coke bed permeability, process stability and hot metal quality. To better understand the effect of slag properties on flow behaviour in the coke bed, a numerical approach was applied to characterize the slag flow through funnel analogues. These analogues were used to represent molten slag flow through the inter-particle voids of a coke packed bed. A critical funnel neck size, through which no slag flowed was experimentally established and confirmed by numerical modelling. The influence of slag wettability on the occurrence of blockage was also determined via numerical modelling. An increase in either contact angle or surface tension can make the occurrence of blockage easier. For a constant neck size, the relationship between surface tension and contact angle is non-linear. The status of the remaining slag in the funnel corresponding to different slag wettabilities was differentiated in terms of the blockage in the upper part and hanging in the lower part of the funnel. Modelling was also undertaken of slag flow through the inter-particle void between spherical particles to evaluate empirical correlations for predicting the remaining slag in the packed bed. These results show that the numerical approach is very useful in providing some level of guidance to help understand and predict the slag flow behaviour in the blast furnace ironmaking process.

Molten slag is a critical material generated during blast furnace (BF) ironmaking. Slag flow behavior in the lower part of BF is closely related to the selection of charge materials, coke packed bed permeability, process stability, productivity, and hot metal quality. To better understand slag flow behavior, a numerical approach was applied to characterize the slag flow through a coke funnel analog and further, in a packed bed. The funnel analog was used to represent the flow of molten slag through the inter-particle voids of a coke packed bed. A critical funnel neck size, through which no slag flowed was experimentally established and confirmed by numerical modeling. The effect of wettability on slag flow shows the existence of an optimal contact angle for smooth slag flow in a funnel. The model was then applied to provide a deeper understanding of molten slag flow behavior in a packed bed, e.g., visualization of accumulation, coalescence, and breakup of slag at a particle scale. Specifically, the results show that the flow characteristics of discrete slag droplets in the packed bed require a particular quantitative approach for estimating the slag holdup. Packing structure, including pore size and particle shape, significantly affects the occurrence of slag blockage and droplet size, even when overall bed porosity is maintained constant. Slag flow along the vertical direction of the packed bed has a pseudo-steady percolation velocity. These results highlighted that this numerical approach is very helpful to understand the slag flow behavior at a particle scale, providing insight into the general features of slag flow as droplets or rivulets.