Gasification Reactivity and Degradation of Coke Lumps under Simulated Conventional and Oxygen-rich Blast Furnace Processes

The steelmaking industry is under increasing pressure to adopt technologies that reduce its environmental impact. Among the most promising innovations is the Top Gas Recycling Oxygen Blast Furnace (TGR-OBF), which enhances sustainability by reusing top gas and injecting oxygen-enriched blast into the furnace. This process has the potential to significantly cut fuel consumption and CO₂ emissions. This project investigated the critical role of coke quality, focusing on Coke Strength after Reaction (CSR), in maintaining furnace performance under oxygen-enriched conditions, providing actionable insights for optimising blast furnace operations.

The main objective of this research was to assess how oxygen enrichment influences coke reactivity, structural integrity, and mechanical properties, particularly within the shaft zone of the blast furnace, where indirect reduction reactions dominate. By studying cokes of varying CSR values, this project aims to offer steelmakers clear guidelines for selecting appropriate coke grades for oxygen-enriched blast furnace (OBF) operations, ultimately improving fuel efficiency and reducing emissions.

To replicate industrial conditions, steady-state heat and mass balance models were developed using METSIM software for four oxygen enrichment scenarios: Conventional BF, 35% OBF, 50% OBF, and Full Oxygen Blast Furnace (FOBF). The gas compositions from these models were then applied to high-temperature gasification experiments using coke samples made from Australian coals with different CSR values. Advanced techniques, including thermogravimetric analysis (TGA) and micro-CT imaging, were employed to evaluate the cokes' reactivity, microstructural evolution, and performance under these gas conditions.

Key findings showed that higher oxygen enrichment significantly increases coke reactivity, especially under FOBF conditions. High CSR cokes maintained structural integrity and mechanical strength, making them more suitable for oxygen-enriched blast furnaces. In contrast, low CSR cokes exhibited increased porosity, structural degradation, and substantial loss of compressive strength. These results underscore the need for high CSR cokes to ensure stable operations and productivity in oxygen-enriched environments. As blast furnace conditions shift toward FOBF, the infurnace gas atmosphere becomes increasingly similar to the standard Coke Reactivity Intex (CRI) and CSR test environments, which use 100% CO₂. This means that CRI/CSR test results-typically less representative under conventional blast furnace conditions-become more directly applicable under FOBF. As such, CSR becomes a more reliable indicator of in-situ coke performance, reinforcing the value of high CSR cokes in these advanced, low-emission furnace designs.

This study highlights the importance of high-strength cokes for maintaining mechanical stability and operational efficiency in oxygen-enriched blast furnaces. Additionally, it suggests the potential for more flexible and sustainable furnace designs, supporting the steel industry's 2050 decarbonisation goals without compromising economic viability.