High-Recycling Containing Magnesia- Carbon Bricks for Basic Oxygen Furnace Applications

Since 2020, RHI Magnesita has developed over 50 tempered MgO-C products with at least 20% circular raw material for steelmaking applications worldwide. These products are effectively used in both high- and low-wear areas of BOFs, EAFs, and steel refining ladles. Producing these tempered MgO-C products with high levels of circular raw material necessitates stringent quality control of incoming spent refractory materials and specialised knowledge of the required processing steps (Figure 1) [12,14].

Case 1: 210-tonne BOF

A 210-tonne BOF was equipped with Circular-MgO-C material in the top cone area, tapping pad, and upper part of the cylinder, as outlined in red in Figure 2. Table I compares the chemical and physical properties of the standard MgO-C material used in this particular area of the BOF with the Circular-MgO-C material that replaced it. Although the fused magnesia component in both materials was the same, the Circular-MgO-C material contained 20% circular raw material. The total carbon content of both materials was identical. While the standard material contained antioxidants (AOX) based on aluminium, no AOX was added to the Circular-MgO-C. The physical properties of the Circular-MgO-C material were slightly less optimal than those of the standard material; however, its carbon footprint was reduced by 0.716 tonne CO₂equivalent per tonne of product (t CO₂e/t_product). This corresponded to a total carbon footprint reduction of 60.6 t CO₂e per lining, and as described below, the wear rate was equivalent to the standard material.

The integrated steel plant where this trial was conducted features three 210-tonne BOFs, one Ruhrstahl-Heraeus (RH) degasser, and supports two continuous casting machines (CCMs) for billet production, along with two Endless Strip Production CCMs. The facility manufactures structural steel and hot-rolled mild steel. On average, each BOF completes 35 heats per day, with tapping temperatures typically ranging from 1590 °C to 1640 °C. Each BOF is equipped with eight single-hole plugs for bottom gas stirring. The average operational lifespan of a BOF is approximately 11500 heats. For maintenance of the tapping area and the bottom, approximately 800 tonnes of hot patching mix are used per campaign. Additionally, around 120–150 tonnes of gunning mix are applied per campaign, primarily in the trunnion area. Slag splashing is performed after every heat as part of the maintenance routine.

Figure 3 shows the laser scan profile of the BOF equipped with the Circular-MgO-C and, for comparison, the standard MgO-C material. The average wear rate for both the BOF lined with standard material and the BOF with Circular-MgO-C was calculated by dividing the difference between initial lining thickness and remaining lining thickness, as provided in these laser scans, by the number of heats. The area outlined in red indicates where the Circular-MgO-C was installed instead of the standard material. Since areas outside the blue outlined area mainly showed lining thicknesses exceeding the initial thickness, these areas were excluded from the wear rate determination, and only the values inside the blue lines were considered. The reason for these higher values was maintenance performed by gunning and slag splashing. The taphole area, indicated by the small purple square, was also excluded from the wear rate calculation. Based on these measurements, the average wear rate of the Circular-MgO-C lining was 0.008 mm/heat, while the wear rate of the standard lining was 0.009 mm/heat.

Case 2: 150-tonne BOF

In the second case study, a 150-tonne BOF was lined with Circular-MgO-C material in the cylinder area, as marked in red in Figure 4. Table II presents a comparison between the chemical and physical properties of the standard MgO-C material installed in the cylinder area of the BOF and the Circular-MgO-C material that replaced it. While both materials had the same fused magnesia component, the Circular-MgO-C material included 30% circular raw material.

The total carbon content was identical, and both materials contained aluminium-based AOX. The Circular-MgO-C material exhibited minor differences in physical properties compared with the standard material, while its carbon footprint was reduced by 0.704 t CO₂e/t_product, resulting in a total carbon footprint reduction of 31 t CO₂e per lining. As discussed later, the wear rate matched that of the standard material.

This integrated steel facility operates two 150-tonne BOFs and two RH degassers, serving two CCMs for slab production and two CCMs dedicated to round billet production. The plant primarily manufactures bearing steel. Each BOF averages 36 heats per day, with tapping temperatures typically ranging between 1600 °C and 1620 °C. Bottom gas stirring is performed using eight multi-hole plugs. The average service life of a BOF is approximately 10000 heats. About 300 tonnes of hot patching mix are consumed for maintenance of the tapping area per campaign. There is no gunning maintenance, but slag splashing is carried out after every heat.

Figure 5 provides the laser scan profiles of the BOF equipped with the Circular-MgO-C and that lined with the standard MgO-C material. The average wear rate for both BOFs calculated by dividing the difference between initial lining thickness and remaining lining thickness, provided in the laser scans, by the number of heats achieved. The area outlined in red shows where the Circular-MgO-C was installed instead of the standard material. Excluding areas within this field where the lining thicknesses exceeded the initial thickness due to maintenance measures, the average wear rate of the Circular-MgO-C lining was determined to be 0.007 mm/heat, compared with 0.008 mm/heat for the standard lining.

In this article, two case studies have been presented where standard MgO-C was replaced by Circular-MgO-C bricks in high-wear areas of BOF applications. In both cases, the Circular-MgO-C material significantly reduced the carbon footprint while achieving comparable wear rates to the standard material. Since wear rates are influenced by the steelmaking process, and especially maintenance practices, it can be assumed that the wear rates of Circular-MgO-C and standard MgO-C are comparable. Furthermore, it is important to note that the Circular-MgO-C materials presented in the article have replaced the corresponding standard MgO-C materials in regular operation.

The global success of these new types of high-performance Circular-MgO-C bricks is reflected in the development of shipments (Figure 6). From 2022 to the end of 2024, sales volumes have steadily increased and almost tripled. This trend is expected to further accelerate worldwide, driven by the growing need to reduce CO₂ emissions, avoid landfilling, and minimise additional costs for storage and logistics of spent refractory materials.