XXL Electric Arc Furnace Taphole Solution

RHI Magnesita has been supplying tapholes to customers globally for decades. Eccentric bottom tapping (EBT) technology, developed in the 1980s and established in the 1990s [1], is the successor of classic spout tapping in EAFs. Since then, EBT technology has evolved from a simple cylindrical channel shape to conical, and ultimately to CFD-optimised EAF taphole channel designs (Figure 1).

Multiple advantages are associated with CFD-optimisation of the taphole channel [2,3], including:

• Reduced tapping time through higher flow rates and increased throughput (Figure 2).
• Extended taphole lifetime due to non-turbulent flow of the tapped steel melt inside the channel, leading to a reduction of mechanical wear (Figure 3).
• Reduced risk of reoxidation and H2/N2 pickup due to a bundled tapping stream, resulting from less turbulences in the channel (Figures 4 and 5).
• Less slag carry-over due to reduced vortex formation
  (Figure 6).

The following is an example comparing a cylindrical and a CFD-optimised tapping channel design for an 80-tonne EBT furnace. The overall furnace refractory lifetime was around 300 heats, and the key requirement for the taphole channel was to minimise downtime for taphole repair or replacement. The typical taphole lifetime was approximately 110 heats. Figure 7 shows a direct comparison between the cylindrical and CFD-optimised taphole designs for this steel producer.

For the cylindrical design, the inner diameter was 160 mm, whereas the CFD-optimised version had an inlet diameter of 190 mm and an outlet diameter of 150 mm. As refractory wear progresses, the taphole diameter increases, allowing a higher steel flow rate and thereby reducing the required tapping time. If the tapping time becomes too short, this indicates critically high wear of the EBT, which must then be repaired or replaced. Figure 8 provides a direct comparison of the CFD-optimised and cylindrical tapping channel designs with respect to tapping time over successive heats.

The CFD-optimised taphole showed lower wear (slope of the blue line in Figure 8), resulting in an increased taphole channel lifetime from 110 heats to 140 heats before a repair was required. In addition to this 27% lifetime increase with the CFD-optimised geometry, the initial tapping time significantly decreased from approximately 300 seconds to 200 seconds.

The next example provides the same type of comparison at another steel producer with a 125-tonne EBT furnace. In this scenario, the cylindrical channel had an inner diameter of 180 mm, while the CFD-optimised channel had an inlet diameter of 190 mm and an outlet diameter is of 160 mm. As shown in Figure 9, the CFD-optimised taphole lifetime increased from 134 heats to 190 heats, a 42% improvement, while the initial tapping time decreased from about 250 seconds to approximately 210 seconds. Once again, the wear rate of the CFD-optimised taphole design was clearly lower.

A direct comparison between a standard cylindrical taphole design and a CFD-optimised channel used in a 45-tonne EAF is shown in the following case study. The steel plant was equipped with one ladle furnace and a continuous casting machine. The EAF had an average lifetime of approximately 1400 heats, with the taphole lifetime averaging 215 heats without repair. The target was to achieve about 280 heats by the end of one week, which could only be reached with additional piping repairs. The cylindrical channel design had an initial inner diameter of 130 mm, while the CFD-optimised design had an initial inner diameter of 160 mm at the inlet and 120 mm at the outlet. From each channel design, 6 sets were tested in the same period. Figure 10 shows a comparison of the achieved lifetimes.

The 160* and 174* heats achieved with the CFD-optimised channel design in Trials 5 and 6 were the result of premature shutdowns due to logistical reasons. Excluding these results, leads to a more representative lifetime average of 255 heats for the CFD-optimised channel compared to 222 heats for the cylindrical channel design—an increase of 15%.

Figure 11 compares the tapping time of the two channel designs, for the two campaigns with highest lifetime during the trial. These results show that the initial tapping time of both channels was similar, at about 2 minutes. However, while the tapping time of the cylindrical channel dropped quickly, the tapping time of the CFD-optimised channel declined at a much slower rate. At this steel plant, the minimum allowed tapping time was 1 minute. Since the cylindrical channel reached this limit too quickly and did not stabilise like the CFD-optimised channel, a repair was required at about 209 heats. Another repair followed at 245 heats for the cylindrical channel, while the CFD-optimised channel only required a single repair at 256 heats. Clearly, the CFD-optimised channel showed a lower wear rate, resulting in less maintenance and more production time gained.

The aforementioned examples consistently demonstrate the advantages of the CFD-optimised taphole channel design. Therefore, CFD-optimisation was also applied in the development of XXL taphole solutions. The following example illustrates such a design for a 350-tonne EAF (Figure 12). The steel plant operates four ladle furnaces, one vacuum oxygen decarburisation unit, and two continuous casting machines, producing hot-rolled steel. As shown in Figure 12, this XXL EBT solution follows the CFD-optimised design to achieve optimal performance. For this type of XXL taphole installation, a wider outer diameter of the channel sleeves was required—in this case 450 mm, compared to the standard 350 mm.