During the summer of 2015, a major plant site rebuild was carried out at the SSAB steelworks in Luleå, Sweden. The project included improvements to Blast Furnace No. 3 (Figures 1 and 2) comprising a new refractory reline, installation of a specially designed stave-cooling system, and replacement of the hot-blast main and mixing pot. Thanks to meticulous planning and local prefabrication, the entire operation was completed on schedule within the 75-day planned shutdown period. Blast furnace output could be significantly increased due to a reduction of unscheduled maintenance stops.
Blast Furnace No. 3 at the Luleå steelworks was blown in after a major upgrade in 2000. At that time, the working volume was increased from 1,440 m3 to 2,376 m3, and large-scale infrastructure improvements were also carried out. The furnace performed well but suffered from operational problems after the use of poor-quality coke led to high heat loads on the cooling elements early in the campaign. This condition, coupled with shortcomings in the original design, is considered the cause of damage around the third row of copper staves of the furnace-cooling system and the resulting cracks in the water-cooling pipes. These issues led to repeated unplanned blast furnace stoppages in order to repair the affected stave pipe connections. Furnace production was therefore limited to about 2.1 million tons of hot metal per year.
As other areas of the plant were also nearing the end of their operational life, SSAB Luleå embarked upon a major plant shutdown in 2015. It was decided to completely reline the blast furnace and to replace the existing cooling-stave system as well as the hot-blast main, for which Primetals Technologies was awarded a contract.
New copper stave fixing system
The originally installed copper staves were not supplied by Primetals Technologies. The fixing bolts were positioned much lower than what Primetals Technologies would have advised, and it is believed that this had contributed to the previous failures of the cooling pipes. The SSAB contract stipulated that the existing bolt holes be reused, which presented a problem for the conventional stave-fixing system. Furthermore, a solution had to be found to prevent the staves from bending in at the corners. The solution was the use of a new patented fixing element system that had been previously developed by Primetals Technologies and implemented at Blast Furnace A of voestalpine Stahl in Linz, Austria. The system features a considerably improved design (Figure 3).
Replacement of HOT-BLAST main and mixing pot
The existing blower also had to be upgraded, which meant that the hot-blast main and mixing pot needed to be replaced. As a result of extremely low winter temperatures in Luleå, the hot-blast main is fully enclosed within a building to reduce heat loss. A large amount of pre-shutdown work was therefore necessary, including a temporary modification of the building to provide access for the removal of the old main and installation of the new main within 75 days. Another challenge was that the stoves had to be kept near operating temperatures during the shutdown in order to allow a fast return to normal conditions after restart. It was decided that the best way to meet this schedule was to prefabricate and preinstall refractory material into large sections of the new hot-blast main (Figure 4).
The old hot-blast main was cut into three sections and lowered to the ground with special lifting equipment. The removal of the old refractory material from these sections was carried out remotely. Sections of the new hot-blast main were pre-bricked near the steelworks by a refractory subcontractor and brought to site. These sections were then lifted into place and welded before final refractory installation.
Access to the blast furnace site was possible starting from the beginning of June 2015. All relining and equipment- replacement work was completed by mid-August during the 75-day plant shutdown. Figure 5 shows a series of pictures taken during the removal of the old staves and replacement with the new staves.
Following the completion of the blast furnace reline and replacement of the hot-blast system, the refractory material was gradually dried out. The stove combustion air fans were used to generate low pressure within the main, mixer pot and blast furnace. This allowed a leak test to be performed in these areas, the results of which were checked by the third-party inspector.
Successful project completion
During the blast furnace shutdown period, all demolition and construction work proceeded according to plan and within the tight time schedule. The entire project was fast-tracked from the inquiry phase up to blast furnace blow-in, after which SSAB Luleå issued the Taking Over Certificate. Another notable achievement in connection with the on-time project completion was that no lost-time accidents occurred.
The blast furnace rebuild by SSAB Luleå and Primetals Technologies in 2015 resulted in increased plant availability and an annual steel output of up to 2.5 million tons at the Luleå steelworks. Since returning to operation, the plant has demonstrated excellent operating conditions as confirmed by SSAB’s issuing of the performance acceptance certificate for the furnace.