Today the “small” blast furnace 5 at voestalpine Stahl GmbH will be blown-in again: what marks the start of another operating period is simultaneously the final stage in an intensive preparation period for the blast furnace workforce and sales team.
The countdown has started. At blast furnace 5 at voestalpine Stahl GmbH, pressure hoses feed natural gas and oxygen into the massive burning lance, and in every corner tools indicate that work has finished, while the display board counts down the time to blow-in. Time to restart!
Return to normal operations
Having a cold blast furnace is an unusual situation at the voestalpine Stahl GmbH site in Linz. But back in March, the COVID-19 pandemic forced the shutdown of “No.5” as demand for steel products fell. As a result, the workforce is all the more pleased that, after almost six months of downtime, the blast furnace can once again start operating. The moment at which the workforce takes a torch and lights the lance, which is then used in restarting the blast furnace, is almost a symbolic act.
Long starting period
In early October this voestalpine Stahl GmbH blast furnace will return to normal operation. Until then, because of the technology involved, weeks of warm-up are required.
"A blast furnace must be gradually brought up to its operating temperature so that it heats up evenly, including all the coke and pig iron residues which have solidified in the lower section of the furnace—the 'dead man' and the 'salamander'."
The blast furnace team judged the current condition in the shaft and lower section of the furnace by flying drones above and boring down into the core—although Stephen Lackner stresses that you can never be 100% certain about the position and the volume of residue inside the furnace. Furthermore, leaks in the furnace cooling could lead to unwanted cooling, with all its associated complications.
Clear plan of action
Work never stopped on, and in, blast furnace 5 at Linz during the downtime. At least 100 m³ of coke was cleared out after the shutdown, followed by improvements to the shaft using refractory concrete and other maintenance work. Naturally, there was also a plan ready for the subsequent blow-in. It was adapted in response to the results of the inspection and thanks to the experience of the blast furnace team. The key factor is the heat in the furnace:
- feeding in the blow-in furnace charge with coke and lumps of slag
- a natural gas/oxygen burner—the lance—burns a channel through the solidified residues in the furnace, from the tap hole to the starting burden
- the Cowper stoves blow in the “wind”—air heated to 1,200°C (hence “blow-in”)
- continuous tapping of the fluid slag which transfers its heat, especially to the lower part of the furnace
- reaching operating temperature
- feeding with layers of adjusted charge until the normal “operating mix” has been reached
Exceptional performance by the voestalpine sales team
It is also thanks to the good work of the sales personnel in the voestalpine Steel Division that has enabled blast furnace 5 to be blown-in again so quickly. They succeeded in generating sufficient orders to allow the blast furnace to be started up earlier than planned. Furthermore, the commissioning was also a form of neighborly assistance: the two sibling furnaces, 6 and A, are currently running at full capacity and need to be relieved.
Start into a new future
For that reason, over the next weeks at voestalpine Stahl GmbH attention will be focused on blowing-in blast furnace 5: a natural gas/oxygen burner was fed in yesterday, and today the hot wind from the familiar towers next to the blast furnace—the Cowper stoves—will fire up the blast furnace. From this point onwards there is no going back, explains Stephan Lackner, highlighting the significance of this event. He and the almost 300-strong blast furnace team wish each other, and all their voestalpine colleagues, an uneventful and accident-free blow-in, and a successful start into the new future.