How voestalpine Donawitz de-risked four modernization phases with one simulation model

The challenge

voestalpine Stahl Donawitz (VASD) is on a long-term path from BOF steelmaking to EAF-based production — a fundamental transformation driven by decarbonization targets. But this kind of shift doesn’t happen overnight. It plays out across multiple investment phases, each involving new equipment that must integrate perfectly into an already highly optimized production flow.

The risk: every change — a new caster, a new furnace concept, a new converter type — can create bottlenecks in crane logistics, ladle circulation, or tundish handling that only become visible under real production load.

VASD and FESIOS built a comprehensive material flow simulation of the entire melt shop to stress-test each modernization phase before committing capital.

The simulation model

The model covers the full production chain from hot metal delivery to semi-product casting:

• Bay 1 — hot metal pit, 2 HM desulphurization stations, 2 LD converters, CC2 billet caster, 3 cranes (hot metal, scrap/hot metal, steel ladles)
• Bay 2 — 2 ladle furnaces, 2 RH degassers, slide gate stands, heaters
• Bay 3 — CC3 bloom caster
• Transport items — hot metal ladles (4-5 in cycle), steel ladles (8-9 in cycle), tundishes, auxiliary materials

Cranes operate on shared rails with collision avoidance, intelligent yielding, and realistic lifting profiles that account for obstacles and safety heights. The model was validated against historical production data — macro KPIs (production time, ladles in hot cycle, crane tasks) matched real-world data, and heat-level timing showed no sequence breaks.

Study 1: New CC4 caster integration

In 2020, VASD commissioned CC4, a new billet/bloom caster in a newly built Bay 4 — replacing the aging CC2. The caster itself was straightforward: similar casting times meant the production schedule stayed the same.

The real challenge was tundish logistics. Used tundishes from CC4 now had to travel from Bay 4 to Bay 3 for tilting, then all the way back to Bay 2 for relining and preheating. This long cross-bay transport significantly increased crane load.

The simulation confirmed that the crane system could handle the additional tundish movements without compromising production throughput. The heats-per-day target remained at 72.4 — identical to the CC2 baseline.

Study 2: Induction furnace for higher scrap rates

Before the current EAF roadmap was defined, VASD explored an intermediate concept: installing 4 induction furnaces (ITOs) at the former CC2 location to pre-melt scrap, reducing the hot metal ratio at the BOF.

The critical question: would charging ITO steel into the converters slow down the 30-minute tap-to-tap cycle?

The answer required simulating three cranes working in precise orchestration — scrap charging by the middle crane, ITO steel by the east crane, hot metal by the west crane — all in the correct sequence without interfering with each other. The simulation verified that the 33-minute tap-to-tap time was maintained even with the additional ITO charging step.

Study 3: EAF conversion scenarios

The most far-reaching study modelled the full replacement of both LD converters with EAFs — the eventual target of VASD’s green steel strategy. Two configurations were evaluated: double tapping and twin-shell EAF.

Through iterative simulation, the bottleneck in the new layout was identified and resolved. The target productivity — matching the original BOF baseline — was achievable in both EAF scenarios.

However, the simulation also flagged a cost factor that isn’t visible in throughput numbers alone: the EAF layout requires two additional ladles in hot cycle and results in higher liquid steel dwell times. This means increased ladle refractory wear and higher maintenance costs — a critical input for the investment decision.

The result

One simulation model, four studies, years of modernization decisions supported with quantified data. From the CC4 commissioning in 2020 to the long-term EAF conversion roadmap, each step was stress-tested under realistic production conditions before capital was committed.

This study was presented at the European Oxygen Steelmaking Conference (EOSC) 2022.