A blast furnace is a countercurrent gas-solid reactor: ore, coke and flux descend from the throat while hot blast air, injected at the tuyeres, burns coke in the raceway (C + O₂ → CO₂, then the Boudouard reaction C + CO₂ → 2CO) and rises as CO-rich gas. That gas indirectly reduces the descending iron oxide as it climbs: Fe₂O₃ + 3CO → 2Fe + 3CO₂. This sim tracks the two numbers real furnace operators watch:
RAFT ≈ 1900 + 0.55·(Tblast−1000) − 0.4·(coke−380) + 0.3·(blast−100)
η(CO) = clamp(0.42 + 0.10·(Tblast−1000)/300 − 0.12·(blast−100)/60, 0.28, 0.58)
reduction(u) = min(1, 1.15 · η(CO) · u) [u = fraction of descent completed]
Higher blast temperature speeds up reduction kinetics and raises CO utilization (more efficient — less coke wasted as unburned CO2 exhaust). A faster blast rate shortens gas residence time in the shaft, which lowers utilization even as it raises throughput. A higher coke rate raises the raceway flame temperature (RAFT) but is less fuel-efficient per tonne of hot metal. Ore chunks are colored from rust-red (Fe₂O₃) to silver (metallic Fe) as their tracked reduction(u) climbs; rising gas bubbles fade from blue (CO-rich) to grey (spent CO₂) the higher they travel.
- CO utilization — fraction of CO gas that actually reduces ore before exiting the throat as top gas.
- Fe reduction — average reduction degree of ore currently descending through the shaft.
- Liquid pool — molten hot metal + slag accumulated in the hearth since the last tap.