In a hydrogen direct-reduction (H2-DRI) shaft furnace, solid iron-ore pellets (mostly Fe₂O₃, hematite) are fed in at the top and sink slowly downward while hot reducing gas — mostly H₂, made by electrolysing water with renewable electricity — flows counter-current, upward through the bed:
Fe₂O₃ + 3 H₂ → 2 Fe + 3 H₂O (ΔH ≈ +99 kJ/mol, endothermic)
This replaces the classic blast-furnace route, which reduces ore with carbon monoxide from coke:
Fe₂O₃ + 3 CO → 2 Fe + 3 CO₂ (releases CO₂ instead of H₂O)
Each pellet's conversion is modelled with a shrinking-core-style first-order rate law. The local rate constant follows an Arrhenius form in furnace temperature T, and scales with the partial pressure (purity) of H₂ in the gas:
dx/dt = k(T) · f(H₂%) · (1 − x)
k(T) = A · exp(−Ea / (R·T))
- Temperature — raises k(T) exponentially; industrial shaft furnaces run roughly 700–950 °C to stay below softening/clustering limits of the pellets.
- H₂ purity — a leaner reducing gas (more inert/residual gas mixed in) lowers the effective driving force and slows conversion.
- Feed rate — a faster feed shortens the time each pellet spends in the shaft, so if it outruns the kinetics the exiting pellets are less metallized.
Because the reducing agent is H₂ instead of carbon, the exhaust is water vapour rather than CO₂ — when the hydrogen itself is made with low-carbon electricity, this route can cut ironmaking's direct CO₂ emissions by roughly 90% versus the coke blast-furnace + basic-oxygen-furnace path, which is why it is one of the most closely watched decarbonization technologies in heavy industry.
Note on this build: the 3D sibling of this simulator uses a pre-exponential factor (A = 4.2×10⁴ s⁻¹) that, numerically checked against its own residence time, drives every slider combination to ≈100% metallization — the sliders visibly changed particle-fall speed but the exit-metallization readout barely moved. This 2D engine rescales A to ≈16.9 s⁻¹ (keeping the same Eₐ = 55 kJ/mol and the same first-order form) so metallization genuinely spans roughly 35–100% across the full temperature/purity/feed range — verified with a standalone numerical check before shipping.