Predicted effects of rectangular geometry on a hydrogen-based direct reduced iron shaft furnace

The use of pure hydrogen (H 2 ) as the reducing agent, instead of carbon monoxide (CO) containing syngas, in direct reduced iron (DRI) processes is limited by heat management in DRI shaft furnaces (SFs) due to hydrogen’s low volumetric density and the strongly endothermic reduction reactions. In conventional SFs with radial injections, the large lateral distance between the injection wall and the furnace centre results in a progressive imbalance between convective H 2 supply and consumption by endothermic reactions as the injected gas travels inward, leading to both lower H 2 concentrations and temperatures toward the furnace centre, which consequently causes incomplete reduction of the iron ore and compromised DRI quality. To overcome these limitations, we numerically explored a rectangular furnace (RF) geometry, which reduces the maximum lateral distance between the sidewalls where the hot reducing gas is injected and the furnace centre, thereby shortening the path over which H 2 is depleted and inlet sensible enthalpy is consumed. A steady-state multiphase Eulerian computational fluid dynamics (CFD) model of the reaction zone, integrated with the unreacted shrinking core model (USCM) and validated against published MIDREX SF data under syngas operation, was developed to simulate gas-solid reactive flows in (a) a conventional cylindrical SF and (b) rectangular furnaces with cross-sections of different length-to-width ratios. Our simulations predict that the RF geometry could potentially enhance the minimum metallization rate ( MR min ) of the DRI from 54.4% in the cylindrical SF to 98.2% in the RF and slightly improve the gas utilization rate ( UR ) from 24.3% to 25.5% (example results for 1.5 times the baseline hot gas flow rate of around 74 Nm 3 /s). These numerical findings suggest there are opportunities for innovative shaft furnace geometry designs to optimise H 2 -based DRI process, which is until now an under explored design factor. We acknowledge there are practical challenges to fabricate and operate rectangular shaft furnaces that must be addressed before experimental validation and pilot scale testing to confirm the RF performances predicted by our simulations.