A three-dimensional computational fluid dynamics (CFD) model for the HIsarna off-gas system is set up and validated by real plant data. In the model detailed reaction mechanism and kinetic data for post-combustion of CO-H2 mixture and carbon particles are incorporated. The results are presented and discussed in another study (Part 1) by the same authors. In the present paper, the focus will be on geometry modification of the off-gas system and the effects on the operating parameters. The effect of this modification on heat loss, temperature profile, carbon conversion and gaseous phase composition across the off-gas system is investigated. It is shown that the modified geometry leads to a higher heat loss through the reflux chamber walls which can change the temperature profile and consequently species composition. The modified geometry also offers possibility of higher CO-H2 mixture and carbon particles conversion rate and reduce unwanted emission from the reflux chamber.

The HIsarna process is a new and breakthrough smelting reduction process for hot metal (liquid iron) production from iron ores and coal directly fed into the reactor. The flue gas from the main reactor enters the off-gas system containing small amounts of H₂, CO and carbon particles which need to be removed before further treatment by post combustion oxygen injection. A three-dimensional Computational Fluid Dynamics (CFD) simulation of the HIsarna off-gas system is performed and validated using a detailed reaction mechanism and kinetic data for post-combustion of a CO–H₂ mixture and carbon particles. Using the validated model, a series of simulations were performed to investigate the effect of water quenching and post combustion oxygen injection. It was found that water quenching can significantly reduce the off-gas temperature. It is also possible to reduce oxygen injection during operations where inlet CO content of the off-gas system is low.