Process modelling for the production of hydrogen-based direct reduced iron in shaft furnaces using different ore grades

Abstract

This process modelling study explored the behaviour of hydrogen-based direct reduced iron (DRI) manufacturing in a shaft furnace. Various performance parameters such as metallisation ratio (MR), consumption of hydrogen per tonne of DRI, production of by-products, reactor energy demand and total energy demands for the process have been analysed with respect to temperature, ore grade (gangue content), and reactant conditions. The HSC Chemistry (H: enthalpy, S: entropy and C: heat capacity) SIM (simulation) module was employed for the modelling coupled with the Gibbs energy minimisation calculation. The shaft furnace was divided into three zones to model the three-step reduction of iron ore in a counterflow arrangement. Results show that temperature and hydrogen supply have a significant effect on the metallisation of DRI. Increasing temperature and hydrogen flow rate were predicted to increase the MR or reducibility. A full metallisation can be achieved with hydrogen supply of 130, 110, 100 and 90 kg/tDRI at 700, 800, 900 and 1000°C, respectively, using the best-grade ore (Fe 69 wt.%, gangue 5.2 wt.%). However, the hydrogen consumption in full metallisation was calculated to be 54 kg/tDRI (tonne of DRI). At full MR, the reactor energy consumption (supplementary electrical energy) was calculated to be 0.56 to 0.59 MWh/t Fefeed using the reactor temperature from 700 to 1000°C. Ore grade or gangue content has a significant impact on reactor energy demand. For example, at 900°C, the top-grade ore was calculated to consume 0.69 MWh/tDRI compared to 0.88 MWh/tDRI using the lowest grade ore. A certain percentage of CO (i.e. 15%) blended with hydrogen was predicted to be beneficial for metallisation, hydrogen consumption, and overall energy demand. However, increasing CO would increase CO2 emissions significantly.