Reducing CO₂ emissions, energy consumption, and decarbonization costs in manganese production by integrating fuel-assisted solid oxide electrolysis cells in two-stage oxide reduction

Manganese is one of the most consumed metals due to its use in iron and steel making, which generates between 7%–9% of all CO₂ emissions produced globally per annum. For the first time, this work explores the potential of a novel process concept to reduce CO₂ emissions, energy consumption, and decarbonization costs in manganese production, which involves integrating fuel-assisted solid oxide electrolysis cells (FASOECs) in a two-stage scheme for the reduction of raw manganese ores. In this scheme, higher oxides that are present in raw manganese ores (MnO2, Mn2O3, Mn3O4) are pre-reduced using CO, yielding manganese monoxide (MnO) that is further reduced to Mn in a submerged arc furnace (SAF) using coke and electricity. In the proposed FASOEC integration concept, off-gas from the manganese ores after pre-reduction (a mixture of H₂, CO, and CO₂) is supplied to the FASOECs’ anode as fuel, in order to produce high-purity H₂ in the cathode that is directed to the first stage of manganese reduction. H₂ has enhanced reaction kinetics for reducing higher manganese oxides in comparison to CO; therefore, integrating FASOECs can improve manganese oxide conversion rates during pre-reduction, resulting in lower consumption rates of coke and energy in the SAF. The off-gas supplied to the FASOECs’ anode also lowers the amount of energy required for H₂ production in the cathode (can also generate electricity, simultaneously) and produces anode exhaust gas containing only CO₂ and steam. Since steam can be easily condensed from this stream, the integration of FASOECs also enables efficient decarbonization of the manganese production process, thus eliminating the need for a designated CO₂ capture system. The techno-economic analysis performed herein demonstrates that directing the full supply of off-gas produced by the SAF to the FASOECs’ anode at 800 °C reduces the overall energy consumption of manganese production by up to 18% in comparison to conventional processes. This results in decarbonization cost reductions by as much as 3%–15% and a corresponding decarbonization price range of $4-32 per ton of manganese product for plant capacities of 50 and 200 kt, respectively. © 2024 The Authors

Author keywords
Decarbonization; Fuel-assisted solid oxide electrolysis; Manganese production; Off-gas utilization; Techno-economic analysis