Integrating a Top-Gas Recycling and CO₂ Electrolysis Process for H₂-Rich Gas Injection and Reduce CO₂ Emissions from...

Introducing CO₂ electrochemical conversion technology to the iron-making blast furnace not only reduces CO₂ emissions, but also produces H₂ as a byproduct that can be used as an auxiliary reductant to further decrease carbon consumption and emissions. With adequate H₂ supply to the blast furnace, the injection of H₂ is limited because of the disadvantageous thermodynamic characteristics of the H₂ reduction reaction in the blast furnace. This paper presents thermodynamic analysis of H₂ behaviour at different stages with the thermal requirement consideration of an iron-making blast furnace. The effect of injecting CO₂ lean top gas and CO₂ conversion products H₂-CO gas through the raceway and/or shaft tuyeres are investigated under different operating conditions. H₂ utilisation efficiency and corresponding injection volume are studied by considering different reduction stages. The relationship between H₂ injection and coke rate is established. Injecting 7.9-10.9 m³/tHM of H₂ saved 1 kg/tHM coke rate, depending on injection position. Compared with the traditional blast furnace, injecting 80 m³/tHM of H₂ with a medium oxygen enrichment rate (9%) and integrating CO₂ capture and conversion reduces CO₂ emissions from 534 to 278 m³/tHM. However, increasing the hydrogen injection amount causes this iron-making process to consume more energy than a traditional blast furnace does.