Integrating a Top-Gas Recycling and CO2 Electrolysis Process for H2-Rich Gas Injection and Reduce CO2 Emissions from an Ironmaking Blast Furnace

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.