Technical assessment for enhancing environmental sustainability of metallurgical exhaust gases to methanol process via electrochemical energy conversion

Abstract

The iron and steel industry is considered as one of the hard-to-abate heavy sectors due to the massive demand for metallurgical coke in the energy-intensive blast furnace (BF) ironmaking process. In this work, an electrochemical conversion of two major metallurgical exhaust gases, namely, blast furnace (BFG) and coke oven gas (COG) into renewable methanol (CH₃OH) is proposed for deeply decarbonizing steel production. An innovative low-carbon BF ironmaking process, which combines solid oxide cells (i.e., renewable-powered co-electrolysis and COG-fed solid oxide fuel cells) and oxyfuel combustion for CO₂ capture, is thermodynamically modeled to evaluate various performance metrics in terms of energy conversion efficiency, product yield, and carbon intensity of renewable methanol. To enhance the process conversion efficiency, four different recycling configurations are designed and compared for efficient tail gas utilization: Scenarios 1 and 4 (co-electrolysis and methanol synthesis via short-loop recirculation) and Scenarios 2 and 3 (co-electrolysis and methanol synthesis via long-loop recirculation). The results indicate that efficient tail gas utilization via long-loop recirculation into the co-electrolysis unit could generate a much higher methanol yield than the short-loop design. Up to 73 % carbon conversion efficiency can be achieved, while 30 % energy conversion efficiency can be attained using long-loop design at a recirculation ratio (RR) of 0.8. Nevertheless, a higher RR operation results in increased energy demand associated with the methanol synthesis process, which in turn leads to higher indirect carbon emissions. Overall, the carbon intensity of methanol ranges from approximately 1.05–1.48kg-CO₂/kg-CH₃OH across the four process configurations under the selected RRs. The long-loop design is likely to offer a reduction in CO₂ emissions of up to 57 % compared to the traditional blast furnace ironmaking process. In particular, a maximum energy conversion efficiency of 38 % can be achieved through heat integration, while net negative CO₂ emissions are achievable based on the evaluated system boundary. The developed process not only has great potential to close the carbon loop between steel makers and chemical producers but also efficiently stores energy in the form of renewable methanol.