Blast furnace gas utilization with calcium-assisted steel mill off-gas hydrogen production (CASOH) technology: technical evaluation

Abstract

In pursuit of decarbonizing the iron and steel industry through the utilization of blast furnace gas (BFG), this study investigates the technical feasibility of a Ca–Cu looping technology known as calcium-assisted steel mill off-gas hydrogen production (CASOH). The process is modeled and analyzed using Aspen Plus software. The key technical performances of two versions of CASOH were evaluated and compared with more traditional solvent-based technology for the precombustion decarbonization of BFG using methyl diethanolamine (MDEA). The first case (base case, CASOH-B) uses part of the BFG to regenerate the sorbent; therefore, it concentrates CO2 up to 54%. In the second case (enhanced, CASOH-E), low-pressure steam is used for the calcination reaction. In the case of CASOH-B, the integration with a CO2 purification unit outperforms the other configurations regarding the CO2 capture efficiency, with values of up to 97% compared to 91% for CASOH-E and 83% for MDEA. However, CASOH-E demonstrated a significantly higher thermal output (224.5 MWLHV vs 77.6 MWLHV for CASOH-B), resulting in better cold gas efficiency and lower specific CO2 emissions (76% and 29.8 kgCO2/GJLHV for CASOH-E compared to 26.3% and 105.7 kgCO2/GJLHV for CASOH-B). Various scenarios were analyzed to meet the heat and power requirements of the process. When relying on an external energy source such as natural gas, biogas, or photovoltaic panels, the solvent-based case outperforms the CASOH configurations with a specific energy consumption per CO2 avoided (SPECCA) of 0.5–0.7 MJLHV/kgCO2, compared to 1.1–3.3 MJLHV/kgCO2 for CASOH configurations. However, if the hydrogen-rich stream produced in CASOH-E is used to meet energy demands, then CASOH-E becomes the most favorable option. These findings emphasize the importance of operational parameters in optimizing BFG decarbonization strategies by balancing thermal output, efficiency, and emissions capture.