Minimizing CO2 emissions with renewable energy: a comparative study of emerging technologies in the steel industry

Abstract

CO₂ emissions from the steel industry are amongst the most difficult to abate, since carbon is used as a stoichiometric reducing agent in most steel mills. This carbon ends up as a CO/CO₂ mixture in the steel mill gases, which are combusted to generate heat, electricity, and more CO₂. Strategies to capture and store (CCS), utilize (CCU) or avoid CO₂ in steel production exist, but are highly dependent on the availability of renewable electricity for the production of low-carbon H₂. Steel mill gas contains energy, and can thus be re-used more easily than combustion gas or process gas from the cement industry. In this study, we evaluate several strategies to reduce CO₂ emissions in the steel industry and rank them according to their renewable electricity requirement. We propose the following steps: (1) shut down the steel plant's power plant, since it produces electricity with a carbon intensity that is even higher than coal-based power plants; (2) replace steel mill gas with natural gas to generate heat within the steel mill; (3) recover the reducing gases, H₂ and CO, from the steel mill gases: e.g., using pressure swing adsorption to obtain a H₂-rich stream from COG, and sorption-enhanced water gas shift to obtain a H₂-rich stream and a pure CO₂ stream from BFG and BOFG; (4) the recovered H₂ converts some of the CO₂ to methanol, excess CO₂ is stored. The proposed CCUS scenario can retrofit existing infrastructure, uses proven technology and reduces CO₂ emissions by 70% for a marginal renewable electricity demand. Other energy-intensive alternatives have the potential to reduce CO₂ emissions by 85%, but require an order-of-magnitude more renewable electricity.