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