Biochar as a prospective renewable energy candidate could be incorporated into the iron and steel production system to replace part of fossil fuels and reduce high-intensity greenhouse gas emissions. However, great uncertainties still exist on biochar’s emission reduction capacity and economic feasibility, depending on different biochar precursors, substitution scenarios, energy consumption of biochar production and financial cost. This study aimed to explore the optimized substitution strategies concerning the above issues. A systematic carbon accounting was performed by material flow analysis method (MFA). Two biochar incorporated iron and steel production routes, integrated production route (BF-BOF) and short production route (EAF), which took the proportion of 71.5% and 28.2% in worldwide production, were considered. CO2 Supply Curve (CSC) was conducted to carry out a quantitative economic viability analysis of biochar substitution under carbon emission trading schemes (ETS). Results showed that compared with straw-based biochar, wood-based biochar showed stronger carbon reduction capacity of 1.47 t CO2e (CO2-equivalent) /t crude steel, and the reduction potential reached 66.94% mostly. Among all the steel production processes, Blast furnace in BF-BOF route had the largest emission contribution proportion (72.06%), achieving the best GWP100 reduction potential of 73.66%. The incorporation of wood-based biochar in sintering (-0.037 yuan/t CO2e) was selected as the scenario with both reduction potential and economic viability. If the scenario was fully implemented in China, it could reduce 2.01 million tons of CO2e in 2021. This study would play a vital role in guiding iron and steel industry for biochar substituted fuels.
