CO ₂ emission reduction and exergy analysis of smart steelmaking system adaptive for flexible operating conditions

The iron and steel industry accounts for approximately 45% of the CO ₂ emissions in the Japanese industrial sector, and therefore is investing in improvements to reduce the CO ₂ emissions. Current projections are for the stock of scrap iron and steel products to increase in the future. Being already in the reduced state, such scrap can be regenerated to steel with lower CO ₂ emissions than iron ore. The “Packed bed type Partial Smelting Reduction process” (PSR), which concurrently smelts scrap and reduces iron ore, is a promising method to utilize scrap iron. This work evaluates the feasibility of combining PSR with top gas recycling, a process commonly called the ‘SMART steelmaking system’. In the SMART system, CO ₂ derived from the PSR gas is reduced into CO or CH ₄ and recycled to the furnace as a reducing agent. The integrated whole process including shaft furnace, CO ₂ electrolysis, pressure swing adsorption, and other conventional auxiliary systems was modelled in Aspen Plus, and CO ₂ emissions reduction and exergy analysis of the system adaptive for flexible operating conditions was performed. Increasing the scrap ratio by 5% consistently lead to a 4% reduction in CO ₂ emissions. Similarly, increasing the CO input rate by 100 kg/THM consistently resulted in a reduction of CO ₂ emissions of approximately 3%. The maximum CO ₂ emissions reduction of 22% was achieved at the condition of the operably highest scrap ratio and CO input rate.