Energy-carbon synergistic optimization of a lime rotary kiln coupled with steel slag carbonation via combustion restructuring

Addressing the critical source-sink mismatch in steel industry decarbonization, this study proposes an active synergistic strategy coupling a lime rotary kiln with steel slag carbonation. A high-fidelity multi-scale simulation model was developed and validated, integrating computational fluid dynamics (CFD) with discrete element methods for the kiln and pore-scale kinetics for slag. By implementing an energy-efficient combustion restructuring strategy with 40% oxygen enrichment and a 50% flue gas recirculation ratio, the exhaust CO2 concentration is increased to 53%, which significantly exceeds the approximately 18% typically achieved under conventional air combustion, while NOx emissions are reduced to 72.8 mg/Nm3. This high-quality emission source enables downstream slag mineralization to achieve a 15.92% carbonation degree under a mildly pressurized scenario with a CO2 partial pressure of 1 bar, effectively overcoming thermodynamic barriers while bypassing the need for conventional energy-intensive high-pressure compression. Additionally, a dynamic scheduling framework was established to reconcile the flow discrepancy between continuous kiln emissions and intermittent slag discharge. The results demonstrate that this integrated coupled system achieves a net energy consumption reduction of 6.32 kgce/t-lime and a stable carbon capture rate of 73.23 kg/min. This work provides a scalable technical pathway for low-energy, deep process integration and energy-carbon synergistic optimization in industrial waste valorization.