Smelting Characteristics of Raceway Under Ammonia and Pulverized-Coal Co-Injection Condition in a Blast Furnace

Ammonia co-injection with pulverized coal in blast furnace (BF) ironmaking offers a pathway to reduce carbon emissions by utilizing NH₃ as a hydrogen carrier. This study combines thermodynamic analysis, HMB modeling, and 3D computational fluid dynamics (CFD) simulations to evaluate NH₃’s impact on raceway smelting characteristics. Thermodynamic calculations reveal NH₃ directly reduces Fe₂O₃ to Fe₃O₄ below 873 K with higher feasibility than H₂, while decomposing into H₂ and N₂ above this threshold. HMB modeling indicates 10% NH₃ injection increases bosh gas volume by >30%, enhancing permeability, but causes minor fluctuations (<1%) in gas utilization. CFD simulations show NH₃ decomposition lowers raceway temperatures due to endothermic reactions, shifting iron formation toward the bosh region and slightly reducing smelting intensity. Although the effective heat utilization coefficient rises marginally (93.4% to 93.9%), incomplete NH₃ dissociation in the raceway limits hydrogen availability for direct reduction. Results highlight a trade-off: NH₃ substitution reduces coke dependency and CO₂ emissions but requires thermal compensation to mitigate raceway cooling and delayed iron formation. Optimizing injection ratios and coordinating with auxiliary heat sources are critical for practical implementation. Under the blast furnace operating conditions investigated in this study, an NH₃ injection rate of 5-7.5% has been identified as relatively balanced. This work provides foundational insights into ammonia’s dual role as reductant and hydrogen precursor, advancing strategies for low-carbon BF ironmaking.