Hydrogen injection in blast furnaces: Effects of hydrogen injection temperature under various injection conditions

• Hydrogen injection is studied using a 3D CFD BF process model. • The study focuses on preheated hydrogen and its interaction with PCI. • Preheating hydrogen offers the advantage of mitigating coke combustion. • Hydrogen and PCI interaction is manageable to lower the fuel rate. • Pure hydrogen injection significantly cuts fuel use but needs high temperatures. The use of hydrogen in blast furnace (BF) ironmaking offers a significant potential for reducing carbon footprint. This paper comprehensively studies preheated hydrogen injection into a 400-m 3 BF via hearth tuyeres under different conditions using a BF process model. Two scenarios are first considered under fixed bosh gas volume, hot metal (HM) temperature, and flame temperature to ensure smooth operation and consistent HM quality: (1) injection of preheated hydrogen at varying hydrogen injection rates and a constant coal injection (PCI) rate and (2) interactions between hydrogen injection temperature (HIT) and PCI rate. The numerical results show that injecting hydrogen into a BF under a given HIT decreases the fuel rate, though excessive injection increases it. These results help identify the optimal hydrogen usage for minimizing fuel consumption. Increasing the HIT reduces the fuel rate and increases the optimal hydrogen injection. A detailed analysis of the BF’s inner states reveals that the advantage of lifting HIT is its ability to prevent an increase in coke combustion. Moreover, the interaction between preheated hydrogen and PCI is demonstrated to be controllable, allowing for a significant reduction in the fuel rate. In addition, the pure injection of preheated hydrogen is compared to the optimal case identified at varying HITs and PCI rates and to the conventional base case under the same bosh gas volume and HM temperature. The pure injection can significantly reduce fuel consumption— about three times that of the optimal case. However, it requires an exceptionally high hydrogen temperature and cannot completely omit coke consumption by direct reduction. To evaluate BF performance, the concept of total energy consumption in a BF is introduced, considering the contributions of different thermal and chemical energy resources in a unified manner. It demonstrates that increasing HIT or the hydrogen injection rate reduces total energy consumption. The findings from this study provide some valuable guides for designing and controlling BF with hydrogen injections under different conditions.