Heat Transfer Conditions in Hydrogen-Fired Rotary Kilns for Iron Ore Processing

This work analyzes the heat transfer conditions in a rotary kiln used for the heat treatment of iron ore pellets in the grate-kiln process. The analysis concerns conditions relevant to fuel switching from coal to hydrogen gas. A modeling assessment of the radiative heat transfer in the kiln is conducted including the pellet bed and inner kiln wall temperature conditions. The results show that the heat transfer rate to the iron ore pellets under conditions of a pure hydrogen flame is comparable to the conditions relevant to coal firing. However, it is higher at the kiln wall surfaces near the burner region and lower in the remaining parts of the kiln. Increasing the particle concentration in the hydrogen flame represents a practical implication of co-firing coal with hydrogen. By adding particles, the emittance of radiation from the flame is significantly influenced, leading to further increased kiln surface temperatures closer to the burner position. Increased flame length also showed enhanced heat transfer rates to the kiln wall, although further away from the burner region.