Characteristics of NH3–H2 Reducing Pellets

The reduction of hematite with ammonia is a potentially environmentally friendly method of ironmaking. Previous studies on ammonia reduction of pellets typically involved samples weighing only 2.8 g and lacked detailed activation energy analysis for the ammonia-hydrogen co-reduction of pellets. Therefore, to further investigate the reduction thermodynamics and kinetics of NH3–H2 reduction of pellets, this study uses 50 g pellets for reduction experiments. By increasing the pellet mass, the study expands the scope of kinetic research on ammonia reduction of pellets. The results indicate that nitrogen gas produced from ammonia decomposition reduces the equilibrium components of the reducing gas. In the temperature range of 700–850 °C, the formation of iron nitride exhibits a narrow range during ammonia reduction of hematite. In the reduction of 50 g of pellets, the reduction rate using 100% NH3 is lower than that using a 50% NH3 and 50% H2 mixed gas, which is, in turn, slower than using 100% H2. As temperature increases, the reduction effect of 50% NH3 and 50% H2 approaches that of 100% H2. Among common gas-solid reaction mathematical models, the Phase-boundary-controlled model with the Contracting Cylinder Model is selected as the most plausible mechanistic function. For the reduction of 50 g of pellets, the activation energies for reactions using 100% NH3, 50% NH3 and 50% H2, and 100% H2 are 65.42, 54.37, and 29.17 kJ/mol, respectively. The decomposition of NH3 has a negative effect on the reduction of Fe2O3. XRD analysis and electron microscopy element line scanning show that Fe4N is formed during the reduction of Fe2O3 with 100% NH3. The use of a 50% NH3 and 50% H2 mixture significantly reduces the formation of Fe4N during the reduction of the pellets.