Direct reduction of iron ore pellets in bulk using synthetic cracked ammonia: effect on reduction degree and reaction kinetics

The use of cracked ammonia is being proposed as a reducing gas for the production of Direct Reduced Iron (DRI) pellets. The viability of this approach has been investigated using a synthetic hydrogen–nitrogen mixture in order to simulate the use of decomposed ammonia. Experiments have been conducted using a modification of the already-existing direct reduction vessel at the Institute of Iron and Steel Technology (IEST) at TU Bergakademie Freiberg. The reaction rates have been studied at temperatures between 600 °C and 1000 °C using commercial blast furnace-grade iron ore pellets. Experiments show a stronger temperature dependency and an overall slower reaction rate as well as a lower final degree of reduction in comparison to using pure hydrogen gas as the reducing agent. Different reaction rate models have been discussed and activation energy of the reaction calculated accordingly, showing that the activation energy in this proposed fixed-bed setup of iron ore pellets is lower than other experimental setups, suggesting an influence of gas flow regimes. Additionally, results suggest that the rate-limiting step in the initial stage of the process is a gas diffusion mechanism.