Reduction kinetics of combusted iron powder using hydrogen

Despite extensive research on reduction of iron oxides in literature, there is no consensus on the most accurate reduction kinetics, especially for micron-sized iron oxide powders with high purity. Such data is particularly important for the application of metal fuels and chemical looping combustion, in which high purity iron powders function as dense energy carriers. Hence, in this work, hydrogen reduction of iron oxide fines, produced by iron combustion, were investigated using thermogravimetric analysis (TGA). The isothermal reduction experiments were conducted at the temperature range of 400–900 °C and at hydrogen partial pressures of 0.25–1.0 atm. Scanning electron microscopy (SEM) showed that the morphology of the reduction products depends on the reduction temperature but not on the hydrogen partial pressure. Reduction at higher temperatures leads to larger pore sizes. Based on an extended Hancock-Sharp “lnln”-method the appropriate gas-solid reaction models are determined, suggesting that the reduction can be described by a single-step phase boundary controlled reaction at temperatures below 600 °C, whereas a multistep mechanism is required for the description of reactions at higher temperatures.