Kinetics and Mathematical Modeling of Hydrogen Reduction of NiO–WO₃ Precursors in Fluidized Bed Reactor

Abstract

In the present work, Fluidized bed reduction of NiO-WO3 precursors was investigated isothermally at temperatures 973-1 273 K. The reaction progress was monitored by analysis of H2O evolved during the reaction process using a gas chromatograph instrument. A theoretical model based on intrinsic chemical reaction rate constants and thermodynamic equilibria was developed to estimate the apparent reaction rate constant for the reduction reaction. In developing the model, the particles are considered to be in a completely mixed condition and gas flow is described as plug flow. The proposed model is also suitable for scale-up calculations.The interfacial chemical reaction model was found to fit the experimental results. The apparent activation energy values of the reduction process at different stages were calculated accordingly. The present investigation proved that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

Reduction kinetics of cobalt oxide powder by methane in a fluidized bed reactor

“…They reported that using fluidized bed reactor operating at a lower temperature and just above the minimum fluidization velocity has been found to be acceptable in obtaining nano scale-sized particles of Fe 2 Mo. Ahmed et al [28] studied the kinetics of NiO-WO 3 precursors with hydrogen in a fluidized bed reactor operating at just above the minimum fluidization velocity. They suggested that the process conditions would have impact on the particle size of the product.…”

Gas-Solid Reaction Route toward the Production of Intermetallics from Their Corresponding Oxide Mixtures

“…Minimum fluidization velocity (U * m f ) at room temperature was firstly determined experimentally and corresponding U m f values at higher temperatures were calculated according to Equation (1). More details of the experimental setup can be found elsewhere [3]. The fluidized-bed reduction experiments were conducted isothermally.…”

“…However, XRD results of reacted NiO-WO 3 precursors revealed the presence of WO 2 phase in NiO-WO 3 precursor as a main phase formed at 1048 K together with W, Ni, WN 2 and WN. This phase resulted from the stepwise reduction of WO 3 . With further rise in temperature, the WO 2 phase is subsequently reduced to W metal, which is then reacted with N 2 gas to produce tungsten nitrides (WN and WN 2 ).…”

“…The intrinsic reaction rate k f can be determined from dX TGA which refers to the extent of reduction in TGA. Further details about model derivation and assumption can be found elsewhere [3] …”

“…In view of these arguments, the radiation effect can be ruled out under the present experiment conditions. Effective thermal conductivity is calculated based on λ = αC p ρ where α is the thermal diffusivity cm 2 /s, C p is the heat capacity J/Kg and ρ is the density g/cm 3 . In this, the apparent densities of the samples were calculated based on their volume and mass.…”