W tym miesiącu polecamy artykuł au torstwa Eweliny Ksepko, Piotra Babińskiego i Lori Nalbandian który ukazał się w Applied Energy (Volume 190, 15 March 2017, Pages 1258?1274) pod tytułem:

The redox reaction kinetics of Sinai ore for chemical looping combustion applications

Abstract:



The objective of this work was to study the use of Sinai ore, a Fe?Mn-based ore from Egypt, as a low-cost oxygen carrier (OC) in Chemical Looping Combustion (CLC). The Sinai ore was selected because it possesses relatively high amounts of iron and manganese oxides. Furthermore, those oxides have low cost, very favorable environmental and thermodynamic properties for the CLC process. The performance of the Sinai ore as an OC in CLC was compared to that of ilmenite (Norway Tellnes mine), the most extensively studied naturally occurring Fe-based mineral.

The kinetics of the reduction and oxidation reactions with the two minerals were studied using a thermogravimetric analyzer (TGA). Experiments were conducted under isothermal conditions, with multiple redox cycles, at temperatures between 750 and 950 °C. For the reduction and oxidation reactions, different concentrations of CH4 (10?25 vol.%) and O2 (5?20 vol.%) were applied, respectively. The kinetic parameters, such as the activation energy (Ea), pre-exponential fac tor (A0), and reaction order (n), were determined for the redox reactions. Furthermore, models of the redox reactions were selected by means of a model-fitting method. For the Sinai ore, the D3 model (3-dimensional diffusion) was suitable for modeling reduction reaction kinetics. The calculated Ea was 35.3 kJ/mole, and the reaction order was determined to be approximately 0.76. The best fit for the oxidation reaction was obtained for the R3 model (shrinking core). The oxidation (regeneration) reaction Ea was equal to 16.7 kJ/mole, and the determined reaction order was approximately 0.72.

The crystalline phases present, as well as the morphology and inhomogeneities in elemental composition were studied for both materials, fresh as well as after multiple redox cycles, by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) combined with X-ray Microanalysis – Energy Dispersive Spectroscopy (EDS). Structural and morphological changes were detected and correlated to the reaction temperature as well as the reactant compositions and thus the stability of the ores in repetitive CLC cycles was determined.

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