Abstract
This work was devoted to study experimentally and numerically the oxygen carrier (NiO/NiAl2O4) performances for Chemical-Looping Combustion applications. Various kinetic models including Shrinking Core, Nucleation Growth and Modified Volumetric models were investigated in a one-dimensional approach to simulate the reactive mass transfer in a fixed bed reactor. The preliminary numerical results indicated that these models are unable to fit well the fuel breakthrough curves. Therefore, the oxygen carrier was characterized after several operations using Scanning Electronic Microscopy (SEM) coupled with equipped with an energy dispersive X-ray spectrometer (EDX). These analyses showed a layer rich in nickel on particle surface. Below this layer, to a depth of about 10 µm, the material was low in nickel, being the consequence of nickel migration. From these observations, two reactive sites were proposed relative to the layer rich in nickel (particle surface) and the bulk material, respectively. Then, a numerical model, taking into account of both reactive sites, was able to fit well fuel breakthrough curves for all the studied operating conditions. The extracted kinetic parameters showed that the fuel oxidation was fully controlled by the reaction and the effect of temperature was not significant in the tested operating conditions range.
Highlights
In the current environmental context, greenhouse gas emissions should be limited to stabilize or to reduce global warming
The study was carried out with the oxygen carrier NiO/NiAl2 O4 in the fixed bed reactor according to the experimental design
To investigate the influence of the operating parameters, several series of tests were performed according to a design of experiments (DOE)
Summary
In the current environmental context, greenhouse gas emissions should be limited to stabilize or to reduce global warming. The second technology is operating batch-wise, with the alternative injection of the different (oxidation/reduction) gases [10] This technology requires an intermediate step (injection of non-reactive gas) to avoid the simultaneous presence of fuel and air in the reactor. The development of this technology (strategic focus for CLC efficiency) requires finding suitable oxygen carrier with good mechanical properties, reactivity and stability. The porous binder provides better mechanical, thermal and chemical properties, limiting agglomeration and attrition Among these oxygen carriers and binders, the academic community deemed NiO/NiAl2 O4 to be efficient and a reference material. Different kinetic models are used to simulate experimental results of chemical-looping combustion of carbon monoxide in a fixed-bed reactor. Experimental and numerical results are compared and discussed with regards to characterization results
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