Numerical Modeling of Oxygen Carrier Performances (NiO/NiAl2O4) for Chemical-Looping Combustion

Abstract

Abstract:This work was devoted to study experimentally and numerically the oxygen carrier (NiO/NiAl 2 O 4 ) 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.

Exergy Analysis of Gas Switching Chemical Looping IGCC Plants

“…A set of gas switching (GS) valves controls the reduction and oxidation cycle lengths of each reactor. Several oxygen carriers have been tested in the lab scale and a nickel oxide (NiO) with alumina (Al 2 O 3 ) support has proved to be mechanically stable and fluidize well at high air reactor temperatures [6], which are required to attain high thermal efficiencies [7].…”