Thermal stability study of NiAl2O4 binders for Chemical Looping Combustion application

Abstract

The influence of the preparation method of NiAl 2 O 4 binders on their thermal stability was studied. For this purpose, the reactivity of two different NiAl 2 O 4 binders with CO as fuel was studied in a fixed bed reactor device. Successive oxidation-reduction cycles were performed-2/19-on the two binders to study their reactivity with the fuel and their structural modifications as cycles proceed. Results reveal that binders are not inert in reducing atmosphere; they both react with the fuel to produce CO 2. The total reduction capacity (TRC) of the first binder (B1, synthetized by pyrolytic pulverization) increases during the first cycles and levels off after 20 cycles. However, the TRC of the second binder (B2, synthetized by calcination of a mixture of Ni(OH) and γ-Al 2 O 3), increases progressively and reaches a maximum after 80 cycles. The growing amount of available oxygen in the binders leads both binders to structural modifications. X-Ray Diffraction studies performed on fresh and aged binders presented a shift of the peaks related to NiAl 2 O 4. Moreover, quantitative X-Ray Diffraction studies and Temperature Programmed Reduction measurements were performed in order to quantify the NiO present in each binder before and after oxidation-reduction cycles. These experiments revealed the presence of NiO in fresh binders due to the preparation method, and an increase of this amount after oxidation-reduction cycles. Therefore, NiAl 2 O 4 in the binder is progressively decomposed producing NiO and Al 2 O 3. Finally, the decomposition of the binder NiAl 2 O 4 as cycles proceed was also observed in studies performed on the oxygen carrier NiO/NiAl 2 O 4. This work showed that the binder reacts with the fuel and therefore it can contribute to the modification of the oxygen carrier reactivity.

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

“…To observe the temperature influence, experimental tests should be performed at high flow rates (i.e., with immediate percolation of the combustible gas). At the same time, the increase of overall oxidized CO with temperature is certainly due to the separation of the binder (NiAl 2 O 4 ) phase to NiO and Al 2 O 3 , as previously observed [11]. …”

“…For these different reasons, this OC was widely used in laboratory studies. However, previous studies showed that the binder can react with fuel and lose partly its properties [11][12][13].…”

Supplied Oxygen Properties of NiO/NiAl2O4 in Chemical Looping Re-Forming of Biomass Pyrolysis Gas: The Influence of Synthesis Method

“…Therefore, the high value utilization of biomass pyrolysis gas is promising and urgent. At present, several technologies were considered as potential options for improving the value of biomass pyrolysis gas, such as chemical looping re-forming (CLR), steam re-forming, and so on. , CLR is a competitive option to produce H 2 as well as capturing CO 2 …”

“…1,2 CLR is a competitive option to produce H 2 as well as capturing CO 2 . 3 Moreover, oxygen carriers (OCs) are one of the most important factors in the CLR; in particular, the supplied oxygen properties of OCs such as supplied oxygen content, supplied oxygen rate, and supplied oxygen temperature were the key point for improving the effectivity during the CLR. 4 However, research about the supplied oxygen properties is rare.…”

Recent Advances and Development of Various Oxygen Carriers for the Chemical Looping Combustion Process: A Review

“…80 At high temperature, the Ni support with alumina formed the NiAl 2 O 4 spinel compound. 81 The spinel compound has a strong interaction with an alumina support that cannot take part in reductive and oxidative reactions. This causes loss of Ni contents in the OC after a few redox cycles.…”