Reactivity of a NiO/Al2O3 oxygen carrier prepared by impregnation for chemical-looping combustion

Abstract

15The reactivity of a Ni-based oxygen carried prepared by hot incipient wetness 16 impregnation (HIWI) on -Al 2 O 3 with a NiO content of 18 wt% was studied in this 17 work. Pulse experiments with the reduction period divided into 4-second pulses were 18 performed in a fluidized bed reactor at 1223 K using CH 4 as fuel. The number of pulses 19 was between 2 and 12. Information about the gaseous product distribution and 20 secondary reactions during the reduction was obtained. In addition to the direct reaction 21 of the combustible gas with the oxygen carrier, CH 4 steam reforming also had a 22 significant role in the process, forming H 2 and CO. to the design of a CLC system were investigated. When formation of NiAl 2 O 4 occurred, 5 the average reactivity in the fuel reactor decreased. Therefore, the presence of both NiO 6 and NiAl 2 O 4 phases must be considered for the design of a CLC facility. 7 8

Reduction and oxidation kinetics of nickel-based oxygen-carriers for chemical-looping combustion and chemical-looping reforming

“…The relative amount of NiO in the NiO18-Al particles after consecutive redox cycles is related to the reducing conversion reached during the previous reduction-oxidation cycles. The conversion during the preceding cycles was complete and this favoured the formation of free NiO and therefore a higher reactivity [53]. However, when the reduction degree decreased, a lower fraction of NiO was formed and the reactivity was lower.…”

“…As can be seen, in the case of NiO18-Al, the reduction of the oxygen carrier particles proceeded in two stages. There was a first period where the reduction rate was fast, attributed to the reaction of NiO with the fuel, and then a stage of low reactivity which corresponded to the reaction of the nickel aluminate with the fuel [18,53]. The use of -Al 2 O 3 as support allowed reducing the interaction support-active phase [51] minimizing the formation of nickel aluminate and part of the impregnated nickel remained in this case as free NiO, increasing the reactivity of the NiO18-Al oxygen carrier.…”

“…However, when the reduction degree decreased, a lower fraction of NiO was formed and the reactivity was lower. Dueso et al [53] demonstrated that, regardless solid conversion variation, 80% of the Ni reduced in the fuel reactor was oxidized to free NiO while the remaining Ni was oxidized into NiAl 2 O 4 . In this cycle, formation of free NiO also took place in NiO21-Al but in lower amounts than using NiO18-Al particles.…”

“…Dueso et al [53].carried out in a previous work several experimental series in TGA at 1223 K which consisted of 10-redox-cycle experiments using different reduction times between 6 seconds and the time needed to reach full conversion of the particles. 5% of Figure 6.…”

Progress in Chemical-Looping Combustion and Reforming technologies

“…However, thermal treatments do not avoid completely the formation of the spinel compound. Dueso et al [215] observed that reactivity of these particles prepared by impregnation was dependent on the conversion reached during the reduction stage. These differences were attributed to the different free NiO [150].…”