Methane Combustion in a 500 W_th Chemical-Looping Combustion System Using an Impregnated Ni-Based Oxygen Carrier

Abstract

ABSTRACT. Chemical-looping combustion (CLC) is a promising method for the combustion of fuel 11 gas with CO 2 capture and sequestration (CCS). This paper presents the methate combustion results 12 obtained in a continuous CLC prototype using an oxygen carrier containing 18 wt% NiO impregnated 13 on alumina. The design of the CLC prototype was a circulating fluidized bed reactor, consisting of two 14 interconnected fluidized bed reactors, the fuel reactor (FR) and the air reactor (AR). The main operating 15 conditions affecting combustion, as fuel gas flow, solids circulation rate, and FR temperature, were 16 analyzed. The CLC operation was carried out using methane as fuel gas in the FR with a thermal power 17 between 500 and 850 W th . The prototype was successfully operated during 100 h, of which 70 h were at 18 2 combustion conditions. No methane was detected at the FR exit, being CO and H 2 the unconverted 1 gases. Increasing the temperature in the FR or the solids circulation rates increased the combustion 2 efficiency, reaching efficiencies values as high as 99% at temperatures in the range 1073-1153 K, and a 3 solid inventory in the FR of 600 kg per MW th . The effect of operating conditions on the performance of 4 the oxygen carrier in the CLC prototype was analyzed. During operation of the CLC prototype, no signs 5 of agglomeration or carbon formation were detected and the main properties of particles did not vary. 6The two different phases in the oxygen carrier, NiO and NiAl 2 O 4 , were active to transfer oxygen to the 7 fuel gas. The NiO/NiAl 2 O 4 ratio increased with a decrease in the solids circulation rate, which affected 8 to the reactivity of the oxygen carrier. 9INTRODUCTION. 10

Evaluation of different oxygen carriers for biomass tar reforming (I): Carbon deposition in experiments with toluene

“…Figure 3 shows [63]. In those cases, the first stage was correlated to the fast reduction of the free NiO phase and the second one to the slow reduction of NiAl 2 O 4 .…”

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

“…Chemical looping reforming experiments using CH 4 as fuel were performed with the NiO21-Al particles for 50 hours (40 h of reaction time) [49], while combustion tests were carried out with NiO18-Al for 100 hours (70 h of reaction time) [45]. Table 1 shows the main properties of the fresh and used materials.…”

“…When it was tested in a 500 W th continuous pilot plant, free NiO was present in the oxygen carrier in a significant percentage about 20-25 % from total nickel amount [45]. The presence of both NiO and NiAl 2 O 4 must be taken into account to fit the complete conversion-time curve.…”

“…NiO18-Al oxygen carrier had been previously used successfully in CLC with different fuels [45][46] even in the presence of impurities, such as sulphur [47] and light hydrocarbons [48]. Both NiO18-Al and NiO21-Al particles were also tested in CLR experiments in a continuous plant [49] and at pressurized conditions in a batch reactor [50].…”

Syngas combustion in a chemical-looping combustion system using an impregnated Ni-based oxygen carrier

“…Two different zones can be distinguished. The first stage corresponds to the fast reduction of the free NiO phase and the second one is the slow reduction of NiAl 2 O 4 [38]. For the fresh OC particles, the relative amount of free NiO with respect to the total Ni in the particle was about 65 %.…”