On the mechanisms of oxygen carrier degradation during multiple CLC cycles

Transcription

1 Renewable energies Eco-friendly production Innovative transport Eco-efficient processes Sustainable resources On the mechanisms of oxygen carrier degradation during multiple CLC cycles Arnold Lambert, E. Comte, D. Marti, T. Sozinho, S. Bertholin IFP Energies nouvelles, Solaize, France H. Stainton, M. Yazdanpanah Total RC, Gonfreville, France 6th High Temperature Solid Looping Network Meeting, Milan, 2-3 sept. 2013

2 INTRODUCTION CLC technology proven at various scales (up to 1 MW th ), with different reactor designs and fuels High CO 2 capture rate, low energy penalty Many oxygen carriers have been tested successfully Natural ores Industrial metal wastes Synthetic particles Reactivity Oxygen Transfer Capacity Agglomeration Attrition rate and yet the search for oxygen carriers is ongoing : Higher reactivity, OTC (R 0 ) lower cost, attrition rate 2

3 BUT Thorough characterization of ilmenite particles used in Chalmer s 100kW th pilot plant : Purpose of this talk : - Fast TGA and batch fluidized bed ageing of various particles : SEM characterization as a useful tool to determine morphology changes - First thoughts on the mechanisms of particles ageing 3 L.S. Fan Porosity et al. (AIChE increase J., 2015, : 61, 2) reckon that ionic migration and volume changes during - higher redox reactivity cycles (activation) have been underestimated - lower attrition resistance Fe and Ti segregation : - ionic diffusion P. Knutsson, C. Linderholm, 3rd international Conference on Chemical Looping, September 9-11, 2014, Göteborg, Sweden

4 Automated ageing devices TGA (SETARAM TAG24) Fixed bed Full solid conversion 20 mg sample : short cycle time (500 cycles in ~3 days) SEM only Ageing conditions 900 C Batch fluidized bed Fluidized bed Tunable solid conversion 100 g sample : long cycle time (250 cycles in ~4 days) SEM, Hg porosimetry, XRD Ageing conditions 900 C Reduction: 10% CH % CO 2 Oxidation: Air Nitrogen flush between reactions Reduction: 100% CH 4 Oxidation: Air Nitrogen flush between reactions 4 Fast but not very representative of CFB-CLC More representative of CFB-CLC, but longer experiments

5 Fresh materials characterisation Material Porosity 1 XRD phases SEM Ilmenite <1 % FeTiO 3 + impurities (Fe 2 O 3, (Ca,Na)(Si,Al) 4 O 8 ) Pyrolusite 15% MnO 2 + impurities (Al x Si y O z, K, Mg ) NiO/NiAl 2 O 4 (60/40) 28% NiO, NiAl 2 O 4 CuO/Al 2 O 3 (13% CuO) 40% CuO, CuAl 2 O 4, α-al 2 O measured by Hg-porosimetry

6 TGA ageing (500 cycles) Ilmenite Pyrolusite NiO/NiAl 2 O 4 CuO/Al 2 O 3 Activation over 20 cycles, R 0 max = 4.3% Activation over 120 cycles, R 0 max = 4.8% Deactivation! R 0 = 13% 7.4% Stable activity, R 0 = 2.4% With the ores (bulk active phases), redox cycles trigger such a large porosity increase that samples are pulverized despite the lack of fluidization Pulverization, large sample volume increase (i.e. porosity increase) 100 µm With supported particles, the active metal phase diffuses outwards and also tends to segregate inside the particles Strong Agglomeration Pulverization, large sample volume increase (i.e. porosity increase) No visible sample volume increase Weak agglomeration No visible sample volume increase Fe and Ti segregation Outwards Mn migration (in particles containing Si and Al) Large Ni/NiO bridges between particles Cu accumulation at the periphery of particles + Cu nodules inside 6

7 Fluidised bed ageing (250 cycles) Ilmenite Pyrolusite NiO/NiAl 2 O 4 CuO/Al 2 O 3 Activation over 30 cycles, low reactivity (20% CH 4 conv. at ΔX s = 28 %) Deactivation over 40 cycles, from 50% CH 4 conv. (ΔX s = 35 %) to 30% (ΔX s = 21 %) No deactivation, ~99% CH 4 conv., ΔX s = 30 % 99% CH 4 conv. for 130 cycles (ΔX s = 96 %), then slight decrease. Pulverization + large porosity increase, Fe and Ti segregation Similar to TGA evolution Pulverization + large porosity increase Similar to TGA evolution No visible porosity evolution, not many fines, no visible Ni migration unless we look at the particles' surface: Ni is migrating outwards Lots of fines and cracked particles, Cu migration inside the cracks and to the periphery of particles 7

8 To summarize With the ores, similar morphological evolution using TGA and FB ageing Large porosity increase, leading to pulverization of the particles With ilmenite, Fe and Ti segregation With pyrolusite, Mn outwards migration in Si and/or Al rich particles With NiO/NiAl 2 O 4, no deactivation in FB: Possibly due to lower solid conversion; Ni migration does occur, but fluidisation avoids agglomeration Hg porosimetry : large porosity increase (28 40%) Deactivation in TGA might be due to some of the Ni in the bridges becoming less available 8 With CuO/Al 2 O 3, the alumina matrix does not withstand the numerous cycles in FB: Too much H 2 O V? Cu migration also occurs to a large extent

9 Some (light) theory The Kirkendall effect is the motion of the boundary layer between two metals that occurs as a consequence of the difference in diffusion rates of the metal atoms. (A.D. Smigelskas, E.O. Kirkendall, Trans. of the AIME, 171 (1947) 130) Atoms migration occurs by a vacancy mechanism : Example : Cu diffuses faster into Ni than Ni into Cu vacancy accumulation and condensation in Cu, leading to pore formation 9

10 Kirkendall effect Used for the preparation of void nanoparticle oxides: Ionic migration due to Kirkendall effect might ultimately lead to complete loss of active phase. - Adanez et al. have reported on the loss of active phase in Fe and Cu supported on Al 2 O 3, Metallic which stops ions after diffuse a few hours faster on stream in the oxide layer than oxide ions Could explain outwards diffusion, e.g. in Ni based particles aged by TGA : O 2 CH 4 N cycles O 2 Reduced particle Oxidized particle Reduced particle

11 Pyrolusite FB ageing 35 cycles 100 cycles Kirkendall effect (Mn 2+ migration through Mn 3 O 4 layer) Kirkendall unlikely : - Volume variations? (c.f. L.S. Fan et al.) 11

12 Conclusions Lifetime assessment of particles should be based on long term testing AND thorough analysis of used particles Low attrition rates may well become very fast after a certain time on stream if porosity increases with each cycle Natural ores challenge: avoid active metal ions migration avoid large porosity increase ( understand mechanism) C.R.Forero, PhD Thesis, 2011 Supported particles challenge: avoid metal ions migration (minimise Kirkendall effect) increase support s inherent mechanical/chemical resistance 12

13 Thank you for your attention Questions? 13

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