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Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed C. Roßkopf, M. Haas, M. Linder, A. Wörner German Aerospace Center (DLR), Stuttgart, Germany

www.DLR.de • Slide 2 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Thermochemical Heat Storage Application & Potential Application: - Storage of industrial waste heat - Reduction of energy generation cost - Base load capability of renewable energy systems Potential: - High storage densities - Long-term and loss-free storage - Heat release at any time - Possibility of heat transformation

www.DLR.de • Slide 3 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Thermochemical Heat Storage Reaction System Reversible Gas-Solid-Reaction: CaO (s) + H 2 O (g) ⇌ Ca(OH) 2(s) + 99,5 kJ/mol Temperature range ~ 400-700 ° C  Main advantage: Low price (55-65 € / ton) - Poor thermal conductivity and permeability of CaO/Ca(OH) 2  High demand on reactor geometry leads to high costs  Adjustment of reactor to required power  Supply of capacity in cheap tanks  Material flow through the reactor is essential!

www.DLR.de • Slide 4 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Motivation Separation of Power and Capacity CaO (s) / Ca(OH) 2(s) Heat transfer Process integration Process integration fluid Heat transfer CaO (s) / fluid Ca(OH) 2(s) Heat transfer fluid Heat transfer fluid CaO (s) / Ca(OH) 2(s) H 2 O (g)

www.DLR.de • Slide 5 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Challenge Poor Powder Properties Reaction Bed Heat Conduction Low thermal conductivity vs Poor flowability Heat Flux v Reaction Bed HTF HTF Plate heat exchanger

www.DLR.de • Slide 6 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Approaches  Pellets unstabile during  Increasing the cycling roughness of particle surface

www.DLR.de • Slide 7 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Modification of Material Increasing the Roughness of Surface Extension of Van-der-Waals Eq. : 𝑆 2 𝐷 𝐼 𝑆∙𝑠 R 𝐺 𝑊𝑊𝑊 = 𝑏 2 ( 𝑆+𝑠 ) + ( 2𝑏 𝑄 ) 2 ∙2𝑆 6 x 0 2h r  Increasing of the roughness of the surface x 0 α x 1 and distance between the particles by R addition of nano particles State of the art: - 1 Improving powder flowability in bulk and pharmaceutical industries - 2 Combination of nano particle agglomerates with CaO to improve fluidization behavior for CO 2 adsorption  Coating of Ca(OH) 2 by nano particles in order to improve flowability is uninvestigated 1 K.Köpker et al., Application of nano particles , Landesanstalt für Umwelt, Messungen und Naturschutz Baden-Wuerttemberg,2007 2 Pontiga et. al, Dry fas-solid carbonation in fludized beds of Ca(OH)2 and nanosilica/Ca(OH)2 at ambient temperature and low CO2 pressure, Chemical Engineering Journal, 2013

www.DLR.de • Slide 8 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Dry particle coating Ca(OH) 2 + 0,5 - 15% Aerosil 300

www.DLR.de • Slide 9 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Results of Material Modification Effects of Variable Power Inputs Aerosil 300 2% Compressive strength ( σ 1 =6000) / N/m² Aerosil 300 6% 3000 Aerosil 300 11% 2500 2000 1500 0 1000 2000 3000 4000 5000 6000 7000 Mixing intensity / U/min

www.DLR.de • Slide 10 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Cycling stability Tests in pilot-scale reactor

www.DLR.de • Slide 11 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Cycling stability After Cycling  Calcium silicates lead to - Reduction of storing capacity - Hardening of surface structure Roßkopf et al., Investigations of Nano Coated CaO/Ca(OH) 2 Cycled in Thermochemical Storage , in preparation

www.DLR.de • Slide 12 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Conclusion & Outlook - Thermochemical Heat storage based on Ca(OH) 2 demands a flow-through of the reactor - Improvement of Ca(OH) 2 flowability by adding nano particles at ambient conditions is shown - Homogeneous flow through thermochemical reactor at room temperature achieved - Cycling stability is proven over 10 cycles in pilot-scale reactor  Flow behaviour during thermochemical reaction will be investigated

www.DLR.de • Slide 13 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Thank you for your attention

www.DLR.de • Slide 14 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Thermodynamic equilibrium

www.DLR.de • Slide 15 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Storage densities Typical storage densities in kWh/m³: - Sensible, mortar, Δ T=50K 25 - 30 - Sensible, Water, Δ T=50K 50 - Latent, solid-liquid 50 - 100 - Physical oder chemical sorption 50 - 140 - Thermochemical reaction 100 – 700 - Storage capacity in 1 kg Ca(OH)2 0,373 Wh - Storage capacity of pilot-scale reactor ~200 kWh/m³

www.DLR.de • Slide 16 > 7 th World Conference on Particle Technology > Christian Roßkopf • Improving Powder Flowability by Adding Nanoparticles for Thermochemical Heat Storage with Moving Reaction Bed > 19 th to 22 nd May 2014 Particle size Pelletizing the material - Increase of weight force by increasing the particles diameter  Problem: Volume change of the material by chemical reaction leads to tensions within the pellet  Cracking of the pellet after few cycles in thermochemical reactor