Running Chemical Reactions at Ultra-High Temperatures for Solar Energy Storage. Potential and Challenges

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1 Running Chemical Reactions at Ultra-High Temperatures for Solar Energy Storage Potential and Challenges Dr. Ivo Alxneit Solar Technology Laboratory Paul Scherrer Insitut

2 Solar Technology Laboratory (STL) our mission is to develop the science and technology that is required for transforming, at an industrial scale, solar energy into chemical fuels with a thermochemical process that effects this conversion more competitively than any other solar-to-fuel process concentrate store transport

3 Outline general motivation: concentrated solar radiation solar fuels concepts thermochemical cycles basics energetics / efficiencies instrumentation: example: Zn / ZnO cycle carbon free carbothermic solar furnace / solar simulator

4 Electricity Consumption Japan 1.0 Entwicklungs Index development index TW world wide TW CH USA Kanada Polen China Island Russland Norwegen Qatar Südafrika Indien 0.6 Simbabwe 0.4 Sambia Sierra Leone electricity pro per capita Elektrizität Kopf [kw] / kw nuclear renewables biomass hydro coal gas oil 0 to be replaced

5 Solar Radiation < annual energy consumption = TWh annual solar input = 2300 kwh/m2 energetic efficiency (solar to electricity) = 20% land use factor = 25% 2500 (kwh/m2 ) area used: ca km x 1000 km

6 Concentrated Solar Radiation: High Temperatures Stagnation Temperature 6000 C TS K = K = 375 C K = 879 C K = 1776 C K = 2791 C K = 3371 C 5000 T [K] C σ = 5.67x10-8Js-1m-2K-4 absorbed power = emitted power Solar Chemistry 1000 Trough Solar Tower Dish CI I[kW/m [kw/m]2] irradiation: I = 1 kw/m2 (1 Sun) C=1

7 Concentrated Solar Radiation: High Efficiency peak efficiency (maximum power point) T = 1500K, C = 5000 ηmax = Carnot 0.9 ηabs x ηcarnot Temperatur [K]

8 Instrumentation: Solar Furnace Konzentration: Sonnen maximum power (60 mm aperture): 10 kwth 2 peak concentration: 5'000 kw/m (5000 suns) Leistung: 40 kw thermisch N S

9 Instrumentation: Solar Simulator lamps: 10 Xe-arc lamps (water-cooled) power: 15 kwel per lamp feeds: 10 rectifiers air and water cooling unit Lambertian target: flux measurement plattform: 3-axis stage maximum: 500 kg experiment at secondary focus: maximum power (60 mm aperture): 20 kwth peak concentration: > kw/m2 (suns) reflectors: ellipsoidal reflectors coated Al layer

10 Solar Fuels gasification of biomas C + H2O H2 + CO concentrated solar radiation Zn / ZnO cycle hydrogen syngas ceria cycle syngas CO2 carbonaceous materials H2O gasification of carbonaceous waste C + H2O H2 + CO thermochemical cycles longterm solar thermal gasification CxHy C + H2 short- / mediumterm solar fuels (hydrogen, syngas, liquid fules) cracking of hydrocarbons steam reforming CH4 + H2O CO + 3H2 (CO + H2O CO2 + H2)

11 Thermochemical Cycles: oxygen Hydrogen from Water in Two Steps zinc water hydrogen zinc oxide metal: base metals noble metals (oxide is more stable than water) (low reduction temperature of oxide) other candidates Fe / Ce / Sn

12 Thermochemical Cycles: carbothermal - (only) solar process heat + lower temperatur +- syngas carbon monoxide syngas direct + one pot reaction + simple / cheap zinc zinc Variations zinc / air battery - electricity - transport (Zn / ZnO) oxygen Water / CO2 zinc zinc oxide zinc oxide zinc oxide syngas coal

13 Thermochemical Cycles: water splitting reaction: CO2 reduction : Black Box H2O H2 + ½O2 CO2 CO + ½O2

14 Energetics: H2O H2 Concentrated Solar Energy ZnO SOLAR REACTOR ½ O2 ZnO Zn + ½ O2 H = 557 kj/mol, T = 2000 K Zn HYDROLYSER Zn + H2O ZnO + H2 H2O H = -62 kj/mol, T = 700 K recycle ZnO H2 Fuel cell ZnO

15 Solar to Fuel Efficiency: 2nd Law Analysis quenching with inert gas to separate Zn(g) / O2 solar-to-chemical WFC Qsolar! 39% ZnO/Zn-cycle 29% Fe3O 4 /FeO-cycle process efficiency will be lower: optical efficiency, support,...

16 Zn / ZnO Cycle: feeder 10 kw Solar Reactor I ZnO Zn / O2 rotary joint cavity sintered ZnO or Al2O3 window rotary feeds gas / water 20% SiO2 - Al2O3 insulation aperture concentrated solar radiation water-cooled front

17 Zn / ZnO Cycle: 10 kw Solar Reactor II Thermal Dissociation transport of Zn(g) / O2 purge gas feeder retraced quench sepn. Zn / O2 Zn(s) / O2 ZnO thermal dissociation

18 Zn / ZnO Cycle: 10 kw Solar Reactor III Feeding screw feeder rotates fresh ZnO

19 Zn / ZnO Cycle: ZnO container rotary joint ZnO feeder data acquisition 10 kw Solar Reactor ZnO-tile cavity IV porous Al2O3 insulation water-cooled reactor front Al2O3 CMC front cone Ar nozzles water-cooled Cu aperture lateral front wall

20 Zn / ZnO Cycle: 10 kw Solar Reactor V feed: 120 g ZnO (each) solar power O2 from ZnO dissociation temperature O2 rate (mol s ) Solar power input (W) Temperature behind ZnO tiles (K) mass balances heat transfer analysis efficiencies Time (s) models

21 Quench: Pure Zinc start I quench rate condensation rate S nucleation sets in surface is made available condensation starts time net rate becomes zero ( p - ps= 0 ; S = 1) condensation rate > quench rate small slope system follows phase boundary

22 Quench: Zn / O2 (Quench Rate) II oxidation continues (ps,zn = ps,o2 = 0.0) time increased quench rate results in increased nucleation super saturation and nucleation rate more surface is created all surface reactions become faster (slopes do not vary a lot) condensation and oxidation evaporation and oxidation (evaporation not included) avoid leaving region Znliquid (or Znsolid)

23 Quench: Zn / O2 (Initial Dilution) III parallel curves same rates increased dilution delays nucleation reaction(s) occur at lower pzn and T smaller slope of vapor pressure curve at lower T system remains longer within liquid phase even more favorable: resublimation

24 Comparison Model Experiment IV Zn Yield Quench: ptot = 100kPa stoichiometric mixture 66 kpa Zn / 33 kpa O2 pzn [Pa] (after quench) model experiment model explains experimental observations on a qualitative level large amounts of inert gas to be recycled (solar process?)

25 Zn / ZnO Cycle: insulation Scale Up to 100 kw I rotary joint cavity receiver front cone ZnO quartz window Zn + ½ O2 outlet tube concentrated solar radiation rear panel quench unit center casing front cap front shield

26 Zn / ZnO Cycle: bosch profile Scale Up to 100 kw screw feeder II ZnO container mixer motor screw motor support for radiation shield filter motorized wheels for cavity rotation movable carriage product gas outlet data acquisition system

27 Zn / ZnO Cycle: Scale Up to 100 kw III MWSF: PROMES-CNRS Font Romeu Odeillo 63 heliostats (2835 m2) dish (1830 m2) 1 MW (80 cm aperture) peak concentration: 10'000 suns

28 Zn / ZnO Cycle: Scale Up to 100 kw IV no results yet: - installation completed - start up / initial testing under way - experimenting starts soon

29 Carbothermic Reduction of ZnO CH4 ZnO + CH4 CO + 2H2 CarbothermicC reduction of ZnO: ZnO + C Zn + CO ZnO is stable in presence of Tmin for no ZnO in thermodynamic equilibrium 2000 carbon free ZnO Zn + ½O minimum carbon No ZnO scale up kwth ZnO 1200 ZnO + ¼CH4 Zn + ¼CO2 + ½H2O } o T [ C] C Temperature 1800 ZnO + ½C Zn + CO ideal syngas nznzno; /nc =mol [-] C/mol ZnO =mol CH4/mol 1.0 ZnO + CH4 Zn + CO + 2H2

30 Carbothermic Reduction: SRFU: Beam Down Concept Weizmann Institute of Science hyperboloidal mirror (70 m2) 64 heliostats (3584 m 2) seconadary concentrator aperture of experiment 0.5 MW (0.5 m aperture) 4000 suns

31 Carbothermic Reduction: 300 kwth pilot reactor upper cavity above separation plates upper part (stationary) I principle: 300 KW solar power input quartz window 2 cavity reactor fixed bed of ZnO/C mixture 1 batch per day features: Drxn chamber = 1.4 m lower part offgas pipe with heater carrier gas inlet lower cavity (reaction chamber) Zn( g)+ C 140 cm O Hbed 0.5 m capacity 500 kg ZnO/C lining: SiC plates insulation: Al2O3 SiO2 separation plates: graphite, SiC on graphite lower part easy to lift down for refilling ZnO/C batch

32 Carbothermic Reduction: 300 kwth pilot plant II Impressions

33 Carbothermic Reduction: 300 kwth pilot plant III 100 Kg ZnO / 16 Kg beech char coal Temperature separation plates C kg/h ; Vol-% CO Bed bottom temperature kg Zn/h Temperature reaction chamber side wall 10 CO h h h h h h

34 Acknowledment people: - staff at LST / PSI - staff at PRE / ETHZ (former and present) (former and present) funding: - SFOE - EU - KTI (PSI / ETHZ)