Solar Thermochemical Reactors Solar Reduction 2 - Sollab SUMMER... · Solar Thermochemical Reactors Solar Reduction 2 Gaël LEVEQUE, ... low pressure/high neutral gaz flow ... Centrifugal

Solar Facilities for the European Research Area

Solar Thermochemical Reactors Solar Reduction 2

Gaël LEVEQUE, PROMES-CNRS

SFERA II 2014-2017, Solar Reduction 2, 2014/06/27, Odeillo, France

Introduction

Definition of volatile oxide cycles

Theoretical efficiency

Thermal reduction

Carbothermal reduction

Products reactivity

Solar reactor technologies

Rotating cavity type

Beam-down and other vertical configurations

Carboreduction specialized

Conclusions

SUMMARY

2

Introduction



Thermal reduction


Products reactivity





Conclusions 3

INTRODUCTION

Volatile oxide cycle: - Cycle based on an oxide which reduction temperature is higher than the boiling temperature of its reduced specie

𝑀𝑂𝑥 = 𝑀𝑂𝑥−𝑦 𝒈 + 𝑦2 𝑂2

Examples of purely thermal volatile oxide cycles:

Oxide/Reduced

specie

Reduction

Temperature

Boiling point

of the product

Productivity

mmolH2/goxide

ZnO/Zn 2070°C 907°C 12 Most advanced couple

GeO2/GeO 1830°C 1000°C ? 10 Transparent in infrared, melts

at 1115°C

CdO/Cd 1590°C 767°C Poor reactivity with water

In2O3/In 2206°C In2O3: 1913°C

In: 2072°C

Impractical

SnO2/SnO 2060°C 1527°C 7 Similar to ZnO/Zn

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INTRODUCTION

5

Theoretical efficiencies

ZnO/Zn(g) SnO2/SnO(g)

TΔG=0 (°C) >2070 >2060

habsorption =1 −σT4

IC 0.66 0.66

hexergy, max= ηabsorption ∗

ηcarnot 0.57 0.58

Qreactor net (kW) =

𝑛 ΔH + 𝑛 cpdT 560 710

Qsolar (kW)= 𝑄𝑟𝑒𝑎𝑐𝑡𝑜𝑟 𝑛𝑒𝑡

ηabsorption 848 1076

Qquench (kW) 209 413

WFC,α=0(kW) 237 237

hexergy= 𝑊𝐹𝐶

𝑄𝑠𝑜𝑙𝑎𝑟 0.28 0.22

C = 5000, I = 1 kW/m², 1 mol/s of oxide

INTRODUCTION

6

Theoretical efficiencies

Improve the theoretical efficiency:

- Reduce the temperature (hsolar/fuel=0.3 for SnO2 at 1600°C)

Low pressure, high dilution: Cost ?

- Reduce the heat sinks (heat recovery).

Limited by the quench of the products

ZnO equilirium calculations

INTRODUCTION

Main issue: Handling 𝑀𝑂𝑥−𝑦 𝒈 + 𝑦

2 𝑂2

- Reduced specie preferably obtained in the form of a nanopowder by condensation

(high specific surface area) Cooling of the gases and gas-solid separation

But

Reaction inversion, products recombine as the temperature is lowered (heterogeneous reaction from nucleation sites, gases metastables)

To obtain high purity reduced specie:

- Quenching of the gases (temperature drop faster than reaction)

- Dilution of the products to limit recombination

- Oxygen separation ? (oxygen exchange membrane, reducing agent…)


7

INTRODUCTION

Carbothermal reduction (CR)

MOx + aC = MOx-y + (2a-y)CO + (y-a)CO2

Carbon source: methane, coal…

Reduction rate and purity drastically improved:

- C and CO are reducers metal oxide reduced at lower temperature

- CO2 is less a good oxidizer than O2 recombination limited

Drawbacks:

- Consumption of a carbonaceous feedstock (pseudo-cycle), CO2 emission

- Carbon excess

Oxide/Reduced

specie

CR

Temperature

Boiling point of

the product

ZnO/Zn 950°C 907°C Most advanced couple

MgO/Mg 1850°C 1090°C

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INTRODUCTION

Carbothermal reduction - Choice of the reducing agent

Solid carbon:

Reduction reaction mainly drove by CO:

MOx + yCO = MOx-y + yCO2

yCO2 + yC = 2yCO limiting step

Beech charcoal generally preferred: good specific surface area, non-fossil sourced, mineral content

Easy to mix with ZnO as powders, good absorber

Methane:

Possibility of combination of carbothermal reduction with CH4 reforming:

MOx + aCH4 = MOx-y + (2a-y)CO + (y-a)CO2 + 2H2

Mixing more difficult, harder to heat

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INTRODUCTION

Products reactivity

Typical characteristics:

- BET surface in the range 20-40 m²/g for both SnO and Zn

- Mean particle size up to 10 µm, important volume of nano-sized pore

- Micro-sized conglomerate of nano entities (disk-shaped for SnO, needle-shaped ZnO)

- Dependent of the conditions

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INTRODUCTION

Products reactivity

Highly reactive toward CO2 and H2O (more than any commercial powder)

Morphology

- High specific surface area

- Small particles

Presence of reoxidized specie

- Limits sintering

- Support for Zn(g) oxidation

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Limits surface passivation (~20nm)

Comparative reoxidation at 600°C with H2O

INTRODUCTION - CONCLUSION

Particular features of the volatile oxide cycles: - High temperature (really) - Importance of the recombination reaction for the final purity Low O2 partial pressure: low pressure/high neutral gaz flow Temperature issues: quenching of the gases, cold points and deposits - Particles generally retrieved (filtered) out of the solar reactor Allows continuous operation of the solar reactor Solar reactor designed for only one step - Reduced particles nano-sized (obtained by condensation) Specific surface area regenerated at each cycle High reactivity

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Introduction



Thermal reduction


Products reactivity





Conclusions

SUMMARY

13

SOLAR REACTOR TECHNOLOGIES

Roca reactor: 10kW, 1999, PSI-ETH 1

Designed for ZnO thermal reduction

3- Quartz window protected from particles deposition by a gas flow (8)

4- CPC

1- Rotating conical cavity receiver

7- ZnO layer

6- Screw powder feeder

9- Gas outlet

10- Quenching device

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1 Haueter, P., S. Moeller, R. Palumbo, and A. Steinfeld. “The Production of Zinc by Thermal Dissociation of Zinc Oxide—solar Chemical Reactor Design.” Solar Energy 67, no. 1–3 (July 1999)


Roca reactor: 10kW, 1999, PSI-ETH Objectives:

- Low thermal inertia, thermal shocks resistance Allowing fast start/stop to follow the availability of the solar resource

- Respect the chemistry of the reaction 1850 K < T < 2250 K (ZnO melting point) Quenching of gases

Why a rotating cavity ? Centrifugal force evenly disperses ZnO into a thick layer (2.5 cm) and holds it: used as absorbant, reactive material and insulation. Thick layer ablative regime for improved exergy efficiency Results - Dilution with N2 ~20-25 - Low conversion (35% of zinc)

Unsufficient quenching of the gases

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1kW, 2007, PROMES-CNRS2

2 Abanades, Stéphane, Patrice Charvin, and Gilles Flamant. “Design and Simulation of a Solar Chemical Reactor for the Thermal Reduction of Metal Oxides: Case Study of Zinc Oxide Dissociation.” Chemical Engineering Science 62, no. 22 (November 2007)


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1kW, 2007, PROMES-CNRS

- Similar design

- Reduced pressure (18kPa)

- Up to 1700K

- ~70 mg/min ZnO

- Limited ZnO conversion

Air-tightness issues, difficult to monitor the reaction (O2 and temperature measurement)


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Zirrus reactor: 10kW, 2008, PSI-ETH 3

Designed for ZnO thermal reduction

3 Schunk, L. O., P. Haeberling, S. Wepf, D. Wuillemin, A. Meier, and A. Steinfeld. “A Receiver-Reactor for the Solar Thermal Dissociation of Zinc Oxide.” Journal of Solar Energy Engineering 130, no. 2 (2008)

Various configurations tested

Similar structure

Improved mechanical stability (ZnO compressed tile)

Straight cavity, dynamic feeder to spread evenly the reacting powder

Window/cavity distance reduced, opening simplified


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Zirrus reactor: 10kW, 2008, PSI-ETH


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Zirrus reactor: 10kW, 2008, PSI-ETH4

Design of an efficient quenching apparatus

4Gstoehl, D., A. Brambilla, L. O. Schunk, and A. Steinfeld. “A Quenching Apparatus for the Gaseous Products of the Solar Thermal Dissociation of ZnO.” Journal of Materials Science 43, no. 14 (July 2008).

Objective:

Prevent the metastable Zn(g)/O2 mix from condensing and recombine on the walls

A- « hot » zone, temperature above ZnO dissociation (TZnO/Zn)

B- Transitory zone. T< TZnO/Zn, metastable gas mix sheathed by an argon flow (T>870 K)

C- Argon cold flux (298 K)

Cooling rate up to 117 000 K/s, 94% Zn purity, for 100NL/s of argon per g/s of oxide reduced


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Zirrus reactor: 10kW, 2008, PSI-ETH5

- Reactor window efficiently protected from particles deposition

- Up to 90% of conversion to Zn with the quenching apparatus (less in

“normal” conditions)

- Kinetic analysis of the reaction

- Development and experimental validation of heat transfer models:

- Solar-to-chemical efficiency ~3%. Major losses from water cooling and gaz

quench (46.7%)

- Up-scaling: potential of 50% and 56% of solar-to-chemical conversion for

respectively 100 kWth and 1 MWth (no water cooling, higher temperature

thus reaction rates, losses reduced by geometry optimization)

5 Schunk, L.O., W. Lipiński, and A. Steinfeld. “Heat Transfer Model of a Solar Receiver-Reactor for the Thermal Dissociation of ZnO—Experimental Validation at 10kW and Scale-up to 1MW.” Chemical Engineering Journal 150, no. 2–3 (August 1, 2009)


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Scaled-up prototype 100 kW, 2013, PSI-ETH6

6 Villasmil, W., M. Brkic, D. Wuillemin, A. Meier, and A. Steinfeld. “Pilot Scale Demonstration of a 100-kWth Solar Thermochemical Plant for the Thermal Dissociation of ZnO.” Journal of Solar Energy Engineering 136, no. 1 (November 8, 2013)


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Scaled-up prototype 100 kW, 2013, PSI-ETH

Multi-material self-supporting insulation

High thermal inertia, good thermal shock resistance, convection losses reduced

Thermal expansion issues treated

Slightly over-pressured, P~86 kPa

Over 1 000 NL/min of argon in the quenching zone


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25

Scaled-up prototype 100 kW, 2013, PSI-ETH

Much steeper relation between dilution and purity than for previous reactors:

50% purity obtained for 0.3 g/min of ZnO and 784 NL/min of argon

Introduction



Thermal reduction


Products reactivity




Carboreduction-specialized reactors

Conclusions

SUMMARY

26


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1kW, 2011, PROMES-CNRS7

Designed for ZnO and SnO2 thermal reduction

Non-rotating cavity to improve air-tightness

Insulated refractory cavity (30mm) to reduce thermal losses

Short straight path for the hot gases products

Reacting pellet are fed upward

7 Chambon, Marc, Stéphane Abanades, and Gilles Flamant. “Thermal Dissociation of Compressed ZnO and SnO2 Powders in a Moving-Front Solar Thermochemical Reactor.” AIChE Journal 57, no. 8 (August 2011)


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- Successfully operated under reduced pressure (as low as 15 kPa) for ZnO and SnO2

reduction

- Significant yields obtained for temperature below 1900K (reactions start at 1663K)

- Half of the products deposited in the exit tube, 10% of reduced species nucleation

- Lower Zn compared to SnO

- Reliable reaction monitoring via gaz analysis / temperature measurement of the pellet surface


31

GRAFSTRR, 2012, University of Delaware-PSI-ETH8

8Koepf, Erik, Suresh G. Advani, Aldo Steinfeld, and Ajay K. Prasad. “A Novel Beam-Down, Gravity-Fed, Solar Thermochemical Receiver/reactor for Direct Solid Particle Decomposition: Design, Modeling, and Experimentation.” International Journal of Hydrogen Energy 37, no. 22 (November 2012)

Gravity-Fed Solar-Thermochemical Receiver/Reactor


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GRAFSTRR, 2012, University of Delaware-PSI-ETH

Main features: moving bed feeding and stabilized vortex flow-pattern

Introduction



Thermal reduction


Products reactivity





Conclusions

SUMMARY

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Synmet reactor: 5kW, 2003, PSI-ETH9

Combined ZnO reduction / CH4 reforming

9 Kraupl, Stefan, and Aldo Steinfeld. “Operational Performance of a 5-kW Solar Chemical Reactor for the Co-Production of Zinc and Syngas.” Journal of Solar Energy Engineering 125, no. 1 (2003)

ZnO + CH4 = Zn + 2H2 + CO, ΔH1300 K = 446 kJ/mol

High-quality syngas + Zn at limited temperature

ZnO fed axially (~15g/min), CH4 tangentially (0.8 – 3.2 NL/min, pulsed)

Helical gas-particles stream


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Synmet reactor: 5kW, 2003, PSI-ETH


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Synmet reactor: 5kW, 2003, PSI-ETH

- Complete conversion of ZnO from 1380 K

- Up to 96% of methane conversion at 1676 K (49% at 1380K)

- Maximum thermal/exergy efficiencies 22% / 5.6%

- CO/CO2 ratio in the range 0.08-0.25

Problematic deposition of unreacted ZnO in the reactor


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Solzinc: 300kW, 2007, SolZinc Eu-project10

10 Wieckert, C., U. Frommherz, S. Kraupl, E. Guillot, G. Olalde, M. Epstein, S. Santen, T. Osinga, and A. Steinfeld. “A 300 kW Solar Chemical Pilot Plant for the Carbothermic Production of Zinc.” Journal of Solar Energy Engineering 129, no. 2 (2007)


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Solzinc: 300kW, 2007, SolZinc Eu-project

Effect of carbon content


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Effect of carbon type


40


Two-cavity reactor (receiver/reactor)

Separated by graphite/SiC

Batch operation

Up to 500 kg of reacting mix ZnO/0.8C

Industrial beech charcoal


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-About 50 kg/h of Zn dust at 1150°C

-Contains 95% Zn, 5% ZnO, below 10µm

-Low CO2 proportion in the off-gas

-Thermal efficiency 30%

Introduction



Thermal reduction


Products reactivity





Conclusions

SUMMARY

44

Solar reactor technologies development status:

- Technical challenges

Severe temperature conditions (levels and gradient)

Air tightness / pressure

Gas quenching / particles collections

- Active research field in the past decade

- Numerous realization, capitalized experience

- Significant prototypes (>100 kWth)

Issues:

- Improving solar-to-chemical efficiency (chemical conversion, thermal efficiency)

- Neutral gas consumption

New cycles? Innovative design? Quenching solutions? Handling of the products ?

CONCLUSIONS

45

Solar Facilities for the European Research Area

Thank You for your attention

Gaël LEVEQUE [email protected]

SFERA II 2014-2017, Solar Reduction 2, 2014/06/27, Odeillo, France

Documents

Solar Thermochemical Reactors Solar Reduction 2 - Sollab SUMMER... · Solar Thermochemical Reactors Solar Reduction 2 Gaël LEVEQUE, ... low pressure/high neutral gaz flow ... Centrifugal