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Solar Facilities for the European Research Area

Introduction to solar reactors

Gilles Flamant, CNRS-PROMES

SFERA II 2014-2017, Summer School, June 25-27 2014

CONTENT

Solar reactors for what?

Typology of solar reactors

Example of laboratory to pilot scale prototypes

Metrics for solar reactors

Modeling

SFERA II Summer School 2014 – Gilles Flamant

FOR WHAT?

1

To use solar heat for performing chemical reactions

Solar Heat → Chemical products

Renewable fuel production (solar fuels)

Chemical commodity production

Waste treatment


Gases:

Hydrogen H2, Methane CH4 , Carbon monoxide CO and Syngas (mixture of H2 and CO)

Liquids:

Methanol CH3OH, Synthetic Hydrocarbons

-CH2-

Solid:

Metal produced by solar thermal reduction

SOLAR FUELS


FOR WHAT?

SOLAR FUELS


FOR WHAT?

To save fossil fuels consumption and CO2 emission:

Classical route: C + O2 = CO2 ∆H°r = -393 kJ/mol

The heat of combustion is the process heat for chemical reactions

To store solar energy for a long time without losses

To use solar energy in the transportation sector


Solar Fuels

Water Splitting

Direct thermolysis Thermochemical cycles

H20

Cracking

Methane Splitting

CH4 H20

Steam reaction

Reforming Gasification

Fossil fuel Biomass

Concentrated solar energy

Solar Fuels: Hydrogen and

Syngas

C and CO2


Solar Fuels

Thermal splitting

Water: H2O H2 + ½ O2 H° = 285.8 kJ/mol

Carbon Dioxide: CO2 CO + ½ O2 H° = 283 kJ/mol

Methane: CH4 2H2 + C H° = 74.6 kJ/mol

Four times less energy to split methane by comparison with water

Chemical routes


Solar Fuels

Chemical routes Reforming and gasification with Steam and carbon

dioxide

Steam Methane Reforming (SMR) CH4 + H2O 3H2 + CO H° = 206 kJ/mole Water Gas Shift reaction (WGS) CO + H2O H2 + CO2 H° = - 42 kJ/mole Carbon dioxide Methane Reforming CH4 + CO2 2H2 + 2CO H° = 247 kJ/mole Coal steam gasification C + H2O H2 + CO H° = 131.3 kJ/mol Syngas to gasoline n(2H2 +CO) (-CH2-)n + nH2O H° = -165 kJ/mol


Solar Fuels

Chemical routes ∆G° = ∆H° - T∆S°

∆G° = 0 at Tinv = ∆H° / ∆S°


Solar Fuels

Chemical routes for Tinv reduction: Oxide-based thermochemical cycles

HT Solar Step -reduction, endothermal- : MxOy MxOy-1+ ½ O2 (1400°C-1800°C) LT step -oxidation, exothermal- : MxOy-1 + H2O/CO2 MxOy + H2/CO (400°C-1200°C) 2 families: Volatile oxides: ZnO/Zn, SnO2/SnO Non volatile oxides: MFe2O4, CeO2 ….


Typology of solar

reactors

TYPOLOGY

Configuration 1: Use of an intermediate heat transfer fluid

Transfer of solar heat to the chemical reactor using a heat transfer fluid (HTF). At high temperature: molten salt (T < 600°C), molten metals, air and other gases. Main advantage: allow to use classical solution for the chemical reactor. Main drawback: heat losses in heat exchangers


Configuration 2: Receiver-Reactor type

Receiver = reactor, no HTF Main advantage: allow to operate at high temperatures Main drawback: process control is complex


TYPOLOGY

Configuration 2: Receiver-Reactor type, 2 options

Use of an opaque heat transfer wall Main advantage: allow to separate the chemical reaction and the radiation (better T control) Main drawback: limitation of heat transfer flux and wall temperature

Direct irradiation of the reactants Main advantage: allow to operate at high solar flux and temperature Main drawback: window is necessary, limitation in size and temperature


TYPOLOGY

Example of laboratory

and pilot scale

prototypes


CONFIGURATION 1


CONFIGURATION 2

Heat transfer wall option


CONFIGURATION 2 Tubes

•7 single graphite tubes (26-18 mm)

•Graphite cavity (360x400x300 mm)

•Aperture diameter 13 cm

50 kW tube-reactor for methane cracking , CNRS Up to 2000K 5-10 kW tube-reactor for biomass

gasification, Univ of Colorado – NREL Up to 1400K


10 kW rotating tube-reactor for calcite decomposition, PSI (Switzerland) Up to 1400K; SiC tubes.

5-10 kW fluid wall aerosol flow reactor for methane cracking, NREL and Univ. of Colorado. Graphite wall, up to 2000K


CONFIGURATION 2 Tubes

CONFIGURATION 2 Heat transfer wall

50 kW 2D-fluidized bed, CNRS Up to 1200K (tested with inert particles only); Inconel.

5 kW radiant plate or 2-cavity reactor for steel dust (metal recovery) or carbonaceous wastes processing , ETH and PSI (Switzerland); SiC wall, up to 1400K


Two-cavity pilot reactor

300 kW radiant plate (or 2-cavity) reactor for ZnO carbothermal reduction (Zn metal production), SOLZINC EC Project 2001-2005, CNRS,ETH and PSI (Switzerland), WIS (Israel) and Scanarc (Sweden). SiC wall, up to 1500K.

ZnO + C → Zn + CO


CONFIGURATION 2 Radiant wall

Beam down facility at WIS Solar reactor



Experimental results

Wieckert et al. J Solar Energy Engng, 129 (2007)



Solsyn pilot plant at Plataforma Solar de Almeria (CESA-1 tower) PSI-ETH (Switzerland)

Solsyn pilot plant in operation

up to 200 kW solar power input

into solar reactor

Gasification of carbonaceous wastes



Wieckert C. et al. Energy & Fuel (2013) 27, 4770

Syngas composition average over complete test

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Bee

ch c

harco

al

Bee

ch c

harco

al

Low ran

k co

al

Low ran

k co

al

Low ran

k co

al

Ind. S

ludge

I

Ind. S

ludge

II

Fluff I

Fluff II

Fluff II

DSS-M

DSS-M

Bag

asse

Tire

chip

s

Tire

chip

s

Tire

chip

s

C3H6 (GC)

C2H6 (GC)

C2H4 (GC)

CO2 (GC)

CO (GC)

CH4 (GC)

H2 (GC)



CONFIGURATION 2

Direct heating option



Four main categories:

• Fluidized bed • Rotary kiln • Entrained-particles • Porous media


Fluidized Bed

First 1 kW fluidized bed at CNRS (1977) Decarbonation of calcite, 1200K

Lab FB with draft tube. Niigata University, Japan, for coke gasification and then to split water cycles using ferrites.


Rotary Kiln

Solar rotary kiln developed by CNRS in the seventies to melt, to purify and to spheroidize refractory oxides (Al2O3, ZrO2, SiO2.)


Rotary Kiln

The 400 kW rotary kiln particulate receiver combined with cold and hot storages and a 100 kW multi-stage fluidized bed heat exchanger developed at CNRS in the mid-eighties. Sand up to 1200K.


Rotary Kiln

quartz window

cavity-receiver

water/gas

inlets/outlets

Zn + ½ O2

ZnO

Concentrated

Solar

Radiation

ZnO feeder

quartz window

cavity-receiver

water/gas

inlets/outlets

Zn + ½ O2

ZnO

Concentrated

Solar

Radiation

ZnO feeder

Improved 10 kW rotary solar reactor for ZnO reduction developed at ETH/PSI

1 kW reduced pressure rotary kiln developed at PROMES-CNRS.


Entrained particles

Vortex flow solar reactor developed at ETH/PSI for carbonaceous matter gasification

10 kW tornado solar reactor developed at WIS for methane splitting.


POROUS MEDIA

Monolith honeycomb,

Ceramic foams or fibers or fins or wires

Porous monolithic ceramics


Monolith honeycomb

Principle of the solar cycling of reactive honeycomb monolith for hydrogen production using 2-step thermochemical cycles based on ferrite. The ferrite material is deposited on SiSiC honeycomb and experiences successive reduction and hydrolysis cycles in the temperature ranges 1400-1700K and 1100K-1300K respectively.


Monolith honeycomb

HYDROSOL-II EC project resulted in the development of a 50-100 kW pilot reactor tested at PSA-CIEMAT


Counter Rotating Ring Receiver Reactor Recuperator (CR5). The reactor is composed of a stack of disks on which the redox material is deposited (the disk may also be composed of the redox material itself). Reactor developed by SANDIA Nat. Lab (USA) for CO2 or H2O splitting using 2-step redox reactions.

Porous support


Ceramic foam

Porous reactor based on cerium oxide developed by the alliance ETH/PSI and CALTECH. 2kW reactor with reduction temperatures in the range 1700K-1910K and oxidation temperature of about 1100K.

500 cycles.

Solar reactor for methane reforming based on catalyst-on-foam concept developed by DLR.


Ceramic fin

Pin-fins porcupine solar reactor developed at WIS (Israel)


Metrics for solar reactors


Efficiencies

Chemical (thermochemical) efficiency

ηch = mo,RXR∆Hr(To→Tr) / (Qsolar + Qaux) m for molar flow, R for reactant, r for reaction, XR is the conversion of R, Qsolar is the incident solar power at the entrance of reactor. For solar fuels: ηch = mfuel.LHVfuel/ (Qsolar + Qaux)

Overall reactor efficiency

ηov = ηch + ηth

With ηth = [mo,R (1-XR)∫ToTrCp,RdT + FI ∫To

TrCp,IdT] / (Qsolar + Qaux)

I for inert gas


Efficiencies

For reforming and gasification

Solar-to-fuel energy conversion efficiency (Qaux = 0)

Energetic upgrade factor

For example, solar gasification of coal (C + H2O) leads to U = 1.33


Example

Efficiency of the 50 kW SR for methane cracking

cracking

0

2

4

6

8

10

12

14

1698 K 1798 K 1808 K 1873 K

Thermochemical efficiency (%)

Thermal efficiency (%)

Ar=49 NL/min

CH4=21 NL/min

Ar=49 NL/min

CH4=21 NL/min

Ar=49 NL/min

CH4=21 NL/min

Ar=21 NL/min

CH4=21 NL/min solar

)Treactor(Products)T(ReactantCHCH0,

ch044

.X.m

Q

H s

solar

T

T

)Treactor(Products)(ReactantsCHCH0,CH

T

T

CHCH0,

th

..X.m.dCp).X1.(mreactor

0

0444

reactor

0

44

Q

dTCpmHT ArArT

The best thermochemical efficiency is reached for 50% of CH4 and exceeds 10%


Dynamic modeling of solar reactors


Modeling

Zno decomposition in a solar reactor

Internal Energy U

Inlet Outlet

External Power Qsolar

Solid ZnO + N2

at To Reactor + Reaction at T

O2 + Zn + ZnO + N2

All gas species at T

ZnO (s) Zn (g) + ½ O2 H° = 479 kJ/mol, 2000K Zn (s) + H2O ZnO + H2 H° = -62 kJ/mol, 800K

Charvin at al. Chem. Engng Res. & Des. (2008) 86


Modeling

Mass balance

Unsteady mass balance equation for compound j (j = ZnO, Zn, O2, N2) N2 is added as sweeping and quenching gas

n = mole number F: molar flow rate y: mole fraction ν: stoichiometric coefficient

(For solid ZnO)


Modeling

Heat balance

General form: q + FinHin = FoutHout + dU/dt


Modeling

Results

Size effect

Lab-scale

Ind. scale


Modeling

Results

Chemical Threshold effect

50 MW scale

Effect of pressure


Modeling

Industrial scale 50 MW

Results

Thermal inertia effect


Modeling

Overall process optimization: from heliostats to fuels

Pitz-Paal et al. Solar Energy, 85 (2011)

Heliostat field must be associated with a CPC secondary concentrator to increase the mean concentration ratio.

Optimization procedure

Solar reactor

Heliostat field


Modeling

Expected overall efficiencies: 40% for gasification and 30% for zinc oxide splitting

Overall process optimization: from heliostats to fuels

Solar Facilities for the European Research Area

Welcome in the solar thermochemistry world

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SFERA II 2014-2017, Summer School, June 25-27 2014

introduction to solar reactors - sollab · introduction to solar reactors gilles flamant,...

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