High Flux Solar Simulator and Solar Photo-Thermal Reactor:

Characterization and Design

Saroj Bhatta, Dassou Nagassou, and Juan Pablo Trelles

Department of Mechanical Engineering and Energy Engineering Graduate Program University of Massachusetts Lowell

ASME 2014 8th International Conference on Energy Sustainability Boston, MA, June 30 - July 2, 2014

Motivation: Solar Chemical Synthesis Solar Chemical

Synthesis:

Activation Energy

- Solar for targeted chemical reactions - Value-added products (e.g. solar fuels)

Solar Spectra

•  Water splitting •  Artificial

photosynthesis

artificial leaf 4 water splitting 3

3 http://www.sciencedaily.com/releases/2013/12/131213093310.htm 4 Nocera, D.G., Science 334(6056) (2011) 645-648

Photo-chemical Process

1 Pregger , T., Internat. J. Hydrogen Energy 34 (2009) 4256-4267 2 Chueh, W.C., 6 Sep. 2012, SPIE Newsroom. DOI: 10.1117/2.1201208.004440

Solar Intensity

methane cracking 1

Thermo-chemical Process

redox cycle 2

•  Thermal decomposition

•  Redox cycles

Photo- Thermo-chemical Process

Solar Intensity + Spectra

•  Combines advantages (?) •  New processes (?)

Solar Photo-Thermochemical Processes

•  High temperature, but potentially lower than thermochemical •  Photons on photocatalyst – promotion of molecules to excited

states (e.g. vibrational transitions, electronic excitation)

Reactants + Thermo-catalyst Products Solar Intensity

•  High temperature à high reactivity •  ~ Independent of heat source

Thermo-chemical:

Reactants + Photo-catalyst Products Solar Spectra

•  Low temperature à low throughput •  Depend on solar spectrum (e.g. UV)

Photo-chemical:

Reactants + Products

Solar Intensity + Spectra

Photo-Thermochemical: High-temperature

Photo-catalyst  

Concentrating Solar Plants

a. Parabolic mirror with Stirling engine at Plataforma Solar de Almería , Spain b. Sierra Sun Tower, Lancaster, CA, USA c. CSP plant under the Jawaharlal Nehru National Solar Mission (JNNSM), India

b

a

c

d. University of Minnesota e. MIT f. ETH-Swiss Federal Institute of Technology

Solar Simulators

e

d

f

Ideal for lab R&D: •  Simulate sun using different light source d. Xenon arc, e. Metal halide, f. Argon •  Ellipsoidal reflectors

Solar fields: •  Wide temperature range a. High (>1000o), b. Medium (~600o), c. Low (~400o) •  Mirrors, parabolic reflectors, troughs

Solar Simulator @ UMass Lowell

Spectral Characterization: - 6.5 kW Xenon short arc lamp - 1.5 kW Metal halide lamp - Daylight (clear day, Lowell, MA)

Ø  Xenon arc à better emulation of daylight in visible range

High-Flux Solar Simulator:

- 6.5 [kW] (variable) - Xe short arc Lamp - Magnetic stabilization - Ellipsoidal Reflector - Rectifier 80-170 [A], 110 [V]

Xenon Arc Lamp

Ellipsoidal reflector Anode

end

Horizontal alignment

Anode cable

Housing exit

Xenon Lamp Luminous Intensity Distribution

•  Fills solid angle of 10 steradians •  Small angular section à no luminous flux

Lamp Luminous Emission

•  Lamp + reflector assembly •  Most flux distribution covered by reflector •  Regions with voids expected

Cathode Anode

Electrode gap (7.5 mm)

Ellipsoidal Reflector

Truncated Reflector Enclosure

Ray Tracing Analysis

Assumptions: •  Point source •  Specular reflection •  Perfect alignment of optics

Target at focus: •  All rays are focused at target center

Ray Tracing Analysis Intensity Distribution at Target

As target departs from focus: •  Intensity distribution widens •  Intensity decreases •  Dark center spot start appearing

Dark spot

Stand & Cable shadow

Ray Tracing Analysis Intensity Distribution at Target

Intensity Mapping Procedure

•  Target: Black flat plate with reference points

•  Device: Camera + neutral density filter

•  Position: Focused & aligned with center of intensity field

o  Projective image transformation & processing à Matlab

l2  

Set-up for Intensity Mapping

Simulator  

Camera  with  Neutral  Density  

Filter  

Target  plane  

Bench  

l3  

ϴ l1  

Imaging Steps

Ø  Procedure suitable for In-Field system evaluation e.g. intensity at target from parabolic concentrator

Intensity Distribution

Raw image at focal plane

Image Transformation and Processing

Final processed image

2 cm

Focal Focal + 1.6” Focal + 2.6” Focal - 1.6” Focal - 2.6”

Processed Image at Different Target Planes

0 0.5 1 Relative intensity

Mapped image

Ø  Optical distortion away from focus

Photo-Thermochemical Reactor S-1 Reactor Schematic

S-1 Reactor @ UML

Characteristics: •  Quartz interior (Reactor Integrity) •  Reflective interior (Optical resonance cavity) •  Gas flow <> Solar flux (Counter flow heat exchanger)

•  Solar Flux: (in progress) Max: ~ 3000 [sun] Ave: ~ 300 [sun]

•  Design Operating Temperature ~ 1000 [oC]

input gas

synthesized gas

Reactor Design Rationale Reactor – Simulator Operation:

Temperature distribution

Velocity distribution Ø  Large recirculation à high

gas residence & mixing Ø  No catalyst yet (porous)

catalytic monolith

l3  focal point

input gas

Rationale:

- High residence:

Photons (reflection) &

Gas (recirculation)

- Catalytic Monolith: “Optically-tuned” porosity High temp. photocatalyst

synthesized gas

Experimental Set-up

Cold Line Diagnostics:

•  Spectrometer •  Flow meters •  Pressure gauges •  Thermocouples •  IR Thermometer •  Gas analyzer

Process Schematic Set-Up

Hot Line

Rationale: •  Two gas lines: natural separation high/low temp. •  Extendible, open- and closed- loop operation

Reactor Operation Calibration Run

Radia?on  in  Inlet  

Outlet  

Probe  in  

Reflec1on  Loss  

Ongoing work: Ø  Decomposition of CO2 Ø  Metal foams + photocatalyst coatings Ø  Reactor-scale fluid flow – radiation modeling

Simulator – Reactor Coupling

Loss  

Reflec1on  

Optical Resonance: High optical losses in the

absence of catalytic monolith

Summary and Conclusion

•  Rationale: Solar Photo-Thermochemical Processing à combine advantages of high-temperature reactivity + photo-catalytic activation

•  Simulator Characterization: –  Spectral distribution: Xe vs. metal halide vs. daylight

–  Intensity distribution: Analytical and experimental

•  Photo- Thermo-chemical Reactor Design: Optical resonance + flow recirculation + “Optically-tuned” catalythic monolith à long residence photons & gas

•  Ongoing: CO2 decomposition w. high-temperature photocatalysts

Thank You

Additional

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ES-FuelCell2014-6829: High Flux Solar Simulator and Solar Photo-Thermal Reactor: Characterization and Design Chemical processing using solar energy for chemical synthesis is an appealing alternative to extend the reach of renewable energy utilization and to mitigate environmental emissions. High-flux solar simulators provide the flexibility to evaluate and optimize the design of concentrated solar energy utilization devices under laboratory conditions, before prototyping for in-field testing. The characterization of a 6.5 kW high-flux solar simulator at UMass Lowell is presented. The solar simulator is used for the design and evaluation of a novel reactor design for gas-phase solar photo-thermochemical processing. The high-flux solar simulator operates with a short arc xenon lamp coupled with a truncated ellipsoidal reflector to deliver high flux radiation onto a target. The spectral radiative intensity distribution from the simulator is compared with the intensity distribution from a metal halide lamp and evaluated against solar irradiance for Lowell, MA. Experimental results of intensity distribution over a target plane are contrasted against ray tracing calculations and used for the optimal dimensioning of the optical aperture of the solar photo-thermochemical processing reactor. The interior of the reactor resembles an optical resonant cavity that allows high residence time of solar photons and gas flow to promote gas-phase thermochemical as well as photochemical reactions, while permitting the testing of different catalytic monoliths. Experimental diagnostics of the reactor operation for gas-phase chemical processing are also presented.

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