Solar Driven H2O/CO2 Splitting via Thermochemical Cyclesenergy.columbia.edu/files/2012/11/Diver-Sustainable-Fuels-Conf-5-10.pdfSplitting via Thermochemical Cycles Presented by Richard

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,for the United States Department of Energy’s National Nuclear Security Administration

under contract DE-AC04-94AL85000.

Solar Driven H2O/CO2

Splitting via Thermochemical Cycles

Presented by Richard B. Diver

May 4, 2010

Funding – Sandia Laboratory Directed Research and DevelopmentPrincipal Investigator – James E. MillerProject Manager - Ellen B. StechelSystems Daniel Dedrick, Terry Johnson, Chad Staiger, Greg Evans, Josh Deetz

(student intern,) Christos Maravelias (U-WI), Carlos Henao (student,) Jiyong Kim (PD)

Reactor Solar Reactor - Rich Diver, Nathan Siegel, Tim Moss, D. Ray, John Kelton, Reactive Structures - Nathan Siegel, Terry Garino, Nelson Bell Detailed Reactor Models - Roy Hogan, Ken Chen, Bob Podgurski, Darryl

James (TTU,) Luke Mayer (student)Materials Reactive Materials Characterization & Development - Andrea Ambrosini, Eric

Coker, Mark Rodriguez, Stephanie Livers, Lindsey Evans Bulk Transport & Surface Reactions - Gary Kellogg, Ivan Ermanoski, Taisuke

Ohta, Randy Creighton Thermodynamics & Reaction Kinetics - Mark Allendorf, Tony McDaniel, Chris

Wolverton (Northwestern University), Bryce Meredig (student), Heine Hansen (PD), Al Weimer (CU,) Jon Scheffe (student)

S2P Project Elements and Team

Incorporating CO2 into the Hydrogen Economy captures the benefits of hydrogen while preserving the advantages of the Hydrocarbon Economy.

Vision: Directly apply a solar thermal energy source to effectively reverse combustion and “energize” CO2 and H2O into hydrocarbon form in a process analogous to, but more efficient than, the one that produces bio- and fossil fuels.

Sunshine to Petrol

Energy Input(Reduction)

CO2H2O Fuel

O2

Energy Recovery(Oxidation/combustion)

Sunlight + CO2 + H2O → Fuel + O2

“Beyond Hydrogen”

OV - 4OV - 4

For now and for transportation fuels, liquid hydrocarbons are the “Gold Standard”

OV - 4OV - 4

Hydrocarbons are the Ultimate for Large Scale/Long Term Energy Storage

• Energy Density• Infrastructure• Fueling Rate• Airplanes • Heavy Vehicles• etc.

FuelEnergy per Unit Mass

Energy per Unit Volume

Gasoline 1 1JP-5 0.97 1.1Methanol 0.44 0.51Ethanol 0.61 0.69Liquid H2 (-253°C) 2.6 0.27Metal Hydride 0.046 0.36Methane @ 3000 psi 1.1 0.29H2 gas @ 3000 psi 2.6 0.06Liquid Propane @ 125 psi 1 0.86Methane @ 10000 psi 1.1 0.97H2 gas @ 10000 psi 2.6 0.2Lithium Ion Battery 0.019 0.035

Direct Chemical Routes?

CO + 2H2 → CH3OH → C2H6O(DME) + H2OCapitalize on decades of Synfuel technology, e.g.

Note that WS and CDS are linked by the Water Gas Shift reaction

CO + H2O ↔ CO2 + H2

We are only required to carry out one reaction - WS or CDS

4H2O + energy → 4H2 + 2O2 (water splitting)2CO2 + energy → 2CO + O2 (carbon dioxide splitting)

2CO2 + 4H2O + energy → 2CO + 4H2 + 3O2

Focus on the following critical conversions:

Energy Efficiency (sunlight to fuel) is a key consideration

Nominal Equivalent Land Area Required to Produce 20 mbpd at a given efficiency.

Sunlight to fuel efficiency assuming solar resource equivalent to Albuquerque – 2600 kWh/m2/yr.

U.S. Petroleum consumption - 20 million bbls/day

100% - Delaware10% - NJ + MA

3% - Georgia

0.1% - Western U.S.

Fossil oil ~ 2x1 0- 4

Bioethanol routes currently < 1 %.Photosynthesis < 6% (Theoretical)

Photosynthesis < 0. 5% (actual, large area crops)

Electrochemistry Sets the Standard for Efficiency

PV powered Electrolysis

Electrical (%)

H2

(%)Conversion to

Fuel (%)

Sun to Fuel(%)

Efficiency 10-15 75 40-50(1)

50(2)~ 3-6 (?)

Limiting factors include photon to electric conversion and

unfavorable thermodynamics for the reaction of H2 and CO2.

WGS Reaction of CO2 and H2requires additional energy input.

CO + H2O = CO2 + H2

Temperature (°C)0 200 400 600 800 1000 1200 1400

Equ

ilibriu

m S

toic

hiom

etry

0.0

0.2

0.4

0.6

0.8

1.0 CO2 and H2

CO and H2O

(1) Electrical to Fuel; Mignard and Pritchard Trans IChemE, Part A, September 2006.(2) H2 + utilities to Methanol; Henao, Maravelias, Miller and Kemp, presented @ FOCAPD 2009.

6.2 % Reported

Efficiency, Technology, and Costs

Assumptions: gge = 36 kWh, solar resource = 2600 kWh/m2/yr, favorable financing (5% interest, 30 years)

For capital cost < $5/gge, expenditure can be no more than:$60/m2 for 1% Eff. (solar to fuel)

$600/m2 for 10% Eff. (solar to fuel)Benchmarks:

$60/m2 ≈ $250,000/acrePV module ~ $680/m2

Parabolic dish ~ $300/m2

Current option - PV with 5% solar to fuel

> $11/gge from capital with favorable assumptions

Capital expenditures ($/m2)

1 10 100 1000 10000

Con

tribu

tion

to fu

el c

ost (

$/ga

l)

1

10

0.1%0.5%1%5%10%20%

Accomplishing Unfavorable Reactions via Thermochemical Cycles

A cyclic process with two or more

thermodynamically favorable reactions that net a third desired, but unfavorable, reaction.

Avoids thermal to electrical conversion.

Concentrating solar power allows for

consideration of simple two-step metal oxide

cycles (ultra-high temperatures).

WO analogous to CDO

Temperature500 1000 1500 2000 2500 3000

∆G

(kca

l/mol

)

-20

0

20

40

CO2 = CO + 1/2 O2

AOx = AO(x-1) + 1/2 O2

AO(x-1) + CO2 = AOx + CO

AOx → AO(x-1) + ½O2 (TR)AO(x-1) + CO2 → AOx + CO (CDO)

CO2 → CO + ½O2

The Archetypical Metal Oxide Cycle: Splitting Water with Ferrites

Mechanical complexity

Extreme environment limits lifetime –melting, sintering, volatilization, etc.

Thermodynamics requires reactions be carried out at different

temperatures.

Without Recuperation max efficiency = 36%With Recuperation max efficiency = 76%

8.44 kcal

H2O (g)

H2O (l)

11.12 kcal

1.90 kcal 2.08 kcal

H2

½O2

3FeO

3FeO

16.46 kcal

57.86 kcal

94.36 kcal 118.78 kcal

Fe3O4

Fe3O4 600 K

2300 K

Cycle is equivalent to a heat engine with a metal oxide “working fluid”“Inherent” separation of gaseous

products.High end temperatures of ~1500°C

couple well with “sweet spot” of CSP.FeO

Fe3O4

O2

Heat

H2O

H2

< 1300 °C

> 1300 °CFeO

Fe3O4

O2

Heat

H2O

H2

FeO

Fe3O4

O2

Heat

H2O

H2

FeO

Fe3O4

FeO

Fe3O4

O2

Heat

H2O

H2

< 1300 °C

> 1300 °C

TRWO

Challenges in “Reactorizing” Metal Oxide Thermochemical Cycles

• Achieving Continuous Operation (No wasted sunlight) … While isolating reactions from one another … and using thermal energy efficiently (recuperation).

• Solar/Metal oxide interfaceAggravating Factors

• Coupled heat/mass transfer/reaction• Intermittent resource (unsteady operation)• Limited data• Materials challenges (more later)• Systems challenges (separations, recycle, distributed

resource, balance of plant, etc.)

Counter- Rotating- Ring Receiver/Reactor/Recuperator (CR5)

“Reactorizing a Countercurrent Recuperator”Enabling Attributes:• Continuous flow• Spatial product separation•Thermal Recuperation

Analogous to mechanical heat enginesH2, H2O or CO, CO2

Concentrated solar flux

O2

H2O or CO2 H2O or CO2

O2

x

yx

y

z

Set of Counter-Rotating Rings

Reactive material

Insulation

H2, H2O or CO, CO2

Concentrated solar flux

O2

H2O or CO2 H2O or CO2

O2

x

yx

y

z

Set of Counter-Rotating Rings

Reactive material

Insulation

Concentrated solar flux

O2

H2O or CO2 H2O or CO2

O2

x

yx

y

z

Set of Counter-Rotating Rings

Reactive material

Insulation

O2

H2O or CO2 H2O or CO2

O2

x

y

x

yx

y

z

Set of Counter-Rotating Rings

Reactive material

Insulation

OV - 13

Dish/Stirling is the Base Solar System

• Technology features:– Autonomous operation – High-efficiency

• Stirling engine world-record efficiency (31.25% net solar-to-electric)

– High concentration ratio for high temperature operation

– Size suitable for windowed reactors

Current R&D focus for Dish Stirling is on Deployment, Reliability improvements, and Cost Reduction.•Economy of Scale by Numbering up –not Scaling up•Adjacent technology

Metal Oxide Wish List

• Negative ∆G for both thermal reduction and water oxidation reactions• At reasonable temperatures that couple with energy source• Can compensate by providing work in the form of separation or reduced pressure (will reduce system efficiency)

• High melting/Low volatility• Active over millions of cycles with no intermediate processing• Amenable to Fabrication/integration with engine design concept • Efficient volumetric/mass usage

• High surface area or bulk transport• Can compensate to some extent with recuperation

• Fast kinetics• No physical or chemical degradation with cycling

• Compatible with other materials of construction• Resistant to thermal shocking • Small volumetric changes with T or phase

CR5 Requires Cycle Times ~1 min.

30 g Cobalt ferriteTR ≥ 1350-1400 oC

CO2 Oxidation ≥ 1050-1100 oCCO2/He flow rate: 1 SLPM

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

10950 11150 11350 11550 11750 11950 12150

Time, s

%C

O

950

1000

1050

1100

1150

1200

1250

1300

1350

Mid

plan

e Te

mpe

ratu

re, C

CO concentrationMid-plane temperature

2 minute reactions 1 minute reactions

Water cooled panel

Window retaining clips

Quartz window

Gas inlet port

Ceramic insulation ring

Reactive material assembly

Water cooled panel

Window retaining clips

Quartz window

Gas inlet port

Ceramic insulation ring

Reactive material assembly

Splitting of CO2over Cobalt Ferrite MonolithSmall volume solar reactor

Reaction Kinetics Over Monoliths

Time (min.)0 10 20 30 40

Raw

Rat

e (c

m3 /m

in)

0.00

0.05

0.10

0.15

0.20

1400 °C1350 °C1300 °C1250 °C1100 °C1000 °C

1/T (1/K)

0.0006 0.0007 0.0008 0.0009In

itial

Oxi

datio

n R

ate

(µm

oles

/sec

)e-6

e-5

e-4

e-3

e-2

T (°C)9001100 100012001400

Ea = 21.7 Kcal/mol

Ea = 16.4 Kcal/mol

875 Torr CO2234 Torr H2O875 Torr CO2 (different sample)

Oxidation of 3% Fe2O3 in 8YSZ ("fully soluble")sample weight = 0.812 g

nominal surface area = 6 cm2

CO2 and H2O oxidation: Fe2O3/YSZ, CeZr, CeZr + Catalysts, CeO2

CO2 + 2Fe2+ = CO + (O-2 + 2Fe3+)

Comparison of Families of Materials

Time (minutes)

0 10 20 30 40 50 60R

ate

(cm

3 /min

)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

CeO2 800 °C3% Fe2O3/YSZ 1400 °CCe0.5Zr0.5O2 1400 °C

Time (minutes)

0 5 10 15 20 25 30

Rat

e (c

m3 /m

in)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

CeO2 800 °C3% Fe2O3/YSZ 1400 °CCe0.5Zr0.5O2 1400 °C

Utilization - CO (% of theor.)

Utilization – O2 (% of theor.)

Ea CO2 (kcal/mol)

Ea H2O (kcal/mol)

n [CO2]n

3% Fe2O3/YSZ 49 57 22 16 1-0 Ce0.5Zr0.5O2 8.7 33 30-40 22 0.6

CeO2 6.9 12 11 n.m. 0.75

Benchmarking Kinetics: Defined Flux

heig

ht

spacing

Simple Plates

1: h=s (2)2: h=4s (8)

3r3r

height

Vertical Pins

3: h=20r (14.3)A.R. = 10

4: h=40r (28.2)A.R. = 20

CO2 → CO + ½ O2Flux = 0.017 kW/cm2

Surface Area / Projected Surface Area0 10 20 30 40

Req

uire

d R

eact

ion

Rat

e (µ

mol

es/s

ec-c

m2 )

0.01

0.1

1

10

1 2 3 4

1%5%10%15%20%

Thermal to ChemicalEfficiency

CO2 + CeO2-x = CO + CeO2-x+δ (800 °C)

1000 °C*

CR5 Prototype Under Development

National Solar Thermal Test Facility

CR5 Prototype Test System

• Flow control challenging

– Need to avoid crossover between reactors

– ΔP between reactors extremely small (few Pa)

– O2 vacuum pump flow based on flow measurements, not differential pressure

CR5 Reactive Materials Are Challenging

• Robocast cobalt ferrite reactant spalled in first test (5/14/09)

– Poor solar penetration– Stress risers along thermal

gradients– Robocast design leaves no

room for failure (jams drive)• New “fin” design attempts to

addresses issues (10/15/09)– Good solar penetration– No stress risers (notches)– Failure less likely to bind rings– Thermal stresses/shock still

result in failures

CR5 Prototype Testing Ferrite/Thin Plate Geometry

• Temperatures controlled• No issues with quartz

window/cavity

October 15, 2009

0

200

400

600

800

1000

1200

1400

1600

0 500 1000 1500 2000 2500 3000 3500 4000

Time, sec

Tem

pera

ture

, C

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

Attn

uato

r Fra

ctio

n, D

NI,

kW/m

2 , RPM

Attenuator

DNI

TR Temp

Oxidation Temp

Window Temp

RPM

(a)

CR5 Prototype Testing Ferrite/Thin Plate Geometry

• CO2 splitting demonstrated• Continuous operation

• Separation of product CO and O2

0.00

5.00

10.00

15.00

20.00

25.00

0 500 1000 1500 2000 2500 3000 3500 4000Time, sec

Flow

, lit/

min

0.001

0.010

0.100

1.000

10.000

Con

cent

ratio

n, %

O2 Conc.

CO Pump Flow

CO Conc.

Ar Injector Flow

CO Injector Flow

Internal Purge FlowO2 Pump Flow

(b)

Thermochemical Cycles Are Heat Engines

• CR5 is analogous to conventional engines

– Converts high temperature thermal energy to work

– Operating temperatures & irreversibilities of internal processes are key to high efficiency

• Operation of CR5 prototype has power/efficiency tradeoffs

– Similar to conventional engines

– Thermochemical analogs to power and torque

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8Speed, RPM

Effic

ienc

y

0

1

2

3

4

5

6

7

8

Qso

lar,

kW

Reaction Extent

0.050.030.030.05

0.02 0.02

0.01

0.01

TTR = 1800 KTWO = 1000 KP = 0.2 atm

Reaction Extent

0

100

200

300

400

500

600

700

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8Speed, RPM

H2 P

rodu

ctio

n, li

t/hr

0.03

0.05

0.02

0.01

Reaction Extent

TTR = 1800 KTWO = 1000 KP = 0.2 atm

Baseline System Architecture Produces 10,000 kg/hr MeOH

Distributed CO2 splitting Centralized liquid fuels production

17,622 CR5/dishes

Economics: 30 year amortization with 15% interest

Capital associated with CO2 splitting is the major cost component

Current market price of methanol: $0.56/kg ($0.09/kW-hr)

Cost of methanol from baseline system: $1.75/kg ($0.25/kW-hr)4.8 kg/gallon

1.120

0.294

0.050

0.029

0.069 0.189

CR5 system

Separation system

WGS system

MS system

Raw material

Indirect capital cost and others

Total S2P costs per year: Total contribution of each S2P component:

Assumes: BOP electricity and steam are bought at market values30 year amortization with 15% interest

Summary

• Solar Fuels encompass more than biology.

• Efficiency is key for scalability (avoiding resource limits) and cost.– Sunlight is the high cost feedstock (capital to capture)– Adjacency to other technologies offers benefits

• Thermochemical approaches have great promise.– Potential for high efficiency– Field is rapidly advancing

• Advances are needed in materials– Chemical challenges: higher rates, better utilization– Physical challenges: high surface area, inert, low volatility,

resistant to thermal shock