Direct Energy Conversion by Proton- Conducting Ceramic

1

Direct Energy Conversion by Proton-Conducting Ceramic Fuel Cell Supplied

with CH4 and H2O at 600 – 800oC

Department of Applied Quantum Physics and Nuclear EngineeringKyushu University

S. Fukada, S. Suemori, K. Onoda

HTTR-WS, JAERI-Oarai, Oct. 7, 2005

2


3

Hydrogen production

• Thermo-chemical reaction of water• Electrolysis of water• Hydrogen production from natural gas or oil1. Partial oxidation reaction

2CH4 + O2 = 2CO + 4H22. Steam reforming reaction

CH4 + H2O = CO + 3H23. Direct decomposition

CH4 = C + 2H2


4

Energy balance from CH4 to electricityCH4 1mole

Burning CH4+2O2=2H2O+CO2

O2

〜

110Wh electric power

Steam reforming CH4+2H2O = 4H2+CO2

H2

O2

O2 H2

〜

Hydrogen turbineFuel cell

106Wh electric power

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5

Advantages of ceramic fuel cell operated at high temperature

• Direct energy conversion supplied with CH4 and H2O.• Endothermic heat can be converted to electricity directly.• It can work even when CH4 is supplied.• The temperature condition is almost the same with HTGR.• The use of Ni can decrease the cost of electrodes.

Ni electrode

CH4

CO2 H2O

electron

proton

CO

hydrogen

SrCe0.95Yb0.05O3-x

To external circuit

(1)

(2) (3)Ni wire

(4)Deposited Carbon

Fig. 2 Mass and charge transfer on proton-conducting ceramics cell


6

The purpose of the present study

H2 production using HTGR heat and high-temperature H2 usage system

HTGR800 - 900℃

H2 production

Heat exchanger Heat exchanger

Heat inputHeat pump systemHeat pump system

HH22 StorageStorage

H2

600℃

H2 Supply Alloy

Heat outputH2 purification

ceramic FC

A

Thermochemical water dissociation

Steam reforming or partial oxidation

Alloy

• Feasibility of ceramic fuel cell is studied to investigate direct energy transformation at operation conditions of HTTR.

• Comparison of overall proton conductivity of ceramic fuel cell• Whether carbon deposition can affect the fuel cell performance

or not.


7

Ceramic fuel cell without CH4 reformer

CH4+H2O|Ni|SrCe0.95Yb0.05O3-a|NiO|O2+H2O

Cathode

Anode

Glass GasketGlass Gasket

SrCe 0.95 Yb0.05 O3-aSrCe 0.95Yb 0.05O3-a

Ni electrodeNi electrode

O2+Ar INO2+Ar IN

CH 4 +H 2O INCH 4 +H2O IN

Gas OUTGas OUT

Gas OUTGas OUT

Ni wireNi wire


8

Ni/SiO2 catalyst• Fine Ni particles disperse• SiO2 support material

Fig. 1 SEM photo of Ni/SiO2 catalyst before use

NiO 67.70%SiO2 24.30%CuO 2.85%Al2O3 2.04%Cr2O3 1.91%Fe2O3 0.425Co2O3 0.36%K2O 0.31%MnO 0.10%

X-ray fluorescence analysis


9

I-V curves for SrCe0.95Yb0.05O3-a ceramic

Cell potential, E, can be expressed by a linear curve of E=E0-Id/σΑ.EMF, E0, was correlated by the Nernst equation.


10

EMF of ceramic fuel cell supplied with CH4

• Nernst equation

E0 =−ΔGH2O

2F−

RgT2F

lnpH2O,cathode

pH2,anodepO2,cathode0.5

⎛

⎝ ⎜ ⎜

⎞

⎠⎟⎟

H2 + (1/2)O2 = H2O + ΔGH2O

EMF versus H2O vapor pressure at anode


11

Proton conductivity of SrCe0.95Yb0.05O3-a

PEM-FC

Other proton-conducting ceramics

Oxygen-conducting ceramics


12

SEM photo and deposition of carbon in porous Ni electrode

Carbon deposition profile

(A) (B) (C)0

5

10

15

20

25

(C) Electrode-Electrolyte interface(B) Electrode internal(A) Electrode surface

Position

Car

bon

amou

nt [A

tm%

]

Depsited Carbon

Direct decomposition might occurred at the interface between electrode and electrolyte.

CH4 + H2O = CO + 3H2

CH4 = C + 2H2.


13

Estimation of ceramic fuel cell surfaces

For electricity conversion• Current density of 1mA/cm2 corresponds to 1.2x10-6Nm3-H2/m2s.• SrCe0.95Yb0.05O3-a of 8.6x105m2 can produce 1Nm3-H2 /s.

For tritium reprocessing• Current density of 1mA/cm2 corresponds to 11MBq/cm2s.• SrCe0.95Yb0.05O3-a of 5.7m2 can process tritium production rate of

0.63TBq/s (to maintain 1GW fusion power).


14

H2 permeable membrane tube supplied with CH4

Methods to produce H2 from CH4

• Water-reforming• Partial oxidationReaction mechanism

CH4 +12

O2 = CO + 2H2

CH4 + 2O2 → CO2 + 2H2O → 4 CO + 2H2( )3CH4Prettre(1946)

CH4 → C + 4H* → CO + 2H2

(1/2)O2

Complete oxidation

reformingHickman(1993)

Direct catalytic oxidation of CH4

Overall reaction (Texaco method)No catalyst, no need to supply heat 1300oC

use catalyst, 700oC

Two-step reaction of CH4

CH4+O2 H2, CO, H2O, CO2, CH4, O2

Catalyst bed

CH4 + H2O = CO + 3H2Need catalyst, need to supply heat, 800oC

Study effects of flow rate, CHStudy effects of flow rate, CH44/O/O22 ratio and temperature on conversion ratioratio and temperature on conversion ratio


15

Permeable-membrane reactor

Experimental apparatus for CH4-O2 or CH4 decomposition

・ CH4 gas cylinder・ O2 gas cylinder・ H2 gas cylinder・ Ar gas cylinder・ mass flow controller・ pressure gauge・ thermocouple・ electric furnace・ molecular sieve 3A・ gas chromatograph・ flow meter・ needle valve・ Ni tube・Ni catalyst

・・

・

・

VENT

・・・

・

・

VENT

VENT

・

・・

・

・

・・

・

CH4+O2

Ar


16

ΔG values of CH4 oxidation

Material balance of C, H, O

CH4 +12

O2 = CO + 2H2

CH 4 + 2O2 = CO2 + 2 H2 OCH4 + H2O = CO + 3H2

CH4 + CO2 = 2CO + 2H2

CO + H2O = CO2 + H2

CO +12

O2 = CO2

H2 +12

O2 = H2O

up CH4in = v pCO

out + pCO 2out + pCH4

out( )4 upCH 4

in = v 2 pH 2out + 2 pH 2O

out + 4 pCH4out( )

2upO2in = v 2 pCO2

out + pCOout +2 pO2

out + pH 2Oout( )

pCH4

in + pO2

in = pin

pCH4

out + pO2

out + pH 2

out + pH2Oout + pCO2

out + pCOout = pout

p out = pin + ΔP

CH4+O2H2, CO, H2O,

CO2, CH4, O2

Catalyst bed

、

η =vx

H2

out

2uxCH 4

in

conversion ratioFig. 3

(1)

(2)

u v

(3)(4)

(5)

(6)

(7)

H2 mole in product2CH4 mole in feed

=


17

Hydrogen permeability through Ni and comparison with Pd


18

Effects of temperature and contact time on outlet concentration

• CH4-to-H2 conversion was almost independent of contact time• T < 900K : CH4 → H2O and CO2

• T > 900K : CH4 → H2 and CO

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

x iout (i

=H2,

CO

2, C

O, C

H4,

O2,

H2O

)

12001000800600400

Temperature [K]

exp. cal.H2 CO CH4 O2 CO2 H2O

H2

CO

CH4

H2O

CO2

O2

xCH4

in=0.67, xO2

in=0.33, W=0.6sec-1

Fig. 4 Fig. 5

Inlet conditionInlet condition

Inlet conditionInlet condition

Conversion is very fast


19

Fig. 8 CH4-to-H2 conversion ratio and CO selectivity as a function of total inlet pressure

Fig. 7 Fraction of permeated amount to H2 amount produced in Ni tube

Dependence of H2 permeation rate and CO selectivity on H2 pressure


20

Fig. 6 Variations of reaction rate constant with reciprocal of temperature

r1, f = k1, f pCH4pO2

r2, f = k2, f pCH4pH2O

r3, f = k3, f pCH4pCO2

r1, b =k1, f pCO2

pH2O2

K1

r2, b =k2, f pCO pH2

3

K 2

r3, b =k3, b pCO

2 pH2

2

K 3

Rate constant for CH4 reformation determined by Ni tube reactorHTTR-WS, JAERI-Oarai, Oct. 7, 2005

21

Reaction mechanism proposed

CO2CO

O

H2O

Ni particle

Support material

H2O

CH4

CH2

CO

H

Ni particle

CH4

Support material

C

High temperatureHigh temperature

CHCH44 rich conditionrich condition

Low temperatureLow temperature

OO22 rich conditionrich condition

CO2

O2

O2H2O

H

Reactant

product


(Prettre & Hickman) (Prettre)

22

conclusions

• SrCe0.95Yb0.05O3-a ceramic could work as a fuel cell even without any external CH4 converter.

• Only the steam-reforming reaction occurred on the surface of Ni electrode under proper CH4/H2O concentration ratio.

• Some CH4 decomposed to H2 at the interface of Ni electrode and ceramic, because of high proton conductivity and comparatively low CH4-to-H2 conversion.

• The rate-determining step was CH4 reformation reaction on anode electrode.

• The proton conductivity was independent of H2O vapor pressure.


23

Integrated hydrogen usage at higher temperature proposed here

• To utilize H2 with less heat loss while maintaining high temperature flow from HTGR• Each subsystems (production, purification of H2, heat pump and FC) to raise H2 usage were

experimented from a view of chemical engineering field.

Figure 1. H2 production using HTGR heat and high-temperature H2 usage system

HTGR800 - 900℃TH

TL

H2 production

Heat exchanger Heat exchanger

Heat input

Thermochemical water dissociation

Steam reforming or partial oxidation

Proposed hereProposed here

TM

Heat pump systemHeat pump systemHH22 StorageStorage

H2

H2, CO, CO2 600℃

H2 Supply

Alloy

Alloy

Heat output

H2 purification

Oxide FC

A


24

Heat pump cycle operating at higher temperature proposed here

• Heat pump of LaNi5, TiMn1.5 or their derivative alloys were operated at room temperature

• ZrV2 has one of the largest ΔH among all alloys. • H2 equilibrium pressure of Zr(V1-xFex)2 depends on x.• Two types Zr(V1-xFex)2 alloys are selected.• PCT curves were presented in JAC, 375 (2004) 305JAC, 375 (2004) 305

1/TM1/TH 1/TL

H2

H2

Log

P

Ma→ MaHX MbHX→ Mb

heat supply

heat supply

heat extract

heat extract

昇温ヒートポンプサイクル作動図

MaHX→ Ma

Mb→ MbHX

10-10

10-8

10-6

10-4

10-2

100

102

p H2 [a

tom

]

1.00.80.60.40.20.0

x [Zr(V1-XFeX)2]

-250

-200

-150

-100

-50

0

Enth

aly

chan

ge [k

J/m

ol]

pH2

ΔH

HTGR

H2 production plantH2

600oC(power generation)

900℃900oC(He gas coolant)

Chemical heat pump

TM

TL

H2TM

600oC

250oC〜

TH

②

①

③

④MbH2=Mb+H2

Fig. 7 Heat pump cycle diagram

Ma+H2=MaH2

Fig. 6 Heat pump cycle and High-Temperature Gas-cooled nuclear Reactor

Fig. 8 Relation between pH2 and x in Zr(V1-XFeX)


25

Experiment of hydrogen storage at higher temperature

• Dual-concentric-tube vessel with an inner porous tube and an outer insulated tube• Hydrogen permeates through in the one-dimension direction and is absorbed.• Temperature rise are determined using 6 thermocouples inserted in the vessel.• ZrV1.9Fe0.1 can absorb H2 at 600 oC and shows even temperature rise

C-A thermocouple

φ 38mm

ZrV1.9Fe0.1

Internal heaterH2 gas inlet

160mm

Heat insulator

Inner porous tube

Outer tubeφ 140mm

Fig. 9 Experimental apparatus for hydrogen storage at higher temperature

Fig. 10 Temperature jump after 600 oC H2 supply to ZrV1.9Fe0.1 bed


26

Analysis of temperature variations with time in ZeV1.9Fe0.1 bed2.0

1.5

1.0

0.5

0.0

(T-T

0)/T

0 [-]

1.00.80.60.40.20.0qm/q0 [-]

experiment calculationT0=294K

T0=374K

T0=523K

T0=621K

W=7.5L(NTP)/minz=100mm, r=38mm

500

400

300

200

100

0

T max

-T0 [

-]

900800700600500400300

T0 [K]

2.5

2.0

1.5

1.0

0.5

0.0

q 0 [H

/ZrV

1.9F

e 0.1]

Key Flow rate 1.5L/min 3.5L/min 5 L/min 7.5L/min 10 L/min q0 (from PCT curve)

Fig. 11 Variations of temperature with time Fig. 12 Temperature rise for different flow rates

1 − ε( )ρScS∂T∂t

+ ερgcp,g∂T∂t

+ ∇ ρgcp,gTv( )= ∇ λe∇T( )+ Q

dxdt

=3DH MS

ρSr02(RgT )0.5

pH2

0.5 − pH2 ,eq0.5

(1 − x)−1 / 3 −1

v = −KDarcy

μ∇p

ε∂ρg

∂t+ ∇ ρgv( )= −φ

Heat balance

Absorption rate H2 balance

Darcy’s permeation rule


27

Hydrogen supply and recovery at 700 oC

Fig. 13 Variations of absorption flow rate and pressure with time after H2 introduction

Fig. 14 Variations of desorption flow rate with time

100

80

60

40

20

0

H2 e

volu

tion

rate

[cm

3 /s]

0.100.080.060.040.020.00

Temperature increase rate [K/s]

Fig. 15 H2 desorption rate as a function of temperature increase rate

Flow meter Absorption or desorption

ZrV1.9Fe0.1 bed

t.c.

Internal heater


100

80

60

40

20

0

Hyd

roge

n ev

olut

ion

rate

[cm

3 (NTP

)/sec

]

1000080006000400020000

Time [sec]

500

400

300

200

100

0

Tem

pera

ture

[o C

]

Documents

Direct Energy Conversion by Proton- Conducting Ceramic