DEN/VRH/DTEC/SGCS/LGCIDenis ODEGLOBAL 2007 – Boise USA September 9-13 Modeling a filter press electrolyzer By using two coupled codes within nuclear Gen

1/19DEN/VRH/DTEC/SGCS/LGCI Denis ODE GLOBAL 2007 – Boise USA September 9-13

Modeling a filter press electrolyzer By using two coupled codes within nuclear Gen. IV hydrogen production

Jean-Pierre Feraud, Florent Jomard, Denis Ode, Jean Duhamet

Commissariat à l’Énergie Atomique

DEN/DTEC/SGCS/LGCI

Site de Marcoule BP 17171

30207 Bagnols sur Cèze, France

Yves du Terrail Couvat

Laboratoire EPM, Madylam

1340 Rue de la Piscine

Domaine Universitaire

38400 Saint Martin d’Hères, France

Jean-Pierre Caire

LEPMI, ENSEEG

1130 Rue de la Piscine

38402 Saint Martin d’Hères, France

Modeling a filter press electrolyzer by using two coupled codes within nuclear Gen. IV

hydrogen production.

Jacques Morandini

Astek Rhône-Alpes

1 place du Verseau

38130 Echirolles, France



I. Introduction

II. The Westinghouse sulfur cycle

III. Modeling objective

IV. Coupling of physical phenomenawith Fluent® / Flux Expert® codes

V. Electrolyzer modeling, boundary conditions

VI. Software coupling results

VII. Conclusion – Future prospects



Extensive use of energy = hydrogen mass production

High-temperature cycles for hydrogen production

- 100% thermochemical: Bunsen Cycle…

- Hybrid cycle: Westinghouse sulfur cycle, Deacon cycle…

- 100% electrochemical cycle: high-temperature electrolysis of water

I. Introduction

High-temperature hydrogen production technologies could be provided by using:

- Gen. IV nuclear power plants

- Thermal solar facilities…



H2, product½ O2

by-product

II. The Westinghouse sulfur cycle Hybrid Sulfur Process block

H2Ofeed

Westinghouse sulfur Westinghouse sulfur cyclecycle



H2, product½ O2

by-product

II. The Westinghouse sulfur cycle Hybrid Sulfur Process block

H2Ofeed

Thermalenergy

Filter pressElectrolyzer (50 – 100°C)

Concentration

Evaporation

Decomposition

Absorption

300°C

Concentration 300°C

Thermal decomposition 850°C

Evaporation 600°C

Thermalenergy

Thermalenergy

H2O + SO2 + ½ O2 H2SO4

Electrical energy

Compression H2SO4

sideSO2

side

H2S

O4

SO2

Cooling

SO2

H2O

SO2

H2O

SO2

H2O

Absorption25°C



Within the framework of the Westinghouse cycle studies

The aim of our works consists of modeling a filter press electrolyzer

for hydrogen production.

III. Modeling objective

Our studies have to take into account numerous physical interactions:

- electrokinetics (overpotential),

- thermal behavior (Joule effect),

- fluid dynamics (forced convection),

- multiphase flow (electrolyte + bubble plume).

We expect that the virtual filter press design will work as a real one



IV. Coupling of physical phenomena with realizable Fluent® / Flux Expert® codes

( )

( ) 0

( ) ( )p V S S

uu u g

t

ut

Tc u T k T Q Q

t

Physical phenomena:

- Thermohydraulics solved with Fluent®

Navier-Stokes continuity equations

Heat transfer equation

- CFD, Fluent model selected

- so-called “realizable” k-ε turbulence model- two-phase flow description: Euler-Euler - separate phase: disperse phases

Two-phase fluid dynamics



0 =V)(-.

.V-j

IV. Coupling of physical phenomena with Fluent® / Flux Expert® codes

Physical phenomena :

- Electrokinetics solved with Flux-Expert®

Charge balance, Laplace equation

Ohm’s law, primary current distribution (a)

RT

nF

RT

nF

eejj)1(

0

Secondary current distribution, Butler-Volmer Law (b)

Ele

ctr

od

e

Electrolyte

(j)

Pote

nti

al

(V)

Cell width

(a)

Inte

rface

gap

)j(f

j

n

nei

(1)(1)

(2)(2)

(b)

(a)



IV. Coupling of physical phenomena with Fluent® / Flux Expert® codes

Software coupling:

FLUENT® UDF Swap

functions

Main memory

Data files

FEcoupling.c UDF FEcoupling.c

Proprietary operators : prxxxx.F

FLUX

EXPERT®

Main memory

Swap functions

Main memory

Main memory

Fluent®–Flux Expert® coupling flowchart

= message-passing function

Physical phenomena can be solved by using different meshes (structured or unstructured)

Communication between the two codes: simple and robust message-passing library

Algorithms developed are mainly location and interpolation algorithms




The FM01-LC laboratory scale electrolyzer::

0.16m

0.04m

0.013m

H++H2SO4

H2SO4

+ SO2

H2SO4

+ SO2

H2SO4

H2

+-

zx

y

Electrolyzer operating principle

cathode hydrogen release area catholyte membrane anolyte anode




CA

TH

OL

YT

E

CA

TH

OD

E

mem

bran

e

AN

OL

YT

E

AN

OD

E

Overpotential Area

0 V

Y (mm)

Overpotential area

Z (mm)

2000 A.m-2

CA

TH

OL

YT

E

CA

TH

OD

E

me

mb

ran

eA

NO

LY

TE

AN

OD

E

Flux-Expert

Hydrogen bubble velocity: 0.01 m·s-1

Bubble emission angle: 45°

Uniform electrolyte velocity profile

,,k,cp: temperature-dependent

No heat exchange with outsideHydrogen area

160

mm

V = 0.07 m·s-1 T = 323 K

V = 0.07 m·s-1 T = 323 K

CA

TH

OL

YT

E

CA

TH

OD

E

me

mb

ran

e

AN

OL

YT

EA

NO

DE

0 1.5 6.5 6.6 11.2 13 mm

Fluent

Boundary conditions to produce 5 NL·h-1 of hydrogen



1 2 3

VI. Numerical results

Residual continuity u residual sulphuric acid u residual hydrogen v residual sulphuric acid v residual hydrogen w residual sulphuric acid w residual hydrogen T1 residual sulphuric acid

T2 residual hydrogen

K residual sulphuric acid residual sulphuric acid (1–K) residual hydrogen

FLUENT iterations

Code Coupling Behavior

Interaction between the two codes is demonstrated by the convergence of the computational residuals with successive iterations

FLUX-EXPERT iterations



T =323 Kυ = 0.069 m.s-1

T =323 Kυ = 0.069 m.s-10.16 m

0 m


0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

322 324 326

Anolyte Catholyte

Temperature (K)

Height (m) Thermal problem:

Graded color scale

Temp. (K)



3 mm


Cat

holy

te

Cat

hode

H2 (vol.%)

Cat

hode

Ano

de

membrane

Hydrogen plume area approx. 1 mm

Two-phase problem resolution:

Maximum concentration 0.2 mm from cathode

Hydrogen volume fraction < 72%




H2 (vol.%)

Cat

hode

Ano

de

Graded color scale

0

10

20

30

40

50

60

70

80

0.0014 0.0019 0.0024 0.0029 0.0034distance from cathode (m)

hyd

rog

en c

on

cen

trat

ion

(%

)

h_0.15

h_0.08

h_0.01

height = 0.15m

height = 0.08m

height = 0.01m

Two-phase problem resolution:



Anolyte


Fluid dynamic calculation:

Anolyte flow appearance:

Flat (uniform velocity) + wall effect on membrane and anode sides

Characteristic of turbulent flow

Catholyte flow appearance:

Wall effect on membrane side,

Increasing velocity on cathode side (×4)

Characteristic of air lift effect

CatholyteFlow rate (m·s-1)

Membrane



Anodic overpotential = 70% of cell potential

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0 0 0.01 0.01 0.01 0.01 0.01Length (m)

Ele

ctri

cal p

ote

nti

al (

V) 0,73 V

cathodic over potential

0.03 V

anodic over potential

0.47 V

Cell potential: 0.73V

Goal:

improve cell designing to obreach 0.6 V of total potential


Electrokinetics calculation:

Potential (V)V)



Modeling with Flux-Expert / Fluent Codes

Performed with message-passing library

Only 24 h of computing on Pentium IV (Flux Expert) + Core 2 Duo (Fluent) PCs

CFD results

Electrolyte temperature rise: 4°C

Catholyte motion (×4), hydrogen bubbling effect

Electrokinetics calculation

Electrochemical irreversible process taken into account with Flux Expert®

Total cell voltage obtained: 0.73 V (in accordance with published results)

VI. Conclusion – Future prospects



VI. Conclusion – Future prospects

Calculation / Experiments

Experiments required to complete the lack of anodic overpotential law

Check the validity of two-phase flow behavior

Model a stack of cells before scaling up

Optimize the future electrochemical process by designing numerical

experiments

Documents

DEN/VRH/DTEC/SGCS/LGCIDenis ODEGLOBAL 2007 – Boise USA September 9-13 Modeling a filter press electrolyzer By using two coupled codes within nuclear Gen