WP2 – LAB-SCALE: INFLUENCE OF

POLLUTANTS ON SOFC ANODES, FUEL

PROCESSING REACTIONS, AND GAS

CLEANING

D2.4 EFFECT OF POLLUTANTS ON

SHORT STACKS. SCIENTIFIC ADVANCES

IN POISONING MECHANISMS

SOFCOM – M24

Politecnico di Torino

1

Roadmap for TOFC short-stack testing

2 Politecnico di Torino – M24 SOFCOM meeting

Test ID Description Max. contaminant

concentration Test Status Stack # Post-mortem

0 (baseline) To investigate the threshold level

of tolerance to H2S 3 ppm COMPLETED by TOFC 0 n.a.

1a To investigate the threshold level

of tolerance to C2H4 1,000 ppm COMPLETED by POLITO 1

No carbon observed. Report

included in D2.3.

1b To investigate the threshold level

of tolerance to COS 200 ppb COMPLETED by POLITO 1

S traces observed. Report

included in D2.3.

2a To investigate the threshold level

1 ppm COMPLETED by POLITO 2 No Cl effects observed. Report to

be delivered to POLITO. of tolerance to C2Cl4

x To investigate the threshold level

of tolerance to HCl 5 ppm

Failed due to compressor

failure / water injection in the

cathode side

3 Waiting for TOFC report.

2b To investigate the threshold level

of tolerance to HCl 5 ppm COMPLETED by POLITO 4 POST-MORTEM required

3 To investigate the threshold level

of tolerance to D4 1 ppm Test will start in Oct. 2013 5

4 Combined effect of H2S and D5 3 ppm H2S, D5 at the

threshold level

Stack to be delivered by

Nov. 2013 6

5 Combined effect of H2S and C2Cl4 3 ppm H2S, C2Cl4 at the

threshold level

Stack to be delivered by

Nov. 2013 7

6 Combined effect of H2S and C2H4 3 ppm H2S, C2H4 at the

threshold level

Stack to be delivered by Jan.

2014 8

7 Combined effect of D5 and C2Cl4 D5, C2Cl4 at the threshold

levels

Stack to be delivered by Jan.

2014 9

8 Combined effect of D5 and C2H4 D5, C2H4 at the threshold

levels

Stack to be delivered by

Mar. 2014 10

9 Combined effect of C2H4 and C2Cl4 C2H4, C2Cl4 at the

threshold levels

Stack to be delivered by

Mar. 2014 11

10 Combined effect of D5, C2Cl4 and C2H4 D5, C2H4, C2Cl4 at the

threshold levels

Stack to be delivered by May

2014 12

Sulfur compounds

3 Politecnico di Torino – M24 SOFCOM meeting

On an H2S-equivalent basis, less than 70 ppm(v) are

found on average in the biogas stream (in-situ

abatement with iron-salts within the digester is

carried out).

Chlorine compounds

4 Politecnico di Torino – M24 SOFCOM meeting

Both inorganic and organic (halocarbons) chlorine compounds are found in sewage

biogas.

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

M1 M2 M3 M4 M5 M6 M7

Con

cen

trati

on

mg/n

m3

HCl HF HBr C2Cl4 C2H2Cl2

HCl (~0.6 ppm)

Siloxanes

5 Politecnico di Torino – M24 SOFCOM meeting

0

5

10

15

20

M1 M2 M3 M4 M5 M6 M7

Co

nce

ntr

ati

on

mg/N

m3

D3 D4 D5 L2

L3 L4 L5 TMSSiloxanes are the most dangerous

compounds, regardless the prime

power involved (engine, turbine or

HTFC).

C6H18O3Si3 (D3) Hexamethylcyclotrisiloxane

C8H24O4Si4 (D4) Octamethylcyclotetrasiloxane

C10H30O5Si5 (D5) Decamethylcyclopentasiloxane

C6H18OSi2 (L2) Hexamethyldisiloxane

C8H24O2Si3 (L3) Octamethyltrisiloxane

C10H30O3Si4 (L4) Decamethyltetrasiloxane

C12H36O4Si5 (L5) Dodecamethylpentasiloxane

C3H10OSi (TMS) Trimethylsilanol

Gas analysis with monthly monitoring

D5 (~1.1 ppm)

Impact of C2Cl4 on stack performance

6 Politecnico di Torino – M24 SOFCOM meeting

0,7

0,72

0,74

0,76

0,78

0,8

0,82

0,84

8,00

8,20

8,40

8,60

8,80

9,00

9,20

9,40

9,60

9,80

10,00

0 50 100 150 200 250 300 350 400 450 500 550 600

Cel

l v

olt

ag

e (V

)

Sta

ck v

olt

ag

e (V

)

Elapsed time (hr)

Vstack V1 V3 V5 V7 V9 V11

C2Cl4 ~ 160 ppb

V1

V3

V5

V7

V9

V11

VSTACK

C2Cl4 ~ 500 ppb C2Cl4 ~ 1000 ppb Clean syngas

25 A, FU = 65% 20 A, FU = 60%

Impact of HCl on stack performance

8 Politecnico di Torino – M24 SOFCOM meeting

Stabilization phase: >400 hr (!).

9 Politecnico di Torino – M24 SOFCOM meeting

Impact of HCl: 0.5 – 5.0 ppm(v)

10 Politecnico di Torino – M24 SOFCOM meeting

Effect of HCl 0.5 ppm(v) at different FUs

11 Politecnico di Torino – M24 SOFCOM meeting

HCl conversion inside the stack

12 Politecnico di Torino – M24 SOFCOM meeting

y = 0,9642x - 3,4391

R² = 0,9966

0

20

40

60

80

100

120

140

160

180

200

0 20 40 60 80 100 120 140 160 180 200

HC

l st

ack

ou

t (p

pm

v)

HCl stack in (ppmv)

HCl

Impact of sulfur on single cell performance

13 Politecnico di Torino – M24 SOFCOM meeting

y = 47,699Qs - 36,965

R² = 0,9908

0

1

2

3

4

5

6

7

0,00 0,20 0,40 0,60 0,80 1,00

Cel

l p

erfo

rma

nce

dro

p (

%)

Sulfur coverage (Qs)

Q

2

55 ln1017.41053.945.1pH

SpHTT S

s

y = 51,159Qs - 38,986

R² = 0,9826

0,0

1,0

2,0

3,0

4,0

5,0

6,0

0,00 0,20 0,40 0,60 0,80 1,00

Cel

l p

erfo

rma

nce

dro

p (

%)

Sulfur coverage (Qs)

Performance drop vs Sulfur coverage

2 different commercial Ni-SOFC anode-

supported cells were tested at 700-750 °C,

showing consistent trends in term of

‘performance drop vs. sulfur coverage (ƟS)’

H2S dissociative chemisorption on Ni-

SOFC anode is best described by a Temkin-

like isotherm (Hansen, 2006).

The performance drop is linearly dependent

with S-coverage of the anode electrode

Active sites (TPB) are blocked.

14 Politecnico di Torino – M24 SOFCOM meeting

715

720

725

730

735

740

745

750

755

760

0 50 100 150 200 250 300

Cel

l V

olt

age

(mV

)

Elapsed time (h)

H2S

0,84ppmv

H2S

0ppmv

H2S

0ppmvH2S

0ppmvH2S

0ppmv H2S

0ppmv H2S

0ppmv H2S

0ppmv

H2S

0ppmv

H2S

0,89ppmvH2S

1,29ppmv

H2S

1,69ppmv H2S

2,44ppmv

H2S

4,04ppmv

H2S

5,44ppmvH2S

6,40ppmv

The effect of sulfur (H2S) up to 6.4 ppm(v) on a commercial Ni anode supported cell: full

performance recovery is not achieved after sulfur removal.

Impact of sulfur on single cell performance

15 Politecnico di Torino – M24 SOFCOM meeting

y = 0,0047x + 0,9427

R² = 0,9245y = 0,7454x + 0,6006

R² = 0,968

0

1

2

3

4

5

6

7

1 10 100 1000

Per

form

an

ce d

rop

(%

)

Gas concentration (ppm(v))

H2SHCl

15

At low concentrations (i.e.,

below 10-20 ppm), Cl-coverage

of the Ni anode seems to follow

a different kinetics than S.

A marked irreversible

performance drop is observed

when HCl > ~20 ppm.

At low p(Cl) in the anode

stream, the performance loss is

almost negligible.

680

685

690

695

700

705

710

715

720

725

730

0 50 100 150 200 250

Cel

l V

olt

ag

e (m

V)

Elapsed time (h)

HCl

1ppmv HCl

5ppmv

HCl

11,1ppmv

HCl

20,1ppmvHCl

40,3ppmvHCl

80,1ppmv

HCl

200,1ppmv

HCl

500,2ppmv

HCl

1000,3ppmv

HCl

0ppmvHCl

0ppmv HCl

0ppmv HCl

0ppmv

HCl

0ppmv

HCl

0ppmv

HCl

0ppmvHCl

0ppmv

Impact of D4 (siloxane) on single cell performance

16 Politecnico di Torino – M24 SOFCOM meeting

- Biogas reformate (SOFCOM composition) - D4 concentration from 50 ppb(v) up to 1 ppm(v)

- Unsealed ceramic housing configuration (limitations on max. FU)

Impact of D4 (siloxane) on single cell performance

17 Politecnico di Torino – M24 SOFCOM meeting

500

600

700

800

900

1.000

1.100

0,00 0,10 0,20 0,30 0,40 0,50 0,60

Volt

age

(mV

)

Current density (Acm-2)

H2 - 30h sofcom mix - 46h H2 - 498h sofcom mix - 499h

-14,37%

-14,12%

Impact of D4 (siloxane) on single cell performance

18 Politecnico di Torino – M24 SOFCOM meeting

500

550

600

650

700

750

800

850

900

950

1.000

150 200 250 300 350 400 450 500

Volt

age

(mV

)

Elapsed Time (h)

syngas D4

0ppbvD4

111ppbv

D4

193ppbv

D4

470ppbvD4

943ppbv

D4

1447ppbvD4

1923ppbv

syngas D4

0ppbv