Coal Syngas Testing at NETL

Energy Systems Dynamics Division

2008 SECA WorkshopAugust 5-7, 2008Randall GemmenKirk GerdesGreg Hacket

National Energy Technology Laboratory

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Goal

Identify the effects of trace coal syngas species on SOFC anodes, and identify the trace material exposure levels

that will be acceptable to fuel cell operation.

At present, no data exist to guide developers on how to design At present, no data exist to guide developers on how to design coal syngas cleanup systems suitable for SOFC operationcoal syngas cleanup systems suitable for SOFC operation

Trace elements:

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Effect of Trace Species on SOFC Anode

• Affect the ability of Ni to promote the electrochemical reactions− Trace species on Ni surface inhibit the adsorption of

H2, CO, or dissociation of H2• Affect the ability of YSZ to transport oxygen ion

− Formation of secondary zirconia phases • Affect the electrical conductivity

− Formation of secondary nickel phases such as nickel-phosphide

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Questions

• What is the variability of trace elements in coal?• What is the effect of different gasification

technology on the potential for anode attack?• Aside from trace metal species, are other

‘contaminants’ (e.g., tars) important to consider?• Is individual contaminant testing representative

of actual coal syngas operation?

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Outline

• Analysis−Assess the contaminants in variety of coals− Identify potential sensitivities of gasification design

on trace species attack• Experimental

− Individual trace specie evaluations−Direct coal syngas testing

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Advanced Coal Based IGFC System

ASU

GasCleaning

air

N2

coal

SOFC Anode

SOFC Cathode

air

Pressurized SOFC Oxy-Comb

HeatRecovery

oxygen

CO2Condenser

CO2 Compressor& dryer

oxy-comb O2

stackgas

expander

expander

Gasification

Water Recycle

compressor

EnhancedOil Recovery

Deep SalineAquifer

UnmineableCoal Beds Depleted Oil & GasReservoirs

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Trace Metal Contaminants(Coal-Type Dependency)

• USGS analysis of trace elements in coals.

• Different coals have different levels of given a given contaminant.

• Data given here shows deviations (from average) approach 140%.

0

10

20

30

40

50

60

70

As Cr Ni Co Sb Pb Cd Zn Be Mn Th UTrace Element

Con

cent

ratio

n in

Coa

l [m

olar

ppm

]

WyodakElkhorn/HazardPittsburghIllinois #6

Ref. USGS, 1998

0%

20%

40%

60%

80%

100%

120%

140%

160%

As Cr Ni Co Sb Pb Cd Zn Be Mn Th U

Trace Contaminant

Stan

dard

Dev

iatio

n [%

of A

vera

ge V

alue

]

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1 ATM/700oC

1 ATM/900oC

1

1—Swartz Pumpe2—Exxon Singapore3—Tampa4—El Dorado5—Fife6—Pernis & KBR7—Valero-Delaware8—Eastman & PSI 9—Sarlux10—ILVA11—Catalytic12--KRW

23

7

8

46

9

10

1 ATM/800oC

5

11

12

Gasification Dependencies

0%

20%

40%

60%

80%

100%

Schw

artz P

umpe

Exxo

n Sing

apor

eTa

mpa

El Do

rado

Fife

Pern

isKB

R

Valer

o-Dela

ware

KRW

Eastm

an PSI

Entra

ined*

Sarlu

xILV

A

Catal

ytic G

asifie

rCum

ulat

ive

Mol

e Pe

rcen

t [%

]

H2

CO2

CO

H2O

N2

CH

4

Ref.: Jones and Schilling (2002) (*Trembly et al., 2007)

0.0%0.2%0.4%0.6%0.8%1.0%1.2%1.4%1.6%1.8%

Catal

ytic

Schw

artz

Fife

ILVA PS

IEn

traine

dSa

rlux

Exxo

nKR

WTa

mpa

El Do

rado

Eastm

anPe

rnis

KBRPe

rcen

t Ni R

eact

ed in

400

Hr [

%]

C(s)

Trembly et al. (2007)

Contaminant Loading from Trembly et al. (2007)

0

0.2

0.4

0.6

0.8

1

1.2

Catal

ytic

Schw

artz

Fife

ILVA PS

IEn

traine

dSa

rlux

Exxo

nKR

WTa

mpa

El Do

rado

Eastm

anPe

rnis

KBR

Frac

tion

Syng

as C

onta

min

ant

Rea

cted

With

Ni [

1]

Sb

P

As

(Warm Gas Cleanup = 400 oC; Cell Temperature = 800 oC; 1atm; FU=const.; 400 Hr Run)

(anode inlet conditions)

(anode inlet conditions)

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Gasification Tars• Gasifier syngas consists of tars in addition to H2, CO, CO2, H2O, char, and volatile trace material.• A typical tar yield is about 3–4%, by weight, of the coal

charged (Menéndez and others, 2000).• Coal tar elemental analysis: 80% C, 6% H, 1% N, 3% S, 10%

O.• Benzene soluble tar components by volume:

− Benzenes (3%), Naphthalenes (15%), Aromatics (12%), Acenaphthenes (12%), Fluorenes (9%), Indenes (5%), Dibenzofurans (6%), Phenylnaphthalenes (7%), Others (31) (Bureau of Mines (1974))

• Tars = All organic components having molecular weight higher than benzene. (Bergman et al. 2002).

• Major factors affecting tar composition are the temperature profile, gasifying agent, partial pressure of hydrogen, the residence time of the coal in the gasifier, and coal structure (Miller et al. 1980).

• Syngas treatment: − Filters and scrubbers− Cool syngas to below 100 to 260 oC to remove tars. (e.g., U.S. Patent 4198212)− Catalytic reaction beds

• Short term exposures (ca. 20 hrs) of Ni/GDC anode to tar from bio-fuel gasifier result in no carbon or fuel cell performance changes. (Hofmann et al. 2008)

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Outline

• Analysis−Assess the contaminants in variety of coals− Identify potential interactions between trace species

and anode across a variety of gasification systems• Experimental

−Perform individual trace specie evaluations• H2Se and Benzene

−Perform direct coal syngas testing

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Methodology to Identify Cleanup Target Levels

• Single trace material testing is used to assess impact of specific species− Attack on active sites at the electrochemical TPB (relatively short time constant)− Attack on SOFC material to generate resistive secondary phase (relatively large time

constant)− Other … ?

0.00

0.03

0.06

0.09

0.12

1.E-05 1.E-03 1.E-01 1.E+01

• Method of attack characterized by V(t) and post test analysis (XRD, SEM, EDS) from test data:− 0.1 ppm, 1 ppm, 10 ppm

• Rates extrapolated to ‘zero-effect’level (continually refined as more data is available!)

• Avoid time and expense required to experimentally show “zero-effect”

Extrapolated range Tested range

hrs

days

mos

yrs

decs

Acceptable degradationZero-effect

Trace Material Concentration PPM

Deg

rada

tion

[%/1

000

hour

s]

http://theodoregray.com/PeriodicTable/Samples/033.5/index.s12.html

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900 °C

700 °C

Experimental Methodology

• Anode supported SOFCs with Ni/YSZ anodes operated between 750-800ºC

• Cells operated with simulated coal syngas containing single trace species of interest

• VI scans and EIS methods used during testing• Post trial SEM, EDS, and XRD used

Ca—Pt Mesh/Paste; An—Ni Mesh/Paste

PermeationTube

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Results: H2Se Testing

SOFC VoltageOperating at 800 °C at 0.25 Acm-2 Over Time with 5 ppm H2Se

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200 250Time [hr]

Cel

l Vol

tage

[V]

Initial H2Conditioning

Start Pure Syngas Injection

Start 5ppm H2Se Injection

Return to H2

Return toPure Syngas

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“Light Tar” Test

No visual carbon was observed on cell after test.No significant carbon was measured via XPS.

0.000

0.200

0.400

0.600

0.800

1.000

1.200

0.0 100.0 200.0 300.0 400.0 500.0 600.0Time (h)

Cel

l Vol

tage

[V] /

Cur

rent

[A]

Condition on 97% H2/H2OStart of Syngas + 150 ppm benzene

SOFC Operation on Direct Syngas

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PSDF Process Flow Diagram

Gas Analysis

MCA Test Rig

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Test RigMulti-cell Array

• Permits parallel operation of 12 button cells

• Divided into 4 channels of 3 cells each• Improves testing method

− Rapid collection of repeat data− Reduces systematic experimental error

• Reduces sources of contamination− Seals− Materials

• Status− Field test started on Mississippi lignite

coal.

2

2

2

4

4

4

5

5

5

2

2

2

4

4

4

5

5

5

2

2

2

4

4

4

5

5

5

2

2

2

4

4

4

5

5

5

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Gas Analysis—Mercury

m/z 195 197 199 201 203 205

25

Hg

m/z 195 197 199 201 203 205

25

Hg

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Gas Analysis—Cadmium

m/z 108 109 110 111 112 113 114 115 116 117 118 119

5000 Cd

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Gas Analysis—Selenium

m/z 75 76 77 78 79 80 81 82 83 84 85 86

50

Se

m/z 75 76 77 78 79 80 81 82 83 84 85 86

50

Se

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Gas Analysis—Phosphorus

Phosphorus

0.E+005.E+061.E+072.E+072.E+073.E+073.E+074.E+074.E+075.E+07

0 20 40 60 80Time [sec]

Cou

nts

per s

econ

d

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Gas Analysis—Mercury

Hg 198-204

0

100

200

300

400

500

600

700

0 50 100 150 200Time [sec]

Cou

nts

per s

econ

d

Hg 198Hg 199Hg 200Hg 201Hg 202Hg 204

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Cell Conditioning on Hydrogen(92% H2/H2O)

Cell 6

0

0.2

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0.8

1

1.2

0.00 20.00 40.00 60.00 80.00Time [hr]

Cel

l Vol

tage

[V]

Cel

l Cur

rent

[am

p]

V

I

Cell 5

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0.00 20.00 40.00 60.00 80.00Time [hr]

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l Vol

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[V]

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l Cur

rent

[am

p]

V

I

Cell 2

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1

1.2

0.00 20.00 40.00 60.00 80.00Time [hr]

Cel

l Vol

tage

[V]

Cel

l Cur

rent

[am

p]

V

I

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Syngas Started

Cell 4 / OCV

0

0.2

0.4

0.6

0.8

1

1.2

0 10 20 30 40Time [hr]

Cel

l Vol

tage

[V]

Cell 6 / 0.05 A/cm2

0

0.2

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0.6

0.8

1

1.2

0 10 20 30 40Time [hr]

Cel

l Vol

tage

[V]

0123456789

0 10 20 30 40Time [hr]

Gas

Flo

w [S

LPM

]

Air

H2 Syngas

•Planned end date for syngas run is mid August.•Post test analysis--Cells will be examined using a variety of micro analytical techniques to assess possible trace material effects.

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Trace Coal Species Summary

• Some variability of trace metals due to coal types—this will need to be accounted for in cleanup design.

• Tars may be present for low temperature gasifiers, but no negative impact has been shown yet—suggest further studies on higher MW compounds.

• Continuing individual coal trace species studies to determine impact on fuel cell performance

• Awaiting completion of SOFC operation on direct syngas to assess actual effect of operating on coal syngas

• Our work and work of other labs will be brought together in the future to give clear cleanup target levels

Programmatic driver: Quantification of cleanup target levels for trace materials

in coal syngas delivered to SOFC

Coal Syngas Testing at NETLGoalEffect of Trace Species on SOFC AnodeQuestionsOutlineAdvanced Coal Based IGFC SystemTrace Metal Contaminants�(Coal-Type Dependency)Gasification DependenciesGasification TarsOutlineMethodology to Identify Cleanup Target LevelsExperimental MethodologyResults: H2Se Testing“Light Tar” TestSOFC Operation on Direct SyngasPSDF Process Flow DiagramTest Rig�Multi-cell ArrayGas Analysis—MercuryGas Analysis—CadmiumGas Analysis—SeleniumGas Analysis—PhosphorusGas Analysis—MercuryCell Conditioning on Hydrogen�(92% H2/H2O)Syngas StartedTrace Coal Species Summary