Air Pre-heater Corrosion Behavior Related to Halogens for Oxy-coal Retrofit of Utility Boilers

Oxyfuel Combustion Conference 3Ponferrada, Spain

September 9-13, 2013

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Concerns Regarding Bromine and APH Corrosion

• Brominated activated carbon injection (Br-ACI) can accelerate APH corrosion rates– Supplier-dependent impacts have been noted– Low temps in APH suspected to exacerbate problem

• EPRI/URS boiler bromide addition study [Dombrowski, 2013]– 18 units with > 1yr operation had conducted

inspections– 7 of these units noted accelerated corrosion– Increased corrosion in PRB/lignite units has been

particularly severe

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Possible APH Corrosion Mechanisms • Possible Mechanisms:

– Direct condensation of HBr– Absorption of HBr by condensed SO3– Adsorption of HBr by flyash or ACI– Gas-phase attack by HBr

• Condensation appears likely– Hydrobromic acid is one of the strongest mineral acids

known – Simple calculations for relevant concentrations of bromine

addition indicate dew points in the 90-105 °F range– Dew points for oxy-combustion as high as 150 °F

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EN Corrosion Monitoring

• Advantages– Sensitivity– Instantaneous

response allowing real time measurement

– Direct indication of corrosion

– Quantitative measurement

– Response can be related to corrosion mechanism

Control BoxProbe Hardware

Data Acquisition

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Quantitative Validation

0

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18

0 1 2 3 4 5 6 7 8 9 10

Profilometry Corrosion Depth (micron)

ENC

R C

orro

sion

Dep

th (m

icro

n)

F5

F7

LLL

L

L- Laboratory test in 100 MBtu/hr furnaceF5- Field test in 680 MW Coal-fired Boiler (5th floor)F7 - Field test in 680 MW Coal-fired Boiler (7th floor)

Profilometry

CFD Modeling

Corrosion Resistant Borders

Corroded Carbon Steel Sensor Element

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Pilot-scale Corrosion Measurements

Objective:• Measure changes in corrosion rates at temperatures

representative of an air heater,• In the presence of various mercury control additives

(baseline, bromine, activated carbon),• Under both air-fired and oxy-fired conditions

Method:• Use air cooled corrosion probes positioned in the flue gas

just upstream of the baghouse• Vary probe cooling to control element surface temperature in

a range considered representative of air heater temperatures, especially the colder extremes

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Previous Work (OCC2)

Oxy-combustion under possible retrofit conditions affects both waterwall (slight decrease) and superheat (significant increase) corrosion rates

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Complementary Pilot-Scale Measurements

• Objective - Measure impact of oxy-combustion on performance of mercury control technologies

• Approach– L1500 pilot-scale furnace– PRB and bituminous coals– Air and oxy-firing– Two Hg control technologies

• Bromine boiler additive (CaBr2)• Activated carbon injection

– Hg measured before and after baghouse– Three different Hg measurement techniques– Testing in May and June 2013

Ohio LumexCEM

Tekran CEM

30B Metering Box

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Operating Conditions

Br addition:Solid CaBr2 injected immediately before coal entered burner(~8-75 ppm Br wet on coal)

ACI:Darco Hg injected through first port following convective section(~0.5-10 lb/MMacf)

Sample Locations:Gas-phase Hg (& O2)HgP

FG Species

Coal Condition Firing Rate(kW)

O2(%, dry)

CO2(%, dry)

BH inlet(F)

BH outlet(F)

PRB Air-Fired 780-860 4.0 14 380 250

PRB Oxy-Fired 780 3.5 83 300 140

Bituminous Air-Fired 775-1025 3.5 15 356 239

Bituminous Oxy-Fired 775-880 3.4 87 341 146

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Black Thunder PRB

Coal Analyses Mineral Matter Analyses

C 54.04 Al 14.19

H 3.74 Ca 16.13

N 0.82 Fe 5.99

S 0.38 Mg 3.33

O 13.69 Mn 0.04

Ash 5.66 P 0.71

Moisture 21.67 K 0.47

Volatile Matter 36.77 Si 36.76

Fixed Carbon 35.91 Na 0.93

HHV, Btu/lb 9320 S 10.11

Hg, g/g 0.047±0.004 Ti 1.11

Coal Analysis

Pratt Bituminous

Coal Analyses Mineral Matter Analyses

C 69.23 Al 25.91

H 4.82 Ca 3.41

N 1.69 Fe 13.20

S 2.22 Mg 1.18

O 6.54 Mn 0.04

Ash 13.14 P 0.83

Moisture 2.38 K 2.33

Volatile Matter 35.64 Si 44.78

Fixed Carbon 48.85 Na 0.47

HHV, Btu/lb 12659 S 3.72

Hg, g/g 0.21±0.01 Ti 1.25

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Corrosion Probe Placement

Probe “A”

Probe “B” (Opposite side of duct)

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ECN Corrosion Probes

Carbon steel corrosion sensor

elements

Stainless Steal Probe Body

Sensor array(centered in flue gas

duct)

Signal wires and thermocouple leads

Cooling air into probe

Sensor surface temperatures were varied between ~350 °F and ~100 °F

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250

0

0.12

0.24

0.36

0.48

0.6

11:30:00 11:37:30 11:45:00 11:52:30 12:00:00 12:07:30 12:15:00 12:22:30

Prob

e temp (°F)

Corrosion rate

Probe A CorrosionProbe A Temperature

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0.36

0.48

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15:23:00 15:38:00 15:53:00 16:08:00 16:23:00 16:38:00 16:53:00 17:08:00

Prob

e temp (°F)

Corrosion rate

Probe A CorrosionProbe A Temperature

With Bromine

Without Bromine

Corrosion Rates (air-fired)(bituminous coal)

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250

0

0.12

0.24

0.36

0.48

0.6

16:30:00 16:45:00 17:00:00 17:15:00 17:30:00 17:45:00 18:00:00 18:15:00

Prob

e temp (°F)

Corrosion rate

Probe A CorrosionProbe A Temperature

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250

0

0.12

0.24

0.36

0.48

0.6

14:20:00 14:35:00 14:50:00 15:05:00 15:20:00 15:35:00 15:50:00 16:05:00

Prob

e temp (°F)

Corrosion rate

Probe A CorrosionProbe A Temperature

With Bromine

Without Bromine

Corrosion Rates (oxy-fired)(bituminous coal)

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Peak Corrosion Rates

Air w/o Br Air w/ Br Oxy w/o Br Oxy w/ Br

Corrosion Ra

te (m

m/yr)

0.030.07

0.22

0.55

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Dew Point Corrosion Considerations

No Br, 149°F No Br, 105°F 18ppm Br, 106°F 18ppm Br, 99°F

Oxy-firingBituminous Coal

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Dewpoint Corrosion with PRB

0 F

20 F

40 F

60 F

80 F

100 F

120 F

140 F

160 F

180 F

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0.02

0.04

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0.08

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0.14

0.16

0.18

0.2

13:26 13:40 13:55 14:09 14:24 14:38 14:52

mm

/yr

Time

Probe B ENCR

Probe B Temp

Air-fired42 ppm Bromine

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• Corrosion rates at air heater temperatures can increase dramatically with bromine addition, if temperatures are sufficiently low

• Oxy-coal combustion has the potential to significantly increase air heater corrosion rates

• Dew point mechanisms are indicated and appear to involve sulfuric acid, HBr, HCl and water– Rates dependent on flue gas concentrations and moisture

level (both higher with oxy-combustion)• Data regarding the impact of temperature cycling has

been collected and will be reviewed in the near future• ACI appears to have a more complex impact on

corrosion rates and is under review

Summary

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For more info contact:davis@reaction-eng.com

This material is based upon work supported by the Department of Energy under Award Number DE-NT0005288;

Andrew Jones, Program ManagerCost share and technical support from Praxair.

Acknowledgment

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Disclaimer

This material is based upon work supported by the Department of Energy under Award Number DE-NT0005288. Project Manager is Andrew Jones. This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.