Selective Catalytic/Non Selective Catalytic/Non

-

Reduction Reduction Confere

Confere

SCR Operation Optimizat

SO3 Removal to Optimize Catalyst 

Distribution in Wastewa

SCR Operation Optimizat

SCR Operation Optimizat

SO3 Removal to Optimize Catalyst 

Removal to Optimize Catalyst 

Distribution in Wastewat

Distribution in Wastewa

Presented by:

Thomas Wright

Parsons Energy & Chemicals 

Chattanooga, Tennessee

October 30, 2003
1

Agenda

! INTRODUCTION! NH3 SLIP DISTRIBUTION

! SCRíS INCREASED SO3

! SO3:NH3 MOLAR RATIO

! WASTEWATER TREATMENT! ECONOMICS! CONCLUSION
2

Introduction

! Last Yearís Paper

ñ SCR catalyst life " limited NH3 slip to ~2 ppm to 

bisulfate (ABS) deposits in air heater

ñ NH3 slip is removed in air heater deposits, on ES

slurry

ñ NH3 is soluble & eventually will end up in a wast

! Last yearís Recommendation

ñ Install SO3 removal system before air heater, to 

distribution between ESP & FGD

ñ NH3 slip sampling for NH3 balance, especially añ Determine critical ABS deposition number (ìRad

increasing NH3 slip to cause deposits
3

NH3 SLIP DISTRIBUTION

! ABS

ñ ABS vapor forms at temperatures >600 Fñ SO3 below 400 F is mostly H2SO4 vapor " 50% 

at 400 F

ñ ABS condensate or aerosol forms from 330 F to 

temperatures at higher SO3 & NH3 concentration

ñ ABS is a viscous liquid " ìstickyîñ Temperature drop required for condensing ABS 

heater

ñ Condensate or aerosol formation completed at ~

SO3 & NH3 (< 1 ppm)

ñ Molar Ratio - SO3:NH3 = 4.7 SO3 ppm per ppm 
4

NH3 SLIP DISTRIBUTION (continued)

! Air heater

ñ Radian developed a thermodynamic & kinetic m

formation in regenerative air heaters (1982)

ñ Radian Equation for ABS deposition number:

! SO3 ppm x NH3 ppm x[T(IFT) - T (rep)]! Where ìT (rep)î is a combination of air heater gas 

end metal temperature

ñ Preliminary literature survey showed a ìbreak po

for the Radian number from minimal ABS depospressure dropî deposits

ñ NH3 slip Guidelines " from literature review & ty

! Low sulfur ñ 6 ppm! Medium sulfur ñ 4 ppm! High Sulfur ñ 2 ppm
5

NH3 SLIP DISTRIBUTION (continued)

! Air Heater (continued)

ñ Acid Dew Point ñ higher ADP from increased SO

ash deposits in air heater

ñ Literature shows that some ABS deposits may d

combustion air side of air heater

ñ Worst case - 2 ppm slip at end of catalyst life & 

operation " up to average ~3,000 ppm NH3 in w
6

NH3 SLIP DISTRIBUTION (continued)

! ESP

ñ Flue gas conditioning reactionñ Byproduct Ash ñ can evolve NH3 when mixed w

" 100 ppm NH3 in ash is typical limit

ñ Worst case ñ 2 ppm NH3 slip at end of catalyst l

! Wet Sluice to Pond " up to ~2 ppm in sluice wat! Dry Conveying to Landfill

ñ Ash " up to ~ 175 ppm (adsorbed on ash)

ñ Leachate " up to ~150 ppm (for a 1 year active c

! FGD

ñ Residual NH3 after air heater & ESP absorbed iñ Byproduct gypsum (wallboard) "ñ Worst Case ñ 2 ppm NH3 slip at end of catalyst 

! Open Loop ñ up to ~10 ppm! Closed Loop - up to ~100 ppm
7

SCRís INCREASED S03

! Impact

ñ SCR ~ doubles boiler SO3 " up to 50+ ppm for ñ Visible plume " at > 15 to 20 ppm SO3ñ Acid Dew point (ADP) corrosion " ADP ~300 F 

! Removal Economics

ñ Very few SO3 removal systems " limited cost & 

experience ñ see Gavin papers

ñ Boiler injection only removes boiler SO3 ñ not Sñ Assume hydrated lime system after SCR

! Process Design ñ lime stoichiometry ~3! Capital - ~$10 per KW " ~ $0.15 per MWH! O&M ñ lime at $100 per ton " ~ $0.15 per MWH! Total " ~ $0.3 per MWH
8

SO3:NH3 MOLAR RATIO

! SO3

ñ Boiler + SCR SO3ñ High (3.0%) " 25 + 25 = 50 ppmñ Medium (1.7%) " 14 +14 = 28 ppmñ Low (<1%) " 6 + 6 = 12 ppm

! SO3:NH3 Molar Ratios

ñ For typical ìend-of-lifeî catalyst " 2 ppm NH3ñ 1 molar SO3 :NH3 = 4.7 NH3 ppm per ppm SO3ñ ABS formation impacted by Molar Ratio " highe

results in lower temperature drop. For 95% form

! At 1.0 MR " ~75 F! At 0.5 & 2.0 MR " ~45 F! At 5.0 MR " ~40 F
9

SO3:NH3 MOLAR RATIO (continued)

! Cases

ñ Without SO3 removal & 2 ppm NH3 ñ With SO3 removal & 2 ppm NH3ñ Early catalyst replacement " 1 ppm NH3ñ Late catalyst replacement " 4 ppm NH3

! ABS Deposition Number (ìRadianî Numbe

ñ ABS deposits (measurable pressure drop) in air 

ìRadianî number of ~5,000 to 7,000
10

SO3:NH3 MOLAR RATIO (continued)

W/O SO3Removal

WITH SO3

Removal

NH3 End of Catalyst 

Life

2 2 

SO3 High Sulfur 50 5 to 10 Molar Ratio

SO3: NH3 ~5 1 to 2 

ABS Deposit #

(add washes)

~6500 

(1)

~1200 

(0)

Air Heater NH3 Removal ~30% ~10% 

Wash Water NH3 ppm

~750 ~500 
11

SO3:NH3 MOLAR RATIO (continued)

W/ SO3Removal

W/O SO3

Removal

EC

ESP NH3 Removal ~70% ~70% 

Sluice Waterppm

Up to 1.2 Up to 1.2 

Dry Ash ppm Up to 120 Up to 120 U

FGD NH3 Removal 0 ~20% 

Open Loop ppm

0 Up to 2 

Closed Loop ppm

0 Up to 20 
12

SO3:NH3 MOLAR RATIO (continued)

! Medium Sulfur Coal

ñ Less removal in air heater " lower MRñ Only Early Catalyst has no FGD wastewater treañ Only Late Catalyst has additional air heater was

! Low Sulfur Coal

ñ Same removal in air heater & ESP ñ 10% & 70%ñ All cases need WWT for FGD to maintain bypro
13

WASTEWATER TREATMENT

! Conventional Options

ñ Mechanical " result in a NH3 off-gas or a conceñ Biological "ñ ABS deposits result in just a different waste for f

! Quantity (gpm /MW)

ñ Air Heater Wash Water <0.5ñ Ash Landfill Leachate <0.5ñ FGD Blowdown (closed loop) NA (only entrañ FGD Blowdown (open loop) ~2ñ Ash Sluice (~0.5% slurry) ~14ñ NPDES ~20
14

WASTEWATER TREATMENT (continued)

! Comprehensive Treatment

ñ Byproduct recovery from wastewaterñ Increase wastewater pH, strip NH3 & absorb NH

sulfuric acid " an ABS byproduct fertilizer(liquid

! Economics

ñ Air Heater " $2 per KW & $0.04 per MWHñ Ash Landfill Leachate " $2 per KW & $0.04 peñ FGD Blowdown (open loop) " $5 per KW & $0.ñ Ash Sluice " $18 per KW & $0.25 per MWHñ NPDES " $22 per KW & $0.35 per MWH
15

ECONOMICS

! Catalyst Life

ñ Catalyst = ~10% of SCR cost " ~$10 per KWñ For 20,000 hours (2 ppm NH3) " ~$0.17 per MWñ Early (1 ppm NH3) at 15,000 hours " +$0.05 peñ Late (3 to 4 ppm NH3) at 25,000 hours " -$0.04 

! Byproduct Sales

ñ For every $10 per ton for disposal, loss of bypro

high sulfur coal) due to NH3 contamination " co

for fly ash & gypsum

! Air Heater Washing 

ñ Washing Crew (for high pressure washing) " ~ñ 50% Loss of Load for 3 days " ~$0.05 per MWñ Total cost per additional washing " ~$0.1 per M
16

ECONOMICS (continued)

W/O SO3REMOVAL

WITH SO3

REMOVAL

W/O 

REM

CATALYST REPLACEMENT

BASE BASE EA

SO3 REMOVAL 0 0.3 

WWT ñ ASHLEACHATEWWT ñ AIR HEATER

0.04 0.04 0

WWT ñ FGD (open loop)

0 0.08 
17

ECONOMICS (continued)

W/O SO3REMOVAL

WITH SO3

REMOVAL

W/O 

REM

CATALYST REPLACEMENT

0 0 +0

AIR HEATER WASHING

0.1 0 

BYPRODUCTS ASH

00

BYRPODUCTS FGD

00

TOTAL 0.14 0.42 0
18

Conclusions

! Wastewater Treatment

ñ All SCR may require wastewater treatment for th

water

! SO3 Removal

ñ For high sulfur coal, the cost of additional air he

wastewater treatment is significantly less than thremoval

! Catalyst Life

ñ Early catalyst replacement cost ~ air heater WWñ Earlier catalyst replacement eliminates the need 

(high sulfur coal)
19

Recommendations

! SO3 measurements

ñ Before and during SCR operation ñ determine w

and removed

ñ During SCR operation ñ determine whether perc

removed is constant with increased SO3

! NH3 measurements

ñ Wash air heater after first ozone season and co

samples to estimate NH3 in air heater. Monitor 

outlet) and NH3 in fly ash " determines NH3 sli

ñ After first ozone season, increase NOx removal 

slip ñ to point where deposits are formed in air hplant specific Radian number