# SCR Operating Experience EPRI SCR Workshop October 31 st 

### , 2006

# Agenda

• Regulatory Overview



# • Plant Locations

• SCR Overview



# • System Detail

• Lessons Learned



# • Summary

# 1 - Hour Ozone Nonattainment Areas

# Emission Rate Based Control System

• Atlanta Region
– Georgia Power

– 0.13 lb/MMBtu 5 - plant average

• Bowen , Hammond , McDonough, Wansley , and Yates



## – 0.20 lb/MMBtu 7 - plant average

• All plants in 5 - plant average, plus Branch and Scherer


# • Birmingham Region
– Alabama Power

– 0.21 lb/MMBtu 2 - plant average

• Gorgas, Miller


# • Gulf Coast Region
– Gulf Power

– 0.20 lb/MMBtu Plant Crist averageAlabama Power Georgia

Power Gulf Power Mississippi Power Scherer Branch Hammond Bowen McDonough Yates

Mitchell Miller Gorgas Gaston

Gadsden

Greene Co.

Barry

Smith Crist Scholz Daniel McIntosh Kraft

Coal Fired Plants SCR Installations Watson Wansley 

# 14 SCR Units Currently in Operation

One Additional SCR Under ConstructionPlant Hammond

Plant Bowen

Plant Miller Plant Gorgas Plant Wansley Plant Gaston Plant Crist

# SCR Installations Summary

Plant, Unit MW Startup Date Additional Notes Bowen 1 700 2001 High - dust, ozone season Bowen 2 700 2001 High - dust, ozone season Hammond 4 500 2002 High - dust, ozone season Gorgas 10 700 2002 High - dust, ozone season Bowen 3 880 2003 High - dust, ozone season Bowen 4 880 2003 High - dust, ozone season Miller 3 660 2003 High - dust, ozone season Miller 4 660 2003 High - dust, ozone season Wansley 1 865 2003 High - dust, ozone season Wansley 2 865 2003 High - dust, ozone season Miller 1 660 2005 High - dust, ozone season Miller 2 660 2005 High - dust, ozone season Crist 7 500 2005 High - dust, year round Gaston 5 880 2006 Low - dust, ozone season Barry 5 700 2008 High - dust, ozone season 15 Units 10,810 2009 All Units year round

# SCR Systems Overview

Flow from Unit 5. Balance of Plant (BOP) Rectifier

Spare catalyst layer 1. Ammonia Injection and Static Mixers
2. Flue Gas Analysis 3 + 1 Reactor

4. SCR Catalyst 3. LPA Screens

# 1. Ammonia Systems and Static Mixers

• All plants use Anhydrous Ammonia

• Ammonia Injection Grid (AIG) systems:

– Cormetech, Siemens, Sulzer, Eco - Diva

– Usually supplied by the original SCR catalyst manufacturer

• Cormetech AIG uses a dense injection nozzle arrangement

• All other AIG designs are coupled with static mixers

# 1. Ammonia Systems and Static Mixers

- Lessons Learned

• Replacement of pressure relief valves on ammonia storage tanks has proven difficult, with most requiring tank emptying and nitrogen purge.

• Ammonia forwarding pumps are unreliable. Southern Company is auditing its ammonia delivery systems to ensure proper performance in year - round operation.

• For ammonia injection using dilution air, the AIG is started up and shut down with ammonia flow turned off. The tuning valves are opened 100% to free any ash buildup in the injection lines.

• Static mixers can cut down on frequency of AIG tuning, but correlating the injection grid to the measurement grid can prove difficult.

# 2. FGAS – Flue Gas Analysis System

• Circulating flue gas sampling system

– double extraction
• Continuous average NOx concentration

– SCR inlet (8 locations per reactor)

– SCR outlet (7 locations per reactor)

• Consists of ducting, fans, probes, sample lines, and analyzers

# 2. FGAS

- Lessons Learned

• FGAS analyzers were bought as duplicate systems to the plant’s CEMs.

– Familiarity of maintenance and calibration procedures

• High particulate loading in sampling system is problematic.

– Fan housing and blade wear, sample line plugging, probe contamination

# 3. Large Particle Ash (LPA), Screens

• Bowen 1 & 2 SCRs were taken offline in their first season of operation due to catalyst plugging.

• Since then, all existing and new SCR retrofit designs include LPA screens with accompanying ash - fallout hoppers.

# 3. LPA, Screens

- Lessons Learned

• Screens are a high O&M - cost solution for LPA mitigation ( D P and wear)

• Ongoing iterative process of optimum screen design (material, coating, geometry, location, and flow modeling)

• LPA best solved though duct design, low velocity fallout before SCR MW Catalyst Layer 1 dP Operating time

# 4. SCR Catalyst

• Coal - fired SCRs built to receive any manufacturers catalyst design

• Standard 1m x 2m geometry

• 9 Units have honeycomb catalyst

– (7.1, 8.2, and 9.2 mm pitch)

• 3 Units have plate catalyst

– (5.7 mm pitch)

• 1 Unit has mixed plate and honeycomb layers

• 1 Unit has corrugated - fiber catalyst

# 4. SCR Catalyst

- Lessons Learned

• Still relatively young in catalyst age

• Oldest unit began operation in 2001

– < 20K operation hours

• Preliminary test results:

– E. Bit. units indicate arsenic poisoning

– PRB units show masking via gypsum/calcium sulfate formation

– Some evidence of phosphorus poisoning on PRB units As Pb Na
K CaSO 4 P

As F Cl

# 5. Balance of Plant

• Ammonia slip

– ammonia - in - ash

– air - heater plugging

• Unit turndown

– Minimum Operating Temperature

• Draft loss

– catalyst plugging

# 5. Balance of Plant

- Lessons Learned

• SCR systems were installed on largest generating units

– Base - loaded in Summer Peak

• Loss of plant equipment

– Boiler - feed pumps , mills, etc.

• Ammonia - in - ash can vary dramatically

– Best samples are collected in - situ

– Alternative is cumulative sample on bulk - ash transfer line

– Data from hopper samples is very noisy

# Summary

• Preventative maintenance on ammonia systems is key for uninterrupted operation. Ammonia forwarding systems need improvement.

• FGAS is a main contributor for uninterrupted SCR operation. High - particulate gas streams can cause excess equipment wear.

• LPA is best mitigated by duct design. Never assume that you do not have it.

• Catalyst is still young, but early indicators are that bituminous coals are depositing arsenic and PRB coals are forming gypsum.

• Ammonia slip has not been a problem.

• Concerns over boiler equipment failures and MOT.

# Future Challenges

• CAMR
– Clean Air Mercury Rule

– SCR - FGD co - benefit for mercury capture

– Impacts of low - oxidation catalyst

• CAIR
– Clean Air Interstate Rule

– Year - round SCR operation