Performance of the

Boswell Energy Center Unit 

Environmental Improvement Pro

Karen E. Burchardt, P.E., Burns & McDo

Tom Coughlin, P.E., Minnesota Powe

Paper #57

MEGA Symposium

Baltimore, MD

September 1, 2010
Outline

• Introduction• Description of unit• Description of project• Project challenges• Performance testing results• Conclusions
Introduction
Regulatory Drivers

Clean A

Mercury R

Clean Air 

Interstate Rule

Minnesota 

Mercury Rule

Regional H

Rule

Regulatory 

Drivers
Objectives

• Install APC equipment to comply wit

future regulations by 2010

• Significantly reduce SO2, NOx, merc

emissions
Description of Unit
Boswell Unit 3

• 335 MW (net) 

355 MW (gross)

• Cohasset, MN• COD 1973• C-E (Alstom) 

tangentially-fired unit

• Fuel: PRB coal
Boswell Unit 3

• NOx control:

– BOOS to simulate OFA

• SO2/PM control:

– Single-stage wet particulate scrubber (

• Shares chimney with Boswell Units 
Boswell Unit 3

Unit 3 Boiler

Unit 3 Scrubber

Unit 1, 2, & 3 Stack

Unit 4

Unit 1 & 2
Description of Project
Equipment Added

• Low NO

x burners and overfi

system

• SCR system• Wet FGD system• Fabric filter baghouse• Activated carbon injection sy• ID fans

{{
Equipment Added

• Ammonia storage system• Limestone handling and prep. syste

– Conversion of existing Unit 4 lime syst– Powdered limestone delivered to site

• Fly ash handling and storage system
Schedule

• Engineering kickoff – February 2006• Main equipment contracts in place:

– SCR, FGD, ductwork: Dec. 2006– Baghouse, SI system: Dec. 2006– ID fans: March 2007
Schedule

• Construction:

– SCR: Oct. 2007 – Oct. 2008– FGD: March 2008 – July 2009– Baghouse: April 2008 – April 2009

• Unit outage: Aug. – Nov. 2009• Start-up: Nov. – Dec. 2009• Performance testing: Jan. – Feb. 20
Project Challenges
Challenges

• Limited site space• Installation of SCR reactor and supp

truss

• Tight schedule
Limited Site Space

Lake

Existing

scrubber

Boiler
Limited Site Space

Existing

scrubber

Existing

stack

Lake
Limited Site Space

Lake

Existing

scrubber
Limited Site Space

• Needed to reclaim some of the lake

– Sheet pile wall needed– Limited to 3 acres total area reclaimed– Limited to 1 acre wetland impact
Sheet Pile Wall
Sheet Pile Wall
Limited Site Space

Crane placed on baghouse foundation for SC
Limited Site Space

Baghouse pre-assembled in laydown 
Limited Site Space

Absorber building space minimize

New FGD 

Building Outline
SCR Reactor/Truss

• SCR elevated above existing scrubb• Supported by truss (160 ft. long)

SCR Support

Truss
SCR Reactor/Truss

• Large foundations needed

– Highly compressive soil– Existing underground utilities to re-rout

• Settling near existing structures

– Pressure grouted augercast piles used– Pile installation limited to 7 months of y

to cold climate
SCR Reactor/Truss

• Single large crane used

– Maintain access to existing scrubber– Space for crane available on N side on

• Placed on baghouse foundation• Deep foundation needed for crane
SCR Reactor/Truss
SCR Reactor/Truss

SCR Support

Truss

SCR Reactor
Scheduling

• Alliance contractors worked on T&M 

to construct “work packages”

• Work packages issued ASAP to exp

construction

• Winter construction in Northern MN• Foundation design early
Performance Testing Resu
Performance Targets

• SO

2: 98% removal

• HF: 90% removal• HCl: 95% removal• H

2SO

4: 25% removal
Performance Targets

• NO

x:

– 0.18 lb/mmBtu at economizer outlet– 0.05 lb/mmBtu at SCR outlet

• Ammonia slip: 2 ppmvd at 3% O

2

• SO

2–to-SO

3 oxidation: 3.1% across 

catalyst
Performance Targets

• PM10: 0.012 lb/mmBtu (filterable),

0.08 lb/mmBtu (filt. + cond.)

• Opacity: 5% at FF outlet• Mercury (total): 90% removal• Mercury (oxidized): 70% removal
FGD System 

Performance Testing

• Measured at inlet and outlet of FGD 

absorber:

– SO2, PM10 (filt. and cond.), Hg2+, HCl, 

H2SO4

• Inlet and outlet measurements used 

determine % removal in absorber
FGD System 

Performance Testing

• SO2:

– EPA Method 6C– Average: 99+% removal

• PM10:

– EPA Methods 5B and 202– Average filterable: 0.0010 lb/mmBtu– Average condensible: 0.0033 lb/mmBt– Average total: 0.0044 lb/mmBtu
FGD System 

Performance Testing

• Hg2+:

– Ontario-Hydro Method– Hg2+ below detection limit at inlet and o

– Cannot determine % removal

• H2SO4:

– Controlled Condensate Method– H2SO4 below detection limit at inlet and 

– Cannot determine % removal
FGD System 

Performance Testing

• HCl and HF

– EPA Method 26A– Average HCl removal: 82.6%– Average HF removal: 71.2%– Test results being further evaluated to 

design performance was met.
SCR System 

Performance Testing

• NOx:

– EPA Method 7E– Econ. outlet/SCR inlet: 0.15 lb/mmBtu – SCR outlet: 0.029 lb/mmBtu (average)

• NH3:

– CTM-027– Average: 0.04 ppm at 3% O2
SCR System 

Performance Testing

• SO2–to-SO3 oxidation:

– SO3: Controlled Condensate Method

– SO2: EPA Method 6C– Oxidation = (SO3,outlet – SO3,inlet)/SO2,in

– Average: 1.33%
SCR System 

Performance Testing

• SCR performance exceeded design

– Common with new catalyst

• Catalyst deactivates Æ performance 

degrades

• Change catalyst as approach design 
Fabric Filter 

Performance Testing

• PM10 (filterable):

– EPA Method 5B– Average: 0.0038 lb/mmBtu

• Mercury (total):

– Measured based on coal data, stack C– Average: 92% removal
Conclusions
Conclusions

• Challenges

– Tight space– Tight schedule

• Construction completed on schedule• Performance testing completed

– Most design performance criteria met
Near Completion

SCR

Baghouse

ID Fan 

FGD B

Sheet Pile 

Wall

PAC Silo
Conclusions

“It’s an amazing engineering feat. A

just an engineering feat, but executiothe engineering. It’s beautiful and veexciting.” – Senator Al Franken
Questions?

Karen Burchardt, Burns & McDonne

kburchardt@burnsmcd.com

816-822-3430

Tom Coughlin, Minnesota Power

tcoughlin@mnpower.com

218-722-5642, ext. 3549