One Sour

Wha

Lisauskas

Cla

Robe

A

DOE’s Environmental Control Con
SCR Technology

• System uses NH3 or urea injected into the 

upstream of active reduction catalyst

• In the catalyst, NOx is reduced selectively 

produce N2, & H20

• Catalyst reduces temperature for reducti

~600F

• Catalyst requires proper temperature, ho

NOx/ NH3 mixture, homogeneous tempe

uniform flow distribution at its inlet to pe

– Catalyst typically is honeycomb or pla

configuration

– Life is dependent on poisons present i

typically 8,000 to 24,000 hours of oper
Operating History of SCR Ret

•

Before 1998 < 1,000 MW

•

By 2005 

≈85,000 MW

•

By 2009 140,000 MW

• N

O

x r

e

m

o

v

a

l

– 85 – 92%

•

Availability

– >99%
Technological Challenge

•

Currently most SCRs 

operate during ozone season 5 months per year

•

Under new CAIR rules 

NOx control will be required 12 months per year

–

Catalyst management

–

Outage scheduling
CAIR Retrofit Cost Chall

•

High Cost Low Revenue Units

– O

l

d

e

r U

n

i

t

s

–

Smaller Units

– Peaking Units–

High Heat Rate Units

•

High Retrofit Cost

– T

a

i

l

-

e

n

d S

C

R

s

– M

a

r

g

i

n

a

l C

o

s

t

•

Boiler Modifications
CAIR Retrofit Challeng

•

Fuel flexibility

–

Catalysts are a component 

of fuel cost

–

Poisons, NOx compliance 

–

PRB proliferation

•

Shorter emission 

averaging times

• M

e

r

c

u

r

y

, S

O

3

–

Higher S fuels

–

New catalyst
New SCR Challenge

•

Most new SCR will not be buil

bypass system

–

Lower capital and maintenan

–

May limit fuels burned

–

Need improved catalyst 

management/fuel use strateg

– S

O

3 conversion

• Future value of NOx and SO

2 c

–

Banking, availability, $
$ Impact of 600 MW SCR O

Increased S

C

R P

erformance O

ver 80% Efficie

0

200400600800

1,000

78%

80% 82%

84% 86% 88% 90% 

NOx Removal (

%)

Normalized NOx Removed

(Tons)
SCR Options

• “Full” SCR System• Compact In-Duct SCR Reacto• Hybrid SNCR/ In-Duct SCR 

(“Cascade®”)

• Tail-end SCR systems (RSCR
Full SCR System

EconEcon

Cross Mixers
In Duct SCR
Hybrid Project Overvi

•

BPE has been selected to provide 

SNCR/In-Duct SCR to coal-fired p

•

Fuel Tech to supply Noxout reage

injection and controls

•

BPE to provide static mixers to ho

the flow and excess slip, SCR reaccontrols

•

Unit will be in operation 5/2006

•

Overall NOx reduction of ~ 65% r
Tail-End SCR Systems

•

Installed upstream of stack, downstream of partic

–

Clean gas

–

Low temperature gas (~300F)

•

Only practical SCR solution for WFB, WTE plants 

poisoning issues) space limitations –

Mercer Stati

•

Erected, then tied in; minimal disruption to opera

•

Requires energy input/heat recovery to minimize 

•

Typical tail-end unit consists of:

–

Heat exchanger

–

Duct burners

–

Ammonia injection

–

SCR reactor

–

Booster fans

•

NOx reductions 60-

90%; energy efficiency ~70%; 
Self Tuning SCR

•

170 MW Gas Plant with Single Feed 

Forward/Feed Back Control

•

Two Injection Points with Delta Wi

•

Modified with Additional Outlet N

Two Feed Back Loops

•

Installed in Summer 2005

•

Extended Time Between Injection P

Ups’
Trends in SCR Specifications Req

•

Lower Specified SO

2 Conversion Rates

–

Industrial Experience 

–

Anticipating the Use of Higher Sulfur 

Scrubbers

•

Higher Removal Efficiencies ( 91% to 92%

–

> 10 Units with > 90% Removal

•

‘Pre-Engineered’ Large Particle Ash Rem

•

Year Round Operation

–

Units without SCR Bypasses 

•

No Clear Winner on Reagent 

–

Anhydrous, Aqueous, or Urea 

•

High Ash Loading Criteria 
SCR Effect on WFGD Mercury 
SCR – Effect on Mercury Ca

• Reaction Hg + 2Cl -> HgCl2 Downstream 

Capture

• Full Scale Bituminous Test Results

– Mg-Enhanced Lime, Lime Venturi, Lim

Oxidation

– Hg Capture Efficiency of 80% to >90%

• Some indication that catalyst Hg Oxidati

similar to DeNox Deactivation 

• No affect on PRB coals to assist in Hg cap

– Lack of chlorine
Large Particle Ash Des

•

LPA Properties

–

Size >

4.0 m

m

–

Density 0.7 to 1.25 g/cc

–

Sphericity

0.7 to 0.99

–

Coefficient of Restitution 0.15 to 0.2

•

Screen Desig

•

Pluggage

• E

r

o

sio

n
Large Particle Ash Des

•

Design and Modeling 

–

CFD Modeling

– Industry Coated Screens–

Experience From Past

•

Soot Blowers 

• L

o

w V

elo

cit

y

•

Low Pressur
Start Up and Availabilit

•

Clean Tuning and Start Up Over th

•

No Gross Difference in Reliability o

Ammonia Systems

–

Urea , anhydrous, or aqueous sy

•

Overall system Availability 
One Sour

The Cascade The Cascade® System
Hybrid NOx Control Syst

“Cascade®”

3

6

7

8

9

10

12

I.D. FAN(S)

ESP(S)

FLYASH

F.D. FAN(S)

AIR

PREHEATER(S)

ECONOMIZERBYPASS

623 MW STEAM TURB

SCR MODUL

CATATRAY

ECONOM

• SNCR

(using urea)

• Compact In-duct SCR• SNCR slip

consumedin SCR

• Up to 80% overall NOx

reduction

• Low capital costs
Cascade® Process

• System Description

– The Combination of In-Furnace SNCR 

downstream Selective Catalytic ReducExtend the NOx Reduction Capability Improve Overall SNCR Reagent UtilizMitigate Downstream Balance of Plan

• A Redesigned SNCR system with SCR• Higher NOx reduction and utilization tha

• Lower capital costs than full-scale SCR• Greater operational flexibility• Seasonal NOx emission limits
Cascade Process Application and Li

•

Single Layer of Catalyst (SCR Requireme

–

Space Restrictions, 16 – 20 fps face vel

– N

H

3 Scrubber vs. Significant NOx Red

•

No Requirements for new fans

–

Utilize existing fans or re-tip

–

Deploy in conjunction with backend A

such as new scrubbers/baghouses whinew fans

•

Limited Structural Steel Modifications

•

No New Foundation Requirements

• N

o N

H

3 Injection Grid Required
Summary of Cascade

® Pro

•

Cascade Performance Ranges from 55 to 

Reduction

–

NH3 “Mop” vs. NOx Reduction

•

1/4 to 1/2 Capital Cost of Full SCR System 

•

Improved Chemical Utilization over SNC

•

Shorter Boiler Outage Requirement

•

Single Layer of Catalyst; Easy Removal a

•

Staged Installation; SNCR 1st Followed b

Later
Summary

• SCR options exist to reduce NOx to meet • More expensive systems than SNCR and/

burners

• Removal efficiencies much higher than S• Higher performance than needed to mee

generate revenues from NOx credits

• Unique mixing technology enables in-du

systems

– Lower capital costs than conventional – Greatly reduced installation costs– Performance comparable to full SCR o
SCR System Performa

0.0000.1000.2000.3000.4000.5000.6000.7000.8000.9001.0001.100

1/1/03

1/29/03

2/26/03

3/26/03

4/23/03

5/21/03

6/18/03

7/16/03

8/13/03

9/10/03

10/8/03

% Load

Stack Gross L

oad (

M

W

g) 2

4

Hr R

ollin

g

N

Ox E

missi

o

n

R

ate (lb/mmB

T

U) 24Hr R

ollin

N

Ox E

missi

o

n

R

ate (lb/mmB

T

U) 30 D

ay R

ol
0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

123 4 5 6789 10 11 12 13 14 15 16 17 18 19 20 

Lowest Outlet NOx U

Source US EPA
Results – Unit Size

• 19 units between 90 and 1,300 

achieving above 90% 

• 34 units between 200 and 1,300 

achieving 87% to 90% (19,757 

• 44 units between 200 and 1,300 

achieving 80% to 86% (26,205 

• 33 units between 150 and 1,300 

achieving 70% to 80% (15,043 

• Availability not sensitive to unit 
0.60

0.650.700.750.800.850.900.951.00

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

49

51

53

NOx Removal Efficiency (fraction)

Results –

Catalyst Type

Corrugated

Honeycomb

Plate
0.60

0.650.700.750.800.850.900.951.00

1

4

7

10

13

16

19

22

25

28

31

34

37

40

43

46

49

52

55

58

61

NOx Removal Efficiency (fraction) Urea Based 

Aqueous Am

Anhydrous 

Results –

Ammonia Typ
0.60

0.650.700.750.800.850.900.951.00

1

4

7

10

13

16

19

22

25

28

31

34

37

40

43

46

49

52

55

58

61

64

67

70

73

76

79

82

85

NOx Removal Efficiency (fraction) Tail E

Low 

High 

Results –

Arrangement Ty
0.60

0.650.700.750.800.850.900.951.00

1 2 3 4 5 6789 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 

NOx Removal Efficiency (fraction)

Results –

SCR Supplier
Data Analysis

• 90% NOx removal achieved by ~1• Outlet emissions on less than 0.05 

achieved by multiple units 

• Availability insensitive to catalyst 

types have achieved 90% 

• Availability insensitive to ammon

types have achieved 90%

• Arrangement type appears to affe

due to sample size
Data Source

• Data downloaded from

– Acid Rain/OTC Program Hou

Emission Data 

– www.epa.gov/airmarkets/em

• Analysis period year 2004• Ozone season June 1st to Septem

– Some states had one month st

• Single stack only data, common 

removed