LESSONS LEARNED FROM SCR EXPERIENCE OF

COAL FIRED UNITS IN JAPAN, EUROPE AND USA;

ARE THESE ENOUGH?

Dr. Anupam Sanyal

International Environmental & Energy Consultants, Inc.

Naperville, Illinois 60563

And

William Ellison

Ellison Consultants

Monrovia, Maryland 21770

Presented at the

 2002 Conference on Selective Catalytic Reduction

 And Non-Catalytic Reduction for NOx Control

Pittsburgh, Pennsylvania, May 15-16, 2002

Sponsored by U.S. Department of Energy,

National Energy Technology Laboratory
Outline

l Introduction

l The Japanese & European Experience

– Coal

– Boiler Design

– Performance – NOx Removal, NH3 Slip, APH, Catalyst

l The US Experience

– Applicability of This Experience to the Advanced US SCR Needs

W.R.T.

l Coal

l NOx Removal Efficiency

l Opacity Compliance

l What Else is Required?

– Coal/Ash Characterization

– Catalyst Development

– Chemicals as Remedial/Preventive Measure

– Arsenic Poisoning/SO3 Plume Mitigation/Prevention

l Conclusions and Recommendation
Introduction

Development of SCR in Japan, Europe & USA

l ~23,100 MW Total Japanese Utility

Capacity Comprising 61 Plants

l ~55,000 MW Total European Utility

Capacity

l ~Until end 90’s, 2,211 MW of US Capacity.

By 2004, this is Expected to Increase to

over100,000 MW ≡ Over 33% of the Total

Coal Fired Capacity of the USA
Pioneers of Japan, Europe & USA for SCR

Installations on Coal Fired Commercial Units

Sequence of Milestones

1

st Arsenic poisoning in Stanton #2 of OUC

2000

1

st PRB Application Feb 2000 to AECI’s 600 MW New Madrid #2

 E NOx 93%, NH3 Slip 3ppmvdc

 1st largest cyclone unit (700 MW) firing high sulfur bit coal to TVA’s

Paradise #2 Spring 2000; ENOx 90% NH3 Slip 2 ppmvdc

1995

1

st New US P.C. Fired PG&E’s 265 MW Carney’s Point Cogen Plant &

1

st Retrofit Merrimack Unit 2 (1st US Gas Unit is LADWP Haynes)

1990

Arsenic Poisoning reported in German pilot plants. 1st coal fired German

Dry Bottom Commercial Unit is Neckerwerk’s Altbach/Deizisau 420 MW

Unit 5 & 1st coal fired German slag tap 175 MW unit of Knepper C

1985

Fed. Rebuplic of Germany’s ordinances for 111 ppm (0.12 lb/Mbtu)

(200 mg/Nm3) from large boiler installations

1980

Japanese – Pilot plants firing oil, gas & refinery gas. 1st coal fired Japanese

demo. on 1⁄2 x 175 MW of Chogoku Electric’s Shimoneski Unit followed by

Hokkaido Electric’s Tomato - Atsuma (1/4 x 250 MW ) & EPDC’s Takehara

250 MW Unit 1 Low Dust Demo.

1975
Performance of Earlier Japanese SCR Plants

on Coal Fired Utility Boilers

Tohuku Sendai 1 175 Plate 2,600 400 160 60 2 1983

Electric

Chuguku Shin-Onada 1 500 Honeycomb 7.4 2,800 200 40 80

Tokyo Yokosuka 1,2 265 Honeycomb 7 4,000 200 60 70 1 1984

Shikoku Saijo 2 250 Honeycomb 7.5 - 330 90 70 1 1983

Shikoku Saijo 1 156 Honeycomb 7 4,000 380 130 65 1 1983

Chuguku Mizushima 2 156 Plate 6 2,200 350 120 65 2 1984

Chuguku Shin-Ube 3 156 Honeycomb 7 4,000 400 140 65 2 1981

Chugoku Shimonoseki 1 175 Honeycomb 10 3,000 420 180 57 1 1980

EPDC Takehara 3 700 Plate 10 2,370 250 48 81 2 1983

250 Tube - 2,000 350 67 81 4 1981

x 1⁄2

EPDC Takehara 2

250 Plate 10 2,300 350 67 81 4 1981

x 1⁄2

EPDC Takehara 1

Up

Year

NH3

(ppm)

Slip

DeNOx

(%)

NOx (ppm)

In Out

SV

{h-1}

Pitch

(mm)

Catalyst

Type

Boiler

No. MW

Plant Plant Site

Owner
Typical European Units

 Providing NOx Reduction >85%

(High Performance SCR)

Franken 83 1785 1250 220 Excess catalyst volume

Relatively large reactor, with excess of

catalyst, APH corrosion/SO3

Kiel 83 2308 1528 350

Catalyst volume is not excessive, but

tower design boiler and small reactor

promote good gas distribution and

mixing

Bremen 85 3152 2364 170

Tiefstack 85 1257 943 100 Excess of catalyst, small reactor size

Reactor size is one of the largest for

high performance SCR Catalyst

Management

Staudinger 3 85 - - 293

Staudinger 1⁄2 84 - - 63 Extremely small reactor size

Walheim 85 2449 1839 140 + 40 Same as Kneper

Combined high initial NOx, small

reactor size, and relatively low space

velocity provide ideal conditions for

maximum NOx removal

Knepper C 90 Not defined 1412 175

Comment

Reactor

Size

(MW)

Final Space

Velocity (h-1)

Initial

Space

Valocity (h-1)

NOx

Unit %
Japanese & European Coal

Quality Indigenous and

Imported
Analyses of Typical Japanese Coals

Horonai 8.2 3.4 48.4 14,490 33.7 38

Hahoro 16.8 12.9 55.8 14,510 33.7 36

Akama 30.8 2.6 46.4 14,590 33.9 54

Yubetsu 21.6 2.4 44.9 14,740 34.3 53

Bihai 15.1 3.6 45.9 14,330 33.3 47

Hokkaido Sunagawa 38.0 1.6 49.7 13,710 31.9 49

Yamaguchi Sanyo 31.7 2.2 9.5 14,900 34.7 72

Shikoku Takamatsu 29.7 4.4 47.6 14,040 32.6 38

Shinkokusko 23.3 3.6 46.9 14,690 34.2 51

Meiji-Saga 15.4 2.2 51.7 14,800 34.4 47

Yamano 51.3 2.2 45.8 13,400 31.2 43

Onoura 23.8 2.4 46.2 14,440 33.6 46

Kokura 39.1 6.1 53.6 13,160 30.6 37

Hiyoski 24.5 3.0 40.0 14,700 34.2 49

Iizuka 22.1 2.2 48.3 14,410 33.5 44

Kyushu Tagawa 35.4 3.9 51.2 13,660 31.81 45

Hardgrove

Grind.

Moisture and Ash-Free

 HHV

% VM Btu/lb MJ/kg

As Received

% Ash % H2O

Mining District

Area or Seam
Sulfur (%) 0.9% 0.3% 0.6% 0.6% 0.9%

Total Ca/S 10.78 3.33 15.00 1.83 3.78

Total Alkali/S 16.18 10.00 22.00 6.02 9.78

Total Alkali 14.56% 3.00% 13.20% 3.61% 8.80%

Error

SO3

P

Ti

K

Na

Mg

CA

Fe

Al

Si

Ash Chemistry

N

H

C

Sulfur

Heating Value

Moisture

FC

VM

Ash

Analysis

0.41% 0.71% -0.81% 1.30% 1.30%

8.34% 0.20% 6.00% 1.00% 2.00%

0.10% 0.50% 2.00% 0.40% 0.50%

0.80% 1.00% 1.50% 1.00% 1.60%

1.185% 1.00% 0.50% 1.50% 2.20%

0.48% 0.40% 2.00% 0.90% 1.00%

2.53% 0.60% 1.70% 0.11% 2.20%

9.70% 1.00% 9.00% 1.10% 3.40%

11.60% 3.00% 4.00% 9.00% 7.00%

23.20% 21.00% 32.00% 24.00% 25.00%

38.90% 70.00% 43.00% 57.00% 51.00%

Pct of Ash Pct of Ash Pct of Ash Pct of Ash Pct of Ash

1.9% 1.4% 1.6% 1.2% 1.1%

5.0% 4.0% 4.0% 5.0% 4.4%

69.0% 64.0% 65.0% 69.0% 55.7%

0.90% 0.30% 0.60% 0.60% 0.90%

12,858 10,854 11,240 11,755 9,926

4.90% 13.00% 8.00% 9.00% 7.50%

0% 54.0% 54.0% 48.0% 43.5%

37.7% 25.0% 24.0% 36.0% 28.0%

9.5% 8.0% 14.0% 7.0% 21.0%

Columbia Poland

Guasare

S. Africa

Transvaal

Australia

N.S. Wales

Germany

Ruhr Valley

Characteristics of Typical European Indigenous & Coals Imported by Europe & Japan
Highlights of SCR Experience of

Japan & Europe

l Coal – Mostly imported, med. Sulfur, low arsenic sub-bit.

l Design Features Remarks

Inlet NOx lb/Mbtu 0.50-1.25

deNOx E 50-90%

NH3 Slip ppmvdc 1-10

SO2-SO3 Conv. % <2%

SV hr-1 1,257-4,000

Low/High Dust Both

l Catalyst Pitch & Geometry Pitch 7-10 mm; pipe, honeycomb, 

plate, (graduated) fiberreinforced corrugated

Composition V2O5, TiO2,MoO3 on S.S. or Ceramic

Management By coupon testing, inspection, cleaning

regularly, poisoning/blockage 
Highlights of SCR Experience of

Japan & Europe (Cont’d.)

l SCR Process Parameters

Gas Velocity Dist N 15-20% SD

NH3/ NO Ratio SD 4-6%

Physical & CFD Modeling Yes

l Reactor Layout Various – e.g. For simple tower boilers

“Elbow” to complicated layouts 

achieved by prior modeling of specific needs – e.g. wide load 

range

l Reagent Type & Application Anhydrous NH3

 (Mostly)

AIG Designs – High Density 

Injectors & Low Density Injectors 

w/Mixing Devices

l Reagent Monitoring From flyash; shiftwise or weekly
Highlights of SCR Experience of

Japan & Europe (Cont’d.)

l Air Heater European mostly Enamel Coated

 DP up to 8 in. w.g., Deposition

l Flue Gas Handling Typically 3-7 in. w.g. Equipment

upgrade during FGD retrofit 

mostly accommodated SCR requirement

l I & C Feed forward Signal for reagent

demand from boiler NOx with a

feedback signal based on outlet 

NOx
Summary of European & Japanese

SCR Experience

l Coal sulfur mostly within 1.7%

l Av. Max. 85% NOx removal

l Significant number of tower boilers with a few SCR

operating problems

l Routine use of combustion controls

l Graduated catalyst geometry

l Inconsequential Am. Sulfate/bisulfate deposition – low

SO3 - <2 ppm NH3 slip – enameled APH surfaces

l Alkali injection – arsenic bonding and SO3 control

l Catalyst channel blockage by unburned carbon and

coarse fly ash

l Ammonia slip monitoring

l Catalyst performance monitoring & regeneration
Evaluation of Transferability of

Japanese & European Experience to

U.S. SCR Application

l Japanese & European experience mostly transferable to US with

respect to deNOx effy., NH3 Slip, SO2/SO3 Conv. E, SV, High/Low

Dust, Catalyst Composition, Geometry & Management

– Gas Velocity Distribution

– NH3/NO Ratio SD

– Air Heater Performance

US Situation Differs With Respect To:

l Reactor layout due to boiler design difference

l Reagent – Aq. Ammonia & Urea

l Higher deNOx effy. – advanced goal

l Most importantly Coal Type & its concomitant issues – e.g. Arsenic

Poisoning, Pore Blockage by PRB Coal Ash & SO3 Plume
Typical U.S.

SCR Experience
Typical U.S. Performance

Serial # 1 2 3 4 5 6 7 8 9 10 11 12

Unit

New

Madrid #2 Gavin Somerset

Paradise

#1&2

Bowen

 1 & 2

Bowen

3 & 4 Gorgas #10 Birchwood Roxboro

#4

Hawthorn

#5

Brandon

Shores Logan

Size Mwe 640 2 x

1,300

675 700 756 950 780 250 2 x 735 500 1370 200

Utility AECI AEP AES TVA GA PWR GA PWR AL Pwr So Energy CP&L KCP&L Constellatio

n

PG&E

Date

Commissioned

2/7/00 5/01 7/99 Spring

2000 &

2001

5/01 5/03 5/02 11/96 7/01 5/01 5/01 9/94

Firing Mode Cyclone W all Wall Cyclone Corner Corner Corner Corner PC PC PC PC

Coal Type 100%

PRB

High Vol.

Bit.

Bit./PRB Bit. Bit. AL Bit Bit. PRB Low S Bit.

Inlet NOx

lb/Mbtu

1.5 0.55 0.86-1.6 0.45 0.45 0.55 0.46 0.225

Outlet NOx

lb/Mbtu

0.105 0.05 0.07 0.07 0.08 0.1 0.097 0.099

DeNOx Eff. % 93 90 90 90 85 85 85 79 56 90 63

NH3 Slip PPM 3 <0.2 3 2 2 2 2 5 2 2 2 (1

achieved

initially)

SO2 lb/Mbtu 0.4 4.75-6.5 2 2 3.0

% Sulfur .23 3.4 1.5-4..60 2-3 1 1 1.5 1.5 0.56 <1.0

SO2 to SO3

Conv. %

3.0 1.6 0.75 0.75 <1.0 <0.75

Catalyst Type Plate Plate Plate Plate Honeycomb Honeycomb Honeycomb Plate Plate Plate Plate

Pitch mm 9.2 5.6 6.0 8.2

Reagent Ammonia Urea NH3

anhy.

NH3 NH3 anhy. NH3 anhy. NH3 anhy. NH3 anhy. Ammonia Ammonia Am.Aq.

SCR/deltaP

(Iwg)

8 2.8

Catalyst Life

Hrs.

20,000 24,000 20,000 24,000

Catalyst m3897 314 477

Arsenic ppm <20 2

deltaP Catalyst

(Iwg)

1.3 2.0 New

General Remarks World’s

1

st SCR

for 100%

PRB

Lime

addition

Continuous Low Dust Continuous Low Dust High

Dust
U.S. Coals
Coal Quality Parameters Affecting SCR Performance

Coal Parameter:

Sulfur:

Arsenic:

Calcium:

Sodium & Potassium:

Chlorine & Fluorine:

Unburnt Carbon:

Ash Burden

• Impact

• SO3 Formation in catalyst chamber by V-oxide

• Catalyst pluggage by am. sulfate/bisulfate

• High ammonia usage

• Catalyst surface masking

• Airheater corrosion & pluggage

• Catalyst surface & pore blockage

• Catalyst poisoning by arsenic oxide.

• Reduction in available catalyst sites by fine lime particles from PRB

coal

• Blockage also by Na&K-sulfates

• Reduction in active catalyst site by formation of vanadium

chloride/fluoride

• Catalyst pore blockage by Am-chloride/fluoride

• Increased ammonia usage

• Blockage of initial catalyst layers

• Higher the ash burden, higher catalyst deactivation & air heater

corrosion/blockage
Table 1

Typical Mineral Ash Analysis

Of U.S. Bituminous Coals

Constituent weight percent of ash

 Origin

Sample No.

SiO2 A1202 Fe2O3 TiO2 CaO MgO Na2O K2O SO3

Sample

No. Comments

Kentucky Deane 2

3

59.6

68.5

26.7

20.8

4.2

2.6

3.4

3.6

2.3

1.4

0.7

0.4

0.8

0.6

0.1

<0.1

1.8

1.7

2

3

High in silica

Illinois Carrier 

Mills

Utah Horse Canyon

26

67

17.5

25.6

9.2

21.0

64.1

20.5

0.4

0.6

4.1

15.8

0.4

0.7

0.3

2.0

1.0

0.2

1.8

10.9

26

67

Low in silica, sample 26, exceptionally high 

in iron; sample 67 moderately high in iron 

and calcium

Utah Horse Canyon 124 42.0 26.5 7.5 1.2 7.9 1.6 1.2 1.6 9.5 124 Moderately high in silica

West Virginia, 

Bickmore

127 46.1 34.5 7.5 1.5 2.5 0.7 0.3 2.0 3.0 127

Pennsylvania, 

Ebensburg

142 19.4 10.5 36.6 0.4 8.9 5.8 0.4 1.1 15.9 142 Low in silica, exceptionally high in iron

Oklahoma, 

Redstone

143 29.2 14.2 27.8 0.5 7.1 5.1 0.6 1.5 14.0 143

Table 2

Typical Mineral Ash Analysis

Of U.S. Sub-Bituminous/Lignite

Constituent weight percent of ash

Origin

Sam

ple 

No.

SiO2 A1203 Fe2O3 TiO2 CaO MgO Na2O K2O SO3

Sample

No. Comments

North Dakota, 

Zap lignite

87

88

20.0

23.5

9.3

13.6

7.5

5.7

0.5

0.5

20.8

18.3

6.0

5.4

11.5

8.3

0.4

0.3

21.9

21.7

87

88

Exceptionally high in sodium, fairly high in 

calcium, low in silica and alumina

Montana, 

Savage

lignite

91

92

17.0

12.5

14.6

13.3

1.2

6.8

0.4

0.3

34.6

26.1

13.3

10.4

0.3

0.3

0.1

0.1

14.3

26.17

91

92

Low in sodium, exceptionally high in calcium, 

low in silica and alumina

Wyoming, 

Glenrock and 

Gilette subbituminous

99

100

39.8

9.8

19.4

12.9

3.9

6.7

0.9

1.0

15.0

33.4

2.4

7.9

0.2

1.6

1.1

0.2

16.2

21.7

99

100

Glenrock fuel-ash sample moderately high in 

calcium; Gilette sample exceptionally high in 

calcium and exceptionally low in silica and 

alumina

Texas; Darco

lignite

140

141

38.4

62.1

21.0

16.8

11.2

3.9

1.1

0.9

10.0

5.2

1.7

1.1

0.7

0.5

0.5

0.6

14.6

8.9

140

141

Sample 140 moderately high in calcium and iron; 

sample141 exceptionally high in silica
A Typical Example of

The Difference in the Form of

Presence of Alakaline & Alkaline Earth Components in

US bituminous & Sub-Bituminous Coal

Fe203 34 66 15 85

Ti02 100 0 72 28

Al203 91 9 55 45

Si02 100 0 100 0

K20 84 16 31 69

Na2O 56 44 0 100

MgO 46 54 6 94

CaO 70 30 3 97

Coal Ash 80 20 46 55

Organically

Associated

Mineral

Matter

Organically

Associated

Mineral

Matter

% Total In

Each Portion

Illinois Bituminous Wyoming Sub-Bituminous
Main Features of U.S. Coals With Adverse

Impact on SCR Technology

Bituminous

• Higher sulfur than the coals used in Europe & Japan

• Higher arsenic (comes with sulfur)

• Higher ash burden (compared to sub-bituminous)

• More slagging type coal

Sub-Bituminous/Lignite

• Higher calcium & Magnesium mostly coal bound as in PRB

• (These in European & Japanese cases are in form of minerals)

• Higher sodium & potassium

• These pose perhaps the greatest challenge to U.S. SCR

installations

Eastern/Western Blends

• Still contains coal bound calcium, magnesium

• Little European & Japanese experience (blends are of imported

coals low in sulfur, calcium & sodium)
Mechanism of Catalyst Deactivation

by PRB Fly Ash

• PRB coal contains high (up to 30% of ash) calcium &

high (up to 10% of ash) magnesium

• These are mostly (up to 80%) present in the coal matrix

• These are readily released in the furnace as fine

particles of reflective calcium oxide & magnesium

oxides & silicates which combine with sulfur trioxide in

the convective pass to form calcium (and magnesium)

sulfates which plug the catalyst pores.

• Sodium ( and potassium) of PRB coals form sticky

sulfates and phosphates on the catalyst sites promoting

additional deposition of fly ash.
What Are Required?

And What Should Be Done?
Use Chemicals to Improve Catalyst Pore Blockage

using PRB Coal, Reduce LOI and Catalyst Surface

Masking Firing Bituminous Coal

• Convert fine calcium oxides & magnesium oxides into

compounds prior to contact with SO3 and thereby minimize

formation of Ca & Mg sulfates and reduce catalyst pore

blockage

• A chemical has been developed to control PRB’s reflective

ash generated slagging. This is considered to be able to

minimize Ca & Mg sulfate formation & thereby reduce

catalyst pore blockage

• Used over adecade, a chemical is used by the U.S. utility

industry firing bituminous coals to reduce LOI and improve

cycle efficiency by recovering superheat & reheat steam

temperatures.
Improved Understanding of Coal

and Ash Quality

Laboratory Studies for Inorganic Coal

Constituents & Ash Deposit evaluation

Physical

Computer controlled scanning electron

microscopy & X-ray Diffraction

Chemical

Fractionation for modes of occurrence of

calcium, magnesium, sodium & potassium in

coal
Arsenic Poisoning Mitigation
Mean Arsenic content of U.S. Coals

Source: U.S. Geological Survey

As PPM

• Appalachian Basin 22

n 2835

• Illinois Basin 10

n 298

• Powder River Basin 2.6

n 160

• Colorado Plateau 3.1

n 180

• Gulf Coast Lignites 5.1

n 135

n represents number of measurements
Physical & Chemical Deactivation Mechanisms

Physical – Arsenic Oxide (As2O3) Molecules Condense in Catalyst

Pores

Chemical – As2O3 Reacts with V2O5 to form Non-Catalytic Arsenic

Vanadate Compounds

Mitigating

 Measures: 1) Molybdenum Oxide (MoO3) Added to Catalyst

Composition which form Arsenic Molybdate –

More reactive than As-Vanadate which slows down

de- activation of active V2O5 sites

2) Calcium Oxide (CaO) added in furnace form CaArsenide [Ca3

(AsO4)2] which reduces As2O3 conc. in boiler

Reliable method of measurement of coal arsenic by EPA 2051 or

ASTM D6357 required & NOT by ASTM D4606
SO3

 Plume Visibility

Prevention
TABLE 1

(Ref.. Mineral Impurities in Coal Combustion – E. Raask P. 404

Table 19.1 SO3 concentration, dewpoint temperature, and acid deposition in coal-fired boilers

<285 <1

(<54)

Low sulfur, <1 >10 <1

 high calcium

285-295 1-2.5

(54-72)

Medium sulfur, 1-2.5 5-10 1-5

Medium calcium

 295-400 2.5-5

(72-261)

Medium sulfur, 1-2.5 2-5 5-10

 low calcium

400-410 5-10

(261-279)

High sulfur, >2.5 2-5 10-25

 low calcium

Maximum Acid

Deposition Rate

(mg m-2)

Dewpoint

Temperature

K (F)

SO3 in

Flue Gas

(ppm v/v)

CaO

In Ash

(%)

Sulfur

In Coal

(%)

Type of Coal
Development of Improved Prediction Method

Required For SO3 Concentration

Across High Sulfur Flue Gas System

(Current Methods Found

 Inapplicable To Field Performance)

l Coal Sulfur, Ash Chemistry, Flue Gas SO3 Conc. & Acid

Dew Point Relationship need review and development

l Mechanism of SO3 Concentration Enhancement by ESP

needs to be Ascertained

l Multi-Point Application of Chemicals for SO3 Mitigation

Should be Considered
• Alternative Catalyst Development

Without Oxides of Vanadium, Titanium,

Molybdenum & Tungsten

• Catalyst regeneration

• Reliable on line ammonia slip monitoring
Conclusions

l Over 100,000 MW of coal fired units in the USA might

need SCR retrofit by 2004 in response to EPA’s SIP Call

rule

l Evolved from two generations of design in the 70’s &

80’s in Japan & Europe, SCR technology has made great

strides W.R.T. NOx removal, NH3 slip, catalyst, reactor

design, process conditions, etc.

l While this experience has been utilized by the US SCR

industry, it is not adequately transferable to meet the

challenges of US boiler designs and especially the unique

US coal quality

l High sulfur & high arsenic bituminous & high coal-bound

calcium based PRB coal have not been experienced in

Europe & Japan
Conclusions (Cont’d.)

l Elimination of SO3 plume formation firing high sulfur

bituminous coal in units with wet FGD needs:

ÿ Development of improved SO3 formation prediction

methods

ÿ Improved understanding of the role of process

equipment/conditions

ÿ Multiple control strategy

• Use of additives to control catalyst deactivation by calcium

oxide & arsenic needs immediate consideration since the

deactivation mechanisms are understood & additives

effectiveness are proven

• Development of non-vanadium based catalyst formulations

for high dust application needs promotion

These goals need to be achieved as

“Necessity is the Mother of Invention”