BPE-PP-0011-v1-2008

One Source…Many Solutions…One Purpose2008 SCR User’s Group Conference

Copyright © 2008 Babcock Power Inc. All rights reserved.www.babcockpower.com

11/

Babcock Power Inc.

One Source Many Solutions One Purpose

How Does An SCR Work?

Presented by:

Bill Medeiros

2008 SCR User’s Group Conference

Copyright © 2008 Babcock Power Inc. All rights reserved. www.babcockpower.com

Basic SCR Chemistry

NOX NH3

N2 H2O

4 NO + 4 NH3 + O2 4 N2 + 6 H2O

7 N2 + 12 H2O6 NO2 + 8 NH3

Undesirable side reactions

SO2 + 1/2 O2

NH3 + SO3 + H2O

SO3

NH4 HSO4

Basic reaction equations

Typical coal flue gas95% NO & 5% NO2

2 NO2 + O2 + 4 NH3 3 N2 + 6 H2O



Basic SCR Chemistry



SCR Reactor Configuration

High Dust

Low Dust

Tail End




High Dust Arrangement



SCR Reactor Between

Hot ESP and Air Heater


Low Dust Arrangement




Tail End Arrangement




In Duct Arrangement





SCR Configurations

SCR BypassOTAG Operation Only

Start Up

SCR Low Load Temperature Control (High Dust SCR)Economizer Bypass

Bypass Damper Only

Bypass Damper and Backpressure Damper

Economizer Heat Transfer Surface Reduction

Water Bypass

In-Duct Gas Burners

Steam Bypass



Boiler Startup Bypass

Econ. FurnRoof

& CP PSH SSH

HPT

RH

#8 Htr. #7 Htr.

Flash Tank

Cond.

#6 Htr.

220

Valves

207

Valves

DEA

BFP

242

Valve



Static Mixers – Delta Wings



Ammonia Flow Control•Adjusted based on testing



Ammonia Injection & Flue Gas Mixing

PLANT 3

Burner NOx Test 1

300

350

400

450

500

550

600

0 20 40 60 80 100

Width, ft.

NO

x, p

pm

Series1

Series2

Series3

Series4

Series5

Series6

Inlet variations of

flue gas

composition

Load and burner

group dependent

Mix prior to

ammonia injection



Mixing Prior to Ammonia Injection

Gas Flow

from Boiler



Large Particle Ash (LPA)

LPA Properties

Size >4.0 mm

Density 0.7 to 1.25 g/cc

Sphericity 0.7 to 0.99

Coefficient of Restitution 0.15 to 0.2

Screen Design Important

Pluggage

Erosion



LPA Screen Design

Design and Modeling

CFD Modeling

Industry Coated Screens

Experience From Past

Soot Blowers

Low Velocity

Low Pressure Loss



Catalyst - Types

• Honeycomb

• Corrugated

• Plate



Catalyst Manufacture





Catalyst Vendors

Vendor Name Catalyst Type Fuel Type

Argillon (Siemens) Honeycomb Gas, Oil, Coal

Plate Coal High Dust

KWH Honeycomb Gas, Oil, Coal – Low Dust, Coal High Dust

Cormetech Honeycomb Gas, Oil, Coal – Low Dust, Coal High Dust

Haldor Topsoe Corrugated Gas, Oil, Coal – Low Dust, Coal High Dust

Ceram Honeycomb Gas, Oil, Coal – Low Dust, Coal High Dust

Nippon Shokubai Honeycomb Gas, Oil, Coal – Low Dust, Coal High Dust

Hitz America Corrugated Gas, Oil Limited Coal Experience

Hitachi America Plate Gas, Oil, Coal – Low Dust, Coal High Dust



Riley Standard Module



Catalyst Design Parameters

Fuels

Initial catalyst life (hours of initial operation)

Maximum ammonia slip

Flue-gas conditions

SO2 to SO3 conversion rate (initial – final)

NOx reduction

Catalyst layout (module size and number of modules per layer)

Flue-gas distribution across top layer of catalyst

Geometry – arrangement



Catalyst Pitch Selection

• High dust honeycomb (bituminous)

– 7 mm pitch - 500 m2/m3

• High dust honeycomb (sub-bituminous)

– 8.2 mm pitch - 420 m2/m3

• Low dust

– 5.9 mm pitch - 580 m2/m3

• Plate

– 5.6 pitch - 350 m2/m3



Catalyst – Fuel Impact

Major Considerations

Sulfur content (ammonium salts)

Ash loading

Arsenic

CaO

Vanadium (‘pet’ coke, heavy oils)

Other trace elements



Catalyst – Deactivation



Arsenic Effect on Catalyst Life

First noted in wet bottom 100% ash recycling boilers

Poisoning from As2O3 (gaseous)

Reacts with CaO to form non-poisoning Ca3(AsO4)2 (solid)

CaO addition proven in Europe and US

Additional effects

Increased ash loading

Lower SO3 production in boiler



CaO Deactivation MechanismThe deactivation is rate limited by CaO deposition

Step 1CaO is caught on the

catalyst surface

Process is dependent on availability and adhesion of CaO

•Rate controlling process for deactivation•Very slow concentration changes (~104 hours)

CaO

CaO

catalystsurface CaO

active sites

•Fast reaction time (~101 hours)

Step 2

SO3 bonding & diffusion

Process is function of mass transfer and concentration

CaO

active sites

SO3catalystsurface



Step 3

Diffusion and expansion CaO + SO3 CaSO4

Reaction is a function of diffusion rate and SO3 concentration

CaO Deactivation MechanismCaSO4 blocks active deNOx sites on catalyst surface

•Reaction time (~101hours) •Particle expansion of 14%

CaSO4

active sites

catalystsurface

Deactivation: NH3 & NOx can’t reach masked active sites

CaSO4

inactive sites

Step 4

Deactivation is a function of CaOloading over time

active sites

catalystsurface



Catalyst – Minimum Continuous Operating Temperature (Tmcot)

Minimum operating temperature for SCR without

formation of ammonium salts

High partial pressure in catalyst pores

Dew point in pores >> Dew point in duct

Tmcot = f(SO3,NH3,H2O)

Excess of NH3 and H2O at catalyst inlet

SO3 from boiler limiting factor

↑S in Fuel, ↑Tmcot



Flow Model Objectives

NH3/NOX distribution @ 1st layer

Gas velocity distribution

Temperature distribution

Gas flow angle @ 1st layer

Dust distribution

System pressure loss

Air heater requirements

Influence testing

Catalyst Requirements



Flow Modeling – Model Scales

Gas mixing and design 1:40 to 1:35

Larger scale (smaller model) allows for faster design

changes

Experience with transition between larger scale to

smaller scale to full scale

Dust layout 1:16 to 1:12

Necessary to satisfy the Barth number



SCR Flow Models

2u

pEu

ρ∆

=mm

gas

Dd

lCBa

ρ

ρ=

νbu

=Re



SCR Flow Model



Multiple Injection Points



SCR Dust Model



Catalyst – Cleaning

Steam Sootblowers

Requires controlled steam quality, dry steam

Rake type sootblower

Required for high ash concentration (> 20 g/Nm3)

Sonic Horns

Compressed air requirements typical of service air

Low air quantities required

Continuous operation

U.S. application and popularity increasing



Anhydrous Ammonia

Hazardous chemical

governed by codes

Aqueous Ammonia

Concentration based

codes, maybe changed in

future

Urea Based Ammonia

Safe storage, more equipment and complex

Ammonia Systems



Ammonia System – Safety Codes & Standards

3 Levels of alarm and detection

35 ppm (Lights): Threshold Limit Value – Short Term

Exposure Limit (TLV-STEL) by the American Congress of Governmental Industrial Hygienists

(ACGIH)

50 ppm (Lights & Horns): OSHA 8 hour exposure limit

300 ppm (Lights, Horns, & E-Stop): Immediately Dangerous to Life or Health (IDLH) limit from the

National Institute for Occupational Safety and Health (NIOSH) and OSHA



Ammonia InjectionAnhydrous

Vaporizers

Direct injection

Dilution air, 5% by volume

Aqueous

Vaporizers

Direct injection

Urea

Direct injection

Dilution air, 5% by volume



Ammonia System – Anhydrous

99.5% NH3, 0.5% H2O

Method of vaporization

Flooded vaporizer with storage tank

Level controlled vaporizer

Direct injection

Dilution air

5% ammonia by volume (lower explosive limit 15%)

Typically 175 to 300°F at duct injection location



Ammonia System – Anhydrous Codes

OSHA 29 CFR 1910.111, Storage and Handling of

Anhydrous Ammonia

ANSI/CGA K61.1, Safety Requirements for the

Storage and Handling of Anhydrous Ammonia

ASME B31.3, Process Piping



Direct Injection Anhydrous Ammonia System

Hot Water Coils(Redundant)

Flow Control Valves(Redundant)

Ammonia Pump

Dilution Air Header

Delta WingsTM

3-5% NH 3

300°F

Minimizes Tuning and Adjustment Requirements

Dilution Air Fans(Redundant)



Ammonia System – Anhydrous Equipment Selection

Storage Tanks

-28°F to site maximum design temperature

250 psig design pressure minimum

Code ASME Section VIII vessel

Excess flow valves on all nozzles

Two methods of level indication




Transfer pumps

Seal-less pump design

Magnetic drive

Canned pump

Suction pipe design

Recirculation vs. injection rate




Piping / Valves

No copper, brass, or galvanized steel

Conforming to ASME B31.3, Process Piping

Minimum number of threaded connections

Hydrostatic relief required on all isolatable sections

Leak / pressure tests of system prior to service

All instrumentation suitable for anhydrous ammonia




Truck / Railcar Unloading

Snappy Joes and breakaways to protect ammonia

equipment

DOT Regulations to be followed

Railroad unloading procedures per ammonia / railroad supplier

Truck unloading procedures per ammonia / truck supplier



Ammonia System – Aqueous

3 Common concentrations

9% Ammonia

19% Ammonia

29% Ammonia

No definitive codes or standards

Sound engineering practices need to be applied



Ammonia System – Aqueous Equipment Selection

Storage tanks

ASME Section VIII

API 610

Pumps same as anhydrous

Pipes and valves


Typical ASME B31.1 acceptable

Unloading by truck only



Dual Fluid Nozzle Injector



Ammonia System – Urea

Multiple conversion technologies available

Typically delivered in dry or liquid form

Best stored on site as liquid


Good engineering practices need to be applied

Heat tracing critical

Urea quality issues



Urea Systems (Others)

• FuelTech

– Thermal breakdown of urea by gas

combustion

– High gas use if ambient air is used



Catalyst in Place

Catalyst Staged

Catalyst Doors

Reactor Layer Detail



Domestic Shipment of Catalyst



Overseas Shipment Containers(Honeycomb Catalyst)



Lifting Catalyst on Hoist



Catalyst in Position for Loading



Catalyst Module Being Pushed into Reactor



Installation of Catalyst Module Seals



Requirements of NOx Measurement Instrumentation for SCR Control

Provide inlet and outlet NOx measurement in ppm for the forward

feed with back trim ammonia injection control loop

Respond quickly to changes in the NOx values to reduce the risk of

over/under feeding ammonia to the process

The ability to service the instrument, including probe in flue gas duct

without removing boiler or SCR from service



Types of Available NOx Measurement Instrumentation

Extractive, extractive systems draw flue gas at temperature from the

system in a heated sample line to the analyzer

Dilution Extractive, dilution extractive system draw flue gas from the

system and dilution the gas with air to lower the concentrations of

SO3, H2O, etc to eliminate the need for heated sample lines to

the analyzer

In Situ, in situ system place the measuring device directly in the flue

gas path



SCR Performance

11/



Units 1&2 Background

642 MWG CE balanced draft boilers

Eastern bituminous coal

High sulfur (3%)

Fuel oil burned at startup

U2A reagent

Routinely operate at minimum load of

33% MCR



Design Requirements

High NOx removal

92.5% NOx removal

0.045 lb/MBtu outlet

LPA Mitigation

LPA screen

Baffle and deflector plates

Minimum load of 33% MCR with 0.045 lb/MBtu outlet



Guarantees

Guarantees Values

Outlet NOx 0.045 lb/MBtu

Ammonia slip 2 ppmvd

Pressure drop 8.4 iwg

SO2 oxidation rate 0.50%

Ammonia consumption 1260 lb/h



SCR Design Parameters

Parameter Maximum Load Minimum Load

Boiler heat input, MBtu/h 5,800 2,400

Flue gas flow rate, lb/h 5,885,000 3,076,438

Inlet NOx, lb/MBtu 0.6 0.45

Outlet NOx, lb/MBtu 0.045 0.045

Economizer exit gas temperature, oF 700 495



SCR Design Features

Two four layer reactors per unit

Three initially installed layer and one future layer of catalyst

Inlet and outlet NOx analyzers

SCR inlet temperature control (per reactor)

Two double louver economizer bypass dampers

One single louver backpressure damper

Delta Wing™ static mixers with six ammonia injectors

Six sonic horns per installed catalyst layer



SCR Design Features

CFD model

Performed to examine screen location and pressure loss

Baffle location

LPA deflector plate

Identify lowest velocity zone

One LPA screen per reactor

No NOx components supplied screen

Hexagonal perforated plate

Low velocity

Minimize catalyst pluggage



SCR Temperature Control

Maintain SCR inlet temperature at all loads

Economizer bypass provides hot flue gas at low loads

Backpressure damper partially closes to force economizer bypass



SCR Flow Modeling

Two model scales performed

Flow model

1:40 scale

Optimize mixing

Identify performance parameters

Flow model photo courtesy of Ruscheweyh Consult andBalcke Dürr GmbH



SCR Dust Modeling

Dust model

1:15 scale

Verify flow model

Identify particulate settlement

Measure ash distribution at catalyst inlet

Flow model photo courtesy of Ruscheweyh Consult andBalcke Dürr GmbH



SCR Results

Acceptance test results

Reactor 1A full load

42 test ports

NH3/NOx profile

Guarantee of 5% rms

Tested 1.8% rms at 93% NOx removal



SCR Results

Acceptance test results

Reactor 1B full load

42 test ports

NH3/NOx profile

Guarantee of 5% rms

Tested 2.2% rms at 94.6% NOx removal



SCR Results

Reactor 1A Reactor 1B Reactor 1A Reactor 1B

Reactor inlet temperature, oF 667 653 677 675

Inlet NOx , lb/MBtu 0.43 0.59 0.495 0.52

Outlet NOx , lb/MBtu 0.032 0.032 0.043 0.054

NOx removal, % 92.6 94.6 91.3 90.0

Ammonia slip, ppm 0.08 0.11 0.1 <0.1

Ammonia consumption, lb/h 482 657 N/A N/A

Pressure drop, iwg 7.1 7.4 N/A N/A

ParameterMaximum Load Minimum Load



SCR Results(Thirty Day Rolling Average)

0.000

0.020

0.040

0.060

0.080

0.100

0.120

June-07 August-07 September-

07

November-07 January-08 February-08 April-08

Date

Avera

ge N

Ox R

ate

(lb

/mm

Btu

)



SCR Achievements

High Removal Efficiency (> 92.5%)

Low Ammonia Slip (< 2 ppm)

Low SO2 to SO3 Conversion (< 0.5%)

Wide SCR Operating Range (33% to 100%)

Proven Long Term Operation



SCR Performance Enhancements

11/



Improved Tuning



South Bay Unit 3Chula Vista, CA

Boiler Manufacturer Riley Stoker

Generator Manufacturer General Electric

Gross Generating Capacity 183 MW

Heat Input 2,145 MMBtu/hr

Operating Date 1964

Fuel

SCR NOx Control

Natural Gas and/or # 6 Oil

March 2001



South Bay Unit 3 SCR Arrangement



South Bay Unit 3 SCR



Initial Test Results – Gas Fired

.91[0.0104]8.4[0.0736]59.6Actual Low Load

10[0.0105]8.5[0.1544]125Design Low Load

5.21[0.0137]11.1[0.1784]144.4Actual Full Load

10[0.0143]11.6[0.1544]125Design Full Load

NH3 ppm

slip

Outlet NOxInlet NOx

ppmdv @ 3%O2 [lbs/MMBtu]



Operating History

2001 Acceptance test

2004 Stack tests NH3 slip exceeds California limits

NH3 >> 10.5 ppm

Top to bottom outlet NOx gradient

Inspection: ammonia injection valve plugged

2004 SCR re-tuned NH3 slip 2.2 ppm (high load)

Low load ammonia flow control difficult

2005 Enhanced control system installed

2005 Testing

Ammonia feed control at high/low load

Inlet/outlet NOx profiles



Flow Model Inlet NH3 Profiles

Economizer Outlet (West)

Economizer Outlet (East)

Injection

Nozzle A

Injection

Nozzle B

0

2000

4000

6000

8000

100000

10002000

z [mm]

0

0.5

1

1.5

2

2.5

3

0

0.5

1

1.5

2

2.5

3

n

01000

2000

z [mm]

0 bis 0.250.25 bis 0.5

0.5 bis 0.750.75 bis 1

1 bis 1.251.25 bis 1.51.5 bis 1.75

1.75 bis 22 bis 2.252.25 bis 2.5

2.5+

A: 100%, B: 100% A: 118%, B: 82%



Flow Model Inlet NH3 ProfilesSingle Nozzle Tests



Injection Nozzle A

Injection Nozzle B

0

2000

4000

6000

8000

100000

10002000

z [mm]

0

0.5

1

1.5

2

2.5

3

0

0.5

1

1.5

2

2.5

3

n

01000

2000

z [mm]

0 bis 0.25

0.25 bis 0.5

0.5 bis 0.750.75 bis 1

1 bis 1.25

1.25 bis 1.5

1.5 bis 1.751.75 bis 2

2 bis 2.25

2.25 bis 2.52.5+

Nozzle A Nozzle B

Normalized Inlet Duct Ammonia Distribution

From Each Injection Nozzle



Injection Nozzle A

Injection Nozzle B



Injection Nozzle A

Injection Nozzle B



Injection Nozzle A

Injection Nozzle B

0

2000

4000

6000

8000

100000

10002000

z [mm]

0

0.5

1

1.5

2

2.5

3

0

0.5

1

1.5

2

2.5

3

n

01000

2000

z [mm]

0 bis 0.25

0.25 bis 0.5

0.5 bis 0.750.75 bis 1

1 bis 1.25

1.25 bis 1.5

1.5 bis 1.751.75 bis 2

2 bis 2.25

2.25 bis 2.52.5+

Nozzle A Nozzle B



0

2000

4000

6000

8000

100000

10002000

z [mm]

0

0.5

1

1.5

2

2.5

3

0

0.5

1

1.5

2

2.5

3

n

01000

2000

z [mm]

0 bis 0.25

0.25 bis 0.5

0.5 bis 0.750.75 bis 1

1 bis 1.25

1.25 bis 1.5

1.5 bis 1.751.75 bis 2

2 bis 2.25

2.25 bis 2.52.5+

Nozzle A Nozzle B





Outlet NOx Profiles*June 2004

0 5 10 15 20 25 30

WidthFlow Out of Page

0

5

10

15

20

25

30

Heig

ht (f

t) W

est

0 5 10 15 20 25 30

WidthFlow Out of Page

0

5

10

15

20

25

30

Heig

ht (f

t) W

est

* Testing by FERCo

Test 1, 165 MW Test 8, 158 MW

Avg NH3 slip 2.2 ppm



SCR Control



NOX Measurement

Rea

ctor

Outlet

SCR Outlet NOx Probe Locations

Option 2

Option 1


NOx Probe Location


NOx Probe Location

NOx / O2 Analyzer Shelter Location

(Adjacent to Existing CEMS Building)R

eact

or

Outlet


Option 2

Option 1


NOx Probe Location


NOx Probe Location

NOx / O2 Analyzer Shelter Location

(Adjacent to Existing CEMS Building)


A-Side (east) B-Side (west)


A-Side (east) B-Side (west)



Ammonia Dual RangeFlow Control

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500

Ammonia Flow, lb/hr

Va

lve

Po

sit

ion

, %

op

en

High Flow Valve(1/2"w /Trim E, CV=0.5) High Flow Valve(1/2"w /Trim F, CV=0.32)

Low Flow Valve(1/2"w /Trim J, CV=0.05)

Full Load Oil

Full Load Gas

Low

Load

East

West

Purge



Outlet NOx Profiles*July 2005

0 5 10 15 20 25 30

Width (ft)Flow Out Of Page

0

5

10

15

20

25

30

Heig

ht (f

t)

West

0 5 10 15 20 25 30


0

5

10

15

20

25

30

Heig

ht (f

t)

West

0 5 10 15 20 25 30


0

5

10

15

20

25

30

Heig

ht

(ft)

W

est

East

Manual Control

Automated Control

35 MW

107 MW

140 MW

* Testing by FERCo



Summary

Limited number of NH3 injectors

Clearly defined influence fields for each injector

Demonstrated improved performance with automatic control of injector NH3 flow



System Testing – NH3/NOx Distribution

Calculated from inlet & outlet NOx grids

Calculate for every point on outlet

Formula:

Variation > 0 excess ammonia, < 0 excess NOx

10013 ⋅

−

−

−=

AVEOUTLETAVEINLET

POINTOUTLETAVEINLET

X NOxNOx

NOxNOx

NO

NH



System Optimization – Influence Testing

Insight into ammonia distribution

Aids in injector tuning

Influences can be simulated in the flow model for

comparison



System Optimization – Influence Testing

5 10 15 20 25 30 35 40 45 50

5

10

15

20

25

30

35

40

45

304

299

305

304

268

321

333

339

312

305

346

371

399

390

373

449

424

422

460

480

518

518

496

508

510

540

531

521

515

514

545

532

527

520

520

557

548

544

539

537

#1#2#3#4#5#6

100%0%0%0%0%0%

5 10 15 20 25 30 35 40 45 50

5

10

15

20

25

30

35

40

45

310

298

308

308

271

329

332

341

307

312

356

366

394

383

377

446

417

425

450

475

516

504

502

499

513

539

526

502

519

522

549

530

531

526

525

563

547

547

547

547

#1#2#3#4#5#6

420422424426428430432434436438440442444446448450452454456458460462464466468470

0%100%0%0%0%0%

Valve 1 Valve 2



Optimization Technique

∑=

=N

j

jiji XKB1

∑=

=M

i

i

avgM

BAMM

1

∑∑

∑=

=

=

−=M

iM

j

j

avg

i

iM

i

i

M

A

AMM

A

BABSD

1

1

1∑∑

==

×=M

i

i

N

j

j AX11

η

Linear constrained optimization

technique to minimize ∑=

M

i

iD1



Optimized Distribution Tuning

• Simulated in flow model

• Has been used to manually tune SCR

• Patent pending on automated tuning



Retrofit – Low Load Operation



Operational Issues

• 610 MW unit

• Daily operation down to <350 MW

• Minimum catalyst operating temperature 570oF

– Turning off ammonia flow at 440 MW

– Non-compliance to 30 day rolling average



Initial Findings

• Significant temperature stratification in catalyst inlet face

– Lack of mixing between economizer outlet and bypass flow

• Insufficient economizer bypass flow to achieve desired catalyst operating temperature

• Possible solutions

– Better mixing of economizer and economizer bypass flows

– Increased bypass flow

• Backpressure damper

• Raising feedwater temperature



Thank You

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