boiler optimization for nox emision reduction

8/22/2019 Boiler Optimization for nox emision reduction

1/40

Boiler Optimization for Mercuryand NOx Emissions Reduction

EPGAs 2005 Power Generation ConferenceSeptember 7-8, 2005

ENERGY RESEARCH CENTER

Carlos E. Romero

Harun BilirgenNenad SarunacEdward K. Levy


2/40

BACKGROUND

[1] Controlling Power Plant Emissions:

Overview, USEPA Web Site.

Approximately 75 tons ofmercury are found in the coaldelivered to coal-fired power

plants each year and abouttwo thirds of this mercury isemitted to the air, resulting inabout 50 tons being emittedannually. This 25-tonreduction is achieved in thepower plant boilers and indifferent ways throughexisting pollution controlssuch as FFs and ESPs forparticulate matter, scrubbers

for SO2 and SelectiveCatalytic Reduction (SCR)systems for NOx Emissions1.

State Mercury Emissions Limits

NJ CTMA (Phase 1)

MA (Phase 2)

WI (Phase 1)

WI (Phase 2)

Federal (Phase 1)

Federal (Phase 2)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

2004 2006 2008 2010 2012 2014 2016 2018 2020 2022

Implementation Date

Reduction


3/40

Three forms of mercuryemissions are produced:

Elemental mercury (Hg0

) insoluble, volatile.

Oxidized mercury (Hg+2)

water soluble, easy toabsorb.

Particulate mercury (Hgp) associated with the fly ash.

At combustion temperaturesall mercury is present as Hg0.Mercury speciation andreduction occurs as thecombustion gases cool downin the convective pass andinteract with the ash andAPCDs.

After Zygarlicke, J., et.al.After Zygarlicke, J., et.al. Fundamental Mechanisms of HgFundamental Mechanisms of Hg

Species Formation in Coal Combustion Flue Gas.Species Formation in Coal Combustion Flue Gas.

MERCURY FORMATION IN

COAL-FIRED BOILERSOptimization Process

Occurs AfterCombustion


4/40

Concentration of Hg0 fromcoal-fired boilers varies

from 10 to >90%. Itdepends on:

Coal (Blend) Characteristics

Boiler Design/Equipment

Boiler OperatingConditions!!

Coal (blend) effect on Hgemissions is related to the

Cl concentration in thecoal and to some extent toother elements such as S,Fe and Ca.

After Senior, C., et.al.After Senior, C., et.al. Modeling Gaseous Hg BehaviorModeling Gaseous Hg Behavior

In Practical Combustion Systems.In Practical Combustion Systems.

MERCURY EMISSIONS FROM

COAL-FIRED BOILERS


5/40

BOILER EQUIPMENT IMPACT ON

MERCURY EMISSIONS

Mercury removal varies

across air pollution controldevices :

Cold-side ESPs 20-40%

Hot-side ESPs 0-10%

Fabric Filters 30-60%

Wet/dry FGD and spray dryerabsorbers 60-90% ofbivalent Hg

SCR 40-60%

0

20

40

60

80

100

0 20 40 60 80 100Hg-ESpecies Concentration, %of Total Hg

CESP+FF

CESP+SDA

FF+SDA

FF

Higher fraction of Hg0 is a problem indifferent APCDs.


6/40

BASELINE MERCURY SPECIATION

FROM SELECTED POWER PLANTS(ICR Database)M ercury Speciation at Selected Pow er Plants

0

2

4

6

8

10

12

14

16

18

Allia

ntEnerg

y

Allia

ntEnerg

y

Domini

onEnerg

y

FirstE

nergyCorp

.

PPLGen

eration,LLC

U.S.

Gen

.

U.S.

Gen

.

U.S.

Gen

.

PSE&G

MercuryConce

ntration(ug/dscm)

Elemental Mercury

Oxidized Mercury

Particulate Mercury


7/40

To achieve 90 percentHg control by AC,

approx. 18,000:1 C/Hgratios are needed for 10m particles.

AC is forecasted to incur

an approximated costfactor of 0.4 mils/kWh(assumes injection ratiosof C/Hg of 10,000:1,

$0.50/lb of AC).Anticipated level of AC

injection represents 1 to2 percent of ash loading.

From EPRI Journal On-Line.http://www.epri.com/journal/details.asp

MOTIVATION - ACTIVATED CARBON

FOR MERCURY CONTROL

DisposalProblems

IECMCalculation

Untreated AC


8/40

IMPACT/IMPORTANCE OF BOILEROPERATING CONDITIONS ON MERCURY

The fate of Hg emissions is impacted by the chemical and physicalprocesses occurring in the boiler convective pass and APCDs.Homogeneous Hg oxidation is a kinetically controlled process occurring in the flue

gas. It is affected by flue gas time-temperature trend and composition.

Heterogeneous oxidation and adsorption is affected by the combined effect ofsurface chemical kinetics and mass diffusion. It is promoted by the nature of the flyash and flue gas conditions and composition.

Link between boiler conditions and Hg emissions:Time-temperature history - flue gas temperature, APH performance, stack flow.

Fly ash characteristics - mill classification, low-NOx firing system operation, fuel

blending.Flue gas conditions excess O2 level, reduced NOx emission level.

Other links - operating practices, boiler load profile, sootblowing, etc.

Importance of getting a handle on the operating conditions impacts:Interpretation of Hg test data.

Development of Hg emissions control options.

Reduce the cost of compliance.

These variables ensure that Hg speciation is site-specific.


9/40

BOILER OPTIMIZATION FOR MERCURY

CONTROL PROJECTS AT THE ERCFeasibility Study (included modeling/review)

Boiler Optimization Project

Activated Carbon Injection Project

Objectives:

Develop technical understanding and analytical model of Hgbehavior in the flue gas in relation to appropriate boilercontrollable parameters.

Investigate the extent of Hg reduction by optimization of boileroperation through field testing at full-scale boilers.

Investigate activated carbon injection requirements for Hgcompliance in combination with optimized boiler control settings.


10/40

POWER PLANT OPTIMIZATION

EXPERIENCE ERC experience with coal-

fired plant optimization

includes: combustion

optimization, sootblowingoptimization, and SRC and

ESP tuning.

There is a trade-off between

Hg oxidation and reduction

and:

Other emissions such as CO and

NOx.

The level of unburned carbon inthe fly ash.

Unit heat rate.

ESP collection efficiency and

stack opacity.

8,900

8,950

9,000

9,050

9,100

9,150

9,200

9,250

9,300

0.40 0.45 0.50 0.55 0.60 0.65

NOxEmission Rate [lb/MBtu]

UnitHeatRate[Btu/kWh]

100 Btu/kWh


11/40

MERCURY MODELING

Mercury model includes a reaction scheme with 35 species and 92 reactionsand the heterogeneous Hg oxidation by fly ash.

Model validated against a range of datasets.

Model used to interpret test data and guide parametric testing.

35%

40%

45%

50%

55%

60%

65%

70%

75%

211 212 213 214 215 216 217 218

Temperature Drop Across APH (Deg. C)

GaseousHg

0OxidationAcross

APH

Experimental Results

Homogeneous Model Results

Homo+Hetero Model Results

Baseline O2

LOI = 1.4 LOI BL

Low O2

LOI = 1.7 LOI BL

Reduced APH

Rotation Speed

LOI = LOI BL

APH Steam Coil On

LOI = LOI BL

Open SOFA

LOI = 1.3 LOI BL

High O2

LOI = 1.3 LOI BL


12/40

MODEL RESULTS

Effect of APH Gas Inlet Temp. on Hg Oxidation Operation of the air preheater impacts the Hg0/HgCl2 ratio at the air

preheater outlet.


13/40

MODEL RESULTS

Example of Boiler Operation vs. Hg Oxidation Each trend corresponds to a combination of boiler control settings that result in

changes to flue gas conditions and, consequently, the Hg0/HgCl2 ratio.

Elemental Mercury Reduction for Different Boiler Operating Conditions

700 MWgWall-Fired Boiler; 3 Elevations of Low-NOx Burners

0

10

20

30

40

50

60

70

80

90

100

110

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Time (sec.)

ElementalHginFlu

eGas(%)

Operating Conditions 1




Furnace Exit

Economizer Inlet

Air Preheater Inlet

Air Preheater Outlet

Stack


14/40

FIELD TESTING

Testing at three coal-fired units that firebituminous coals was performed:

Site #1 is a 108 MW, T-fired boiler. Cold- and hot-ESP, andtubular APH. Conventional burners. Unit burns low-Sulfur EasternU.S. bituminous coal.

Site #2 is a 250 MW, T-fired boiler. Rotating APH with two coldESPs in series. LNCFS-III low-NOx firing system. Unit burns U.S.bituminous and imported coals.

Site #3 is a 650 MW, opposed wall-fired boiler. Rotating APH with

two cold ESPs in series. DRB-XCL low-NOx burners with OFA. Unitburns U.S. bituminous and imported coals.


15/40

Analytical capabilities:

Baldwin and Apogee

inertial filtration probes.Pretreatment/conditioning

units.

PSA SCEMs for Hg

speciation.OHM with EPA Method

17 (performed on-site).

Coal, pyrite and fly ashanalyses (ultimate and

proximate analyses, Hg,Cl, S, LOI).

Oxygenanalysis

Frequent

replacement of

syringe and

septum

Independent

check of MFC

Direct

measurement

of HgO

source

(CavKit outlet)

Oxygen

analysis

Sample Gas

Conditioning

& Transport

Directinstrument

calibration

Independent

check leakage

of probeGold trap & Hg Lamp

High span

Blank

High span

BlankHigh span

Blank

Sample Gas

ExtractionHg

Measurement

Note: SCEM Ports OHM Ports

FIELD TESTING


16/40

Feasibility phase involved fivedays of boiler manipulation perboiler, at two boilers.

Boiler optimization project attwo units involved a ten-daytest schedule that includedbaselining, parametric testing,and optimal condition tests.

Parameters investigated: unitload, excess air, OFA settings,mill bias and O/S configurationand classification, APH back-end temperature, ESPenergization and rapping, andsootblowing.

AC injection project involvedtesting at two units at differentAC conditioning rates undernormal and optimal low-Hgoperating conditions.

Sample Boiler Optimization Schedule

FIELD TESTING


17/40

Overall Removal Efficiency = 38.4%Average Excess O2 = 2.13%Fly Ash LOI = 9.93%

Feasibility Field Test Results Site #1

Overall Removal Efficiency = 20.0%Average Excess O2 = 2.69%

Fly Ash LOI = 6.68%


18/40

Correlation Between Hg Concentration at the HESP Inlet and in the Coal

y = 89.565x - 0.8351

R2= 0.903

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0.03 0.04 0.05 0.06 0.07 0.08 0.09

Hg Concentration in the Coal (ppmw)

GaseousHg

TC

oncentrationatHESPinlet

(ug/dscm)



19/40

Gaeseous Hg concentration at HESP Inlet and Outlet

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

1/16/04

8:38

1/16/04

9:07

1/16/04

9:36

1/16/04

10:04

1/16/04

10:33

1/16/04

11:02

1/16/04

11:31

1/16/04

12:00

1/16/04

12:28

1/16/04

12:57

1/16/04

13:26

Time

GaseousHg

Tc

oncentration(ug/dscm

)

Hg at HESP in

Hg at HESP out

Test 8 - Low O2

Test 9 - Baseline

SCEM Hg Analyzer ReadingFrequency = 6 min.



20/40

Fly Ash LOI Effect on Hg Emissions

0

1

2

3

4

5

6

7

8

9

10

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Fly Ash LOI (%)

Hg

TConcentration

atHESPInlet(ug/dscm

)

0.020

0.025

0.030

0.035

0.040

0.045

0.050

0.055

0.060

0.065

0.070

Hgp

ConcentrationinFlyAsh(ppm

)

Test 7

Test 7

Test 6

Test 6

Test 9

Test 9

Test 10

Test 10

Test 8

Test 8

Test 15

Test 15


High O2

Baseline

Low O2


21/40

Hg Reduction across APH - Effect of Unit Load

0

5

10

15

20

25

30

240 250 260 270 280 290 300

Temperature Difference across APH (deg. F)

GaseousHg

TRedu

ctionacrossAPH(%)

Test 16 - 98 MW

Test 17 - 72 MW

Test 18 - 40 MW

Unit Load: 40 MW

72 MW

90 MW



22/40





23/40

Effect of Combustion Conditions on Total HgNew Cold ESP Inlet

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 50 100 150 200 250 300 350 400 450 500

Time (min.)

TotalGaseous

HgConcentration

(ug/dsc

m@3

%O2)

4-Mills I/S

OFAs at 80/10/5%

Excess O2= 2.5%

4-Mills I/S

OFAs at 80/10/5%

Excess O2= 3.5%

4-Mills I/S

OFAs at 80/10/5%

Excess O2= 1.8%

3-Mills I/S

OFAs at 100/90/5%

Excess O2= 2.2%

3-Mills I/S

OFAs at 5/5/5%

Excess O2= 2.2%

3-Mills I/S

OFAs at 100/90/5%

Excess O2= 2.5%

LOI = 18.8%

LOI = 17.4%

LOI = 22.3%LOI = 18.0%

LOI = 20.7%

LOI = 22.1%



24/40

Hg Concentration v.s. Fly Ash LOI

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

16 17 18 19 20 21 22 23 24

Fly Ash LOI @ Old ESP Hoppers (%)

TotalGaseous

HgConcentration

(ug/dscm

@3

%

O2)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

HgConcentrationinFlyAsh(ppm

)

HgT at New ESP inlet

HgT at Stack

Hg0 at New ESP inlet

Hgp in Fly Ash (E3)



25/40

Effect of Air Preheater Temperature Trace on Hg OxidationAPH Inlet and Outlet

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

410 412 414 416 418 420 422 424 426

Temperature Drop Across the Air Preheater (deg. F)

Percentage

ofHg

0Reduction

Baseline, 3-Mills

Reduced APH Rot. Speed, 3-Mills

Steam Coils ON, 3-Mills

Baseline, 4-Mills

Low O2, 4-Mills

High O2, 4-Mills



26/40

Sootblowing Effect (on 1/28-29/2004)

0.5

1.0

1.5

2.0

2.5

3.0

1/28/0419:12

1/28/0420:09

1/28/0421:07

1/28/0422:04

1/28/0423:02

1/29/040:00

1/29/040:57

1/29/041:55

1/29/042:52

1/29/043:50

1/29/044:48

1/29/045:45

1/29/046:43

1/29/047:40

1/29/048:38

1/29/049:36

Time

ExcessO2(%)/Hg(ug/dscm)

250

252

254

256

258

260

262

264

FlueGasTe

mperature(deg.F)

O2

Hg

New ESP inlet Temperature

Stack Temperature

APH IR 15, IR 21 IK 3 APH IR 17, IR 25 IK 4 APH IR 2-9


Elemental

Total


27/40

Impact of Comb. Conditions on Hg Site #2


28/40

Field Test Results Site #2

Total Mercury Concentration at the Stack

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Test

1-Ba

seline

Test2-Low

NOx

Test3-Low

NOx

Test4

Test5

Test6-Low

NOx

Test7

Test8

Test9

Test1

0

Test1

1

Test1

2

Test

13-LowH

g

Test

14-LowH

g

Hg

TC

oncentrationatNewESPoutlet

(ug/dscm)

SCEM

OHM

NOx = 0.328 lb/MBtuCO = 11 ppm

NOx = 0.263 lb/MBtuCO = 98 ppm


29/40

Unit 1 July 4, 2004 - ESP In and Out

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

7/4/04 14:24 7/4/04 15:36 7/4/04 16:48 7/4/04 18:00 7/4/04 19:12 7/4/04 20:24 7/4/04 21:36

Time

ElementalHga

tESPInletandOutlet

(u

g/dscm)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

TotalHgatE

SPInletandOutlet

(u

g/dscm)

Hg0 Inlet

Hg0 Outlet

HgT Inlet

HgT Outlet

TEST- 14

Low-Hg Settings



30/40

Activated Carbon - Mercury Tests

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0.0 5.0 10.0 15.0 20.0 25.0 30.0

AC Normalized Injection Rate [lb/MMacf]

Hg

TRemo

valEfficiency(%)

(BasedonAPHinlet-ESPoutlet)

BL+AC Injection

Low-Hg+AC Injection

Calculated Injection Rate

Assummes a 33,350 ksch

Stack Flow @ 272 deg. F



31/40



0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

BL+13

AC

BL+13

AC

BL+17

AC

BL+17

AC

BL+26

AC

BL+26

AC

BL1

BL+4AC

BL+4AC

BL+10

AC

BL+10

AC

Low-Hg

1

Low-Hg+4

AC

Low-Hg

+10AC

Low-Hg

+10AC

Low-Hg

+20AC

Low-Hg

+20AC

Low-Hg

2

Low-Hg

3

Low-Hg+4

AC

BL2

BL3

StackHg

TCo

ncentration(ug/nm

3@

3%O2)

OHM

SCEM

Compliance

0.7

ug/n


32/40

Impact of Comb. Conditions on Hg Site #3


33/40

Field Test Results Site #3Total Mercury Concentration at the Stack

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Test

1-Ba

seline

Test

2-Ba

seline

Test

3-Ba

seline

Test

4-Ba

seline

Test5

Test6

Test7

Test8

Test9

Test1

0

Test

11-LowH

g

Test

12-LowH

g

Test13

-Ba

seline

Test14

-Ba

seline

Hg

TC

oncentrationatNewESPoutlet(ug/dscm)

SCEM

OHM

Outlier


34/40

Impact of ESP Operation on Hg Site #3

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

7/3/2004 6:36 7/3/2004 9:00 7/3/2004 11:24 7/3/2004 13:48 7/3/2004 16:12 7/3/2004 18:36

Time

Hg

TandHg

0atESPOutlet(ug/dscm,correctedto3%O2)

Hg0 at Stack

HgT at Stack

Implementation of

ESP low-Hg Settings

Reverse of ESP

low-Hg Settings


35/40



0

10

20

30

40

50

60

70

80

90

100

110

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0

AC Normalized Injection Rate [lb/MMacf]

Hg

TRemovalEfficiency(%)

(BasedonAPHinlet-ESPoutlet)

BL+AC Injection

Low Hg+AC Injection





36/40



0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

BL1 BL2 BL3

BL+8

AC

BL+8

AC

BL+16AC

BL+16AC

BL+6

AC

BL+6

ACLo

w-Hg

LowHg

+9AC

Low-Hg

+9AC

LowHg

+3AC

LowHg

+3AC

LowHg

+12AC

LowHg

+12AC

LowHg

+15AC

BL+3

AC

BL+3

AC

BL+3

AC

LowHg

+10AC

LowHg

+10AC

StackHg

TConcentration(ug/nm

3@

3%O2)

OHM

SCEM


37/40

Field Test Results Site #3Activated Carbon - Mercury Tests

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0

AC Injection Rate [lb/MMacf]

StackHg

TCon

centration(ug/nm3@

3%O2)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

Instantaneou

sStackOpacity(%)

BL+AC Injection

Compliance Limit

Opacity Low Hg

Opacity BL

Low Hg+AC Injection




0.74

ug/nm3


38/40



0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 100 200 300 400 500 600 700

AC Injection Rate [lb/hr]

Hg

0/HgTR

atioattheStack

OHM

SCEM


39/40

CONCLUSIONS

Mercury regulations are an urgent issue for the power industry. Low-cost reductions in the 30-50 % range are attractive.

Analytical and experimental studies have suggested that boileroperating conditions can influence mercury oxidation and emissions

from coal-fired boilers. Target parameters are: residence time (in-flight capture), flue gas

temperature, and fly ash size and unburned carbon level.

Testing performed at three units, rated at 108, 250 and 650 MW,

burning bituminous coals confirms the merit of optimizing boileroperation through changes to the control settings for mercuryemissions reduction. This also results in a NOx emissions reductionsco-benefit.

An optimization test strategy involves unit baselining, parametric

testing, extended test at optimal conditions and testing to determineAC requirement for trim control.


40/40

Questions

boiler optimization for nox emision reduction

Documents