MANSFIELD UNIT 2BOILER SLAG ANALYSIS

JANUARY 9, 2001

AGENDA

Introduction

Coal Characteristics

Combustion Contributors to Slagging

Dolomite Issues

Slagging Analysis

Conclusions / Corrective Actions

C. Swanson

J. Mooney

J. Davis

M. Lamison

S. Harding

C. Swanson

Mansfield Unit 2 was forced off-line Sunday,

12-17-00, as a result of a large slag fall that

caused multiple leaks in the north and south

bottom ash hopper slope tubes.

SEQUENCE OF EVENTS

10-02-00 Started the long term dolomite test on Unit 2.

10-30-00 Operations noted unusually heavy slag build-up on the pendant slope area.

11-01-00 Approximate start of high sulfur fuel deliveries.

11-08-00 Slag observation guidelines were provided to Operations and the dolomite feeders were shut off daily to improve slag observations.

11-22-00 Initiated water blasting of pendant slag to evaluate its effectiveness.

SEQUENCE OF EVENTS (CONT)

11-28-00 2G mill was taken off for an overhaul increasing top mill operation at high loads.

12-05-00 Boiler average furnace exit gas temperature (FEGT) started to trend upward on Unit 2.

12-16-00 Boiler slope blowers 25 and 26 became obstructed with slag that is believed to have slid down from the upper pendants.

12-17-00 Unit 2 tripped off-line.

THEORETICAL CONTRIBUTORS TO SLAGGING

• CHARACTERISTICS OF THE COAL – Iron and ash content

• ASH FUSIBILITY– Furnace Exit Gas Temperature (FEGT)

PRACTICAL CONTRIBUTORS TO SLAGGING

• HIGH SULFUR MCELROY FUEL

• DOLOMITE INJECTION

• 2G MILL OUT-OF-SERVICE FOR REBUILD

• HIGH UNIT CAPACITY FACTORS

• BOILER COMBUSTION DEFICIENCIES

FUEL QUALITY

SULFUR CONTENT (LB/MMBTU)

3.75

3.91

3.35

33.13.23.33.43.53.63.73.83.9

4

NORMAL RECEIVED CONTRACT UPPERLIMIT

MAX LEVELSRECEIVED

(Max levels based on individual barge analysis)

DOLOMITE INJECTION

• BLOCKS SLAG OBSERVATIONS VISUALLY AND BY THE CONTROL ROOM CAMERAS

• POTENTIALLY INCREASES SLAGGING TENDENCIES OF SOME FUELS BY LOWERING THE ASH FUSION TEMPERATURE

• RESULTS IN HIGHER ASH LOADING

• CHANGES CHARACTERISTICS OF THE SLAG THAT IS FORMED

2G MILL UNAVAILABILITY

• REQUIRES THE USE OF UPPER MILL 2D FOR LOAD

• ADVERSLY EFFECTS COMBUSTION DUE TO SINGLE TOP MILL OPERATION

• REQUIRES HEAVIER MILL LOADING DUE TO THE UNAVAILABILITY OF A 7th MILL

• INCREASES FURNACE EXIT GAS TEMPERATURE (FEGT)

HIGH CAPACITY OPERATION

UNIT 2 CAPACITY FACTORS(DEC 2000 THROUGH 12/16)

7478

55

8478

87

0

20

40

60

80

100

Oct Nov Dec

1999

2000

BOILER COMBUSTION DEFICIENCIES

• INCREASES FURNACE EXIT GAS TEMPERATURES

• CREATES A REDUCING ATMOSPHERE HIGHER IN THE FURNACE LOWERING THE ASH FUSION TEMPERATURE OF THE COAL

• CAUSES COMBUSTION INBALANCES THAT RESULT IN LOCALIZED SLAGGING

• AGGRIVATED BY HIGH MILL OUTPUT

Slagging Report-1-9-00

Coal Contribution to U2 Slag Incident

Jim Mooney

Comments from 1997 Testing

Documentation (Dr.Simon Hansen, CONSOL)

• The one parameter in coal that can be used to predict slagging is sulfur.

• “For every 1/10th lb. Of Sulfur per mmbtu you will increase peak FEGT by 20 degrees.”

• Primary Slag Controls are:– FEGT control, Coal, Burner Arrangement,

Firing Rate and Sootblowing

Mansfield Coal History

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

Sul

fur

#/M

MB

TU

Unit 1

Unit 2

Unit3

October McElroy Delivery

33.13.23.33.43.53.63.73.83.9

#S/m

mbt

u Monthly Avg 3.51 #S/mmbtu

October 2000 Consol Supplied S#/MMBTU

2.00

2.20

2.40

2.60

2.80

3.00

3.20

3.40

3.60

3.80

4.00

1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103 109 115 121 127 133 139 145 151 157 163 169 175

#Sulfur Per barge

Monthly Avg

3.47# Sulfur/MMBTU on Monthly Average298,453 Tons

October Cumberland #Sulfur

0.00

0.50

1.00

1.50

2.00

2.50

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

55

57

59

61

#S/mmbtu

average

Cumberland October 2000

70,651 Tons

November 2000 Consol Quality

2.00

2.50

3.00

3.50

4.00

4.50

Average Consol Supplied Coal 3.57

295,453 TONS

November Cumberland

0.00

0.50

1.00

1.50

2.00

2.50

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55

#S by Barge

Average #S/mmbtu

63,435 Tons

December Consol Supplied #S/MMBTU

#S/MMBTU

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

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

December Average #S/MMBTU 3.40 89,664

Through 12-20

Short Prox ResultsSample DateComments LSN AR MoistureAR Ash AR SulfurAR BTU

12/17/00 mn2b-12-17,ult,prox,ash mineral anal.ash fus.anal.both ox&re96 7.55 10.86 2.5 1218112/17/00 ult,prox,ash min anal.ash fus.anal.both oxidizing&reducing97 8.31 16.93 4.61 1088312/17/00 ult,prox,ash min anal.ash fus anal.both oxidizing&reducing98 10.08 12.22 3.25 1139912/17/00 ult,prox ash min anal.ash fusion anal.both oxidizing&reducin99 9.81 15.95 2.73 1076712/17/00 ult,prox,ash min.anal.ash fus.anal.both oxidizing&reducing100 8.07 12.87 2.88 1180812/17/00 ult,prox,ash min.anal.ash fus.anal.both oxidizing&reducing101 9.2 15.37 2.71 1111912/29/00 barge 4819 v.c.696210 7.44 13 3.92 1197712/29/00 v.c.696 barge or 4821211 5.03 13.98 4.07 1205612/29/00 v.c.696-barge or 4756212 4.65 13.4 3.92 1218812/30/00 barge 13505 hand sample213 4.32 14.66 4.27 1209212/30/00 scf 9204 vmc 696 214 5.45 16.71 4.37 1128012/30/00 35-36 crusher 215 6.43 11.76 3.71 12199

1/3/01 41-42-crushers truck coal216 7.43 12.71 3.3 116361/3/01 coal hand samples truck hopper-truck coal217 8.55 14.31 3.55 114241/3/01 coal hand sample north pile truck coal218 6.62 13.63 4.06 11890

Bunker Samples Post Trip

RecentMcElroy

Yard

Samples

Affect of Operating Parameters on Slag Accumulation in

Mansfield Unit 2 Upper Furnace

Jake Davis

GTSD-FSS

January 9th, 2001

Background

• “The characteristics of slag deposits… are a function of deposit temperature and deposit composition… which is a function of the local atmosphere, particularly for ash with significant iron content.”

B & W Steam Book

40th Edition - 1992

Factors Affecting Slag Formation and Accumulation in the Furnace

• Coal - Jim Mooney

• Dolomite - Mark Lamison

• Furnace Exit Gas Temperature

• Combustion - O2, CO, LOI, Balance

Affects of Combustion on Slagging

• Local reducing atmospheres in the furnace negatively affect the ash fusion temperatures of most Mansfield coals by up to 250 oF.– Local reducing atmospheres are caused by:

• Inadequate excess air in the furnace• Unbalanced fuel and air flows at the burners• Unstable combustion, or “swings”

• Combustion also affects FEGT.

Affect of Combustion on Ash Fusion Temperatures

Desired Conditions for Boiler Optimization

Maintain 2.6% minimum oxidizing environment at furnace exit

Balance pulverizer fuel flow to + 10%

Maintain mill fineness 99.5% passing 50 mesh

Maintain bulk exit gas temperature of 2200 oF with no areas above 2350 oF.

MN2 = 1.7% in center

MN2 = 98.5%

MN2 = 2182 oF Peak = 2475 oF

MN2 = 17.7%

Typical Mansfield 2 Combustion Profile

Mansfield Unit 2 Furnace O2

Port #1Port #3

Port #5Port #8

Port #9Port #11

3

6

9

12

15

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

O2 (%)

Port Location

Port Depth

Mansfield 2 Upper Furnace O2 Readings1/3/2001

No data taken for ports #1 or #3.

Mansfield Unit 2 Furnace CO

Port #1Port #3

Port #5Port #8

Port #9Port #11

3

6

9

12

15

1

10

100

1000

10000

100000

CO (ppm)

Port Location

Port Depth

Mansfield 2 Upper Furnace CO Readings1/3/2001

No data taken for port #3

Maximum CO in center of furnace of 35,000 ppm

Combustion Stability

• Unstable combustion results in localized reducing atmospheres in the upper furnace

• Unstable combustion results from changes in unit conditions– Changing mills / burners– Changing load

– OFA control problems

OFA Port Swings Resulting in Unstable Combustion

OFA Swing

TOTAL OFA FLOW FLUE GAS OXYGEN FLUE GAS OXYGEN SETPOINT 12/28/2000 4:00:00 PM 12/29/2000 12:00:00 AM8.00 Hour(s)

MN_2JBLRGAS_2OFA1P09

KPPH MN_2JBLR____B2055

PCT MN_2JBLR____B2045

PCT

300

350

400

450

500

550

600

650

250

700

2.8

4

3.2

4365.84048

3.50226

3.46953

MN_2JBLRGAS_2OFA1P09

KPPH MN_2JBLR____B2055

PCT MN_2JBLR____B2045

PCT

Reasons for OFA Flow Swings

• High OFA port temperature due to low OFA port flow (high NOx curve)

• Controls open 100% on high port temperature and then close back to control NOx to setpoint once temperature is OK

Combustion Conclusions

• Mansfield Unit 1 and 2 combustion profiles result in localized reducing areas of the furnace, which lower ash fusion temperatures by 250 oF.

• OFA Port control issues contributed to combustion instability on the unit.

Affects of FEGT on Slag Accumulation

• “When temperatures in the furnace are below the measured initial deformation temperature, the majority of the ash particles… impacting on heating surface will bounce off and be re-entrained in the gas stream. At temperatures above the IT ash… particles have a greater potential to stick to heating surface.”

B & W Steam Book

40th Edition - 1992

Factors Affecting FEGT

• Sootblowing

• Mill Combinations

• Available Heat Transfer Surface

• Load

• Excess Oxygen

• Coal

• Combustion

• Mill Fineness

Sootblowers on Mansfield Unit 2

• 11 of 58 furnace blowers running at time of trip

• Usually ran 3 to 4 times per day

Affect of Furnace Wall Blowers on FEGT

Affect of Mill Combinations on FEGT

• Running with one or both upper mills in service generally raises FEGT by 80 to 120 oF.

• During the period leading up to the significant slag accumulation on Mansfield 2, a top mill was in service almost without interruption.

Top Mill Operation Affect on FEGT

Affect of Increase in Load on FEGT

Capacity factor for December was 87% compared to normal values of 65 to 75%.

Affect of Furnace Surface Area on FEGT

• More SA to absorb heat yields lower FEGT

• Corners of Mansfield furnaces have more SA and lower temperatures

• Slag generally worse in middle of boiler

Mansfield Unit 2 Furnace Temperature

Port #1Port #5

Port #8Port #9

Port #113

6

9

12

15

1800

1900

2000

2100

2200

2300

2400

2500

Te

mp

era

ture

(D

eg

. F

)

Port Location

Port Depth

Mansfield 2 Upper Furnace Temperature Readings1/3/2001

2400-2500

2300-2400

2200-2300

2100-2200

2000-2100

1900-2000

1800-1900

High FEGT on Mansfield 2 Prior to Slagging Incident

• 11 of 58 wall blowers operated in furnace.

• Average run cycle of 3.4 times per day.

• High load demand on the unit in December– 87% capacity factor MTD leading up to trip

• Ran top mill non-stop from 12/3 to 12/17

• Temperature stratified in center of boiler

• Approximately 150 oF hotter than baseline FEGT

Baseline FEGT vs. Load

2000

2050

2100

2150

2200

2250

2300

2350

2400

2450

700 705 710 715 720 725 730 735 740 745 750 755 760 765 770 775 780 785 790 795 800 805 810 815 820 825 830 835 840 845 850 855 860 865 870 875 880 885 890 895 900

Gross MW

FEG

T (D

egre

es F

)

FEGT Baseline

Ash Softening Temp at 4.6% S

Ash Softening Temp at 3.8% S

Baseline FEGT on Mansfield 2

FEGT on Mansfield 2 during DecemberFEGT With D Mill On for Two Weeks Prior to Tube Leak

2000

2100

2200

2300

2400

2500

2600

Gross MW

FE

GT

(D

eg

ree

s F

)

FEGT Last 2 Weeks

Ash Softening Temp at 4.6% S

Ash Softening Temp at 3.8% S

FEGT ComparisonMansfield 2 FEGT Increase from Baseline

2000

2050

2100

2150

2200

2250

2300

2350

2400

2450

Load (GMW)

FE

GT

(D

eg

. F

)

FEGT Baseline

FEGT Last 2 Weeks

Ash Softening Temp at 4.6% S

Ash Softening Temp at 3.8% S

FEGT Conclusions

• FEGT took an approximately 150 oF step change higher during the two weeks prior to the unit trip.– Load was significantly higher than typical for

long periods of time– Top mills were run more than during low NOx

firing conditions– Current wall blower operation is not effective in

maintaining low FEGT and reducing slag

Recommendations

• Achieve mill performance of + 10% Fuel Balance, 75% passing 200 mesh fineness and 99.5% passing 50 mesh fineness.

• Maintain balanced oxidizing atmosphere in upper furnace through combustion improvements.

• Lower the FEGT

Mill Performance

• Balance the burners by clean air testing to + 2%.

• Maintain mill outlet temperatures above 170 oF.

• Maintain mill ball charges to ensure 135 to 140 mill motor amps.

• Continue investigation of adjustable classifier modification on 2F mill.

• Reinvestigate using smaller balls with larger lift bars to improve fineness.

• Test all auxiliary air dampers for leakage. This could be affecting mill balance.

• Model classifiers to troubleshoot fineness and distribution problems.

Combustion Improvements

• Balance furnace excess oxygen profile using HVT probe to achieve an average 2.6% O2 with no points < 2%.– Pay close attention to combustion characteristics in noted high

slag areas.

– Adjust secondary air registers to balance combustion.

– More accurately profile the O2 distribution along the side-walls.

– Experiment with biasing of mills to troubleshoot burner problem and optimize combustion.

– Experiment with upper mill burner configurations to optimize combustion.

Combustion Improvements (contd)

• Correct the OFA port “swings” to aid combustion stability.

• Increase utilization of the Unit 2 MK Engineering LOI and Temperature monitoring device to assist with combustion balancing.

• Maintain stack CO indications below 100 ppm at high loads. Low load CO should be minimal at all times.

• Inspect all burner swirlers.• Inspect all burner and damper tolerances during the

outage.

Lowering FEGT

• Return to service all available furnace wall blowers.• Investigate use of water lances in the furnace area.• Optimize combustion in the upper furnace.• Compare furnace HVT profile to current FEGT

measurement to better understand its range.• Model the Mansfield 2 boiler to assist in evaluating

operational changes on the FEGT.

FEGT Conclusions

• FEGT took a 100 to 200 oF step change higher during the two weeks prior to the unit trip.– Load was significantly higher than typical for

long periods of time– Top mills were run more than standard practice– Sootblowing on Mansfield 2 is not as effective

as desirable

DOLOMITE

January 9, 2001

Dolomite Visual Results

Dolomite Analyses

National MulzerMineral Analysis (% weight)

Silicon as SiO2 0.88 6.84

Aluminum as Al2O3 0.25 1.04

Iron as Fe2O3 0.36 1.84

Calcium as CaCO3 50.7 62.00

Magnesium as MgCO3 39.5 31.97

Potassium as K2O 0.15 0.29

Sodium as Na2O 0.2 0.17

Sulfur as SO3 3.8 0.03

Grindability 76 62

Potential Problems

• Increased Low Temperature Fouling

• Increased Slagging

• Increased Economizer Outlet Temperature

• Increased Scrubber Scaling

• Injection Method and Location

• SCR Catalyst

• Scrubber Operation

• Thickener Chemistry

• Unit #3 ESP

Low Temperature Fouling

• Microbeam study indicated a higher propensity for low temperature fouling

• Significant fouling has occurred in the convection passes.

• Fouling has not blocked gas path.

• Economizer outlet temp up 60 to 80 °F

• Firing boiler harder to achieve temperatures

Unit #1 Superheater Fouling13th floor -11/24/99

Slagging

• Slagging indices indicate varied affects from dolomite

• Lab blending tests

• % Basic Vs Ash Fusion Curve

• Dolomite increases ash loading

• Microbeam Study indicated no increase in propensity to slagging, but possibly higher strength

• 9 day test in July 1999 showed no increased slag even possible improvement

• DOE Dolomite testing indicated some slag accumulation, but also with MacElroy coal above 3.8% Sulfur.

Slagging Indicators

• Conflicting information from indicators

• The value are indicators and have a wide scatter

• Assuming lignitic ash

• Dolomite is not mixed directly with coal

• Ash fusion temperature biased down by CaSO4 & MgSO4

Coal for Lab Blending Analyses

PROXIMATE ANALYSIS Design MacElroy Coal MacElroy& 5% Dolomite

Ash % 12.5 11.95 15.89Sulfur % 4.32 3.85 3.80Btu/lb 11,900 11,983 12,136

Sulfur (lb/mmBtu) 3.63 3.21 3.13

LAB Blending Results

Design MacElroy 5% DolomiteASH FUSION OXIDIZING

Softening F 2475 2411 2217

ASH FUSION REDUCING

Softening F 2193 2017 2135

T250 F 2300 2050(Derived from Ash Analysis)

Ash Fusion Temp Vs. Basic Components

McElroy

McElroy +5% Dolomite

Cumberland

Microbeam Technologies Factors

Blend RatioFuel / Dolomite

Erosion AbrasionWall

SlaggingSulfation Silication

T250 ºFUrbain

Strength2200 ºF

100% fuel 0.16 2.00 4.69 2.24 16.39 1814 0.7597.5% / 2.5% 0.15 2.74 3.98 3.45 16.68 1830 1.0695% / 5% 0.15 3.37 3.59 4.33 16.61 1880 1.36

2A Mill Dolomite Injection

• Difficult controlling rate of injection

• Can not minimize injection at low loads

• Highly stratified injection

• Auxiliary air high to maintain velocities at low injection rates

Mill Dolomite Flow Pipe to Pipe(Deviation from Average)

-60

-40

-20

0

20

40

60

Dev

iati

on fr

om A

vera

ge %

Burner 3 Burner 4 Burner 1 Burner 2

7 Tons/Hour (No/AuxAir)15 Tons/Hour (AuxAir)

EAST WEST

Recommendations

• Further evaluation of slagging potential (actual viscosity measurements)

• Inject dolomite with lower slagging coal

• Try injecting dolomite through outside burner pair - (lower FEGT area)

• Variable speed drives on mill feeders

• Discuss mixing directly with coal

• Explore the use of convection pass sonic horns

Deposition AnalysisFirstEnergy Mansfield Station

Review Meeting

Mansfield Station

N. S. Harding

January 9, 2001

Slagging vs Fouling

Slagging

Fouling

Definitions

• Slagging – deposition where radiation is the predominant form of heat transfer

• Fouling – deposition where convection is the predominant from of heat transfer

Deposition Mechanisms

– Condensation of inorganic vapors

– Inertial impaction and sticking of particles

– Chemical reactions

– Thermophoresis

Principal Effects of Deposition

– Retard heat transfer and eventually reduce boiler efficiency

– Grow until they restrict flow through the boiler

– Can be associated with corrosion

Selective Species Role in Deposition

– Alkali (Na and K)• Mostly volatilized and react with sulfur to form low

melting sulfates; very dense and reflective• Can react also with iron and sulfur to form corrosive

iron trisulfates

– Alkaline Earth (Ca and Mg)• More refractory and probably not completely

volatilized• If intimately mixed with ash, reduces melting

temperature

Selective Species Role in Deposition

– Sulfur

• Completely vaporized and forms very low melting solids

• Usually found as “glue” which holds deposits together

– Iron

• Reacts with alkalis and sulfur to produce low melting materials

• Has relatively low melting temperature and causes ashes to melt at lower temperatures

Deposition Parameters

– Coal Slagging and Fouling Parameters• ASME Publication, Research Committee on

Corrosion and Deposits from Combustion Gases

– Slagging and Fouling in Pulverized-Coal-Fired Utility Boilers

• EPRI Publication, CS-5523 (Work performed by Battelle)

Ash Definitions

– Ash Type• If CaO + MgO < Fe2O3 then Bituminous ash

• If CaO + MgO > Fe2O3 then Lignitic ash

– Base-to-Acid Ratio• Sum of bases (Na2O+K2O+Fe2O3+MgO+CaO)

divided by

• Sum of acids (Al2O3+SiO2+TiO2)

Example: McElroy + Dolomite

– Ash Type• 100% McElroy – Bituminous

• 99% McElroy/1% Dolomite – Bituminous

• 98% McElroy/2% Dolomite – Bituminous

• 97% McElroy/3% Dolomite – Lignitic

• 96% McElroy/4% Dolomite – Lignitic

• 95% McElroy/5% Dolomite – Lignitic

Example: Slagging Indices (100% McElroy)

Ash Type: CaO+MgO/Fe2O3 0.22 Bituminous

Total Bases: Na2O+K2O+CaO+MgO+Fe2O3 30.50Total Acids: Al2O3+SiO2+TiO2 65.86

Base/Acid Ratio: Sum Bases/Sum Acids 0.46

SLAGGING PARAMETER FORMULA VALUELow Medium High Severe

Slagging Factor Base/Acid*%S 1.92 X Iron to Dolomite Ratio %Fe2O3/(%CaO+%MgO) 4.65Boiler Age Year Placed in Serv ice 1976 X Steam Rate/W wall lb steam/hr-ft2 (waterwall) 85.70 X AFT-Initial Def. (Red) 1976 XIron in Ash %Fe2O3 23.00 XCalcium in Ash %CaO 4.21 XIron in Coal %Fe2O3 in coal, dry 2.96 X Calcium in Coal %CaO in coal, dry 0.54 XSilica to Alumina Ratio %SiO2/%Al2O3 2.43 X

Iron to Calcium Ratio %Fe2O3/%CaO 5.46 X

Silica + Alumina to Iron (%SiO2+%Al2O3)/Fe2O3 2.82 X

Silica + Alumina to Calcium (%SiO2+%Al2O3)/CaO 15.42 X

Silica + Alumina to Iron + Calcium (%SiO2+%Al2O3)/(Fe2O3+CaO) 2.39 X

Silica + Alumina to Iron + 6*Calcium (%SiO2+%Al2O3)/(Fe2O3+6*CaO) 1.35 X

(%SiO2+%Al2O3)/(Fe2O3+6*CaO)

+0.00704*(Stm/plan area)-7.27

Hensel-Halfinger B/A, ash input, Softening AFT Graphical

TENDENCY

Furance Slagging Index (FSI) 3.66 X

Example: Fouling Indices (100% McElroy)

Example: Slagging Indices (95% McElroy/5% Dolomite)

Ash Type: CaO+MgO/Fe2O3 1.77 Lignitic

Total Bases: Na2O+K2O+CaO+MgO+Fe2O3 47.84Total Acids: Al2O3+SiO2+TiO2 47.38

Base/Acid Ratio: Sum Bases/Sum Acids 1.01

SLAGGING PARAMETER FORMULA VALUELow Medium High Severe

Slagging Factor(1) (HAFT (max)+4*IDAFT(min))/5 2073 XSlagging Factor(2) Base/Acid*%S 3.98Boiler Age Year Placed in Service 1976 XAsh Rate per Wall Blower lb/hr 3991 XAFT-Softening (Red) 2135 XIron in Ash %Fe2O3 16.52 XCalcium in Ash %CaO 18.49 XCalcium in Coal %CaO in coal, dry 3.19 XSilica to Alumina Ratio %SiO2/%Al2O3 2.44 X

Iron to Calcium Ratio %Fe2O3/%CaO 0.89 X

Silica + Alumina to Iron (%SiO2+%Al2O3)%/Fe2O3 2.83 X

Silica + Alumina to Calcium (%SiO2+%Al2O3)/%CaO 2.53 X

Silica + Alumina to Iron + Calcium (%SiO2+%Al2O3)/(%Fe2O3+%CaO) 1.33 X

Silica + Alumina to 3.3*Iron + Calcium (%SiO2+%Al2O3)/(3.3*%Fe2O3+%CaO) 0.64 XBase to Acid Ratio Sum Bases/Sum Acids 1.01 XSilica Percentage %SiO2/(%SiO2+%Fe2O3+%CaO+%MgO) 0.42 XMill Fineness Check Months Between Fineness Checks 12.0 X

TENDENCY

Example: Fouling Indices (95% McElroy/5% Dolomite)

Ash Type: CaO+MgO/Fe2O3 1.77 Lignitic

Total Bases:Na2O+K2O+CaO+MgO+Fe2O3 47.84Total Acids:Al2O3+SiO2+TiO2 47.38

Base/Acid Ratio:Sum Bases/Sum Acids 1.01

FOULING PARAMETER FORMULA VALUELow Medium High Severe

Fouling Factor %Na2O in ash 0.63 X

Total Alkalies in Coal (%Na2O+0.6589*%K2O)*%Ash/100 0.26 X Total Alkalies Fired lb Alkali/MMBtu 0.30 X Steam Rate/Wwall lb steam/hr-ft2 (waterwall) 85.70 X AFT-Softening (Red) 2135 XCalcium in Ash %CaO 18.49 X Sodium in Coal %Na2O in Coal 0.11 X Calcium in Coal %CaO in Coal 3.19 XSilica to Alumina %SiO2/%Al2O3 2.44 X

Silica to Sodium %SiO2/%Na2O 52.80 X

Silica to Calcium %SiO2/%CaO 1.79 X

Silica + Alumina to Calcium (%SiO2+%Al2O3)/%CaO 2.53 X

Calculated Viscosity T10000 1601 XCoal Fineness %Passing 200 Mesh Screen 72.0 X

TENDENCY

Example: Hensel-Halfinger Plot

Estimated Ash Temperatures

1900

2000

2100

2200

2300

2400

0 1 2 3 4 5

Dolomite in Blend, wt.%

Te

mp

era

ture

, F Melting

T250

FEGT

Ternary Diagram (Si-CaO-Fe2O3)

2200oF

2800oF

4800oF

Quaternary Diagram (Si-Mg-Ca-Al)

2370oF

Summary

McElroy coal may be problematic• Especially if higher sulfur

Furnace Exit Gas Temperature is above ash melting temperature

Dolomite addition enhances problems

Recommendations Monitor FEGT, maintain below ~2300 F

Limit sulfur content to maximum in contract

Maintain operation of wall blowers

Add dolomite to side burners-avoid hot spots

Operate without top row of burners as much as possible

CONCLUSIONS

SHORT / LONG TERM CORRECTIVE ACTION

C. Swanson

PRIMARY CONTRIBUTOR

• High sulfur McElroy fuel

SECONDARY CONTRIBUTORS

• High furnace exit gas temperatures• 2G mill unavailability• Combustion stratification• Insufficient wall blower availability• Unavailability of mid sulfur fuel to replace McElroy• Dolomite injection

SHORT TERM CORRECTIVE ACTION

• Control tuning is progressing to minimize OFA flow swings.

• Combustion O2 curves have been modified to increase minimum full load O2 from 3.2 to 3.4% to improve combustion.

• Initiated increased slag monitoring and observations.

• Draft flow charts have been developed to provide operator guidance on required corrective action for light-heavy slagging conditions.

• More aggressive load reductions have been taken based on observed slag conditions.

SHORT TERM CORRECTIVE ACTION (CONT)

• High pressure water blasting has been used with some success to remove slag build-up from pendant leading edge tubes.

• Precision Blasting, Inc. is looking at methods to reach center slag build-up for explosive removal of slag.

• GTSD is providing full time support to identify and correct combustion issues related to slagging.

• Storm Engineering will be brought in to support GTSD with combustion testing and analysis.

• Unit operation has been limited to 2 PA fan operation to optimize mill performance.

SHORT TERM CORRECTIVE ACTION (CONT)

• A detailed sootblower monitoring program has been developed by operations for review at the daily plant status meeting.

• A cross-functional team of plant personnel has been set-up and has begun addressing sootblower unavailability.

LONG TERM CORRECTIVE ACTION

• Installation of 6 leading edge sootblowers will occur on Unit 2 during the Spring scheduled outage.

• An additional FEGT monitor will be installed to give improved indication of exit gas temperatures.

• Training for plant operations personnel is being looked into to provide general awareness of combustion and slagging issues.

• Restoring the Digital Fuel Tracking System (DFTS) to monitor fuel quality is in progress.

• GTSD will investigate the use of Diamond Power’s water lances for select wall blower replacement.