Dr V T Sathyanathan - IndiaCoreindiacore.com/bulletin/papers-tpi2/v-t-sathya... · Bharat Heavy Electricals LimitedTIRUCHIRAPALLI Committed to making a better world Dr V T Sathyanathan

Bharat Heavy Electricals Limited TIRUCHIRAPALLI

Committed to making a better world Dr V T Sathyanathan



Blending of Imported Coal Blending of Imported Coal with Indian Coals &with Indian Coals &

Its Associated Effects on Its Associated Effects on Boiler Design and OperationBoiler Design and Operation

Dr V T Sathyanathan General Manager / Quality

B H E L, Trichy 620014



Dr V.T.Dr V.T.Sathyanathan Sathyanathan Born in 1948 in Pondicherry StateGraduated from Coimbatore Institute Of Technology,Coimbatore, Tamilnadu, India under Madras University, India with First Class Degree in Mechanical Engineering in 1971. Masters Degree with Distinction in “Design and Production of Thermal Power Equipment” from Regional Engineering College under BharathidsanUniversity Trichy Tamilnadu, India in 1984.Ph.D from Regional Engineering College underBharathidsan University Tiruchy, Tamilnadu India in 1998. Ph.D thesis was on “Prediction of Unburnt Carbon in Tangentially Fired Boiler Using Indian Coals”.



Dr V.T.Dr V.T.SathyanathanSathyanathanJoined BHEL in 1973 in the R&D Department, in 1974 moved to Field Engineering Services & worked in various capacities till 2000Worked as Additional General Manager / R&D for two years –Jul 2000 to Jul 2002Was heading as Additional General Manager / FES & SAS for two years – Jul 2002 to Jul 2005 Head whole Engineering Department as the Additional General Manager /Engineering (FB) -Jul 2005 - Aug 2006Presently working as General Manager / Presently working as General Manager / QualityQuality..



Dr V.T.Dr V.T.SathyanathanSathyanathanSpecialized in combustion, boiler performance optimization, boiler testing and troubleshootingHas wide experience in the following areas:

Trouble shooting boiler problems in the areas of high pressure valves and boiler systemsTrouble shooting of all combustion problems in high pressure boilersPerformance optimization of high pressure boilersPerformance testing of all boilersTrouble shooting of Chemical Recovery boilers in paper plantsPerformance optimization of Chemical Recovery boilersBoiler Life Assessment StudiesPlant Performance Improvement studies in old boilersCoal petrography studies to understand combustion problems in coal fired boilers



Dr V.T.Dr V.T.SathyanathanSathyanathanWas appointed as the enquiry committee member by Government of Tamilnadu, for investigation of a severe explosion in the Rotary Holding Furnace (RHF) in Copper Smelting Plant of M/s. Sterlite Industries (I) Ltd., Tuticorin TamilnaduHas presented more than 35 papers in both National and International Seminars & Journals.Member of ASME, USA Vice – Chairman IIM Trichy Chapter. Life Member Indian Institute of Engineers. Member IIWChairman ISNT Trichy ChapterHas guided more than 15 projects for both UG & PG students of EngineeringTeach M.E Design & Production of Thermal Power Equipment Students of REC Trichy Teach Special Subjects In Horticulture to M.Sc / B.Sc students -Art Of Bonsai & Cacti



ArrangementArrangementBlending of coalEstablishment of ProcedureGrouping of Indian Coals for Boiler DesignEffect Of Coal Quality On Boiler PerformanceEvaluations carried outConclusions



Blending of coalBlending of coal




Burnsgivingheat

Organics

Behaviourfriendly

not friendly

Inorganics

Transportdrying

Moisture

Coal



Sudden or low change in furnace behavior leading to low boiler efficiency, load reduction and serious outageTime to turn around is normally highCan also lead to irrecoverable change in furnace behaviour

Why Fear Blending of coalWhy Fear Blending of coal



Decision about coal blending must deal with

uncertainty and variability in coal propertiesthe effect of off-design coal characteristics on power plant performance and cost.





Can pose peroblem

High Moist High VM Low FC

low rank

Low Moist Low VM High FC

High rank

Organics

Composition Trasformation Deposition Transport Aglomeration Trace Elements

In-organics

Blending

Drift In-situ

Type of Formation

Lignite Bituminus Anthersite

Rank of Coal

Blending of Coals

Time of residence

High swirl Low Swirl

PC FBC

Combustion

Temerature Size

Reducing Oxidising

Oxygen

Effected by



Can pose problem

Organics In-organics

Blending

Drift In-situ

Type of Formation

Lignite Bituminus Anthersite

Rank of Coal

Blending of Coals.




High Moist High VM Low FC

low rank

Low Moist Low VM High FC

High rank

Organics In-organics

Blending




Organics

Composition Trasformation Deposition Transport Aglomeration Trace Elements

In-organics

Blending




Time of residence

High swirl Low Swirl

PC FBC

Combustion

Temperature

Furnace Particle

Size

Reducing Oxidising

Oxygen

Effected by



Establishment of ProcedureEstablishment of ProcedureFor Blended Coal Firing



Need For Blended Coal FiringNeed For Blended Coal Firing

Indian coals contain high ashPreferable to limit ash content of coals fired at TPS to 34%Price of low ash imported coal with higher HHV is equivalent to that of Indian coalsAvailability of new fuels like petcoke, refinery residue, etc at a comparatively lower price



Procedure Developed Procedure Developed

Laboratory analyses of fuel samplesTrials at Fuel Evaluation Test Facility at various blend proportions and optimising the blend proportionImplementation of the recommended blend proportion at TPS for long duration observationFurnace inspection during shut down after long duration operation





Basis for recommendationBasis for recommendationFlame stabilityCarbon lossHeat flux reduction due to slagging and foulingHeat flux regain ability on wall blowingSH and RH spray levelsEmissionAcid dew pointAsh resitivity



Coal Boiler FurnaceDesign

BoilerOperation

Slagging



ElivationHeat Loading

Vol HeatLoading

Size

Slop AngleAvoid Ash Load

Shape

Furnace

High Swirl Low Swirl

Burner

Water Steam

Type Nos

Soot Blower MillSizing

Air / CoalRatio

Primary

WindboxControl

Secondary

AirDistribution

ID FanSizing

Slagging



Calcite Pyrites Ouartz

Oxidizing Reducing

700 .C S1H2SFeS.Fe2 (SO4)3 FeO Fe TemperatureFeo (Partial Melt) invesions(Partial melt) 950 .C

970.C S1H2S1000.TO 1100.C

CO2

Fe

Cao liquid Fe2 O3 SiO2

2570.C liquid liquid1600 .C 1723 .C

Phase Transforamation Of Some Mineral Matter Commonly Found In Coal



Kaolinite Illite

Metakaolinite (A12 O3 2sio2

950 .C925 .C SI O2

(Clay lattica destroyed) Spinal amorphous quartzA12 O3 Mgo glass Si O2

Silion Spinel 1050.C(2A12 O3.3 Si O2

1100 .C Si O2

1100.C

Mullite1:1Mullite type phase 1300.C (3A12 O3

(A12 O3.Si O2) 2Si O2

1400 C Sio2(Coristobailite) 1400.C

Mullite3A12 O3 . 2Si O2 liquid glass

May not be completelyliquid untill 1800 .C

Phase Transforamation Of Some Mineral Matter Commonly Found In Coal



MAJORSILICATES -[ CLAY MINE RALS KAOLINIT E Al2 Si 2 O5 (OH) 4

ILLITE - CLAY MINERALQUARTZ Si O2

MINORCALCITE Ca CO3

CARBONATE DOLOMITE (Ca, Mg) ( (CO3) 2ANKERITE CA (FE, Mg) CO3

SIDERITE FECO3

DISULFIDES PYRITE Fe S2 CUBICMARCASITE Fe S2 ORTHORHOMBIC

COFUIMBITE Fe2 (SO4)3 9H2 OSZOMOLONOKILE Fe SO4 2H2 O

SULFATES GYPSUM Ca SO4 2H2 OBASSANITE Ca SO4 1/2 H2OANHYDRITE Ca SO4

JAROSITE K Fe3 (SO4) 2 (OH)6

FELDSPARE PLAGIOCLASE (NaCa) Al (Alsi) Si2O8

ORTHOCLASE KALSi3 O8

Common Coal Minerals



1 LB COAL1.7 SLON

1.7F 1.75

1.7 FLOAT 1.7 SINK1.5 SOLN 1.9 SLON

1.55 1.9F 1.951.55x1.7F 1.75 x 1.9FPRACTION PRACTION

1.5F

1.5 FLOAT 1.9 SINK1.3 SLON 2.1 SLON

2.1F

1.35 .95 x 2.7F 2.15FRACTION

1.35 x 1.5F 2.1 SINKFRACTION 2.5 SOLN

1.3F2.5F

2.551.3 F 2.15x2.9FFRACTION FRACTION

2.5 SINK2.95

2.55x2.9FFRACTION 2.95

2.95FRACTION

Gravity Separation Procedure



EXPERIENCE SEVERE SEVERE MODERATE NONE NONE

CYCLONE INDEX MED - HIGH LOW-MED. LOW LOW LOW

SULFUR SLAGGING INDEX HIGH MEDIUM LOW LOW LOW

FUSION SLAGGING INDEX SEVERE SEVERE MEDIUM LOW LOW

VISCOSITY SLAGGING INDEX MED - HIGH LOW - MED LOW LOW LOW

Slagging Index Matrix



SlaggingSlagging/deposition indices/deposition indicesAsh deformation temperaturesLower the number, higher the tendency for depositionBase/ Acid RatioIn certain ranges the combinations have low melting temperatures, resulting in higher depositionIron/ Calcium ratiolower fusiblity temperatures in certain rangesIron Content in AshHigher the content , more the propensity for depositionSilica / Alumina RatioLower fusiblity temperatures at higher ratiosViscosity Index



Grouping of Indian Coals Grouping of Indian Coals for Boiler Designfor Boiler Design



44 major coal fields in peninsular India - 450 seams

Raniganj, Talcher, Ib-Valley, Jharia, N.Karanpura, Korba, Godavari, Singareni, Rajmahal, Karanpura, Singarauli, Wardha and Bokaro, account for 90% of the reserves.

Most of the coal resources are concentrated within 78 to 88 E longitude and 22 to 24 N latitude



Distribution of Fuel RatioDistribution of Fuel Ratio

0

10

20

30

40

50

60

70

80

0.0-0.2 0.2-0.4 0.4-0.6 0.6-0.8 0.8-1.0 1.0-1.2 1.2-1.4 1.4-1.6 1.6-1.8 1.8-2.0 2.0-2.2 2.2-2.4 2.4-2.6 2.6-2.8Range of Fuel Ratio



Distribution of AshDistribution of AshPer MillionPer Million KcalsKcals

010203040506070

20-40 40-60 60-80 80-100

100-120

120-140

140-160

160-180

180-200

Ash Range (Kgs)

Num

ber o

f Coa

ls



Distribution of Initial Distribution of Initial Deformation TemperatureDeformation Temperature

020406080

1000

-1020

1020

-1040

1040

-1060

1060

-1080

1080

-1100

1100

-1120

1120

-1140

1140

-1160

1160

-1180

1180

-1200

1200

-1220

1220

-1240

1240

-1260

1260

-1280

1280

-1300

IDT Range (Deg.C)

Num

ber o

f Coa

ls



FIXED CARBON / VOLATILE MATTER - DISTRIBUTION ( Group 1 - 0.6 to 1.2 ; Group 2 - 1.2 to 1.8 ; Group 3 - 1.8 to 3.01)

101

144

33

0

20

40

60

80

100

120

140

160

1 2 3Coal Group

No.

of C

oals



ASH LOADING - DISTRIBUTION( Group 1 - 20 to 90 Kg/MKcal; Group 2 - 90 to 140 Kg/MKcal;Group 3 -140 to 200 Kg/MKcal)

88

148

42

0

20

40

60

80

100

120

140

160

1 2 3

Coal Group

No.

of C

oals



INITIAL DEFORMATION TEMPERATURE - DISTRIBUTION( Group 1 -1000 to 1100 Deg C; Group 2 - 1100 to 1200 Deg C;

Group 3 - 1200 to 1290 Deg C)

24

161

93

0

20

40

60

80

100

120

140

160

180

1 2 3

Coal Group

No.

of C

oals



COAL GROUPING CONSIDERING ALL THE 3 ASPECTS

30

223

16

0

50

100

150

200

250

1 2 3

Coal Group

No.

of C

oals



Effect Of Coal Quality On

Boiler Performance



Coals vary widely in their properties

mine to mine and seam to seamCoal firing therefore presents a varying set of demands before the boiler designer



Boiler designBoiler designCoal Properties influence

The sizing of the boiler heat transfer surfacesThe flue gas velocitiesThe size of boiler auxiliaries



Effect Of Fuel On Boiler DesignWide range of coal properties

Lead to oversized pulverising/firing equipment• Limitation on turn down • Auxiliary power consumption will go up.

Oversized furnace• Attaining rated SH, RH outlet temperature becomes

difficult.Oversizing pulverisers and airheaters to handle occasionally high moisture coals

when handling normal moisture coals• there will be excessive tempering air• higher gas outlet temperature



Heat Transfer in Furnace Heat Transfer in Furnace -- UncertaintiesUncertaintiesFurnace wall condition

The deposition potential prediction by use of slagging indices still subjective

Laboratory determination of emissitivity & absorptivity does not reflect the furnace conditions.Heat release rates

FC/VM ratio only indicative ; coal petrography may indicate different results

Particle finenessHigher fineness at times can separate the slow reactive particles from the high reactive, resulting in delayed

combustion.Accuracy of Prediction by theoretical methods affected by complexity of factors



Designing for erosion protectionDesigning for erosion protectionIndian coals contain large quantum of ashThe quantity of ash passing thru the boiler is of the order of 125 kg/ Million kcal (compared to 40 kg/Mkcal for an average grade coal)

Indian coal-ash highly erosive- 60% Silica.Flue gas velocity in the range of 10-12 m/s adoptedAdditional thickness provided on tubes in erosion prone areasSacrificial shields/ baffles provided on leading tubes/ bends



Design of heat transfer surfacesDesign of heat transfer surfaces

Furnace design is the most crucial part of boiler design

Coal characteristics decide the heat release rates, furnace wall conditions and consequently the the furnace heat transfer

Proper understanding of the coal behaviour w.r.t combustion and heat transfer very essential in designing for satisfactory boiler performance



Furnace Heat TransferFurnace Heat TransferFurnace wall condition

Combustion Heat release rateEmissivity, absorptivity and thermal conductivity of deposits.

Ash dust loading

Pulverised fuel finenessMill Combination (Top, Middle, Bottom)Air regime for combustion



Evaluations carried outEvaluations carried out



Evaluations carried outEvaluations carried outBlended firing of Petcoke (Reliance) and coal for GEB, Sikka TPSBlended firing of Indian coals with Indonesian coal at Raichur TPS for KPCLCo-firing imported coal with oil for TATA Power, TrombayCo-firing ground nut shell with bagasse for EID parry, NellikuppamREL Dahanu 250 MW – 30% Indonesian Coal + 70% Indigenous washed coal



Evaluations carried out Evaluations carried out –– ContCont

GSECL Gandhinagar unit 1 & 2 120 MW –20% imported coal in one exclusive mill elevationGNVFC Bharuch 200 t/hr – 50% imported coal – Australian, Chinese,South AfricanMahagenco Chandrapur 500MW unitsTNEB Mettur 210MW – Indonesian & AustralianTNEB Tuticorin 210MW – Indonesian & Australian



ConclusionsConclusions



ConclusionsConclusionsBlending of coals expected to grow over the next decade as electric utilities attempt to

Reduce costMeet SO2 emission limitsImprove combustion performance of their coals

All aspects of a blend’s behaviour & its effect on all components of the power stations, from the stock pile to the stack, should be considered before the most appropriate blend composition is chosen

IEA Publication



Conclusions Conclusions (cont.)(cont.)

At present, the effect of coal blending on power station performance are not completely understoodEven if the blended coal closely resembles the design coal for the boiler, the blend does not perform the sameA limitation to blending coals is the compatibility of the coals themselves; problems are more likely when blending petrographically different coals or coals with different ash chemistry

IEA Publication




The impact of blending coals of different hardness on the finalize distribution & compositional distribution of the pulersied coal is sill not understoodNon-additivity properties make blend evaluation for power generation inherently complexTraditional indices for ash deposition are unreliable when applied to blends

IEA Publication




More work is required on understanding how the inorganic components of coals in the blend interact & how it affects ash behaviour, including its emisivity, reflectivity & thermal conductivitySO2 can be predicted with reasonable accuracyNo adequate means of predicting Nox

IEA Publication




Because of the complexity of the combustion process and the number of variables involved (which are still not fully understood), it is difficult to extrapolate small - scale results to full - scale plant. Thus, power station operational experience in a wide range of plant configurations with a variety of coal feedstock is essential for determining the practical significance of results from bench - and pilot -scale tests. More published data on how the behaviour of the coals / blends utilise in these tests differ from their actual performance in power station boilers are required.

IEA Publication




Tests are widely utilised, providing a preliminary indication of the behaviour of the coal / blend. One of the most successful outcomes of blending is in providing a fuel of consistent quality.Coal is a heterogeneous material and its properties and composition vary even within a single seam or single shipment / train load. There is a need to minimise the variability. This can be achieved by blending. Indian power stations use mainly blended coals only.

IEA Publication



Prime ConcernPrime ConcernBoiler furnace Slagging

Lead to outages in many casesLead to load reductionPerformance parameters change

Arriving at the right proportion Maintaining the right mix

My conclusion



How power stations to viewLook at proximate and ash analysisLook for FC/VM ratio – idea on reactivityAsh composition ratios – slagging

Trial with low mixture ratio – 95% + 5%95% of regular usage coalWatch parameters like SH spray, steam temp, exit gas temp, unburnt carbon,load on bottom ash collection after maintaining load, steam pressure, excess air& mixture ratio for about a week

Blending of coalBlending of coalMy conclusion



ANY QUESTIONS PLEASEANY QUESTIONS PLEASE



Thank You AllThank You All





BLENDED FIRING OF INDONESIAN COAL WITH INDIAN COALS IN UNIT 3 BOILER OF RAICHUR TPS DURING FEB 2001FIG: COMPARISION OF THE TREND OF SUPER HETER SPARY.

05

1015

2025

3035

40

0 100 200 300 400 500

TIME IN MINUTES FROM THE START OF TEST

TON

S / H

OU

R

sh spary TEST 1 100% SASTIsh spary TEST 4 78% SASTI+ 22% INDOsh spary TEST 7 70% SASTI & PRP+30% INDO




0

5

10

15

20

25

30

35

40

0 50 100 150 200 250 300 350 400 450 500


TON

S / H

OU

R

sh spary TEST 1 100% SASTI sh spary TEST 15 100% MAHANADHI




0

5

10

15

20

25

30

0 100 200 300 400 500


TON

S / H

OU

R

sh spary TEST 4 78% SASTI+ 22% INDO

sh spary TEST 14 80% MAHANADHI +20% INDO




0

5

10

15

20

25

30

0 100 200 300 400 500


TON

S / H

OU

R

sh spary TEST 7 70% SASTI & PRP+30% INDO

sh spary TEST 12 70%YELLANDU+ 30%INDO



BLENDED FIRING OF INDONESIAN COAL WITH INDIAN COAL IN UNIT 3 BOILER OF RAICHUR TPS

COMPARISON OF FURNACE TEMPERATURE PROFILE

11000

20000

29000

38000

47000

1000 1200 1400 1600 1800

FURNACE TEMPERATURE (DEG.C)

FUR

NAC

E EL

EVAT

ION

(MM

)

100% SASTI COAL 78% SASTI + 22% INDONESIAN COAL70% SASTI + 30% INDONESIAN COAL




COMPARISON OF INCIDENTAL RADIATION HEAT FLUX PROFILE

11000

20000

29000

38000

47000

50 100 150 200 250 300 350 400

INCIDENTAL RADIATION HEAT FLUX (KW/SQ.M)

FUR

NAC

E EL

EVAT

ION

(MM

)

100% SASTI COAL78% SASTI + 22% INDONESIAN COAL70% SASTI + 30% INDONESIAN COAL




COMPARISON OF FURNACE TEMPERATURE PROFILE

11000

20000

29000

38000

47000

1000 1100 1200 1300 1400 1500 1600 1700 1800

FURNACE TEMPERATURE (DEG.C)

FUR

NAC

E EL

EVAT

ION

(MM

)

100% MAHANADHI COAL 80% MAHANADHI + 20% INDONESIAN COAL




COMPARISON OF INCIDENTAL RADIATION HEAT FLUX PROFILE

11000

20000

29000

38000

47000

50 100 150 200 250 300 350 400

INCIDENTAL RADIATION HEAT FLUX (KW/SQ.M)

FUR

NAC

E EL

EVAT

ION

(MM

)

100% MAHANADHI COAL 80% MAHANADHI + 20% INDONESIAN COAL



Typical Coal YardTypical Coal Yard

Coal Stockpile

Wetlands

Rail CarUnloader

Rail Line

Material Handling System Crusher House

Main Conveyor



Literature example of the differences in actual HGI Literature example of the differences in actual HGI and calculated HGI for coal blendsand calculated HGI for coal blends



NOxNOx--results for individual coals and results for individual coals and blendsblends



Normally specified Coal Properties

Proximate Analysis

Ultimate Analysis

Calorific Value

Ash Constituents

Ash Fusion Temperatures

Hard Grove Index

YGP Index



Moisture and ash free

C (%) O + N (%) H (%)

Wood 50 44 6

Peat 55-64 39-35 5-7

Brown Coal 60-75 34-17 4-8

Bituminous Coal 78-90 19-4 4-6

Anthracite 94-98 3-1 1-3

Graphite 100 -- --

Carbonisation Of Solid Fuels



Coal Analysis Coal Analysis --Typical Indian CoalsTypical Indian CoalsProximate AnalysisProximate Analysis

Unit Design Coal

Worst Coal

Best Coal

Fixed carbon % 22.0 20.0 25.0 Volatile matter % 21.0 19.5 23.0 Moisture % 15.0 16.5 14.0 Ash % 42.0 44.0 38.0 Total % 100.0 100.0 100.0 HHV Kcal/kg 3300 3000 3600



Unit Design Coal Worst Coal Best Coal Carbon % 33.73 30.90 38.26 Hydrogen % 2.35 2.09 2.49 Oxygen(difference) % 5.48 5.00 5.96 sulphur % 0.37 0.36 0.38 Nitrogen % 0.75 0.85 0.57 Moisture % 15.00 16.50 14.00 Ash % 42.00 44.00 38.00 HARD GROVE INDEX 55 54 56

Coal Analysis Coal Analysis --Typical Indian CoalsTypical Indian CoalsUltimateUltimate AnalysisAnalysis



Ash Characteristics Ash Characteristics --Typical Indian CoalsTypical Indian Coals Design Worst Best

Initial Deformation Temp. Deg.C 1150 1100 1200

Hemispherical Temp. Deg.C 1400 1400 1400

Fusion Temp. Deg.C 1400 1400 1400 Ash Analysis: A – SiO2 % 60.08 61.40 60.30 A – Al2O3 % 29.50 28.50 29.80 B – Fe2O3 % 4.10 3.90 4.70 B – CaO % 1.70 1.93 1.57 B – MgO % 0.75 0.92 0.59 B – Na2O + K2O % 0.65 0.85 0.53 A – TiO2 % 1.70 1.60 1.80 - P2O5 % 0.80 1.10 0.13 - SO3 % 0.27 0.31 0.25



Ash AnalysisAsh Analysis

Provides indicators to

Slagging / fouling / deposition potential

Erosion potential

Corrosion potential



SLAGGING INDICESSLAGGING INDICES( based on a typical design stage input)( based on a typical design stage input)

Design Coal Worst Coal Best Coal

Base / Acid Ratio

0.11 Low 0.11 Low 0.15 Low

Iron / Calcium Ratio

1.32 High 1.39 High 4.86 Severe

Silica / Alumina Ratio

2.13 Medium 2.26 Medium 2.20 Medium



Normally specified Coal Properties

Proximate Analysis

Ultimate Analysis

Calorific Value

Ash Constituents

Ash Fusion Temperatures

Hard Grove Index

YGP Index



Moisture and ash free

C (%) O + N (%) H (%)

Wood 50 44 6

Peat 55-64 39-35 5-7

Brown Coal 60-75 34-17 4-8

Bituminous Coal 78-90 19-4 4-6

Anthracite 94-98 3-1 1-3

Graphite 100 -- --

Carbonisation Of Solid Fuels



Coal Analysis Coal Analysis --Typical Indian CoalsTypical Indian CoalsProximate AnalysisProximate Analysis

Unit Design Coal

Worst Coal

Best Coal

Fixed carbon % 22.0 20.0 25.0 Volatile matter % 21.0 19.5 23.0 Moisture % 15.0 16.5 14.0 Ash % 42.0 44.0 38.0 Total % 100.0 100.0 100.0 HHV Kcal/kg 3300 3000 3600



Unit Design Coal Worst Coal Best Coal Carbon % 33.73 30.90 38.26 Hydrogen % 2.35 2.09 2.49 Oxygen(difference) % 5.48 5.00 5.96 sulphur % 0.37 0.36 0.38 Nitrogen % 0.75 0.85 0.57 Moisture % 15.00 16.50 14.00 Ash % 42.00 44.00 38.00 HARD GROVE INDEX 55 54 56

Coal Analysis Coal Analysis --Typical Indian CoalsTypical Indian CoalsUltimateUltimate AnalysisAnalysis



Ash Characteristics Ash Characteristics --Typical Indian CoalsTypical Indian Coals Design Worst Best

Initial Deformation Temp. Deg.C 1150 1100 1200

Hemispherical Temp. Deg.C 1400 1400 1400

Fusion Temp. Deg.C 1400 1400 1400 Ash Analysis: A – SiO2 % 60.08 61.40 60.30 A – Al2O3 % 29.50 28.50 29.80 B – Fe2O3 % 4.10 3.90 4.70 B – CaO % 1.70 1.93 1.57 B – MgO % 0.75 0.92 0.59 B – Na2O + K2O % 0.65 0.85 0.53 A – TiO2 % 1.70 1.60 1.80 - P2O5 % 0.80 1.10 0.13 - SO3 % 0.27 0.31 0.25



Ash AnalysisAsh Analysis

Provides indicators to

Slagging / fouling / deposition potential

Erosion potential

Corrosion potential



SLAGGING INDICESSLAGGING INDICES( based on a typical design stage input)( based on a typical design stage input)

Design Coal Worst Coal Best Coal

Base / Acid Ratio

0.11 Low 0.11 Low 0.15 Low

Iron / Calcium Ratio

1.32 High 1.39 High 4.86 Severe

Silica / Alumina Ratio

2.13 Medium 2.26 Medium 2.20 Medium



Coal reactivityCoal reactivity

1.181.41FC/VMFuel ratio (6) % (4)6

31.039.5%FC5

37.025.5%Ash4

26.328.0%VM3

5.57.0%Moisture2

Proximate

42004980Kcal/KgCV1

Coal 2Coal 1



HEAT RELEASE PROFILES OF Coal 1 & Coal 2 (courtesy - Mr. K. Nandakumar AGM R & D / BHEL, Trichy.

30405060708090

100110

0 2 4 6 8 10 12

TIME IN MINUTES

% H

EAT

REL

EASE

Coal 2 Coal 1

Heat from VM

Heat from FC

2



Coal petrography gives a better insight into coal combustion behaviourModelling studies will help in understanding the effect of variables like combustion regime, ash quantity, fineness etc.Characterisation of coals by Pilot scale testing and comparing with unit operating data will help in predicting the performance for similar coals more accurately

Furnace Absorption Prediction



Combustion Heat Release RateCombustion Heat Release Rate

Fixed Carbon/Volatile Matter ( FC/VM) fromthe Proximate analysis

provides an insight into the reactivity of the coal lower the FC/VM ratio , better thecombustibilty ( generally)



Emissivity & Absorptivity Of Ash

Radiative heat transfer properties influence furnace absorptionAbsorptivity & emissivity will decide the heat absorption in water wallVaries with ash constituents and prevailing furnace environment



Ash Ash quantityquantityInfluences the furnace heat transfer by shielding the radiation.

Higher the ash quantity, greater the shielding of furnace walls

Flame temperature lowered by increased ash quantum



PulverisedPulverised fuel finenessfuel fineness

Finer particles promote faster

heat release by ensuring better

access to oxygen in the Furnace



Boiler AuxiliariesBoiler AuxiliariesMills

More number of bigger size mills required for low grade coals; wear resistant materials to improve the life of wear parts

FansLarge PA fans are required to meet the primary air requirement.ID fans are provided with replaceable wear liners considering the erosive nature of Ash in the flue gas stream.

Air HeatersAccelerated seal erosion due to erosive ash; double seal arrangement to reduce leakage

Dust collectorsIncreased dust burden and high ash resistivity calls for larger size of electrostatic precipitators.



Boiler EfficiencyBoiler Efficiency

This is influenced by coal properties, ambient temp. & relative humidity,Boiler exit gas temp.

Determines the heat input to the boiler

Forms the basis for air & gas weight

calculations,quantity of coal fired



Boiler Efficiency Boiler Efficiency (contd..)(contd..)

Every 20degc increase in exit gas temp. reduces the boiler efficiency by 1%

Increase in excess air by 1%reduces the boiler

efficiency by 0.04%

Higher moisture and higher H2 content and lower

calorific value of coal decreases the boiler efficiency

-1%H2 increase leads to approximately 1.3% loss

and 1%M increase leads to 0.2%loss in efficiency



Effect Of Ash On Boiler Design



Boiler Design At Various Ash Levels

5694124Ash kg / Mkcal fired505050HGI

431536103400kcal/kgHHV

243442%Ash

141312%M

252222%VM

373124%FC

Proximate Analysis

Washed Coal-2

WashedCoal-1

ROM unwashed

Coal



%Ash 42 34 24

Weight Base -7% -11%

SG package cost Base -6% -10%

Boiler weight and cost

Documents

Dr V T Sathyanathan - IndiaCoreindiacore.com/bulletin/papers-tpi2/v-t-sathya... · Bharat Heavy Electricals LimitedTIRUCHIRAPALLI Committed to making a better world Dr V T Sathyanathan