combustion.ppt

Dr. T K Ray

DGM - PMI

NTPC Limited

E-mail: [email protected]

Combustion

Factors influencing combustion, Coal composition

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Coal

8 January 2013

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The most easily and abundantly available, cheap and transportable, energy source
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8 January 2013

T K Ray NTPC

Burning of coal in pulverized form is one of the most significant achievement in boiler technology

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Pulverized form of coal
It has made modern steam generating units highly thermal efficient, reliable and safe.Pulverized coal is the most efficient way of using coal in a steam generator..It provides good control over coal air mixture proportion, flame stability with minimum level of unburnt carbon.Pulverized coal burns like gas, can be easily lighted and controlled.Pulverized coal boiler can be easily adapted for other fuels like gas and oil.LARGE size boiler could be made
8 January 2013

T K Ray NTPC

T K Ray NTPC

Coal pulverizers are essentially volumetric devices, because the density of coal is fairly constant, are rated in mass units of tons/hr.Increased combustible loss can occur if the furnace volume or mill capacity is less than desirable for a particular coal.
Coal pulverizer

8 January 2013

T K Ray NTPC

T K Ray NTPC

Size reduction is energy intensive and generally very inefficient with regard to energy consumption. In many processes the actual energy used in breakage of particles is around 5% of the overall energy consumption. There are four operations going concurrently within the mill body, coal drying, transport, classification and grinding.For coal pulverizers the capacity of a mill is normally specified as tonnes output when grinding coal with a HGI of 50, with a particle size of 70% less than 75 micron and 1 % greater than 300 micron and with a moisture in coal of less than 10%.
Coal pulverizer

8 January 2013

T K Ray NTPC

T K Ray NTPC

History of coal pulverization
Carnot envisaged a pulverized coal fired engine in 1824.Diesel had envisaged using pulverized coal for his diesel engine in 1890Pulverized coal firing was first developed in cement industryTHOMAS ALVA EDISON, NIEPCE brothers were pioneers in pulverized coal firing
8 January 2013

T K Ray NTPC

T K Ray NTPC

After world war I the effort on using pulverized coal firing got tremendous boost in power industryJohn Anderson Chief engineer of power plants of Wisconsin Electric power company introduced pulverized coal firing in power stations.
History of coal pulverization

8 January 2013

T K Ray NTPC

T K Ray NTPC

5 January 2013

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Coal an organic complex polymer

Sequential events
Devolatilization (Pyrolysis)Heating causes its structure to decomposeWeaker chemical bonds break at lower temperaturesStronger ones at higher temperaturesVolatile yield can be up to 50% greater than indicated by proximate analysis
SEM of a de-volatilizing coal particle

5 January 2013

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Burning of volatile mattersHomogeneous gas phase reaction around the particle Char burningHeterogeneous combustionOccurs at the char surface and pore surfaces (porosity~0.7; surface area ~100 m2/g)Guided through competing effects of heat and mass transfers to the char surface and chemical reaction
Char particle at the early stage of burning

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Coal Combustion

coal particle

p-coal, d=30-70m

De-volatilization

volatiles

char

homogeneous

combustion

heterogeneous

combustion

CO2, H2O,

CO2, H2O,

tchar=1-2sec

tvolatiles=50-100ms

tdevolatile=1-5ms

t

Temperature, Turbulence, Time and Size

Heating

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Vol. combustion intensity, Iv is in the range 150-250 kW/m3.FEGT

If 1-2% is +50 in BS mesh sieve (300 m), most of this coarse coal will not burn and end up in C in BA

It also frequently causes slagging around the burners

If -200 mesh (75 m) fineness is poor, results in high C in FA

If the coal is not properly ground, the distribution to the burners may not be even

Resulting in air-fuel imbalances at one or more burners

Coal particle size distribution

5 January 2013

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Problems Associated With Indian Coals

Inconsistent Coal Properties

Presence Of Extraneous Matters In Coal

High Quantum Of Ash With High Percentage Of Quartz

Highly Abbrasive Nature Of Coal Ash

Due To Low Sulphur Content- Extremly High Electrical Resistivity Of Ash

Low Heating Value Of The Coal

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Boiler design

Coal Properties influence

The sizing of the boiler heat transfer surfaces

The flue gas velocities

The size of boiler auxiliaries

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Ash Analysis

Provides indicators to

Slagging / fouling / deposition potential

Erosion potential

Corrosion potential

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The Three Ts & One S Practice

Size the Coal and Add the Air !!!

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TechnologyTimeTemperatureTurbulenceSizeStokerlargeMediumLowBigPulverizedShortHighMediumTinyCycloneShort+V HighHigh MediumFluid BedMediumLowHigh Medium

Normally specified Coal Properties
Proximate AnalysisUltimate AnalysisCalorific ValueAsh ConstituentsAsh Fusion TemperaturesHard Grove IndexYGP Index
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Coal Analysis -Typical Indian Coals
Proximate Analysis

5 January 2013

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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

Coal Analysis -Typical Indian Coals
Ultimate Analysis

5 January 2013

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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

Ash Characteristics -Typical Indian Coals

5 January 2013

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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

Coal Analysis - 500 MW Units

Stn 1 Stn 2 Stn 3

Units-1 & 2 Units-3,4,5&6Units-5 & 6

2 x 500MW4 x 500MW 2 x 500MW

DCWCDCWCDCWC

FC %2420222023.520.5

VM %22192119.51715

M %14151516.516.518.5

Ash %404642444346

HHV kcal/kg330028003300300028502450

Ash kg/Mkcal121165128147151188

IDT oC11001100-12001150110011001100

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Nomenclature-Bowl Mills
583 XRS / 803 XRP Bowl mills58,80 stands for bowl diameter in inchesIf the number is even then its shallow bowl mill.If the number is odd then its deep bowl mill3 - number of rollers three nos.X - frequency of power supply 50 cycles. In USA x means 60 cycles.R- Raymond, name of the inventorS- suction type with exhauster after millP- pressurised type with P.A. Fan before mill.
8 January 2013

T K Ray NTPC

T K Ray NTPC

Bowl

Motor

Gear

Spring-Assly

Roller

Inner Cone

To Boiler

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Hot Air

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6.psd7.psd

Factors affecting Mill performance
Moisture in the coal.Coal grindability index.Mill inlet and outlet temp.Mill differential Pr. (DP)Mill loading.Air Flow in the Mill.Mill Motor current.Coal Mill finenessGrindabilityMoisture contentFineness Pri air quantity & temp
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T K Ray NTPC

Effect of Grindability
The grind ability of the coal is an empirical indexIt is not an inherent property of coalRelative ease of grinding as compared with standard coal It is determined in laboratory using 50 g of air dried sample of properly sized coal in a miniature pulveriser which is set to rotate exactly 60 revolutions grinding the coal sample.The hard grove Gindablility index is calculated G.I. (hardgrove) = 13+6.93WWhere W= weight of dust passing through 200 mesh sieve.
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T K Ray NTPC

Higher the HGI more is the capacityNormally mill capacity is indicated at 50/55 HGI. Actual Mill capacity varies with HGI
8 January 2013

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T K Ray NTPC


8 January 2013

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T K Ray NTPC
Mill cap vs HGI707075758080858590909595100100105105110110Output at coal fineness of 70 % passing through 200 MeshOutput at coal fineness of 75 % passing through 200 meshHGIOutput ( TPH)Maximum mill capacity vs HGI at coal moisture of 12 %32.195121951230.491803278733.495934959331.803278688535.121951219533.114754098437.073170731734.754098360738.699186991936.06557377054038.0327868852404040404040Mill Cap vs moisture1011121314151617181920Maximum mill output at coal HGI of 100-110MoistureMill output ( TPH)Maximum mill Capacity vs coal moisture at coal HGI 100-110 and PF Fineness of 70 % passing through 200 Mesh40.776699029140.38834951464039.223300970938.834951456338.446601941737.669902912637.281553398136.504854368936.116504854435.7281553398Mill Cap vs PF fineness6570758085&APage &PMill output at raw coal moisture and at Coal HGI 100-110Maximum Mill capacity vs PF fineness at 12 % Raw coal moisture and at Coal HGI 100-110404038.153846153835.692307692333.8461538462Calculation sheetHGIOutput at PF fineness of 70 % passing through 200 meshOutput at PF fineness of 80 % passing through 200 meshOutput ( 1000 LB/Hr)Output ( TPH)Output Factoroutput factor by considering 40 TPH at 110 HGIOutput ( 1000 LB/Hr)Output ( TPH)Output Factoroutput factor by considering 40 TPH at 110 HGI7099450.8032.2093420.7630.4975103470.8433.5097440.8031.8080108490.8835.12101460.8333.1185114520.9337.07106480.8734.7590119540.9738.70110500.9036.0795123561.0040.00116530.9538.03100123561.0040.00122551.0040.00105123561.0040.00122551.0040.00110123561.0040.00122551.0040.00MoistureOutput at PF fineness of 70 % passing through 200 mesh and coal HGI of 100 - 110Output ( 1000 LB/Hr)Output ( TPH)Output Factoroutput factor by considering 40 TPH at 12 % moisture and coal 100- 110 HGI1010547.631.0240.781110447.171.0140.391210346.721.0040.001310145.810.9839.221410045.360.9738.83159944.910.9638.45169744.000.9437.67179643.540.9337.28189442.640.9136.50199342.180.9036.12209241.730.8935.73Coal FinenessOutput at PF fineness of 70 % passing through 200 mesh and coal HGI of 100 - 110Output ( 1000 LB/Hr)Output ( TPH)Output Factoroutput factor by considering 40 TPH at 12 % moisture and coal 100- 110 HGI6513058.971.0040.007013058.971.0040.007512456.250.9538.158011652.620.8935.698511049.890.8533.85

Moisture in Coal
Moisture: Inherent and surfaceInherent moisture locked up within the structure Inherent moisture is constant for a particular seamSurface moisture variesCoal must be dried to remove the surface moisture totally before grindingBeside drying primary air alsoCreate circulationTransport coalProvide initial oxygen for combustionPA quantity is 15 to 28% of total air
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T K Ray NTPC

Moisture in Coal

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T K Ray NTPC

Effect of Moisture

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T K Ray NTPC

Temperature Of Coal Air Mixture At Mill Outlet
The temperature of pulverised coal and air mixture at pulveriser outlet should be maintained at least 15 C Above the dew point of air at pulveriser pressure to avoid condensation and consequent plugging of the coal pipes. The pulveriser mill outlet temperature should be maintained above 65 C. The higher limits are 90 C For high volatile (above 24%) coals and 110 C for low volatile coals (below20% VM)..
8 January 2013

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T K Ray NTPC

Effect of Fineness
Fineness of pulverised coal More the fineness less is the capacity70% through 200 meshNumber of opening per linear inch.50 mesh sieve will have 2500 openings per square inchVolatile content below 16% would required higher degree of fineness i.E.75 to 80% through 200 mesh sieve, whereas the higher volatile coals (above 24%) will ignite and burn with ease with lower fineness of 60% through 200 mesh sieve.
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T K Ray NTPC

Effect of Fineness

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T K Ray NTPC

Effect of fineness

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T K Ray NTPC

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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

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

SiO

2

%

60.08

61.40

60.30

A

Al

2

O

3

%

29.50

28.50

29.80

B

Fe

2

O

3

%

4.10

3.90

4.70

B

CaO

%

1.70

1.93

1.57

B

MgO

%

0.75

0.92

0.59

B

Na

2

O + K

2

O

%

0.65

0.85

0.53

A

TiO

2

%

1.70

1.60

1.80

-

P

2

O

5

%

0.80

1.10

0.13

-

SO

3

%

0.27

0.31

0.25

Maximum mill capacity vs HGI at coal moisture of 12 %

30.00

32.00

34.00

36.00

38.00

40.00

42.00

60708090100110120

HGI

Output ( TPH)

Output at coal fineness of 70 % passing through 200 MeshOutput at coal fineness of 75 % passing through 200 mesh

Maximum mill Capacity vs coal moisture at coal HGI 100-110 and PF Fineness of 70 % passing through 200

Mesh

35.00

36.00

37.00

38.00

39.00

40.00

41.00

42.00

101112131415161718192021

Moisture

Mill output ( TPH)

Maximum mill output at coal HGI of 100-110

Maximum Mill capacity vs PF fineness at 12 % Raw coal moisture and at Coal HGI 100-110

33.00

34.00

35.00

36.00

37.00

38.00

39.00

40.00

41.00

6570758085

Mill output at raw coal moisture and at Coal HGI 100-110

combustion.ppt

Documents

coal pulverizer8

coal composition

density of coal

particular coal

ray ntpcburning of coal

pulverized coal boiler

pulverized coal firing8

pulverized coal burns