Coal Blending With Fly Ash-An Approach

7/31/2019 Coal Blending With Fly Ash-An Approach

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Coal blending with Fly ash an

approach

Pradip chanda, AGM (CP)

Navinkishore, Manager (CP)


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Import coal blending is inevitable for Indian

power sector

0.66

0.42

0.57

1.24

3.14

4.53

6.56

6

8.71

9.87

9.44

10.31

8.69

11.56

21.7

25.2

27.76

37.92

44.28

0.36 0.220.28

0.59 1.371.85

2.61 2.37

3.273.54

3.21 3.37

2.66

3.33

5.78

6.32 6.57

8.28

9.08

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FY-93

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FY-01

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FY-09

FY-10

a

CoalImport(milliontons)

Rising Coal Imports-Non Coking Coal

Imports Imported coal as %age of domestic coal


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Blending for Indian power boiler -issues

In general high heat value coals are procured through

import.

Blending proportion adopted by experience.

Releases of heat in the furnace zone and slagformation, restricts the percentage of imported coal

use in the blend.


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Blending for Indian power boiler -issues

Less availability of domestic coal further restricts

usage of imported coal.

With mismatch in demand and availability of domestic

coal Indian power sector require higher percentage of

usage of imported coal in the blend

Higher proportion of import is possible through gas

recirculation in the boiler. But few boiler have the

provision.


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Increasing import proportion by blending it

with fly ash an approach

This paper has come out with a concept to substitute

the role of GR fan by fly ash injection for flame

temperature control .

Blending fly ash with high CV Imported coal is

expected to

Increase thermal loading around the flame and therebywill reduce the furnace zone temperature

Enable enhancement of proportion mix of imported

coal to a great extent


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Outline of the study

Earlier practices if any

Flame temperature modeling

Furnace temperature modeling

Ash slagging possibility

Proposed blending technique


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Riley Stoker Corporation


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WE Energies developed coal ash beneficiation processes

for carbon and ammonia removal.

The processes take advantage of utilizing residual

energy in high carbon fly ash and bottom ash

New ash beneficiation processes are designed as stand

alone systems or potential additions to existing powerplants.

Existing practices


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Flame temperature model

The flame temperature is modelled from mixedadiabatic temperature of the constituent burning

gases.

using the equation become

, T= (Tadb-Tref) --------------- (1)

Xri =Reactant , Ypj= Product, Cp= Sp. Heat.

Tadb/Tref=Adiabatic flame temperature/ ref. temp

Pjj

PjRii

Ri hYhX TChavgp

,

i j

T

T

PPipPj

T

T

RRipRi

ad

ref

R

ref

dTcYdTcX,,


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Furnace temperature model

The furnace zone flue gas temperature is modelled

as.

= Mass flow rate, H/h= Enthalpy/ change in enthalpy

= Stiffen Boltzman const. = Flame emissivity

Aww = Water wall area. Tfl = Flue gas temp.

flfl

wwadwwashashairairfuelfuelfuelfuel

refflCM

TTAhMhMHMhMTT

)()()(

44

M


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Simulating the model for a 200 MW boiler

Two coal sample data (one of domestic coal and one

from imported coal) from NTPC Korba used for flame

temperature model simulation.

Numbers ofblended scenario created with ash

blending.

Mass fraction of fuel component determined separately

for each blend type and used as input to the model.


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Simulating the model for a 200 MW boiler

Model is simulated on excel spread sheet**.

Result shows that with blending of fly ash the flame

temperature gets slightly reduce.

**The componentII (combustion) spread sheet of Engineeringsoftware (www.engineering-4e.com ) used for determining

the enthalpy of individual reactants and products.


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Mass fraction(mass/mass)

BlendCase-ID/I/A90/10/0

BlendCase-IID/I/A85/10/05

BlendCase-IIID/I/A75/15/10

BlendCase-IVD/I/A65/20/15

BlendCase-VD/I/A55/25/20

Flame tempKEA-20%

-0.99%2398.011 2397.547 2392.348 2386.933 2381.295

2380

2382

23842386

2388

2390

2392

2394

2396

2398

2400

0

10

2030

40

50

60

70

80

90

100

0 5 10 15 20 25

Flametem(

degK)

Im

p&Domb

lending%

Ash blending %

Adiabatic Flame Temperature trend on blending

Import

Domestic

Flm Temp

Fig-I


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Simulating the Furnace temperature

The model is further simulated in Excel spreadsheet.

(Emissivity of the flame calculated from mean beam lengthand furnace geometry. The value obtained is 0.67. The fly ash

specific heat capacity is assumed as 0.227 Kcal/deg K.)

This time the imported coal percentage kept fixed at

40 % varying domestic and ash percentage.

Result shows that with blending of fly ash a major

portion of heat is absorbed by the ash resulting in

reduction of furnace zone temperature.


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Cases BlendCase-ID/I/A60/40/0





Mass of flue

per Kg fuel

(EA- 20 %) 8.15 7.85 7.71 7.57 7.43T (Fur Zone)

K 1447.30 1434.52 1420.84 1406.15 1390.34

Furnace Zone Flue gas temperature

The trend follows a 2nd order relation. Temp = -0.020x2 - 2.442x + 1447 where x= % blending


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Furnace Slagging possibility

The ash fusion temperature (AFT) of blends increased

with increasing amounts of Al2O3, CaO, K2O, Na2O and

TiO2.

as per Carpenter (1995) the base to acid ratio iscommonly used to predict the slagging propensity of a

coal. It is defined as:

A value of the base to acid ratio between 0.4 and 0.7

indicates a high slagging propensity. Values outside

this range indicate a lesser likelihood to slag.

The blended coal acid to base ratio is tabled in next

slide.


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Ash quality in blended coal

Oxide(%)

SiO2

TiO2

Al2O3

CaO

MgO

Fe2O3

MnO K2O&Na2

0Ratio(A)Fe:Ca

Ratio (B)Basic:

Acidic

(1) (2) (3) (4) (5) (6) (7) (8)(6)/ (4) [(4)+(5)+

(6)+(8)]/[(1)+(2)+

(3)]Coal-I 54.80 1.88 24.50 3.57 1.87 9.08 0.10 1.50 2.54 0.19Coal-II

52.00

0.00

31.80

2.70

4.70

4.90

0.00

2.70 1.81 0.18

Blend

(90/10/0) 54.73 1.84 24.69 3.54 1.94 8.98 0.10 1.53 2.53 0.20Blend(85/10/0

5) 54.73 1.84 24.68 3.55 1.93 8.98 0.10 1.53 2.53 0.20Blend(75/15/1

0) 54.70 1.82 24.76 3.54 1.97 8.93 0.10 1.54 2.53 0.20Blend(65/20/15

) 54.67 1.80 24.84 3.53 2.00 8.89 0.10 1.56 2.52 0.20Blend(55/25/2

0) 54.64 1.77 24.92 3.52 2.03 8.84 0.09 1.57 2.51 0.20Ratio (A) range of slagging is from 0.3 to 3.0 with maximum slagging possibility near 1.0Ratio (B) range of slagging is from 0.4 to 0.7


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0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 5 10 15 20 25 30

basic:Acidicindex

Ash blending %

Ash slagging study

Iron:Calcium

base to acid

Fig 3

Iron: Calcium ratio beyond the range from 0.3 to 1.0 indicate lesser likely hood of

slagging

Acid to base ratio beyond 0.4 to 0.7 indicated lesser likely hood of slagging.


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BLENDING TECHNIQUE

1. Stock pile lending

2. Inline Blending

3. Blending in side

the furnace

Feeding at mill outlet


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Conclusion

A study conducted on fly ash blending with a blend of Indian

and imported coal.

Additional Fly ash loading reduces the flame as well as

furnace zone temperature and carries away heat in the

convective portion of the furnace.

This will enable a higher blending ratio for imported coal and

will address the issue of less domestic coal availability.

The blend apparently will not adversely effect the slagging of

the ash.


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Reference:[1].Reburning of coal ash Bruce W. Ramme, Wisconsin Electric Power Company, US

patent No. 5,992,336, Nov. 30,1999.[2] Ash Fuel Reburn and benefication at We Energies, A report- Bryna Goeckner, Bruce

Ramme[3] Characteristics of Coal Ash Emissivity in high temperature atmosphere- Shimogori,

Yoshizako, Mark Richardson, ISME International Journal, series B, Vol 4.9, No. 2, 2006[4] Ash emissivity characterization & prediction Christopher J, Zygarlicke, Donald P.

McCollor, Charlone R. Crocker, Final report, U.S. department of Energy, 1999[5] A study on Coal properties and combustion characteristics of blended coals in

Northwestern China- Chanan Wang, Yinhe Liv, Xiaoming Zhang, Defuche Energy &

Fuels, American Chemical Socity publication, 2011[6] Effects of coal ash on combustion system, Anne M. Carpenter et.al, Coal on line,

IEA Clean Coal Centre, 2005[7] Su S, Combustion behaviour and ash deposition of blended coals, PhD Thesis, The University of

Queensland, Brisbane, 1999[8] A new Distinguish Method of Blending of Coals slagging characteristics- Yonghua Li,

Energy & Power Engineering, 2011

[9] Boilers and Brners, Prabir Basu, Cen Kefa, Louis Jeslin, Springler, 1999[10] A review of the state of the art in Coal blending for power generation Prof Terry Wall,

Liza Elliot, Dick Sanders, Ashley Conroy, University of Newcastel, Australia, 2011[11] A cause- Effect analysis of Furnace heat transfer Lecture presentation by Dr. P.M.V.

Subbarao, IIT, Delhi[12] Energy Conversion with plot 1.1 Engineering software Demo version,


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THANK YOU

A pilot study with Imported coal and ash will be able to analyzethe pros and cons of the approach.


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Ultimate analysis

Domestic

Coal

Imported

CoalCarbon 40.02 61.00

Hydrogen 2.37 4.00

Oxygen 2.27 6.50

Sulphur 0.19 1.60Nitrogen 1.65 1.40

Moisture 4.40 14.00

Ash 49.10 11.50

Total 100.00 100.00

CV 3200.00 5650.00

BACK

Ul i l i f Bl d d C l BACK


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Ultimate

Analysis(%)

Coal-I Coal-II BlendCase-ID/I/A90/10/0





Carbon 40.02 61.00 42.118 40.117 39.165 38.213 37.261Hydrogen 2.37 4.00 2.533 2.4145 2.3775 2.3405 2.3035Oxygen 2.27 6.50 2.693 2.5795 2.6775 2.7755 2.8735Sulphur 0.19 1.60 0.331 0.3215 0.3825 0.4435 0.5045Nitrogen 1.65 1.40 1.625 1.5425 1.4475 1.3525 1.2575Moisture

4.40 14.005.36

5.14

5.4

5.66

5.92

Ash 49.10 11.50 45.34 47.885 48.55 49.215 49.88CV 3200.00 5650.00 3445 3285 3247 3210 3172

Ultimate analysis of Blended Coal

Mass fraction(mass/mass)

BlendCase-ID/I/A90/10/0





Carbon 0.7705 0.7698 0.7612 0.7524 0.7434Hydrogen 0.0463 0.0463 0.0462 0.0461 0.0460Oxygen 0.0493 0.0495 0.0520 0.0547 0.0573Sulphur 0.0061 0.0062 0.0074 0.0087 0.0101Nitrogen 0.0297 0.0296 0.0281 0.0266 0.0251

Mass fraction (Kg/Kg) ash free basis

BACK


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Input Values:Fuel Composition

MW Mass Basis MW[kg/kmol] [kg/kg] [kg/kmol]

12 Carbon 0.780 44 Carbon Dioxide2 Hydrogen 0.050 18 Water Vapor32 Sulfur 0.030 64 Sulfur Dioxide28 Nitrogen 0.040 28 Nitrogen32 Oxygen 0.080 32 Oxygen18 Water 0.020

Fuel Total 1.000Fuel HHV [Kcal/Kg] 7,789.51

Combustion Efficiency [/] 1.000Oxidant Composition MW Gas

MW Mole Basis [kg/kmol][kg/kmol] [kmol/kmol] 44 Carbon Dioxide

32 Oxygen 0.21 18 Water Vapor28 Nitrogen 0.79 64 Sulfur Dioxide

28 Nitrogen

Oxidant Total 1.00 32 OxygenMW Mass Basis

[kg/kmol] [kg/kg]32 Oxygen 0.23

28 Nitrogen 0.77

Oxidant Total 1.00Stoichiometry [/] 1.00


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Output Values: Combustion Products CompositionMass Basis Mass Basis Mole Basis Mole Basis

[kg] [kg/kg] [kmol] [kmol/kmol]Carbon Dioxide 2.860 0.249 0.065 0.170

Water Vapor 0.470 0.041 0.026 0.068Sulfur Dioxide 0.060 0.005 0.001 0.002Nitrogen 8.097 0.705 0.289 0.759Oxygen 0.000 0.000 0.000 0.000

Total 11.487 1.000 0.381 1.000Stoichiometric Oxidant to Fuel Ratio [/] 10.487

Oxidant to Fuel Ratio [/] 10.487

Gas Gas Kappa Gas Constant Specific Heat[/] [J/kg*K] [J/kg*K]

Carbon Dioxide CO2 1.30 188.90 845.00Water Vapor H2O 1.33 188.50 1,690.00Sulfur Dioxide SO2 1.26 130.00 622.00Nitrogen N2 1.40 296.90 1,038.00Oxygen O2 1.40 259.80 916.00

Combustion Products 1.37 264.70 1,014.45

Fuel Temperature [K] 298 OxidantTemperature [K] 298

Fuel Enthalpy [kJ/kg] -317.5Oxidant Enthalpy [kJ/kg] -0.2

Flame Temperature [K] 2,484 BACK


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Flue gas production per Kg of coal (mass)

Flame Temperature

Mda 5.4328256 2398.011253 2397.54718 2392.348 2386.933 2381.295

Sp.coal 0.725689405 0.76103501 0.769941 0.778816 0.788146

Tda 6.08476467 Tfl 1390.562006Mwa 6.08476467

Mflue 7.9066378 Furnace zone temperature

Fur zone 1447.30 1434.52 1420.84 1406.15 1390.34

Wc (gas prod)

1.7266136

Blend

import 40 40 40 40 40

Blend ash 0 5 10 15 20

O2 (Th) 1.2898936 1.2548136Blen Dom 60 55 50 45 40

Mflue 8.15 7.85 7.71 7.57 7.43

Air(Th) 5.97530286

N2 4.72048926 0.94409785

Excs air 1.19506057

Exce O2 0.25096272Flue gas 7.64216343

F+Ash 7.99608343

Tot O2 1.54085632

Tot N2 5.66458711

Ratio O2 0.21384615

Ratio N2 0.78615385


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Combustion -- Coal

Input Values: Output Values:

Fuel Composition

Combustion

Products

Composition

MW Mass Basis MW Mass Basis Mass Basis Mole Basis Mole Basis

[kg/kmol] [kg/kg] [kg/kmol] [kg] [kg/kg] [kmol] [kmol/kmol]

12 Carbon 0.780 44 Carbon Dioxide 2.860 0.210 0.065 0.143

2 Hydrogen 0.050 18 Water Vapor 0.470 0.035 0.026 0.058

32 Sulfur 0.030 64 Sulfur Dioxide 0.060 0.004 0.001 0.002

28 Nitrogen 0.040 28 Nitrogen 9.709 0.714 0.347 0.764

32 Oxygen 0.080 32 Oxygen 0.490 0.036 0.015 0.034

18 Water 0.020

Total 13.588 1.000 0.454 1.000

Fuel Total 1.000

Stoichiometric

Oxidant to Fuel

Ratio [/] 10.487

Fuel HHV [Btu/lbm] 14,162.76

Oxidant to Fuel

Ratio [/] 12.588

Combustion Efficiency [/] 1.000

Oxidant Composition MW Gas Gas Kappa Gas Constant Specific Heat

MW Mole Basis [kg/kmol] [/] [J/kg*K] [J/kg*K]

[kg/kmol] [kmol/kmol] 44 Carbon Dioxide CO2 1.30 188.90 845.00

32 Oxygen 0.21 18 Water Vapor H2O 1.33 188.50 1,690.00

28 Nitrogen 0.79 64 Sulfur Dioxide SO2 1.26 130.00 622.00

28 Nitrogen N2 1.40 296.90 1,038.00

Oxidant Total 1.00 32 Oxygen O2 1.40 259.80 916.00

MW Mass Basis

Combustion

Products 1.38 268.35 1,013.70

[kg/kmol] [kg/kg]

32 Oxygen 0.23 Maximum 1,000 Maximum 5,000

28 Nitrogen 0.77 Fuel Temperature [K] 323

Oxidant

Temperature [K] 573

Minimum 273 Minimum 273

Oxidant Total 1.00 Fuel Enthalpy [kJ/kg] -279.3

Oxidant Enthalpy

[kJ/kg] 282.4

Stoichiometry [/] 1.20

Flame Temperature

[K] 2,383

( )

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Coal Blending With Fly Ash-An Approach