coal blending with fly ash-an approach
TRANSCRIPT
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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-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
BlendCase-IID/I/A55/40/05
BlendCase-IIID/I/A50/40/10
BlendCase-IVD/I/A45/40/15
BlendCase-VD/I/A40/40/20
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
BlendCase-IID/I/A85/10/05
BlendCase-IIID/I/A75/15/10
BlendCase-IVD/I/A65/20/15
BlendCase-VD/I/A55/25/20
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
BlendCase-IID/I/A85/10/05
BlendCase-IIID/I/A75/15/10
BlendCase-IVD/I/A65/20/15
BlendCase-VD/I/A55/25/20
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
( )