The presentation discusses the various factors which affect the performance of Power Boilers including the quality of coal, airheater performance, air ingress etc.

1. Factors affecting Boiler
Performance
By
total output power
solutions

2. Factors affecting Boiler Performance
Testing Techniques & Performance
Optimisation
Thrust Areas for Improvement
Presentation Coverage

3. Factors affecting Boiler Performance
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4. Introduction
Boiler performance depends on

Boiler design

Operating practices / parameters

Component condition

Coal Quality
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5. Boiler Performance Characterisation
• Combustion / Thermal Efficiency - Conversion
of chemical heat in fuel to production of steam –
adequate Time / Temperature / Turbulence
• Auxiliary Power Consumption – The total
power being consumed by ID, FD, PA fans and
the mills.
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6. OFF – Design/Optimum Conditions
Parameter Deviation Effect on Heat
Rate
Excess Air (O2) per % 7.4 Kcal/kWh
Exit Gas Temp per o
C 1.2 Kcal/kWh
Unburnt Carbon per % 10-15 Kcal/kWh
Coal moisture per % 2-3 Kcal/kWh
Boiler Efficiency per % 25 Kcal/kWh
Effect of Boiler side Parameters (Approx.)
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7. Boiler – Control Volume

8. Factors affecting Boiler efficiency include
• Design
• Coal Quality
• Mill Performance - PF Fineness
• Burner-to-burner PF balance
• Excess Air Level
• Boiler Air Ingress
• AH Performance
• Furnace / Convective section Cleanliness
• Quality of Overhauls
• Water Chemistry, boiler loading, insulation etc.07/07/19 tops 8

9. 210 MW NTPC NCTP - Dadri
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10. 500 MW NTPC Singrauli 6
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11. 500 MW Talcher – NTPC
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12. Efficiency Vs Ambient
Temp / RH
Assumptions
Exit Gas Temp - Constt.
Excess Air - 20 %
GCV - 3700 kal/kg
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13. Efficiency Vs Moisture
in Coal
Assumptions
Exit Gas Temp - Constt.
Fuel Moisture - 20.5 %
Excess Air - 20 %
GCV - 3700 kal/kg
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14. Efficiency Vs Hydrogen
in Coal
Assumptions
Exit Gas Temp - Constt.
Fuel Hydrogen - 2.33 %
Excess Air - 20 %
GCV - 3700 kal/kg
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15. Efficiency Vs HHV of
Coal
Assumptions
Exit Gas Temp - Constt.
Fuel Moisture - Constt
Fuel Hydrogen - Constt
Excess Air - 20 %
GCV - 3700 kal/kg
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16. Efficiency Vs Excess
Air
Assumptions
Exit Gas Temp - Constt.
Ambient Temp - 27 C
GCV - 3700 kal/kg
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17. • Proximate Analysis, Ultimate Analysis, Calorific Value, Ash Constituents,
Ash Fusion Temperatures, FC/VM ratio, Hard Grove Index, YGP (Yeer
Geer Price) Index
• Typical Proximate Coal Analysis - Fixed Carbon - 32.4 %, Volatile matter
- 21.6 %, Moisture 16.0 %, Ash 30.0 %, GCV 4050 kcal/kg
• +ve aspects - Low Sulfur, Low chlorine, Low iron content and High Ash
fusion temp
-ve aspects - High ash, moisture, high silica / alumina ratio, low calorific
value, high electrical resistivity of ash,
Problem
Variation in heating values, moisture, ash content and volatile matter
The Coal
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18. CAsh H O N S Mi M
As received basis
Air dry basis
Dry basis
Dry & Ash free basis
A FC VM M
Coke Volatile
Ultimate
Proximate
Coal Composition -
Different bases of representation
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19. • Coal characteristics decide the heat release rates, furnace wall
conditions and consequently the furnace heat transfer
• Deterioration in Coal quality affects boiler capability to operate at rated
parameters.
• Change in coal quality affects capacity, efficiency and combustion
stability.
• Increase in moisture affects mill drying, tempering air requirement,
gas velocities, ESP & Boiler efficiency.
• Ash quality / quantity affects boiler erosion, mill wear, slagging and
fouling propensity, ash handling system, sprays, sootblowing
requirements etc.
• Change in coal characteristics affects mill wear parts life &
throughput of Pulverizers.
• Increased dust loading & change in dust characteristics may affect
ESP performance.07/07/19 tops 19

20. FACTORS AFFECTING MILL PERFORMANCE
0
0.4
0.8
1.2
1.6
60 65 70 75 80 85 90 95 100
FINENESS - % THRU 200 MESH
CAPACITYFACTOR
0.85
0.9
0.95
1
1.05
0 4 8 12 16 20
% MOISTURE
CAPACITYFACTOR
0
0.5
1
1.5
2
40 50 60 70 80 90 100
HARDGROOVE INDEX (HGI)
MILLOUTPUTX100%
• GRINDABILITY (HGI)
• FINENESS
• MOISTURE
• SIZE OF RAW COAL
• MILL WEAR (YGP)
• MTC PRACTICES
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21. PF fineness
Typical recommended value of pulverised fuel
fineness through 200 mesh Sieve is 70% and
1% retention on 50 mesh sieve.
Fineness is expressed as the percentage pass
through a 200-mesh screen (74µm).
Coarseness is expressed as the percentage
retained on a 50-mesh screen (297µm).
Screen mesh indicates the number of openings
per linear inch.07/07/19 tops 21

22. PF fineness is influenced by
• Coal Quality
• Mill loading, settings, mill problems
• PA flows / velocities
• Sampling Techniques
 Conventional Cyclone / ASME Sampler
 64 point rotary sampler
• Sampling location
 Near mill / burner
 single pipe / average
• Manual / motorised sieve shaker
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23. EFFECT OF FINENESS ON BOILER OPERATION
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24. Excessive PF fineness would cause
• Reduction in mill capacity
• Increased mill component wear
• Increased mill and fan power combustion
Excessive PF fineness may not necessarily result
in improved combustion
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25. Control Room
Boiler
1
2 3
4
Mills
• Mill discharge pipes offer different resistance to the flows due
to unequal lengths and different geometry layouts.
• Fixed orifices are put in shorter pipes to balance velocities /
dirty air flow / coal flows. The sizes of the orifices are
specified by equipment supplier.
A B C D E F
Burner Imbalance
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26. TANGENTIAL FIRING
Uneven fuel and air
distribution can result in
• High unburnt carbon in
flyash
• Non - uniform release and
absorption of heat across the
furnace resulting in
temperature imbalance
• Reducing furnace leading to
slagging and fouling
• High furnace and boiler exit
gas temperatures
• Water wall wastage and tube
metal overheating
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27. Burner Imbalance
• Primary Air Flow
• Coal Flow
Dirty air flow distribution should be with in
+/- 5.0% of the average of fuel pipes
Coal distribution should be with in +/-10% of
the average of fuel pipes
Balanced Clean air flows do not necessarily
result in balanced Dirty air flows.
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28. Burner Balance
Balanced PF flows are an essential pre-requisite to an
optimized combustion. Usually the imbalance gets
camouflaged by additional excess air, thereby losing out
on boiler efficiency and operating flexibility.
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29. Excess Air
• Typically 20 % excess air is recommended for boiler
operation; Actual optimal value would vary from boiler to
boiler depending on coal quality, fineness and other
operating practices.
• Optimum level of oxygen could be less than value
specified by OEM.
• O2 instruments are installed at the economizer exit, where
they can be influenced by air infiltration. The O2 reading
in control room may not be necessarily representative of
the actual O2 in furnace.
07/07/19 tops 29

30. Comparision of Flue Gas Oxygen at Various Locations
Data From Boiler Optimization Tests 200 MW Unit
1
2
3
4
5
6
7
8
9
2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5
Flue Gas Oxygen Eco Outleft Left from DAS (%)
FlueGasOxygen(%)
O2 In Flue Gas From HVT Probe - Left O2 In Flue Gas From HVT Probe - Right
Flue Gas O2 at Econ RH Out APHs Inlet Flue Gas Oxygen -Grid
"A" APH Gas Outlet O2 "B" APH Gas Outlet O2
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31. Comparision of Flue Gas Oxygen Levels at APH
Inlet/HVT with Oxygen at Eco Outlet fron DAS
(500 MW Unit)
3
3.3
3.6
3.9
4.2
4.5
4.8
2.15 2.2 2.25 2.3 2.35 2.4 2.45 2.5 2.55 2.6 2.65
Flue Gas Oxygen at Eco Left (DAS) %
Oxygen%
Avg.Furnace Exit (HVT) Oxygen APH Gas Inlet Oxygen %
8 1323
10
9
APH Inlet FG Oxygen
Furn Exit Gas Oxygen
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32. Excess Air
C+ O2 = CO2 + 8084 kcal / kg of Carbon
2C+ O2 = 2CO + 2430 kcal / kg of Carbon
2H2+ O2 = 2H2O + 28922 kcal / kg of H
S + O2 = SO2 + 2224 kcal / kg of Sulphur
We lose 5654 kcal for each kg of CO formed.
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33. Excess Air
Low excess air operation can lead to
• unstable combustion (furnace puffs)
• increased slagging of waterwalls and SH sections
• Loss in boiler efficiency due to increased CO / unburnt
combustibles
High excess air operation can lead to
• Increased boiler losses
• High SH / RH temperatures
• Higher component erosion
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34. Boiler Air Ingress
• Cold air leaks into the boiler from openings in the furnace and
convective pass and through open observation doors.
• Some of the boiler leakage air aids the combustion process;
some air that leaks into the boiler in the low temperature zones
causes only a dilution of the flue gas.
• This portion of air appears as a difference in O2 level between
the furnace exit and oxygen analysers at economizer exit.
Actual oxygen in the furnace could be much less.
• Also, boiler casing and ducting air ingress affects ID fans’
power consumption and margins in a major way.
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35. Furnace
Outlet
Air-in-
leakage
Zirconia
O2 Probe
AH
Seal
Lkg
ESP
Expansion Joints
Air Ingress Points – Furnace Roof , Expansion joints, Air
heaters, Ducts, ESP Hoppers, Peep Holes, Manholes,
Furnace Bottom
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36. Air ingress can be quantified by the increase in oxygen %
in flue gas; The temperature drop of the flue gas from air
heater outlet to ID fan discharge also provides an
indication of the same.
Oxygen % at various locations in boiler
0
2
4
6
8
10
Furn Outlet AH Inlet AH Outlet ID outlet
O2%
210 MW 210 MW 500 MW 210 MW
Boiler Air Ingress
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37. Air Heaters
Factors affecting performance include
• Operating excess air levels
• PA/SA ratio
• Inlet air / gas temperature
• Coal moisture
• Air ingress levels
• Sootblowing
• No. of mills in service
07/07/19 tops 37

38. Air Heaters
Factors affecting performance include
• PA Header Pressure
High pressure results in increased AH leakage,
higher ID fan loading, higher PA fan power
consumption, deteriorates PF fineness & can
increase mechanical erosion
• Upstream ash evacuation
• Maintenance practices
Condition of heating elements, seals / seal setting,
sector plates / axial seal plates, diaphragm plates,
casing / enclosure, insulation
07/07/19 tops 38

39. Boiler Exit Gas Temperature
Ideal flue gas temperature at stack outlet should be just above the
dew point to avoid corrosion; Higher gas temperatures reduce
efficiency; Possible causes of temperature deviations are
• Dirty heat transfer surfaces
• High Excess air
• Excessive casing air ingress
• Fouled/corroded/eroded Air heater baskets
• Non - representative measurement
Contd..07/07/19 tops 39

40. Air Heaters - Exit Gas Temperatures
Factors affecting EGT include
• Entering air temperature - Any changes would
change exit gas temperature in same direction
• Entering Gas Temperature - Any changes would
change exit gas temperature in same direction
• X-ratio - An increase in X-ratio would decrease exit
gas temperatures & vice versa
• Gas Weight - Increase in gas weight would result in
higher exit gas temperatures
• AH leakage - An increase in AH leakage causes
dilution of flue gas & a drop in ‘As read’ exit gas
temperatures07/07/19 tops 40

41. AUXILIARY POWER CONSUMPTION
Major auxiliaries Consuming Power in a Boiler are
FD fans, PA fans, ID fans and mills. Reasons for
higher APC include
* Boiler air ingress
* Air heater air-in-leakage
* High PA fan outlet pressure
* Degree of Pulverisation
* Operation at higher than optimum excess air
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42. Main Steam/ Reheated Steam
Temperature
While an increase in steam temperatures is beneficial
to Turbine Cycle Heat Rate, there’s no benefit to
boiler efficiency, infact it affects reliability adversely.
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43. Testing Techniques & Performance Optimisation
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44. Test Objectives – To generate feedback for
change in opn & mtc. strategy
•To determine current boiler efficiency levels
•To determine each component of the heat loss to
find the reasons for deterioration
•To establish the cost / benefit of annual boiler O/H
•To establish baseline performance data on the
boiler after major equipment modifications
•To build a database for problem solving and
diagnosis, for maintenance planning prior to
outages and maintenance evaluation following an
outage
07/07/19 tops 44

45. Suggested Frequency of Testing
QuarterlyBoiler Efficiency
Pre/Post O/H & Six
monthly
FG Path O2
mapping
QuarterlyAH Perf. Test
Pre/Post O/HDirty Air Flow
Frequency
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46. Boiler & Air Heater Tests
Tests to be conducted under defined operating regime (O2
level / PA Header Pressure / no. of mills) at nominal load
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47. Pre Test Stabilisation Period
Prior to the test run, equipment must be operated at steady
state conditions to ensure that there is no net change in
energy stored in steam generator envelope.
Minimum Stabilisation Time - 1 hour
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48. Pre Test Checks
• Sootblowing completed at least one hour before start of the test
• Steam coil air preheaters’ steam supply kept isolated
• All feedwater heaters in service with normal levels, vent settings
and with normal drain cascading
• No sootblowing or mill change over during the test. In case oil guns
are used, the test shall be repeated
• Air heater gas outlet dampers are modulated to ensure minimum
opening of cold air dampers to mills
• Auxiliary steam flow control kept isolated or defined during the test.
• CBD / IBD blowdowns kept isolated for the test duration
• Bottom hopper deashing after completion of test and not during the
tests
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49. Test Duration
Should be sufficient to take care of deviations in parameters
due to controls, fuel variations & other operating conditions.
When point by point traverse of Flue gas ducts is done, test
should be long enough o complete atleast two traverses.
In case of continuous Data Acquisition System & use of
composite sampling grids, shall be based on collection of
representative coal & ash samples.
Could be 1/2 to 2 hours in case of parametric optimisation
tests or 4 hours for Acceptance Tests.
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50. Frequency of Observations
Parameter readings to be taken at a maximum interval of 15
minutes & a preferred interval of 2 minutes or less
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51. Measurements during a Boiler Test
• Coal Sample for Proximate analysis & GCV
• Bottom Ash and Flyash Samples
• Flue Gas Composition at AH Outlet
• Flue Gas Temperature at AH Inlet / Outlet
• Primary / Secondary air temp at AH inlet / outlet
• Dry / Wet bulb temperatures
• Control Room Parameters
(All measurements / sampling to be done simultaneously)
07/07/19 tops 51

52. Coal Sampling
• Coal Samples are drawn from all individual running
feeders from sampling ports in feeder inlet chutes
• Composite sample is collected from all running feeders
• One sample is sealed in an air tight container for total
moisture determination
07/07/19 tops 52

53. Flyash Sampling
• Flyash is collected in several hoppers as Flue Gas goes
to stack; Heavier particles fall out first due to turns in
gas stream
• Relative distribution of ash to various hoppers is not
accurately known
• Preferred way to collect a) a representative sample b)
sample of the test period is to use High Volume
Sampler probes on both sides of boiler
07/07/19 tops 53

54. High Volume Sampler
This sampler uses 2-3 ksc air through an aspirator to
create vacuum to pull out a large volume of flue gas & ash
into probe’s canister; A filter catches the ash but allows
the gas to pass through.07/07/19 tops 54

55. Bottom Ash Sampling
• Bottom ash samples are collected every 15 minutes from the
scrappers system during the test
• In case of impounded hoppers, incremental samples are
collected from bottom ash hoppers’ disposal line at slurry
discharge end
• Sample in slurry form should be filtered and dried to avoid
segregation of carbon particles.
• Lab sample is prepared by coning and quartering
• Unburnt carbon is determined as LOI (Loss on Ignition)
07/07/19 tops 55

56. Need for Off line Grid Measurement
‘On Line’ Instruments are adequate to monitor air
heater performance but not good for assessing
degradation. PG tests also necessitates installation of
grid in air and flue gas ducts.
a) Flue gas O2 measurement at AH outlet is not
available
b) Single point Orsat can be misleading due to
stratification in flue gas
c) The grid also validates & cross checks
representative ness of online feedback
07/07/19 tops 56

57. FG
Economizer
FG
APH
Sampling
Locations
APH
Expansion
Bellow
Test Locations - AH Inlet & Outlet
• Inlet Sampling plane to be as close to AH as possible; Outlet
grid to be a little away to reduce stratification
• AH hopper / Manhole air ingress can influence test data
07/07/19 tops 57

58. Sampling Ports in Flue Gas Ducts (Typical )
Sampling Point for Flue Gas Temperature & Composition
100mm
Flue Gas Duct is divided into equal cross-sectional areas
and gas samples are drawn from each center07/07/19 tops 58

59. Thermocouples
l/6 l/2 5/6 l
Gas Side Probes
Air Side Probes
Gas
Analysers
Datascan
Boxes
Vacuum Pump
Desiccant
Jar
Condenser
FG Sample
from probes
Bubble Jar
Flue Gas Sampling Train
07/07/19 tops 59

60. HVT Probe – A Diagnostic Tool
• To establish furnace gas exit temperature profile
• To establish CO & O2 profile at furnace outlet
• To confirm proper distribution of fuel and air
• To quantify air ingress between furnace outlet and
AH inlet
07/07/19 tops 60

61. HVT - High Velocity Thermocouple Probe
07/07/19 tops 61

62. Typical problems

High Economiser / AH exit gas temperature

Air ingress from furnace bottom, penthouse and
second pass

Boiler operation at high excess air

Metal temperature excursions

High Unburnt carbon in ashes

Uneven Flyash Erosion

Flame failures

Shortfall in steam temperatures

Imbalance in Left - Right steam temperatures07/07/19 tops 62

63. • Air heaters
• Boiler air Ingress
• Boiler Optimum Regime
• Condenser
• HP/IP Turbine Efficiency
• High energy drains
• Cooling Towers
Thrust Areas – HR Improvement
07/07/19 tops 63

64. • Deterioration of Boiler efficiency and increase in auxiliary
power is generally on account of Air Heater performance
degradation from O/H to O/H.
• AH Performance degrades from one O/H to next O/H .Major
symptoms are
• Increased flue gas volume, affecting ESP performance in a major way
• Lower flue gas exit. temperatures due to high air heater leakage, an
erroneous boiler efficiency feedback generating complacency.
• Lower fan margins, at times limiting the unit output
• Boiler operation at less than optimum excess air specially in units
where in ID fans are running at maximum loading
Air Heaters
07/07/19 tops 64

65. Air Heaters
• AH sootblowing immediately after boiler light up.
• Monitoring of Lub oil of Guide & Support bearings
through Quarterly wear-debris analysis.
• Hot water washing of air heaters after boiler
shutdown - flue gas temperature ~ 180 to 150 C
with draft fans in stopped condition. (Ideally pH
value can verify effective cleaning)
• Basket drying to be ensured by running draft fans
for atleast four hours after basket washing.
07/07/19 tops 65

66. Air Heaters
• Baskets cleaning with HP water jet cleaning during
Overhauls after removal from position
• Heating elements to be covered with templates during
maintenance of air heaters.
• Gaps between diaphragms & baskets to be closed
for better heat recovery & lower erosion rate at edges.
• Ensuring healthiness of flushing apparatus of Eco &
AH ash hoppers
07/07/19 tops 66

67. Basket Replacement
•Replacement of baskets recommended when
Weight loss of heating element baskets > 20-30 %
Thinning of element thickness > one-third
Erosion of heating elements is > 50 mm depth
Trends of Gas side and air side efficiency before and
after Overhaul may also supplement the replacement
decision.
07/07/19 tops 67

68. Basket Replacement
•Reversal of baskets not recommended;
•Used as a temporary measure only when
 Erosion of heating element > 50 mm depth
 Thinning of element edge thickness > one-third
07/07/19 tops 68

69. • Apart from degradation of AH baskets’ performance,
another reason for lower heat recovery across air heaters
is boiler operation at lesser SA flows.
• This is on account of air ingress from furnace bottom,
peep holes, penthouse roof and expansion joints.
• The actual oxygen in the furnace is much less than what
is being read at economiser outlet by online zirconia.
• Difference between oxygen at furnace outlet and AH
inlet / economizer outlet has been observed to be in the
range of 1.0 to 2.5 % in many boilers.
Air Ingress
07/07/19 tops 69

70. • Boiler operation under adverse conditions continues as in
majority of units ‘On line’ CO feedback is not available.
• All boilers need to be equipped with ‘On line’ CO monitors
at Eco Outlet / ID fan discharge.
• Air ingress across AH outlet to ID suction observed to be
generally in the range of 5 to 9%.
• Flue gas ducts & expansion joints at Eco outlet and
APH inlet / outlet inspected thoroughly during O/H
• Replacement of Metallic / Fabric Expansion joints in 10
years / 5 years cycle
Air Ingress
07/07/19 tops 70

71. Boiler Parametric Optimisation
• A structured exercise to evolve an optimum operating
regime for a boiler; a set of operating parameters and
equipment settings for safe, reliable and efficient
operation.
• To establish interrelationships between different
operating parameters.
• To build a repeatable database for problem solving and
diagnosis by various parametric tests.
• All the more necessary when firing blended coals.
07/07/19 tops 71

72. THANKS
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