1. CASE STUDY ON AS
RUN BOILER ENERGY
AUDIT AND REPORTING
D PAWAN KUMAR & R VIRENDRA
NATIONAL PRODUCTIVITY COUNCIL,
INDIA
(16 January 2012)
2. OBJECTIVES
Efficiency of Boiler
As run Boiler efficiency, at three representative load
setting over 9 trials
Assessment of Boiler Loss Profile and Heat rate during
trial conditions
Assessment of Heat Exchangers Effectiveness of Heat
Exchangers such as Air Preheaters, Economisers,
Condensers etc
3. INSTRUMENTS REQUIRED
Flue gas analysers
Portable temperature indicator
On-line instruments of boiler control room.
Facilities of the chemistry lab or outside lab for coal /
ash / water analysis. (coal proximate or ultimate
analysis, un-burnt in bottom and fly ash, TDS, pH of
feed water / blow-down / condensate.
Power analyser for power measurement of ID fan, FD
fan, ESP, crushers, BFP (boiler feed water pump) cool
handling plant/ash handling plant, etc.
4. METHODOLOGY
Boiler Efficiency trials are normally conducted at three
representative typical load ranges namely, 100% of NCR, 80% of
NCR and 60% of NCR
Performance assessment chosen is the indirect method of heat
loss and Boiler Efficiency calculation, drawn from Indian Standard
(IS-8753/1977) and the deployed relations are presented as follows
During the Boiler trials, following key parameters are monitored as
Power Generation, Coal Consumption, GCV of Coal, Total Air Flow,
Mill rejects, GCV of Mill rejects, Combustibles in bottom ash,
Bottom ash Quantity, Combustibles in ECO/APH ash, ECO/APH
ash Quantity, Combustibles in Fly ash, Fly ash Quantity, Flue gas
analysis APH outlet for %CO2, %O2 and temperature, Ambient air
dbt, wbt and RH%, P.A. (Proximate Analysis) of coal, V.A. (Ultimate
Analysis) of coal, various flows, pressure and temperature in
steam, water, air, flue gas path, power measurement at key
auxiliaries.
7. BOILER PARAMETERS
THE LIST OF NEARLY 136 BOILER PARAMETERS
MONITORED AND THE CORRESPONDING
TRASNDUCER REFERENCES VIS-À-VIS THE DAS
SYSTEM ARE ALSO TO BE REPORTED.
DESIGN OPERATING PARAMETERS
(Reference values) are also to be reported
Design Flow, Temperatures and Pressures for
Steam, Water, Fuel & air and Flue gas along with
Pressure drops as relevant are also reported.
Design heat balance is also reported as reference
basis.
8. Present case is of a 200 MW boiler
AS RUN AUDIT FINDINGS
PLANT ROAD
Available data is for 100%, 80%, 60% NCR.
The three typical load ranges at which the
Boiler Performance could be assessed was
Load Setting
No of
Trials
a) > 90% of NCR 6
b) > 80% of NCR 1
c) > 70% of NCR 2
Total: 9
9. KEY BOILER TRIAL FINDINGS
The Key Boiler trial findings in respect of Auxiliary
Consumption, Feeder wise Coal Consumption,
Coal GCV, DM Water Consumption, Power
Generation, Specific Coal Consumption and
Overall Heat Rate are presented in the following
tables.
13. KEY PARAMETERS DURING TRIALS
VIS-A-VIS DESIGN
The key Boiler parameters, pertinent to Thermal
Efficiency, namely the MW Generation (Load),
Coal Consumption, GCV of Coal, Total Air Flow,
Mill Rejects, GCV of Mill Rejects, Combustibles
in Bottom Ash, Fly Ash, Flue Gas Anal1ysis at
APH Out, Ambient conditions, Proximate
Analysis of Coal, alongside the design values,
are reported as under.
14. BOILER PERFORMANCE EVALUATION: SUMMARY OF KEY PARAMETERS DURING BOILER TRIALS
S
Trial
. Operating Parameters U nit Design Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Trial 6 Trial 7 Trial 8
9
N
o
1. POWER GENERATION MW 200.00 194.07 194.95 191.98 153.33 153.15 185.92 166.30 181.67 180.67
2. % OF NCR % 100.00 97.04 97.48 95.99 76.67 76.58 92.96 83.15 90.84 90.34
3. COAL CONSUMPTION TPH 103.00 117.94 116.55 118.18 104.11 103.11 123.04 107.26 111 .90 112.67
16795. 16607.
4. G C V OF COAL KJ/KG 17974.00 19215.46 17096.20 18601.00 16661.48 16147.34 14638.36 16531.90
24 14
5. TOTAL AIR FLOW TPH 725.40 773.92 769.30 738.56 706.29 691.94 743.79 598.50 615.40 703.00
6 MILL REJECTS KG/HR 339.90 389.20 384.62 389.99 343.56 340.26 406.03 353.96 369.27 371.81
2500.0 1800.0
7. G C V OF MILL REJECTS KCAUKG 1800.00 2610.00 2660.00 2550.00 2420.00 2150.00 1860.00 1880.00
0 0
8. COMB. IN BOTTOM ASH % 2.01 5.10 5.00 4.10 3.70 2.59 3.60 2.50 2.65 2.25
33766. 33766.
9. C V OF CARBON KJ/KG 33766.04 33766.04 33766.04 33766.04 33766.04 33766.04 33766.04 33766.04
04 04
1
BOTTOM ASH QTY. (Dry basis) KG/KG 0.05 0.04 0.04 0.04 0.05 0.05 0.05 0.06 0.05 0.05
0.
20. STATEMENT OF BOILER
EFFICIENCY
A Comprehensive Statement of as run
Boiler Thermal Efficiency presenting the
Boiler Load, Heat Balance, Thermal
Efficiency and Overall Heat Rate for the
nine trials conducted is presented in
following tables:'
21. SUMMARY STATEMENT OF BOILER EFFICIENCY
Desi
S.N Parameters Units Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Trial 6 Trial 7 Trial 8 Trial 9
gn
o
1 DATE
0900- 1445- 0915- 1015- 1500- 1915- 1430- 1430- 1430-
2 DURATION HRS
1300 1845 1315 1415 1900 1315 1830 1830 1830
3 POWER GENERATION MW 200 194.07 194.95 191.98 153.33 153.15 185.92 166.3 181.67 180.67
4 % LOAD % 100 97.04 97.48 95.99 76.67 76.58 92.96 83.15 90.84 90.34
KCAUK
5 G C V OF COAL 4300 4597 4090 4450 3986 4018 3863 3502 3955 3973
G
6 FLUE GAS TEMP. AFTER APH DEGC 138 132.5 148.06 142 133.65 147 135.5 144.6 151.8 152.5
23.5
7 % EXCESS AIR % 22.09 25.07 23.53 38.34 43.05 29.15 18.64 16.02 16.86
3
23. DISCUSSION:
The Controllable losses, include Sensible
heat lost in Dry flue gases & Unburnts in
Carbon (in Fly ash, Bottom ash and
Economiser / APH hopper ash) account for
5.08% of Overall Input heat to Boiler or
44.80% of the Total Heat losses. The losses
due to Radiation, Moisture & Hydrogen in
Coal and Moisture in Combustion air account
for the uncontrollable losses.
24. Trial findings indicate the range of total losses to be as under
Total losses in Boiler
Range (%) Average (%)
Unit data 12.54 to 14.1 13.32
Design 11.33
Share of controllable losses in total
Range (%) Average (%)
Unit data 5.27 to 6.86 6.00
Design 5.08
25. SENSIBLE HEAT LOSS IN DRY
FLUE GASES
Heat losses in Dry flue gases, are characteristically influenced
by Excess Air Quantity and Exit Flue Gas Temperature, which
in turn, are variant with, Coal Quality (GCV, Fineness, Ash
content) and Air In leaks. The profile of Sensible heat in Dry
flue gases during trials is summarized as under.
% loss due to sensible heat in dry flue gases
Range (%) Average (%)
Unit data 4.15 to 5.79 4.74
Design 4.67
26. VARIATION OF SENSIBLE HEAT LOSSES IN DRY FLUE GAS
S
. Item Reference Unit Design T1 T2 T3 T4 T5 T6 T7 T8 T9
N
o.
1 G C V of Coal Kcal Kg 4300 4597 4090 4450 3986 4018 3563 3502 3955 3973
% of excess air
2 % 23.5 22.1 25.1 23.5 38.3 43.1 29.1 18.6 16 16.9
level
FGT at APH
3
outlet
°C 138 132.5 148 142 133.6 147 135.5 144.6 151.8 152.5
% loss due to S.H.
4 % 4.67 4.15 5 4.64 4.91 5.79 4.59 4.27 4.51 4.59
in DFG
27. EXCESS AIR
Excess air is crucial factor in Boiler Thermal
efficiency. Excess Air levels depends to a large
extent on variants like, GCV of Coal, Ash Content,
Fineness of Pulverized Coal, Moisture in Coal and
Air In leaks especially before and after APH.
The Excess Air quantity admitted to Boiler
during the trials was seen to vary as under.
Range (%) Average (%)
Unit data 16.00 to 43.10 25.90
Design 23.50
28. EXIT FLUE GAS TEMPERATURE
The flue gas temperature after Air pre heater is
a key Factor affecting Boiler Efficiency
Range (%) Average (%)
Unit data 132.5 to 152.5 143.1
Design 138.0
29. INLEAK AIR
In leak Air, especially in the Air Preheated Flue gas
path, has the detrimental effects of reducing heat
Transfer Effectiveness of APH, shifting the draft
levels in the Flue gas path and increasing ID Fan
duty in terms of Capacity
% In leak Range Across
% In leak Range from
APH to ID Fan in
APH
Unit data 4.73 to 16.94 9.41 to 21.40
Continuous upkeep of APH Seals, Monitoring and Strict control of
Inleak Air is recommended, to minimize the Inleak Air quantities and
losses thereof
30. AIR PROFILE IN FLUE GAS PATH AND AIR INLEAK ASSESSMENT
S.
Item Reference Unit T1 T2 T3 T4 T5 T6 T7 T8 T9
N
o.
1 O2 APH-A in % 2.68 3.50 3.55 5.50 6.18 3.05 2.25 2.96 3.00
2 O2 APH-B in % 2.08 2.18 2.28 4.58 4.95 2.10 2.85 2.83 3.06
3 O2 APH-A out % 4.18 4.85 4.53 6.20 688 5.65 327 3.96 4.10
4 O2 APH-B out % 3.43 3.58 3.48 5.45 5.78 3.93 4.12 3.76 4.03
5 O2 ID Fan-A in % 5.65 6.25 5.83 7.48 7.45 6.25 5.47 5.96 5.83
6 O2 ID Fan-B in % 5.10 4.75 4.98 6.65 6.73 5.20 6.05 5.80 5.66
116. 116.6
7 Total air level at APH-A in (Theoretical +Inleak) % 114.60 120.00 120.34 135.48 141.65 116.99 112.00
41 7
115. 117.0
8 Total air level at APH -B in (Theoretical +Inleak) % 110.96 111.55 112.15 127.85 130.84 111.11 115.70
58 6
123. 124.2
9 Total air level at APH-A in (Theoretical +Inleak) % 124.81 130.03 127.47 141.89 148.67 136.81 118.44 24 6
121. 123.7
10 Total air level at APH-B in (Theoretical +Inleak) % 119.49 120.52 119.83 135.05 137.93 122.99 124.41 81 5
139. 138.4
11 Total air level at ID Fan-A in (Theoretical +Inleak) % 136.81 142.37 138.39 155.27 154.98 142.37 135.22 63 3
138. 136.9
12 Total air level at ID Fan-A in (Theoretical +Inleak) % 132.08 129.23 131.05 146.34 147.11 132.91 140.47
16 0
13 Inleak Across APH-A (wrt APH-A in) % 8.92 8.36 5.92 4.73 4.96 16.94 5.75 5.87 6.51
14 Inleak Across APH-B (wrt APH-B in) % 7.68 8.03 6.85 5.63 5.42 10.69 7.52 5.39 5.72
19.9
15 Inleak After APH-A (wrt APH-A in) % 19.38 18.64 14.99 14.60 9.41 21.69 20.73 18.66
5
19.5
16 Inleak After APH-B (wrt. APH-B in) % 19.03 15.85 16.85 14.46 12.43 19.62 21.40 16.95
4
31.
32. COAL QUALITY
The GCV of Coal, against the design
requirement of 4300 Kcal/Kg was seen
to range from 3502 to 4597Kcal/Kg as
under, during the trial period
Range (%)
Unit data 3502 to 4597
Design 4300
33. Ash % in Coal
Increase of Ash Content leads to Increased un
burnts, Loss due to Sensible heat in ash,
Increased Soot blowing frequency, Increased
mill load for same useful output
% Ash in Coal
Range (%) Average (%)
Unit data 24.21 to 39.96 31.90
Design 32.00
34. M & H LOSSES IN FLUE GASES
S.
N
o Item Reference Unit Design T1 T2 T3 T4 T5 T6 T7 T8 T9
.
144.0 151. 152.
1 FGT APH out O
C 138 132.5 148.06 142 133.65 147 135.5
6 8 5
240.
Heat loss in flue 242.9
2 KCal/Kg 223.6 263.4 256.85 254.1 242.74 244.29 236.0 237. 7
gases due to M&H 8
6
11.2
3 M in Coal % 10 13.6 13.85 12.7 12.65 12.4 13 11.66 10.6
5
4 H in Coal % 2.82 3.18 2.99 3.09 2.91 2.93 2.88 2.91 3.03 3.02
395
5 GCV of Coal KCal/Kg 4300 45.97 4090 4450 3986 4018 3863 3502 3973
5
Loss due to
6 M & H in Coal % 5.2 5.73 6.28 5.71 6.09 6.08 6.29 6.74 6.01 6.06
Corrected loss due to
7
M & H in Coal
% Ref (5.20) 5.48 5.83 5.49 5.62 5.73 5.84 6.13 5.66 5.71
35. COAL FINENESS
Against the design Coal Fineness requirement of 70%
passing through 200 mesh, the decreased fineness is
known to affect the Boiler Efficiency detrimentally
through Increased Excess Air requirements as well as
Higher percent Unburnts in Ash.
Unit data Fineness rejects 48 to 63 %
across 200 mesh
It is our considered opinion that improvements in Mill operations
towards achieving rated Coal Fineness should be a prime area of
concern. The results would be manifest as reduced Excess Air
Losses and Reduced Unburned in Ash Loss.
36. HEAT LOSS DUE TO UNBURNTS
IN ASH
Heat loss due to un burnts in ash is a
manifestation of fuel Combustion efficiency and
is known to depend upon operational factors like
% Ash, Fineness of Coal, Excess Air level, Wind
box Pressure, Primary & Secondary Air
Distribution and Hot Air temperature, condition of
burners, as also Ash fusion temperatures
Percentage Loss Due to Unburnts in Ash
Range (%) Average (%)
Unit data 0.68 to 1.82 1.29
Design 0.41
37. FD AIR FLOW & PA/SA DISTRIBUTION
FD Air constitutes one of the influencing factors on Combustion Efficiency. The FD Air
flow, Air to Coal ratio, Primary Air flow, Primary Air to Secondary Air ratios and Primary
Air to Coal ratio during all the Boiler trials are assessed, vis-a-vis the design values for
the Boiler and the findings indicate satisfactory performance levels in all these respects.
The findings are presented in following tables.
F.D. AIR FLOW INDICATORS
S
. Desi
N Item Reference Unit T1 T2 T3 T4 T5 T6 T7 T8 T9
gn
o
.
725.
1 Total Air Flow TPH 4 773.9 769.3 738.5 726.3 691.4 743.8 598.5 615.4 703
Total Air to Coal
2 Ration Kg/Kg 7 6.56 6.6 6.25 6.78 6.7 6 5.58 5.5 6.24
38. A,B,D, ABC A,B, A.B
A,B,D, A,B.C A,B,C,
E D AB,D D BC,D,E C,
3 Mills Run 5 E 0 D
, , F , ,F D,
,F F F
F F F F
246.3
4 Primary Air Flow TPH 216.2 232.9 233.5 241 198 201 229 222 229.3
5
508. 490.
5 Secondary Air Flow TPH 509.2 541 535.8 497.5 497.5 369.4 393.4 473.7
3 4
6 Primary Air Flow % 29.8 30.1 30.4 32.6 28.1 29.1 33 38 36 32.6
7 Secondary Air Flow % 70.2 69.9 69.6 . 67.4 "71.9 70.9 67 62 64 67.4
Primary Air to Coal
8
Ratio
Kg/Kg 2.09 1.97 2 2.04 1.9 1.95 2 2.13 1.98 2.03
39. WIND BOX PRESSURE
Wind Box pressure is known to be one of the
key factors affecting Combustion Efficiency. Trial
findings indicate the actual Wind Box pressure to
be less than 50 mmWC as against 160 mmWC
design value.
Significant power savings potential exists in FD
Fans by incorporating Variable speed drives, etc
40. SECONDARY AIR
TEMPERATURE
Combustion Efficiency is closely linked with temperature of
Secondary Air and effects of temperature drop (Secondary
Combustion Air) are normally manifest as commensurate
rise in % Unburnts in Ash.
Range (OC) Average (OC)
Unit data 210.9 to 240.0 225.0
Design 263.0
41. The Secondary Air temperature being lower
from design value is expected to effect
Mill performance in terms of Moisture removal and
final Coal Output Fineness
Unburnts in Ash
The main influencing factor for low Secondary Air temperature
is felt to be the lower Flue Gas temperature at APH inlet as
shown below
Range (OC) Average (OC)
Data 241.0 to 290.0 270.0
Design 337.0
42. Focus areas for improvement are felt
to be
Wind Box pressure
APH Effectiveness (Inleak Air at APH
inlet)
Coal Mill performance
