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By
M. A PatilM. A Patil
Senior Director
FICCI
� As per design, the boiler consisted of 2 pass of ESP’s to cater the total boiler flue
gas.
� ESP efficiency deteriorated, high PM concn at stack found by PCB
� PCB directed to reduce PM emissions at stack
To comply with the new environment norms, the plant installed an additional ESP � To comply with the new environment norms, the plant installed an additional ESP
so that it would be able to meet the emission norm.
� Did it solve the problem?
� Was there additional Opex?
� Is root cause addressed?
� Are there new additional problems?
� Can 3rd ESP would have been avoided?
� Any impact on ESP efficiency?
� Impact on Fly ash management?
Description Unit Value
Make
Type
Steam generation (MCR)
Steam pressure TPH
BHEL
PF Firing
430
Boilers’ design parameters
Steam temperature
Efficiency based on HCVkg/cm2(g)oC
%
138.0
540.0
87.36
Measurement of O2% and gas temperature was done at APH I/L, APH O/L
and at ESP I/L and at ESP O/L of all the passes.
In addition, actual gas volumes were directly measured in all the three
passes at ESP O/L by measuring velocity pressures
at several traverse points across the duct cross-section in minimum two port
holes.
Gas velocities were calculated based on the average velocity pressures and
the gas volume was then obtained by multiplying with the cross-sectional
area.
The measured value at various locations is shown in Table
Consolidated table of measurement for Boiler 1
Date of monitoring 31.1.2018 Power Generation (MW) 116.18 Steam Generation (TPH) 342.14
Location of
measureme
nt Time
O2% AT various portholes Pass AvgOverall
Avg O2%Temperature profile
Pass
Avgoverall Avg Temp Gas flow
Static
Pressure
Porthole 1Porthol
e-2
Portho
le-3
Porthole
1
Porthole
2
Porthole
3m3/hr Nm3/hr % SHARE mmWC
% % % % % deg C deg C deg C deg C deg C
APH I/LPass A 12:34 2.3% 2.8% 2.6% 2.6% 2.5% 305.5 314 310 310 311
Pass B 12:52 2.2% 2.8% 2.5% 309.9 313.5 312
APH O/LPass A 13:10 2.6% 6.7% 2.8% 4.0% 4.6% 167 147 166.2 160 161
Pass B 13:21 2.4% 7.5% 5.4% 5.1% 174 149 163 162
ESP I/L
Pass A 15:24 6.8% 7.3% 7.1% 6.1% 146 145.5 146 148
Pass B 15:53 6.8% 7.0% 6.9% 143.7 140 142
Pass C 15:38 4.1% 4.7% 4.4% 157.3 156.5 157
ESP O/L
Pass A 16:25 7.3% 7.2% 7.3% 7.2% 135 141 138 142 516337 342969 44% -190
Pass B 16:45 7.3% 7.5% 7.4% 140.6 139 140 363614 240471 31% -182
Pass C 16:15 6.8% 7.0% 6.9% 149.4 148 149 303129 196239 25% -187
AVG/
TOTAL 1183080 779679
� For simplification of the above table for further analysis, the individual values of
Portholes are taken out form the table for both O2% &temperature and only the
average values are retained which could be compared and used for further
analysis.
� (the values in the three portholes given above increase the confidence level of � (the values in the three portholes given above increase the confidence level of
measurements and hence included in the above table).
� As the gas flow can only be compared based on normalised flow at 25 deg C, the
actual flow in m3/hr has been taken out of the table for subsequent analysis.
And only Nm3/hr is retained.
� The simplified table is as below:
Simplified Consolidated table of measurement for Boiler 1
Location of
measurement Time
Pass AvgOverall Avg
O2%Pass Avg
overall
Avg TempGas flow
Static
Pressure
Nm3/hr % SHARE mmWC
% % deg C deg C
Pass A 12:34 2.6% 2.5% 310 311APH I/L
Pass A 12:34 2.6% 2.5% 310 311
Pass B 12:52 2.5% 312
APH O/LPass A 13:10 4.0% 4.6% 160 161
Pass B 13:21 5.1% 162
ESP I/L
Pass A 15:24 7.1% 6.1% 146 148
Pass B 15:53 6.9% 142
Pass C 15:38 4.4% 157
ESP O/L
Pass A 16:25 7.3% 7.2% 138 142 342969 44% -190
Pass B 16:45 7.4% 140 240471 31% -182
Pass C 16:15 6.9% 149 196239 25% -187
AVG/
TOTAL 779679
� Ideally, all 3 ESPs should get 33.3 % flow each.
� But, ESP – A is overloaded by 11% and
� ESP-C is underloaded by 8%.
� This would increase gas velocity in ESP-A and hence reduced residence time for
dust particles dust particles
� and hence it would reduce the efficiency of ESP.
� The gas volumes are directly measured in all the three passes at ESP O/L only.
� The gas volumes are extrapolated at ESP I/L based on O2%.
� The values are as in below table
Extrapolated gas volumes at ESP I/L in Pass A, B & C
Location of
measurement TimePass Avg
Overall Avg
O2%Pass Avg
overall Avg
TempGas flow Leakage
volumes Leakage %
Nm3/hr % SHARE Nm3/hr
% % deg C deg C
APH I/LPass A 12:34 2.6% 2.5% 310 311
APH I/LPass B 12:52 2.5% 312
APH O/LPass A 13:10 4.0% 4.6% 160 161
Pass B 13:21 5.1% 162
ESP I/L
Pass A 15:24 7.1% 6.1% 146 148 338051 43% 4917 1.5%
Pass B 15:53 6.9% 142 231944 30% 8527 3.7%
Pass C 15:38 4.4% 157 166685 21% 29554 17.7%
AVG/
TOTAL 736681 42999
ESP O/L
Pass A 16:25 7.3% 7.2% 138 142 342969 44%
Pass B 16:45 7.4% 140 240471 31%
Pass C 16:15 6.9% 149 196239 25%
AVG/
TOTAL 779679
� There seems to be substantial ingress of air in
� ESP-C (29554 Nm3/hr, 17.7%)
� as compared to only 1.5% leakage in ESP-A &
� 3.7% in ESP-B.
� In fact, based on these gas volumes at inlet of ESPs, the ESP-C gets only 21% of
total gases, i.e. 12.3% lesser.
� Additionally, it has substantial leakages of atmospheric air.
Heat Balance for ESP
The cross checking for the correctness of the air leakage quantity at the ESP, a heat balance of heat in
and heat out of the ESP is done below tableTable 5: Cross Checking of Air Leakage at ESP by Heat Balance for Boiler 1
.
Heat input to ESP kCal/hr 33714729
Heat Out from ESP kCal/hr 34044420
Heat leaking into ESP kCal/hr 329691
Ambient air temp oC 25
Calculated quantity of ambient air leakage in ESP
through heat balanceTPH 54.9
Measured quantity of air leakage at ESP TPH 55.3
The cross checking of leakage air quantity in ESPs calculated by heat balance fairly matches with the
measured air leakages quantity through direct measurements and hence reasonably accurate estimation
� The gas volumes at ESP I/L are further extrapolated to APH O/L based on O2% as
given in the table below. The total flow in the three passes at ESP I/L is divided
equally for APH-A and APH-B. It is represented in the below Table
Extrapolated gas volumes at APH O/L in Pass A & BLocation of
measurement TimePass Avg
Overall Avg
O2%Pass Avg
overall Avg
TempGas flow
Leakage
volumes Leakage %
Nm3/hr % SHARE Nm3/hr
% % deg C deg C
APH I/LPass A 12:34 2.6% 2.5% 310 311
Pass B 12:52 2.5% 312
APH O/LPass A 13:10 4.0% 160 161 333598 50%
Pass B 13:21 5.1% 162 333598 50%
AVG/
TOTAL4.57%
667197 69484 10.4%
ESP I/L
Pass A 15:24 7.1% 146 148 338051 43% 4917 1.5%
Pass B 15:53 6.9% 142 231944 30% 8527 3.7%
Pass C 15:38 4.4% 157 166685 21% 29554 17.7%
AVG/
TOTAL6.12%
736681 42999
ESP O/L
Pass A 16:25 7.3% 138 142 342969 44%
Pass B 16:45 7.4% 140 240471 31%
Pass C 16:15 6.9% 149 196239 25%
AVG/
TOTAL7.2%
779679
� The above table reveals that the O2% increases substantially between APH O/L to ESP I/L in all the three passes, from overall average of 4.57% to 6.12%.
� This indicates substantial ingress of atmospheric air into the flue gas stream between APH and ESP.
� Some of the areas where such ingress can happen are the water seals at bottom hoppers, the poking holes, the leakages through loose flanges of manholes and other leakages in the ducts between APH and ESP. leakages in the ducts between APH and ESP.
� The quantity of leakage is of the order of 69484 Nm3/hr, which is about 10.4 % of the total flow and is highly un=productive and increases auxiliary power consumption of ID fans & also reduces efficiency of dust collection in ESPs.
� During planned shut-downs these leakages remain unattended.
� Identification of the air leakages in bottom hoppers, the poking holes, the manholes, loose flanges and other leakages in the ducts between APH & ESP and plugging them is generally not done during Annual over hauling of the Boiler.
� The cross checking for the correctness of the air leakage quantity between APH &
ESP, a heat balance of heat in and heat out is done below:
Particular Unit Value
Heat input to APH kCal/hr 33206761
Heat Out from ESP kCal/hr 33714729
Heat leaking into ESP kCal/hr 507968
Ambient air temp oC 25
Ambient air leakage in ESP TPH 85
Measured quantity of air leakage at ESP TPH 89
The cross checking of leakage air quantity between APH & ESPs calculated by heat balance fairly matches with the
measured air leakages quantity through direct measurements and hence reasonably accurate estimation.
� The gas volumes at APH O/L are further extrapolated to APH I/L, based on O2%
Extrapolated gas volumes at APH I/L in Pass A & BLocation of
measurement TimePass Avg
Overall Avg
O2%Pass Avg
overall Avg
TempGas flow
Leakage
volumes Leakage %
Nm3/hr % SHARE Nm3/hr
% % deg C deg C
APH I/LPass A 12:34 2.6% 310 311 307055 26543 8.6%
Pass B 12:52 2.5% 312 286714 46884 16.4%Pass B 12:52 2.5% 312 286714 46884 16.4%
AVG/
TOTAL2.5%
593769 73427 12.4%
APH O/LPass A 13:10 4.0% 160 161 333598 50%
Pass B 13:21 5.1% 162 333598 50%
AVG/
TOTAL4.57%
667197 69484 10.4%
ESP I/L
Pass A 15:24 7.1% 146 148 338051 43% 4917 1.5%
Pass B 15:53 6.9% 142 231944 30% 8527 3.7%
Pass C 15:38 4.4% 157 166685 21% 29554 17.7%
AVG/
TOTAL6.12%
736681 42999
ESP O/L
Pass A 16:25 7.3% 138 142 342969 44%
Pass B 16:45 7.4% 140 240471 31%
Pass C 16:15 6.9% 149 196239 25%
AVG/ 7.2%
� Based on the measured values as mentioned in the above table following conclusions can be drawn:
� The O2% increases from APH I/L to APH O/L in both passes,
� from average 2.5 % to 4.57 %,
� which indicates substantial leakage of air, predominantly from FD and PA fans, � which indicates substantial leakage of air, predominantly from FD and PA fans, into the flue gas circuit.
� The % ingress of air in Pass A and Pass B in the APH is 8.6% and 16.4% respectively.
� (As per OEM of APH, about 6%-8% leakage is within allowable limits, accordingly the leakage in pass B APH is substantially higher to 16.4% and should be reduced)
Share of leakages at APH, between APH & ESP and at ESP in overall gas volume
Location of
measurement Time
Pass AvgOverall
Avg O2%Pass Avg
overall Avg
TempGas flow Leakage
volumes Leakage %
Overall %
share
overall %
leakage
Nm3/hr TPH % SHARE Nm3/hr
% % deg C deg C
APH I/LPass A 12:34 2.6% 2.5% 310 311 335174 396 28974 8.6%
Pass B 12:52 2.5% 312 312970 369 51177 16.4%Pass B 12:52 2.5% 312 312970 369 51177 16.4%
648144 765 80151 12.4% 76% 9.4%
APH O/LPass A 13:10 4.0% 160 161 364148 430 50%
Pass B 13:21 5.1% 162 364148 430 50%
AVG/
TOTAL4.57%
728295 859 75847 10.4% 86% 8.9%
ESP I/L
Pass A 15:24 7.1% 146 148 369009 435 43% 5367 1.5%
Pass B 15:53 6.9% 142 253184 299 30% 9308 3.7%
Pass C 15:38 4.4% 157 181949 215 21% 32261 17.7%
AVG/
TOTAL6.12%
804142 949 46936 94% 5.5%
ESP O/L
Pass A 16:25 7.3% 138 142 374376 442 44%
Pass B 16:45 7.4% 140 262493 310 31%
Pass C 16:15 6.9% 149 214210 253 25%
AVG/
TOTAL7.2%
851078 1004 100% 23.8%
� The above table reveals that,
� about 9.4% of the total volume going to stack is the air leakages at APH,
� other 8.9% is atmospheric air leakages between APH and ESP and
� additional 5.5% are the leakages in ESPs.
� These quantities are substantially higher than allowable limits.
�
� i) Make the gas flow distribution uniform to all 3 ESPs by appropriately adjusting
the dampers such that each ESP gets about 33.3 % gases.
� ii) Identify and Plug the leakages in ESP-C. (Practically it is impossible to make
zero leakages, but about 1.5% leakage, like ESP-A, is very much possible to
achieve).achieve).
� iii) It is strongly recommended that the air leakages in bottom hoppers of APH,
the poking holes, the manholes, loose flanges and other leakages in the ducts
between APH & ESP shall be identified & plugged during all periodic/annual
shutdowns and all efforts be made to reduce or rather eliminate these leakages
of atmospheric air into the flue gases.
Reduction in overall volume by reducing leakages to allowable limits
Location of
measurement Time
Gas flowLeakage
volumes Leakage %
allowable
leakage %
estimated
volumes after
reducing
leakages
Nm3/hr % SHARE Nm3/hr
APH I/LPass A 12:34 307055 26543 8.6% 6% 307055
Pass B 12:52 286714 46884 16.4% 6% 286714
593769 73427 12.4% 593769
APH O/LPass A 13:10 333598 50% 325478
Pass B 13:21 333598 50% 303917
AVG/ TOTAL 667197 69484 10.4% 5% 629396
ESP I/L
Pass A 15:24 338051 43% 4917 1.5%
Pass B 15:53 231944 30% 8527 3.7%
Pass C 15:38 166685 21% 29554 17.7%
AVG/ TOTAL 736681 42999 660865
ESP O/L
Pass A 16:25 342969 44% 1%
Pass B 16:45 240471 31% 1%
Pass C 16:15 196239 25% 1%
After implementation of the above, the overall gas volume handled by ID fans will be reduced by about 13% After implementation of the above, the overall gas volume handled by ID fans will be reduced by about 13%
and the proportionate reduction in power consumption by ID fans is expected to be of the order of 10%.
The entire boiler system showing the gas flow path, O2%, gas volumes and air leakages is provided in Figure 1
After implementation of the above, the overall gas volume handled by ID fans will be reduced by about 13% and the proportionate reduction in power consumption by ID fans is expected to be of the order of 10%. The entire boiler system showing the gas flo
� Presently the leakage of air is happening at 3 locations, the APH, between APH &
ESP and at ESP. The present leakages are very much in higher side compare to
best practices and OEM suggested values of leakages.
� If the existing be reduced to allowable limit of leakages, in overall the gas volume
handled by ID fan would come down by about 12.7 %. handled by ID fan would come down by about 12.7 %.
� The comparison of existing and proposed leakage volumes is given below.Table 12: Existing & New leakage volume
Leakage at
Existing
leakage
quantity
Proposed
Leakage QuantityReduction in leakage by
Nm3/hr Nm3/hr Nm3/hr TPH
APH A & B 80151 38889 41263 48.69
Between APH & ESP 75847 34352 41495 48.96
Leakage at ESP 46936 21642 25295 29.85
Total leakages 202935 94882 108053 127.5
� After reducing the leakages as above, the power consumption of ID fan as well as
FD & PA fans would reduce proportionate to the reduction in the volumes. The
calculation towards the saving are given in the table belowParticular Unit ID Fan FD & PA
ID Fan power consumption kW 835 1639
Present Flow handled by Fan TPH 1004 859Present Flow handled by Fan TPH 1004 859
Expected reduction in flow to be handled by fan TPH 128 49
Savings in Fan power consumption % 13% 6%
ID fan operating duration hr/year 7920 7920
Electrical Unit Cost Rs./kWh 3.5 3.5
Correction factor % 90% 80%
Savings kW 95 74
kWh/year 755541 588287
Rs. Lakhs/year 26 21
Net Savings kWh/year 1343828
Rs. Lakhs/year 47
Investment Rs. Lakhs 40
� Apart from saving in fan power as discussed above, reduced leakages in APH would improve the hot air temperature supplied to boiler.
� AS per design, the hot air temperature should be about 280 oC (at NCR), whereas the actual temperature about 262 oC, which may improve by estimated 5 to 10 oC.
� This would proportionately improve the boiler efficiency also. Increased quantity of hot air availability to the boiler,
� would also help increase the steam generation proportionately.
� Implementation of the recommendation would lead to annual saving of Rs. 47 Lakhs. The estimated investment towards reducing the leakages in terms of revamping of leaking seals, man hols, ducts, flanges etc. is assumed to be Rs. 40 Lakhs. The simple payback period would be around 1 year.
� Also, the reduced leakages would mean reduced volume
� & reduced Gas velocity in ESP,
� which will improve the performance of ESP
� Coarse Dust would get collected in Field -1
� Reduced carry over of coarse dust to Field 2
� Improved Fly ash quality in Field 2, 3 ESP Hopper
� .