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

� .