Proj Yashvardan Cesc
Transcript of Proj Yashvardan Cesc
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Unmesh-12,Summer Internship programmme
Increasing BBGS Unit # 3 efficiency by reduction of
boiler feed pump power consumption & un-burnt
carbon in ash
Project byYashvardhan Joshi
Project guideMr. Souvik dutta,DGM,Budge Budge
Generating Station.CESC Ltd
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Acknowledgement
At the onset I must thank all the people at BBGS without whose active support
this project would not have materialized. In view of this I would like to extend my
sincere thanks and gratitude to everyone who has supported me during the
UNMESH 12 internship programme.
I am highly indebted to Mr. Souvik Dutta for his guidance and constant
supervision as well as for providing necessary information regarding the project &
also for his support in completing the project. I would also thank Mr. Kaushik
Chaudhuri, Mr. Suman Sengupta, Mr. Debashish Chatterjee, Mr. SharnathBanarjee, Mr. Sk. Sabir Ali, Mr. Tapas Ghosh and Mr. Subhendu Ghosh for their
constant support and guidance.
I would also like to express my special gratitude and thanks to industry people
and CESC HRD for giving me such attention and time.
My thanks and appreciation also goes to my parents, family and professors
from IIT Kharagpur who have willingly helped me out to achieve my objective.
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Certification
This is to certify that Yashvardhan Joshi has worked
under my guidance on Increasing BBGS Unit # 3
efficiency by reduction of boiler feed pump power
consumption & un-burnt carbon in ash under the
UNMESH 12 internship program from 14th
May 2012 to
7th
July 2012. He has successfully completed the project.
Date:
Signature
Mr. Souvik Dutta
Deputy General Manager
Budge Budge Generating
Station , CESC
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Objective
1).Improvement of BBGS Unit3 boiler efficiency by
reducing un-burnt in ash.
2). Reduction of BBGS Unit3 auxiliary consumption
power by reducing boiler feed pump power
consumption
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Content
1. Introduction
2. Improvement of BBGS Unit3 boiler efficiency by reducing un-burnt in ash.
Boiler efficiency calculation
Un-burnt in plant calculation and trends
PF fineness calculation and role of mills
Variation in un-burnt with PA flow and net savings
3. Reduction of BBGS Unit3 auxiliary consumption
power by reducing boiler feed pump power
consumption
Importance of drum level control and methods
Types of BFP controls and their advantages
Energy consumption in various operational modes of BFP
Net energy savings using 3-Element control mode.
4. Conclusion
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Introduction
Energy projects are among the most capital intensive infrastructure investments. Decisions
made today will form our lives for decades, and it is important that these decisions are based on facts
and a proper economic assessment of available options. The global power sector is facing a
number of issues, but the most fundamental challenge is meeting the rapidly growing demand
for energy services in a sustainable way, at an affordable cost and in the environmentally
acceptable manner. This challenge is further compounded by the fact that the major part of the
increase in demand for power and hence in the emissions in the future, will come from
developing countries, who strive to achieve a rapid economic development.
A power plant produces electrical energy and also consumes substantial amount of this
energy in the form of auxiliary consumption. Auxiliary power comprises the power consumption
by all the unit auxiliaries as well as the common station requirement such as station lighting, air
conditioning etc. Plant auxiliariesinclude all motor-driven loads, all electrical power
conversion and distribution equipment, and all instruments and controls. Therefore Auxiliarypower in a power plant can define in three categories of auxiliary systems.
1. Drive power components such as pumps, fans, motors and their power electronics
such as variable frequency drives. These provide drive power for fuel handling, furnace draft,
and feed-water pumping. These systems and components will be referred to as Drivepower.
2. Electrical power systemsconversion, protection, and distribution equipment,
excluding motors and variable-frequency drives. This includes power transformers and LV and
MV equipment. These systems and components will be referred to as ElectricPower Systems.
3. The instruments, control, and optimization systems. These provide boiler-turbine and
other control functions. These systems and components will be referred to as Automation
This auxiliary equipment has a critical role in the safe operation of the plant and
equipments used for auxiliary power are varying for different types of power plant. Reduction
of auxiliary power consumption could thus help increase the efficiency of a power plant.
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Figure 1: Various losses in a thermal power plant
The boiler losses represent around
35% of the total losses. Of these losses
combustion losses represent around 3% of the
total losses. For coal to burn effectively thereare three factors necessary, namely:
Temperature
Time
Turbulence
The time required for carbon to burn depends
on the average size of the coal particles, which
in turn depends on the type of boiler. In apulverized fuel boiler the average size of coal
particles is about 75 micron.
Figure 2: Losses in a boiler
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While various losses are controlled by theoretical and metallurgical restriction the
combustion losses are due to un-burnt carbon. Un-burnt carbon is carried with either the
bottom ash or the fly ash. Insufficient time or insufficient oxygen can also lead to carbon
monoxide formation which is also a part of combustion losses. While various other losses are
difficult to reduce the combustion losses can be reduced significantly by optimizing the
operation conditions. The PF fineness of coal plays a significant part in un-burnt carbon
percentage control. The PF fineness is measured according to standards set by ASTM and is a
primary measure of the fineness of the fuel and consequently the time required for
combustion.
Un-burnt in ash can also be reduced by reducing the PA flow. The PA flow is used to
carry pulverized fuel to the boiler, when the PA flow is reduced the velocity of coal going into
the furnace is reduced, consequently giving the coal particles more time to burn.
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Improvement of BBGS Unit3 boiler efficiency by
reducing un-burnt in ash.
Boiler efficiency calculation :
Table-1: Coal analysis of composite coal sample from all the running coal feeders except
Feeder D
Description Unit Value
Coal analysis
Carbon % 40.16
Hydrogen % 2.59
Nitrogen % 1.02
Oxygen % 5.39
Sulphur % 0.44
Moisture % 1.85
Ash % 48.55
TOTAL % 100
GCV kCal/kg 4020
During boiler efficiency test flue gas is measured with flue gas analyzer at APH outlet and it is
given below.
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Design parameter of Air Pre-heater
The Air heater leakage percentage at the SAH is computed by following equation.
% AHL = O2 outlet- O2 inlet X 0.9 X 100%
21-O2 outlet
Where
%AHL - Air heater leakage, percentage gas flow entering air heater
O2outlet - Oxygen at air heater outlet on a dry basis, measured, %
O2inlet - Oxygen at air heater inlet on a dry basis, measured, %
21 - Constant, percentage oxygen in ambient air
The Air heater leakage percentage at the SAH Pass A is
= 2%
The Air heater leakage percentage at the SAH Pass B is
= 3%
Secondary Air Pre-heater performance
Description A pass Flue gas Temperature, 0C Oxygen, % Leakage,%
SAH Inlet 305 2.6 2.0
SAH Outlet 146 3.0
Description B pass Flue gas Temperature,0
C Oxygen, % Leakage,%SAH Inlet 322 2.4 3.0
SAH Outlet 152 3.0
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Observation:
here is an increase in oxygen percentage, indicating air leakage
Effectiveness of Air Pre Heater
Towards assessing the performance of air heater, the air and gas temperatures have been
measured. The effectiveness of the heater is given below:
The corrected flue gas outlet temperature from the APH is computed by the following equation.
Corrected gas outlet temperature (TGONI)
AL X CpaX (TGOTAI)TGONI = ---------------------------------- + TGO
100 X Cpg
Where,
AL = Air leakage into APH system (%)
Cpg = Specific heat of Gas (kCal/kg/0C)
Cpa = Specific heat of air at inlet of APH (kCal/kg/0C)
TAI = Temperature of air at inlet of APH (0C)
TGO = Temperature of Gas at outlet of APH (0C)
The Corrected gas outlet temperature (TGONI) at outlet of SAH A
2.0 X 0.24 X (14637)
TGONI = ---------------------------------- + 146
100 X 0.23
= 148.270C
The Corrected gas outlet temperature (TGONI) at outlet of SAH B
3.0 X 0.24 X (15236)
TGONI = ---------------------------------- + 152
100 X 0.23
= 155.630C
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Corrected gas outlet temperature of SAH
Description Unit APH A APH B
O2 at APH inlet % 2.6 2.4
O2 at APH outlet % 3.0 3.0
Air leakage % 2.0 3.0
Cp of air kCal/Kg/0C 0.24 0.24
Gas leaving temp.0C 146 152
Air entering temp0C 37 36
Cp of flue gas kCal/Kg/0C 0.23 0.23
Corrected temperature of flue gas0C 148.27 155.63
The effectiveness (Gas Side Efficiency) of the air pre-heater is calculated by the following
equation
Flue Gas Analysis at APH outlet
Description Unit Boiler-3
Flue gas Temperature0C 149
Corrected Temperature0C
151.95
Ambient Temperature 0C 35
DBT0C 35
WBT0C 29
Oxygen % 3
CO2 % 16
CO ppm 28
During boiler efficiency test fly ash and bottom ash sample is collected and the ash analysis
report is given below.
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Table-3: Fly Ash and Bottom Ash Analysis
Description Unit Boiler-3
Fly Ash Analysis
Un-burnt % 2.745
Carbon in fly ash kg/kg of fuel 0.01133
Bottom Ash Analysis
Un-burnt % 7.515
Carbon in bottom kg/kg of fuel 0.0055
The procedure of calculation of un-burnt in both fly ash and bottom ash is described later in this
document.
Observation:
Un-burnt in bottom ash is found in higher side.
Boiler efficiency:
Boiler efficiency is calculated by indirect method based on flue gas, coal and ash analysis reportas given below,
The boiler efficiency is calculated by the indirect method and is as follows.
Theoretical Air requirement = [(11.6 C) + {34.8 (H2O2/8)} + (4.35S)]/100
(Kg / kg of fuel)
Where,
C = Weight of Carbon in fuel (%)
H2 = Weight of Hydrogen in fuel (%)
O2 = Weight of Oxygen in fuel (%)
S = Weight of Sulphur in fuel (%)
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Theoretical Air requirement = [(11.6 40.16) + {34.8 (2.595.39 / 8)} + (4.35
0.44)] / 100 (kg / kg of fuel)
= 5.34 kg/kg of fuel
O2%
Excess air (%) = ------------------- x 100(21 - O2%)
3
Excess air (%) = --------------- x 100
(213)
= 16.67 %
Actual mass of air supplied per kg of Fuel (AAS)
AAS = (1+ (Oxygen content measured at the exit of boiler / (21 - Oxygen content measured at
the exit of boiler) X Theoretical air required
AAS = (1+ (3 / (21- 3)) X 5.34
= 6.23 kg / kg of coal
Mass of the dry flue gas = (1+ Actual mass of air supplied per Kg of fuel)
Mass of the dry flue gas = (1+ 5.29 kg / kg of coal)
= 7.23 kg / kg of coal
Heat Loss in Dry Flue Gases (%) = m X CpfX (Tf-Ta) X 100
GCV of Fuel
Where,M = Mass of dry flue gases (kg)
Cpf = Specific Heat of Dry flue gases (kCal/kgOC)
Ta = Temperature of ambient air (OC)
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Heat Loss in Dry Flue Gases (%) = 7.23 X 0.23 X (151.95-35) X 100
4020
= 4.84%
Percentage heat loss due to evaporation of water formed due to H2in fuel
= 9 X H2 X {584 + Cp X (Tf- Ta)} X 100
GCV of Fuel
Where,
Cp = Specific Heat of water, (kCal/kg0C)
Percentage heat loss due to evaporation of water formed due to H2in fuel
= 9 X (2.59/100) X {584 + 0.45 X (151.9535)} X 100
4020
= 3.69%
Percentage heat loss due to moisture content in fuel
= MfX (584 + (Tf- Ta) X Cp) X 100
GCV of Fuel
Where, Mf = Mass of moisture content in fuel
Percentage heat loss due to moisture content in fuel
= (1.85/100) X (584 + (151.9535) X 0.45) X 100
4020
= 0.29%
Percentage of heat loss by moisture in air= {AAS X Humidity Factor X Cp X (Tf- Ta)} X 100
GCV of Fuel
Where, AAS = Actual air supplied (kg/kg of dry air)
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Percentage of heat loss by moisture in air
= {7.23 X 0.0229X 0.45 X (151.9535)} X 100
4020
= 0.22%
Loss due to CO present in flue gas= CO X C X 5744 x100
(CO + CO2) X GCV of Fuel
Where,
C = Weight of carbon in fuel (%)
CO = % in the flue gas
CO2 = % in the flue gas
Percentage of heat loss by incomplete combustion
= (28/1000000) X (40.16/100) X 5744 x100((28/1000000) + (16/100)) X 4020
= 0.0015 %
Percentage heat losses due to radiation and convection losses & unaccounted (Q) (assumed)
= 1.5 %
Percentage of heat loss by un-burnt in Fly AshCarbon in fly ash= (Un-burnt in fly ash/100) X (85/100) X (ash % in coal/100)
= (2.745/100) X (85/100) X (48.55/100)
= 0.0113 kg/kg of fuel
Percentage of heat loss by un-burnt in fly ash
= Carbon in fly ash, kg / kg of Fuel burnt X GCV of carbon X 100
GCV of Fuel
Percentage of heat loss by un-burnt in Fly Ash= 0.0113 X (33820/4.184) X 100
4020
= 2.28 %
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Percentage of Heat Loss by un-burnt in Bottom Ash
Carbon in bottom ash= (un-burnt in bottom ash/100) X (20/100) X (ash % in coal/100)
= (7.515/100) X (15/100) X (48.55/100)= 0.0055 kg/kg of fuel
Percentage of Heat Loss by un-burnt in Bottom Ash
= Carbon in bottom ash, kg / kg of Fuel X GCV of carbon X 100
GCV of fuel
= 0.0055 X (33820/4.184) X 1004020
= 1.11%
Sensible Heat Loss from Fly Ash
= Total mass of fly Ash X 0.2 X (Tf- Ta) X100
GCV of Fuel
= (48.55 X 0.85/100) X 0.2 X (151.95-35) X100 / 4020
= 0.24%
Sensible Heat Loss from Bottom Ash
= Total mass of bottom Ash X 0.2 X (Tb- Ta) X100
GCV of Fuel
= (48.55 X 0.15/100) X 0.2 X (800-35) X100/ 4020
= 0.28%
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Total losses= 4.84+3.69+0.29+0.22+0.0015+1.5+2.28+1.11+0.24+0.28
= 14.45 %
Boiler Efficiency (%)= 100Total Losses
= 10014.45= 85.55%
As per manual design boiler efficiency at design coal is 87.69%
A deviation in the boiler efficiency from the design efficiency points to the
fact of an existing scope for improvement in the present operation conditions.
We observe that the un-burnt carbon in bottom and fly ash contribute to about
25% of the total losses in a boiler.
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Un-burnt in plant calculation and trends
Un-burnt in ash:Fly ash is a byproduct of coal combustion and it contains many differentmineral matters such as carbon, iron oxide and Sulphur. Unburned carbon in fly ash is a major
index to determine the efficiency of coal combustion in a power plant. Fly ash with a high
volume of unburned carbon not only indicates poor combustion efficiency, which results in a
high emission of pollutants and higher fuel requirement, it also prevent power plants from
selling the coal fly ash to secondary markets for recycling. In order to ensure the combustion
efficiency and maintain low unburned carbon content in fly ash, the power industry is
constantly investigating the most effective way to monitor the unburned carbon in fly ash.
Un-burnt carbon in Bottom ash
The PG design of the unit states the un-burnt in bottom ash as 4.3%.
However the un-burnt carbon in bottom ash has a higher average compared to the PG test
recommendations. The following is the procedure for the for calculating the un-burnt carbon in
bottom ash
Un-burnt carbon in Bottom ash calculation procedure1. Take 10-15 grams of bottom ash sample in a watch
glass.
2. Place the sample in a hot air oven at 108 2 C for a
sufficient period of time so that the weight becomes
constant (2 hours).
3. Take 1 gram of this ash sample in an ash crucible.
4. Burn this in a furnace at 810 10 C for 1 hour.
5. Cool the sample for 10 minutes in a desiccators.
6. The final weight of the ash sample is taken.
7. The loss in weight is the amount of combustibleresent in ash.
Figure 3: Weight balance
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The following is the trend for the un-burnt in bottom ash for Unit-3 for the FY 2011-12:
Un-burnt carbon in Fly ash
The PG design of the unit states the un-burnt in bottom ash as 1.5%. However the yearlyaverage is relatively higher than the PG test recommendations. The following is the procedure
for calculating the un-burnt carbon in bottom ash.
Figure 4: Bottom ash un-burnt carbon trend
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Figure 5: Hot air oven
Figure 6: Muffle Furnace
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Un-burnt carbon in Fly ash calculation procedure
1. Take 10-15 grams of fly ash sample in a watch glass.
2. Place the sample in a hot air oven at 108 2 C for a sufficient period of time so that the
weight becomes constant (3045 min ).3. Take 1 gram of this ash sample in an ash crucible.
4. Burn this in a furnace at 810 10 C for 1 hour.
5. Cool the sample for 10 minutes in a desiccators.
6. The final weight of the ash sample is taken.
7. The loss in weight is the amount of combustible present in ash.
The following is the trend for the un-burnt in bottom ash for Unit-3 for the FY 2011-12:
Figure 7: Fly ash un-burnt carbon trend
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The higher values of the un-burnt in both fly ash and bottom ash could be due to various
reasons. One such reason could be related with PF fineness of coal. The PF fineness of the coal
might be low resulting in larger average surface area, leading to more un-burnt coal in ash. We
observe the PF fineness characteristics of various mills in Unit-3.
PF fineness is done using iso-kinetic sampling of coal from various mills.The PF grading test is as follows
PF fineness calculation and role of mills
PF grading procedure
1. Air drying of sample is recommended if high moisture (>10%) coal is being fired or sieving is
not performed immediately after sample extraction. This is to prevent the coagulation of
sample on top of sieve screens which prevents particles to pass through screens and results in
non-representative coal fineness. Coagulation of coal sample usually appears as small "balls" of
coal on 100 Mesh screens. ASTM D-197 specifies drying at 1827F above room temperature
until weight loss is less than 0.1% difference.
This step can usually been eliminated if the following criteria have been established: Pulverizer Discharge temperature above 160F
Fuel moisture is moderate
Collected samples are placed in air-tight Ziploc bags
Sieving is performed immediately after extraction
No coagulation of coal is observed during sieving
2. Remove 50 grams of coal from the sample. This is done by using an ASTM riffler or by
rolling the sample (usually between 200 g and 800 g). We advocate the riffler method which
is cleaner and more efficient. A 50 gram sample can not be simply scooped or spooned from
the whole sample; this may result in a disproportionate quantity of fine or coarse particles. If
sample is not exactly 50 g, be sure to weigh and record initial sample weight. The figure belowillustrates a coal riffle as specified by ASTM D 197-87.Plot the percentages passing each sieve
to the Rosin and Rammler equation. The percent passing 50, 100 and 200 Mesh should fall on a
straight line. If the plotted line is not linear, the sample is non-representative and must be
extracted. The Figure below illustrates representative coal fineness plotted against the Rosin
and Rammler equation. Non-representative sampling is the result of one of following:
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Sampling rate not isokinetic
Testing error or error in calculating sampling rate
Sample Splitting or Coal sieving error
Excessive sample Moisture
Weight of Test Sample 50 g 50.00
Weight of Residue on 50 Mesh R1g _____________
Weight of Residue on 100 Mesh R2g _____________
Weight of residue on 140 mesh R3g _____________
Weight of Residue on 200 Mesh R4g _____________
Weight of Sample in Pan (Passing 200 Mesh) R5g _____________
% Passing 50 Mesh (50.00 - R1 ) 100
3. Shake the sample through a series of
50, 100, 140 and 200 Mesh U.S. Standard
sieves. Figure 8illustrates the order of thesieves.
4. Record the weight of coal residue on
each screen and coal in the bottom pan
(passing 200 Mesh). Great care should be
taken in weighing coal sample residue on
each screen. Residue on 50 Mesh will be
very small and must be weighed
accurately to yield representative data. A
scale capable of accuracy to 1/1000
(0.001) must be utilized.
Coal Sieving Procedure
5. Calculate the percentage of total
sample passing 50, 100, 140 and 200
Mesh.Figure 8: ASTM riffler
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50.00
% Passing 100 Mesh (50.00 - (R1 + R2 )) 100
50.00
% Passing 140 Mesh (50.00 - (R1 + R2+ R3 )) 100
50.00
% Passing 200 Mesh (50.00 - (R1 + R2 + R3+ R4 )) 100
50.00
% Recovery (R1 + R2 + R3 + R4+ R5 ) 100
50.00
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Coal Sieving Procedure
6. Plot percentages passing each sieve to the Rosin and Rammler equation. The percent passing50, 100 and 200 Mesh should fall on a straight line. If the plotted line is not linear, the sample is
non-representative and must be extracted. The Figure below illustrates representative coal
fineness plotted against the Rosin and Rammler equation. Non-representative sampling is the
result of one of following:
Sampling rate not isokinetic
Testing error or error in calculating sampling rate
Sample Splitting or Coal sieving error
Figure 9: Sieve shaker setup
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Excessive sample Moisture
Figure 9
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Using this procedure the PF grading of Mill 3D was calculated and the following were the
observations
PF grading for Unit -3 (mill 3-D) on 31.05.2012
The weight of the -200 sample
Time Weight
15 minutes 30.38 grams
+2 minutes 4.12 grams
+2 minutes 3.12 grams
+2 minutes 0.92 grams
+2 minutes 0.57 grams
Total weight 39.11 grams
Category Weight present Percentage
+52 0.05 .1
+100 , -52 2.12 4.24
+200 , - 100 8.72 17.44
-200 39.11 78.22
The following is the trend of the PF fineness from various mills of BBGS unit #3
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PF fineness grading
Report for Mill-3A
Sl No Date 52 -52/100 -100/200 -200
1 11-Mar-10 0.16 4.9 15.78 79.16
2 6-Apr-10 0.6 7.88 20.58 70.94
3 23-Apr-10 0.28 4.64 12.18 82.9
4 25-Apr-10 0.24 4.28 17.32 78.165 6-May-10 0.14 3.02 12.96 83.88
6 11-May-10 0.2 5.52 18.62 75.66
7 19-May-10 0.22 6 18.82 74.96
8 23-May-10 0.14 3.54 16.42 79.9
9 5-Jun-10 0.56 9.24 23.08 67.12
10 29-Jun-10 0.36 5.68 17.3 76.66
11 3-Jul-10 0.6 7.62 19.68 72.1
12 4-Aug-10 0.32 6.56 21.24 71.88
13 3-Sep-10 0.28 3.24 11.38 85.1
14 14-Sep-10 0.52 7.06 18.84 73.58
15 14-Oct-10 0.72 10.18 26.52 62.58
16 6-Nov-10 0.38 6.24 19.44 73.94
17 5-Dec-10 0.76 8.2 21.04 70
18 19-Jul-11 0.84 10.5 22.12 66.54
19 11-Aug-11 0.5 10.26 20.12 69.12
20 31-May-12 0.48 12.16 27.82 59.54
Average 0.415 6.836 19.063 73.686
Figure 10: PF fineness Mill 3-A
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Report for Mill-3B
Sl No Date 52 -52/100 -100/200 -200
1 11-Mar-10 0.08 3.46 12.78 83.68
2 25-Mar-10 0.3 4.54 17.1 78.06
3 30-Mar-10 0.16 4.78 18.28 76.78
4 6-Apr-10 0.82 7.22 17.84 74.125 23-Apr-10 1.38 14.1 28.44 56.08
6 25-Apr-10 1.08 10.16 20.04 68.72
7 6-May-10 0.66 11.84 25.46 62.04
8 16-May-10 0.18 6.5 22.54 70.78
9 23-May-10 1.14 11.36 21.8 65.7
10 9-Jun-10 0.64 8.14 21.26 69.96
11 29-Jun-10 2.16 9.9 16.78 71.16
12 8-Jul-10 0.58 12.8 30.12 56.5
13 26-Jul-10 1.12 8.94 19.78 70.16
14 8-Aug-10 0.66 8.62 25.26 65.46
15 9-Sep-10 0.64 7.72 16.62 75.02
16 3-Oct-10 0.68 9.3 22.38 67.64
17 6-Nov-10 0.1 3.84 25.62 70.44
18 15-Dec-10 1.3 11.42 24.36 62.92
19 1-Jan-11 0.32 8.14 22.16 69.38
20 15-Mar-11 0.78 8.42 24.06 66.74
21 3-Apr-11 0.84 9.56 23.14 66.46
22 20-Apr-11 1.08 9.2 13.28 76.44
23 6-May-11 1.6 18.46 13.4 66.54
24 22-May-11 1.02 11.62 22.32 65.04
25 8-Jun-11 0.7 9.1 20.74 69.46
26 24-Jun-11 1.32 12.52 22.62 63.54
27 10-Jul-11 1.12 11.12 23.74 64.0228 28-Jul-11 0.96 11.2 23.62 64.22
29 14-Aug-11 0.62 7.78 25.3 66.3
30 29-Aug-11 0.56 7.46 24.5 67.48
31 13-Sep-11 1.58 12.42 23.46 62.54
32 18-Sep-11 1.5 10.66 24.18 63.66
33 28-Sep-11 0.86 7.92 15.22 76
34 29-Sep-11 0.86 7.92 15.22 76
35 15-Oct-11 1.22 12.92 24.24 61.62
36 30-Oct-11 1.04 10.4 22.54 66.02
37 12-Nov-11 0.78 9.3 20.34 69.58
38 24-Nov-11 0.88 10.26 22.94 65.92
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39 9-Dec-11 0.92 9.8 21.78 67.5
40 24-Dec-11 0.06 4.64 19.94 75.36
41 9-Jan-12 0.16 6.12 22.56 71.16
42 19-Jan-12 0.2 7.72 26.04 66.04
43 20-Feb-12 0.16 6.8 29.92 63.12
44 22-Apr-12 0.18 5.6 21.06 73.16
45 28-May-12 0.14 6.68 23.56 69.62
46 31-May-12 0.1 5.02 20.42 74.46
Average 0.766 8.987 21.712 68.535
Figure 11: PF fineness Mill 3-B
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Report for Mill-3C
Sl No Date 52 -52/100 -100/200 -200
1 2-Mar-10 0.68 6.64 16.28 76.4
2 26-Mar-10 1.12 8.46 18.66 71.763 24-Apr-10 1.98 12.5 21.08 64.44
4 30-Apr-10 1.9 11.98 20.46 65.66
5 14-May-10 2.02 8.66 18.84 70.48
6 21-May-10 0.88 8.72 19.94 70.46
7 23-May-10 2.12 15.42 24.8 57.66
8 12-Jun-10 2 11.62 21.44 64.94
9 29-Jun-10 0.4 6.4 17.28 75.92
10 6-Jul-10 1.78 11.22 17.36 69.64
11 11-Jul-10 2.46 12.02 24.62 60.9
12 10-Aug-10 2.22 11.64 23.22 62.92
13 14-Sep-10 1.28 12.9 20.66 65.16
14 18-Sep-10 1.88 12.2 24.88 61.04
15 3-Oct-10 3 15 21.12 60.88
16 20-Nov-10 0.78 7.88 16.98 74.36
17 18-Dec-10 1.02 8.14 18.84 72
18 6-Jan-11 3.76 18.02 24.3 53.92
19 2-Feb-11 2.06 13.7 20.76 63.48
20 15-Feb-11 1.22 10.58 18.08 70.12
21 14-Mar-11 1.76 11.5 19.52 67.22
22 3-Apr-11 0.22 8.3 26.16 65.32
23 21-Apr-11 1.8 11.06 19.36 67.78
24 7-May-11 0.82 14.06 24.66 60.46
25 11-Jun-11 2.32 15.5 24.04 58.1426 26-Jun-11 2.74 15.32 22.2 59.74
27 12-Jul-11 2.04 16.22 19.5 62.24
28 30-Jul-11 1.66 15.04 20.38 62.92
29 15-Aug-11 3.1 15.66 21.44 59.8
30 30-Aug-11 2.74 13.56 19.8 63.9
31 9-Sep-11 1 9.76 20.36 68.88
32 17-Sep-11 4.14 15.18 21.66 59.02
33 17-Sep-11 4.5 16.5 24.5 54.5
34 28-Sep-11 3.32 17.54 25.48 53.66
35 3-Oct-11 3.3 15.64 22.5 58.56
36 19-Oct-11 3.4 17.94 22.66 56
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37 5-Nov-11 1.98 17.52 27.5 53
38 20-Nov-11 1.28 11.04 22.7 64.98
39 6-Dec-11 2.74 18.06 26.32 52.88
40 20-Dec-11 0.1 5 25.94 68.9641 4-Jan-12 0.18 6.68 27.3 65.84
42 15-Jan-12 0.1 6.12 25.96 67.82
43 4-Feb-12 0.22 8.54 33.22 58.02
44 22-Feb-12 0.32 8.48 34.2 57
45 12-Apr-12 0.2 3.98 24.82 71
Average 1.79 11.953 22.484 63.773
Figure 12: PF fineness Mill 3-C
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Report for Mill-3D
Sl No Date 52 -52/100 -100/200 -2001 11-Mar-10 4 11.84 15.94 68.22
2 15-Mar-10 3.46 14.96 22.74 58.84
3 26-Mar-10 1.56 10.92 21.38 66.14
4 27-Mar-10 1.5 9.76 20.9 67.84
5 9-Apr-10 2.4 14.3 23.4 59.9
6 19-Apr-10 4.04 15.74 19.42 60.8
7 29-Apr-10 5.24 18.72 25.68 50.36
8 22-May-10 5.6 18.94 21.66 53.8
9 23-May-10 6.46 19.36 24.24 49.94
10 2-Jun-10 3.94 11.04 17.98 67.04
11 15-Jun-10 5.34 19.3 23.42 51.9412 29-Jun-10 0.2 3.3 16.04 80.46
13 8-Jul-10 0.56 9.9 25.76 63.78
14 18-Aug-10 0.12 5.08 20.44 74.36
15 14-Sep-10 0.14 5.56 20.86 73.44
16 15-Sep-10 0.08 3.3 21.48 75.14
17 11-Oct-10 0.14 3.94 17.04 78.88
18 9-Nov-10 0.06 3.12 18.34 78.48
19 25-Dec-10 0.1 2.98 22.04 74.88
20 11-Jan-11 0.18 5.96 19.4 74.46
21 13-Jan-11 0.16 7.04 27.72 65.08
22 4-Feb-11 0.26 7.42 21.88 70.44
23 17-Mar-11 0.22 5.08 22.8 71.924 6-Apr-11 0.24 10.36 18.4 71
25 24-Apr-11 0.16 12.16 18.16 69.52
26 10-May-11 0.32 6.14 22.74 70.8
27 25-May-11 0.18 5.86 20.28 73.68
28 10-Jun-11 0.2 5.44 19.54 74.82
29 25-Jun-11 0.32 6.54 22.52 70.62
30 11-Jul-11 0.56 7.04 20.84 71.56
31 29-Jul-11 0.16 6.58 24.7 68.56
32 16-Aug-11 0.1 4.78 21.86 73.26
33 31-Aug-11 0.64 6.24 22.28 70.84
34 9-Sep-11 0.22 5.86 23.86 70.06
35 16-Sep-11 0.16 6.52 23.94 69.38
36 18-Sep-11 0.4 12.84 31.88 54.88
37 28-Sep-11 0.6 9.16 27.52 62.72
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38 29-Sep-11 0.6 9.16 27.52 62.72
39 2-Oct-11 0.34 8 24.36 67.3
40 17-Oct-11 0.1 4.82 23.86 71.22
41 3-Nov-11 0.02 4.16 22.76 73.06
42 17-Nov-11 0.12 7.36 28.6 63.92
43 4-Dec-11 0.16 3.9 21.74 74.2
44 16-Dec-11 0.16 4.62 22.5 72.72
45 1-Jan-12 0.1 6.1 24.34 69.46
46 14-Jan-12 0.22 9.92 29.22 60.64
47 3-Feb-12 0.12 7.84 28.46 63.58
48 17-Feb-12 0.22 5.68 23.22 70.88
49 17-Mar-12 0.16 7.44 26.96 65.44
50 2-Apr-12 0.2 8.32 28.88 62.6
51 18-Apr-12 0.14 7.26 26.5 66.152 2-May-12 0.16 5.96 22.4 71.48
53 31-May-12 0.1 4.24 17.44 78.22
54 5-Jun-12 0.1 2.5 13.3 84.1
Average 0.982 8.155 22.614 68.249
Figure 13: PF fineness Mill 3-D
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Report for Mill-3E
Sl No Date 52 -52/100 -100/200 -200
1 11-Mar-10 0.48 6.6 16.9 76.02
2 7-Apr-10 1.8 11.8 23.44 62.96
3 9-Apr-10 2.94 14 20.88 62.18
4 10-Apr-10 0.8 9.06 18.22 71.92
5 24-Apr-10 3.86 17.7 24.58 53.86
6 30-Apr-10 7.24 26.08 29.28 37.4
7 10-May-10 5 13.16 22.16 59.68
8 16-May-10 8.82 17.14 18.58 55.46
9 20-May-10 7.62 20.94 25.06 46.38
10 18-Jun-10 0.66 9.2 19.5 70.64
11 12-Jul-10 1.78 13.22 22.98 62.02
12 16-Jul-10 0.58 10.86 22.12 66.44
13 22-Aug-10 0.4 6.3 17.68 75.62
14 14-Sep-10 0.48 6.48 17.24 75.815 22-Sep-10 0.6 10.5 26.5 62.4
16 3-Oct-10 3.62 17.02 22.16 57.2
17 12-Nov-10 0.58 7.52 20.3 71.6
18 13-Jan-11 0.6 9.2 21.64 68.56
19 6-Feb-11 0.36 7.32 19.88 72.44
20 22-Apr-11 1.32 10.8 18.96 68.92
21 8-May-11 0.62 11.82 23.5 64.06
22 23-May-11 0.16 10.22 23.32 66.3
23 24-May-11 0.84 8.38 17.94 72.84
24 9-Jun-11 0.76 9.94 16.54 72.76
25 5-Jul-11 1.16 9.06 16.84 72.94
26 26-Jul-11 0.82 9.54 23.48 66.16
27 12-Aug-11 0.82 10.64 22.72 65.82
28 27-Aug-11 0.8 8.96 21.1 69.14
29 9-Sep-11 1.22 10.3 19.66 68.82
30 19-Sep-11 1.48 10.66 21.76 66.1
31 24-Sep-11 1.04 9.5 18.46 71
32 28-Sep-11 1.6 12.42 23.68 62.3
33 28-Sep-11 1.6 12.42 23.68 62.3
34 29-Sep-11 1.6 12.42 23.68 62.3
35 29-Sep-11 1.6 12.42 23.68 62.3
36 13-Oct-11 2.2 14.14 20.36 63.3
37 29-Oct-11 1.1 9.78 21.2 67.9238 16-Nov-11 2.2 14.82 22.56 60.42
39 27-Nov-11 0.04 5.14 22.02 72.8
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40 14-Dec-11 0.9 8.48 19 71.62
41 16-Jan-12 0.46 7.96 21.8 69.78
42 9-Feb-12 1.26 10.16 24.46 64.12
43 13-Apr-12 1.96 11.62 21.54 64.88
44 4-May-12 1.12 7.8 19.58 71.5
45 6-Jun-12 0.9 8.9 20.18 70.02
46 7-Jun-12 0.9 8.9 20.18 70.02
Average 1.711 11.115 21.326 65.848
Figure 14: PF fineness Mill 3-E
From the above trends we observe Mill 3A PF fineness decreasing over the past few
months, the mill was subsequently shut down for overhauling and maintenance.
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Variation in un-burnt with PA flow and net savings
Un-burnt carbon is not only controlled by PF fineness but also with other factors like the
amount of primary and secondary air flow. The following experiment was carried out at BBGS
unit #3 on 22/06/2012.
PrincipalReducing the PA flow into the mill would reduce the velocity of coal going into thefurnace, which would give coal more time for combustion. Consequently this
would mean lower un-burnt carbon in ash.
ProcedureThe PA flow set point in general operation for Unit #3 at BBGS is about 90 TPH toeach mill making the total PA flow set point 360 TPH. This set point was reduced
to 80 TPH to each mill making the total PA flow about 320 TPH. Ash samples were collected for
both these set point conditions.
Observation -
PA Flow Un-burnt carbon % in Bottom Ash Un-burnt carbon % in Fly Ash
360 TPH 10.03% 2.39%
320 TPH 4.91% 2.59%
The net reduction in un-burnt carbon in ash is calculated below (assumption 85% ash is fly ash
remaining is bottom ash).
Reduction
=(10.034.91) x 15/100 + (2.392.59) x 85/100
= 0.598 % un-burnt reduction is ash
Coal Savings = 0.435 TPH
= 3,814,923.06 Kg / year
Power saving = 6,368,819.79 units / year
Cost saving = Rs 3,37,54,744.94 / year
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Reduction of BBGS Unit3 auxiliary consumption
power by reducing boiler feed pump power
consumption
Importance of drum level control and methods
The drum is a buffer vessel that is used to separate water from steam. Steam is
separated form water using a cyclone separator. For the separator to work properly a minimum
level of water must be maintained in the drum. However the steam flow would fluctuate from
time to time causing the drum level to fluctuate. A system must thus be set into work to control
the drum level at all times. This is done by controlling the feed water flow by varying the
operation conditions of either the Boiler feed pump or the Feed control station.
The BFP for BBGS Unit #3 make specifications are:
Booster Pump Press stage
Type Cent Horiz Single Stage Cent Horiz
Quantity 891 TPH 892 TPH
Gen. Pressure 9.15 kg/cm2
191.3 kg/cm2
Speed 1406 rev/min 5730 rev/min
Pump efficiency 80.5 % 81 %
Power absorbed 308 KW 6392 KW
NPSH required at
3% HD
4.3m 4.9m
Boiler Feed pump motor
Type Cage Induction CACW
Frame size EL 710/2800 J
Rating 8800
Supply 6.6KW
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BFP suction strainer
Type Duplex
Element 80 mesh
Degree of filtration 185 micron
Temperature 170 C
The Boiler Feed pump and the de-aerator are strategically placed so as to provide
sufficient suction pressure for the BFP. This is done by placing the de-aerator at a height (22.5
m) and then placing the BPF right under it at ground level.
The BFP used in BBGS Unit3 has hydraulic coupling with scoop control to vary the
speed of the driven shaft. In hydraulic coupling pumps torque transmitted between the driver-driven shaft is varied by varying the oil levels using scoop control. Typical efficiency of a
hydraulically coupled motor is about 98% .
Types of BFP controls and their advantages
3Element control method is a control process that constantly generates the amount of
feed water that needs to be supplied by the boiler feed pump to the boiler in order to keep the
drum level in control. A function using the drum level and the steam flow as inputs is used to
generate the feed flow required. A system is said to be in 3 element control when it takes the
feed flow rate generated by the 3 element control function and then functions towards
maintaining that flow rate.
Figure 15: Line diagram of Feed water
system
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There are two methods to control the drum level:
1. Operating the feed control valves in 3 element control and the BFP scoop would in DP
control mode. The advantage of operating FCS valves in 3 element control and BFP in
scoop is its quick response to large fluctuations in load.
2. Operating the BFP scoop in 3 element control mode. The advantage of this process is
the its energy efficient working scheme where there is least amount of throttling loss
across the valves of the feed control station.
Energy consumption in various operational modes of BFP
Observations
Energy saving using BFP scoop in 3 element control mode
The energy saving were noted for the following control conditions
i. BFP in DP control with DP set point at 1.8 kg/cm2.
ii. BFP in DP control with DP set point at 3.5 kg/cm2.
iii. BFP in scoop control with :-
a. 1 full load valve of feed control station completely open and the other valves
closed.
b. 1 full load valve and 1 low load valve open.
c. all valves of feed control station completely open.
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The following are the results :-
Date TimeAvg.
suctionFCS DP
Average
FCS DPLoad
Average
loadFrequency
Total
power
BFP aux %
of total
generation
30-05-
12
1000
832.15
1.769
1.85775
259.5
259.9725 49.7 5.3636 2.063141020 1.927 260.36
1040 1.927 258.32
1100 1.808 261.71
1100
815.7
1.808
3.087
261.71
262.12 49.63 5.684 2.168471120 3.534 261.98
1140 3.456 263.05
1200 3.55 261.74
1400
837.05
2.239
2.2275
260.71
261.0525 49.6 5.3848 2.062731420 2.205 261.161440 2.202 260.98
1500 2.264 261.36
1500
850.55
2.264
1.13333
261.36
261.9367 49.73 5.2572 2.007051530 0.568 263.04
1600 0.568 261.41
1600
851.53
0.568
0.49933
261.41
262.12 49.93 5.143 1.962081630 0.512 263.37
1700 0.418 261.58
Figure 16: BFP auxiliary consumption
vs. DP across FCV v/v
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Net energy savings using 3-Element control mode.
At 250 MW generation:
The BFP at 1.8 DP set point power consumption = 5157.85 units/ hour
BFP scoop in 3 element control power consumption = 4905.2
(With 3 FCS V/V FULLY OPENED) units/hour
The total power saving = 252.65 units/hour
= 22,13,214 units/year
Cost saving = Rs 1,17,30,034.2 /year
Coal saving = 13,25,715.186 kg/year
CO2emission reduction =16,45,433.5 kg/year
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Conclusion
Reducing the PA flow into the mills reduces the un-burnt carbon losses significantly.
When the coal quality is good it would require lower time and turbulence to burn properly as
compared to a bad grade of coal. Reduction of PA flow into the mill increases the time coal has
for combustion, however the turbulence is also partly reduced. Lower grades of coal might not
be able to optimally burn in low turbulence condition. For down shot boilers, increasing the PA
flow would increase the velocity of coal flowing into the furnace, leading to higher un-burnt in
bottom ash. In corner fired boilers higher velocity would mainly reduce the coal-air mixing time,
leading to poorer combustion.
It was found that when the BFP scoop is put in 3- element control, the loss that was
occurring at the feed control station valves is reduced significantly, making this a cost efficient
method. However as compared to the conventional method of putting the feed control station
in 3- element control and the BFP scoop controlling the DP set-point across the feed control
station, the response time required in the higher. Thus when the load fluctuates rapidly for a
unit, the conventional method becomes a little more bankable. For normal operation however
the energy savings by putting BFP scoop in 3- element control is significant.