Proj Yashvardan Cesc

7/23/2019 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


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 140 mesh R3g _____________


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




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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33

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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34

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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35

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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36

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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37

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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38

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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39

Reduction of BBGS Unit3 auxiliary consumption


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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40

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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41

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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42

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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43

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.

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