Slide 1


Slide 2

Combustion Optimization


Slide 3

Bharat Heavy Electricals Limited

TIRUCHIRAPALLI

1.

Higher Availability & Reliability

2.

Highest Plant efficiency

3.

Lower Heat Rate

4.

Minimum Auxiliary Power Consumption

5.

Ability to operate under adverse grid conditions/fluctuation in
demand

6.

Minimum emission of Pollutants

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Slide 4

Bharat Heavy Electricals Limited

TIRUCHIRAPALLI

Boiler side:
1.

Minimum flue gas temperature at AH outlet

2.

Minimum excess air at AH outlet

3.

Minimum un-burnt Carbon loss

4.

Minimum RH spray

5.

Minimum SH spray

6.

Reduced Auxiliary Power Consumption

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Slide 5

Bharat Heavy Electricals Limited

TIRUCHIRAPALLI

Turbine side measures
1.
1.

Higher steam parameters
( MS Pressure & SHO/RHO Steam Temp).
Adoption of double reheat cycle

2.

Increasing feed water temperature with
Enhanced Regenerative feed heating

3.

Increase in condenser vacuum

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Slide 6

Bharat Heavy Electricals Limited

TIRUCHIRAPALLI

2a. Boiler - Various Losses
By Gas

Dry Gas Loss
Loss due to Moisture in Gas

Due to Fuel Moisture
Due to moisture formed by H2 in fuel
Due to air moisture
By Ash

Unburnt carbon Loss
Sensible heat loss in Fly ash
Sensible heat loss in Bottom ash

Other Loss

Carbon monoxide Loss

Radiation Loss
Heat loss through Mill rejects

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Slide 7

Bharat Heavy Electricals Limited

TIRUCHIRAPALLI

Factors Influencing Various Losses
No

Loss

Factor

1

Dry Gas Loss

Flue Gas Temperature, Excess Air & Fuel

2

Unburnt Carbon Loss In Ash

Ash in Fuel & Unburnt Carbon In Fly /
Bottom Ash

3

Mill Reject Loss

Reject Rate & CV Of Reject

4

Due to Moisture formed from
Hydrogen

Hydrogen Content In Fuel & Flue Gas
Temperature

5

Due to Fuel Moisture

Moisture Content In Fuel & Flue Gas
Temperature

6

Due to Air Moisture

Humidity Of Combustion Air, Excess Air
Level & Flue Gas Temperature

7

Radiation & Convection Loss

Insulation Of Boiler

8

Sensible Heat Loss In Ash

Ash Temperature

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Slide 8

Bharat Heavy Electricals Limited

TIRUCHIRAPALLI

Methods to reduce unburnt carbon loss
 Ensure consistent mill fineness - +50, - 200
 Good burner maintenance
 Proper secondary air adjustment - SADC
 Reduce PA air to the minimum possible – min PA velocity
variation
 Cut out oil support at higher loads where coal flame is
stable as oil preferentially deplete o2 in the area and
reduces ‘o2 ‘ for coal particles to burn

 Check coal property and tune combustion
 Keep boiler heat transfer surface clean so that losses can
be reduced thus reducing the coal input
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Slide 9

Bharat Heavy Electricals Limited

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TIRUCHIRAPALLI

Correct excess air
High mill outlet temp.
Better combustion – combustion tuning
Arrest air ingress
Air heater performance – leakage , proper elements
Cleanliness of the heat transfer surfaces

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Slide 10

Bharat Heavy Electricals Limited

TIRUCHIRAPALLI

Optimization of Boiler Efficiency
1

HHV 

All Losses 

2

FG APH out Temp 

Dry gas, Sensible heat in Ash, H 2, Fuel and
Air Moisture Loss 

3

Excess air 

Dry gas, Unburnt & Air Moisture Loss 

4

Fuel Moisture 

Fuel Moisture Loss 

5

Air Moisture 

Air Moisture Loss 

6

H2 in Fuel 

H2 Loss 

7

Mill reject rate or GCV 

Mill reject Loss 

The Major parameters to be looked into for Better Efficiency:
1.

FG Temp

2.

Excess air Level

3.

Mill reject rate and

4.

Unburnt carbon in ash

Control / Optimization of other parameters (i.e GCV, H2, Fuel moisture and Air Moisture) are not
possible.
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Slide 11

Bharat Heavy Electricals Limited

TIRUCHIRAPALLI

Major reasons for increase in APC

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Operation of unit with higher excess air
Air heater leakage
Higher PA fan outlet pressure
High mill fineness, more no. of mills
Air ingress into boiler
Pluggage in line / ducting
Partialy blocked APH

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Slide 12

Bharat Heavy Electricals Limited

TIRUCHIRAPALLI

Sources of air ingress
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Furnace roof
Expansion joints
Air heaters
Ducts
Esp hoppers
Peep holes
Manholes
Furnace bottom

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Slide 13

Bharat Heavy Electricals Limited

TIRUCHIRAPALLI

Factors affecting APC - a summary
FACTORS AFFECTING AUXILIARY POWER
ID FANS
AH LEAK
GAS TEMPERATURE
DUCT LEAKAGES
EXCESS AIR
LOAD/ PLANT HEAT RATE
DRAUGHT LOSS
AH CHOKING
FD FANS
AH LEAK
WIND BOX PR.
EXCESS AIR
LOAD/ PLANT HEAT RATE
PRESSURE LOSS
AH CHOKING
SCAPH CHOKING
PA FANS
AH LEAKAGE
PA HEADER PR.
MILL AIR FLOW
PRESSURE LOSS
AH CHOKING
MILL
COAL QTY.
GCV
LOAD/ PLANT HEAT RATE
COAL
MOISTURE
HGI
COAL FINENESS
MILL CONDITION

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Slide 14

Bharat Heavy Electricals Limited

TIRUCHIRAPALLI

Capacity Reduction in a Boiler
Fuel input
Low cv coal
Milling capacity
Grinding capacity
Drying capacity
Carrying capacity
Drive capacity
Draught system
ID fan limitations
Pressure drops high
AH choking
Chimney back pressure high
High volume
AH leakages
Duct leakages
High gas temperatures
Worn out impellers
Metal temperatures high
High spray requirements
Fouling of surfaces
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Slide 15

Bharat Heavy Electricals Limited

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Slide 16

Bharat Heavy Electricals Limited

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TIRUCHIRAPALLI

Problem:
Heavy clinkering build up upto S-panel /Bottom of burner
reported from many boilers

Investigations:



Poor mill fineness (50% through 200 mesh)
Non-working of SADC as per control
Poor coal quality – usage of ground stock
Non- working of wall blowers
Improper evacuation of bottom ash

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Solution:After taking above corrective actions no further

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problems faced.

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Slide 17

Bharat Heavy Electricals Limited

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TIRUCHIRAPALLI

Problem: Frequent choking of coal pipe
Investigations: Clean air flow test
Checking of orifice
Calibration of coal flow/air flow -check
Foreign material entrapped in classifier (
cloth)
Solution: Problem resolved after removal of
foreign material from classifier.

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Slide 18

Bharat Heavy Electricals Limited

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TIRUCHIRAPALLI

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