1. A presentation on
Steam Generator

2. Coal to Electricity ….. Basics
Coal
Chemical
Energy
Super Heated
Steam
Pollutants
Thermal
Energy
Turbine
Torque
Heat LossIn
Condenser
Kinetic
Energy
Electrical
Energy
Alternating current
in Stator
Mech. Energy
LossASH
Heat
Loss
Elet. Energy
Loss

3. Major Energy
Sources of
India

4. Why Coal?
Coal
55%
Gas
10%
Diesel
1%
Hydel
26%
RES
5%
Nuclear
3%
Share of Coal in Power
Generation
Advantages of Coal Fuel
•Abundantly available in India
•Low cost
•Technology for Power
Generation well developed.
•Easy to handle, transport,
store and use
Shortcomings of Coal
•Low Calorific Value
•Large quantity to be Handled
•Produces pollutants, ash
•Disposal of ash is
Problematic
•Reserves depleting fast
•India’s Coal Reserves are estimated to be 206 billion tonnes. Present consumption is
about 450 million tonnes.
•Cost of coal for producing 1 unit of electricity (Cost of coal Rs 1000/MT)is Rs 0.75.
•Cost of Gas for producing 1 unit of electricity (Cost of Gas Rs 6/SMC)is Rs 1.20.

5. Knowing more about Coal
Coal production
•Surface Mining
•Underground Mining
Coal
Transportation
•Rail
•Truck
•Conveyor
•Ship
Coal Properties
•Calorific Value
•Grade of Coal (UHV)
•Proximate Analysis
•Ultimate Analysis
•Ash and Minerals
•Grindability
•Rank
•Physical
Characteristics
Coal Beneficiation
•Why?
•Processes
•Effectiveness
Coal production
•Surface Mining
•Underground Mining
Useful Heat Value (UHV)
UHV= 8900-138(A+M)

6. Boiler/ steam generator
 Steam generating device for a specific purpose.
 Capable to meet variation in load demand
 Capable of generating steam in a range of operating
pressure and temperature
 For utility purpose, it should generate steam
uninterruptedly at operating pressure and
temperature for running steam turbines.

7. Boiler/ steam generator
 Raw materials for design
of boilers
1. Coal from mines
2. Ambient air
3. Water from natural
resources (river, ponds)
o Generating heat energy
o Air for combustion
o Working fluid for steam
generation, possessing
heat energy
A 500MW steam generator consumes about 8000 tonnes of coal every day
It will be considered if it requires about 200 cubic meter of DM water in a day
It will produce about 9500 tonnes of Carbon di Oxide every day

8. Coal analysis
 Typical composition (Proximate analysis)
1. Fixed carbon
2. Fuel ash
3. Volatile material
4. Total Moisture
5. Sulfur
o High calorific value/ Lower calorific value
(Kcal/kg)
o Hardgrove Index (HGI)

9. Combustion of coal
 Carbon, hydrogen, sulfur are sources of heat
on combustion
 Surface moisture removed on heating during
pulverization.
 Inherent moisture and volatiles are released at
higher temperature, making coal porous and
leading to char/ coke formation. (Thermal
preparation stage)

10. Fuel Oil
 Three liquid fuels used in power plants
• 1. Heavy Fuel Oil (HFO)
• 2. LSHS (Low Sulfur Heavy stock)
• 3. High speed Diesel (HSD)
Oil firing is preceded by
 Lowering viscosity and increasing flowability on
heating for better combustion in given turn down ratio.
(125o
C)
 Droplet formation on atomization (by steam/
compressed air/ mechanical pressurization)
 Combustion initiation by High energy spark ignition

11. Combustion of reactants
 Reaction rate depends on concentration of one of
the reactants
 Concentration varies on partial pressure of the
reactants.
 Partial pressure is a function of gas temperature.
 Therefore, reaction rate depends on temperature
and substance that enter the reaction.

12. Combustion Reactions (Carbon)
 Main reactions
2C + O2 = 2CO + 3950 BTU/lb(Deficit air)
C + O2 = CO2 +14093 BTU/lb
Secondary reactions
2CO + O2 = 2CO2 + 4347BTU/lb
C + CO2 = 2CO -7.25MJ/kg

13. Combustion Reactions (Carbon)
 Carbon reaction
2C + O2 =2CO [Eco =60kJ/mol]
C + O2 =CO2 [Eco2 =140kJ/mol]
reaction at 1200o
C
4C + 3O2 =2CO + 2CO2 (Ratio 1:1)
Reaction at 1700o
C
3C + 2O2 = 2CO +CO2 (Ratio 2:1)
It is desirable to supply combustion air at lower temperature
regime in furnace

14. Combustion Reaction (H2, S)
 Hydrogen reaction
2H2 + O2 = 2H2O +61095 BTU/lb
 Sulfur reaction
S + O2 = SO2 + 3980 BTU/lb
(undesirable)

15. Coal for combustion
 Anthracite
 Semi-anthracite
 Bituminous
 Semi-Bituminous
 Lignite
 Peat
 High CV, low VM
 High CV, low VM
 Medium CV, medium VM
 Medium CV, medium VM
 Low CV, high VM, high TM
 Very low CV, high VM & TM

16. Heat Generation in furnace
 Heat input in the furnace
 Efficiency of thermal power plants is 37%-45%
for different types of cycle
 For typical conventional P.F. boilers, coal flow
rate is
290-350 T/hr For 500 MW units
120-145 T/hr For 200 MW units
Cycle
Elect
Furnace
MW
Q
η
=

19. Tangential Firing System

23. MAIN EQUIPMENTS OF FUEL & FIRING SYSTEM
• MILLS OR PULVERISERS
• FEDDERS
• BURNERS
TYPES OF FEEDERS
• VOLUMETRIC FEEDRES
• GRAVIMETRIC FEEDERS

24. PULVERIZERS
OBJECTIVES
• TO CRUSHED THE COAL
• REDCED TO A FINENESS SUCH THAT 70-80% PASSES THROUGH A
200MESH SIEVE
ADVANTAGES OF PULVERISED COAL FIRING
• EFFICIENT UTILISATION OF CHEAPER GRADE OF COALS
• FLEXIBILITY IN FIRING WITH ABILITY TO MEET FLUCTUATING LOADS
• BETTER COAL COMBUSTION INCREASING THE BOILER EFFICIENCY
• HIGH AVAILIBILITY

25. X R P
( B H E L )
E M IL L S
( B A B C O C K )
M P S
B O W L /
B A L L & R A C E
V E R T IC A L S P IN D L E
P R E S S U R IZ E D
T U B E
C L A S S IF IC A T IO N O F M IL L S

26. BOWL MILL
Model no. Base
capacity(T/Hr)
623XRP 18.4
703XRP 26.4
763XRP 33.8
803XRP 36.5
883XRP 51.1
903XRP 54.1
1003XRP 68.1
1043XRP 72.0
BASE CAPACITY(T/HR)
AT
HGI -55
Total Moisture-10%
Fineness-70% THRU 200
MESH

27. BALL& RACE MILL(E MILL)
Model no. Base
capacity(T/Hr)
7E9 25
8.5E10 35
8.5E9 40
10E10 55
10.9E11 61
10.9E10 70
10.9E8 80

28. TUBE MILL
Model no. Base
capacity(T/Hr)
BBD4760 83
BBD4772 90

29. AIR AND DRAFT SYSTEM
OBJECTIVES
• THE AIR WE NEED FOR COMBUSTION IN THE FURNACE AND FLUE
GAS THAT WE MUST EVACUATE
• TRANSPORT AND DRY THE PULVERISED COAL
• SEALING OF BEARINGS FROM COAL/DUST
DRAFT SYSTEM
DRAFT MEANS THE DIFFRENCE BETWEEN THE ATMOSPHERIC PRESSRE
AND PRESSURE EXISTING IN THE FURNACE
•NATURAL DRAFT- OBTAINED BY TALL CHIMNEY
• INDUCED DRAFT- BY ID FANS
• FORCED DRAFT- BY FD FANS
• BALANCE DRAFT - BY ID AND FD FANS
•GENERALLY IN POWER PLANT BALANCE DRAFT SYSTEM IS USED.

30. FANS IN POWER PLANT
• FORCED DRAFT FAN
• INDUCED DRAFT FAN
• PRIMARY AIR FAN
• SEAL AIR FAN
• SCANNER AIR FAN
THE BASIC INFORMATION NEEDED TO SELECT A FAN ARE
• AIR OR GAS FLOW-KG/HR
• DENSITY(FUNCTION OF TEMPERATURE AND PRESSURE)
• SYSTEM RESISTANCE(LOSSES)

31. AIR PRE HEATERS
OBJECTIVES
• TO RAISE THE TEMPERATURES OF PRIMARY AND SECONDARY AIR
BY UTILISING HEAT FROM FLUE GAS AT LOW TEMPERATURE
ADVANTAGES OF AIR PREHEATERS
• INCREASE THE BOILER EFFICIENCY
• STABILITY OF COMBUSTION IMPROVED BY USE OF HOT AIR
• PERMITTING TO BURN POOR QUALITY COAL

33. Ljungstrom type Bisector

34. TWO PASS BOILER
ARRANGEMENT

35. Electro Static Precipitator
To remove fly ash from the flue gases
electrostatic precipitators are used.
They have collection efficiency over 99.5%
The efficiency depends on various
parameters such as velocity of flow,
quantity of gas, resistivity of ash, voltage
of fields, temperature etc

36. Principle of Operation
The fluegas laden with flyash is sent through ducts having negatively charged
plates which give the particles a negative charge. The particles are then routed
past positively charged plates, or grounded plates, which attract the now
negatively-charged ash particles. The particles stick to the positive plates until
they are collected by periodically rapping.

39. SELECTION OF BOILER
TYPE OF BOILER
Based on steam parameter- Subcritical/ Supercritacal
Based on steam/ water circuit-Once throuh/ drum type
Based on air/ flue gas path- Tower/Two path/ T-type
Type of fuel- Coal fired/ oil fired
Type of draft system-
Type of burner arrangement- Tangential/Front/ opposed
Selection of Firing system- Type of mills
Single reheat/ double reheat
Type of water wall tube- Plain, rifled
Type of tubing arrangement- Spiral/ straight

40. • Tube leakages from boiler pressure parts.
• Erosion of tubes due to high ash content and velocities
• Over heating of tubes
• Passing from valves causing difficulty in maintaining the parameters
• Failure or incorrectness of measured parameters
• Overloading of boiler due to very poor quality of coal
• Deposition of ash (clinkers) on furnace walls.
• Difficulties in removal of ash from the boiler
• Reduced effectiveness of heat transfer leading to loss of efficiency.
• Improper combustion of coal in the boiler.
Typical Boiler Problems

41. • Air ingress from the nose arch, penthouse and boiler second pass
and quantification thereof
• Difference between on line reading and the actual oxygen in the flue
gas duct
• Difference between actual and 'on line' temperature
• measurement of air heater air / gas outlet temperatures
• Fouling and Slagging
• High unburnt Carbon in flyash or bottomash
• High air heater leakage
• Boiler operation at high excess air
Typical Boiler Problems contd..

42. A Few words on Super Critical Boiler
Definition
“CRITICAL” is a thermodynamic expression
describing the state of a substance beyond
which there is no clear distinction between
the liquid and gaseous phase.
 The critical pressure & temperature for
water are
 Pressure = 225.56 Kg / cm2
 Temperature = 374.15 C

43. SUPERCRITICALTHERMAL CYCLE
ADVANTAGES (1)
 Improvements in plant efficiency by
more than 2 %
 Decrease in Coal Consumption
 Reduction in Green House gases.
 Overall reduction in Auxiliary Power
consumption.
 Reduction in requirement of Ash dyke
Land & Consumptive water.

44. SUPERCRITICAL – ADVANTAGES (2)
 Sliding pressure operation because of Once
through system .
 Even distribution of heat due to spiral wall
arrangement leading to less Boiler tube failure,
thereby improving system continuity and
availability of the station.
 Low thermal stress in Turbine .
 The startup time is less for boiler.

45. SUPERCRITICAL – DISADVANTAGES
Higher power consumption of BFP
Higher feed water quality required.
More complex supporting and framing in
Boiler due to Spiral Wall tubes.
Slight higher capital cost.

46. Description unit 660 500
S/H STEAM FLOW T/HR 2225 1625
SH STEAM PR KG/CM2
256 179
SH STEAM TEMP 0
C 540 540
RH STEAM FLOW T/HR 1742 1397.4
RH STEAM TEMP INLET 0
C 303.7 338.5
RH STEAM TEMP OUTLET 0
C 568 540
RH STEAM PRESS INLET KG/CM2
51.17 46.1
FEED WATER TEMP 0
C 291.4 255.2
COMPARISION OF 660 MW Vs 500 MW BOILER

47. COST COMPARISON FOR
660 MW vs. 500 MW
DESCRIPTION 660 MW 500 MW
1. 1Cost of Boiler alone 1970.73 Cr 1020.54 Cr
2 Cost of ESP 153.00 Cr Included above
3 Total cost of Boiler + ESP 2124.00 Cr 1020.54 Cr
4 Boiler cost Per MW 1.07 Cr 1.02 Cr
5 Cost of TG for entire stage 1204.72 Cr 634.31 Cr
6 Cost of TG Per MW 0.6Cr 0.63 Cr