WHAT IS BOILER ??
BOILER
means any closed vessel exceeding
22.75 litres in capacity and is used expressively for
generating steam under pressure and includes any
mounting or other fitting attached to such vessel
which is wholly or partly under pressure when the
steam is shut off.
“BOILER”
- IBR
STEAM
“Steam
is the technical term for water vapor,
the gaseous phase of water, which is formed when
water boils
STEAM PIPE
“STEAM PIPE” means any pipe through which steam
passes from a boiler to a prime mover or other user or
both if pressure at which steam passes through such
pipes exceeds 3.5 kg/cm2 above atmospheric pressure
or such pipe exceeds 254 mm in internal diameter and
includes in either case any connected fitting of a steam
pipe.
- IBR
BOILER CODES
Boiler Codes have been written by various nations in the
past century to ensure safety of personnel and to avoid loss
of property. Boiler codes cover the whole gamut of
activities including Design, Fabrication, Testing,
Construction and Operation. The various aspects of IBR
Regulations are called out and consolidated against major
items like drum, headers, lines & links, etc. The following
codes have been used widely.
1.
2.
3.
4.
IBR 1950
ASME Section-I
BS 1113
DIN TRD 300.
THERMODYNAMICS OF
POWER PLANT
SENSIBLE HEAT
 The Heat required to bring the water from 00c to
boiling point is the enthalpy or heat content of the
liquid measured in Kcal/Kg.
OR
The sensible heat of a thermodynamic process may be
calculated as the product of the body's mass (m) with
its specific heat capacity (c) and the change in
temperature ( T):
Q=mc T
LATENT HEAT
 Latent heat is the amount of energy in the form of heat
released or absorbed by a substance during a change of
phase (i.e. solid, liquid, or gas), – also called a phase
transition
SUPERHEAT
 When the steam is heated out of contact with water ,
the steam temperature increases above saturation
temperature .Such a heating is known as super
Heating
OR
In physics, superheating (sometimes referred to
as boiling retardation, or boiling delay) is the
phenomenon in which a liquid is heated to
a temperature higher than its boiling point, without
boiling
CRITICAL POINT
With the increase in pressure for
steam generation , the sensible heat
required increases with decrease in
latent heat. At every pressure
between saturated water and
saturated steam a phase called wet
steam exists. However at one point
the water turns into steam on
addition of sensible heat alone
without going through the phase of
wet steam . This occurs at
temperature of 374oC and
224.6kg/cm2 absolute pressure.
This is called critical point.
THE RANKINE CYCLE
Basic Rankine Cycle
Temperature ( 0
C)
OUTPUT INCREASE
B
D
C
E
F
24 deg C
A
-273
0
Entropy KJ / Kg K
DIFFRENCE BETWEEN
POWER AND ENERGY ??
Energy is an amount of work generated or used, and
has units such as Joules, BTU, calories, or or watthours or kW-hours.
Power is the RATE of generating or using energy, and
has units of watts, which are Joules per second. Or
kW or MW (standard SI prefixes apply)
MEANING OF 1 MW POWER
If 10 bulbs of 100 Watt glows at a time in one home.
It will consumes 1 kilo-watt of power.
Let us assume, load of one home is 1 kilo watt
1 MW
= 1000 kW
= 1000 X 1000 W
= 1000 X (load of one home)
= load of 1,000 homes
Hence, 500 mw plant will benefit 5,00,000 homes (provided each home uses 1kw
power at a time)
MEANING OF 1 UNIT OF
ELECTRICITY
if 10 bulbs of 100 watt glows at a time in one home for one hour. it will consumes 1
kilo watt hour (1kwhr) of power. this is called as 1 unit in our electricity bills.

If 500 MW plant, when run for one full day, it will produces
500 mw = 500 mw x 24 hr = 12,000 mw hr
= 12,000 x 1,000 kW- hr
= 1,20,00,000 units of electricity
(12 million units per day)
EFFICIENCY
Efficiency of any plant or equipment is the ratio of output to its input.
Output of power plant is energy sent out to the grid
Input is the heat energy of the fuels fired in boiler
Mathematically,
(Energy sent out in KW) X 860 Kcal / KW
Efficiency =
(CV of fuel in Kcal / Kg) X (Fuel burnt in Kg)
HEAT RATE
Heat rate is the ratio of heat added to steam in boiler (in Kcal) to the Electrical
energy sent out (in kWh)
Efficiency and Heat Rate are related terms. Lower the heat rate more efficient is
the plant.
Heat rate for thermal project is in the range of 2200 to 1950 Kcal / kW-hr
EFFICIENCY OF VARIOUS COMPONENTS OF
THERMAL POWER PLANT
TYPE
EFFICIENCY
BOILER (1)
84-92 %
TURBINE (2)
84-92 %
GENERATOR (3)
96-98 %
THERMAL CYCLE (4)
50-55 %
OVERALL PLANT
EFFICIENCY (5)
= (1)X(2)X(3)X(4)
34-40 %
CRITICAL POINT
 Increasing the pressure of steam will increase saturation
temperature of steam at which evaporation takes place.
 A point on T-S graph, where saturated liquid line &
saturated vapour line meets, so that associated latent
heat for phase conversion is zero, that point is called
Critical Point.
The critical pressure & temperature for water are
 Pressure
= 224.56 Kg / cm2
 Temperature = 374.15 deg C
SUB CRITICAL
&
SUPERCRITICAL BOILERS
 Boiler operating below the critical point range and
have some amount of latent heat addition in steam
during phase conversion from liquid to Gaseous
state are termed as “Sub Critical Boilers”.
 Boilers operating above the critical point range are
termed as “ Super Critical Boilers”
BOILER CLASSIFICATION
TYPES OF BOILERS
(A) BASED ON APPLICATION :
1. Utility Boilers are large capacity steam generators
used purely for electrical power generation.
2. Industrial Boilers are small capacity boilers intended
for use in the process industries.
Types Of Boilers…….contd
(B) BASED ON CONSTRUCTION:
1. Vertical Recovery-V2R
2. Vertical Unit 40-VU40
3. Vertical Unit 60-VU60
4. Modular Unit-MU
5. 2 Pass Single Arch
6. 2 Pass Double Arch
7. Close couple
8. Box Type
9. Tower Type
Types Of Boilers…….contd
 Single Pass (Tower type) :
If boiler configuration is such that flue gases from
furnace continue to rise upward and all subsequent
heat absorbing coils are kept in this vertical passage,
boiler is referred as tower type boiler.
 Double Pass or Two Pass:
However, if configuration is designed such that after
furnace flue gases take a horizontal turn followed by
downward path in a separate chamber, where heat
absorbing coils like Super heaters and Economizers
are kept, it is referred as Two pass boiler.
Types Of Boilers…….contd
 Top Suspended Boiler:
When all heat absorbing surfaces are suspended
from top structure and are free to expand downward,
the boiler is referred as top suspended.
Some boilers are bottom supported also. (like CFBC
Boilers)
But invariably large capacity boilers are top
suspended for distinctive advantage of smooth down
ward expansion of pressure parts.
Types Of Boilers…….contd
(C) BASED ON FUEL FIRING:
1.
Oil Fired Only
2.
Coal ( Sub-Bituminous) Fired
3.
Lignite Fired (CFBC Boiler)
4.
Black Liquor (For Paper Mills)
5.
Baggase (Stoker Fired)
Types Of Boilers…….contd
(D) BASED ON TYPE OF FIRING:
1.
WALL FIRING ( Only in CFBC Boilers)
2.
CORNER TANGENTIAL FIRING
3.
STOKER
Types Of Boilers…….contd
Corner Tangential Fired Boiler
 When burners are located in corners of furnace wall
such that the protruded flames from them form a
tangent to an imaginary circle in the center of the
furnace, the furnace (boiler) is called tangential fired
boiler.
 210/250/270/500MW boiler is invariably of this
design.
Boiler)
(All Conventional Pulverized fuel fired
Types Of Boilers…….contd
(E) BASED ON NO. OF DRUMS:
1. SINGLE DRUM
2. BI- DRUM
3. NO DRUM (Vertical Separator)
Types Of Boilers…….contd
(F) BASED ON CIRCULATION:
1. NATURAL
2. CONTROLLED
2.1 FORCED Circulation (Pump)
2.2 CONTROLLED Circulation (+Orifice)
2.3 CC+ (Pump + Orifice + Rifled Tubing)
3. ONCE THROUGH
Boiling Mechanism
Circulation refers to flow of steam and water mixture
generated in water walls to drum.
Steam generated forms bubbles which in any case
should immediately flow and should not stick to water
wall surface, which is termed as Nucleate Boiling.
In case, the bubbles formed are not able to flow and
sticks to water wall, thus making a film that disrupts
contact with flowing water for heat transfer is termed as
Film Boiling which is not desirable.
Thus Deviation from Nucleate Boiling (DNB) leads
to tube failures due to higher metal temperatures.
Rifled tubing (Inside surface has Helical profile) avoids
the deviation from Nucleate Boiling
Controlled Circulation Boiler
Normal Conditions
Smooth Tubing
uali
ty
30%
Quality
Minimum Safety Margin
~10%
y
Qualit
e
l
b
a
Allow
DNB
Region
Gen
e ra t
10%
Elevation
ed Q
Al
lo
w
ab
le
Generated Q
Elevation
Rifled Tubing
Q
ua
lit
y
uality
FURNACE WALL OUTLET
Quality
Minimum Safety Margin
~30%
DNB
Region
Circulation in Boiler
The ratio of the weight of water to the weight of steam in
the mixture leaving the heat absorption surfaces is called
Circulation Ratio.
Controlled circulation system
• use of controlled circulation pump
• used for pressure up to 194kg/cm2
(sub critical pr.)
• circulation ratio > 1
Natural Circulation
At lower drum operating pressure (below 175 kg/cm2),
there is a considerable difference in densities of water
and steam.
Drum and down comers are full of relatively cold water
whereas upper portion of water walls and risers tubes
are full of wet steam. The circulation in furnace, in this
case, takes place due to Thermo-Siphon principle.
The density difference is the driving force and this
balances the frictional losses, establishes a rate of
circulation. The furnace is called Natural Circulated.
Thus Natural circulation is the ability of water to circulate
continuously, with gravity and changes in temperature
being the only driving force known as "thermal head“.
Forced Circulation
Beyond 175 kg/cm2 operating pressure, the driving
force due to density difference reduces considerably
and unable to establish such circulation.
Now circulation is assisted by providing pumps in
down comer path to over come frictional losses. The
amount of water, flowing in water wall tubes, is
controlled by providing orifice in each tube.
The boiler (furnace) is referred as Controlled
Circulated.
500MW boilers need controlled circulation. Less than
500MW units are generally natural circulation type.
Why controlled circulation is required?
Diff in Density
Types Of Boilers…….contd
(F) BASED ON DRAFT:
1. Forced draft
2. Induced Draft
3. Balanced Draft
Types Of Boilers…….contd
Balanced Draft Furnace
 When the secondary air being supplied to furnace by
Forced Draft (FD) fans to facilitate combustion and flue
gases of combustion from furnace are suck out by the
Induced Draft (ID) fans are adjusted in such a way that
the interior pressure of furnace is maintained at slightly
negative pressure (minus 10 mm of water column as
compared to atmospheric pressure), the boiler is
categorized as Balanced Draft furnace.
 210/250/270/500 MW boiler is invariably a balanced
draft boiler
Boiler Pressure Parts
PRESSURE PARTS
(A) BASED ON CONFIGURATION :
1. HEADERS
2. PANELS
3. COILS
4. CONNECTING LINKS
5. SUPPORTS & SUSPENSIONS
(B) BASED ON SYSTEM :
1. ECONOMISER SYSTEM
2. CIRCULATION SYSTEM
3. SUPERHEATER SYSTEM
4. REHEATER SYSTEM
WATER WALLS
LOOKING FROM
OUTSIDE
WATER WALLS LOOKING FROM INSIDE OF THE BOILER
Downcomers
 There are down comers in boiler ( 6 no. in 270 MW) which
carry water from boiler drum to the bottom ring header.
 They are installed from outside the furnace to keep density
difference for circulation of water & steam.
WATER
WALLS
 HEATING AND EVAPORATING THE FEED WATER SUPPLIED TO
THE BOILER FROM THE ECONOMISERS.
 THESE ARE VERTICAL TUBES CONNECTED AT THE TOP AND
BOTTOM TO THE HEADERS.
 THESE TUBES RECEIVE WATER FROM THE BOILER DRUM BY
MEANS OF DOWNCOMERS CONNECTED BETWEEN DRUM AND
WATER WALLS LOWER HEADER.
 APPROXIMATELY 50% OF THE HEAT RELEASED BY THE
COMBUSTION OF THE FUEL IN THE FURNACE IS ABSORBED BY
THE WATER WALLS.
Water Walls Tubes Construction
 Membrane Panel Furnace
walls:
When tubes are welded
together using either welded
metal between tubes
(membrane walls) or a filler
plate welded to both adjacent
tubes (fin welded), the wall is
called Welded Wall.
Construction of Water Walls
 Tangent tube The
construction consists of
water wall placed side by
side nearly touching each
other. An envelope of thin
sheet of steel called "SKIN
CASING" is placed in
contact with the tubes,
which provides a seal
against furnace leakage.
Pressure Parts …..contd
(C)BASED ON FLOW
1. ECONOMISER
2.1 Eco inlet Link
2.2 Eco inlet Header
2.3 Eco Coils
2.4 Eco Intermediate Headers
2.5 Eco Hanger Tubes
2.6 Eco Outlet Header
2.7 Eco Connecting Links to Drum
2. DRUM With Internals
3. DOWN COMERS
(C) Based on Flow …contd
4. WATER WALL INLET HEADERS
5. WATER WALL PANELS
5.1 Front
5.2 Rear
5.3 Side
5.4 Extended Side
6. WATER WALL Loose tubes
(Arch, Extended Side, Hanger and screen)
7. Water wall outlet headers
8. Risers
9. Drum
Water Path in Boiler (270MW)
Economizer
(From BFP
discharge lines)
Collected in outlet
water wall headers
& discharged to
steam drum through
riser tubes
Steam Drum
(Via economizer
links to drum)
Rises through
furnace wall tubes
- front/rear,left
,right side(absorbs
latent heat)
Via Downcomers
bottom ring
headers
Inside drum water separated
from steam-water
mixture through
turbo separators &
screen driers
Dry saturated
steam exits the
drum & enters into
1st stage of
superheating
SH STEAM OUTLET
CRH IN
HRH OUT
DRUM
REAR ROOF
FRONT ROOF
EXTENDED
WW
LTSH
Economiser
WATER INLET
WATER WALL BOTTOM RING HEADER
Steam Path in Boiler
SH SCW
side outlet
hdrs(4) (F/R;
left/right)
Backpass
SCW front
wall inlet
header
SH
connecting
tubes
SH steam
cooled Back
Pass side
walled tubes
SCW front
& screen
tubes
SH Radiant
Roof Inlet
Header
SH Steam
cooled
(Backpass)
sidewall
inlet header
Backpass
rear roof
tubes
Steam Drum
SH Radiant
Roof tubes
(Ist Pass)
SH Radiant
Roof outlet
Header
Backpass
LTSH &
economiser
supports
lower
SH steam
cooled rear
wall tubes
upper
SH rear roof
junction
header
LTSH &
economiser
support
tubes
LTSH &
economiser
support
headers
Steam Path in Boiler (contd.)
SH steam
cooled rear
wall inlet
header
SH PLATEN
inlet header
SH Platen
Coil Assembly
SH steam
cooled rear
wall tubes
LTSH TO SH
Platen HDR
SH outlet
headers
LTSH steam
cooled rear
wall tubes inlet
header
LTSH outlet
headers
Main Steam
(MS) line
LTSH
horizontal
spaced coils
LTSH coil
terminals
Transfer of Energy in SH
Super heater heats the high-pressure steam from its
saturation temperature to a higher specified temperature.
Hot Flue
Gas
Thermal Structure
SH
Convection &
Radiation HT
Drop in Enthalpy
of Flue Gas
SH Steam
Convection HT
Mechanism of Heat Transfer
Rise in Enthalpy of
Steam
Mechanism of Heat Transfer :
Rate of heat transfer from hot gas to cold steam is
proportional to:
 Mean Temperature difference between Hot Gas and Cold
Steam.
 Surface area of heat transfer
Thot gas,in
Tcold gas,out
TSH steam,out
Tcold steam,in
SUPERHEATER (For 270 MW Units)
SH heating surfaces are in the form of coils which are
made by bending the tubes in cold or hot condition. The
superheater is composed of four basic sections.
The platen section is located directly above the furnace
in front of the furnace arch. It absorbs heat mainly by
radiation.
The pendant spaced section (Final Superheater) is
located in back of the screen wall tubes. The mode of
heat transfer is convection.
The horizontal section of the superheater (LTSH) is
located in the rear gas pass above economiser.
The steam cooled wall sections form the side, front and
rear walls and roof of the vertical gas pass.
SUPERHEATER HEADER & TUBES
Platen Superheater
•
•
•
•
Flat panels of tubes located in the
upper part of the furnace, where
the gas temperature is high.
The tubes of the platen SH
receive very high radiation as well
as a heavy dust burden.
Mechanism of HT : High
Radiation & Low convection
Thermal Structure:
–
–
–
–
No. of platens
No. of tubes in a platen
Dia of a tube
Length of a tube
Geometry of Thermal Structure : Platen SH
• The outer diameter of platen SH is in the range of 32 – 42
mm.
• The platens are usually widely spaced,
S1 = 500 – 900 mm.
• The tubes within a platen are closely spaced, S2/d = 1.1.
• The number of parallel tubes in a platen is in the range of 15
– 35.
Convective Superheater (Pendant)
•
•
•
S1
S2
•
•
•
•
Convective super heaters are vertical
type (Pendant ) or horizontal types.
The Pendant SH is always arranged in
the horizontal crossover duct.
Pendant SH tubes are widely spaced
due to high temperature of flue gas
and ash is soft.
Transverse pitch : S1/d > 4.5
Longitudinal pitch : S2/d > 3.5
The outside tube diameter : 32 – 51
mm
Tube thickness : 3 – 7 mm
Convective Superheater (Horizontal)
•
•
•
•
•
•
•
•
•
•
The horizontal SH are located in the back pass.
The tubes are arranged in the in-line configuration.
The outer diameter of the tube is 32 – 51 mm.
The tube thickness of the tube is 3 – 7 mm.
The transverse pitch : S1/d = 2 – 3.
The longitudinal pitch :S2/d = 1.6 – 2.5.
The tubes are arranged in multiple parallel sets.
The desired velocity depends on the type of SH and operating steam
pressures.
The outside tube diameter : 32 – 51mm
Tube thickness : 3 – 7mm
S1
S2
76
Reheater ( 270 MW)
Purpose
RE-HEAT the steam (at 350 deg C) from HP TURBINE
to 540 deg C for I.P Turbine.
The Reheater - Single stage – 2 Sections.
Front & rear pendant vertical spaced.
The front section is located between the superheater
platen section and the rear water wall hanger tubes.
The rear section is located between rear wall hanger
tubes and water wall screen.
Reheater
• The pressure drop inside re-heater tubes has an
important adverse effect on the efficiency of turbine.
• Pressure drop through the re-heater should be kept as
low as possible.
• The tube diameter : 42 – 60mm.
• The design is similar to Final (Pendant) super-heater.
CRH to HRH
HRH line
CRH line
DeSH
Reheater
Vertical platen
inlet header
Reheater
vertically
placed rear
outlet header
Reheater
vertical spaced
coil
FRONT REHEATER PANEL
Supports & Suspensions For
Super Heater &
Re Heater
SUPPORTS & SUSPENSIONS FOR SH & RH
1. Vertical Assemblies are suspended from the ceiling.
2. In Pendant assemblies, the Tie Lugs are welded in
between tubes at the top row to transfer the load from
centre to end terminals.
3. The horizontal Super heaters are supported by
Economiser hanger tubes through strap supports.
SUPPORTS & SUSPENSIONS FOR SH & RH
Contd
4.
The pendant coils are suspended by high crown
supports. The high crown plates are welded on either
side of seal band and the load is transferred through
end bar.
5.
The headers will be independently supported from the
ceiling through tie rod assemblies with or without
variable spring hangers as the case may be.
SPACERS FOR SH & RH:
•Spacer are used to maintain pitches along and across
coil assemblies. The type of spacers generally used
are transverse spacers and alignment ties.
•Fluid Cooled Spacers or Mechanical Spacer Bar are
used as transverse spacers.
•Alignment Ties are used to maintain pitch between
tubes in the same assembly.
•Flexible Connector and Alignment Band are used as
alignment ties. Flexible connectors in combination
with fluid cooled spacers are used. Mechanical spacer
bars in combination with alignment band are used.
The spacers are all made of stainless steel.
In pendant SH or RH assemblies the tie lugs are
welded in between tubes at the top row to transfer
the load from centre to end terminals
Economizer
Economiser are feed-water heaters in which the heat from
waste gases is recovered to raise the temperature of feedwater supplied to the boiler.
Economizer
 The economizer preheats the feed water by utilizing the residual heat of the
flue gas.
 It reduces the exhaust gas temperature and saves the fuel.
 Modern power plants use steel-tube-type economizers.
 Design Configuration: divided into several sections : 0.6 – 0.8 m gap
16 April 2013
PMI Revision 00
92
Advantages of Economizer
6oC raise in feed water temperature in economizer
corresponds to a 1% saving in fuel consumption.
220 C reduction in flue gas temperature, increases
boiler efficiency by 1%.
Location and Arrangement




Placed ahead of air-pre heaters in back pass.
Placed below the Low Temp Super-heater.
Heat Transfer in counter-flow arrangement
Horizontal in-line arrangement of tubes (facilitate
complete draining)
 Recirculation valve and Non-return valve incorporated to
ensure recirculation in case of no feed-flow
 Ash hopper placed below, as flue gas takes a turn.
ECONOMIZER TUBES
( Horizontal Inline Arrangement)
ECONOMIZER & LTSH HANGER TUBES
Type of Construction
 Plain Tube : Several banks of tubes with either-in-line or
staggered type formation. Staggered arrangement induces
more turbulence than the in-line arrangement. This gives a
higher rate of heat transfer and requires less surface but at
the expense of higher draught loss.
 Welded Fin-tube : Fin welded design is used for
improving the heat transfer.
Finned Economizers
Materials Specifications for
Boiler Pressure Parts
Economizer System
S.
Description
No.
1.
Economiser
Material
Coils
Headers
SA 210 GrA1
SA 106 Gr C
Design
Temp.
326 °
398 °
Circulating System
S.
Description
No.
Material
Design
Temp.
1.
SA 299
368°
Tubes
SA210 Gr C
398°
Headers
SA 299, SA106
Gr C
370°
2.
Drum
Water
Walls
Roof & Steam Cooled walls
Sl.
Description
No.
1.
2.
Roof
SC walls
Material
Design Temp.
Tubes
SA 213 T11
413 °
Headers
SA106 Gr C
368°
Tubes
Headers
SA210 Gr C
SA106 Gr C
405°
368° -394 °
Superheater System
Sl.
Description
Material
No.
Coils
T11
LTSH
1.
Headers SA106 Gr. C
SA335 P12
T11, T22,
Coils
Div.
T91
2.
Panel
Headers SA335 P12
3.
Platen
(Final)
T22, T91,
Coils
TP347H,
Headers SA335 P12
SA335 P22
Temp. Range
404° - 477 °
394 ° -452 °
409 ° - 535 °
420 ° - 496 °
478 ° - 600 °
489 ° - 572 °
Reheater System
S.
Description
No.
Coils
1.
RH
Headers
Material
Temp. Range
T11, T22,
351 ° - 589 °
T91, TP347H,
SA106 Gr C
SA335 P22
361 ° - 590 °
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