explanation shortly about fans in power plants

general knowledge about fans in power plants

1. FANS IN THERMAL POWER
PLANTS
ABDUL REHMAN

2. Fan
o A fan can be considered a mechanical device that
moves a volume of fluid such as air, gas, or vapor
through a pressure driven flow.
o Large capacity fan units typically consist of a bladed,
rotating impeller enclosed in a stationary casing.
o The rotor system causes the motion of the air/gas
and
the casing directs the output
flow.
o The rotor can be powered through a driver such as a
motor, a turbine driver, or a fluid-driver.

3. Fan Components
Inlet Vane Linkage
Upper Bearing
Housing ~
I
Sleeves<
Bearing Concrete
1+--Bearing Pedestals
~C:'§~--Bearing Soleplate
Pier
Inlet Flanges

4. Types of Fans
o A fan is classified by the
direction of its flow
through the bladed
passages of the impeller.
o A centrifugal fan
moves the air
perpendicular to the
rotational axis of the
impeller .
o an ax ial fan moves the
air parallel to the
rotational axis of the
impeller.

5. Centrifugal (radial) Fan Blade Types
A. 4
Backwardly
Inclined
Solid Blade
A.
4
Radial Tip
A. •
Backwardly
Inclined
Airfoil
A. •
Radial

6. Function of Fans in Boiler
o Supply air required for combustion
o Remove products of combustion
o Deliver fuel to the burners
o Circulate the gases for better heat
transfer

7. Types of Power Plant Fans
There are four main types of fans used
in fossi I power pia nts.
o Forced draft fans,
o Induced draft fans,
o Primary air fans,
o Gas-recirculation fans.

8. Draft Fans
o Draft fans are generally responsible
for maintaining the flow of gases
through the boiler.
o A balanced draft system uses both a
forced
draft fan at the
inlet of the
system and an induced draft fan at the
outlet of the boiler system.

9. BOILER
0000
~~~ ::Tl Reheater
11!.--f-1~ Final Super
heater
LTSH
Economizer C
1
b nk
oa u er
•
er

10. Forced Draft Fans
o Forced draft fans (FD) supply the air
necessary for fuel combustion by pushing the
air through the combustion air supply system
and
into the furnace.
o These fans are
typically the most efficient
fans in
the power
plant because they have
the cleanest operating environment .
o Typically, these fans are centrifugal fans
utilizing radial airfoil blading or variable pitch
axial fans.

11. Induced Draft Fans
o Induced draft fans (ID) are placed at the outlet of the
boiler system and exhaust all gaseous combustion
products, or flue gas, from the boiler by creating a
negative pressure or suction within the furnace.
o These fans handle hot flue gas, they are generally
more susceptible to erosion and corrosion even with
particulate removal equipment (ESP).
o If greater wear resistance is necessary, a modified
radial, forward-curved, or backward-inclined blading
can be used at the expense of efficiency loss.

12. Primary air fans
o Primary air fans (PA) are high pressure fans used to
supply the air for the transportation of coal directly from
the pulverizer to the furnace .
o These fans provide a positive pressure upstream of
the coal pulverizer and handle relatively clean air .
o A PA fan upstream from the pulverizer, or a "cold" PA
fan, pushes the coal/air mixture through the
pulverizer and is most commonly usecf.
o Cold PA fans typically are airfoil centrifugal fans or
multi-stage axial fans similar to FD fans.

13. Gas Recirculation Fans
o Gas-recirculation fans are used to control steam
temperature, furnace heat absorption, and slagging of
heating surfaces.
o These fans extract gas from the economizer outlet
and the pre-heater inlet and then discharge the gas
either to the bottom of the furnace for steam
temperature control or to various locations in the
furnace.
o The duty cycle of a gas recirculation fan is very
stringent due to heavy dust loads and extreme
temperature excursions.
o Straight or modified radials or forward curved,
backwardly inclined centrifugal wheels are appropriate
for gas-recirculation fans.

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16. Draft System -500 MW
AHP
+156
mmwcl
SECOND
FURNAGE PASS
-5
mmwd
AHP ESP
-73
mmwcl
AHP
ESP
-221 +36
mmwcl mmwcl
Chimney
FD AH p URNACE SECO~N'r\D--1......_
FAN __ ~------------------ ~PA~S~S----~---- ~~~ ------4- ~-----------

17. Axial-Flow Fan
Gas Flow Inlet Box
Rotor Assembly
Removable Upper Fan Housing
Diffuser
Gas Flow
Removable Variable-Pi tch
Rotating Blades
Main Bearing Assembly
Stationary Blades
Blatele Pitch Control Mechanism

18. Airfoil-Blade Centrifugal Fan

19. Damage Mechanisms
Most common damage mechanisms
associated
with power plant fans
failure are :
o Erosion,
o
Corrosion,
o Vibration
which are responsible
for serious and
costly maintenance.

20. Erosion
o One of the most common damage
mechanisms associated with power plant
fan failure is erosion, which is
responsible for serious and costly
maintenance.
o The rate of erosion depends on
suspended particles I fly ash, in the flue
gas.

21. EFFECT OF BLADE TYPE ON EROSION
RESISTANCE AND EFFICIENCY
BLADE TYPE
RADIAL
RADIAL
TIP
BACKWARDLY INCLINED
SOLID
AIRFOIL
TYPICAL MAX STATIC TOLERANCE TO
EFFICIENCY (
0
/o)
70
80
85
90
EROSIVE
ENVIROMEMT
HIGH
MEDIUM TO
HIGH
MEDIUM
LOW

22. Resistant to Erosion
o The rate of erosion experienced by fans used in
harsh applications is often controlled by the use
of repairable liners, replaceable liners, or
renewable coatings.
o Reducing fan speed and selecting a fan blade
type that is more resistant to erosion will slow
down the abrasive wall thinning experienced by
fan unit surface.

23. Abrasion-Resistant Impeller
o Fans that operate
in flue gas, such as
induced
draft fans
(IDF) for coal-fired boilers, are
required
to be
resistant to
abrasion by ash in
the
flue gas.

24. CORROSION
o The following list is the most common types of
corrosion problems found in boiler power
plants.
o • Erosion corrosion
o • Crevice corrosion
o • Galvanic corrosion
o • Pitting
o • General corrosion (wastage)
o • Differential Oxygenation
o • Biological corrosion
o • Intergranular corrosion

25. Vibration
o Possible reasons as to why vibration
occurs
in fan units are
listed below.
o • Improper balancing
o • Loose components
o • Worn/ damaged/cracking of fan parts
o • Improper Lubrication
o • Improper clearance of moving parts.
o • Excitation of a resonant frequency
o • Corrosion, erosion, high/low cycle fatigue effects
o • Misalignment or bent shaft
o • Improperly designed or deteriorated foundations
o • Build-up of material on the rotor

26. Output Air Flow Control
o A centrifugal fan utilizing inlet vanes
controls the airflow I
o Most axial fans are operated by
variable pitch axia I blades, I
o A fan that is run with a variable speed
motor can adjust the speed to control
the output flow properties I

27. Inlet Vanes of Centrifugal Fan
Air Flow
'----Inlet Vanes
FAN

28. Variable Airfoil Blading of an
Axial-flow Fan
,.
- f •
-

29. m
-
Fan Laws
Flow :c Sp t>~d Prt>ssurt> x (SpHd )l Powt>r x (SoHdY
100% 100'14 100'101
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0
SPEED
1 00'*>
.....
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SPEED
100%
Ql N1
SP1 ( N1 )
2
kW1 ~(N1J -~-
Q2 N2
-=-
SP2 N2 kW2 N2
J aryiug the RPJ1 by 10% Re tludug the RP.\1 ~1' 10% Reduciug the RP.\1 ~~ ·
decreases or iucreases air decrease~ tile static 10'• decrease<> tile poll'er
delil'tr)' by 10 "~ . presmre by 19°, aud a 11 requiremmt by 17"~ a11d
in
creaJe in
RP.\1 ~ · 10% a11 i11crease iu RP.\1 by
iucrea.ses the static I o•, increases tile poll'er
loressure br 11 ~ •. requiremmt br .H%.
Where Q -flow. SP-Stattc Pressw-e. kW -Power and N-s~ed (RP~
(BEE India, 2004)
9
CUNEP2006

30. CONDITION MONITORING
o Condition monitoring is the use of advanced
technologies to determine equipment
condition and, potentially, predict failure.
o It includes technologies such as the
following:
o • Vibration measurement and analysis
o • Oil analysis
o • Nondestructive examination (NDE)
o • Infrared thermography
o • Motor current analysis

31. STARTUP PROCEDURES OF DRAFT FANS
o The startup procedures, in addition
to the controls and interlocks,
should follow the requirements of
NFPA 85.

32. FANS -500 MW BOILER
FAN
lYPE
NO per boiler
FLOW ,M3/S
PRESS,mmwc
TEMP,DEG C
DRIVE
SPEED,RPM
MOTOR ,KW
CONTROL
F D FAN
AXIAL
2
251.6
390
45
MOTOR
980
1225
VARIABLE PITCH
CONTROL
PA FAN
AXIAL
2
184.0
1200
50
MOTOR
1480
2725
VARIABLE PITCH
CONTROL
ID FAN
RADIAL
2
574.6
467
150
MOTOR
580
3950
INLET DAMPER+
VFD

33. FANS -200 MW BOILER
FAN
1YPE
NO per boiler
FLOW ,M3/S
PRESS, mmwcl
TEMP,DEG C
DRIVE
SPEED,RPM
MOTOR KW
F D FAN PA FAN
AXIAL Reaction RADIAL
2 2
105 75
510 1187
so 50
MOTOR MOTOR
1480 1480
750 1250
ID FAN
AXIAL impulse
2
225
356
136
MOTOR
740
1100

34. ID FAN under erection-sao MW

35. Distribution of Aux Power Consumpti on in a
210 mw Power Plant
DISTRIBUTI ON OF AUX. POWER CONSUMPTION
•IOhn
• FOF•n FANS
•PAFAN
• Coal Moll
•BFP
•CWP
•
CEP
PAFM ZI2J
•ESP UST
•SST
• AHP
•CHP
•WTP

36. Difference between fan and
Compressor
o Fans are
similar to compressors; the
difference is that fans create a flow of gas
whereas compressors increase
the pressure
of the gas.
o ASME
PTC-11, "Performance Test Code for
Fans," defines a fan as froviding a
compression
ratio of 1. or a density
change of 7°/o.
o
ISO 5801 defines the uf:1per limit of fans as
a pressure increase
of
20 inches Wg (30
kPa).

37. STANDARDS
o 1. NFPA 85, Boiler and Combustion
System Hazard Code.
o 2. AMCA 803, Site Performance Test
Standard.
o 3. AMCA 202, Fan Application Manual.
o 4. AMCA 203, Field Performance
Measurements.
D ASME PTC 11