FANS_Power_Plants_thermal_NTPC_mouda.ppt

above document contains different types of fans used in turbine of power plants

1. Fans in Power Stations
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2. ESOE 505221 Fluid Mechanics 2
Power Plant Schematic
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3. ESOE 505221 Fluid Mechanics 3
Need of Fans
BoilerCombustion Air
Flue Gases
• Air needed for combustion
• Flue are needed to be evacuated
• Losses due to flow need to be overcome
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4. ESOE 505221 Fluid Mechanics 4
Fan Operation
Fans cause pressure increase by:
Centrifugal force created by rotation of the
column of air trapped between two blades
Kinetic energy is supplied to the air through
the impeller
Total pressure = velocity head + static
pressure
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5. ESOE 505221 Fluid Mechanics 5
Selection Considerations
Quantity of air to be moved per unit time
Estimated system resistance and
expected variations
Amount of noise permitted
Space available for fan
Economic implications
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6. ESOE 505221 Fluid Mechanics 6
SYSTEM RESISTANCE
When a gas is forced through a duct
system, a loss in pressure occurs. This
loss in pressure is called system
resistance.
System resistance is composed of two
components:
Friction losses and
Dynamic losses.
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7. ESOE 505221 Fluid Mechanics 7
Variation of System Resistance with Flow
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8. ESOE 505221 Fluid Mechanics 8
Draft Losses
Total losses

p
Percent Boiler Rating
Furnace, SH & RH Losses
Economizer Losses
Ducts & dampers losses
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9. ESOE 505221 Fluid Mechanics 9
Fan Classification
Designated as dynamic pumps
Centrifugal
Further classification by entry and exit of fluid/gas through
impeller
4 aerodynamic classifications:
Axial flow
Radial flow : referred to as “centrifugal fan”
Cross flow
Mixed flow
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10. ESOE 505221 Fluid Mechanics 10
Centrifugal Fans
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11. ESOE 505221 Fluid Mechanics 11
Components of Centrifugal Fan
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12. ESOE 505221 Fluid Mechanics 12
Centrifugal Fan Operation
Fans cause a pressure increase through two methods
– Centrifugal force is created by the rotation of the column of air
trapped between two blades.
– Kinetic energy is supplied to the air through the impeller
– Total pressure = velocity head + static pressure
Blades are airfoil-type, backward-curved, forwardcurved, or radial
(straight)
– Airfoil-types are complex and expensive but very efficient;
they’re used for large systems where the cost is justified.
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13. ESOE 505221 Fluid Mechanics 13
Wheel Blade Types and Rotation
Applications where the fans will handle clean air or clean gas, the highly
efficient backward inclined airfoils are the preferred design. In an
application where the fan is subject to erosion due to heavy dust
loading, a straight radial type fan provides erosion resistance, but at the
expense of efficiency.
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14. ESOE 505221 Fluid Mechanics 14
Backward-Curved Fan Blades
Have a self-limiting power characteristic, so
if sized correctly the motor won’t overheat
or burn out even if conditions change.
High efficiency and stable operation make
this blade type popular.
Choose the operating point to be just to the
right of the peak pressure flow rate to
achieve both high efficiency and a stable
flow rate.
This type of fan operates stably because
the pressure difference provided by the fan
drops if the flow rate goes up. If the
opposite were true, increased an increased
flow rate would cause increase fan power,
which is unstable.
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15. ESOE 505221 Fluid Mechanics 15
Section of a Centrifugal Fan
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16. ESOE 505221 Fluid Mechanics 16
Radial Blades
Similar performance to a
backward-curved except that it’s
easier to overheat because as flow
rate goes up, so does power.
Easier to maintain, so it’s used in
dirty situations (easy to clean
straight blades, and they don’t
collect as much)
Blades are stronger than other
types.
Used primarily in industrial systems
in a corrosive or erosive
environment, such as material
handling of airborne particulate or
where high static pressure is
required.
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17. ESOE 505221 Fluid Mechanics 17
Airfoil-blade centrifugal fan
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18. ESOE 505221 Fluid Mechanics 18
Forward-Curved Blades
Have problems with instability
because a specified pressure
rise can fit three different flow
rates.
Burnout can also be a
problem because fan power
increases with flow rate.
Quieter than other fans; used
for most furnace blowers
Usually limited to clean
service applications
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19. ESOE 505221 Fluid Mechanics 19
Axial Flow Fans
Common types: propeller, tubeaxial,
vaneaxial
Tubeaxial: impeller is inside a tube
to guide airflow and improve
performance
Vaneaxial: like a tubeaxial except
vanes either up or downstream of
the impeller are used to reduce swirl
and improve performance
Used to deliver large flow rates but
small increase in pressure
Examples include fans used for
ventilation without ductwork, mobile
room fans, and fans used to cool
computers
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20. ESOE 505221 Fluid Mechanics 20
Two-Stage Axial Fan Assembly
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21. ESOE 505221 Fluid Mechanics 21
Axial-flow fan for induced-draft service
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22. ESOE 505221 Fluid Mechanics 22
System Pressure Effects
Fan curves are typically given in terms of total pressure vs.
volumetric flow rate
A typical fan running at a fixed speed can provide a greater
volumetric flow rate for systems with smaller total pressure drops (if
we’re to the right of the peak in the fan curve).
Total pressure loss=static pressure loss+dynamic pressure loss
If exit and inlet area of a duct are about the same, the dynamic
pressure loss (or gain) may be minimal.
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23. ESOE 505221 Fluid Mechanics 23
Effect of Blade Type on Erosion
Resistance and Efficiency
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24. ESOE 505221 Fluid Mechanics 24
Fan Curves
Manufacturer will provide a fan curve for each fan
The fan curves predict the pressure-flow rate
performance of each fan.
Choose a fan that gives you the volumetric flow rate you
need for your system pressure drop.
Choose a fan that has its peak efficiency at or near your
operating point.
Sometimes will provide data in a table rather than in a
graph.
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25. ESOE 505221 Fluid Mechanics 25
Centrifugal Fan Performance Curve.
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26. ESOE 505221 Fluid Mechanics 26
Fan Laws
Flow ? Speed Pressure ? (Speed)
2
Power ? (Speed)
3



1 1
2 2
Q N
Q N

2
1 1
2 2
SP N
SP N
 

 
 

3
1 1
2 2
kW N
kW N
 

 
 

Varying the RPM by 10%
decreases or increases air
delivery by 10%.
Varying the RPM by 10%
decreases or increases the
static pressure by 19%.
Varying the RPM by 10%
decreases or increases the
power requirement by
27%.
Where Q – flow, SP – Static Pressure, kW – Power and N – speed (RPM)
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27. ESOE 505221 Fluid Mechanics 27
Fan Laws
Law 1 – relates to effect of changing size, speed, or density on
volume flow, pressure, and power level
Law 2 – relates to effect of changing size, pressure, or density on
volume flow rate, speed, and power
Law 3 – shows effect of changing size, volume flow, or density on
speed, pressure, and power
The laws only apply to aerodynamically similar fans at the same
point of rating on the performance curve.
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28. ESOE 505221 Fluid Mechanics 28
Fan Applications in Power Plant
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29. ESOE 505221 Fluid Mechanics 29
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Scheme of Air and Gas Path

30. ESOE 505221 Fluid Mechanics 30
FD
Fan
Duct APH DuctFurnace DuctAPH
Back
pass
ESP
ID
Fan
Chimney
D
u
c
t
D
u
c
t
Draught System Pressure Variation
Pressure drop calculation in air & gas path and its
comparison with design value.
Assessment of ID and FD fan power as a function of
furnace pressure.
Assessment of effective kinetic rate coefficient as a
function of furnace pressure.
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31. ESOE 505221 Fluid Mechanics 31
Pressure Variation
Furnace Pressure At Various Points in Boiler
-300
-250
-200
-150
-100
-50
0
50
100
150
200
250
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Points in Boiler
F
u
r
n
a
c
e
P
r
e
s
s
u
r
e
1
FD Fan Inlet
2
FD Fan Outlet
3
Airheater Inlet
4
Airheater Outlet
5
Windbox Pressure
6Furnace
7
Superheater Platen Inlet
8
Reheater Inlet
9LTSH Inlet
10
Economiser Inlet
11
Airheater Inlet
12
E.P. Inlet
13
I.D. Fan Inlet
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I.D. Fan Outlet
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32. ESOE 505221 Fluid Mechanics 32
Induced Draft Fans
Move the combustion flue gas through the boiler, air heater, and
precipitator or the baghouse, scrubber, and chimney to the
atmosphere
typically consume approximately 2% of the gross electrical output.
ID fans have the largest design margins of any major equipment in a
fossil-fueled power plant. typically 15% on flow, 30% on head, and
15°C on temperature.
Large margins are intended to allow for the following
Uncertainty in determining system requirements
Allowance for wear
Operating flexibility
Allowance for pluggage and leakage
Air infiltration
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33. ESOE 505221 Fluid Mechanics 33
Gas to be handled by ID fan
Theoretical air for combustion
Excess air required at burner
Infiltration
Leakage air-to-gas through the air heater
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34. ESOE 505221 Fluid Mechanics 34
Forced Draft & PA Fans
FD fans provide combustion air for boilers
In pulverized coal-fired boilers, approximately one-third
of the combustion air is PA that is used to transport the
pulverized coal to the burners.
The PA fan application is similar to the FD fan;
The FD fans for a coal-fired plant consume
approximately 0.7% of the gross electrical output.
The design margins on FD fans are typically smaller than
the margins on ID fans but still larger than on other major
equipment. Margins of 15% on flow and 30% on head at
the maximum expected ambient temperature are
common.
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35. ESOE 505221 Fluid Mechanics 35
Two-Stage Axial Fan Impeller
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36. ESOE 505221 Fluid Mechanics 36
Balanced Draft
The draft to be provided by the fan is determined
by losses through the following boiler
components:
Furnace
Boiler and Super-heater
Economizer
Air heater
Precipitator or Bag-house
Ductwork
Flue gas desulfurization system (scrubber)
Stack
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37. ESOE 505221 Fluid Mechanics 37
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Other Fans in The System
Ignitor Air Fan: Provide combustion air to the ignitors.
Take suction air from the atmosphere and supplies air
to the ignitor wind box.
Scanner Air Fan: Supplies cooling air to flame
scanners. Normally there are two fans taking suction
from FD Fan discharge duct.
Mill Seal air fan: Seal air fans provide air for the
sealing of Mill bearing. Suction is from cold Primary air
and pressure is boosted up to maintain the differential
pressure

38. ESOE 505221 Fluid Mechanics 38
Fan Controls
Inlet Vanes
Inlet vanes introduce a swirl to the flow entering a fan.
The major disadvantage of inlet vanes is poor efficiency at lower loads.
Inlet vanes are subject to erosion if ash concentrations are high
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39. ESOE 505221 Fluid Mechanics 39
Inlet Dampers
Inlet dampers control air flow by introducing a
swirl in the flow and pressure drop.
Inlet dampers have a low initial cost, are simple,
and are not as prone to erosion as inlet vanes.
inlet vanes and can be located completely
outside the duct.
The biggest disadvantage of inlet dampers is
their low efficiency at low loads.
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40. ESOE 505221 Fluid Mechanics 40
Two-Speed Motors
The fan selection with two-speed motors is
the same as with inlet vane control or inlet
damper control. The fans for two-speed
motors are often sized so that the fan can
operate on low speed at full load and at
normal operating temperature. The high
speed provides the design margin.
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41. ESOE 505221 Fluid Mechanics 41
Fluid Drive
Fluid drive is a method of varying the fan speed for flow control.
The fan selection is essentially the same as the inlet damper
alternative, except that a fluid drive is located between the motor
and the fan to control the fan speed.
Inlet dampers are typically used in addition to the fluid drive to
increase the speed of response to avoid furnace pressure
excursions during transients
The use of the dampers for control during normal operation is typical
but can be eliminated in most installations.
Using speed control with the dampers full open can result in a
significant power savings
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42. ESOE 505221 Fluid Mechanics 42
Hydraulic Coupling
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43. ESOE 505221 Fluid Mechanics 43
Variable-Speed Motors
Variable-speed motors are directly connected to the fan.
The speed of the motor is continuously variable from approximately
10% up to the full speed.
Synchronous or induction motors can be used with variable
frequency drives, and the frequency of the power to the motor is
controlled by an electronic system.
The incoming ac power is converted to adjustable voltage dc power
by a thyristor.
The adjustable dc power is connected to an inverter, which
converts it to an adjustable ac power output.
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44. ESOE 505221 Fluid Mechanics 44
Variable-Pitch Blades (For Axial Fans )
Axial fans can be controlled by varying the blade pitch or speed or
by using variable inlet vanes.
Either varying the blade pitch or using variable inlet vanes controls
the flow by operating on the same principle as do variable inlet
vanes on a centrifugal fan.
Varying the blade pitch is more efficient than using variable inlet
vanes because the flow resistance of the vanes is absent.
Variable-pitch blades can provide efficiency as high as that of
variable-speed control over most of the load range for a lower initial
cost.
Variable-pitch blades are the most common method of control;
variable inlet vanes are used occasionally, and variable-speed
control is rare.
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45. ESOE 505221 Fluid Mechanics 45
Variable-Pitch Axial Fan Components
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46. ESOE 505221 Fluid Mechanics 46
Bearings
Both centrifugal and axial fans can use either ball
or roller bearings; however, ball and roller
bearings are more common on axial fans. Sliding
contact bearings are more common on centrifugal
fans.
Ball and roller bearings consist of four major
components:
• Outer race
• Inner race
• Rolling elements
• Spacer for the rolling elements
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47. ESOE 505221 Fluid Mechanics 47
Sleeve Bearing Components
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48. ESOE 505221 Fluid Mechanics 48
Lubrication Systems
Static lubrication in which each bearing has a fixed supply of oil in
their sumps is very common.
This method is simple and very cost-effective; however, it relies on
operator vigilance to detect low oil levels or poor oil quality.
Use of temperature sensors to provide remote warning to the control
room operators, in case of a hot bearing, offers added protection for
this method.
A gear pump attached to the input shaft of the driver is a second
method used to provide lube oil to fan and motor bearings.
A third method, the use of fluid drives to supply oil to the bearings,
is also used on some fans.
A fourth method involves the use of a dedicated circulating lube oil
system.
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49. ESOE 505221 Fluid Mechanics 49
THANKS
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