ABHISHEK T MENDHE
Ramdeobaba College of Engineering & Management ,NAGPUR
FANS AND BLOWERS
• Fans and blowers provide air for ventilation and industrial
• Fans generate a pressure to move air (or gases) against a
resistance caused by ducts, dampers, or other components in a
• Large capacity fan units typically consist of a bladed rotating
impeller enclosed in a stationary casing.
• The rotor system causes the motion of the air/gas and the casing
directs the air flow.
•The fan rotor receives energy from a rotating shaft and transmits
it to the air.
DIFFERENCE BETWEEN FANS,BLOWER
• As per “ASME” Depending on the specific ratio and rise in system
Equipment Specific Ratio Pressure rise
Fan Up to 1.11 1136
Blower 1.11 to 1.20 1136 to 2066
Compressor More than 1.20 More than 2066
TYPES OF FANS AND BLOWERS
2)Axial Flow Fan:-
Air enters and leaves the fan with no change in direction.
1)Centrifugal Flow Fan:-
Airflow changes direction twice - once when entering and
second when leaving .
• Depending on types of flow, fans are categorized as,
• Major blower types are,
Similar to centrifugal fan but can achieve high pressure.
2)Positive Displacement Blower:-
Provides constant volume of air.
A. Centrifugal Fans:-
• Rotating impeller increases air velocity.
• Air speed is converted to pressure.
• This fans produces High Pressure which
ranges from 550 mmwc to 1400 mmwc.
• Efficiency varies from 60-83 %.
• Used for Dirty air stream condition
and material handling application.
It categorized by blade shapes,
1.Radial 2.Forward curved 3.Backward curved
Fig. Centrifugal Fans
1.Radial Blade Fan
• Usually contain 6 to 16 impeller blades.
• High static pressures up to 1400 mm WC
can achieve with low flow rates.
• low/medium airflow rates only.
• Efficiency ranges from 69% - 75%.
• Simple in Design.
• Suitable for handling heavily contaminated
airstreams like dust laden, saw dust etc .
• These are widely used in corrosive and high-
Fig. Radial Blade Fans
2.Forward curved Blade Fan
• Usually contain 24 to 64 impeller blades.
• Produces low pressure up to 5 in-wg
• large airflow rates against relatively
low static pressure.
• Efficiency ranges from 60% - 65%.
• Lighter in construction and less expensive
• Suitable for clean air environment as,
blades easily accumulated dirt
• Well suited for low pressure HVAC such as
packaged air conditioning equipment
• Not constructed for high pressures or
Fig. Forward curved blade
3.Backward Curved Blade Fan
• Usually contain 6 to 16 impeller blades.
• Produces high pressure (40 in wg)with high
• More efficient than forward curved blade
efficiency ranges from 79% - 83%.
• High maintenance cost.
• Only recommended for clean air stream
containing no condensable fumes or vapours
• A common application is forced-draft . Fig. Backward Curved Blade Fan
B. Axial Fans
• Air is pressurized by blades which creating aerodynamic lift.
• Typically provide large air volumes at relatively low pressures
pressure ranges from 250mmwc to 500mmwc.
• Efficiency varies from 45% - 85%.
• Popular with industry as compact, low cost and
• Axial fans are frequently used in exhaust
applications where airborne particulate
size is small, such as dust streams, smoke,
It categorized as,
1.Propellor Axial Fan
2.Tube Axial Fan
3.Vane Axial Fan Fig. Axial Fan
1.Propeller Axial Fan
• Have two or more blades that generate very high
• Produces low static pressure (20-50)mmwc
• Very low efficiencies of approximately 50 % .
• Light weight and inexpensive.
• Noise levels are higher than tube axial and
vane axial fan.
• Air circulation within a space or ventilation
through a wall without attached ductwork.
• Ideally used for make up or replacement air supply.
Fig. Propeller Axial Fan
2.Tube Axial Fans
• Tube axial fans have a wheel inside a cylindrical housing which
improves the air flow efficiency.
• Numbers of blades range from 4 to 8 .
• Capable of developing a more useful
static pressure range(250-400 mmWC ).
• Efficient up to 65 %.
• Frequently used in exhaust applications.
• Also used in some industrial applications
such as drying ovens, paint spray. Fig. Tube Axial Fan
3.Vane Axial Fans
• Vane-axial fans are similar to tube-axial fans
with guide vanes that improves efficiency by
directing the flow.
• Typically have 5 to 20 aerofoil type blades
with a large hub diameter.
• such fans generally used for pressure (up to
• They can achieve efficiencies up to 85%.
• Typically used in high-pressure applications,
such as induced draft service for a boiler
exhaust. Fig. Vane Axial Fan
•Blowers can achieve much higher pressures than fans, as high as
•The impeller is typically gear-driven and rotates as fast as 15,000
•They are also used to produce negative pressures for industrial
1. Centrifugal blowers
• Typically operate against pressures of 0.35 to 0.70 Kg/cm2.
• they are most often used in applications that are not prone to
2. Positive-displacement blowers
• They are especially suitable for applications prone to clogging,
since they can produce enough pressure up to 1.25 Kg/cm2 - to
blow clogged materials free.
Functions of Fans in Power Plant
• Supply air for complete combustion of the fuel in the furnace.
• For evacuation of the gaseous combustion products continuously
from the boiler furnace.
• To create Draft for required flow of air or combustion gas .
• Supply air for cooling of equipments working in hot zones.
• Supply air for sealing of gates , feeder and mills bearing .
• Circulate the gases for better heat transfer.
In Power Plant ,Air Used for Combustion is divided into two major
parts which are,
Portion of total air sent through mills to the furnace. This
air dries the pulverized coal and transport it to the furnace for
2. Secondary Air:-
Large portion of total air sent to furnace for supply of
necessary oxygen for the combustion. hence, increases the
Types of Power Plant Fans
There are three main types of Fans used in Power Plant which are,
1. Forced Draft Fans
2. Primary Air Fans
3. Induced Draft Fans
1.Forced Draft Fan
• They installed at inlet to the air preheater.
• Forced Draft Fans (FD) supply the air necessary for fuel combustion
by pushing the air through combustion air supply system and into
• Forced Draft fan produces pressure up to 510 mmwc at volume flow
rates 20 to100 m3/s and operates against temperature 25 to 50°C for
200 MW plant.
• These fans are typically the most efficient fans in the power plant
because they have the cleanest operating environment.
• For good reliability, 2 FD fan operating in parallel are used.
• Centrifugal Fans with Backward curved blades are normally used.
Forced Draft Fan Cycle
FD FAN A
FD FAN A
2.Primary Air Fan
• Supply high pressure primary air through APH needed to dry &
transport coal directly from the pulveriser to the furnace.
• PA fan operate at temperature up to 70 °C and produces pressure
up to 1187mmwc at 75 m3/s volume flow rate for 200MW plant
• Power requirement of PA fan is higher.
• Centrifugal fan with backward curved blades are used.
Primary Air Fan Cycle
APH A PA FAN
3.Induced Draft Fan
• Located in between the ESP and foot of the stack.
• Sucks the combustion gases out of the furnace and discharge them
into the stack .
• Handles large volume hot dust/ash laden flue gases which are
exhaust from furnace.
• High power requirement than FD fan ,it require 1100 KW motor for
200MW plant .
• Induced-draft fans produces volume flow rate up to 225 m3/s at
inlet temperatures between 130 and 150°C and pressure ranges
from 356 mmwc for 200MW plant.
• Centrifugal fan with Radial blades are used.
Induced Draft Fan Cycle
APH A ESP A ID
IDESP BAPH B
Fan Performance Evaluation
Done by System resistance curve(System curve) and Fan curves.
System resistance curve:-
•The system resistance is the sum of static pressure losses in the
•The system resistance is a
function of the configuration of
ducts, pickups, elbows and the
pressure drops across equipment
• It is used to determine what
volume the fan will produce.
•The system resistance varies with
the square of the volume of air
Fig. System curve
• The fan curve is a performance curve for the particular fan under a
specific set of conditions.
• The fan curve is a graphical representation of a number of inter-
• Fan curves are use to define the operating point.
• Understanding this relationship is essential to designing, operating a
fan system and it is the key for optimum selection of fan.
It consist of three curves,
1. SP vs Air Flow rate.
2. BHP vs Air Flow rate.
3. Static efficiency vs Air Flow rate.
• The intersection of the system curve(SC) and the static pressure curve
defines the operating point.
• When the system resistance changes, the operating point also change
• Once the operating point is fixed, the power required could be found
from fan curve, similarly we can
find the efficiency of fan.
• In this figure,
For fan speed N1.
the fan’s actual operating point
at, flow (Q1) against press (P1) .
The fans operate under a predictable set of laws concerning speed,
power and pressure.
1. Technology Menu on Energy Efficiency (NPC)
2. SADC Industrial Energy Management Project
3. Energy Audit Reports of NPC
4. Text book on “Power plant engineering” by P. K. Nag.