Fans And Blowers.pptx

FANS AND BLOWERS CHAPTER 5 ME LAB 2 JONNAH MAE AL-AG MAYLYN TABUGOC

FANS • •

• • •

Fans and blowers provide air for ventilation and industrial process requirements. Fans generate a pressure to move air (or gases) against a resistance caused by ducts, dampers, or other components in a fan system. 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.

FAN TYPES: Centrifugal Fan Axial Fan

CENTRIFUGAL FAN • Used a rotating impeller to move the air stream. • Airflow changes direction twice - once when entering

and second when leaving .

• 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.

APPLICATIONS:  Because of the high pressure they create,

centrifugal fans are ideal for high pressure applications such as drying and air conditioning systems. As all of their moving parts are enclosed and they also have particulate reduction properties that makes them ideal for use in air pollution and filtration systems.

Categorized by blade shapes: Radial Forward curved Backward inclined

1.Radial Blade Fan Characteristics: • A fan with flat blades

• Usually contain 6 to 16 impeller blades. • High static pressures up to 1400 mm WC • Low/medium airflow rates only. • Efficiency ranges from 69% - 75%. • Simple in Design. • Have large running clearance

Applications: • Suitable for handling heavily contaminated

airstreams like dust laden, saw dust etc . • These are widely used in corrosive and hightemperature environments.

2.Forward curved Blade Fan Characteristics:

• Have forward-curved blades. • Usually contain 24 to 64 impeller blades. • Produces low pressure up to 5 in-wg • Efficiency ranges from 60% - 65%. • Lighter in construction and less expensive • Provide a low noise level and relatively small air flow with a high increase in static pressure.

Applications:

• 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 harsh service.

3.Backward Curved Blade Fan Characteristics: • With blades that tilt away from the direction of

rotation: flat, curved, and airfoil • Usually contain 6 to 16 impeller blades. • Produces high pressure (40 in wg) with high

flow rates.

• More efficient than forward curved blade efficiency ranges from 79% - 83%. • High maintenance cost.

Applications:

• Only recommended for clean air stream containing no condensable fumes or vapours • A common application is forced-draft .

Axial Fans • Move the air stream along the axis of the fan. • Air is pressurized by blades which creating

aerodynamic lift. • Typically provide large air volumes at relatively low pressure ranges from 250mmwc to 500mmwc. • Efficiency varies from 45% - 85%. • Popular with industry as compact, low cost and light weight. • Axial fans are frequently used in exhaust applications where airborne particulate size is small, such as dust streams, smoke, and steam.

APPLICATIONS:  Because of the low-pressure high-volume

airflows they create, axial fans are best suited for general purpose applications. For example, they excel at moving air from one place to another, cooling confined spaces such as computers, and cooling larger spaces such as work spaces.

Categories: • Propeller Axial Fan • • Tube Axial Fan • Vane Axial Fan

1.Propeller

Axial Fan

Characteristics:

• Have two or more blades that generate very high airflow volumes • 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.

Applications:

• Air circulation within a space or ventilation through a wall without attached ductwork. • Ideally used for make up or replacement air supply.

2.Tube Axial Fans Characteristics:

• A Propeller fan placed inside a cylinder. • 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 %. 

Applications:

• Frequently used in exhaust applications. • Also used in some industrial applications such as drying ovens, paint spray.

3.Vane Axial Fans Characteristics:

• 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 500 mmwc). • They can achieve efficiencies up to 85%.

Applications:

• Typically used in high-pressure applications, such as induced draft service for a boiler exhaust.

FAN LAWS

FAN CURVES • Fan characteristics can be represented in form of fan curve(s). • Includes fan volume, system static pressure, fan speed, and brake horsepower . • 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- related parameters. • 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.

FUNCTIONS OF FANS IN A 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.

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

FORCE DRAFT FANS • •

•

• • •

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 the furnace. 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.

PRIMARY AIR FANS • 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.

INDUCED DRAFT FANS •

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 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

temperatures between 130 and 150°C and pressure ranges mmwc for 200MW plant.

• Centrifugal fan with Radial blades are used.

exhaust

inlet from 356

REPAIR OF FANS Inspection

• Visual inspection • Alignment check • Checks of belts and couplings • Measurement of axial clearances • Disassembly plus visual inspection of parts • Dimensional measurements

EXECUTION OF WORKS • Cleaning & steaming • Sandblasting • Preparation of technical drawings for machining by • • • • • •

in-house engineering team Machining of parts (bearing housings, rotors, …) Balancing of rotating parts Coating of rotating parts Assembly Coating of exterior Alignment (in case of motor-fan combination)

BLOWERS Blowers

can achieve much higher pressures than fans, as high as 1.20 Kg/cm2. The impeller is typically gear-driven and rotates as fast as 15,000 rpm. They are also used to produce negative pressures for industrial vacuum systems.

TYPES OF BLOWERS Centrifugal blower Positive displacement

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 clogging .  Gear-driven impeller that accelerates air  Single and multi-stage blowers  Airflow drops if system pressure rises

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.

 Rotors trap air and push it through housing  Constant air volume regardless of system

pressure

 Turn slower than centrifugal blowers  Belt-driven for speed changes

COMPARISON BETWEEN FANS AND BLOWERS FANS

BLOWERS

DEFINITION

A fan circulates air around an entire room, or space.

A blower circulates the air only on the specific or pointed area.

PRESSURE

It is uses less pressure to produce large amounts of gas.

It is uses high pressure to produce large amounts of gas.

PRESSURE RATIO

The ratio of pressure is below 1.1.

The ratio of pressure is from 1.1 to 1.2.

AIR AREA

It provides air in the complete area.

It provides air in a specific location or point.

As per American Society of Mechanical Engineers (ASME) the specific ratio – the ratio of the discharge pressure to the suction pressure – is used for defining the fans and blowers.

ENERGY EFFICIENCY OPPORTUNITIES 1. Choose the right fan 2. Reduce the system resistance 3. Operate close to BEP 4. Maintain fans regularly 5. Control the fan air flow

1. CHOOSE THE RIGHT FAN  Considerations for fan selection Noise Rotational speed Air stream characteristics Temperature range Variations in operating conditions Space constraints and system layout Purchase/operating costs and operating life

 “Systems approach” most important!  Avoid buying oversized fans Do not operate at Best Efficiency Point Risk of unstable operation Excess flow energy High airflow noise Stress on fan and system

2. REDUCE THE SYSTEM RESISTANCE  Increased system resistance

reduces fan efficiency  Check periodically  Check after system modifications  Reduce where possible

3. OPERATE CLOSE TO BEP Best Efficiency Point = maximum

efficiency Normally close to rated fan capacity Deviation from BEP results in

inefficiency and energy loss

4. MAINTAIN FANS REGULARLY Periodic inspection of all system

components Bearing lubrication and replacement Belt tightening and replacement Motor repair or replacement Fan cleaning

5. CONTROL THE FAN AIRFLOW • • • • • • • • •

Pulley change Dampers Inlet guide vanes Variable pitch fans Variable speed drives (VSD) Multiple speed drive Disc throttle Operating fans in parallel Operating fans in series

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