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FANS IN THERMAL POWER PLANTS:

FANS INTHERMAL POWER PLANTSSHIVAJI CHOUDHURY

Fan:

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

powered through a driver such as a motor, a turbine driver, or a fluid-driver.

Fan Components:

Fan Components

Types of Fans:

Types of Fans A fan is classified by the direction of its flow through the bladed passages of the impeller. A centrifugalfan moves the air perpendicular to the rotational axis of the impeller . an axial fan moves the air parallel to therotational axis of the impeller.

Centrifugal (radial) Fan Blade Types :

Centrifugal (radial) Fan Blade Types

Function of Fans in Boiler:Function of Fans in Boiler Supply air required for combustion Remove products of combustion Deliver fuel to theburners Circulate the gases for better heat transfer

Types of Power Plant Fans:

Types of Power Plant Fans There are four main types of fans used in fossil power plants. Forced draft fans , Induceddraft fans, Primary air fans, Gas-recirculation fans.

Draft Fans:

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

BOILER :

BOILER Platen Super heater Reheater Final Super heater LTSH Economizer Furnace Wind Box Coal Pulverizer F DFan Secondary air duct P A Fan PA duct APH Flue gas duct Coal bunker Coal feeder Boiler drum

Forced Draft Fans:

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

Induced Draft Fans:

Induced Draft Fans Induced draft fans (ID) are placed at the outlet of the boiler system and exhaust all gaseouscombustion products, or flue gas, from the boiler by creating a negative pressure or suction within the furnace. Thesefans handle hot flue gas, they are generally more susceptible to erosion and corrosion even with particulate removalequipment (ESP). If greater wear resistance is necessary, a modified radial, forward-curved, or backward-inclined

blading can be used at the expense of efficiency loss.

Primary air fans:

Primary air fans Primary air fans (PA) are high pressure fans used to supply the air for the transportation of coaldirectly from the pulverizer to the furnace . These fans provide a positive pressure upstream of the coal pulverizerand handle relatively clean air . A PA fan upstream from the pulverizer, or a cold PA fan, pushes the coal/air mixturethrough the pulverizer and is most commonly used. Cold PA fans typically are airfoil centrifugal fans or multi-stageaxial fans similar to FD fans.

Gas Recirculation Fans :

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

PowerPoint Presentation:FD FAN PA FAN PA FAN TO ESP TO ESP APH

PowerPoint Presentation:

ESP ID FAN FLUE GAS FROM APH

Draft System -500 MW:

Draft System -500 MW FD FAN AHP FURNACE SECOND PASS AHP ESP ID FAN FD FAN AHP FURNACESECOND PASS Chimney ESP AHP +156 mmwcl -5 mmwcl -73 mmwcl -221 mmwcl +36 mmwcl

Axial-Flow Fan:

Axial-Flow Fan

Airfoil-Blade Centrifugal Fan :Airfoil-Blade Centrifugal Fan

Damage Mechanisms :

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

Erosion:

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

EFFECT OF BLADE TYPE ON EROSION RESISTANCE AND EFFICIENCY:

EFFECT OF BLADE TYPE ON EROSION RESISTANCE AND EFFICIENCY BLADE TYPE TYPICAL MAX STATIC

EFFICIENCY ( %) TOLERANCE TO EROSIVE ENVIROMEMT RADIAL 70 HIGH RADIAL TIP 80 MEDIUM TO HIGHBACKWARDLY INCLINED SOLID 85 MEDIUM AIRFOIL 90 LOW

Resistant to Erosion:

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

Abrasion-Resistant Impeller :

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

CORROSION:

CORROSION The following list is the most common types of corrosion problems found in boiler power plants.

Erosion corrosion Crevice corrosion Galvanic corrosion Pitting General corrosion (wastage) DifferentialOxygenation Biological corrosion Intergranular corrosion

Vibration:

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

Output Air Flow Control:

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Output Air Flow Control A centrifugal fan utilizing inlet vanes controls the airflow . Most axial fans are operated byvariable pitch axial blades, . A fan that is run with a variable speed motor can adjust the speed to control the outputflow properties .

Inlet Vanes of Centrifugal Fan:

Inlet Vanes of Centrifugal Fan FAN

Variable Airfoil Blading of an Axial-flow Fan :

Variable Airfoil Blading of an Axial-flow Fan

CONDITION MONITORING:

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

STARTUP PROCEDURES OF DRAFT FANS:

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

FANS -500 MW BOILER:

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

FANS -200 MW BOILER:

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

ID FAN under erection-500 MW :

ID FAN under erection-500 MW

Distribution of Aux Power Consumption in a 210 mw Power Plant:

Distribution of Aux Power Consumption in a 210 mw Power Plant FANS

Difference between fan and Compressor :

Difference between fan and Compressor Fans are similar to compressors; the difference is that fans create a flow ofgas whereas compressors increase the pressure of the gas. ASME PTC-11, Performance Test Code for Fans,defines a fan as providing a compression ratio of 1.1 or a density change of 7%. ISO 5801 defines the upper limit offans as a pressure increase of 120 inches Wg (30 kPa).

STANDARDS:

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