Boiler Fans

Presented bySARHAK PATNAIKGET 2011

Definition of Fan

Fan is a rotary machine, which maintain acontinuous flow of air/gas at a pressureratio not normally exceeding 1:1.11

Difference among Fans, Blowers And Compressors

Content

Definition of DraughtPurposeClassification

Definition of FanTypes and purpose of fansWorking Principle of fansClassification of fansFan Controlling Devices

Definition of Draught System

Draught defines a differential pressure between atmosphere & through out the fuel, air and flue gas path in the system. There should be sufficient arrangement to create necessary draft. The system is consisted of feeders, pulverizers, fans (PA, FD, ID, Seal Air, Scanner Air etc.), burners, Wind Box, SADC, boiler fire side, APH, ESP, and Chimney.

To ensure sufficient, efficient and safe flow of fuel, air and products of combustion through the steam generator.

To maintain the standards of other combustion control parameters such as Oxygen in Flue Gas, Carbon in Ash, Sox & NOx in Flue Gas, Flue Gas Velocity, Flue Gas Exhaust Temperature etc.

Purpose of Draught System

Classification

Natural Draught

Induced Draught

Forced Draught

Balanced Draught

Purpose of Fans

To develop moderate pressure of the Air or gas in order to transport it from one place to another at desired Parameters.

Centrifugal Fans Single SuctionDouble Suction

Impeller may have Radial, Forward or Backward curved blades on the basis of application

Axial Fans Single StageDouble Stage

Axial fans are further classified as Propeller, Tube axial and Vane axial

Classification of Fans

Types of Centrifugal Fans

Types of Axial Fans

Types of Boiler Fans

PA Fans FD Fans ID FansSeal Air fans Scanner Air Fans Igniter Air Fans

FD Fan is required to provide air for ensure proper flow of products of combustion and to also to ensure complete combustion of coal or oil inside the furnace. This air is termed as “Secondary Air” because it is supplied after the primary air.

Forced Draught Fan

Application :Provide air for combustion of coal. Number per boiler : Two Type : Axial fan, Single stage Medium handled : Air Orientation : Vertical suction and Horizontal delivery Regulation : Blade pitch control

Specification Axial Fan Used as FD Fan:

SUCTION HOOD

DIFFUSER

UPPER CASING OF IMPELLER

BOTTOM CASING OF IMPELLER

MOTOR

FD FAN

Technical specifications

FD FAN:

• Manufacturer Shanghai Blower Works Co. Ltd.• Fan Type FAF-28-14-1• Adjustment method Blade adjustable• Total pressure boost(Pa) 4523• Flow rate(m3/s) 341.30• Temperature of 32

incoming air(deg C)• Rotating speed(r/min) 990•  Model YKK560-4• Motor rating power(KW) 1850• Voltage(KV) 3.3

Induced Draught Fan

ID Fan is required to extract the product of combustion called flue gas form the furnace and discharge the same to the chimney, which in turn to the atmosphere.

Application : For extraction of Flue gases. Number per boiler : Two Type : Axial fan, single stage Medium handled : Flue gas Orientation : Axially suction delivery Regulation : Blade pitch control

Specification Centrifugal Fan Used as ID Fan:

Suction hood

Motor

Impeller

ID FAN

ID FAN:

• Manufacturer Shanghai Blower Works Co. Ltd.• Fan Type 3AF-37.5-22.4-1• Adjustment method Blade adjustable• Total pressure boost(Pa) 6136• Flow rate(m3/s) 656.6• Temperature of 152.8

incoming air(deg C)• Rotating speed(r/min) 745•  Model YKK560-4• Motor rating power(KW) 4950• Voltage(KV) 3.3

Primary Air Fan

PA Fan is required to provide air to dry the coal in mill and transport it from mill to furnace. This air is termed as “ Primary Air”.Specification Axial Fan Used as PA Fan:

Application : For Coal transportation and drying Number per boiler : Two Type : Axial fan , Double stage Medium handled : Air Orientation : Vertical suction & Horizontal delivery Regulation : Blade pitch and damper control

DIFFUSER

PA FANDOUBLE STAGE

PA FAN :

• Manufacturer Shanghai Blower Works Co. Ltd.• Fan Type PAF-21.1-12.5-2• Adjustment method Blade adjustable• Total pressure boost(Pa) 13139• Flow rate(m3/s) 20460 m3 /s

• Temperature of

incoming air(deg C) 50• Rotating speed(r/min) 1490•  Model YKK560-4• Motor rating power(KW) 3300• Voltage(KV) 3.3

Seal Air Fan

Seal air fan boost up the cold primary air pressure to cater the need of sealing the bearings of the rotating component of pulverizers. For example,three rollers and upper bearing of the bowl ofeach ‘Bowl & Roller Mill’ are supplied with seal airto protect its abrasion by coal particles.

Scanner Air Fan

These fan takes suction either from FD Fan discharge duct or from atmosphere and always supply its discharge air to the ‘Flame Scanners’for their cooling and cleaning.

Fans convert kinetic energy of a prime mover partially into pressure head and remaining into velocity head (kinetic energy), which in turn also converted into pressure head by the diffuser and thus build up the pressure of air or gas being displaced.

Working Principle of Fans

Fan Controlling Devices

Damper Control Inlet Guide Vane Control Pitch Control Speed Control

Damper Control

Fan flow and pressure can be changed by varying the cross section at the suction or discharge side of the fan. This type of control has been provided on the suction ducts having rectangular cross section, which is achieved by damper regulating mechanism powered by different types of motors.

Inlet Guide Vane Control

This type of control has been provided on the suction ducts having circular cross section. In principle, it same as that of damper control but reported to more effective.

Blade Pitch Control

Variation in blade pitch vary the flow and pressure of the air/gas being handled.

Blade pitch is controlled by means of Servomotor.

Control oil is used for the operation of Servomotor.

Speed Control

Flow and pressure can be controlled by varying the speed of the fan by using either a infinitely variable speed hydraulic couplingby using a variable frequency electric motor. Many ID Fans in the thermal power plant have been provided with infinitely variable speed hydraulic coupling.

Sectional view of hydraulic coupling

LUBE OIL CIRCUIT

FD FAN

PA FAN

ID FAN

OPERATION OVERVIEW

1 Oil level -- alarm-fill reservoir2 Lube oil flow >3lt /min -- alarm3 Low oil pressure -- alarm-start aux. pump4 Pump switch-over

event-- alarm-determine cause

of switch over

5 Pump #1 running -- No action-into only6 Pump #2 running -- No action-into only7 Heater on -- No action-into only8 Heater off -- No action-into only9 Bearing temperature

high > 900c-- alarm-check oil cooling

10 Bearing temperature high > 1200c

-- trip fan-leave oil running for 10 min.

11 Fan vibration >4mm /s -- alarm-analyze problem12 Fan vibration >11mm /s -- trip fan

13 Fan operating in stall -- alarm-reduce fan output by reducing blade pitch (closing blades)

14 Pump #1 or #2 running and reservoir temperature< 300C(FD,PA), <250C(ID)

-- turn on heaters

15 Reservoir temperature > 400C(FD,PA), <35OC(ID)

-- shut off heaters

PERFORMANCE CURVE

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