Air Preheaters

7/27/2019 Air Preheaters

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AIR PREHEATERS

LJUNGSTROM REGENERATIVE AIR PREHEATERS

INTRODUCTION:

A high level of eciency of steam generators depends on how

eectively the input energy is recovered for utilization. To recover a

part of the heat energy in the exit ue gases for pre-heating of

combustion air in air heaters located in the outgoing ue gas path is

one such activity aimed at improving the eciency of the boiler. The

advantages of such preheating of air are as under.

. !ot air is used for drying coal as well as transporting pulverized

coal to burner.

". #ven poor $uality fuel can be eciently burn with less unburnt

particles.

%. &ue to hot air admission into the furnace' combustion is more

stable and intensi(ed.

). !igh heat transfer rates are obtained in furnace and faster load

variation is possible.

*. #ciency of boiler increase due to reduction in outgoing ue gas

losses.

TYPES OF AIR HEATERS:

+ased on their operating principle air heaters are broadly

classi(cations'

. ,ecuperative air heaters


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". ,egenerative air heaters

,ecuperative air heaters are of static construction. The heating

medium will be owing on one side and the air in other side of tubes

or plates. Air heaters of this type are further classi(ed as plate type

air heaters and tubular type air heaters.

,egenerative air heaters are of rotating type and the wise

called as rotary air preheaters. The heating medium ows through

closely paced heating elements to raise its temperature and then air

is passed through the same elements to picup heat. Air heaters of this

type are further classi(ed as lungstrom air heaters and rothemunle air

heaters. /n lungstrom type air heaters closely paced heating

elements rotate while in ,0T!#12!3# type air heaters' the elements

are stationary where as the air hoods rotate at about rpm.

SELECTION OF AIR HEATERS:

The following factors are to be considered for selection of air heaters.

. Type of fuel'

". 4uantity of ue gas to air heaters'

%. 4uantity of air from air heaters'

). Available temperature of ue gas at air heater' inlet and desired

temperature of gas at air heater outlet'

*. 5pace re$uirement'

6. &raught loss'

7. &rop in air pressure'


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8. #conomy in construction'

9. #ase of maintenance to ensure surface cleanliness.

ADVANTAGES OF REGENERATIVE AIR HEATERS:

The regenerative air heaters have the following

advantages over recuperative type.

: They occupy less space.

": !eat transfer rate is high

%: ;eight of material used per s$uare meter of heating surface is

les.

): 5urface area for heat insulation becomes less due to the reduced

volume of the air heaters.

*: &raught loss is less.

6: 5ustained high eciency of air heaters during operation

7: #ase of maintenance.

!ence in power station practice regenerative air

preheaters are widely employed. /n tune with this trend two

3ungstrom type air pre heaters are provided for each +oiler in

power station-. The regenerative air preheaters lue gases pass vertically downwards whilst the ow of air is

directed upwards through specially built ducting. ") segments of


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closely spaced corrugated plates are (xed to a rotor and

arranged to revolve at a slow speed inside the casing in the air

heater.

GENERAL DESCRIPTION OF LJUNGSTROM AIR PREHEATERS:

The main components of rotary air heaters are'

: ?asing

": ,otor

%: ,otating gear

): &rive unit

*: 5ealing

6: 3ubrication and cooling system of bearings

7: 5oot blowers

8: ;ater washing system

9: >ire extinguishing system

CASING:

The casing is octangular in shape and is made of welded

carbon steel plates and rolled bars. The body of casing is provided

with stiening ribs and frames. >langes are provided for

accommodating for sealing. The upper and lower bridges of the

casing' which houses the bearings' support the internals.


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The four supporting legs at the bottom of the casing are

secured to the buc stray construction. >langes are provided to

connect the ue gas inlet duct and air outlet duct at the top of the air

heater and to connect the ue gas outlet duct and air inlet duct at the

bottom of the air heater. >our short interconnecting ducts of circular

shape at one end and s$uare shape at the other end' connect the air

heater to the air and gas ducts.

0n the upper side of the air duct' manhole is provided for

changing the heat elements. The upper and lower ends of air and gas

passages are providing with manholes and observing windows.

ROTORS:

The rotor assembly with its vertical shaft is housed inside the

casing. /t is divided in to ") sectors by means of radially located

partition wall plates. ?orrugated heating elements are (xed between

these wall plates. The rotor assembly consists of two sections the top

section of @@ mm height nown as hot side rotor sectorB or hot

end basetsB and the bottom section of )@@ mm height nown as

cold side rotor sectorB or cold end basetsB. /n between these

sections there is a clearance of 6*@mm. The rotor revolves at " ,=1

and the heating basets absorb the heat from the gas and transfer it

to the incoming air.

ROTATING GEAR:


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A slow speed of " rpm for the rotor is obtained through a

pin-toothed wheel mounted on the circumference of the rotor. This

wheel is in mesh with a toothed pinion' which is driven by an electrical

motor through a coupling and reduction gear.

DRIVE UNIT:

There are two drive motors. 0ne is to be normal service and

other serves as stand by. A common reduction gearbox is provided

with clutch arrangements for securing drive transmission from either

one of the motors. The gearbox has a reduction ratio of "C. The drive

gear


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The gas side of air heaters is under vacuum and the airside

is under pressure. !ence prevention of air lea o to the gas duct is to

be ensured at the all points. This is achieved by radial sealing'

circumferencial sealing and axial or shell sealing arrangements. ,adial

and axial seals are of counter weight type and the circumference seal

is of sirt plate type.

LUBRICATION AND COOLING SYSTEM OF BEARINGS:

The vertical rotor shaft has two bearing and is supported by

the bottom bearing. The separate oil pump supplies lubrication oil for

the bearing. Two pumps are provided for this purpose' one to be in

service and the other for being ept as stand by. The lubrication oil

pump is a gear pump driven by a @.@9w motor. /t taes the oil from

the lube oil storage tan and supplies the oil through a (lter and oil

cooler to the bearings. The oil returns bac through two return lines

one from each bearing to the oil tan itself. Auxiliary cooling waters is

used for oil cooler. The lube oil tan is also provided with a vapour

extractor.

SOOT BLOWERS:

To remove the soot and dirt from the heating plates soot

blowers and water spray nozzles are provided in the air heaters. Two

swiveling electric steam soot blowers are installed in each ,A=!' one

operating in the gas-discharging region. 5team is taen is from ,!

inlet header or from auxiliary steam header.


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RAPH WATER-WASHING SYSTEM:

/n spite of soot blowing with steam' some dicult to

dislodge deposits will be still there in ,A=!. 5uch adhering ash

deposits in ,A=! elements cause partial choing in ,A=! indicated by

an increase in dierential pressure across ,A=! such deposits are

removed by water-washing of ,A=!. ;ater washing is an o-load

cleaning operation. /t is to be done while the corresponding /& D >&

fan is stopped.

The water used for water washing is service water. 5ervice

water pressure is boosted up a centrifugal pump located in between

>& fan AD+ of unit %. The discharge from the pump is fed to a bus

from where one tapping for each boiler is taen.

/n each ,A=! there are two water line connections one to

each soot blower. The soot blower nozzle can be used for water

washing. Apart from the above' another water washing tapping is also

provided in each ,A=!. There are number of nozzles in this line which

is (xed to middle frame. The ,A=! is to be continuously rotated at "

rpm itself while water washing.

FIRE FIGHTING SYSTEM:

/n case of any (re in ,A=!' to put out the (re' the number

of water nozzles is provided on top of each ,A=!. Their nozzles are

provided both in airside and gas side of ,A=!. ;ater for (re (ghting is

tapped from (re (ghting waterbus at 7-meter elevation. The (re line


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tapping is divided in to two' one to each ,A=!. #ach line to a ,A=!

again sub-divides into two' one entering the sir side and another gas

side duct of ,A=!.

/n boiler " area & fan "A: there are two (rewater

boaster pumps provided to boost up the (re (ghting water pressure.

This water supply lines are available at higher elevations of boiler to

supply (re (ghting water at locations in higher elevations of boiler in

case of any event utilizes.

RAPH CLEANING SYSTEMS

INTRODUCTION:

Air pre heaters have been in general use for many years for

reclaiming heat from ue gases at lower temperature levels than is

possible with economizers. +y using air pre heaters' much lower gas

temperatures can be achieved with conse$uent improved boiler

eciencies due to the reduction in heat reected to the chimney. 5uch

improved boiler eciency will be achieved only if satisfactory


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performance of air pre heaters is maintained continuously. The

satisfactory and successful performance of air pre heaters not only

depends on adopting due care in selecting air pre heaters' but also

eeping air pre heaters heat transfer areas clean. 5oot blowing with

steam is widely adopted to ensure cleanliness of air heater elements.

This helps to maintaining a low draught loss across air heater and

optimizes >& and /& fans loading. 5winging lance type soot blowers are

employed in ,egenerative air pre heaters of T=5-//E stage F/ steam

generators. /f and when steam soot blowing proves to be ineective

indicated by a large pressure drop across air pre heaters' water

washing of ,A=! is to be resorted to.

RAPH SOOT BLOWERS:

#ach ,A=! is provided with two numbers of soot blowers. The

blowers are located in the ue gas duct. 0ne above the ,A=! and the

other below the ,A=!. 5team at 6-bar pressure is the medium used

for blowing and the source is either from re heater inlet header or

auxiliary steam header.

The ,A=! soot blower consists of steam blowing as well as water

ushing lances (xed to a common frame. The water lance is above and

steam lance is below' the water lance protruding a little bit farther than

the steam lance. A moor through reduction gear drives the lances and

the rotary movement of the motor is converted to a slow swinging

action of ,A=! lances. The ,A=! lances are arranged to swing


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horizontally through *@G thus covering the ,A=! elements radially. This

coupled with the rotary movement of the ,A=! ensures cleaning of all

,A=! elements in one cycle of operation. The driving gear' steam and

water line connections and the stung boxes are located in the outside

of the plate wall of the 3ungstorm air pre heater. The pipes of ushing

water and steam are connected to the stung box housing by means

of anged unctions.

The lances are arranged such that they can swing by about *@G

in ** minutes thereby cleaning all the ,A=! elements while the ,A=!

in rotates. The steam blowing nozzles will be used during normal

operation while the water ushing nozzles are used for cleaning ,A=!

elements when ,A=! fouling is high.

RAPH BLOWER DRIVE:

The drive motor is connected through a coupling to a double

worm gear. The output shaft of the double worm gear is connected

through a coupling to a single worm gear. A lever mechanism

connected to the outlet shaft of the latter gear transforms the rotation

so that the lance will do a swinging through a soot blowing cycle.

1otor C %HI )*vI . J;I 9)@ rpm

&ouble worm gear C /nput speed 9)@ rpm

0ut put speed o.989)

rpm


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Kear ratio C9*@

5ingle worm gear C /nput speed @.989) rpm

0ut put speed o.@8% rpm

Kear ratio C*)

5winging speed of the soot blower C @.@8% rev.

5winging time for one swing C ** minutes

5winging angle C *@G

OPERATION OF RAPH SOOT BLOWERS:

The ,A=! soot blowing is to be carried out at suitable intervals

so as to avoid excess fouling of ,A=! elements indicated by an

increase in pressure drop. The normal pressure drop across ,A=! will

be about @@ to "@ mm wcl in the gas side and about "@ to "* mm

wcl in the airside. /f the pressure drop exceeds by about %@ to )@ mm

wcl from the above value on the gas side' ,A=! steam soot blowers

should be operated. ;henever there is only oil (ring for more than an

hour' ,A=! soot blowing should be carried out.

The ,A=! soot blowing should be done with super heated steam

with a super heat of at least "@ to %@ Gc. #nsuring that can minimize

the fouling problems'

a: The average cold end temperature is maintained at @@Gc.

b: Lormal 5?A=! level is maintained.

c: ,A=! soot blowers arm movement is proper.


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PREPAROTORY WORKS:

The following preparatory wors are to be done before operating

,A=! soot blowers.

. /t is to be checed whether all the gas dampers in the ue gas

way up to chimney are opened. The particular air pre heater and

the /& fan should be in service.

". The blowers should be visually being checed.

%. The hand operated valves in the drain lines of ,A=! steam lines

are to be opened.

). 5upply availability to ,A=! soot blower drive motor and the

motors of the valves in the system is to be ensured.

*. 5team supply from ,! inlet header' or auxiliary steam header is

to be ensured.

6. /n case steam is taen fro ,! inlet header' the drain M-!->-5 66

is to be opened and by opening valves "98'"99' the line is to be

charged and warmed up to valve *85 66 should be

closed. The pressure reducer valve %66 in the ,! steam line will

now open to maintain a pressure of 6 sc in the system.

8. After checing the pressure' the valve *8 is to be opened and

steam can be admitted to ,A=! soot blower lines. Jeeping the


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,A=! steam drains on both sides open until the temperature

rises to about "@@Gc should warm up the lines.

9. /f steam is taen from auxiliary steam header' valve *79 is to be

opened and the lines are to be warmed up by eeping open the

drains on both sides. 56)AD6)+:.

@. After warming up of the lines ,A=! soot blower line' the

drains M!>5 6)A D6)+ is to be closed and the system pressure is

to be checed. or the operation of ,A=! blower' steam releaseB is necessary.

5cheme preparation to obtain steam releaseB can be carried out

either by automatic programmed or completely manually.

/n the manual mode with auxiliary steam' the following

se$uence of operations should be carried out.


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. 5elect ,A=! manual mode by pressing ,A=! 1AL2A3 push

button.

". 0pen the ,A=! steam drain valves left and right 5 6) A

D6) +:.

%. 0pen the auxiliary steam-isolating valve .5 "8 by pressing the open

push button can operate the ,A=! blower. >irst operate the

bottom blower in the left side.

7. After running for the re$uired time of operation >

push button.

8. 5imilarly the next blower


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@. After completing the operation of all the four blowers the

isolating valve *79 should be closed and the drain valves

5 6) A D6)+: should be opened.

MANUAL OPERATION WITH CRH STEAM:

/n the manual mode with ?,! steam' the following se$uence of

operations should be carried out.

. 5elect ,A=! manual mode by pressing ,A=! 1AL2A3 push

button.

". 0pen the cold re heat drain valve M.!.>.5 66.

%. 0pen the hand operated valve "98.

). 0pen the cold re heat line steam isolating valve "99.

*. After the temperature release is obtained in ?,! system


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. After completing the operation of all the four blowers the

isolating valve *8 should be closed and the drain valves

5 6) A D6)+: should be opened.

". ?lose the ?,3 steam isolating valve "99.

%. 0pen the ?,3 drain valve M.!.>.5 66.

NOTE:

. The running blower cannot be stopped unless the blower valve is

closed fully.

". &uring the blower operation if the temperature release left or

right goes o' the valve closes and then the drive switches o.

>O lamps are not glowing.

6. The release lamp A5T or ?,! will be 0L even if the temperature

release on one side


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7. /n manual mode any number of blowers can be put into

operation. !owever it is preferable to operate only one blower at

a time.

PARTIALLY AUTOMATIC OPERATION OF RAPH BLOWERS

PARTIALLY AUTOMATIC OPERATION WITH AUXILIARY STEAM.

. 5elect ,A=! manual mode.

". =re select auxiliary steam by pressing pre select push button of

auxiliary steam.

%. 5witch on the (lling programmed by pressing A2P/3/A,Q 5T#A1

>/33/LK =,0K,A11#B 0L push button.

>rom this moment onwards' the valves concerned cannot be operated

manually. The following se$uence of operations taes place

automatically.

a: ?,! isolating valve


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). Low switch on the drive of a bottom blower and then open the

corresponding valve.

*. After running for the re$uired time of operation' close the valve

and switch o the drive.

6. =roceed in the same manner for the remaining blowers.

7. After completing the operation of all four blowers switch o the

(lling programmed by pressing the A2P/3/A,Q 5T#A1 >/33/LK

=,0K,A11#B 0>> push button. The following se$uence of

operations taes place.

a: Auxiliary steam isolating valve


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a: ?,! drain valve .5 66: opens.


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d: ?,3 drain valve M.!.>.5 66 opens.

NOTE:

a: ?,! pressure setting " sc.

b: Temperature setting "@@Gc

;hen there is a temperature decrease on right or left side' the

annunciation ,#3#A5# AE+E>A23T appears. The blower running on that

side switches o.

operated.: =ost drain taes place in the side on which there was a fault.


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*: Auxiliary steam (lling programmed switches on automatically

and the following se$uence taes place automatically.

a: ,A=! steam drain valves .5 6)A D6) +: open.

b: ,A=! steam isolating valve .5 "8 A opens.

f: After the running time


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i: ;hen the temperature on +-side has sun below "@@ Gc' an

automatic drainage taes place. The right side drain valve

M.!.>.5 6)+ opens. This drain valve closes after the

temperature release is attained.

: ;ith temperature release and pressure release available

,A=! blower + switches on and its valve .5 "8 +:

opens. After the running time is over' the valve closes and

the blower switches o.

: After the waiting time is over' blower +" switches on and

its valve .5 "8+": opens. After the running time is

over' the valve closes and the blower switches o.

l: Auxiliary steam (lling programmed switches o. The

following se$uence of operations taes place.

. Auxiliary steam isolating valve *79 closes.

". ,A=! steam drain valves M.!.>.5 6)AD6)+ open.

%. After this NA2T0 =,0K,A11# ,2LO lamp goes o.

AUTOMATIC OPERATION WITH COLD RE HEAT STEAM:

. 5elect ,A=! auto mode by pressing A2T0 push button.

". =re select ?,! steam (lling programmed.


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%. 5tart the auto programmed by pressing NA2T0 5TA,TO push

button. A2T0 =,0K ,2L lamp glows. The following se$uence of

operations taes place automatically.

a: ?,3 drain valve M.!.>.5 66 opens.

b: After ?,3 drain valve is opened' ?,3 isolating valve "99

opens. /f there is no pressure release within speci(ed time'

the alarm L0 ?,3 =,#552,# appears.

c: After the temperature release is attained' the ?,3 drain

valve closes.

/f the temperature release is not attained within the

speci(ed time' the alarm ,#3#A5# AQB appears. /f the

temperature release is not attained after a further speci(ed

time' the alarm N5T#A1 =,0K ,2LL/LK T/1#O fault

appears.

d: After the drain valve M.!.>.5 66 is closed' the ,A=! steam

drain valves .5 6)A D6)+: open.


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temperature release is attained' the right side drain valve

closes.

;hen the both temperature and pressure release are

attained' ?,! steam release lamp glows.

Note: /f any alarm appears' it is to be acnowledged so

that further processing of the se$uence proceeds.

g: The blowers are put into operation automatically one by

one in the order A' A"' +' and +" as already described

under A2T01AT/? 0=#,AT/0L 0> +30;#,5

;/T!A2P/3/A,Q 5T#A1 NeOto NO

h: After the operation of the blower +"' ?,! steam (lling

programmed switches o. The following se$uence of

operations taes place.

a. ?,! isolating valve


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after the valve closes automatically and the +,#AJ lamp

becomes steady. /n order to identify which blower has been

interrupted' the drive 0>> lamp for the interrupted blower

ashes rapidly until the automatic programmed is started

again with auto programmed 5TA,T =25! +2TT0L. After the

restart' blower operation continues for the remaining time.

": The programmed is put into N+,#AJO state by an alarmed

fault. The drive switches o and the drive o lamp ashes

rapidly' NA2T0 =,0K ,2LO lamp goes o and the N+,#AJO

lamp glows steady after the valve is closed.

%: The automatic programmed can be fully interrupted with the

brea push button. A2T0 =,0K ,2L lamp goes o and A2T0

=,0K 0> lamp glows. The drive switches o after the valve

closing' ?,! release lamp goes o. The ?,3 isolating valve

.5 6)A76)+ open. The ?,3

isolating valve "99 closes after the ?,3 drain valve opens.

): /f during the running time of a blower. Temperature decrease

on one side for example on right side occursI N,#3#A5# +

>A23TO alarm appears. ,A=! blower switches o. The

corresponding valve closes. 5team release is present on the

other side. &rive o lamp ashes rapidly. Accept the alarm.

Low a post drain is initiated automatically. The right side drain

opens. 0nce the temperature release is attained' the drain


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valve closes automatically. Low re starting of the programmed

is possible by pressing the 5TA,T push button.

*: A pressure decrease during the auto programmed results in

alarmOs =,#552,# &,0=O. The blower running at this time

switches o. The drive o lamp ashes. A2T0 =,0K ,2L

lamp goes o. +,#AJ lamp glows steady after the valve is

closed. ?,! steam release lamp goes o. 0nce the pressure is

attained' the steam release lamp glows. Auto programmed

can be started again. The se$uence will continue and the

stopped blower will run for the remaining time.

6: /f steam soot blowing operation with ?,! steam is running'

?,3 isolating valve "99 and ?,3 drain valve M.!.>.5 66 will not

get aected when ,A=! auto programmed is over or when

+,#AJ button is pressed.

7: /f local operation is selected when ,A=! automatic

programmed is running' the running drive will be o after the

valve closes automatically. The +,#AJ lamp will icer and

after the drive is o' the lamp becomes steady. The automatic

programmed will come to a stop. =ressing the 5TA,T push

button after local operation is cancelled can re start the

programmed.

8: The automatic programmed start is prevented if there is a

fault on any ,A=! drive or blower valve at the time of start.


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NOTE FOR RAPH DRIVES:

: The running drive will stop immediately on pressing the local 0>>

push button or on changing the local emergency switch to /

position irrespective of whether the operation is carried out in

local or manual or auto mode.

": /n auto mode' the drive cannot be switched on or o with 0L or

0>> push buttons at the control panel.

%: 0n giving the drive 0L command manually or locally or

automatically' if the 0L feed bac from 1?? is not received

within seconds' alarm ,#M#,T/M# 5/KLA3 appears. ?ommand will

be reset and the fault lamp in the drive will icer.

): /f the drive gets overloaded' #3#?T,/? >A23T alarm appears and

the drive will be 0>> and the fault lamp of the drive will icer.

The alarm has to be accepted and reset in the 1?? module.

*: To operate from the local' local operation is to be selected with

ey switch in the control panel and the local emergency switch

should be ept in N@O position and the local 0L push button

should be pressed.

NOTE FOR VALVES:

: 0n giving the open or close command' if the valve stem does not

leave the end position' alarm 3/1/T 5;/T?! will appear.


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": /f both the open and close limit switches have acted


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%: &uring shut down' inspection is to be carried out to chec

whether cleaning of plates is uniform.

): /f the drive stops during operation due to tightness of the stung

boxes' then steam is to be isolated and stung boxes are to be

loosened.

*: /f the soot blower does not stop' after the scheduled ** minutes'

the timing device to be checed.

ANNUNCIATIONS:

;hen any one of the following annunciations appears' accept the

alarm. The alarm will get cancelled.

! RELEASE DELAY FAULT

This fault appears when ,A=! left or right side temperature

drops' but does not come bac within 6@ seconds after the

respective drain valve is opened.

"! RELEASE FAULT A

/f during operation of ,A=! blowers' T!# T#1=#,AT2,# ,#3#A5#

0L 3#>T side is 0>>'


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/f during operation of ,A=! blowers' the ,A=! steam


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FD AND FANS

FORCED DRAUGHT AND INDUCED DRAUGHT FANS

INDRODUCTION:

The volumetric machines' which impart energy on air or gas' are

fans' blowers and compressors. Those devices developing a pressure

ratio


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THE AXIAL FLOW FANS IN TPS II:

The forced draught fans and induced draught fans for T=5//' stage

/ boilers were manufacturing and supplied by mEs uhnle' opp D

ausch' west Kermany


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the motor. The suction chamber is provided with anges for mounting

the shaft protecting tube and the coupling guard. The suction chamber

is the foundation through the directly transmitted to the foundation

through the supporting feet. 1oreover the inlet duct is of N3O shape and

also converged to fan impeller housing so that it can act as an inector.

IMPELLER HOUSING:

The casing is horizontally split to provide easy inspection and

maintenance for the rotor. An inspection door is provided assembling

and dismantling of blades without removal of impeller casing pro(led

hollow stiness are provided for routing oil pipe' cable for

instrumentation ect. The casing is supported on foundation through

support feet. The sliding supports at the feet of the inlet duct and of

impeller housing can slide free from clearances of the foundation. The

hub of the inlet housing can slide free from clearances of the

foundation. The hub of the inlet housing' core if the fan housing and of

the guide wheel housing' the pitch control mechanism in the diuser

core and the shaft protecting tube are insulated within to protect the

main bearings' pitch control mechanism ect. >rom high temperature

gases.

MAIN BEARINGS:

The rotor is supported by cylindrical roller bearings. An angular

contact ball bearing assembled along with cylindrical roller bearings on

the drive side absorbs axial thrust. The mono bloc bearing housing is


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bolted to the beating supports in the fan housing assembly. These

bearings are lubricated and cooled by a circulating oil lubricating

system. The shaft passages in the bearing housing are sealed o by

radial sealing rings with a labyrinth seal. An oil splash ring is provided

inside.

The centrifugal forces of the rotor blades and the forces released

by the pitch control are absorbed in antifriction bearings. >or this

purpose' the blade shafts are placed in the combined radial and axial

antifriction bearings' which are sealed o on both sides. Temperature

transmitters and vibration pic-ups are provided in the bearing

housing.

ROTOR WITH ADJUSTABLE BLADES:

%*%*%*%*%*ain shaft is a forged piece with a tapered end for

accommodating hub disc. 0ne end of fan shaft is connected to the

intermediate shaft and the other endI the impeller is mounted in an

overhung position. The hub has "% blade assemblies' which are (xed'

on its periphery. #ach blade assembly consists of a blade' blade shaft'

blade shaft bearing and a craning lever. #ach blade assembly is

rotated freely on its shaft bearing. All the blades assemblies are

connected to a slide pad


36/84

;hen slide pad moves horizontally' than this horizontal movement is

converted into rotary movement of blades simultaneously.

PITCH CONTROL UNIT:

The pitch control system comprises of a hydraulic servomotor

and an external actuator connected to hydraulic servomotor. The

hydraulic servomotor consists of a cylinder assembly and piston

assembly. The cylinder assembly' which houses piston assembly' is

mounted on the fan impeller hub. ;henever fan rotates' the cylinder

assembly also rotates.

The piston assembly consists of a control rod' a control slide on a

piston integrated with slide pad. The control rod is of stepped shaft

with three drilled holes in its axis. 0ut of three holes' own to supply oil'

other is to return the oil and the third is to collect leaage oil. This

control rod is ept on bearings' which are housed inside the control

slide so that it can slide inside the control slide freely. This control rod

can be actuated axially from outside through suitable mechanical

linages by an #lectrical actuator


37/84

OPERATION OF PITCH CONTROL UNIT:

The hydraulic servomotor anged to the impeller hub and

rotating with it adusts the blades during operation. This results in a

closed ux of force between adusting force and oil pressure so that no

forces are released to the outside components bearings' housing'

foundation etc. &uring adustment of blades' the translation movement

of servomotor piston is converted into rotation of blades shaft through

the craning levers in order to enable to set blades at various angles.

The restoring moment of the blades results from the rotating

blades. The oil pressure in the servomotor counters them. ;eights at

the blade shafts partly compensate the restoring moments. The

movement of non-rotating control rod in the control slide to initiate the

blade adustment re$uires only small $uality of forces.

The moment of blades otherwise varying the pitch of the blades

is eected in accordance with follow up principle. ;hen the electric

actuator causes the movement of non-rotating control rod in any

direction horizontally' then movement of the control rod is followed up

by the piston cum control slide and slide pad in same direction

resulting rotation of blades.

?ontrol oil conveyed by the oil system reaches the control rod

through a exible hose at a pressure of @-" ata. ;hen the control

rod is moved towards left axially' the right side control edges admit oil

to the right side of the piston. 5imultaneously control oil in the left


38/84

side chamber


39/84

prevents damages to the fan that may arise when the fan is operated

in the stalling zone.

DIFFUSER:

This is also a fabricated assembly with ribs and anges. /t is

supported on the foundation plates through welded feet. /t consists of

a casing and core. This assembly is isolated from the ducting by

means of exible oints. &oors are provided in the core for inspection

of servomotor' linage assembly and oil pipes etc.

RIGIFLEX COUPLING:

The fan shaft is coupled to motor shaft by rig ex coupling. This

is of an all steel coupling designed for in accuracies in assembly or

during operation lie shaft misalignment thermal expansion' this type

of coupling enables easy alignment during installation. =arts that wear

out are not there and no lubrication is warranted. !ence little

maintenance is needed. 1oreover it is capable of withstanding

temperatures up to "7@S?.

/nduced draught fans handle ash laden ue gases and ash

erosion increases with ue gas velocity. 5o' /.&. >ans are generally run

at a lower speed compare to >.&. >ans and an erosion resistance

material is chosen for /.&. >an blades. 5tresses acting on the /.&. >an

rotor become more with high ash concentration and there is a

possibility of /.&. >an blades being subected to sulphur*ic acid

corrosion. !ence the blade material for these fans should have the


40/84

property to resist corrosion as well as erosion and the material chosen

is Lodular /ron KKK )@ or Klobular graphitic cast iron' the corrosion

resistance of which is higher than that of steel.

1oreover' this is more easily cast able than steel and mould

(lling properties are decisively better. &ensity of this material is lower

than that of steel' which results in the rotor being subected to lower

loads. This factor contributes to increased life of blade bearings' which

have to absorb axial thrust resulting from centrifugal forces. /t has also

been found that this material is better than steel for taing up vibration

loads.

LUBRICATION AND CONTROL OIL SYSTEM:

The hydraulic servomotor and the fan bearings are supplied with

oil at dierent pressures from a common oil reservoir. #ach oil system

is provided with two gear pumps of which one will be in services and

the other will be standby. These pumps deliver oil at a pressure of

"@gEcmU". /n the discharge line of each pump' a pressure relief line


41/84

e$uipped with a pressure reservoir' which is mounted in the oil system

before the coolers.

=umped oil is now diverted to oil coolers. Two oil coolers are

provided in each oil systemI one in services and the other reserve.

The oil cooler is of two-pass design in which auxiliary cooling water

ows through tubes and oil ows through shell side. Three way valves

provided at the inlet and outlet of the cooler and operated by a

common lever diverts oil to any of the cooler. Auxiliary cooling water is

tapped from the main bus through a hand operated valve and is

divided into two' and is connected to the cooler with inlet valve. The

outlet from cooler through a valve is taen and two outlets combine to

form a common line. A ow meter cum ow switch with isolation valves

are provided in the outlet line before it oins the auxiliary cooling water

return bus.

0il from cooler is then diverted to thin (lter arrangement. The

(lter has a dierential pressure indicator' which will slowly change

from blue to red with increase in contamination. The display will slowly

change from blue to red with increase in contamination. ?hange over

of (lter can be eected with the help of a lever and the position of the

lever tells which (lter chamber is in use.

After the (lter' the oil ows in two channels' one to the control

oil system and the other for lubrication of bearings. A throttle valve

controls the pressure and oil ow in the lubricating oil system.

3ubricating oil supplied to the bearings returns through a reservoir


42/84

through a return line provided with a sight glass. The control oil

supplied to =?2 returns through a return line and through leaage oil

returns line. Miew glasses are provided in these lines. An ori(ce is

provided in the control oil return line to restrict return oil ow thus

reducing pressure uctuations in the system.

COOLING AIR FANS:

5ince induced draught fans handle hot gases' i.e. at *@ deg.c.

/& fan bearing housing' oil servomotor are exposed to high

temperature. /n order to provide ade$uate cooling' two cooling air fans

are provided for /& fan of the two' one in service and another is in

service and the other stand by draws an atmospheric air and supply

cooling air to bearing housing as well as to oil servo motor unit.

SILENCERS:

Loise is also a form of pollution. ?ontinuous exposure to high

noise levels may aect the hearing ability of operating personnel.

Therefore to muVe the noise levels' silencers are provided in suction

and discharge ducts of >& fan and in discharge duct of the /& fans.

The silencer for the /& fan is constructed in 6 parts each of

width %@@mm standing vertically lie walls. #ach part is constructed

with three pieces. The construction of each part is as under.

0n one side of the partition plate' nine inclined plates are

provided paced with glass wool and covered by a perforated plates

and six inclined plates are provided lie wise in the other side.


43/84

The six parts of the silencer are arranged at 7@8mm pitch'

which allows sucient glass ow. /n the entry point of the silencer a

semi circular plate is provided and a trapezoidal plate is provided in

the exit side. The silencer is positioned in the horizontal portion of the

/& fan discharge duct after the discharge damper. The height and width

of gas duct at this section is )8*@mm to )%*@mm respectively. The

a$uatics property of the glass wool helps to bring down the noise level

to minimum.

The silencer in the suction duct of >& fan is of eight parts and

that in the discharge duct is of four parts. #ach part is of a single piece

in the case of >& fan and the general pattern of construction is similar

in other respects to the silencer provided for /& fan.

OPERATION OF FANS:

The following checs are to be carried out before starting the fan

after shutdown.

PRECHECKS

#nsure that no line clear is pending on the fan and its

concerned e$uipments.

. >an housing and in the suction duct. Ascertain that no tools and

foreign materials have been left around the

". ,elease local latches for fan lubricating oil pumps and for cooling

air fan and main fan.

%. Ascertain the availability of local emergency trip switch.


44/84

). Merify the direction of rotation of fans' pumps' and blowers if any

defect is attended in the cables.

*. ?hec the rigidity of all ducts and tightness of anges.

6. #nsure proper coupling between motor and fan' motor and

pumps.

7. #nsure proper linages between the actuator and pitch control

device.

8. ?hec the availability of auxiliary cooling water' its pressure and

temperature.

9. ?hec the lubricating oil colors in the tan for any contamination.

@. ?hec the 3ub oil tan level and top up if necessary.

. ?harge the oil coolers and eep them ready for operation.

". ?hec the availability of all instruments for its contact

settings and their cold state values.

%. #nsure smooth operation of all dampers from 2?+ and also

at local.

). Avail power supply to fan drive' 3op drive and cooling air

fan drive.

*. 5tart any one cooling air fan and chec for its smooth

operation.

6. 5elect and start one lubricating oil pump.

7. ?hec the lubricating oil pump motor for any spar'

vibration' noise etc.'


45/84

8. ?hec the pump discharge pressure' charge oil in coolers

and (lters.

9. Merify dierential pressure of oil across oil (lters.

"@. ?hec for any oil leaage in the 3ub and control oil pilings.

". ?hecs are to be done for correctness in

"". ,adial blade gap between blades and rotor hub.

"%. Kap between blades and rotor housing.

"). Axial gap between rotor and hub.

"*. Kap between impeller and diuser core.

"6. ?hec the control oil pressure and 3ub oil pressure. /t

should not be " bars and "-".* bars respectively.

STARTING OF FAN:

The start up procedure for >.&. fan and /.&. fan is very similar.

The following is the se$uence that may be followed in starting the fan.

. The discharge damper of the fan


46/84

8. The 3ub oil temperature before and after the cooler is to be

checed.

9. /t should be ascertained that 3ub oil tan level is R

minimum.

@. The damper A&%E" in case of >& fan and K& in

case of /& fan should be opened.

. ,elease the brae manually.

". 5tart the main fan.

%. The damper A& or K&" must be opened within %@

seconds after the fan has reached full speed

). Then the fan blades are to open according to the

re$uirements.

CHECKS DURING OPERATION:

,egular and systematic checs during operation of a fan ensure

smooth and ecient operation of fans.

. ?hec the fan motor and fan for any undue noise' vibration.

". ?hec the oil level in the lubricating oil tan.

%. ?hec the oil system for any oil leaages.

). ?hec the lubricating oil pressure after the pump' after (lters' in

lub and control oil lines.

*. ?hec the lubricating oil temperatures in the reservoir' before

the cooler' after the cooler.

6. ?hec the dierential pressure across oil (lters.


47/84

7. ?hec the oil for any contamination.

8. ;atch the bearing temperature at motor and fans.

9. ?hec for e$ual loading of both the fans.

@. ?hec the fan for loading corresponding to its blade

position.

. ?hec the auxiliary cooling water ow of the oil coolers its

pressure and temperatures.

SHUT DOWN OF FAN:

The fan may be stopped only after gradual unloading. The following

se$uence of operation are to be carried out incase of stopping a fan.

. +ring the fan blades to minimum position gradually in manual

mode.

". 5top the fan.

%. Apply brae when speed drops below *@ rpm.

). ?lose the discharge damper of the fan.

*. 5top the lubrication oil pump when all three bearing temperature

reaches less than *@G?.

6. 5top the cooling air fan when all bearing temperature drops to

less than **G?.

7. /solate auxiliary cooling water supply to oil coolers.

PRECAUTIONS DUERING OPERATION OF AP FANS:

The inlet volume capacity


48/84

loads to increased loads acting upon the blades. /f the inlet volume

capacity is too little' the fed in power may result in non-permissible

heating of the fans. 5o' we should not operate the fans with too little

air or gas intae. /t is also not advisable to operate /.&. fans and >.&.

fans with the twisted blades in closed position.

The fans can be started with closed dampers. +ut continuous

operation with closed dampers is not permissible since with tight close

dampers' the inlet volume capacity becomes zero. !ence after

starting the fan' the dampers should be opened as soon as the fan

attains the operating speed. The rotor blades are to be opened to the

desired extent. 0pening of the dampers should be timed in such a way

that they are opened fully not later than one minute after the fan has

reached full speed.

PARALLEL OPERATION OF THE FANS:

. 5tarting the second fan and paralleling it with the running fan.

". ,unning fan should be brought to manual control.

%. +lade angle of running fan should be chosen in such a way that it

develops a leader pressure that that of the incoming fan.

). /ncoming fans should also be set under manual control.

*. ;ith closed blades' incoming fan should be started.

6. After reaching the full speed' discharge damper of incoming fan

is opened.


49/84

7. +lade angle in both the fans are manually adusted to share the

load.

8. After the above operations' both the fans can be put in automatic

operation.

STOPPING ONE OF THE TWO RUNNING FANS:

.+oth the fans are to be set to manual operation.

".0utgoing fanOs blades are closed gradually.

%.discharge damper of outgoing fan is closed.

).0utgoing fan can then be stopped.

*./f necessary the running fan can be put in automatic operation.

F.D.FAN&S OPERATING CONDITIONS:

0=#,AT/LK =0/LT W

5.L

0

?,/=T/0L 2L/T @*"

*

@@

"*

@* @@ 8@ 6@ 6@

. >anOs in

operation

Los. " " " " " "

". ?apacity 1XEsec *9.7* *@.

6)

"6.

%

9.

@

9*.8

88

78.8

*

6)

%. /nlet =ressure


50/84

,ise bar * " 7 97. &elivery

!eadE/sentropi

c !ead

LmEJg 6@@) *66" %98% %7*7 %)) "79 *)

8. =ower

absorbed at

fan shaft

J; "6* @9@ 6%6 *7@ )@@ %@% )

COMMON OPERATING CONDITIONS:

.1edium !andled -Air

".0perating 5peed -)8@ ,=1

%.,e$uired driving =ower -)@@ J;

).?ontrol 0il =ressure -@ to " bar

*.3ub 0il =ressure -".* +ar

6.3ub 0il Temp at ?ooler outlet -)@ to )*X? anOs in

operation

Los. " " " " " "

". ?apacity 1XEsec "99.7* "8).

9*

"%8.

6

""7.

*

8*.

8

8.

*

%@7

%. /nlet =ressure +ar .968 .97 .978 .98 .998 .99% .97


51/84

lue Kas

".0perating 5peed -99@ ,=1

%.,e$uired driving =ower -7*@ J;

).?ontrol 0il =ressure -@ to " bar

*.3ub 0il =ressure -".* +ar

6.3ub 0il Temp at oil ?ooler inlet -)@ to )*X?


52/84

,02+3#

?A25#

,#=A/,.5ining 0il

=ressure

.>ilter dirty

".3eaages in 0il system

%.Too high oil

temperature

).Lo oil in return line

*.&amaged pressure

?hange 0ver (lter ?lean

(lter

5eal lea areas' replace

sealing elements.

Tighten duct screwings.

?onnect ?ooler. chec

the cooling eect of

coolers.

?hec the oil level in the

reservoir. Add more oil'

chec that there are no

leas.

?hange over and clean

(lter.

?hec the suction eect

of the pump.

#xchange and reset the


53/84

relief valve valve.

>ully open the valveI

slowly tighten the

setting screw until the

original oil pressure has

been set.

". !igh bearing

temperature

oil temperature in

reservoir too high

". 0il too viscous

%.?oolant temperature

extremely high

?onnect cooler

?hange oil' 2se

speci(ed oil

/ncrease cooling water

%. 2n$uiet

running

.2nbalance due to

deposits at rotor

". 2nbalance due to wear

on one side of blades

%. /ncreased bearing

wear.

). Alignment not correct

foundation yields.

,emove deposits

,eplace blades.

?hec bearings' ,eplace

bearings if necessary.

,e-align

). Temporary +earing clearance too ,eplace bearings


54/84

un$uiet ness large

*.Mibrations Ascertain from

fre$uency

?larify whether it is

a case of forced

vibrations or of

resonanceOs with the

foundation.

+lade adustment

ammed.

).connection

between blades and

servomotor

interrupted.

?hec blade bearings

,eplace defective

parts.

&ismount servomotor

chec adusting disc

and lever.

6.2n$uiet running +earing ?learance too

large.

?hec +earings.

,eplace bearings.

?hec motor bearings


55/84

also.7.3ub 0il =ressure Lo ori(ce in the

control oil returns

line.

=ressure reservoir no

longer operable

1ount ori(ce in the

control oil return line.

?hec Litrogen charge'

if re$uired add Litrogen

or replace charge.8.!igh =ressure hoses

at servomotor torn.

.?ontrol slide ams. &ismount control bush

and control slide'

replace them. chec

control bush' control

slide' piston rod with

piston for truth of

rotation.9.0il losses seal at servomotor

defective front seal

inner seal.

5haft seals at main

bearings untight.

3eas in the oil

system.

,eplace seal &ismount

servomotor replace

seal' clean impeller.

1ount spare seals

5eal the lea areas'

tighten

screwings'replace


56/84

sealing rings if

necessary.@.;ater in the oil .0il cooler untight #xamine cooler'replace

cooler tubes or cooler if

necessary.

REGULAR MAINTENANCE OF THE FAN:

. After *@@ operating hours or at least once in every three months.

". ?lean oil (lters and chec oil. /f water is found in the oil' separate

it' (nd its cause and eliminate it. ?hange the oil (lter when

dirtiness is indicated. ?lean the oil (lter part concerned.

%. After "@@@ operating hours or at least once in every six months.

Tightening of all (xing bolts.

). After )@@@ operating hours or at least once in a year. ?hec

entire all charge' re(ll if re$uired.

*. After @@@@ operating hours.

6. ?hec the rotor.

7. ?hec servomotor and blade actuator.

8. ?hec the coupling.

9. ?hec alignment and tolerance' (rst without dismantling the fan.

@. /f there are no problems' continue the operation. 2nder

normal operating conditions' overhaul the fan between @'@@@

and 8'@@@ hours.

Note:


57/84

>ixed intervals for checing the vanes' blades cannot be given'

as their wear mainly depends on the solid matter contents of air or

gas. /t is recommended to chec vanes and blades for wear at

occasional operation standstills.

The two pillow bearings at the adusting shaft are to be regressed

during the inspection by means of a grease gun.

DATA SHEET:

FORCED DRAUGHT FANS:

Lumber of >.& >ans per boiler CTwo

1anufacturer C1E5 Juhnle' Joop and

Jausch' Kermany.

Type CAxial pro(led balding

>an A=

"@E"E"%

A=- Axial

pro(led

-5ingle stage

?apacityC /n parallel operation C *9.7*mXEhr

=ressure developed C 66.8 m bar

?apacityC /n single fan operation C 6).9 mXEsec

=ressure developed fan operation C *9.9 m bar

?apacity >or "@1; load C 9 mXEsec

=ressure developed for "@1; load C ).*7 m bar


58/84

,otor diameter C "@@@ mm

!ub diameter C "8@ mm

Lo. 0f blades on the impeller C "%

+lade material C >orged aluminum alloy

Al 1g 5i > %"

?hemical composition C 1g @.6 to ."W

5i @.7* to .%W

1n @.) to .@W

?r @ to @.%W

>e @.*W

?u @.W

Yn @."W

Ti @.W

DRIVE MOTOR:

=hase C %

Moltage C 6.6 M

0utput C )@@ J;

5peed C )8* rpm

?urrent C )* amps

=ower factor C @.9

#ciency C 9)W

;eight C @.% tonnes.


59/84

FD FAN LUB OIL SYSTEM:

Lumber of reservoirs per fan C 0ne

0il charge C 6%@ liters

0il C Turbine oil

Miscosity C )% to 68 ?5T at )@G?

Lumber of 3ub oil pumps C Two

Type of lub oil pumps C Kear pump L, E@

?apacity C @* liters per minute

&elivery pressure C "@ bar

?ontrol oil pressure C @-" bar

3ubricating oil pressure C "-".* bar

DRIVE MOTOR:

=hase C %

Moltage C )* M

0utput C *.* J;

5peed C ))@ rpm

?urrent C @.) amps

=ower factor C @.8*

#ciency C 86."W

1ounting C Mertical

LUBRICATING OIL PROPERTIES:

3ub oil $uality C 3-T& 68

Miscosity class C /50 MK 68


60/84

Miscosity at "@G? C "@@ mmZEs

Miscosity at )@G? C 6." to 7).8 mmZEs

Miscosity index C 1inimum 9*

=our point C -6G?

>lash point as per ?leveland C 1inimum "@*G?

;ater contents C [ @. gmE@@ ltrs of oil

5olid foreign matter C [@.@* gmE@@ ltrs of oil

&ensity at *G? C @.9 gmEml

INDUCED DRAUGHT FANS:

Lumber of /& >ans per boiler CTwo

1anufacturer C1E5 Juhnle'Joop and

Jausch'

Kermany.

Type CAxial pro(led balding

>an A=

%@E"@E"%

A=- Axial

pro(led

-5ingle stage

?apacityC /n parallel operation C "99.7*mXEsec

=ressure developed C )7.@6 m bar

?apacityC /n single fan operation C %7@ mXEsec


61/84

=ressure developed fan operated C )%.7% m bar

?apacity >or "@1; load C ""7.* mXEsec

=ressure developed for "@1; load C %@.@ m bar

,otor diameter C %@@@ mm

!ub diameter C "@%@ mm

Lo. of blades on the impeller C "%

+lade material C 5pherolitic ?ast /ron


62/84

;eight C .9 tonnes.

ID FAN LUB OIL SYSTEM:

Lumber of reservoirs per fan C 0ne

0il charge C @@@ liters

0il C Turbine oil

Miscosity C )% to 68 ?5T at )@

Lumber of 3ub oil pumps C Two

Type of lub oil pumps C Kear pump L, %E@

?apacity C "@) litres per minute

&elivery pressure C "@ bar

?ontrol oil pressure C @-" bar

3ubricating oil pressure C "-".* bar

3ubricating oil temperature C )@- )*G? < maximum

7@G?:

DRIVE MOTOR:

=hase C %

Moltage C )* M

0utput C J;

5peed C )6@ rpm

?urrent C "@.6 amps

=ower factor C @.8)

#ciency C 89."W


63/84

1ounting C Mertical

COOLING AIR FAN:

Lumber of cooling air fans per /& fan C Two

?apacity C "88@ mXEhr

=ressure developed C "69 gEmZ

DRIVE MOTOR:

=hase C %

Moltage C )* M

0utput C ).7 J;

5peed C "8"@ rpm

?urrent C 8.8 amps

=ower factor C @.9

DRAUGHT SYSTEM

INTRODUCTION:

To have uninterrupted and intensi(ed combustion in the

furnace' enough air is to be supplied and the products of combustion

have to be removing eectively and continuously. The $uantity of air to

be supplied and the amount of products of combustion to be exhausted


64/84

from furnace depend on the steaming rate of the boiler' which in turn

depends on the $uantity of fuel consumed in the boiler per hour.

?reating a pressure dierence' which is called draught' can mae the

movement of air or gas. /f this draught is caused naturally by the

provision of a chimney alone' it is called natural draught and if it is

caused arti(cially with the use of fans' it is now as arti(cial draught.

They should be sucient enough to create the re$uired air or gas ow

and also to over come the frictional losses in the system.

/n a natural draught system' the draught depends on the

height of the chimney and the density dierence between the clod

atmospheric air and the hot ue gas leaving the chimney. ;ith

increased boiler capacities' the draught re$uirements are also more.

!ence' adoption of natural draught for high capacity boilers may not

be feasible' since it would warrant a very high chimney or the need to

eep the temperature of outgoing gases at a very high level. The

former involves increased initial cost and the latter causes increase in

operational losses. !ence' arti(cial draughts are employed in all high

capacity units.

Arti(cial draught systems created with the help of fans may be

classi(ed as forced


65/84

systems are eliminated are draught generators in modern power

stations.

The fans used may be centrifugal fans eciency than the

centrifugal fans though their cost is also more. Among the dierent

power station auxiliaries' fans consume considerable auxiliary power

next to the feed pump. 5aving on auxiliary power consumption can be

eected with the use of ecient fans and careful design of furnace and

heat transfer element to practice' axial ow fans with variable blade

angles are employed to achieve a high eciency at all loads.

FANS:

/n neyveli thermal power station F //' a balanced draught

system is #mployed with two forced draught fans and tow induced

draught fans' both if which are axial ow type.

FORCED DRAUGHT FANS:

#ach forced draught fan is capable of supplying *'7*'@@mcube

air per hour at a pressure of 66.8 millibar


66/84

"@ F peripheral diameter in decimeter

" F hub diameter in decimeter

"% F number of blades

INDUCED DRAUGHT FANS:

The induced draught fans are of A=/ F %@E"@-"% type

and are capable of discharging at the rate of

@'79'@@metercubeEhour.


67/84

tube' air ows in a counter ow pattern and gets heater up' before it

reaches ,A=. The 5?A=! is designed to heat air from *.6 G to %9.) G

at @@W 1.?.,. And to 8@ G at %@W 1.?.,.


68/84

Kas ow before ,A=!

@'@"'76@metercubeE!r

Kas ow after ,A=!

@'*7'8@metercubeE!r

Air pressure before ,A=! %@." millibar

Air pressure after ,A=! ".* milli bar

The centerline of the ,A=! lies at "7-meter level. /f

has a bypass duct' which is made use of' during the starting up' to

minimize the eect of cold and corrosion. The bypass duct has an

isolating damper


69/84

burners. Krate air and mill sealing air tapings are taen from the 2

interconnection between the hot air distribution ducts.

MILL HOT AIR:

1ill hot air at a temperature of "86G ? is used to

temper the hot ue gases' which is at a temperature of @*.8G ?.

Thus the ue gases which is at a temperature of @*.8G ? Thus the

ue gas and hot air mixture going through the resuction duct is bought

to a temperature of 8)G?.

1ill hot air is taen from hot air distribution duct at a

%9-meter level elevation' through 6 ducts of @6 mm diameter and

oins the respective resuction ducts at %9.8-meter level. #ach duct is

provided with a venture type ow meter. At %8.6-meter level' the cross

section of the duct reduces to 6@@ mm \ pneumatically operated

damper is provided to regulate the mill hot air ow.

The hot air is supplied at a pressure of 7.%-milli bars

and at a temperature of "86G ?. Lormal ow rate for mill hot air is

".866 sc. And the duct can handle a maximum ow of 7." sc.

;ith only ) mills at a service at 8@W load' each hot air duct gets

divided in to six circular ducts of )@6.)mm diameter and oins the

starting point of the elliptical resuction duct at 6 points' % on each side

through a distribution piece shaped lie a horseshoe. This type of

arrangement ensures the uniform mixing of hot air with the ue gas.

SECONDARY AIR:


70/84

#very mill feeds two p.f. +urners' one at "@

meters elevation and the other at "7-meter elevation. 1aor portion of

combustion air is supplied as secondary air to the above p.f. +urners.

5econdary air is taen from hot air distribution

duct at %6.9-meter elevation' through six ducts


71/84

secondary air is distribution as under' by the above (ve ducts at

dierent points of a p.f. +urner.

Top p.f. +urner +ottom p.f.

+urner

Top air "8.6* 1.3. ".** 1.3.

Top primary mixing air "7.*) 1.3. "@.)) 1.3.

1iddle air "6.8@ 1.3. 9.7@ 1.3.

+ottom primary mixing air "6.@6 1.3. 8.@6 1.3.

+ottom air ").9* 1.3. 7.%*

1.3.

Top air is admitted through a rectangular duct

with two vertical partitions or bottom air' a rectangular duct is provided with a

horizontal partition. The top section


72/84

section is left free ow of a certain $uantity of air' when is termed as

cooling air.

The p.f. +urners is of double walled construction' and the

above said cooling air has an unrestricted ow through the chamber

formed between the two walls of the burner' and escapes at two

elevations' one between that of top air and top primary mixing air and

the bottom air. At each elevation' four pipes outlets are provided for

the escapes of cooling air' which is restricted by a partition at the

outlet of each pipe.

The rectangular ducts of top' middle and bottom air

connections are provided with an electrically operated damper in each.

Top and bottom primary mixing air ducts are circular in shape and have

a hand-operated damper in each and are set to ux optimum position.

5econdary air supplied at 7.%-millibar pressure and "86G ?

temperature at the rate of %6.)JgEsec. /ts pressure after the ow

meter throat is *.6 millibar.

HOPPER AIR:

#ach boiler has two after burning grates at 7-meter level' where

combustibles in slag are burnt. 5ir for the combustion of the lignite

particles in slag is supplied as hopper air' at the rate of ").9* JgEsec at

a pressure of 7.% millibar.

The hopper air duct of 6"@mm diameter is taen at "7-meter

level from the N2O shaped interconnection of the hot air distribution


73/84

duct. A venturi type ow-measuring element located at 7.)-meter

level is used to determine the rate of ow of hopper air. The circular

duct coming downwards' changes to an 8*@mm s$uare cross section at

6 meter level and is provided with a pneumatic operated diaphragm at

* meter level. The duct then divided into two 6"@mm s$uare ducts'

which go to left and right side grates respectively. #ach of these ducts

is provided with a hand-operated damper.

>ive distribution ducts leave the above duct. #ach of the two

end ducts of small cross section are divided into two ducts' and each of

the above six ducts are divided into two ducts again and connected to

the grate area. Thus the hopper air is supplied to the grate at 6

points

MILL SEALING AIR:

1ill sealing air is supplied at both sides of the mill. /n the

coupling end side' it is supplied at two points one on each side of the

shaft to provided eective sealing. /n the free end side' it is supplied

at three points at "@G interval in between dipper ange and beater

wheel' for the purpose of preventing beater wheel erosion due to the

abrasive silica in the lignite even through the centrifugal force of the

mill rotation itself will prevent beater wheel erosion' the above sealing

air admission is provided to serve as an additional protection and the

$uality of sealing air used for this purpose is a meager fraction of the

total air.


74/84

5ealing air duct of diameter 8% mm is taen from the N2O

shaped interconnecting duct of the hot air distribution ducts at "7-

meter level. The duct meanders down vertically up to meter level

and then divides into two ' # and & from the

left side duct. The diameter of this duct gets reduced from 6@ mm to

*@8 mm and then to )9 mm gradually after every tap o. 1otor

operated regulating damper are provided at 6.7-meter level for

regulation while service. 5ealing air pipe for the dipper ange has a

detachable piece to facilitate moving of the mill door away' when

maintenance is taen up in the mill.

OIL BURNER AIR:

The combustion air supplied to the oil burners on both sides is

speci(cally termed as oil burner air. >or supplying this air' two circular

ducts of 6"@ mm diameter are tapped' one from each side of hot air

distribution duct at %*.8-meter level. #ach duct travels downward and

divides into two


75/84

oil burner at "86G ? and its pressure before the ow meter is 7.%-miili

bar.

The oil burner air is distributed as primary air and secondary air.

=rimary air component entering through a 8@mm duct passes through

a concentric tube of )96mm' surrounding the burner gun. The primary

air $uantity can be regulated with the help of a hand-operated damper

and itOs usually set at an optimum permanent position. This air goes

through 8 stabilizer vanes near the burner tip and gives the vertex

motion for the primary mixing of oil and air. The secondary air

component passing through a 7)6-] 9*@ mm duct goes in the annual

space of width *".*mm. This air along with the primary air helps in

complete combustion of the fuel oil.

AIR DISTRIBUTION:

The total air supplied to the combustion system will be

distributed as followsC

: 1ill hot air "%.7"W

": 5econdary air 67.@8W

%: !opper air or grate air 9."@W

GAS PATH

FURNACE:


76/84

+oiler is having a single pass furnace with more or less' a s$uare

cross section. All heat transfer elements except air preheaters are

located in the furnace itself.

The furnace dimensions are as underC

&epth - front to rear - "'97* mm

;idth - left to right - "'8"* mm

!eight - - 8 meters

Molume - - '%@@ J5?

>urnace plan area - - 66.)m s$uare

The left and the right side of the furnace are vertically straight.

At 8m' meter level' the left and the right side of the walls mae 3

bend and oin in a roof header at the top middle of the furnace. At the

bottom' the front and rear walls form a hopper portion from 6.* meter

elevation to 7.68 meter elevation' to facilitate collection of slag and

unburned lignite' over the beds of the after burning grates.

/n the furnace' the ue gas is traveling upwards. The gas ow is

opposed by the y ash particles falling down' there by limiting the

velocity to 8.7 mEsec. 5ince the value of velocity is less than the

normal limit of @ mEsec.' the tubes are not much aected by ash

erosion. >lue gas reaches an 8-meter diameter ue gas duct through a

rectangular opening of ".8"*-meter ] 6.6 meter from the furnace. /n

this zone' rear evaporator wall tubes overlap each other to give way to

ue gas to escape.


77/84

5uper heater ' super heater %' reheater "' super heater "'

reheater and economizer are arranged one after another in the gas

ow path in the furnace.

The following essentials are (xed to the furnace in the related

areas and the evaporator tubes are suitably bent to accommodate

them.

: =ulverized fuel burners - " nos

": 0il burners - ) nos

%: ;ater soot blowers - %6 nos

): 5team soot blowers - )" nos.


78/84

: +efore 5!

": After 5!/

%: After 5!%

): After ,!"

*: After 5!"

6: After ,!

7: After economizer bottom

ban

8: After economizer middle

ban

9: After economizer top

ban

@)7

96*

866

77"

*7

)**

%89

%%

*

%

@

.)

."

@.9

@.9

.%

".%

-

-

%.%

A4e*9e ;/e 9*+ 4e7o35t< *t e*38 +t*9e'

Lo3*t5o0 Ve7o35t< 50 ,=+e3


79/84

. 5!/

". 5!%

%. ,!"

). 5!"

*. ,!

6. #conomizer middle

ban

7.7

7.*

8.7

8.

8.@

*.)

HEAT RELEASE IN THE FURNACE:

The volume of combustion zone


80/84

At the rear' the above duct diverges to two ducts of cross

section 6%@@mm ] %%@@mm at a NTO oint. These ducts travel

downward' oining there respective ,A=! at "7-meter level.

/solating dampers' of 8 aps each' are provided in these ducts

at %)-meter level for the isolation of Air heater gas side. The above

damper has 9 shafts with " aps in each.

At the bottom of the circular ue gas duct' a big conical hopper

is placed and connected it to through an expansion oint. The hopper

bottom is at "7.) meter level and is connected to a pipe of ash mixing

vessel at N@O meter level for the disposal of ash that may be collected in

the hopper.

The ue gas duct is supported by two cantilever hanging

supports with rectangular frame in the rear' one on either side. These

are actually the extension of horizontal roof girders. 1ultiple expansion

oints in the ducts are provided with collapsible frames with aid in

uniform expansion and contraction and also prevent axial

misalignment. >lue gas velocity in the duct is @mEsec.

FLUE GAS IN RAPH:

/n the ,A=!' the ue gas gives out the heat to the

combustion air and the temperature of gas drops from %6G ? to )9G

? gas velocity is ).86 mEsec. And there is gas pressures drop of %.%

millibar across the air heater


81/84

cubeEhr. to '@*7'8@ Lm cubeEhr. because of 8W leaage of air in to

the gas stream. Let ow area of gas ow is "8.6) meter s$uare.

The air duct is in the front side and the gas duct is in the rear.

The centerlines of the air and the gas ducts are 6"@@mm apart. The

two-ue gas ducts after ,A=! travel downwards and then tae a 9@G

bend towards the rear at 7.@-meter level. #ach duct is divided in to

two and forms two inlets to each of the two streams of electro static

precipitator.

Two hoppers are provided at %.8 13 below the air heater gas

outlet ducts. The y ash particles collecting here' go to the two ash

mixing vessels at N@O13.

FLUE GAS ELECTRIC STATIC PRECIPITATOR:

The boiler is provided with an #5= of streams' each stream

having 6 (elds in series along the gas ow direction. #ach (eld has 6

rows of collecting electrode plates forming 6@ gas passages.

At the inlet of each stream' the cross section of duct increases

from %m]%m to 9.8m]9.8m forming of funnel shape. This reduces the

velocity of the ue gas from ).)mEsec. At the inlet to .""mEsec in the

electrode zone. Two perforated gas distribution screens' which are

located before the electrodes zone uniformly' distribute the gas

throughout the cross section of the #=.

The overall dimensions of the #= are'

3ength along the gas ow %.7* m.


82/84

;idth %m.

!eight ""m

Ash loading in gmsEmU% of gas is %." with "Wash in lignite and

7.8*8 with 7W ash in lignite


83/84

rises to oin the chimney at %.*-meter level. Lon-metallic bellows are

provided at the entry and the exit points of #= and /& fans.

CHIMNEY:

The ue gases of the both /& fans are left out of a chimney of

7@ meters height. The height of the chimney enables the diusion of

ash particles over the very large area and ensures the safe guard of an

environment. 5ince only W of the total ash escaping through chimney

these (ne particles do not settle any where near the power station'

thus ensuring the clean environment for the power station itself.

A hopper is also provided at the bottom of the chimney

extending from 9.*-meter level to ".*-meter level. +elow the hopper

atO@O meter level an ash mixing vessel is provided from whichI the ash

slurry pipe comes out.

DETAILS OF RCC SLAG:

! DIMENSIONS

0uter diameter at N@O meter level F ."67 meters

0uter diameter at 7@-meter level F *.6)" meters.

?oncrete shell at N@O meter level F8)mm

?oncrete shell thicness at 7@-meter level F 8 mm

/nternal diameter at %.*-meter level F 8.7)) mm

/nternal diameter at an exit F ).8* meters

"! REFRACTORY LINING:


84/84

A minimum air gap of @@ mm between the concrete shell and

the refractory lining is maintained through out. A " mm thic ?./ cap

covers it at the top.

Date post:	13-Apr-2018
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