Boiler Mountings and Accessories.pdf

Definition of Boiler Mountings & Accessories, Types of Boiler Mountings, Types of Boiler accessories, Fuctions of different mountings and accessories

1. Prepared by
Ankur Sachdeva
Assistant Professor, ME
Boiler Mountings
& Accessories

2. What is a Boiler Mounting?
•Boilermountingsaremechanicaldevicesthatareconsiderednecessarytooperatetheboilersmoothly&
andsafely.Theyareusuallymountedonthesurfacesoftheboilers.
•Thesearethepartsofthesystemthataremountedontheboiler’sownbodyforprotectionoftheboilerand
forcompletecontrolofthesteamgenerationcycle.
•Variousboilermountingsare:
1.Waterlevelindicator
2.PressureGauge
3.Safetyvalve
4.Fusibleplug
5.Blow-off-cock
6.Feed-check-valve
7.Steamstopvalve

3. Water Level Indicator
Itindicatesthewaterlevelinsidetheboilervessel.Itshowsthe
levelintheboilerdrum.
Construction
•Normallytwowaterlevelindicatorsarefittedintotheboiler.
•Thesearefittedatthefrontendsideofeveryboiler.
•Thewaterlevelindicatorconsistsofthreecockassteam
cock,watercock,draincock,andglasstube.
•Thesteamcockconnectsordisconnectstheglasstubewith
steamspace.
•Thewatercockconnectsordisconnectstheglasstubewith
waterintheboiler.
•Thedraincockisusedtodrainoutthewaterinfromtheglass
tubeatintervalstoensurethatthesteamandwatercockare
clearinoperation.
•Theglasstubeisprotectedbymeansofacoverwhichis
speciallymade.

4. Water Level Indicator
Working
•Whenthesteamcockandwatercockopened,steamrushes
fromtheupperpassage,andwaterrushedfromthelower
frompassagetotheglasstube.
•Thiswillindicatethelevelofwaterintheboiler.
•Twoballsareplacedatthejunctionofthemetaltube.Under
normaloperatingconditions,theballsarekept.
•Fulllinecircleincasetheglasstubeisbroken,steamwill
rushfromtheupperpassageandwaterfromthelower
passageduetopressuredifferencebetweenboilerpressureat
atmosphericpressure.
•Theballsarecarriedalongthepassagetoandoftheglass
tubeandthenclosedpassages.
•ThispositionoftheballisshowninFigbyadottedcircle.
•Thusflowofwaterandsteamoutoftheboilerisprevented.

5. Pressure Gauge
•Apressuregaugeisusedtoindicatethepressureof
steamintheboiler.
•Itisgenerallymountedonthefronttopoftheboiler.
•Pressuregaugeisoftwotypesas
•(i)BourdonTubePressureGauge&(ii)Diaphragmtype
pressuregauge.
•Boththesegaugeshaveadialinwhichaneedlemoves
overacircularscaleundertheinfluenceofpressure.
•Atatmosphericpressureitgiveszeroreading.
•Somegaugesindicateonlythepositivepressurebut
somearecompoundandindicatenegativepressureor
vacuumalso.
•Lookingatthegauge,theboileroperatorcancheckthe
safeworkingpressureoftheboilerandcantake
necessarystepstokeepthepressurewithinsafelimits.

6. Bourdon-Tube Pressure Gauge
Construction&working
•Thebourdontubeisanellipticalspringmaterialtubemadewithspecial
qualitybronze.
•Oneendofthetubeisconnectedtothegaugeconnectorandtheother
endisclosedandfreetomove.
•Aneedleisattachedtothefreeendofthetubethroughasmallgear
mechanism.
•Withthemovementofthetubeunderpressure,theneedlerotatesonthe
circularscale.
•Themovementofthetube&andhenceneedleisproportionatetothe
riseinpressureandsocalibratedwithscale.
•ThepressuregaugeconnectorisattachedtotheboilershellthroughaU-
tubesiphonandthree-waycocks.
•IntheU-tube,condensateremainsfilledandsolivesteamdoesnot
comeindirectcontentofthebourdontubebutitpushesorexerts
pressureonthecondensatewhichfurtherstretchesthebourdontube.
•Steamisnotalloweddirectcontactwiththegaugeduetothehigh-
temperatureeffectonthepressurerecording.

7. Safety Valves
•Safetyvalveisusedtoguardtheboileragainsttheexcessivehighpressureofsteam
insidethedrum.
•Ifthepressureofsteamintheboilerdrumexceedstheworkingpressurethenthesafety
valveallowsblow-offoftheexcessquantityofsteamtotheatmosphere.
•Thus,thepressureofsteaminthedrumfalls.
•Theescapeofsteammakesanaudionoisetowarmtheboilerattendant.
There are four types of safety valve:
➢Dead weight safety valve.
➢Spring-loaded safety valve
➢Lever-loaded safety valve
➢High steam and low water safety valve

8. Spring-Loaded Safety Valve
Construction
•Itconsistsofacastironbodyhavingtwobranch
pipes.
•Twoseparatevalvesareplacedoverthevalveseat.
•Aleverisplacedoverthevalvebymeansoftwo
pivots.
•Theleverisheldtightatitsproperpositionby
meansofaspring.
•Oneendofspringisconnectedwiththelever
whileotherendwiththebodyofthevalve.
•Thevalveiskeptonitseatswithhelpofspring
force.

9. Spring-Loaded Safety Valve
Working
•Inthenormalcondition,thedownwardforce
duetospringishigherthanupwardforce
appliedbysteam.
•Thevalveisclosedduetospringforce.
•Whensteampressureexceedsthenormal
limit,theupwardforceduetosteampressure
becomeshigherthanthedownwardforcedue
tospring.
•Thusthevalvesareliftedfromtheirseats
openingthepassagesforsteamtoreleaseout
oftheboiler.

10. Fusible Plug
•Thefunctionofthefusibleplugistoprotecttheboilerfromdamagedueto
overheatingofboilertubesbylowwaterlevels.
Construction
•Asshowninthefigure,itissimplyahollowgunmetalplugscrewedintothe
fireboxcrown.
•Thishollowgunmetalplugisseparatedfromthemainmetalplugbyanannulus
fusiblematerial.
•Thismaterialisprotectedfromthefiresidebymeansofaflange.
Working
•Whenthewaterintheboilerisatitsnormallevel,thefusibleplugremains
submergedinwateranditstemperaturedoesnotexceeditsmeltingtemperature,
becauseitsheatistransferredtowatereasily.
•Ifundersomeunwantedcondition,thewaterlevelcomesdowntoanunsafe
limit;thefusibleplugisexposedtosteaminplaceofwater.
•Ontheotherside,itisexposedtofire.
•Soitstemperatureexceedsitsmeltingpointduetoverylowheattransferto
steamanditmeltsdown.
•Immediatelysteamandwaterunderhighpressurerushtothefireboxand
extinguishthefire.

11. Blow-Off Cock
•Itisacontrollablevalveopeningatthebottomofwater
spaceintheboilerandisusedtoblowoffsomewaterfrom
thebottomwhichcarriesmudorothersedimentssettled
duringtheoperationoftheboiler.
•Itisalsousedtocompletelyemptythewaterwhenthe
boilerisshutoffforcleaningpurposesorforinspection
andrepair.
•Constructionandworking
•Ithasacasinghavingapassagewithonesideflangeto
connectwiththeboilershell.
•Thepassageisblockedbyacone-shapedplughavinga
crossrectangularhole.
•Sealingismadewithatopandbottomasbestospacking
filledingroovesontheplug.
•Theshankoftheplugpassesthroughaglandandstuffing
boxinthecover.
•Onthetopportionoftheshankaboxspannercanbefitted
torotatetheshankandplugby90
0
toeitheropenorclose
theblow-off-cock

12. Feed Check Valve
•Thefeedcheckvalveisfittedinthefeedwaterlineofthe
boilerafterthefeedpump.
•Itsfunctionistoallowthewatertoflowintheboilerwhenthe
dischargepressureofthefeedpumpismorethantheinside
steampressureoftheboilerandpreventthebackflowincase
thefeedpumppressureislessthantheboilerpressure.
•Thefeedcheckvalveisfittedslightlybelowthenormalwater
levelintheboiler.
Construction&Working
•Inthecasingofthevalvethereisacheckvalvethatcanmove
upordownonitsseatunderthepressureofwater.
•Whenthesupplypressureoffeedwateractingatthebottomof
thecheckvalveishigher,thevalveliftsupandallowsthe
watertofillintheboiler.
•Whensupplypressuredropsbystoppingoffeedpump,the
boilerpressureactsonthetopofthevalveanditsitsonitsgun
metalseatandstopsthebackflowoftheboilerwateroutofthe
boilershell.

13. Steam Stop Valve
•It is fitted over the boiler in between the steam space and
steam supply line.
•Its function is to regulate the steam supply from the boiler
to the steam line.
Constructionandworking
•ItscasinghasaL-shapedsteamflowpassage.
•Itconsistsofavalveandvalveseattostoporallowthe
steamflow.
•Thevalveisattachedtoaspindleandhandle.
•Spindlepassesthroughpackinginthestuffingboxto
preventleakage.
•Thespindlehasexternalthreadsinthetopportionand
movesintheinternalthreatsofafixednut.
•Byrotatingclockwiseandanticlockwisethespindleand
valvemovedownandupthusclosingoropeningthe
valves.

14. What are Boiler Accessories?
•Boileraccessoriesaredevicesthatareinstalledalongtheboilerandthe
surroundingareatoincreasetheefficiencyoftheboiler.
•Thesearenotanindispensablepartoftheboiler,andthuswithout
installingthesedevices,theboileroperationcanbecompletedatlowefficiency.
•Variousboileraccessoriesare:
1.Feedpump
2.Economizer
3.AirPre-heater
4.Superheater

15. Feed Pump
•Afeedpumpisplacedneartheboilerandisusedtofeed
watertotheboilerworkingatahighpressure.
•Thejobofthefeedpumpisnotjusttoputthewaterinthe
boilerbutastheboilerisworkingathighpressure,the
dischargepressureofthefeedpumpmustbesufficiently
higherthanthistopushthewaterinsidetheboiler.
Construction&Working
•Thefeedpumpusedintheboilerisoftwotypes:
•(i)Reciprocatingtypeand(ii)Rotarytype.
•Boththesetypesarepositivedisplacementtypesto
dischargeagainsthighpressure.
•Thedischargepressureofasingle-stagecentrifugalpump
isnothighenoughtoovercomethehighpressureofthe
boilersoamultistagecentrifugalpumpisusedasaboiler
feedpump.

16. Feed Pump
Construction&Working
•Instationarylow-pressureboilersusedinprocessing
industries,amultistagecentrifugalpumprunbyan
electricalmotorismoresuitable.
•Inamultistagecentrifugalpump,anumberof
centrifugalcasingsaresoattachedtoeachotherthat
theimpellerofeachismountedonthesameshaftrun
byanelectricalmotor,anddischargeof1
st
stagegoes
to2
nd
stageandof2
nd
to3
rd
stageandsoon.
•AsshowninFig,ineachstage,thepressureofwater
goesonincreasingandthedischargepressureofthe
finalstageissohighastoovercometheinternal
pressureoftheboiler.
•Thesepumpshaveindependentworkingandhave
smoothoperation.

17. Economizer
•Aneconomizerisaspeciallyconstructedheatexchanger
forharnessingtheheatenergyofoutgoingfluegasesand
utilizingitinpreheatingofboilerfeedwater.
•Itsavestheheatenergyandsothefuelanddecreasesthe
operatingcostoftheboilerbyincreasingitsthermal
efficiency.
Construction&Working
•Economizersareoftwotypes:
•(i)Externaltypeand(ii)Internaltype.
•Theexternaltypeeconomizerisconstructedand
installedapartfromtheboilerandthefluegasesfrom
theboileraredirectedtoflowthroughitbeforeescaping
throughthechimney.
•Itisemployedforboilersofmediumpressurerange.
•Hereanumberofverticaltubesmadeofcastironare
connectedtocommonheadersatthebottomandtop.

18. Economizer
Construction&Working
•Feedwaterflowintothebottomheaderandthenthroughthe
verticaltubesflowoutfromthetopheader.
•Hotfluegasesescapingfromtheboileraredirectedtoflow
acrosstheoutsidesurfaceoftubesthusindirectlyheatingthe
feedwaterflowinginside.
•Toavoiddepositofsootoverthetubesurface,tubular
scrapersarefittedoverthetubes.
•Theseareoperatedbychainandpulleysystemandwhile
movingupanddownslowlyscrapthesootoverthewallof
tubesandsoincreasetheheattransferrate.
•Aninternaltubeeconomizerisfittedinsidetheboilerandis
anintegralpartofit.

19. Advantages of Economizer
1.Stressesproducedintheboilermaterialduetotemperature
differenceofboilermaterialandfeedwaterarereducedbecauseof
increaseinfeedwatertemperature.
2.Evaporativecapacityofboilerincreasesaslessheatwillberequired
togeneratesteamiffeedwatertemperatureisalreadyhighdueto
preheating.
3.Overallefficiencyofboilerincreasesbecauseofmoresteam
producedperkgoffuelburnt.

20. Air-Preheater
•Thefunctionofanairpre-heateristofurtherutilize
theheatoffluegasesaftercomingoutofthe
economizertopreheattheairusedinafurnaceoroil
burner.
Construction
•Itisaplatetypeortubulartypeorstorageheat
exchanger,inwhichfluegasespassthroughthe
tubesononesideoftheplateandairpassesonthe
otherside.
•Instoragetype,arotorfittedwithmeshormatrix
alternativelycomesinthepassageoffluegasesand
airthusexchangingheat.

21. Superheater
1.Thesuperheaterisaheatexchangerwhosefunctionistosuperheat
thewetorsaturatedsteamuptothedesiredtemperaturebytransfer
ofheatenergy.
2.Thesuperheatersareeitherlocatedinthepassageofhotfluegasesor
directlyoverthefurnacedependinguponitsdesignandapplication.
3.Inmodernsteampowerplants,thesuperheatingandreheatingof
steamisdoneintherangeof440°Cto650°C.
4.The40%ofthetotalheatgeneratedinamodernboilerisutilizedby
thesuperheaters.
5.Theadvantagesofsuperheatingandreheatingofsteamare:
(a)Itimprovestheoverallefficiencyoftheplant.
(b)Itreducesthemoisturecontentinthelaststagesoftheturbine.
6.Ithelpsinpreventingtheerosionofbladesandcorrosionofvarious
componentsofsteamturbines.
7.Thesuperheatersaremadeofspecialhigh-strengthsteelsincaseof
superheatingisdoneabove450°Cbutlesscostlycarbonsteelcanbe
usedfortemperaturesbelow450°C

22. Types of Superheaters
•Radiantsuperheatersarethetypeof
superheatersthatareinstalledinaradiationzone
justafterthefurnace.
•Inhigh-pressureboilerswhenthetemperature
differenceinsaturatedandsuperheatedsteamis
around100˚C,superheatersmustbeinstalledina
radiantzone.
•Convectivesuperheatersareinstalledafterthe
convectivebankoftubes.
•Whenthetemperaturedifferencebetweensaturated
andsuperheatedsteamisnotmorethan50˚C,
superheatersmustbeinstalledinaconvectivezone.