BY - V . R . TAYADEBE (MECH) , MBABOILER PROFICIENCY

EXECUTIVE ENGINEER MAHAGENCO , KORADI.

Types of coal millTypes of coal mill

1.1. Ball & Race millBall & Race mill2.2. Bowl millBowl mill

3.3. Ball Tube millBall Tube mill

BALL MILL(Pulverising E Mill)BALL MILL(Pulverising E Mill)

Vertical spindleVertical spindleLarge steel hallow ball between top and Large steel hallow ball between top and bottom racebottom raceBottom race rotating and top race fixedBottom race rotating and top race fixedBall and race wear pattern is more Ball and race wear pattern is more hence less running hrs(3000-4000)hence less running hrs(3000-4000)

BALL & RACE ASSEMBLYBALL & RACE ASSEMBLY

Advantage of ball millAdvantage of ball mill

No lubrication points or bearings with No lubrication points or bearings with in the grinding zonein the grinding zoneCompactCompactCapable of grinding high ash coalCapable of grinding high ash coal

Ball Tube mill 250 MWBall Tube mill 250 MW1.1. BHEL – BBD 4772BHEL – BBD 47722.2. Capacity - 90T/HrCapacity - 90T/Hr3.3. Ball load - 82.5TBall load - 82.5T4.4. Motor - 2400KwMotor - 2400Kw5.5. System - Pressurised / cold P.A.System - Pressurised / cold P.A.6.6. Mill - Double ended(ie .2 coal feeder -1 Mill)Mill - Double ended(ie .2 coal feeder -1 Mill)7.7. Ball Size - 50mmBall Size - 50mm

Advantage of Ball Tube MillAdvantage of Ball Tube Mill

High availabilityHigh availabilityLow maintenance costLow maintenance costBetter finenessBetter finenessConstant capacityConstant capacityHard and Abrasive fuel ground efficientlyHard and Abrasive fuel ground efficientlyLow air to coal ratio Low air to coal ratio

XRP-763/803 (210 MW)XRP-763/803 (210 MW)

BASIC CAPACITY- 33 TPHBASIC CAPACITY- 33 TPH

(55 HGI , Fineness-70% through 200 mesh)(55 HGI , Fineness-70% through 200 mesh)

No. of mill / Blr -6 no.No. of mill / Blr -6 no.Motor 320KWMotor 320KWMotor speed -990 rpm Motor speed -990 rpm Bowl speed – 52.5rpm Bowl speed – 52.5rpm Temp. of air and fuel mixture after classifier- 77/80 CTemp. of air and fuel mixture after classifier- 77/80 C Gear box-single stage reductionGear box-single stage reduction

A. Air flow venturiB. Throat & deflectorC. Classifier vans for improved circulation & air/fuel distributionD. Outlet cylinder for homogenization & 50 mesh particle rejectionE. Inverted cone for coarse particle rejectionF. Orifices for (coal + air) resistance as per pipe length

Coarse partials are dropped down in mill again

Fine partials goes to burners

Hot airCo

al fr

om fe

ederCOAL MILL

BOWL MILLBOWL MILLINLET PIPE

DISCHARGE PIPE

INLET VENTURY

INNER CONEDEFLECTOR BLADES

DEFLECTOR

DEFCTOR REGULATOR

HAND HOLE COVER

JOURNAL SPRING ASSEMBLY

PRESSURE SPRINGJOURNAL HEAD SKIRTJOURNAL ASSEMBLY

GRINDING ROLL

SEPERATOR BODY LINER ASSEMBLY

SEPERATOR BODY

BOWL EXTENTION RINGBULL RING

BOWL BOWL HUB

BOWL HUB SKIRT

SCRAPER

BOWL HUB COVER

MILL SIDE

MILL SIDE LINER ASSEMBLY

AIR SEAL HOUSING

MILL SIDE INSULATION

INSULATION COVER PLATE

OIL GAUGE

MILL BASE GEAR HOUSINGWORM SHAFTWORM

VERTICAL SHAFTANCHOR BOLT

MILL BASE PLATE

WORM GEAR

WORM GEAR HUBOIL COOLER

SEPERATION TOP

J/Assly & Spring AsslyJ/Assly & Spring Assly

Major parts of coal millMajor parts of coal millGrinding element (roll) 3 Nos.Grinding element (roll) 3 Nos.Bull ring segment (set)Bull ring segment (set)BowlBowlVertical shaftVertical shaftWorm shaft & worm gearWorm shaft & worm gearMotor & couplingMotor & couplingClassifierClassifierInner coreInner corePressure spring assemblyPressure spring assemblyMechanical face seal arrangementMechanical face seal arrangementInbuilt oil pump / oil coolerInbuilt oil pump / oil coolerScrapper boxScrapper boxVane wheelVane wheel

Grinding ElementGrinding Element

Bowl AssemblyBowl Assembly

Raw coal feeder - volumetricRaw coal feeder - volumetric

Raw coal rotary feeder 100 lbsRaw coal rotary feeder 100 lbsMake-PIV variator CZECHMake-PIV variator CZECHCapacity- 7.4 - 43.6 TPHCapacity- 7.4 - 43.6 TPHSpeed – 2.7 – 16 rpmSpeed – 2.7 – 16 rpm

Coal FeederCoal Feeder