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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