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Presentation Presentation On On Maintenance of coal mill and coal Maintenance of coal mill and coal feeders feeders
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Page 1: coal mill

Presentation Presentation OnOn

Maintenance of coal mill and coal feedersMaintenance of coal mill and coal feeders

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Maintenance:Maintenance:

Increase availabilityIncrease availability Improve reliabilityImprove reliability Increase efficiencyIncrease efficiency Reduce the downtime / Failure rate of mill.Reduce the downtime / Failure rate of mill. Smooth operationSmooth operation Availability of mills for operation / Availability of mills for operation / main deciding plant load factor main deciding plant load factor

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What is wearing?What is wearing?

Wear is directly proportional to:Wear is directly proportional to:

Abrasive substancesAbrasive substances Service hoursService hours

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COAL MILLCOAL MILL

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TUBE MILLTUBE MILL

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Indications for maintenance:Indications for maintenance:

Reduced mill capacityReduced mill capacity Increase in spillageIncrease in spillage Incorrect coal finenessIncorrect coal fineness Noise levelNoise level

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Wearable mill parts:Wearable mill parts:

Grinding rollsGrinding rolls Bull ring segmentsBull ring segments Separator body linersSeparator body liners Direction vanesDirection vanes Bowl extension ringBowl extension ring ScrappersScrappers Mill side linerMill side liner Mill discharge valvesMill discharge valves

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Factors responsible for Factors responsible for scheduling maintenance scheduling maintenance

program and inspection are:program and inspection are:

Characteristics of fuelCharacteristics of fuel Operating hourOperating hour Availability of millAvailability of mill Availability of maintenance forceAvailability of maintenance force

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Lets see few common Lets see few common problems and problems and troubleshooting…….troubleshooting…….

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Troubleshooting:Troubleshooting:

ProblemProblem: Incorrect coal fineness : Incorrect coal fineness

Possible cause:Possible cause: Uneven deflector blade settingsUneven deflector blade settings Worn or damage deflector bladesWorn or damage deflector blades Low or high spring compressionLow or high spring compression Grinding process Grinding process

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ProblemProblem: In correct coal fineness: In correct coal fineness

(Corrective Action)(Corrective Action)

Calibrate the blades properly.Calibrate the blades properly. Inspect repair and /or replace deflector blades Inspect repair and /or replace deflector blades

as soon as Possible as soon as Possible Check the compression and change as required.Check the compression and change as required. Inspect repair by patching the holes or replacing Inspect repair by patching the holes or replacing

the cone as soon as possible. the cone as soon as possible.

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ProblemProblem: Noise above bowl: Noise above bowl

Possible causePossible cause::

Reject material on bowlReject material on bowl Failed grinding roll Failed grinding roll Uneven spring pressure Uneven spring pressure Heavy reject material Heavy reject material

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ProblemProblem:Noise above bowl:Noise above bowl

(Corrective Action)(Corrective Action)

Stop the pulverize inspect & remove the Stop the pulverize inspect & remove the material.material.

Stop the pulverize repair or replace the Stop the pulverize repair or replace the Journal assembly.Journal assembly. Check the spring pressure and change if Check the spring pressure and change if

required(250 kg/cm2).required(250 kg/cm2). Stop the pulverized and remove the material & Stop the pulverized and remove the material &

Check the damage.Check the damage.

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Lets us now focus on Lets us now focus on Maintenance AspectsMaintenance Aspects

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Overview of maintenance:Overview of maintenance:

Daily maintenanceDaily maintenance Weekly maintenanceWeekly maintenance Shutdown maintenanceShutdown maintenance

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Daily maintenance / checks:Daily maintenance / checks:

Check the gear case oil level ( Daily)Check the gear case oil level ( Daily) Gear case oil bath temperatureGear case oil bath temperature Coal and oil leakagesCoal and oil leakages

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Weekly checks:Weekly checks:

Greasing of spring adjusting boltGreasing of spring adjusting bolt Greasing of journal stop bolt.Greasing of journal stop bolt. Check gear case oil for contaminationCheck gear case oil for contamination

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ShutdownShutdown(Checks after 6-8 months)(Checks after 6-8 months)

Oil level in journal and its quality(800mm)Oil level in journal and its quality(800mm) All internal clearancesAll internal clearances Greasing the gear couplingGreasing the gear coupling

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Industrial Maintenance programIndustrial Maintenance program

Preventive maintenancePreventive maintenance Package overhaulPackage overhaul Capital overhaulCapital overhaul

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Isolation of mill:Isolation of mill:

Hot air shut off gatesHot air shut off gates Cold air shut off gateCold air shut off gate Seal air shut off valvesSeal air shut off valves Mill discharge valve should be closedMill discharge valve should be closed Mill and feeder motor breakers are to be Mill and feeder motor breakers are to be

left open.left open. Disconnect the electricityDisconnect the electricity

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Preventive maintenance:Preventive maintenance:

Grinding rolls and bull ring Grinding rolls and bull ring segments(Clearance 1-1.5mm)segments(Clearance 1-1.5mm)

Spring gap adjustmen(Between journal head Spring gap adjustmen(Between journal head and head of spring assembly)and head of spring assembly)

Check the spring tension.Check the spring tension. Check the condition and height of bowl Check the condition and height of bowl

extension ring(Approx:90-95mm)extension ring(Approx:90-95mm) Check the Condition of cone (eroded / Check the Condition of cone (eroded /

Punctured)Punctured)

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Preventive maintenance:Preventive maintenance:

Check the condition of classifierCheck the condition of classifier Check the height and condition of venturi.Check the height and condition of venturi. Check the sealing arrangement at the Check the sealing arrangement at the

insulation plates (damages due to insulation plates (damages due to temperature difference).temperature difference).

Check the clearance between the Check the clearance between the scrapper and insulation plate regularly.scrapper and insulation plate regularly.

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Preventive Maintenance:Preventive Maintenance:

Check the condition of oil in gearbox and Check the condition of oil in gearbox and level of oil(SP257/1050L)level of oil(SP257/1050L)

Flush the oil coolers if required.Flush the oil coolers if required.

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Packaged Overhaul:Packaged Overhaul:(wear Packaging)(wear Packaging)

Replacement of bullring segments:Replacement of bullring segments:

Procedure:Procedure:

1.Unbolt clamping rings using jack screws.1.Unbolt clamping rings using jack screws.

2.Remove worn out bull ring segment2.Remove worn out bull ring segment

3.Clean all interior surface of bowl3.Clean all interior surface of bowl

4.Install new bull ring segment in numerical 4.Install new bull ring segment in numerical sequence clockwisesequence clockwise

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Packaged overhaul:Packaged overhaul:

Replace the bullring segments contd..Replace the bullring segments contd..

5.After installing bull ring segments if gap 5.After installing bull ring segments if gap exists use shims around the periphery.exists use shims around the periphery.

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Packaged Overhaul:Packaged Overhaul:

Servicing of journal assembly:Servicing of journal assembly:

Procedure:Procedure:

1.1. Lower the journal assembly (Lower edge Lower the journal assembly (Lower edge touches floor)touches floor)

2.2. Remove the set screw or strips welded Remove the set screw or strips welded on the roll lock nuton the roll lock nut

3.3. Remove the roll lock nutRemove the roll lock nut

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Servicing of journal assembly:Servicing of journal assembly:contd..contd..

4.Lift the assembly by sliding over journal 4.Lift the assembly by sliding over journal head assemblyhead assembly

5.If unable to remove use jack and fixture 5.If unable to remove use jack and fixture assembly.assembly.

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Packaged Overhaul:Packaged Overhaul:

Servicing of spring assembly(T624 and Servicing of spring assembly(T624 and T625 Thrust brg.)T625 Thrust brg.)

( Hydraulic jack for adjusting spring tension)( Hydraulic jack for adjusting spring tension) Replacement of coneReplacement of cone Replacement of bowl extension ring and Replacement of bowl extension ring and

vane assemblyvane assembly Servicing of all Mechanical seal if required.Servicing of all Mechanical seal if required. Servicing of Worm shaft assemblyServicing of Worm shaft assembly

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Capital overhaulCapital overhaul

Disassemble the mill completely..Disassemble the mill completely..

Go for complete overhaul…Go for complete overhaul…

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Coal millCoal millDon’ts:Don’ts:

Do not get in to the mill when the motor is Do not get in to the mill when the motor is not isolated and the discharge valves not isolated and the discharge valves closedclosed

Do not use steel hammers on rollsDo not use steel hammers on rolls Do not use direct flame torch for bearing Do not use direct flame torch for bearing

assemblyassembly

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Don’ts:Don’ts:

Do not leave in the tools,workpieces inside Do not leave in the tools,workpieces inside the mill.the mill.

Do not alter classifier setting ,spring Do not alter classifier setting ,spring compression setting, roll ring settings, ring-compression setting, roll ring settings, ring-roll clearance etc.roll clearance etc.

Do not carry out maint. Work inside the mill Do not carry out maint. Work inside the mill with out proper personnel safety equipmentwith out proper personnel safety equipment

Do not weld on the bowl or any part attached Do not weld on the bowl or any part attached to it unless the welding m/c is grounded to to it unless the welding m/c is grounded to the bowl to prevent arcing on surfaces.the bowl to prevent arcing on surfaces.

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Coal Feeders:Coal Feeders:

Coal feeder is installed at the bottom of Coal feeder is installed at the bottom of the coal-bunkerthe coal-bunker

Capacity to supply coal (Range:7.4T/hr -Capacity to supply coal (Range:7.4T/hr -43.6T/hr)43.6T/hr)

Speed (Range:2.7 RPM – 16RPM)Speed (Range:2.7 RPM – 16RPM) Feed is proportional to change in speed.Feed is proportional to change in speed.

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Types of coal feeder:Types of coal feeder:

Volumetric coal feederVolumetric coal feeder Gravimetric feeder-Drag chain Gravimetric feeder-Drag chain

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Maintenance Gravametric feeder-Maintenance Gravametric feeder-Drag chain type:Drag chain type:

(Periodic Checks)(Periodic Checks)

Drive chain links. Drive chain links. Drive wheel teeth. Drive wheel teeth. Drive shaft. Drive shaft. Drive shaft bearings.Drive shaft bearings. Drive and driven shaft sprocket and Drive and driven shaft sprocket and

bearings of the same. bearings of the same.

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Maintenance Gravametric feeder-Maintenance Gravametric feeder-Drag chain type:Drag chain type:

Drag chain link, drag chain link push Drag chain link, drag chain link push plates and drag chain pin links. plates and drag chain pin links.

Drag chain guide angles. Drag chain guide angles. Top and bottom body liners LHS & RHS. Top and bottom body liners LHS & RHS. Guides of the driven shaft. Guides of the driven shaft. Thickness of the bed plate. Thickness of the bed plate. Load cells.Load cells.

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Maintenance (for both types)Maintenance (for both types)

Inspection, repairs or replacement of Inspection, repairs or replacement of gear teeth.gear teeth.

Inspection, repairs or replacement of Inspection, repairs or replacement of gear shaft.gear shaft.

Bearings of gears shafts.Bearings of gears shafts. Inspection of gear-box oil, cleaning of oil Inspection of gear-box oil, cleaning of oil

indicators.indicators. Inspection, repairs or replacement of Inspection, repairs or replacement of

clutch mechanism. clutch mechanism.