ball and race mill
TRANSCRIPT
Ramagundam Super Thermal Power Station NTPC Limited
Ball & Race mill
Namendra AnandSr. Engineer (BM/RM)
Ramagundam Super Thermal Power StationNTPC Limited
Milling system maintenance is a challenge as it requires to use all kinds of
maintenance practices to run the system effectively….
Its an opportunity as it provides vide scope to implement betterment activites….
Ramagundam Super Thermal Power Station NTPC Limited
• To reduce the coal size up to 70 micron size
Ramagundam Super Thermal Power Station NTPC Limited
OBJECTIVE OF PULVERIZER
ARRAMENT OF MILL & PA FAN
1. Raw coal inlet pipe2. Pulverized coal outlet pipe3. Adjustable classifier blades4. Oversize particles return
chute5. Hollow grinding balls6. Rotating lower grinding ring7. Primary air inlet8. Loading cylinders9. Spider guide10.Stationary upper ring11.Air regulating ring12.Gear box13.Reject door
Ramagundam Super Thermal Power Station NTPC Limited
BALL& RACE MILL (E TYPE)
1. Mill gear box to motor coupling2. Reduction Gear Box3. Mill lub oil system4. G/B out put coupling5. Yoke6. Turn plate7. Bottom track/ring8. Coal drop plate9. Grinding ball10. Top track/ring11. Spider/ loading ring12. Loading System13. Classifier Assembly14. Pulverized coal outlet pipe15. Coal inlet pipe16. Pyrites discharge Syste
VARIOUS PARTS OF COAL MILL
Ramagundam Super Thermal Power Station NTPC Limited
REDUCTION GEAR BOX
Gear Box
Gear unit
External
Lub System
InternalFirst reduction one pair of Spiral bevel gears
Second reduction one pair of Single Helical gears
Gear Pump & other
arrangement
Oil distribution system &
Spray nozzles
Ramagundam Super Thermal Power Station NTPC Limited
MILL GEAR BOX
MILL GEAR BOX CROSS SECTION
MILL GEAR BOX INPUT PINION
MILL GEAR BOX I STAGE GEAR
MILL GEAR BOX I STAGE GEAR &II STAGE PINION
MILL GEAR BOX II STAGE GEAR
MILL GEAR BOX EXTERNAL LUB OIL SYSTEM
MILL GEAR BOX INTERNAL LUB OIL LINES
MILL GEAR BOX LABYRINTH SEAL
REDUCTION GEAR BOX
• Speed : 970 / 40.185 rpm• Lub System :
– Roloid gear pump – G/B sump Capacity is 210 liter
Ramagundam Super Thermal Power Station NTPC Limited
HYDRO PNEUMATIC LOADING SYS.
Purpose : exercise a constant load on the ball mills & compensate the wear on same
The system is composed of two parts :1. Pneumatic plant: Determines reqd. load2. Oil system : Lubricate cylinder bushes & keep the gasket in pressure for perfect seal
Ramagundam Super Thermal Power Station NTPC Limited
MILL LOADING SYSTEM
MILL LOADING SYSTEM
MILL LOADING SYSTEM CABINET
LOADING CYLINDER
TOP & BOTTOM RING
GRINDING BALL
GRINDING BALL (NEW & WORN OUT)
LOADING RING
INLET COAL PIPE WITH INVERTED CONE
CLASSIFIER CONE WITH SKIRT PLATES
CLASSIFIER VANES
CLASSIFIER VANES
CLASSIFIER VANES
RELIEF GATE (CLOSED)
RELIEF GATE (CLOSED)
RELIEF GATE (OPENED)
REJECT GATE
CASE STUDY
PROBLEMS FACED&
IMPROVEMENT ACTIONS TAKEN
Ramagundam Super Thermal Power Station NTPC Limited
Improvement actions
1. Highly skilled maintenance practices were developed for mill overhauling
2. Spare mill top housing is being kept ready before hand
3. Readiness of mill bay hoist is ensured
These resulted in reduction of mill overhauling duration from 360 hrs to 72 hrs
Longer mill overhaul period
Problem faced
Ramagundam Super Thermal Power Station NTPC Limited
SPARE MILL TOP BODY ASSEMBLY
Improvement actions
Day 0 : Ensure healthiness of hoistSpare mill top body housing is renovatedAll new spares are available near millErection of necessary approach platforms
Day 1 : Removal of coal pipes
Removal of top mill body assemblyRemoval of loading ringRemoval of top ringRemoval of grinding balls
Day 2 : Cutting & removal of air regulating rings
Removal of bottom ringRemoval of coal drop plateReplacement of middle shell wear platesLoading of new bottom ringReplacement of U clamps, knee assy.
Longer mill overhaul period
Problem faced
Ramagundam Super Thermal Power Station NTPC Limited
Improvement actions
Day 3 : Replacement of air regulating ringFull welding of middle shell wear plates & air regulating rings with protection bars.Loading of new grinding ballsLoading new top ringLoading of spider ringAssembly of U clamp and knee assy.Replacement of mill top body assy. with spare top body assy.Re-fixing of coal inlet pipeRe-fixing of PF discharge pipe
Longer mill overhaul period
Problem faced
Ramagundam Super Thermal Power Station NTPC Limited
Improvement actions
1. Rack & pinion arrangement were taken out side of the tramp iron gate assembly
2. Stone pickers are introduced in CHP
This eliminated the problem of choking / jamming
Frequent choking / jamming of reject passages
Problem faced
Ramagundam Super Thermal Power Station NTPC Limited
Improvement actions
1. Highly skilled maintenance practices were developed for mill gear box servicing.
2. Scheduled replacement of gear box was adopted.
3. Stringent QP for procurement4. Photos
These resulted in elimination of mill gear box break down.
Frequent mill gear box break downs
Problem faced
Ramagundam Super Thermal Power Station NTPC Limited
1. Machining of Turn Plate at landing surface
2. Banding of bottom rings3. Photos
These resulted in reduction of premature failure of grinding rings.
Improvement actionsProblem faced
Pre-mature failure of grinding rings
Ramagundam Super Thermal Power Station NTPC Limited
1. Replacement of original carbon steel PF pipes by ceramic pipes
2. Minimizing flanged joint by direct welding, wherever possible
3. Ensuring proper machined mating surface at flanged joint
This resulted in elimination of mill outages due to PF leakages
Improvement actionsProblem faced
Mill outages due to PF leakage
Ramagundam Super Thermal Power Station NTPC Limited
MAINTENANCE PRACTICES
AT
RAMAGUNDAM SUPER THERMAL POWER STATIONNTPC LIMITED
Ramagundam Super Thermal Power Station NTPC Limited
• To maximize availability of generating units with minimum maintenance cost and downtime.
• To carry out maintenance jobs as per laid downprocedures within stipulated time.
• To plan for overhauls, statutory inspection and toobtain statutory certificate from the competentauthority for the safe running of the equipment.
• To ensure safety during isolation, maintenanceand re-commissioning.
OBJECTIVEOF
MAINTENANCE MANAGEMENT SYSTEM
Ramagundam Super Thermal Power Station NTPC Limited
Our philosophy is for Zero breakdown between
overhaul to overhaul by adopting various new
initiatives like – Outage preparedness index.– Activity Based planning and monitoring– Contract rationalization– Rolling plan of equipment.– REAP
MAINTENANCE STRATEGY
Ramagundam Super Thermal Power Station NTPC Limited
Preventive Maintenance. Predictive Maintenance. Proactive Maintenance. Planned maintenance
(Overhaul/Servicing) Break Down Maintenance Life Assessment.
MAINTENANCE PRACTICES
Ramagundam Super Thermal Power Station NTPC Limited
PREVENTIVE MAINTENANCE
Ramagundam Super Thermal Power Station NTPC Limited
PREVENTIVE MAINTENANCE
PM is time based maintenance. The frequency & scope is based on-
OEM RecommendationSite Experience
After SRCM, this frequency and scope have been revised. This is mainly based on failure modes.
Ramagundam Super Thermal Power Station NTPC Limited
MAINTENANCE PRACTICES :DURING 4 WEEKLY PM CHECKS :
1. Mill Internal inspection & Repair.2. Mill gear box Internal Inspection.3. Loading system rectification.4. Mill coupling Healthiness 5. Checking.6. Measurement of Grinding Rings & Balls.7. Checking of Plough brush assly.
Ramagundam Super Thermal Power Station NTPC Limited
PREDICTIVE MAINTENANCE
Ramagundam Super Thermal Power Station NTPC Limited
Technologies in use : Vibration analysis Infrared thermo graphy Motor current signature analysis Wear debrisanalysis
PdM EXISTING PRACTICE
Ramagundam Super Thermal Power Station NTPC Limited
Vibration monitored at pre determined
frequencies and abnormalities reported
are for corrective action.
Trending done for critical equipments to
keep a track of the equipment behavior.
VIBRATION ANALYSIS
Ramagundam Super Thermal Power Station NTPC Limited
Oil sample is collected from various equipment at pre determined frequencies for wear debris analysis
Being done at site by condition monitoring group If required, sample of the oil is sent to R&D for
detail analysis Trending of the result being done to plan for
inspection Corrective action is taken up after receipt of report
WEAR DEBRIS ANALYSIS
Ramagundam Super Thermal Power Station NTPC Limited
MAINTENANCE PRACTICES :DURING RUNNING :
1. Gear box Oil level and Oil Pressure checking2. Gear box vibration, temperature and abnormal
sound checking3. Monitoring operating parameters4. Checking for PF Leakages5. Checking for hot air leakage6. Checking for any oil leakage7. Any abnormal sound from mill
Ramagundam Super Thermal Power Station NTPC Limited
PROACTIVE MAINTENANCE
Ramagundam Super Thermal Power Station NTPC Limited
PROACTIVE MAINTENANCE
Proactive maintenance is in the case of repeated failures. We go in to root cause of failure & do necessary correction by way of change in operating practices / small modification in system / maintenance practices.
Ramagundam Super Thermal Power Station NTPC Limited
PLANNED MAINTENANCE
Ramagundam Super Thermal Power Station NTPC Limited
Practices:• Pre-overhaul• During overhaul • Post overhaul
PLANNED MAINTENANCE
Ramagundam Super Thermal Power Station NTPC Limited
Pre-overhaul:• Preparing Engineering declaration of all the
units as per OPI guidelines.
• Identification of resources ( materials, contracts & T&P).
• Review of the materials & contracts status.
• Distribution of engineering declaration to all concerned before the start of overhaul
PLANNED MAINTENANCE
Ramagundam Super Thermal Power Station NTPC Limited
During overhaul:
Ensuring proper isolation of the equipments
before start of the work.
Making Quality check protocols
Making Re-commissioning check sheets
Maintaining Communication log book
PLANNED MAINTENANCE
Ramagundam Super Thermal Power Station NTPC Limited
During overhaul:• Safety survey & training to agency personnel.
• Constituting Knowledge team
• Daily review meeting
• Review of works planned & actual done.
• Feed back to all concerned.
PLANNED MAINTENANCE
Ramagundam Super Thermal Power Station NTPC Limited
Post-overhaul:
• Preparing executive summary
• Preparation of Unit overhaul completion
report.
• Post overhaul review of improvement
• Pay back calculation
PLANNED MAINTENANCE
Ramagundam Super Thermal Power Station NTPC Limited
BREAKDOWN MAINTENANCE
Ramagundam Super Thermal Power Station NTPC Limited
• Defect registration is normally done by
operation group
• Emergency Nature : Respective Maintenance
to act immediately
• Other Jobs : Scheduled by MTP and then
maintenance to rectify the defect.
BREAKDOWN MAINTENANCE
Ramagundam Super Thermal Power Station NTPC Limited
Management Information System
1. Daily report
2. Weekly report
3. Monthly report
4. Yearly report
5. Unit overhauling report
Ramagundam Super Thermal Power Station NTPC Limited
PULVERIZER TROUBLESHOOTING
Ramagundam Super Thermal Power Station NTPC Limited
• Reasons for Poor fineness
Incorporated slots in air regulating ring to distribute primary air in the mill properly
Classifier cone may be eroded Incorrect adjustment of
classifier bladesExcessive wear out of grinding
elementOverloading of millFuel quality has deterioratedThe Air/Fuel ratio is very high Increased through put
Pulverizer Troubleshooting
Ramagundam Super Thermal Power Station NTPC Limited
• Reason for abnormal sound from mill
Most probable is the entry of foreign matter in the grinding element
Break down of some internal parts, e.g. U clamp, knee assembly
Pulverizer Troubleshooting
Ramagundam Super Thermal Power Station NTPC Limited
• Reason for High rejects
Change in coal grindability, sulfur & ash
The relief gate is jammed openThe air regulating ring has too
much gap with bottom ring Grinding elements are in
precarious conditions & adding a filler ball is the necessity
Pulverizer Troubleshooting
Ramagundam Super Thermal Power Station NTPC Limited
• Mill lub oil pressure low
Lub oil pump is not developing pressure
Leakage from lub oil linesAir suction in lub oil lineFilter chockage Improper relief valve adjustment
Pulverizer Troubleshooting
Ramagundam Super Thermal Power Station NTPC Limited
• Mill coupling failure
Over load in mill due to some foreign material
Mill motor troubleCoupling material defectMill gear box failure Lack of grease in coupling
Pulverizer Troubleshooting
Ramagundam Super Thermal Power Station NTPC Limited
Pulverizer Troubleshooting
• Lack of capacity orHigh power consumption
High moisture Low GCV Increased raw coal sizeGrinding too fineExcessive wear out of
race
Ramagundam Super Thermal Power Station NTPC Limited
Pulverizer Troubleshooting
• Low coal / air temperature at mill outlet
High moisture in coal Low PA inlet temperaturePassing of cold air damperMill got unloaded
Ramagundam Super Thermal Power Station NTPC Limited
THANK YOURamagundam Super Thermal Power Station
NTPC Limited