VERTICAL VERTICA L RAW RAW MILL MILL AND SEPARATOR
By Phyo Thura Htay
Contents •
Ball mill vs. vertical mill
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Operations
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Structure of a vertical mill
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Working Process
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Components •
Dam Ring
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Armour Ring
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Louver Ring
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Grinding Table
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Rollers
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Separators
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Maintenance
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Performance Improvement
Ball Mill Vs Vertical Mill
Parameters
Ball Mill
Vertica erticall Mill
Crushing
Smaller Impact by Steel Balls/Rubbing
By Compression/ Impact Force
Drying
Limited area and capacity
Larger Drying Capacity
Material Circulation
Only the coarse materials are fed back
Rejected material + Fines are fed back
Energy Consumption
High
Low
Operation Cost
100%
80%
Operations Grinding • •
Raw materials Cement
Drying •
Removal of water
Separation • •
Coarse solids Fine particles
Structure of Vertical Mill
Working Process
Working Process
Material Material & Gas Gas
Components •
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Inlet chute Mill Table •
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Rollers •
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Roller wheels Rocker Arm Hydraulic Hydrau lic cylinder
Separator •
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Dam ring Armour ring Louver ring Grinding table
Cage rotor Reject cone
Scrapers Outlet duct Motor External Circulation
Dam Ring •
Vital part
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Material (bed) thickness
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Retention Time
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Air/gas flow pattern around mill table
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Mill capacity, fineness, vibration, power, etc.
a
a
Armour Ring Armour Ring Mill Body •
Protection of Mill Body Dam Ring
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Separator Performance
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Related with the Dam Ring
Table Air Flow
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Configuration (Inclination)
Low Angle ( < 50 ) °
High Angle ( > 70 ) °
Air Flow into the table
Unnecessary Circulation
Uniform flow of fine particles
Efficient Separation
Louver Louv er Ring Longer time for drying material
Swirling air in mill body
Reduce separator rotor driving power
May or May not be installed
Grinding Table •
Transmits the entire force and mill power
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Depends on •
Feed material size
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Feed material moisture
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Dam ring height
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Grinding fineness
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Air Speed in nozzle ring Table
Grinding bed too low => Vibration
Little Vibration, Efficient Grinding
Grinding bed too high => Insufficient Insufficie nt grinding
Rollers •
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Large, tapering rotating cylinders Large linking elements required between hydraulic cylinder and roller arm Hydraulics critical
Grinding Concept Vertical roller mill Grinding force = Roller weight + (pressure) Force
Roller rolls freely with table Material bed
Feed material
Table moves with drive
Max Particle size in feed: 5-8 % of roller diameter
Feed size: f (Roller Ø )
Separator Reject cone
Cage rotor
Guide vane system
Separator
FR
Air
External Circulations fresh feed
bucket elevator
louvre ring
scraper
collecting conveyor
Maintenance
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Vibration •
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To avoid excess fine on mill table To apply grinding aids To apply water to mill of material To avoid the mill outlet gas temperature more than 100 C °
Typical Wear cycle New rollers
Rollers partly worn peak efficiency
Vibration worsens
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T/H
Rollers need to be replaced. TIME Grinding efficiency worsens as you lose roller shape.
Performance Perf ormance Improv Improvement ement Continuous control of the air flow measurement (annubar vs exhaust fan efficiency)
Water injection peripheral: clogging on-line detection. Water injection on table inconclusive
Dam ring: height regularly controlled. To adapt to table profile
Periodic control of nitrogen pressure
False air reduction
Reduction of the gap Between the table and the Nozzle ring
Maintain in good state the belt height sensors, have a proper calibration
