vrm presentation
DESCRIPTION
Vrm PresentationTRANSCRIPT
ROLLER MILL
Used in cement industry
Vertical Mills used for Vertical Mills used for Pre-grinding of clinker (lumps to coarse Pre-grinding of clinker (lumps to coarse
powder)powder) Finish grinding (lumps to powder) of Finish grinding (lumps to powder) of
– Coal/Petcoke for kilnCoal/Petcoke for kiln– Raw materials for kilnRaw materials for kiln– Cement, OPC or mixedCement, OPC or mixed– Slag, pure or mixedSlag, pure or mixed
VRM Functions
Vertical Roller Mill (VRM) - Details
feed gate(air lock)
mill casing
waterinjection
dam ring
louvre ringnozzle of
material scraper
mill outlet duct
speed reducer withtable bearingand motor
clutch
grinding table
hot gas inlet
hydraulic cylinder
table liner
roller with tyreor segments
roller axlerocker arm
discharge flapseparator
tailings cone
separatorguide vanes
cage rotorseparator
product dischargemill exhaust
Working principle
Vertical mills comprise 2-4 conical rollers which are hydraulically pressed onto a horizontal rotating grinding table.
The roller axis is inclined at 15o to the table and, as axes of rollers and table do not intersect in the plane of the table. the relative motion involves both rolling and sliding which enhances comminution.
Feed material is directed onto the centre of the table and is thrown outward by rotation under the rollers and into a rising air current at the periphery which is directed by means of a louvre ring. The air sweep passes through an integral
rotary classifier; fines pass out with the air current while coarse material falls back onto the feed table.
Material drying occurs in air suspension between table and classifier. Circulating load is typically 800%. Roller mills are prone to vibration due to an unstable grinding bed.
A major cause of material instability is fine, dry mill feed which can usually, be mitigated by spraying water directly onto the bed.
VRM - Working principle
Vertical roller mill
Feed size:f (Roller Ø )
Material bed
Feed material
Max Particle size in feed: 5-8 % of roller diameter
Grinding force =
Roller weight + (pressure) Force
Table moves with drive
Roller rolls freely with table
VRM - Material Flow insideGas & Product Material
Feed Material
Separator Rejects
Internal Circulation
Large Material falls through to scraper
Internal gas flow
Material & Gas
Material
Gas
Separator:
removes fine material
rejects coarse material
VRM - Some Common Mill Configurations
G.Pfeiffer Loesche FLS Atox Polysius
static separator conventional rotor type cage rotor typewith guide vanes
F T
P
F F FT T
P
F F
T
P
T F
P
F =
P =
T = Tailings
Product
Feed
F T
VRM - Built-in SeparatorCage Rotor typeConventional
Rotor type
Static type
Separation control:
1. Vane adjustment
2. Speed control
Separators of 3rd Generation (Vertical roller mill)
Guide vane system
Reject cone
Cage rotor
VRM - AccessoriesRotary valve
Weigh belt Metal extraction
Reduces false air entering with feed material. Good for dry, small size material.
Weighs the passing material ensuring a continuous grinding bed in the mill
Metal objects damage the roller & table. The magnet removes them
VRM - External Circulation
Used for reducing gas flow pressure lost over the mill
(less pneumatic internal circulation)
collecting conveyor
fresh feed
louvre ring
scraper
bucket elevator
VRM - Example flow-sheet
Control points
1 gas flow
2 pressure
difference
3 return gas
flow pressure
4 outlet
temperature
5 external
recirculation
VRM MAINTENNACE
Maintenance
Wear - Rollers & Table– - Separator (sealing!) & Housing– Lubrication & Hydraulics (filters and seals)
Outlet duct Inlet chute
Mill housing
Armour & nozzle rings
Rollers and table liners
Separator cone
Separator
Scrapers
Vertical roller mill internals suffering from wear
• Nihard 4
• High Chromium alloys
Wear resistance material alternatives
% C % Cr % Ni Weldable
< 3.5 < 10 < 6.5 yes
% C % Cr % Other Weldable
< 3.6 < 17 Mo + Ni yes
< 2.6 < 20 Mn No
< 3.5 < 28 < 1.2 No
Example
Chromodur, FMU18, VegalineV16s
FMU 52
FMU 46
Wear resistance material alternatives
• Metallic inserts roller liner
Hard metallic insert
Soft material base
• Ceramic inserts roller and grinding track liners
Wear resistance material alternatives
Metallic base (High Cr)
Ceramic insert
Operation and Optimization of Operation and Optimization of Vertical Roller MillsVertical Roller Mills
Raw material characteristics
Feed Size
Product Fineness
Moisture Content
Grindability
Abrasiveness
Ball Mill Maximum 5% + 25 mm
Vertical Roller Mills Up to 150 mm
Feed Size
5% - 25% + 90 µm
1.0% - 2.0% + 212 µm
Product Fineness
Normal moisture content: 3% - 10% H2O
Possible to dry >20% H2O in vertical mills
Up to 6 to 7%-H2O – Drying with kiln gases
Above 7% H2O – Supplementary heat from auxiliary furnace or cooler
Moisture Content in Raw Materials
OPERATIONAL ASPECTS
Material granulometry Roller pressure Dam ring Louvre ring External circulation
PARAMETERS TO BE MONITORED DURING OPEARATION
Production rate, tonnes/hour Grinding press. (bar) or (kN/m2Grinding press. (bar) or (kN/m2)) Mill Motor (Kw)Mill Motor (Kw) Grinding bed thickness (mm)Grinding bed thickness (mm) Vibration level (mm/s) Pressure drop across the mill Mill outlet temperature Fan flow Rejects (If external recirculation present) Water flow
Additional paramters to be monitered
Operating hours Involuntary downtime hours kWh/tonne (mill motor + fan + seperator) Product fineness on 90/212 microns for raw
mill ,coal mill and blaines for cement mill Feed moisture, % Product moisture, % Feed size
How the nozzle ring velocity corresponds to reject rate and pressure drop
Running with a high velocity in the nozzle ring gives a high pressure loss, but also a low reject rate.
However the lower pressure drop with e.g. 45 m/s is to prefer and will both give considerable power savings on the fan and less wear in the mill body
Operational problems
Vertical roller mill for finish grinding
PROVEN TECHNOLOGY
VERY SUITABLE FOR GRINDING BLENDED CEMENT OR SLAG
COMPACT GRINDING INSTALLATION
ENERGY SAVING - UP TO 30%-40% kWh/Mt
SUITABLE FOR GRINDING MOIST FEED
EASY MAINTENANCE AND OPTIMUM UTILIZATION OF WEARING ROLLERS
VRM versus BALL MILL for CEMENT GRINDING
Blaine Surface, cm2/g: 4000
0
10
20
30
40
50
60
70
Mill Fan, etc.
Cement (OPC) Slag
Grinding systems comparisonPower Consumption when grinding to 3800 cm2/gm for 150 tph capacity
GRINDING SYSTEM
CLOSED CIRCUIT
BALL MILL
ROLLER
PRESS PREGRINDER
ROLLER MILL PREGRINDER
ROLLER PRESS SEMI
FINISH
FINISH GRINDING IN
ROLLER PRESS
OK VRM
Mill (kWh/t) 38.2 29.7 28.0 20.8 / 21.8
Separator and Fans (kWh/t) 4.5 3.9 3.9 6.1 14.2 7.2
Roller Press/Pregrinder (kWh/t) / 4.5 10.0 9.7 20.5 /
Auxiliary (kWh/t) 0.6 1.0 1.0 1.5 1.6 0.2
Total (kWh/t) 43.4 39.0 42.8 38.0 36.3 29.2
Maximum Output (t/h) 200 (300) 275 - 300 275 - 300 300 - 350 < 150 450 tph
Operational Guidelines for Process Optimization
LOWER PRESSURE DROP LESS WEAR OF MILL BODY LINERS
FAN POWER SAVINGS OF 15-30%
Nozzle Ring Velocity versus
Material Rejects and Pressure Drop
N/R Velocity Reject Rate Relative Pressure
Drop
(m/s) (% Fresh Feed) (%)
75-85 Trace 100
60-65 5-10 84
40-45 20-30 60
Air flow
A correct airflow in the mill is important, because the air is transporting the material and also an important factor for efficient separation.
Airflow is kept constant through mill and cyclone/ filter by operating the mill fan with constant power consumption on the motor.
This is normally done by the help of an automatic loop between the mill fan damper position and the power consumption of the mill main motor. Alternatively by the help of an automatic loop between the speed of the mill fan motor and the power consumption of the mill main motor.
Feed
A correct feed rate in the mill is important. if the feed rate is to high and the mill be filled up with material and trip on vibration, because the mill fan don’t have the capacity to transport material out of the mill.
If the feed rate is to low will the mill emptied out and trip on vibration, due to low grinding bed. The feed rate depends on the applied grinding pressure and the grind ability of the material.
The mill differential pressure or the mill motor power consumption is an indication of how much material inside the mill. Normally the feed rate is controlled by the mill motor power consumption through an automatic loop.
Vibrations
A constant and acceptable level of vibrations is important.
If vibrations are to high then the mill be stopped by the safety interlocking of the mill in order not to damage the machine.
The vibrations are minimized by injecting water. The injected amount according to experience.
Operational problems
Changes in feed material properties Equipment problems Deficiencies of control elements Control signal errors External effects
Problems -action
Type of problem Action Mill vibrations, Too high
Reduce feed supply if differential pressure is high. Increase feed supply if differential pressure is low. Check water injection. Reduce grinding pressure. Lift rollers at excessive vibrations.
Mill output, Too low
Check grinding pressure. Check differential pressure. Product fineness very fine. Coarser raw materials. Grindability of raw material changed. Raw materials too wet. Table and roller segments are worn.
Mill product, Too coarse
Increase speed of separator rotor. Check sieving of samples.
Mill product, Too fine
Decrease speed of separator rotor. Increase feed supply.
Type of problem Action Mill outlet temperature, Too high
Hot air amount too high. Hot gas temperature higher than normal. Adjust (close) hot gas damper. Decrease oil for heat generator. Open cold air damper. Increase water injection.
Mill outlet temperature, Too low
Raw material moisture increased. Increase hot air amount. Adjust (open) hot gas damper. Adjust (open) mill fan damper. Increase oil for heat generator. Close cold air damper, if open. Decrease water injection
Grinding pressure, decreases
Check hydraulic system. Piping is leaking. Oil pump fault. Oil level in tank for hydraulics minimum. Oil temperature in hydraulics minimum. Malfunction of valves.
Sealing air pressure, Minimum
Filter blocked. Check electrical equipment.
Type of Problem Action
Starting the mill without grinding layer
Fill mill with material before start. Use automatic program for mill filling. The filling must be done manually by starting transport devices in
correct sequence. Fill in 300 – 500 kg of material.
Heat generator is failing No oil/gas available. Oil/gas filter contaminated. Ignition gas bottle empty. Adjustment of ignition and main burner has changed. Pre-heating of oil not working.
Supply of hot gases from kiln interrupted
Mill operation must be stopped. Check position of kiln (hot) gas damper.
Feeder units disturbed Feed supply from other feeders must be increased. Stop the mill, if feed transport fails.
Type of Problem Action Fee bins almost empty Feed bins must be filled up.
Stop the mill. Oil pressure or oil flow through mill gear minimum
Mill will be stopped automatically. Check leakage in piping. Oil pump fault. Oil level minimum. Electrical fault. Oil temperature too high. Check cooling water supply.
Oil pressure or oil flow through the separator gear minimum
Separator and mill will stop automatically. Check leakage in piping. Oil pump fault. Oil level minimum. Electrical fault. Oil temperature too high. Check cooling water supply.
Mill fan bearing temperature maximum
Automatic stop of fan and mill. Check supply of cooling water. Check greasing of fan bearings. Electrical fault.
Vertical roller mill caluclations
Caluclation of capacity of the mill
Generally speaking, the production capacity refers to grinding capacity and drying capacity of grinding mill.
The material grindability will affect the grinding capacity, the roller pressure and the type of grinding mill.
G=K1 * D2.5 Where G is capacity of the mill K1 is coefficient, which is relevant to the
typer of roller mill, the selected and used pressure, the performance of grinded material. Different specification of roller mill, so the K1 is different.
K1 of Loesche Mills series roller mill is 9.6 and for Atox mills it is 7 and for MPS mills it is 6.6.
D is table diameter Example: for atox 50 mill The capacity of mill is G= 7 * D2.5
= 7* 5^2.5 = 391 TPH~ 400TPH