07 vrm pregrinder
TRANSCRIPT
VRM Cement Pre-grinding system
Cement Manufacturing Services / HGRS
Mechanical Process Technology department /
Grinding Technology group
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SEPT-07HGRS Tikaria_Mill Workshop
Content
Feed Properties
Feed Inlet and Distribution
Dam Ring Modifications
Operation
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SEPT-07HGRS Tikaria_Mill Workshop
Content
Feed Properties
Feed Inlet and Distribution
Dam Ring Modifications
Operation
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SEPT-07HGRS Tikaria_Mill Workshop
Keep correct feed size for roller diameter
d
Limited maximum feed sized < 3 [%] DR for hard materials and < 5 [%] DR for soft material
Particle size distribution: Fraction below 1 [mm] to be kept < 30 [%]
[%]
Particle size [mm]
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SEPT-07HGRS Tikaria_Mill Workshop
Impact of feed which is too fine
d
Vibrations and reduced production
Reasons:
Draw in of feed reduced
Material aeration
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SEPT-07HGRS Tikaria_Mill Workshop
Actions limiting impact of feed which is too fine
Table speed adaptation (slower rotation)
Increase dam ring height if material hard (e.g. slag)
Increase hydraulic pressure of rollers
Inject water
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SEPT-07HGRS Tikaria_Mill Workshop
Impact of feed which is too coarse
Symptoms:
High kW absorption of main drive
Vibrations
Measures:
Modify cooler crusher or install a crusher
Sieving of crusher product
Try to work with higher hydraulic pressure
d
Experience: At Rohoznik too coarse feed leads to permanent overload of the motor to achieve the required production
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SEPT-07HGRS Tikaria_Mill Workshop
Positive results to lower top size
Experiences from India where the vertical raw mill performance was significantly better with finer crusher settings / lower top size:
- Bhatapara, Dorol: 4% production rate increase when hammer crushing setting decreased from 50mm to 25 mm (no change on % particles <2mm)
- Bargarh, Loesche: 8% production rate increase when hammer crushing setting changed from 80mm to 50mm
- Ambuja, 10% production rate increase when the top size was reduced from 100 mm to 75 mm.
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SEPT-07HGRS Tikaria_Mill Workshop
Content
Feed Properties
Feed Inlet and Distribution
Dam Ring Modifications
Operation
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SEPT-07HGRS Tikaria_Mill Workshop
Feed distribution
Basic Rule: Feed on Center of table
product extraction
fresh feed
tailings
coarses
fall through
internalcirculation
(pneumatical)
material
gasgas
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SEPT-07HGRS Tikaria_Mill Workshop
Content
Feed Properties
Feed Inlet and Distribution
Dam Ring Modifications
Operation
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SEPT-07HGRS Tikaria_Mill Workshop
Dam RingMain tasks:
Control of material retention on table
Control of bed depth
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SEPT-07HGRS Tikaria_Mill Workshop
Dam ring Increase the level of material
on the table through an increase of the dam ring height
Optimum dam ring height to be found through trial & error
Modify dam ring height by at least 10 [mm] each time
As the table wears, the dam ring height should be reduced accordingly
In Loesche & Fuller mills, possible additional solution is:
grinding bed
roller
liner
nozzles
table
dam ringControls material bed
thickness
Controls material flow leaving the grinding
zone
100 115 Op. pressure [%]
Vibrations [mm/s]
2.5
3.0
3.5
Low dam ring
Medium dam ring
High dam ringgrinding bed
roller
liner
nozzles
table
dam ring
10 [mm]
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SEPT-07HGRS Tikaria_Mill Workshop
Dam Ring Impact of too high dam ring:
High bed depth Increased power absorption (reduction of pressure required) Reduced grinding efficiency (lower production) Vibrations Lower steepness of PSD
Impact of too low dam ring (also inadequate design):
Low bed depth Vibrations Increased water demand Low power absorption of main drive Lower production Higher PSD steepness
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SEPT-07HGRS Tikaria_Mill Workshop
Problems - SolutionsSituation:
During the operation of the San Sebastian raw mill, a capacity drop was observed over the time of wear of the table. The necessary cut of the dam ring was not done.
Experience:
After the replacement of the table liner with original thickness a significant capacity increase was observed.
Message:
Cut the dam ring as the table wears to maintain optimal material retention and bed depth!
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SEPT-07HGRS Tikaria_Mill Workshop
Problems - SolutionsSituation:
During the operation of the Cartago raw mill, a capacity drop was observed over the time of wear of the dam ring (height was NOT affected).
Experience:
After the repair of the dam ring, the capacity was brought up to the original level. This leads to the conclusion, that primarily the gap contributes to the material retention on the grinding table and not the height of the dam ring.
Message:
Keep the gap between rollers and dam ring small.
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SEPT-07HGRS Tikaria_Mill Workshop
Problems - SolutionsSituation:
During the commissioning of the Ras El Ma cement mill (LM 46 2+2), operation without water let to a reduced production. A Loesche Suggestion was to decrease the dam ring height (removal of 6+8) to reduce vibrations and water injection.
Experience:
After the removal of two dam ring segments the vibrations increased and the production dropped significantly – the water injection had to be increased.
Message:
Lower bed depths do not necessarily lead to an improved grinding performance
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SEPT-07HGRS Tikaria_Mill Workshop
Content
Feed Properties
Feed Inlet and Distribution
Dam Ring Modifications
Operation
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SEPT-07HGRS Tikaria_Mill Workshop
Holcim vertical roller mill distribution vs. reducer damages
Mill Supplier
Nu
mb
ers
of
2822 20
13 10
93
16 1223
4 3
58
0102030405060708090
100
F.L
.Sm
idth
/ Fu
ller-
Lo
esch
e
Lo
esch
e
Po
lysi
us
Geb
r.P
feif
fer
Oth
ers
To
tal
VRM
Damaged Reducer
This seriously affects Holcim’s performance
Statistically every 2nd VRM reducer fails
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SEPT-07HGRS Tikaria_Mill Workshop
Identification of the root cause of a recurrent stoppage is the first step for solving the problem
Symptom Vibrations
Consequence Mill stoppage
Causes
Feed change
Lack of feed
DesignMaintenanceOperation
Low temperatures
High table speedFeeder blockage
But, vibrations can also become a cause for others failures
… …
Hydraulic failed
Worn grinding tools
High operating pressure
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SEPT-07HGRS Tikaria_Mill Workshop
Interlocking and Protection Loop are a MUST
Protection of Mill Main
Drive