l a i r e t a M g n i n i a r T
Process ro cess and Opera Operati tion on Operating Operating Princi ples
Raw LOESCHE Raw
Date: 2009-09-03 2009-09-03
Material Material Mill wit h Classifi er
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LOESCHE Raw Material Mill - Operating Principles
Pos: 1/CustomerService/Basis schulungClassro om/Operatin gPrinciples- RM@8\mod_12519 0225764 1_6.doc@80626@122222 2222
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LOESCHE Raw Material Mill - Operatin g Princi ples To achieve a correct operation concerning product quality, safety as well as in economical respects.
1.1
1.2
1.3
1.4
Material feed –
feed mass flow is measured by belt conveyor weighing cell
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must be continuously, but variable (speed of weighing feeders is controlled)
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grain size must be according to layout (not to big / to fine material)
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temperature of feeding material should be constant
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fast variation / fluctuation cause a disturbance of the operation (vibration)
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pieces of metal must be separated before mill, otherwise they cause a damage of the grinding parts
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interruption of mass flow causes the lifting of the rollers (no Stop Sequence)
Temperature mil l outl et –
is measured behind the classifier, is controlled
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is the indication for the drying process in the mill
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to low temperature: insufficient drying – clocking in the dust transport and raw meal silos
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to high temperature: damages of roller / classifier bearings and sealings
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HH, LL limit, fixed during commissioning cause the stop of the mill fan (HH) or the stop of the mill feed (LL) automatically
Temperature mill inlet –
is measured on mill inlet ducts
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should not exceed a certain value (especially during heating up)
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should be as high as possible to avoid a high amount of reject material
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is measured in the clean duct behind cyclones and controlled
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should be kept constant, independent of fluctuations in pressure or temperature of the system
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The required flow rate will be adjusted during commissioning (depends on the quantity and quality of production)
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air flow is a combination of
Mill air flow
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circulation air
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fresh air
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hot gas (if necessary)
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evaporated water
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false air
to low air flow: ●
accumulation of the material in the mill (product finer)
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LOESCHE Raw Material Mill - Operating Principles
–
1.5
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increasing of reject amount
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operation disturbances
to high air flow: ●
more material can pass the classifier (product coarser)
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higher wear
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no economical operation because higher power consumption
Mill inlet pressu re –
static pressure is measured in both mill inlet gas ducts
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need to be kept constant (controlled by position of recirculation damper “R”)
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negative pressure should be maintained in all operation conditions
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to high pressure (>0): dangerous (getting overpressure) = disturbance of the gas flow and grinding process
– 1.6
to high negative pressure: increasing the power consumption of the mill fan
Mill diff erential pressu re –
Static pressure before and behind mill is measured separately, but 1 pipe of each goes to another transmitter for dp
–
indicates the present charging of the mill
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depends on ●
feed mass flow
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gas flow
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grinding pressure
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classifier speed
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dp should be kept constant between Min and Max
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too low dp: part load condition of the mill = uneconomical operation condition increase of feed rate required
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to high dp: ●
check feed rate
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mill motor power consumption
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grinding pressure
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1.7
height of grinding bed reduce feed rate required HH – stop feeding, start feed after achieving normal values
Grindi ng pressur e –
is generated by the oil pump in the hydraulic system (HSLM)
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will be transferred into the grinding bed via hydraulic cylinder / rocker arm / roller
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grinding pressure and nitrogen pressure in the accumulator must be monitored (even after changing the nitrogen pressure)
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is decisive for the efficiency of the grinding process
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to low pressure: ●
lower mill output / coarser product
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LOESCHE Raw Material Mill - Operating Principles
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–
1.8
to high pressure: ●
higher wear
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rough mill operation
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uneconomical operation
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pressure drop in the hydraulic system below a certain limit (LL) causes a mill stop
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contract: Residue on 90 µm-mesh = 12 %
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is influenced by:
Produc t fineness
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classifier speed (higher speed – finer product)
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air flow (lower gas flow – finer product)
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HSLM grinding pressure
hourly analyse is necessary to keep the product quality ●
1.9
increase of reject quantity and mill differential pressure
adjustment of the classifier speed if necessary
Mill vibr ation –
is measured constantly as velocity mm/s in horizontal direction above the mill door
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HH limit is set during commissioning, in case of exceeding HH-limit the mill motor will be stopped to avoid mechanical damages
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Reason for high vibration level is an imperfect operation: ●
Grinding bed too low with to high grinding pressure
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No stable feed rate to the mill (e.g. 1 component missing)
Feeding material is to fine (grinding pressure needs to be reduced) ●
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To high wear rate of the grinding parts – roller are too low
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