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
Copyright by LOESCHE GmbH Hansaallee 243 D-40549 Düsseldorf Federal Republic of Germany Phone: +49 (0)211 5353-0 Fax: +49 (0)211 5353-500 E-mail:
[email protected] Internet: www.loesche.com
2 The copyright for this document and all appendices is reserved by LOESCHE GmbH
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
1
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
–
must be continuously, but variable (speed of weighing feeders is controlled)
–
grain size must be according to layout (not to big / to fine material)
–
temperature of feeding material should be constant
–
fast variation / fluctuation cause a disturbance of the operation (vibration)
–
pieces of metal must be separated before mill, otherwise they cause a damage of the grinding parts
–
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
–
is the indication for the drying process in the mill
–
to low temperature: insufficient drying – clocking in the dust transport and raw meal silos
–
to high temperature: damages of roller / classifier bearings and sealings
–
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
–
should not exceed a certain value (especially during heating up)
–
should be as high as possible to avoid a high amount of reject material
–
is measured in the clean duct behind cyclones and controlled
–
should be kept constant, independent of fluctuations in pressure or temperature of the system
–
The required flow rate will be adjusted during commissioning (depends on the quantity and quality of production)
–
air flow is a combination of
Mill air flow
–
●
circulation air
●
fresh air
●
hot gas (if necessary)
●
evaporated water
●
false air
to low air flow: ●
accumulation of the material in the mill (product finer)
The copyright for this document and all appendices is reserved by LOESCHE GmbH
3
LOESCHE Raw Material Mill - Operating Principles
–
1.5
●
increasing of reject amount
●
operation disturbances
to high air flow: ●
more material can pass the classifier (product coarser)
●
higher wear
●
no economical operation because higher power consumption
Mill inlet pressu re –
static pressure is measured in both mill inlet gas ducts
–
need to be kept constant (controlled by position of recirculation damper “R”)
–
negative pressure should be maintained in all operation conditions
–
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
–
depends on ●
feed mass flow
●
gas flow
●
grinding pressure
●
classifier speed
–
dp should be kept constant between Min and Max
–
too low dp: part load condition of the mill = uneconomical operation condition increase of feed rate required
–
to high dp: ●
check feed rate
●
mill motor power consumption
●
grinding pressure
●
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)
–
will be transferred into the grinding bed via hydraulic cylinder / rocker arm / roller
–
grinding pressure and nitrogen pressure in the accumulator must be monitored (even after changing the nitrogen pressure)
–
is decisive for the efficiency of the grinding process
–
to low pressure: ●
lower mill output / coarser product
4 The copyright for this document and all appendices is reserved by LOESCHE GmbH
LOESCHE Raw Material Mill - Operating Principles
●
–
1.8
to high pressure: ●
higher wear
●
rough mill operation
●
uneconomical operation
–
pressure drop in the hydraulic system below a certain limit (LL) causes a mill stop
–
contract: Residue on 90 µm-mesh = 12 %
–
is influenced by:
Produc t fineness
–
●
classifier speed (higher speed – finer product)
●
air flow (lower gas flow – finer product)
●
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
–
HH limit is set during commissioning, in case of exceeding HH-limit the mill motor will be stopped to avoid mechanical damages
–
Reason for high vibration level is an imperfect operation: ●
Grinding bed too low with to high grinding pressure
●
No stable feed rate to the mill (e.g. 1 component missing)
Feeding material is to fine (grinding pressure needs to be reduced) ●
●
To high wear rate of the grinding parts – roller are too low
===EndederListefür TextmarkeInha lt===
The copyright for this document and all appendices is reserved by LOESCHE GmbH
5