𝐕𝐑𝐌 𝐓𝐫𝐨𝐮𝐛𝐥𝐞𝐬𝐡𝐨𝐨𝐭𝐢𝐧𝐠

1. Presented by Dipl. Ing. Andreas Gajewski / Vikas Vaish
Customer Service
Senior Commissioning Engineer / Process
Loesche GmbH, Germany
gajewski@loesche.de
www.loesche.com
Training on The Job
Trouble Shooting
Loesche Vertical Roller Mill
LM 56.4 / LM 35.3 D / 56.3 + 3 C/S
for
Pearl Dhar Cement plant

2. 25-Apr-23 2
Training presentation
does not
substitute technical documentation!

3. 25-Apr-23 3
Some of the figures are illustrations and do not illustrate the built version.
For specific details please consult the documentation.
Compliance with safety instructions is mandatory.

4. 25-Apr-23 4
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

5. 25-Apr-23 5
▪ A grinding system is optimised to the surrounding conditions
▪ Material properties
▪ Product qualities
▪ External heat sources
▪ Etc.
▪ Optimum conditions are achieved by optimum adjustments
(mechanical and process wise).
▪ Mechanical optimisation
▪ Spring stiffness tuning
▪ Fitting the grinding force to the related conditions
▪ Dam ring and support ring optimisation
▪ Process optimisation
▪ Utilisation of PID loops
▪ Optimum tuning of PID control loop
▪ Use of master group/expert system
General

6. 25-Apr-23 6
▪ A plant will operate continuously and with highest efficiency and reliability
under the above mentioned conditions.
▪ Apart from smooth operation reliability is one of the most beneficial factors
of an automated process.
▪ Without well planned and scheduled maintenance trouble shooting witll
become costly.
General

7. 25-Apr-23 7
▪ A VRM reacts within minutes or even seconds
▪ Immediate and sometimes major actions / adjustments are needed
▪ During upset conditions typically vibrations occur, ignore until going out of hand
▪ Best case reaction: reduction of working pressure
▪ Worst case: mill trips
▪ Feed stops
▪ Mill motor stops
▪ Rollers raise and stay raised in stand-by mode
▪ Mill fan and HGG are reduced to minimized operation (stand-by)
▪ Dampers go to stand-by adjustments (TBD)
▪ Identify reason for mill trip – do not restart tripped mill
▪ Immediate restart possible since mill is still hot:
▪ Increase fan to > 70 %
▪ Adjust dampers to feed start position
▪ Start mill drive
▪ Start feed, rollers will lower automatically
▪ If operator is available plant will be back to full production in < 15 min
General

8. 25-Apr-23 8
Normal mill operation
Possible factors of disturbance
Lack of mechanical
maintenance
Frequent changes of
feed properties
Improper sealed
electrical connections
Lack of E,C&I maintenance
Operator‘s misinterpretation of
operating conditions
General

9. 25-Apr-23 9
▪ Comparison of operating data, trend and frequent inspection / maintenance
will give information on slowly developing problems.
As for e. g.:
▪ Wear
▪ Drift of indications of operation parameters
▪ Clogging of filters
▪ Pollution of oil
▪ etc.
General
Prevention is the key

10. 25-Apr-23 10
▪ Process Parameters:
Properties that are important to the process but cannot be adjusted directly.
Examples: temperature, gas pressure,…
▪ Process Control Parameters:
Properties that can be adjusted and will influence / control the process and hence the
process parameters. Examples: damper position, fuel rate, ..
▪ Quality Parameters:
Properties of the final Product that cannot be adjusted directly .
Examples: Blaine value, residue on sieves, …
▪ Quality Control Parameters:
Properties that can be adjusted and will influence / control the final product quality.
Examples: classifier rpm, gas flow, ..
Definition of different parameters :
General

11. 25-Apr-23 11
Process parameters and related control parameters
(in sequence of importance)
▪ Gas flow: mill fan rpm / damper position
▪ Mill outlet temperature: HGG fuel / fresh air / recirculation gas flow rates
▪ Mill differential pressure: feed rate / working pressure / gas flow
▪ Mill inlet pressure: stack / recirculation / fresh air damper positions
▪ Mill vibration: various reasons
▪ Power consumption: feed rate / working pressure / position of S-rollers
▪ Grinding bed depth: Feed rate / working pressure / position of S-rollers
General

12. 25-Apr-23 12
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

13. 25-Apr-23 13
Process gas flow

14. 25-Apr-23 14
Measured by
▪ Venturi tube
▪ Various sensors
▪ Mill fan motor power consumption
Influenced by
▪ Mill differential pressure
▪ Recirculation
▪ Stack / fresh air damper positions
▪ HGG on / off
Controlled by
▪ Mill fan rpm
▪ Mill fan damper
SecondaryInfluences
▪ Feed rate
▪ HSLM working pressure
▪ Classifier rpm (mill differential pressure)
▪ Control mill inlet pressure
(Stack/Recirculation Dampers)
▪ Control mill outlet temperature (HGG
function / FreshAir Damper)
Automated control loop necessarydue to multiple influences and major importance
of gas flow for the entire process and product quality
Process gas flow

15. 25-Apr-23 15
Observation Analyse reasons Possible measures
Gas flow increases checking of
– feed
– control loop
– venturi pipe / pitot tube
– product fineness
– classifier
– false air
– closing fan inlet damper or
– decreasing fan speed
Gas flow decreases checking of
– instrumentation
– reject
– control loop
– Δ P (mill or filter / cyclone)
– opening fan inlet damper or
– increasing fan speed
Gas flow < LL checking of
– control loop
– function of fan damper “C” (only RM)
– venturi / pitot tube measurement
– stopping mill feed
Process gas flow

16. 25-Apr-23 16
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

17. 25-Apr-23 17
Mill outlet temperature

18. 25-Apr-23 18
Measured by
▪ Thermometer
▪ Thermocouple
▪ PT100 in mill outlet duct
Controlled by
▪ HGG fuel flow rate
▪ Position of fresh air damper: open
Influenced by
▪ Feed temperature
▪ Water injection
▪ Recirculation gas
SecondaryInfluences
▪ Mill differential pressure control (feed rate – temperature)
▪ Vibration control (water injection)
▪ Control of mill inlet pressure (stack / position of damper in recirculation duct)
Automated control loop necessarydue to multiple influences and major importance of gas
temperature for the entire process / product quality
Mill outlet temperature

19. 25-Apr-23 19
▪ Possible reasons
▪ Temperature control loop failed
▪ Water injection failed
▪ HGG failed
▪ FreshAir damper blocked
▪ …
▪ Mill outlet temperature too hot > 100 °C (except Slag Mill, where limit is > 110 °C)
▪ Usually resulting in mill vibration due to gas flow capacity reduction (gas too
thin to lift sufficient material from table => grinding bed too high, table too full)
▪ Mill outlet temperature too cold < 60 °C
▪ Usually resulting in quality problems with cement strength and low Blaine
value, vibration also possible (gas too dense, lifting too much material from
table => grinding bed too thin, table too empty)
In both cases large correction steps are needed by increasing / decreasing the HGG
fuel flow and / or adjusting the fresh air damper more close / open.
Remark: in Clinker/Slag Mills; Water injection is NOT meant for temperature control!
Mill outlet temperature too hot / too cold

20. 25-Apr-23 20
Observation Analyse reasons Possible measures
Temperature
increases
Temperature > HH
checking of
– control loop
– water injection
– HGG / hot gas supply
– fresh air damper blockage
– blockage of feed system
– feed moisture
– start water injection
Coal mills:
– reduce booster fan speed
– open hot air damper
CS and RM mills:
– open damper „Z“
– reduce HGG load
– quick stop
Temperature
decreases
Temperature < LL
checking of
– control loop
– water injection
– HGG / hot gas supply
– fresh air entrance
– feed rate
– feed moisture
– reduce water injection
Coal mills:
– increase booster fan speed
– close hot air damper
CS and RM mills:
– close damper „Z“
– increase HGG load
– stop mill feed
Mill outlet temperature

21. 25-Apr-23 21
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

22. 25-Apr-23 22
Mill differential pressure

23. 25-Apr-23 23
Measured by
▪ Pressure measurements before / after mill (pressure transmitters)
Controlled by
▪ Mill feed rate
▪ Weigh feeder speed
Influenced by
▪ HSLM working pressure
▪ Gas flow rate
▪ Classifier rotor rpm
▪ Gas temperature
SecondaryInfluences
▪ Quality control (classifier rpm, hydraulic pressure)
▪ Mill fan rpm / damper control (gas flow rate)
▪ HGG fuel rate / fresh air damper position (mill outlet temperature control)
Feed Rate is kept constant, the other parameters are to be adjusted
Mill differential pressure

24. 25-Apr-23 24
Observation Analyse reasons Possible measures
Δ P increases checking of
– working pressure
– feed rate
– classifier speed
– air flow
– temperature
– reduce feed rate
Δ P decreases checking of
– feed
– classifier speed (product fineness)
– air flow
– working pressure
– temperature
– increase feed rate
Δ P > HH checking of
– product quality
– working pressure
– wear of grinding parts
– hydraulic and N2 pressure
– feed
– stop mill feed
Mill differential pressure

25. 25-Apr-23 25
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

26. 25-Apr-23 26
Mill inlet pressure

27. 25-Apr-23 27
Measured by
▪ Pressure measurements before mill (pressure transmitters)
Controlled by
▪ Recirculation damper
▪ Stack damper
Influenced by
▪ Mill differential pressure
▪ Fan pressure/rpm
▪ Fresh air damper position
SecondaryInfluences
▪ Feed rate
▪ HSLM working pressure
▪ Classifier rpm (mill differential pressure)
▪ Temperature control mill outlet (HGG function / freshair damper)
▪ Gas flow control (fan rpm)
Typically an automatic control loop is used to keep this parameter constant
REMARK: Overuse of recirculation gas may cause dew point problems
Mill inlet pressure

28. 25-Apr-23 28
Observation Analyse reasons Possible measures
pressure increases
(going to positive)
CS & Coal mills; check:
– damper „S“ is open
(it should never be closed more than 50%)
– enough wet gas can exit the system
– false air
– position of damper “R”
RM mill; check:
- gas amount from preheater-tower or kiln and
- position of damper “B”
- position of damper “C”
- position of damper “R”
– close damper “R”
pressure
decreases
(going to negative)
CS & Coal mills; check:
- damper „S“ is open
(it should never be closed more than 50%)
- position of damper “R”
RM mill; check:
- position of damper “B”
- position of damper “C”
- position of damper “R”
– open damper “R”
Mill inlet pressure

29. 25-Apr-23 29
Observation Analyse reasons Possible measures
pressure > 2 mbar CS & Coal mills; check:
- if damper „S“ is open
(it should never be closed more than 50%)
- ring duct
- position of damper “R”
- false air
RM mill; check:
- position of damper “B”
- position of damper “C”
- position of damper “R”
- gas flow through the mill
- ring duct
– stop mill feed
Mill inlet pressure

30. 25-Apr-23 30
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

31. 25-Apr-23 31
Mill vibration

32. 25-Apr-23 32
Measured by
▪ Vibration sensor mounted at the mill body
Influenced by
▪ Grinding bed depth
▪ Grinding bed fineness
▪ Grinding bed moisture
▪ S-roller position / rpm
▪ Water injection flow
▪ HSLM working pressure / counter pressure
SecondaryInfluences
▪ Wear of rollers / table (dam ring)
▪ Mill too empty / full (differential pressure, grinding bed depth)
▪ Feed size
▪ Product quality (grinding bed fineness)
▪ Feed moisture (grinding bed moisture)
▪ Nitrogen accumulator charge
REMARK: Changing conditions of feed and wear profile need constant vigilance
Mill vibration

33. 25-Apr-23 33
▪ Increased mill vibration is the most typically upset condition.
▪ If the vibrations exceed level 1 i.e. H alarm, the computer interlocking will try to raise the
rollers in fast mode followed by re-lowering of the rollers.
▪ If this is too late and the vibrations exceed level 2 i.e. HH alarm, the computer interlocking
will stop the feed and the mill motor, keep the rollers raised and adjust the gas ways to
the stand-by mode.
▪ If the vibrations are higher than normal, but not yet at level 1 i.e. H alram, the operator
needs to identify the reason and perform the countermeasures as described in next slide.
Mill vibration

34. 25-Apr-23 34
Observation Analyse reasons Possible measures
Mill vibrations > HH Process disturbances:
- feed material too fine
- working pressure too high
- feed rate too low
- process gas flow too low
Mechanical disturbances:
- metal separator and / or metal
detector do not work properly
- iron parts inside in the mill more,
mill has to be cleaned & checked:
classifier, roller, table, lining
– stop mill motor
Mill vibrations

35. 25-Apr-23 35
Possible causes / indications / countermeasures
Mill too empty / too full
Indications:
▪ Mill differential pressure too low / too high
▪ Grinding bed too low / too high
Countermeasures:
▪ Increase / decrease feed rate
▪ Decrease / increase working pressure (may change product quality)
▪ n. a. / increase water injection rate
▪ adjust position of S-rollers
▪ Increase / decrease classifier rpm (will change product quality)
▪ Decrease / increase gas flow rate
Mill vibrations

36. 25-Apr-23 36
Possible causes / indications / countermeasures
Material on grinding table too wet / dry (too wet unlikelyfor CS mills)
Indications:
▪ M-roller position (grinding bed depth) shaky (frequently jumping up / down)
▪ S-roller rpm in position - control shaky
▪ S-roller position in rpm - control shaky
▪ Mill outlet temperature too low / too high or less / more fresh air required
Countermeasures for too dry material:
▪ Adjust S-roller position (plant specific, TBD)
▪ Decrease HSLM working pressure (may change product quality)
Mill vibrations

37. 25-Apr-23 37
Possible causes / indications / countermeasures
Mechanical or maintenance reasons
▪ Nitrogen accumulators leaky, loss of pressure, loss of shock absorbing
▪ Internal wear of grinding plate / roller tires without re-calibration of roller position
Indications
▪ Excessive wear of grinding plate / roller tires
▪ Faulty indication of gas flow (re-calibration needed)
▪ Mechanic damage to the dam ring (e. g. by tramp metal)
▪ Mechanic damage to the grinding plate / roller tires (e. g. by tramp metal)
▪ ……
Preventive maintenance helps avoiding vibrations due to mechanical reasons.
Mill vibrations

38. 25-Apr-23 38
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

39. 25-Apr-23 39
Vital for roller tires
and grinding plate
Metal detection and separation
Raw material
Metal
Reject material

40. 25-Apr-23 40
▪ Metal detector has to be properly fine tuned to detect even small tramp metal pieces
without being too sensitive
▪ The timing between getting the alarm and switching the pneumatic gate over is critical:
▪ If it opens too slow – tramp metal passes by
▪ If it closes back too fast – tramp metal passes by
▪ If it opens too soon and / or stays open too long – waste of clinker
▪ Over-belt magnetic separator typically on a transport before the detector to separate
most of the magnetic metal
Metal detection and separation

41. 25-Apr-23 41
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

42. 25-Apr-23 42
Observation Analyse reasons Possible measures
Power
Consumption
increases
Checking of
- working pressure too high
- feed rate too high
- blockage in reject transport (ring duct)
- wear of grinding parts
- raw material grindability
- lower temperature
- lower process gas flow
- higher feed moisture
- higher water injection
- higher material bed height
- Take appropriate action
according to analysed
reason
Power consumption - Mill motor

43. 25-Apr-23 43
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

44. 25-Apr-23 44
Observation Analyse reasons Possible measures
External material
recirculation rate too
high
Checking of
- gas flow too low
- mill inlet temperature too low
- working pressure too low
- feed rate too high
- wear of dam ring
- wear tires / table liner
- Take appropriate action
according to analysed reason
External material recirculation i.e Reject System

45. 25-Apr-23 45
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

46. 25-Apr-23 46
▪ If - for any reason - the mill feed drops below a safe level interlocking will automatically
raise the rollers and adjust the grinding system to a stand-by mode until the operator
adjusts the gas ways for a re-start and starts the feed.
▪ In case of the feed dropping to a level too low for good operation but above the
interlocked limit the mill reacts with vibration (too empty) until interlocking try to raise
the rollers (fast mode) and to adjust the stand-by mode.
If the roller raising takes too long the mill will trip.
▪ A good operator catches the potential mill trip (alarms) and pro-actively re-adjusts the
feed rate back to normal (in the beginning slightly above to refill the mill) or initiates a
mill stand-by mode before the computer does so.
Mill feed starvation

47. 25-Apr-23 47
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

48. 25-Apr-23 48
▪ Possible malfunctions
▪ Pressure set points for HSLM working / counter pressure are not followed =>
system either unable to built up pressure or unable to drain pressure
▪ Position or rpm set points for the S-Rollers are not followed => System unable
to pressurise one side or unable to drain pressure from the other side
▪ Leakages in hydraulic cylinders / ring line or cabinet
▪ In any one of these cases the control system will sound an alarm and if the deviation
is not fixed within a programmed time the control system will stop the feed and adjust
the mill to a safe stand-by mode.
▪ If the malfunction is severe typically vibrations occur.
▪ A good operator catches the alarms and initiates a controlled mill stop before the
control system takes over.
▪ Due to the complexity of the hydraulic system an expert should review the
malfunction before a re-start.
Hydraulic malfunction

49. 25-Apr-23 49
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

50. 25-Apr-23 50
▪ It is highly recommended that any alarm related to the mill drive (motor and gearbox)
is immediately reported to be reviewed by experienced personnel.
▪ If the condition moves from alarm level to shutdown level and the mill trips, it is
highly recommended not to re-start until an experienced person has reviewed the
trend lines, alarms and general conditions on site and has given the “good to go”.
Mill drive alarms

51. 25-Apr-23 51
General
Process gas flow
Mill outlet temperature
Mill differential pressure
Mill inlet pressure
Mill vibrations
Metal detection & seperation
Power consumption – Mill motor
External material recirculation i.e. Reject system
Mill feed starvation
Mill Hydraulic malfunction
Mill drive alarms
Product Quality (Fineness)
Table of contents

52. 25-Apr-23 52
Observation Analyse reasons Possible measures
Product too coarse Checking of
- wear of grinding parts, dam ring & classifier
- classifier drive (broken coupling)
- working pressure
- gas flow
- increase classifier speed
- increase working pressure
- reduce gas flow
Product too fine Checking of
- classifier speed indication
- working pressure
- gas flow
- reduce classifier speed
- reduce working pressure
- increase gas flow
Change in PSD
- want to steepen
(i.e. less residue)
Increase working pressure +
classifier rpm + gas flow in
appropriate combination
Change in PSD
- want to flatten
(i.e. more residue)
Reduce working pressure +
classifier rpm + gas flow in
appropriate combination
Product Quality (Fineness)

53. 25-Apr-23 53
Thank you for
your attention!