Ball and tube mill

2. BALL & TUBE MILL
 Tube and ball mills:- These are low-speed machines that grind
the coal with steel balls in a rotating horizontal cylinder.
In stage –II ball & tube mills are used. Ball and Tube Mill
is basically horizontal cylindrical tube rotating type of
mill at low speed on its axis, whose length is slightly
more to its diameter. The inside of the Cylinder shell
is fitted with heavy cast liners and is filled with cast
or forged balls for grinding of coal.

4. Tube mills: The tube mills are low-speed machines that grind the coal with
steel balls in a rotating horizontal cylinder. Due to its shape only, people
call it as Tube Mill and due to use of Grinding Balls for crushing, it is called
Ball Mill. Hence, is the name Ball Tube Mill

5. TUBE MILL
Tube mills are employed to pulverize the pre-crushed
raw coal to the required fineness before it is admitted
into the boiler furnace for combustion.
The operating characteristics i.e. Faster response to
Load variation of tube mills make it the best mill
available for the direct firing system of the coal.

6. TUBE MILL
These are slow speed Mills. The Mills are
designated as BBD-4772
Where,
B – Broyer (Name of inventor).
B – Boulet (French word for Balls).
D – Direct firing.
47 – Diameter of shell (in Decimeters) i.e. 4.7m dia.
72 – Length of shell (in Decimeters) i.e. 7.2 m length.

7. MILL DETAILS
• Design coal capacity- 83.15 Tons/Hr
• Ball charged- 90 Tons
• Speed – 15 to 16 rpm
• Screw assembly- Right hand helix (DE side)
Left hand helix (NDE side)
• Direction of rotation of Shell from NDE end-
Anti-Clockwise.
• Shell door opening- two numbers.
• Shell liners- 600 nos. (10 different varieties)
• weight of liners- 60.26 MT

10. ELECTRO MAGNE TIC BRAKE
SYSTEM

11. STEAM INERTING SYSTEM

12. MILLING SYSTEM OF STAGE-II
 LUBRICATION SYSTEM OF MILL
 PURGING SYSTEM OF MILL
 STEAM INERTING SYSTEM
 GREASING SEQUENCE OF MILL
 CONTROL LOOPS OF MILL
 MILL DP LEVEL MEASUREMENT
 MILL NOISE LEVEL MEASUREMENT

13. MILL LUBRICATION SYSTEM

14. LUBRICATING PUMPS
 02 Nos. HP PUMPS- for lifting of mill shaft from
horizOntal side.
 02 Nos. B&S PUMPS (BALL & SOCKET PUMP)- for lifting
of shaft of mill bearing from bottom side.
 02 Nos. LP PUMPS- Discharge of LP pump provides
suction to HP & B&S PUMP as well as lubrication to mill
bearings also.
 02 Nos. REDUCER LUBE OIL PUMPS- provide lubrication
to mill motor gear box coupling.
 02 Nos. GREASE PUMPS- provide greasing to cylinder of
mill drum gear assembly.

15. Mill greasing & reducer
lubrication

16. GREASING SYSTEM

17.  ‘Mill lubrication OK’ is generated if:
 Any LP pump on
 AND
 Oil flow in LP circuit OK
 AND
 Any HP pump on And pr not low
 AND
 Greasing sequence correct
 AND
 Any reducer pump on
 AND
 Reducer lube oil temp not high
 AND
 Reducer lube oil flow not low
 AND
 Any B&S pump on And pr not low

18. Mill Lubrication Correct
&
Red Lub OK
Brg Lub OK
Greasing Seq OK
>=1
Any B&S Pump On & disch pr. Not low
Mill Lub Correct

19. Mill Lubrication Not Correct
>=
Red Lub not OK
Brg Lub not OK
Greasing Seq not OK for 15 min
Mill Lub Not Correct

20. Mill Brg Lub OK
&
Hp disch > 17Ksc
Any HP p/p on
Oil flow >20 lpm
Any LP p/p on
Mill Lub OK
>=
Mill Brg Lub not OK
Both LP off> 1sec
Both HP off> 1sec
Oil flow < 20 lpm for 3 sec
HP disch pr <17 ksc for 2 sec
Mill Lub not OK

21. Mill Red OK
&
Any pump on>10 sec
Red oil temp<90 deg C
Red Flow >40 LPM
Red lub OK
Red Lub Not OK
>=
Red oil temp>90 deg C > 10 sec
2/3
Red flow s/w 1<40 lpm
Red flow s/w 2<40 lpm
Red disch pr < 0.75 KSC
Both p/p off >10 sec
Red Lub not OK
10 sec delay

22. Greasing Sequence Not Correct
>=
Both Grease p/p off
End limit switch not acted > 2 min
End limit switch acted and air pressure
low within 3 sec
Greasing seq not correct
Note : When aux motor is on , grease pump runs for 5 min and remains off for 10 min.During this 10 min
period if it is required to take mill in service then either aux motor should be turned off or grease pump should be
started so that mill lub OK permissive is available.

23. Girth Gear Greasing System gets start command with any of the
following commands:
Automatically when main or Aux motor is started.
Automatically when aux motor is ON and grease pump is
stopped for >10min
By pressing start PB
The greasing system gets stop command either
Manually through the stop PB when both Main& Aux Motors
are OFF
OR
Automatically 30s after the main and aux motors are OFF
OR
Automatically after 5 min of running of grease pump when Aux
motor is ON
Girth Gear Greasing System

24. MILL MAIN MOTOR PERMISSIVES
NO MFT AT CHANNEL 1,2 & 3
MILL LUBRICATION CORRECT
MILL ELEV. IGNITION ENERGY AVAILABLE (AT ANY
ELEV.CORRESPONDING TO THAT MILL)
ELECTROMAGNETIC BRAKE RELEASED
MILL AUX. MOTOR OFF.
PURGE AIR DAMPER NDE & DE CLOSED
ANY TRUNION SA FAN ON > 10 SEC AND MILL TO SEAL AIR DP
OK .

25. Elevation Start sequence
&
&
Purge air shut off damper open
Mill lubrication correct
PA fan permit
NO MFT Ch-1
NO MFT Ch-2
NO MFT Ch-3
Electromagnetic brake released
Mill AB ignition energy available
All end-A manual coal o/l gate open
RELEASE REQUIRED
Elev release for start

26. Elevation Start
Step-1 Commands
PA gen inlet gate close
Purge air damper end-A close
Mill o/l gate end-A close
Purge air damper end-B close
Mill o/l gate end-B close
Feeder outlet gate end-A &B close.
&
Above all drive’s close limit
Main air damper Close limit
Bypass air damper Close limit
STEP-1 Complete
STEP-1 COMPLETE

27. Step-2 :Commands
Delay
1min
&
Delay
4min
Purge air damper end-
A open command
/limit switch open
Close purge air damper
Pre light up purge complete
Steam inerting
complete
Steam inerting
start command
Pre light up purge complete
Steam inerting complete
Step-2 Complete
STEP-2 COMPLETE

28. a)Blow down sequence start
b)GG seal air fan start
& Step-3 complete
Any reducer p/p ON
Any GG SAF ON
Step-3 :Commands
STEP-3 COMPLETE

29. &
STEP-4 Complete
PA gen inlet gate limit switch open
Aux motor OFF
Main motor ON
STEP-4 COMPLETE
a) Aux motor OFF
b) Main motor ON
C) Mill Outlet gate open
d) PA gen inlet gate open
Mill Outlet gate open
Step-4 :Commands

30. &
&
Feeder outlet gate open limit switch
Mill outlet temp >65 deg
FEEDER-A ON
a) Feeder outlet gate open
b) Start feeder start if
Feeder outlet gate open limit switch
Feeder ON
STEP-5 Complete
Step-5 :Commands
STEP-5 Complete

31.  MFT
 Mill lubrication not correct
 Mill bearing temp very high 60 C
 Mill motor bearing temp very high 100 C
 PA header pressure very low 350mmWC
 Mill/seal air DP not OK (<200mmwc) >60 sec
 Mill ignition energy not available
 Electromagnetic brake engaged
 Both trunnion seal air fans off>10 sec
 Aux. Motor on>10 sec
 Mill emergency trip PB activated
 Mill Outlet Temperature V High >95 C
 Both Feeder Off for more than 10 mins
MILL MAIN MOTOR PROTECTIONS

32. Feeder protections
Sl no Descriptions Value
1 Feeder – On And Feeder O/L Gate Closed. >20s
2 MFT 2/3 Logic
3 Main motor Off
4 Feeder – ON And NO COAL ON BELT
5 Feeder – ON And Discharge Plugged

33. Auto control loops of stage-II mill
 Air flow control (main air & by pass air damper control)
 Mill temp control ( cold air damper & hot air damper control)
 Mill seal air dp control- seal air /PA pressure (seal air control damper
control)
 Mill dp level/ noise level control

34. PRINCIPLE OF DP LEVEL MEASUREMENT IN MILL
THE SYSTEM COMPRISES OF TWO CIRCUITS-
1. MEASURING CIRCUIT 2. PURGING CIRCUIT.
THREE SETS OF PROBES ENTERS IN SIDE OF MILL-
1.MILL INLET BOTTOM: LEFT AND RIGHT (+VE LINES)
2.MILL INLET TOP : LEFT AND RIGHT (-VE LINES)
3.MILL INLET TOP MEASUREMENT : LEFT AND RIGHT
1. MEASURING CIRCUIT-
 INSTRUMENT AIR CONTINUOUSLY FLOW IN MESURING PIPES AT LOW VELOCITY OF 0.3-0.5
m/sec.
> DEPENDING UP ON LEVEL OF COAL A DP WILL EXIST BETWEEN +VE AND –VE LINES. THESE
LINES OF EACH END ARE CONNECTED TO A TRANSMITTER WHICH PROVDE A 4-20 mA MILL
LEVEL SIGNAL TO UCB.
 PRESSURE IN BUFFER TANK IS KEPT 80% ABOVE MILL PRESSURE TO AVOID DUST INGRESS
IN MEASURING PIPES.( mill pressure is 350 MMWC)
2. PURGING CIRCUIT:--
> THIS CIRCUIT INTRODUCES PERIODICALLY COMPRESSED AIR AT HIGHER PRESSURE FOR
PURGING OF MEASURING PIPES.
> PURGING OF DE AND NDE TAKES PLACE ALTERNATELY WITH A GAP OF 15 MINUTES.
> DURING PURGING MILL LEVEL IS FREEZED TO ITS LAST SAMPLED VALUE BEFORE START OF
PURGING.

35. MILL
DP TX
PNEUMATIC
VALVE
PNEUMATIC
ACTUATOR
BUFFER
TANK
E/P CONVER
CONTROLLER
MILL TO BUFF
DP TX
SOLENOID
VALVE

36. TEST
PRESSURE
TAPS
BUFFER TANK
DPT
603
DPT
602
DPT
601
DP
CONTROLLER
PI602
E/P
CONV
.
DPSL
601
SP 10 mBAR
0-1600mmWC
612V
A
PCV608
SP 6
KSC
PI601
0-10KSC
661VA
660VA
PSL
601
SP
0.5KSC
PSH
601
SP 5 KSC 659VA
HV/DI607
HY601 HY602 HY603 HY604 HY605 HY606
HY607
HV601 HV611 HV602 HV612 HV603 HV613 HV614
HV604 HV605 HV615 HV606 HV616
611VA
BALL
&
TUBE MILL
+VE +VE
-VE -VE
619VA
PCV 601
6BAR
PCV602
2.5BAR
DPCV 601
PCV 604
2.4 BAR
654VA
PCV 606
5 BAR
665VA
664VA
663VA
4-20mA
SIGNAL
4-20mA
SIGNAL
INSTRUMENT AIR

37. - VE PROBE
+ VE PROBE
PR MEASURING
PROBE

38. MILL
NOISE LEVE L MEASUREMENT
 NOISE LEVEL IS MEASURED WITH MICRO PHONE WHICH IS INSTALLED
NEAR MILL CYLINDER, AT LOW DP LEVEL NOISE LEVEL BECOME HIGH &
AT HIGH DP LEVEL NOISE LEVEL BECOME LOW.

39. NOISE LEVEL MEASURING SENSOR

40. Thanks