ZGM type of roller grinding coal mill overhauling. Overhauling is done to increase the efficiency of coal mill. Overhauling all equipments to check and avoid accidents. Overhauling is done to proper alligment.

1. CREATED BY: OMPRAKASH PATEL

2. TYPE – (ZGM-123N) RATED OUTPUT – 50.8t/h

3. Why do coal mill overhauling??
 Overhauling is done to increase the efficiency of coal
mill.
 Overhauling all equipment to check and avoid
accidents.
 when the thickness of the roller is reduced and the
coal is not pulverized from the trench, then
overhauling of the coal mill is done.
 Overhauling is done to proper alignment.

4. First let’s check whether the permit was
received.
 Permit was received then checklist the issued date,
lock out take out (LOTO), equipment and isolations.
 After that all the workers understand that what can be
hazard identification and risk analysis(HIRA) in this
work and how to take careful then take the tool box
talk(TBT) of all the workers.
 To be overhauling job work start.

5. ISOLATIONS:
1. Mill main motor power off & LOTO.
2. Both feeder power off & LOTO.
3. Seal air MDV closed, power off.
4. Seal air MOV closed.
5. Feeder I/L MDV closed, power off.
6. HAG closed, power off.
7. HAG, CAD closed.
8. Burner I/L gate to be closed.

6. STEP1: REMOVE ALL EQUIPMENTS
First we remove
chute and pulverize
coal outlet pipe one
by one.
In this mill 4 nos.
coal outlet pipe and
one centre pipe that
is coal inlet pipe.

7. First we removed all classifier bolts and make
free from mill body.

8. Lift the classifier with the help of hoist crane and move forward free space.
See all safety point, move carefully not touch any equipment or structure hanging
body.

9. Move slowly with good skill hoist crane operator as shaking create dangerous due
heavy mass of body. classifier weight around 26 tones.

10. Then we have remove numbers of three tie rod one by one.

11. After that lock three number of rollers with mill body and remove all bolts
from loading frame for loading frame remove freely.

12.  Here we removing loading frame.

13. ROLLER:
Remove
one by one
old grinding
rollers.

14. Remove to old bowl ring we have to replace due to
bowl ring having less thickness.

15. This is nozzle ring if it got damaged than replace it.
This diameter is 3750mm.

16. We have last the cutting through from
remove to static ring.

17. .

18. 1. Check coal line
thickness
 We have first
check the reducing
thickness of the
coal pipe.
Where the hole is,
they do the
punching.
If it gets worse,
then change the
pipe itself.

19. 2.Main Discharge
Valve (MDV)
By changing
the old main
discharge valve ,
the new main
discharge is
installed & the
old one is sent
to fill up.

20. 3.Roller check
First we remove
old tire from
housing and re-
insert new tire on
each housing.

21. Then roller bearing is cleaning &check of
the floating.

22.  After housing the roller, the ATT checked for
30 minutes at 2kg/cm^2 pressure.

23. 4.Check roller head
Roller head is
checked for
thickness & where
the thickness is less,
it is filled with
welding electrode
like 7018 & then
hard facing
electrode.

24. 5.Check nozzle ring
Re –inserting
Nozzle ring after
metal up & hard
facing.

25. 6.Check bowl ring
& liner
 Here replaced all
old liner with
new one & fitting
time we need to
arrange carefully
all segment in
serial numbers.
 The bowl ring
locking bolt we
must to tight
fully.

26. 7.Check classifier
We have check the
classifier of inner &
outer part of the body
in thickness of the cone.
At setting the flap
angle and set the
required angle.
The flange circuit is
installed, let’s check the
new.

27. ASSEMBLY OF COAL MILL

28. Roller assembly is going on.

29. Before the box up, we clean the inside of the mill and fill it
with welding where the thickness is reduced.

30. After roller assembly we insert new roller in mill as same procedure as we
removing. Each roller after inserted we have to lock with mill body.

31. Loading frame
Now after
positioning of
loading frame re-
tight rollers with
loading frame
one by one roller.
Loading frame
adjust on correct
position this is
called loading
frame alignment.

32. .
On every corner
we have to make gap
between loading
frame and coal mill
body as one side
zero and other side
3mm for every
corner same
alignment will done.

33. .
Now after
tightening all
internal parts we re-
installing classifier
body.
After classifier and
mill body separate
sitting we tight all
bolts of body.

34. .
Next go for band
piping re-assemble.
All band pipes re-
positioning and
tight one by one.

35. .
Now mill
ready for trial
after
completed the
works.