coal mill

Presented By

Siddhartha Sankar Bharali

Assistant Engineer

Emp Code : M6B194

1Siddhartha Sankar Bharali M6B194

TECHNICAL DATA ABOUT ZGM MILL

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z

G

M

MEDIUM SPEED

GRINDING ROLLER TYPE

MILL

Siddhartha Sankar Bharali M6B194

Contd.

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113

N NORMAL

AVERAGE RADIUS OF GRINDING TRACK (CM)


Rate power of mill = 512 kWRate power of motor =560 kWVoltage of motor =6600 VRated speed of the motor =990 r/minDirection of rotation of the motor =Counter-clockwise

(front view of output shaft)Rated speed of the mill =24.2 r/minDirection of rotation of the mill =Clockwise (vertical

view )Primary air flow upstream of mill =18.80 kg/s


GRINDING PRINCIPLE OF ZGM MILL ZGM mill is a vertical mill with three

grinding rollers and one grinding track. A grinding table rotates round a vertical

axis. It is driven by a planetary gearbox. The three grinding rollers, mounted in fixed position, are passed down on the table under hydraulic loading.

Raw coal enters through the center of the mill and is deposited on the grinding table. Centrifugal force feeds the coal radially outward where it is ground between the roller tyres and grinding track.

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Sectional View of the millSiddhartha Sankar Bharali M6B194

The pulverized coal is flowed by centrifuged force into the zone over the nozzle ring surrounding the table, where the coal particles are swept upwards by the stream of hot primary air into the classifier.

The intimate contact with the hot primary air causes the moisture contaminated in the coal to evaporate spontaneously. The oversize particles rejected by the classifier fall back onto the grinding table for further grinding. The fine particles, i.e. finished product, are carried out of the classifier with the air.


The grinding force, is statically determined by three grinding rollers, which is generated by hydraulic loading. It starts from loading frame to grinding rollers to grinding track and finally towards the foundation.

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Transfer loop of grinding force


CONSTRUCTION PROCESS FLOW CHART


Contd.


DIFFERENT PARTS OF COAL MILL & ITS CONSTRUCTION DETAILS


BASE PLATEInstallation steps of base

Plate are as follows : To clarify polluted oil, rusting from the

plates and to check weather it is deformed or not.

Base plate is placed on the rubber pad and its alignment is done with respect to foundation center line and the elevation marked by civil authority.

Adjustment for elevation is done with the help of adjustable screw and spacer.

Levelness is is checked with master level and water level is used for transfer of the elevation.

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Grouted Base plate after alignmentSiddhartha Sankar Bharali M6B194

After plate alignment has been completed, bolts are tightened and grouting is done as per requirement.

Some Facts

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Levelness tolerance of the plate surface = ≤ .1 mm/m

Tolerance for elevation should be within 3 mm

Deviation from centre line = ≤ 3mm


GEAR BOX

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Two types of gears are used: 1) Bevel Gears 2) Planetary Gears

Bevel Gear Planetary Gear


GEAR BOX ERECTIONBefore the erection of gear box, bottom surface of gear box and

the top surface of base plate should be cleaned up.Gasket is not allowed to insert inside the gear box. After

erection clearance is checked using filler gauge.

16 TONS

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SOME FACTS

Capacity of EOT Crane (2 nos)

Weight of Gear Box 27 TONSSiddhartha Sankar Bharali M6B194

Contd. 8

15

No. of rope used for lifting

21.5 mm Diameter of steel rope used

± .4 mm Max deviation of centre line


BOTTOM HOUSING Main function of bottom

Housing is :To support the sub- assembly

like middle housing and classifier.

To accommodate the gear box.

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Bottom housing weight =8 Ton


Installation of bottom housingBottom housing is placed on the

channel for location.To have the adjustment for the

elevation of bottom housing top surface, gaskets are inserted in the channel.

After the completion of alignment for bottom housing center and elevation, anchor bolts are inserted and grouted.

After grouting, bolts are tightened with locking washers.


GRINDING TRACK CARRIER & SCRAPPER

The grinding track carrier is used for the torsion-proof and rigid connection to the output flange of the gearbox with 20 M48 bolts. It transfers the torque. At the time, the grinding track carrier must support the load force and the weight of parts inside the mill.

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Total weight = 15.5 Ton


INSTALLATION OF GRINDING TRACK CARRIER The outer flange surface of gear box and bottom surface of track carrier is

cleaned first. Three positioning pins are screwed to the outer flange bolt holes of the gear

box for guidance. Then the track carrier is lifted and placed on the outer flange of gear box.

Guidance pins are removed after positioning the flange connection bolts. Finally the bolts are tightened with locking washers.

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Feeler gauge is used to check the clearance of contact surface of grinding track carrier and gear box outer flange. It is a closed sealing surface. (≤.05mm).


GRINDING TRACK & NOZZLE RING The grinding track and nozzle ring

is composed of rotary parts and static parts. The rotary parts consists of the supporting shell, segment (12 pieces), cone cage etc. running with the grinding track carrier. Static parts are fixed with mill housing face.

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Grinding track weight =15 Ton


INSTALLATION OF GRINDING TRACK Surfaces are cleaned before installation. Transfer pins are installed and track is placed with its guidance. Filler gauge is used to check the clearance of contact surfaces to ensure a

firm contact. Upper part of static ring is welded with the housing.

To check the nozzle clearance. It should be (5 ±.5 )mm.

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Checklist


Siddhartha Sankar Bharali M6B194 22

Track carrier and Grinding track assembly

MIDDLE HOUSINGThe mill housing case consists of :

casing, hot gas entrance, door of maintenance, seal equipment of tie rod, inert gases tube, guiding equipment etc.

The housing case is welded to the bottom housing, and screwed to the classifier by bolt.

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Total Weight = 14.5 Tons



Middle housing, grinding track assembly

INSTALLATION OF MIDDLE HOUSING Middle housing is placed on the bottom housing and its position is marked. Radial gap between nozzle ring and middle housing is checked for its

alignment. Maximum allowable concentricity is 5mm. Then it is welded to the bottom housing.


GRINDING ROLLERThe grinding roller consists of the

thrust piece, roller shaft, roller tyre, hub, bearing, and rotary shaft seal.

The grinding roller is located between the grinding table and the frame fixed by the frame. The incline angle is 15°.

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Weight of each roller = 9 Ton


LOADING FRAME Main purpose of providing loading

frame is to hold the grinding rollers. In order to fix against torsion in operation, the guiding frame is provided on the loading frame.

Loading frame should be positioned slowly. Then alignment is done between loading frame and housing guide device.

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Loading Frame


LOADING FRAME


Loading frame with rollers

TIE ROD Function of tie rod is to hold the

loading frame and roller assembly in its position and absorb the shock.

The tie rods consist of upper tie rod, lower tie rod, they are fixed by connecting sleeve.

The tie rod is connected to loading frame by sphere bearing on the top, and connected with loading hydraulic cylinders via connection cover on the bottom.


CLASSIFIERThe function of the classifier is to

select powders whose sizes meet the requirement of the boiler. Throng adjusting the angle of the baffle door, the sizes of powders can be controlled.

The scope of the adjusting angle is 25°-80°, the working angle commonly is 50°.

The main parts consist of classifier are casing, baffle door, inside cone , out way of the powder and coal intake pipe.

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Total Weight = 20 Ton


ERECTION OF CLASSIFIERTwo nos. of 17.5 mm diameter ropes are used for lifting the classifier. The

rope shall be four times folded for lifting.

The position of the classifier shall be finalized by the sealing pipes of housing and classifier. The flange surface of the housing and classifier shall be cleaned. After positioning it is bolted with the flange.


MOTOR AND GEAR BOX COUPLING


EOT CRANE FOR LIFTING


2 no's of EOT cranes with 16 T capacity each

coal mill

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