Hướng dẫn vận hành máy nghiền bi Operation of the Cement grinding plant

Hướng dẫn vận hành máy nghiền bi Operation of the Cement grinding plant Preconditions: The switch on conditions of the auxiliary units must be fulfilled. • Auxiliary units of the tube mill • Conveying equipment for cement transport • Recirculation transport incl. the foreign body trap • Grits conveyors • SEPOLSeparator • Dedusting system • Mill drive • Mill feed system • Water injection

Operation of the Cement grinding plant

Training

Polysius Headquarters / Germany

19 May – 13 June 2008

Control Loops

• Fresh fee (F) + Grits (G) = constant

• ball mill sound level / mill feed

Control Loop

• Temperature mill outlet /

water injection chamber 1 & 2

Additional monitoring:

Pressure behind ball mill [mbar]

• Pressure behind Separator [mbar]

• Amount of grits [t/h]

• Electrical ear for mill noise [%]

• Power of Bucket Elevator [A or kW]

• Speed of Separator rotor [rpm]

• Water flow chamber 1 & 2 [l/h]

Start up of the Cement Mill

Preconditions:

The switch- on conditions of the auxiliary units must be fulfilled.

• Auxiliary units of the tube mill

• Recirculation transport incl the foreign body trap

Start up of Cement Mill, process adjustments

• Position of guide fans at SEPOL 65 – 70 °

• SEPOL Rotor speed 70 -75 % of max.

• Damper before system fan: 60 – 80

• Jalousie dampers before SEPOL: 100 %

• Fresh air damper before SEPOL: 30 – 50 %

Ball Mill

Diaphragm Ball Charge

Lifter adjustment

Ball Mill Components - Intermediate Diaphragm

Adjustment tool

knee lever

Intermediate Diaphragm

• for equal material flow of material from 1 st to 2 nd compartment.

• adjustable scoops to influence flow characteristics of mill.

• can be set to reduce or accelerate flow of material to second

compartment.

• Scoops adjustment influences material filling degree of compartment 1.

• Longitudinal samples should be taken to determine if scoops need

adjusting.

Mill Outlet with Separation Cone

Air Material

250-600 g/m3

(approx 15 %)

approx 85 %

Coarse grinding in chamber 1.

• Lifting liners for cataract movement.

• Cataract – grinding action by impact, crushing and friction.

• Grinding balls lifted higher; more ejected from surface

at top of mill.

Second compartment used for fine grinding.

• Grinding balls carried up by friction, rolls down surface.

• Cascade movement – grinding by friction (shear) and

compression

Ball Movement depends on these factors:

Mill Speed

• Speed of ball mill is expressed as percentage of critical speed.

• Critical speed is attained when centrifugal force is high enough

that all media sticks to mill wall, rotating with the mill.

• Normal operating speed for finish grinding cement mills

averages about 75 % of critical speed.

Ball Charge

• Mills for cement grinding normally operate at a

25-32% “filling degree”.

• “Filling degree” is defined as volume of grinding media as

percentage of total mill internal volume.

• Mill speed, liner shape and mill diameter are normally constant

parameters.

• Therefore, only an adjustment to filling level and ball size

distribution can be made

Ball Mill Liners

• Protect the mill shell and assist in grinding action.

• First Compartment – Lifting liners: “impact” grinding action for large particle reduction.

• Second Compartment – Classifying Liners – shifting finer media to discharge end of mill where fine grinding

is required; “friction” grinding

Chamber 2:

Classifying liners Chamber 1:

Lifting liners

Lifting Liners

- Most commonly used in cement industry.

- Used mainly for coarse grinding in first compartment

- Lifting liners must lift media high enough to allow

sufficient impact force for coarse grinding.

Classifying Liners

• Used in second or fine grinding compartment.

• The liner shape causes a classification of grinding

media.

• Decreasing ball size along grinding path.

• Grinding efficiency is increased

Theory is, that ball size should decrease with particle size being ground.

Classifying Liners

over the lining hill.

Result: larger balls in the front of second compartment.

Smaller balls at discharge end of mill.

Liner Shape

Mill Optimisation

1 Optimise Chamber 1!!!

2 If chamber 1 is O.K -> Optimization of Chamber 2.

SEPOL - Initial Settings

• Guide Vanes – 65 - 70 degrees

• Fresh Air Inlet Damper 30 -50 %

SEPOL - Inlet Damper

Separating Air

Air channels

Louvers are being adjusted to wear pattern

at the rotor.

NOTE: Dedusting system should be set to 1-2 mbar negative

pressure exists at SEPOL inlet.

SEPOL - Guide Vanes

clockwise rotation

counter-clockwise rotation

SEPOL settings

60 - 65°

• Guide vanes setting acc to the

drawing or to 65 -70°.

• Maximum separating air

• Speed of separator rotor set to suit the required cement fineness.

~65 - 70°

SEPOL - Setting of Guide Vanes

• if residue ratio too low…

set guide vanes more tangentially.

• if residue ratio too high…

set guide vanes more radially.

Adjustments should be carried out in 5-10 degree steps.

After each adjustment samplings are necessary.

(100 - f) (g - a) SEOPL efficiency = -

separator fines, separator grits

a, f, g: fineness feed, fines, grits

(Blaine or residue)

SEPOL - Separator Formulas

= (f - g) / (a - g)

Typical TROMP Curve