Ball Mill Control [Compatibility Mode]

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Grinding Circuit Control Systems

“In the name of Allah, the Beneficent, the Merciful”

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1. Why a control / What to control

2. Available Tools

3. Control Strategies

Summary

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• Optimum Production Rate• Consistent Quality• Smooth Operation• Quick Mill Stabilization (disturbance)

(quality change)• Operator relief

1. Why a Control Systems

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FOR THE OPTIMUM EQUIPMENT EFFICIENCY

Reject FlowFinish product

Feed rate

Ratio material/airsteady

Material flowsteady

Material levelsteady

Total mill flowsteady

Ratio fines/rejectssteady

Reject flowsteady

What to control ?

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• Functional layout• Controller objective• Controller ON-OFF• Controller P.I.D. • Expert system

2. Available Tools

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Setpoints

ControlledQuantities

ManipulatedQuantities

Disturbances

PROCESS

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PROCESS

Manual Control

ControlledQuantities

ManipulatedQuantities

Disturbances

PROCESS

Feedback Control

Hardware

Actions Needed

MeasuredValues

Setpoints

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finalcontrolelement

transmissionsystem

transmissionsystem

feedbackcontroller

ControlledMan

ipul

ated

Disturbances

sensor

errorsignal

inputelements -

+SetpointsPROCESS

Controllerbox On site

Functional Layout of a Feedback Loop

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Setpoint

Setpoint

Setpoint

Time

Time

Time

Controlled variable:reject flow rate , p.e.

Manipulated variable:feed rate , p.e.

Ideal

Reality

1. stay on the setpoint2. track a setpoint change

Controllers Objectives

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Dead Zone

Setpoint

On

Off

Fuel valve

Time

Controlled variable:room temperature

Manipulated variable:

quickly changes to either a maximum ora minimum value (minimum = 0 or off).

Mechanism = usually a simple relay

Discontinuous control

Controllers : On - Off

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K EE c

K ce m

Control algorithm: m = K ec

K = proportional sensitivity or gain

C 1/K X100 = proportional band (PB)

+

-

Rapid responseDynamicaly relatively stable

Offset

E = errorm= Manipulated variable

C

Controllers : Proportional

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Equilibrium

Steam

Undercharge

1

2

3

4

Steam

Integral action

Setpoint

Time

OffsetChargeapplication

Rotationalspeed

Offset

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E1

T pi

ET

t

i

e m

Control algorithm: m = 1/T e dti

Ti = integral timep = action of integration with respect to time (dt)

+

-

Combines advantages of proportionaland the reset of the offset

Tuning difficulty increasedLess stable

m= Manipulated variable

P+I:e=error

Controllers : Integral

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E T pd

E Td d

e m

Control algorithm: m = T d/dt (e)d

Td = derivative timep = action of derivation with respect to time (dt)

+

-

If extensive lagMore stable if well tuned

Tuning difficulty increasedReduced but not eliminated offset,

m= Manipulated variable

P+D:

e=error

D: Not alone in practice, because huge errorIf unchanging error rate

Adds lead to the controller for lag around the loopIt's based on the rate of change of e

Controllers : Derivative

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On -Off:InexpensiveExtremely simple

P:SimpleInherently stable when properly tunedEasy to tuneExperiences offset at steady state

P + D:Stable Less offset than proportional alone

(use of higher Kc possible)Reduces lags, i.e. more rapid response

P + I + D:Most complexMost expensiveRapid responseNo offsetDifficult to tuneBest control if properly tuned

P+ I:No offsetBetter dynamic response than reset alonePossibilities exist for instability due to lag

introduced

P+I+D: the most sophisticated

Characteristics of controller algorithms

Controllers : P I D

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• Rule-based• Combines several methods, and tries to emulate human

responses to given conditions• Based on a decision table, which gives each possible

combination of conditions which could occur for x number of measured parameters

• Although these systems are becoming more and more common, it must be remembered that a considerable amount of study and tuning is required to get the program right.The programmer must, in essence, teach the computerto operate the mill

• The current restriction on these systems is that they act only on one parameter at a time.

Expert Systems

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• HOME MADE SOLUTIONS

• COMMERCIALIZED SOLUTIONS :

3. Control Strategies

- HOLDERBANK (Canada)- SCAP- MILLTRONICS- K-TRON/HASLER- GO CONTROL

• Elevator Control• Ear Control• Reject Flow Control by Fresh Feed• Total Feed Control• Reject Flow Control by Separator Speed

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• SIGNAL USED FOR CONTROL

Strategies

- MILL MOTOR POWER- MILL SOUND (1st OR / AND 2nd COMPARTMENT)- ELEVATOR POWER- REJECT FLOW- SEPARATOR SPEED- (FINISH PRODUCT FINENESS)

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Finish product

Separator speed

Reject

Fresh feedP.I.

Fresh Feed Control by Elevator

Elevator

Set Point+ -

- High Lag time

- Poor Signal from Elevator

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Finish product

Separator speed

Reject

Fresh feedP.I.

Fresh Feed Control by Ear Signal

Sound

Set Point+ -

- Uneven Mill Flow

EAR

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Finish product

Separator speed

Reject

Fresh feedP.I.

Reject Flow Control by Fresh Feed

- Long lag time

- No detection of build up in mill

-+

Total feed

Set Point

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Finish product

Separator Speed

Reject

Fresh feed

P.I.Reject setpoint

-+

++

Total Flow Control by Fresh Feed

- Long lag time

- Material build up not detected

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Finish product

Separator speed

Reject

Fresh feed

P.I.Reject

setpoint -+

Reject Control by Separator Speed

- Not suitable with uneven clinker

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SCAP Strategy

DependentLoop

DependentLoop

MasterLoop

Process

Filling Degree

Elevator Power

Mill Power

Feed

FillingDegreeSet Point

FeedElevatorPowerSet Point

STRATEGY : Maximize Feed Rate and Mill Power

Commercialized solutions

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Milltronics Strategy

k + k + k = 100 %

k %

k %

k %

P I D

1

2

3

ear

reject

elevator

power

Set Point

Feed+

+ +

1 2 3

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HOLDERBANK (MISSISAUGA)Mill Load Control Strategy

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Mill Load Control Strategy

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K-TRON / HASLER Control Strategy

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100(elev)PB

2(ear)Full(ear)Empty

(ear)level_Full Ear

*+

Pid-1 :Fresh regulation set point = Fresh set point + F (pid) (Mill set point Mill flow)

« Grits/fresh » Fresh SetpointMill set point = Fresh set point (1 + Grits/fresh)Mill flow = SFresh + Grits

If full mill : Ear < Full level (ear)Ear P 3

Elevator Then :Mill Setpoint

Mill set-point =

Mill Flow =GritsFreshΣ+ PID 1 Fresh regulation set point

Mill set-point (1 +

% WF 1 % WF2If full mill : elev > full level (elev)

Then :

WF 1 WF 2 Mill set point =

Mill regulation Mill set point (1 +

100PB(elev)

2(elev)Full(elev)Empty

Elev(elev)levelEmpty_

*+

-

K-TRON / HASLER Control Strategy

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Slegten Multivariable and Fineness Control

Fineness SP

Prediction

LaboratorySampling

Separator

Speed

Finish product

Mill

Reject

Feed rate

Finish product

Reject

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Regardless of the control system, the grinding will still be done in the mill, andthe mill should be optimized to be both

effective and efficient

Conclusions