MODERNIZED MICROPROCESSOR SYSTEM
FOR WET GRINDING CONTROL IN RAW MILL
T. Penzov , D. Penev
Innovative Firm TRAPEN, Sofia, Bulgaria, e-mail: trapen@abv.bg
Abstract: The grinding of raw materials in
“VULKANCEMENT” AD – Dimitrovgrad is
performed on three-chamber wet grinding mills
working in open cycle. At the development of
the automation system for this type of mills the
indirect methods for measurement of the basic
technological parameters (finesse of grinding
and slime viscosity) are used. Due to the
investigations and identification carry out on
the raw mills the multiloop control system of
the grinding process is developed. The
systems structure is describe in paper and the
peculiarities of the basic technical means are
given too. The nowadays achieved economical
results from exploitation of the system are
given as well.
Key words: wet grinding mill, indirect
parameters, multiloop control system, technical
means
1. INTRODUCTION
The
grinding
of
raw
materials
in
“VULCANCEMENT” AD – Dimitrovgrad
(BULGARIA) is performed on threechamber
wet mills working in open cycle. In the control
channel the raw mill can present with the
structure shown in Figure 1, where [Penzov T.A
2003]:
Fig.1
M- flow rate of the material sent for grinding
wearing out of the ball charge and the mill
into the mill;
lining);
W – flow rate of the water sent into the mill;
 - viscosity of the ready slime at the mill
Z1, Z2 – indirect measurable parameters;
outlet;
F – disturbances (the changes in the grindability
 - fineness of grinding of the slime.
of initial raw materials,
2. STUDIES AND IDENTIFICATION OF
grinding of the ready product as well. The lack
RAW MILLS
of sure operated viscosimeter at the mill outlet
At the development of automation system for
and the large transport delay (about 20 – 23
this type of mills and the choice of its structure
min) impose to search a indirect parameter for
the indirect methods for measurement of the
control of slime viscosity. The investigation
basic technological parameters  and  are
shows that the impact pulses of the case
used. The investigation carry out on the raw
vibration in the zone of slime formation of
mills in “VULCANCEMENT” AD shows that
second chamber (factor of slime formation FS)
impact pulses of the case vibration (factor of
depend on the filling level of the mill with
grinding FG), measuring at the mill inlet are
material as on the viscosity of the slime in this
very well correlated with the loading (filling
zone as well. In the case that there is built a
level) of the mill and therefore with fineness of
Fig.2
Table 1
Control channel
Z1-M
Z2-M
Z2-W
Parameters
τ0 [min]
T0 [min]
K0
↑
1,6
4,8
0,6
↓
1,4
3,6
0,8
↑
7,1
5,6
0,5
↓
6,3
5,2
0,6
↑
4,3
4,8
0,8
↓
4,6
5,3
0,7
loop for stabilizing of the mill loading by the
ready product by correction of the water sent
signal of the first sensor, the signal of the
into the mill
second sensor is correlated only with the
The aim is to be increased productivity of the
viscosity of the ready slime. In Figure 2 are
grinding aggregate and quality characteristics of
given represented transitional characteristics in
the ready slime.
the control channel of the mill loading, obtained
The system contains the next control loops:
at identification of 5th raw mill as a object of
Control loop of the material
automation. The parameters of the automation
3 – feeder; 4 – speed sensor; 5 – weight sensor;
object approximated with transfer function of a
11 – control system; 13 – driver motor
aperiodical link with delay are defined by the
Control loop of the water
method of the inflex point.
16, 17 – flowmeter; 18 – digital indicator, 19 –
In Table 1 are given the obtained results at the
regulator, 20 – executive mechanism
identification of the raw mill for separated
Control loop of the mill load
control channels.
6 – impact pulse sensor, 7 – converter; 8 –
indicator; 9 – regulator; 10 – set point device;
3. INFORMATION CONTROL STRUCTURE
13 – driver motor
OF THE SYSTEM
Control loop of the slime viscosity
In result of the investigation carry out as well
21 – impact pulse sensor; 22 – converter; 23 –
the identification of the other raw mills is
indicator; 24 – regulator; 25 – set point device;
developed the system the schematic diagram
26, 27 – viscosimeter
of which is given in Figure 3.
The system can work in manual and automatic
The purpose of the system is:
mode of operation. At manual regime of
 to measure the loading (filling level) of the
MILLCONT 2 the operator observes the mill
raw mill with material
loading by the indicator 8 and by means of
 to stabilize automatic the set loading by
keyboard it is changed in the necessary
change of the flow rate of the inlet material
direction. The control of the viscosity of the
 to measure and stabilize automatic the flow
ready slime is made by the analyzes of the
rate of the water sent into the mill
samples from the mill outlet as it is actuated
 to keep up the set ratio material - water at the
manual on the water tap. The manual mode of
control of the mill loading
operation is not basic.
 to measure and control by indirect parameter
At automatic regime MILLCONT 2 is in state
(factor of slime formation) the viscosity of
“automatic”. The operation of the system in this
case is following: the sensor 6 measures the
the sensor 21 measures
factor of grinding which is enough well
formation which depends on as specific mill
correlated with filling level of the mill in
loading with material as well as on the slime
measuring
loop
viscosity in measuring point. At stabilized
containing the elements from 6 to 13 stabilizes
specific mill loading (provided by the first
the specific optimal loading with material as
control loop) the signal measured by the sensor
provides optimal productivity of the mill. The
21 is correlated exclusively with the slime
specific loading is set-up by the set point device
viscosity.
10 and it depends on the necessary grain size,
microprocessor regulator 24 is sent as a
the mill condition and the ball wearing out. The
correcting signal in the ranges  30% to the set
second control loop stabilizes the water send
point of the water regulator 19. At such way the
into the mill and contains the elements from 16
control loop corrects with the prediction the
to 20. The control loop of the slime viscosity
deviations of the ready slime viscosity at the
containing the elements from 21 to 25 works so:
mill outlet.
point.
The
first
control
Fig. 3
The
output
the factor of slime
signal
of
the
The dosage of raw material is performed by the
the size, hardness and grindability of materials.
developed weight belt feeder. The both control
FG reflect one-way and with high sensibility the
loops of the mill loading and slime viscosity
changes of layer thickness and the qualities of
are realized on the basic of the microprocessor
materials. FG are programmed for each
system MILLCONT 2.
concrete case by the choice of the frequency
By means of special remote sensors SRIP
domain in which the impact pulses are located
(Fig.5) mounted approximately 20mm from the
and by the coefficient defining the FG range.
case of the mill are measured impact pulses
The rest part of the FG structure is common for
generated at material grinding (Penzov T. et al.
all cases and represents firm “know-how”.The
2006).
forming FG are sent to two specialized PID-
The signals of the two sensors are sent to
controllers, which change the flow rates of inlet
double-loop microprocessor
module (Fig.6),
materials so that the optimization law to satisfy.
where by software way are formed synthetic
The outputs of the controllers into dependence
“factor of grinding FG”, which are related with
on the type of the actuators are programmed
material resistant layer against the penetration
0(4)  20mA or are relay-operated.
of grinding bodies in the zone, where the
sensors are mounted.The resistance of material
layer depends on its thickness as well as from
Fig.4
Fig.5
The two control loops are solo, but can work in
The obtained parameters Ko, 0, To of the raw
cascade regime. In this case the two sensors are
mill as a object of automation are used at the
mounted in different zones of the mill or one of
choice of the type of regulator and control law.
them is mounted on facility fixed to it.At wet
The
grinding of raw materials
adjustment of the control loops of the system is
when the second
developed
algorithm
for
optimal
sensor is mounted in zone of slime formation
given in Figure 7.
the slime viscosity is measured and it is
The adjustment run in the next consequence:
controlled by inlet water. For this aim “factor of
 Adjustment of the loop for stabilizing of the
slime FS” is synthesized.
water
The advantages of the used principle of
This loop contains microprocessor SIEMENS
operation are followed:
regulator and it isn’t subject of consideration.
- FG and FS aren’t influenced from the work of
 Adjustment of the loop for control of the mill
near-by mills and other aggregates;
load
- Measuring of resistant properties of material
This control loop of MILLCONT 2 contains
layer in the zone of sensor mounting and
regulator with analog output given by the
obtaining in time truthful information for their
formula:
changes as the control accuracy is increased and

T
Yn   Pr X n 
T
i

the start regime of the mill is decreased a few
n
X
K 0
K

Td
X n  X n1  100 %
T
 f обхв.
ways as well;
- Eliminating of uninformation resonance
vibrations of mill’s case;
- In case of FG change it can control the
where:
Yn - output control value;
X n , X n 1 - debalance between set point (SP)
wearing out of grinding bodies and lining;
- At abruptly FG change it can define a mill
breakdowns (destruction of grids and lining,
clogging up from inner bodies etc);
and factor of grinding (FG).
Pr - gain coefficient;
- The sensor signal is sent at distance up to
Ti - time constant of integration;
200 m without additional amplification.
T d - time constant of deviation
T - tact of the control law ;
4.
OPTIMAL
SYSTEM
ADJUSTMENT
OF
THE
f обхв. - range of the input signal
Fig. 6
Table 2
Direction of acting
Adjustments of PI regulator
Pr
Ti [s]
T [s]
Zl [%]
Zn [%]
dO [%]
Increase
0,54
59
10
25
0,6
50
Decrease
0,97
41
10
20
0,8
50
Table 3
Direction of acting
Adjustments of the pulse regulator
Pr
T [s]
Zl [%]
Zn [%]
dO [%]
Increase
0,40
338
20
0,6
50
Decrease
0,51
258
20
0,6
50
According to the parameters of the mill (Tab. 1)

and relationships(Fig.6) are calculated the
an average from 26kWh to 17kWh for cubic
adjustments of the regulator given in Table 2.
meter of the ready slime
 Adjustment of the loop for control of the

slime viscosity
bodies is increased with 3-4 months
In this case the regulator of MILLCONT 2 act

as pulse regulator with analog output. The final
product by fineness of grinding and viscosity is
adjustments of the pulse regulator calculated
decreased with an average of 1,6 times.
according to Figure 7 are given in Table 3.
Besides these good economic results the system
The output signal of the pulse regulator correct
improves the overall labor organization.
The specific power consumption is decreased
The durabillity of the lining and the grinding
The average square deviations of the grind
the set point of the water regulator in the range
 30 % of the maximum flow rate.
The control system of the wet grinding process
stabilizes the outlet parameters(fineness of
grinding and viscosity) of the ready product and
provides optimal throughput of the grinding
aggregate.
REFERENCES
Penzov, T.A. et al., 2003. “An experience from wet
grinding process automation of raw materials” (in
Bulgarian), AUTOMATICS AND INFORMATICS’
03, Sofia, Bulgaria
Penzov, T.A. et al., 2006. “New system for control of
grinding
5. CONCLUTION
The investigation carry out with the system
for wet grinding process control shows the
following:

The productivity of the mills is increased with
30%
process”,
XXIII
International
mineral
processing congress, Istanbul, Turkey
Penzov, T.A., Marinov, D.Z., 2008. “Automatic system
for ore grinding control in single-stage ball mill”,
XXIV International mineral processing congress,
Beijing, China