XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3863
from the first tank to a flat-bottom hydro cyclone, which
currently separates particles greater than 45 µm (depending
on the desired liberation size). The underflow is recirculated
to the mill. The overflow enters the second tank, and from
there the slurry is routed to the solids separation and pro-
cess water recovery system as already described above. This
approach keeps almost the entire water in the circuit and
allows future investigations to capturing extreme fines or
separating ions.
Water can be fed at different points, e.g., to the mill
or directly into the feed mass flow past the belt feeder for
wet milling. The latter is mainly used to moisten dry feed
material adequately and thus to adjust the material’s flow-
ability in the mill. Furthermore, water spraying onto each
individual screen deck is possible in wet milling. Accurate
dosage is possible at all water outlets.
VRM for Wet and Dry Milling
LOESCHE designed and built a modified VRM with spe-
cial features for dry and wet milling. The mill is shown in
Figure 3.
Conical milling rollers are installed in the mill as the
standard configuration. But it is also possible to replace
these with cylindrical milling rollers and thus generate high
shear in the material or rollers of alternative geometries.
Two different variants are shown in Figure 4.
In addition to the milling roller geometry, the mill-
ing table speed, contact pressure of the milling media, and
hydro-pneumatic suspension characteristics of the milling
mechanism can be adjusted at the mill. In current config-
uration pressures in the milling gap between 530 kN/m2
and 1400 kN/m2 per roller can be realized. According to
Reichert, a milling pressure of less than 1500 kN/m2 is typi-
cal for industrial applications and is also fully sufficient for
ore milling (Reichert, 2016).
Plant Control and Recorded Data
The control system is based on the LOESCHE industrial
control system. The entire system is controlled by a PLC
that can be monitored and controlled from a control room
using a PC and a corresponding user interface. To sup-
port the operator, PID controllers are installed for selected
operations.
Most of the process data are recorded continuously for
each test, such as hydraulic pressures, speed and torque of
the milling table, milling bed height, mass throughputs,
flow rates, and filling levels of the tanks. Discontinuous
data acquisition is made for the particle size distribution
(PSD) and moisture of the material at the various sam-
pling points. Each sample is extracted from the material
flow across its entire cross-section. The PSD is determined
using sieve analysis and air jet sieving. For wet milling, the
Figure 3. Vertical roller mill (right hand side), process control desk (left hand side) and
hydro cyclone battery (background) in the pilot plant
from the first tank to a flat-bottom hydro cyclone, which
currently separates particles greater than 45 µm (depending
on the desired liberation size). The underflow is recirculated
to the mill. The overflow enters the second tank, and from
there the slurry is routed to the solids separation and pro-
cess water recovery system as already described above. This
approach keeps almost the entire water in the circuit and
allows future investigations to capturing extreme fines or
separating ions.
Water can be fed at different points, e.g., to the mill
or directly into the feed mass flow past the belt feeder for
wet milling. The latter is mainly used to moisten dry feed
material adequately and thus to adjust the material’s flow-
ability in the mill. Furthermore, water spraying onto each
individual screen deck is possible in wet milling. Accurate
dosage is possible at all water outlets.
VRM for Wet and Dry Milling
LOESCHE designed and built a modified VRM with spe-
cial features for dry and wet milling. The mill is shown in
Figure 3.
Conical milling rollers are installed in the mill as the
standard configuration. But it is also possible to replace
these with cylindrical milling rollers and thus generate high
shear in the material or rollers of alternative geometries.
Two different variants are shown in Figure 4.
In addition to the milling roller geometry, the mill-
ing table speed, contact pressure of the milling media, and
hydro-pneumatic suspension characteristics of the milling
mechanism can be adjusted at the mill. In current config-
uration pressures in the milling gap between 530 kN/m2
and 1400 kN/m2 per roller can be realized. According to
Reichert, a milling pressure of less than 1500 kN/m2 is typi-
cal for industrial applications and is also fully sufficient for
ore milling (Reichert, 2016).
Plant Control and Recorded Data
The control system is based on the LOESCHE industrial
control system. The entire system is controlled by a PLC
that can be monitored and controlled from a control room
using a PC and a corresponding user interface. To sup-
port the operator, PID controllers are installed for selected
operations.
Most of the process data are recorded continuously for
each test, such as hydraulic pressures, speed and torque of
the milling table, milling bed height, mass throughputs,
flow rates, and filling levels of the tanks. Discontinuous
data acquisition is made for the particle size distribution
(PSD) and moisture of the material at the various sam-
pling points. Each sample is extracted from the material
flow across its entire cross-section. The PSD is determined
using sieve analysis and air jet sieving. For wet milling, the
Figure 3. Vertical roller mill (right hand side), process control desk (left hand side) and
hydro cyclone battery (background) in the pilot plant