XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 541
various industrial mineral applications. VRM technology is
arguably the compressive comminution method with the
widest application globally, when all materials needing to
be ground are considered.
VRM units are usually operated in closed circuit with a
dynamic classifier mounted on top of the mill, as shown in
Figure 3. The setup requires a constant gas flow through the
machine but allows a compact combination of grinding,
classifying, and drying.
Operating Principles
Accepting feed sizes up to F100 150 mm and grinding prod-
ucts down to P80 20 µm in a single unit, the Loesche VRM,
illustrated in Figure 3, contains all elements necessary to
take the feed to the final product.
After tramp-metal removal, material to be ground is
fed into the mill and directed to the center of the grinding
table (1). Driven by centrifugal force, it moves outwards
towards the edge of the rotating table and into the path of
the grinding rollers (2). Under compression in the grind-
ing gap, the particles are firstly displaced into existing voids
within the material bed before they start to break under
hydrostatic pressure. This process is known as compressive
in-bed comminution. Breakage is induced mainly by com-
pression, supported by small amounts of shear, resulting
in optimum size reduction, high energy efficiency, and
minimum wear. The advantage of the in-bed comminution
principle is that through the multiple contact points, apply-
ing pressure from all sides on the particle, there is a high
probability for crack initiation on the mineral boundaries
and at other weaknesses. This often results in an improved
degree of mineral liberation when compared to crushing
and conventional tumbling milling, as has been reported
in the literature by Van Drunick et al. (2010), Altun et al.
(2015), Reichert et al. (2015) and Jacobs et al. (2016).
The ground material escapes the confines of the com-
pressive breakage region and continues its movement under
centrifugal force to the edge of the table. All particles fall
into the process gas stream (3) where finer particles are levi-
tated upwards to the classifier (4). The rotational speed of
the classifier, determining the centripetal force to the out-
side, in combination with the inward directed speed of the
gas flow define the cut size of the classifier. Product-sized
material passes through the classifier vanes and leaves the
mill with the gas flow (5) to be collected within the bag-
house filter. Coarse material rejected by the classifier can be
partly or completely discharged from the mill (henceforth
termed as grit), as is done in the Southdown pilot plant test
work. In most VRM installations the grits are not removed
Figure 3. Schematic Loesche vertical roller mill
various industrial mineral applications. VRM technology is
arguably the compressive comminution method with the
widest application globally, when all materials needing to
be ground are considered.
VRM units are usually operated in closed circuit with a
dynamic classifier mounted on top of the mill, as shown in
Figure 3. The setup requires a constant gas flow through the
machine but allows a compact combination of grinding,
classifying, and drying.
Operating Principles
Accepting feed sizes up to F100 150 mm and grinding prod-
ucts down to P80 20 µm in a single unit, the Loesche VRM,
illustrated in Figure 3, contains all elements necessary to
take the feed to the final product.
After tramp-metal removal, material to be ground is
fed into the mill and directed to the center of the grinding
table (1). Driven by centrifugal force, it moves outwards
towards the edge of the rotating table and into the path of
the grinding rollers (2). Under compression in the grind-
ing gap, the particles are firstly displaced into existing voids
within the material bed before they start to break under
hydrostatic pressure. This process is known as compressive
in-bed comminution. Breakage is induced mainly by com-
pression, supported by small amounts of shear, resulting
in optimum size reduction, high energy efficiency, and
minimum wear. The advantage of the in-bed comminution
principle is that through the multiple contact points, apply-
ing pressure from all sides on the particle, there is a high
probability for crack initiation on the mineral boundaries
and at other weaknesses. This often results in an improved
degree of mineral liberation when compared to crushing
and conventional tumbling milling, as has been reported
in the literature by Van Drunick et al. (2010), Altun et al.
(2015), Reichert et al. (2015) and Jacobs et al. (2016).
The ground material escapes the confines of the com-
pressive breakage region and continues its movement under
centrifugal force to the edge of the table. All particles fall
into the process gas stream (3) where finer particles are levi-
tated upwards to the classifier (4). The rotational speed of
the classifier, determining the centripetal force to the out-
side, in combination with the inward directed speed of the
gas flow define the cut size of the classifier. Product-sized
material passes through the classifier vanes and leaves the
mill with the gas flow (5) to be collected within the bag-
house filter. Coarse material rejected by the classifier can be
partly or completely discharged from the mill (henceforth
termed as grit), as is done in the Southdown pilot plant test
work. In most VRM installations the grits are not removed
Figure 3. Schematic Loesche vertical roller mill