BATEMAN has been appointed as an agent to market KHD Humboldt Wedag's
roller presses for the minerals industry in Southern Africa.
This grinding technology was originally introduced to the market
in 1984 and used widely to process cement and limestone. More recently
it has been successful around the world in a variety of mineral-processing
applications where its uses ranged from coarse grinding of pebbles
in excess of 65 mm down to fine grinding of <100 µm.
A total of about 200 units have been installed worldwide.
The Bateman-KHD roller press (also known as high-pressure grinding
rolls) offers low-energy consumptions, in the range 0,8 to 3,0 kWh/t
for most ores, and up to 40 % less than that for other grinding technologies.
Roller presses also have the ability to process ores with up to 10
% moisture, often eliminating the need for costly drying processes.
Overall plant throughput is significantly increased by installing
roller presses and the grade of product is improved.
The capacities of roller presses start at about 50 t/h for the pilot-plant
models to 1 500 t/h for the largest installed units. The power consumption
range is 100 kW to about 3 000 kW with rollers ranging from diameters
of 0,8 m and widths of 0,25 m to diameters of 2,1 m and widths of
1,8 m. The specific throughput of an industrial-scale roller press
may be determined by the more-or-less direct scale-up of laboratory
or pilot-plant testing.
The installations have low maintenance and space requirements, low
vibration and noise, availabilities in excess of 95 % and long-term
reliability.
How roller presses work
Particulate material, choke fed into two counter-rotating rollers,
is compressed to about 85 % of the actual material density. The pressure
applied exceeds the compressive strength of the feed resulting in
microcracks within the particles. The material is discharged in the
form of a compacted flake with a very fragile consistency.
The weakened particles in the flake discharged from the rollers are
very amenable to any subsequent low-energy grinding action. This is
especially advantageous in operations where power is a costly item
and where it is necessary to maintain plant capacity where harder
or leaner ores are encountered.
The size distribution of the crushed particles is wider than that
obtained with standard tertiary crushers (e.g. cone crushers) because
the pressure on the particle bed is exerted equally on the coarse
and fine particles, breaking all of them down further.
In practice, roller presses handle particles up to about 80 mm, which
could be up to about 70 % greater than the operating gap between the
rollers.
As the main grinding action takes place within the particles themselves,
and not between the roller surface and the material, wear is far lower
than in traditional grinding equipment. The amount of wear has been
further reduced in the latest Bateman-KHD equipment by lining the
autogenous wear surfaces of the rollers with wear-resistant hard metal
studs, an application which has been patented by KHD.
The feed to a roller press should preferably contain some moisture
to assist in the generation of a competent autogenous wear surface.
This could be of significant advantage where moist material has to
be ground, as costly drying of the feed will not be required.
Minerals-processing applications
In heterogeneous materials, such as ores, the different reaction
to pressure of the individual mineral species in the ore enables the
beneficiation of the valuable materials. For example, hard diamond
effectively resists the pressure while the surrounding material disintegrates,
liberating the diamonds.
The differential compressive properties of sulphides and base-metals,
compared with the material in the rest of the ore, similarly facilitate
mineral liberation. In the case of malleable materials such as gold,
the gold particles deform while the bed rock disintegrates, making
subsequent leaching action more effective.
More information may be obtained by contacting Willem du Toit, Product
Engineer, on +27-11-201-2300 or email engtech@batemanengineering.com.
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