Over 48mt (million tonnes) of alumina are shipped each year,
38% of which comes through Australian ports. Alumina is a
difficult-to-handle, free-flowing material which is prone to
causing dust pollution during handling operations such as the
filling of ships holds. Unless precautions are taken, air-pollution
levels as high as 200mg/m3 can easily be exceeded. This is a real
health hazard to people working in the vicinity, causes a nuisance
to adjoining properties and over time leads to marine pollution
resulting in potential loss of endangered species.
Historically, alumina was loaded into ships holds by dropping
it down vertical loading chutes often 25m or more in length
which, unsurprisingly, caused huge quantities of dust to be
generated. Some loading systems incorporated a complex dust
extraction system which was not particularly effective, required
regular maintenance to filter packs and consumed large amounts
of energy; clearly a more effective loading system was required.
A more effective shiploading technology became available to
Australian port facility operators when the Cascade loading
chute was developed in the UK, originally to handle potash,
another notoriously difficult-to- handle, dusty material. The
Cascade system overcomes these problems by directing the
material to flow down a chute incorporating a series of inclined
cones which limits the flow velocity thereby preventing the
entrainment of large quantities of air which would otherwise
lead to dust production. Using this technology dust production
is practically eliminated at source without the need for
expensive and energy intensive dust extraction and filter systems.
So effective is the technology that the manufacturer,
Cleveland Cascades Limited guarantees that dust emission levels
will not exceed 5mg/m3 when the system is operating. Port
operators considering the installation of this technology can
request for very accurate air pollution measurements to be
taken before and after installation to demonstrate the
improvements that have been made; this is very useful when
complying with environmental protection legislation.
In some ports where many widely different materials must be
handled, the VariFlow system is available. To optimize flow rate
the VariFlow can operate in three modes. In standard mode,
cone inclination is maintained at a fixed angle to suit the range
of materials anticipated. In remote mode, the cone angles are
adjusted to optimize flow rate for a particular material. In
intelligent mode, sensors in the system monitor the materials
speed of descent and the cone angles are constantly adjusted to
optimize the flow rate. In common with many other materials,
alumina is highly abrasive and special precautions must be taken
to protect the running surfaces within the loading system.
Cleveland Cascades Ltd has developed a process to attach a
ceramic tile lining system to internal surfaces to provide
protection. So effective is this system that installations can be
guaranteed to handle many millions of tonnes of material before
any attention is required. Because the requirements of every
port operator are different, Cleveland Cascade Ltd chutes are
bespoke, tailored to meet each operators needs. Many optional
features can be provided including camera monitoring of the
loading operation, particularly useful if the shiploading machine
operator’s view is obstructed. Rotating trimming devices can
also be fitted to fully utilize hold space under deck coamings and
to help operators to adhere to ship loading plans.