The pumping scheme developed at Vanchem’s vanadium
beneficiation plant in Witbank provided a challenge for engineering
firm Golder Associates Africa.
According to Jaco Snyman, design engineer for Golder Associ- ates
Africa, the pump system was done on a tight schedule.
The company had to design two pumping systems – one to handle
the slimes material and another for the return water.
Regarding the slimes material, the challenge lay in maintaining a
consistent flow.
Therefore, Golder designed two slurry lines, each with five stages
of Weir-Envirotech rubber-lined impeller, slurry centrifugal
pumps.
According to Snyman, the key operating condition that the scheme
had to meet was the volume difference that had to be handled as a
resultair pressure can crusher report of the number of mills opera- tional during day and
night.
Under normal conditions, a thickener plant and the associated
pumping system are designed to operate at a constant density.
However, the pumping scheme in this case had to be operated at a
constant volume rather than a constant density, owing to the volume
changes between day and night.
Regarding the operation of the mills, Snyman states that two would
operate during the daytime and one at night.
Thihow to plan for crusherss meant that the volume of material would be lower at night, but
a constant flow was still neces-sary.
It was decided that, owing to the minimum design criteria, a
constant flow of 48 m3 of slimes would have to be pumped out every
hour, at varying density, in order to manage the waste
efficiently.
Therefore the pumps would put out 1 152 m3 of slimes daily.
Also, the optimum density for pumping would be between 1,35 t/m3
and 1,40 t/m3.
Each mill produces about eight dry totoggle joint application in industryns of material hourly, which
would place great pressure on the pumps.
To increase the flow during the single mill operation period, water
was added to the slimes after it had passed through the thickening
process.
“When we designed the pump system, we had to consider the
material being transported. The particle size meant that we had to
consider different lining systems for the pumps. The life of the
impeller also had to be considered and these and other factors
provided the brock crushing and grindingasis for our pump design,” says Snyman.
Owing to the pumping distance between the plant and the slimes
facility, and scheme-specific volumes, customised casings for the
pumps were required.
Regarding the return water system, Golder designed a two-phase
pumping system.
The design for the return water system had to compensate for
constant change in static head conditions as the facility fills up
– the annual rate rise is said to be three metres.
Phase one of washed and crushed stone equipment picturesthe two-phase pumping approach designed by Golder
would consist of a floating barge and two Flygt submersible pumps
(one duty and one standby).
Phase two comprised of two Warman centrifugal pumps, also one duty
and one standby, to pump water through a 2 800-m long pipeline to
the existing clear-water tank, situated in the process plant.
The Flygt pumps would pump water to a temporary holding tank on the
embankment of the facility.
When the level of the storage tank at the process plant is low, the
Warman pumps would deliver water from the balancing tank to the
plant.
When the balancing tank is near empty, a signal is sent to the
submersible pumps to pump water back into the balancing tank,
thereby ensuring an even flow and distribution of water.
Snyman explains that the submersible pumps are housed in a tray
that is fully submerged in the water.
An overflow weir controls the flow into the tray and this ensures
that the uppermost layer of water is skimmed off.
When considering the slimes delivery system, Snyman says that the
company designed the deposition pipe to comprise western and
eastern legs that extend from the south-western corner of the
facility.
Also, ten delivery stations with twelve discharge points –
the first and last valve stations each having two discharge points
– feed off the deposition pipes.