SPIRAL SEPARATOR AND CONTROL SYSTEM
Technical field
This invention relates to a spiral separator, a control system and a method therefor.
Introduction and background to the invention
Generally, a spiral separator comprises a helical or spiral trough mounted about an upright column, alternately within a frame structure. During operation of a spiral separator of this kind, slurry, containing mineral particles to be separated (or concentrated) is fed to the top of the helical trough. As the slurry descends in the trough under gravity, the mineral bearing particles in the slurry migrate radially outwardly under centrifugal forces according to size or specific gravity. Smaller or less dense particles move under the action of centrifugal forces in a radially outward direction while denser particles migrate radially inward towards the central column.
The term "beneficiation" for purposes of this specification shall be interpreted as to include separation and concentration.
It will be appreciated that the efficiency of a spiral separator will fluctuate with various factors such as viscosity, flow rate, density, particle size, etc.
In a large beneficiating plant, banks of spiral separators may be operating simultaneously, so that a small change in efficiency across the banks may result
in large deviations in operating costs. While the feed systems that provide inflow to a plant are designed for optimum efficiency of the spiral separator banks for certain operational conditions and variations, in practice the conditions and variables fluctuate over time due to changing mineralogical, feed and operational conditions and variables in the process.
Attempts have been made in the past to design systems that allow the spiral separators to be adjusted to enhance their efficiencies. A disadvantage of these designs is that they are impractical, due to the large number of spiral separators that need to be adjusted, as well as the dynamic nature of the process.
Attempts have also been made to increase the efficiencies of the banks of spiral separators as a whole by designing systems which allow sections of the bank of spirals to be switched off or excluded from the beneficiation process, particularly when the plant is operating below design capacity, effectively increasing the flow rate through the individual spiral separators.
Object of the Invention It is accordingly an objective of this invention to provide a spiral separator and control system arrangement that at least partially alleviates the abovementioned disadvantages.
Disclosure of the Invention
According to a first aspect of the invention, there is provided a spiral separator and control system arrangement comprising at least one spiral separator, for beneficiating a slurry stream; measuring means for measuring at least one slurry characteristic; and adjustment means for adjusting in a controlled fashion the slurry stream upstream of the spiral separator, the control of the adjustment means being governed by a control system in accordance with the measured characteristic.
The measuring means may measure the characteristics of the feed slurry flow or the products slurry flow.
The adjustment means may adjust any one or more of the group of slurry characteristics consisting of mineral composition, slurry solids concentration, slurry volumetric flow rate, solids mass flow rate, particle size distribution, particle density distribution, slurry density or any combination of these.
The adjustment means may comprise any one or more of the group consisting of recycling a product stream into a feed stream, fluid addition means, dewatering, passing the slurry through a cyclone, increasing or decreasing the number of spirals, splitting the feed to the spiral separator, or particle size distribution adjustment means.
The fluid added to the system may be dilution water or slurry or both.
The control system may further be based on at least one mathematical model that takes cognisance of the conditions and variables of the beneficiation system.
The control system may be automated.
The control system may operate by means of a feedback loop.
The control system may further comprise mixing means to mix the slurry and the fluid added to the system upstream of the spiral separator.
The fluid addition means may include a tank into which both the slurry and fluid may be added and /or mixed.
Separate fluid addition means may be provided for each spiral separator or for a plurality of spiral separators.
According to a second aspect of the invention, there is provided a control system for beneficiating a slurry stream by means of a spiral separator comprising measuring means for measuring at least one of the slurry characteristics; and adjustment means for adjusting fluid in a controlled fashion to a slurry stream upstream of the spiral separator.
The measuring means may measure the slurry from the feed slurry flow or the product slurry flow.
The adjustment means may adjust any one or more of the group of slurry characteristics consisting of mineral composition, slurry solids concentration, slurry volumetric flow rate, solids mass flow rate, particle size distribution, particle density distribution, slurry density or any combination of these.
The adjustment means may comprise any one or more of the group consisting of recycling a product stream into a feed stream, fluid addition means, dewatering, passing the slurry through a cyclone, increasing or decreasing the number of spirals, splitting the feed to the spiral separator, or particle size distribution adjustment means.
The fluid added to the system may be dilution water or slurry or both.
The control system may be based on a mathematical model.
The control system may further be based on at least one mathematical algorithm that takes cognisance of the conditions and variables of the beneficiation system.
The control system may be automated.
The control system may further comprise mixing means for mixing the slurry and the fluid added to the system upstream of the spiral separator.
The fluid addition means may include a tank into which both the slurry and fluid may be added and/or mixed.
According to a third aspect of the invention, there is provided a method of controlling a spiral separator for the beneficiation of a slurry stream including the steps of measuring at least one of the slurry characteristics; assessing the performance of the spiral separator; and altering feed parameters in a controlled fashion of the slurry stream upstream of the spiral separator in accordance with the assessed efficiency.
The slurry feed parameters may be altered by the addition of fluid. The fluid added to the system may be dilution water.
The feed parameters which may be altered include, but are not limited to, any one or more of the group of slurry characteristics consisting of mineral composition, slurry solids concentration, slurry volumetric flow rate, solids mass flow rate, particle size distribution, particle density distribution, slurry density or any combination of these.
The means by which the feed parameters are altered may be by any one or more of the group consisting of fluid addition means, dewatering, passing the
slurry through a cyclone, increasing or decreasing the number of spirals, splitting the feed to the spiral separator, or particle size distribution adjustment means.
The method of controlling the spiral separator system may be based on at least one mathematical algorithm, which takes cognisance of the conditions and variables of the system.
The altering of the slurry feed parameters may be accomplished automatically by means of a looped feedback system, or by means of a feed forward system.
The altering of the slurry feed parameters may be controlled by means of a predictive mathematical algorithm that models certain performance characteristics of the spiral concentrator.
The method may further include the step of mixing the slurry stream and a fluid upstream of the spiral separator.
Specific Embodiment of the Invention A preferred embodiment of the invention will now be described by way of a non- limiting example only, with reference to the accompanying drawings in which:
Figure 1 shows a spiral separator unit;
Figure 2 shows a schematic layout of the beneficiation system including the control system having the measuring means measuring the slurry characteristics downstream of the mixing tank; and
Figure 3 shows a schematic layout of the beneficiation system including the control system having the measuring means measuring the slurry characteristics upstream of the mixing tank.
Figure 4 shows a schematic layout of the beneficiation system including the control system having the measuring means measuring the slurry characteristics downstream of the spiral splitters.
The same reference numerals are used to denote corresponding parts in the accompanying drawings.
With reference to Figure 1 , a prior art spiral concentrator unit (10) has two helically shaped troughs (11) mounted on central columns (12). The helical troughs (11) are fed with slurry to be beneficiated from a central tank (13) via supply pipes (14), from where the slurry flows under gravity down the height of the helical troughs (11). In a beneficiation plant, large banks of these separator units are used to beneficiate the total slurry stream from upstream mining operations.
In Figure 2, 3 and 4 a spiral separator and control system arrangement (20) is shown including an upstream process from which a slurry stream (1) is
generated. The slurry stream (1) is then fed into a tank (2), where one of the system variables may be altered. The slurry variables include, but are not limited to:
• fluid density • solids concentration
• volumetric flow rate
• solids mass flow rate
• particle size distribution
• particle density distribution • any combination of these
In this embodiment the volume flow rate and density are simultaneously altered by the addition of water from a fluid source (3). A measuring means (5) measures system variables such as viscosity, density, particle size distribution and volumetric/mass flow rate.
Fluid from a fluid source (3), preferably water, is fed into the tank (2) by a fluid addition means, such as a control valve (7), to make up a certain total volumetric flow rate. A mixing means (4) is used to mix the slurry (1) and added fluid (3) to ensure the even mixing of the slurry feed (1) and the added fluid (3). The slurry/fluid mix is then fed to a bank of spiral separators (6), where mineral fractions present in the mix are separated out into a number of fractions (8 and
The measuring means may measure the system variables at any point, including measuring the variables from the feed slurry stream (as shown in Figure 3), the mixed slurry stream (as shown in Figure 2), or from the product slurry stream downstream of the spiral separators (6) (as shown in Figure 4).
The measured properties are then used in a mathematical algorithm to optimize a particular parameter of the slurry product.
The mathematical algorithm is described, but not limited, by the equation:
E = f(Sse, Qsi, Ms, μsι, Xf) γsι, φsι, λsι, N,...)
In which:
E is the efficiency of mineral recovery from the spiral separator;
Sse is the density of the slurry feed;
Qsi is the slurry feed volumetric flow rate;
Ms is the solids mass flow rate;
μsι is the slurry viscosity;
Xf is the feed grade;
γsι is a function describing the particle size distribution;
φsi is the particle density distribution;
λsι is the slurry density; and
N is the number of spirals available.
The mathematical algorithm is predetermined by fundamental principles or empirically or both, for the spiral separator banks (6)
The best possible spiral separator efficiency is worked out for the current system variables, and the efficiency is then optimized by altering one of the system parameters, such as volume flow rate or particle size distribution. This may be by adding or reducing water, or processing the slurry feed through a cyclone (not shown), or by any other means. In this way, the efficiency of mineral recovery can be optimized for the system variables that are in operation at that time, thus increasing the efficiency of mineral recovery.
It will be appreciated that numerous embodiments of the invention are possible without with out departing from the scope of the invention as claimed in the claims hereinafter.