FIELD OF THE INVENTION

This invention relates to an apparatus for classifying particulate material using density separation.

BACKGROUND OF THE INVENTION

Classification may be defined as the separation of solid particles into two or more products according to their velocities when falling through a fluid medium, such as water. The velocity of the particles depends on their size, shape and density. Particles with a higher density and larger size will settle down quickly compared to particles with a lower density and smaller size. Such process is known as density separation.

Hydraulic classification is the separation of particles in a tank by specific gravity, utilising the action of rising water currents to separate the particles into a light fraction and into a heavier fraction. Heavier and larger particles settle down and leave the vessel through an underflow outlet as a relatively heavy aqueous slurry while lighter and finer particles leave the vessel with most of the water as the water overflows from an upper end of the vessel. Hydraulic classifiers are widely used in sand and glass industry.

Due to the high viscosity, low water content and abrasive nature of the slurry passing through the underflow outlet of such classification vessels, the slurry is typically carried to a subsequent process, such as a dewatering process, under the action of gravity, a substantially vertical flow path being provided for the slurry between the classification tank and the subsequent process. However, this requires the entire classification vessel to be mounted at a substantial height to allow the slurry to pass through the underflow outlet under gravity. This greatly increases the overall size of the plant and limits maintenance access to the classification vessel and associated equipment. For example, where the subsequent process for treating the slurry from the underflow outlet of the classification vessel comprises a dewatering screen, it is necessary to mount the entire classification vessel above such dewatering screen.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided an apparatus for classifying particulate material comprising at least one tank for receiving a feed containing said particulate material, at least a portion of said particulate material progressing downwardly to a lower region of at least one tank to be discharged through at least one discharge outlet into a suction line, said suction line extending between a reservoir containing a supply of water upstream of said at least one discharge outlet and a pump downstream of said at least one discharge outlet, wherein said pump is adapted to draw water from the reservoir into which is entrained material from said at least one discharge outlet through the suction line.

In a preferred embodiment the pump is adapted to transfer water from the reservoir and material from said at least one discharge outlet from the suction line to at least one downstream process. Said at least one downstream process may comprise one or more of a hydrocyclones and/or a dewatering screen. Preferably said at least one downstream process is located above said at least one discharge outlet of the at least one tank.

The water reservoir may comprise a sump receiving water and particulate material entrained therein from a further process, such as one or more hydrocyclones, for example the sump may receive an underflow from said one or more hydrocyclones such that material carried in said underflow may be added to the material carried in the suction line from the one or more discharge outlets of the at least one classification tank.

Preferably said suction line extends beneath said at least one tank. Preferably said suction line extends substantially horizontally between said water reservoir and said pump. The apparatus may further comprise means for introducing water into a lower region of the at least one tank whereby water is caused to flow upwardly and through the at least one tank, whereby hydraulic separation of said particulate material takes place within the at least one tank with particles of lower settling velocity progressing upwardly and into means for effecting discharge of an overflow fraction from the at least one tank, and particles of a greater settling velocity progressing downwardly to said lower region of the at least one tank to be discharged through said at least one discharge outlet into said suction line. In one embodiment the apparatus may comprise first and second classification tanks, water being introduced into a lower region of each of the first and second tanks, each tank being provided with means for effecting discharge of an overflow fraction therefrom, wherein at least one transfer passage is provided for transferring material from the lower region of the first tank to the second tank, said at least one discharge outlet being provided in a lower region of the second tank. The at least one transfer passage may comprise an upwardly extending pipe passing through a central region of a lower end of said second tank, said at least one discharge outlet comprise first and second downwardly extending passages extending through a lower wall of the first tank on either side of said transfer passage.

The at least one discharge outlet may include a flow control means. Preferably said flow control means comprises a dart valve.

According to a further aspect of the present invention there is provided a method of classifying particulate material comprising passing a feed containing particulate material into at least one tank, at least a portion of said particulate material progressing downwardly to a lower region of at least one tank to be discharged through at least one discharge outlet into a suction line, operating a pump at a downstream end of said suction line to draw water from a reservoir at an upstream end of said suction line such that material from said at least one discharge outlet of said at least one tank is drawn through the suction line via the pump.

The method may further comprise passing material from said at least one discharge outlet entrained in water from the reservoir in said suction line to at least one further process via said pump. The at least one further process may comprise a dewatering process. The pump may be operated to pump said material from said at least one discharge outlet entrained in water from the reservoir to one or more hydrocyclones and subsequently onto a deck of a dewatering screen. Preferably water level in the reservoir is maintained above a lower end of the at least one tank. The method may comprise controlling the flow of material through the at least one discharge opening by a control means.

According to a further aspect of the present invention there is provided an apparatus for classifying particulate material comprising at least one tank for receiving a feed slurry, means for introducing water into a lower region of the at least one tank whereby water is caused to flow upwardly and through the feed slurry contained therein whereby hydraulic separation takes place within the at least one tank with particles of lower settling velocity progressing upwardly and into means for effecting discharge of an overflow fraction from the at least one tank, and particles of greater settling velocity progressing downwardly to a lower region of at least one tank to be discharged through at least one discharge outlet, wherein the at least one discharge outlet includes a flow control means in the form of a dart valve comprising an axially moveable valve member located within a tapered region of the at least one discharge outlet such that axial movement of the valve member facilitates adjustment of the flow rate therethrough.

BRIEF DESCRIPTION OF THE DRAWINGS

A classification apparatus in accordance with an embodiment the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a part sectional side view of a classification apparatus in accordance with an embodiment of the present invention;

Figure 2 is a further part sectional side view of a classification apparatus of Figure 1 and

Figure 3 is a detailed view of part A of the apparatus of Figure 2. DETAILED DESCRIPTION OF THE DRAWINGS

As illustrated in the drawings, a classification apparatus for classifying and separating sand or similar fine particulate material suspended in a fluid, such as water, for example in the form of a slurry, comprises first and second coaxially arranged classification tanks 2,4. The first (or outer) tank 2 comprises a vertically arranged tubular housing, having substantially square or circular cross sectional outer wall (although it is envisaged that the first tank 2 may have other shape). The second (or inner) tank 4 comprises a vertically arranged substantially cylindrical outer wall located coaxially within the first or outer tank 2. The lower end of the second tank 4 extends below the lower end of the first tank 2. Again, the cross sectional shape of the second tank 4 may be other than cylindrical, for example square section.

A vertically extending transfer passage 6 extends between the first and second tanks 2,4 allowing water, and particulate material entrained therein (for example in the form of a water/sand slurry), to pass between the first tank 2 and the second tank 4 in an upwards direction. The transfer passage 6 comprises a vertically arranged pipe, extending coaxially upwardly into the second tank 4 into a central or upper region of the second tank 4. Preferably the transfer passage 6 is aligned with a central axis of the second tank 4 such that water and entrained material passes from the first tank 2 into the second tank 4 in an upwards direction with minimal turbulence.

Water supply passages 10,12 are provided in a lower region of each of the first and second tanks 2,4 connected to a water supply whereby water is caused to flow upwardly within each tank 2,4 to overflow from an upper end of each tank 2,4 into respective first and second collection chambers 16,26 surrounding the upper end of each tank 2,4. The flow of water from the water supply passages 10 in the first tank 2 may be controlled to be less than the flow of water from the water supply passages 12 in the second tank 4 such that the upward water velocity in the first tank 2 is less than that of the second tank 4, such that the teeter bed in the first tank 2 is higher than the teeter bed in the second tank 4. This may create a pressure differential between the ends of the transfer passage 6, causing slurry to flow through the transfer passage 6 from the first tank 2 to the second tank 4.

An upper edge of the first tank 2 defines a peripheral overflow weir 14 over which water and fine entrained solids within the first tank 2 may overflow into the annular first collection chamber 16 surrounding an upper end of the first tank 2. At least one drain outlet 18 is provided in the first collection chamber 16.

Similarly, an upper edge of the second tank 4 defines a peripheral overflow weir 24 over which water and entrained solids within the second tank 4 may overflow. The second collection chamber 26 is provided around an upper end of the second tank 4, within the first tank 2, for receiving water and entrained material passing over the overflow weir 24 defined by the upper edge of the second tank 4. A drain outlet 28 is provided in a lower region of the second collection chamber 26 connected to a downwardly inclined drain passage 30 extending through the first tank 2 and passing through a side wall of the first tank 2 to drain the overflow from the second tank 4.

One or more drain outlets 32 extend from a lower wall 34 of the second tank 4 for removing heavier material in an aqueous slurry settling in a lower region of the second tank 4, as will be described in more detail below. In the embodiment shown a pair of drain outlets 32 are provided, one on either side of the transfer passage 6.

In use, a feed slurry is discharged into an upper region of the first tank 2, for example from a hydrocyclone, via suitable discharge outlets (not shown) while water is supplied to the water outlets 10 in the lower region of the first tank 2, such that water is caused to flow upwardly through the feed slurry within the first tank 2. Very fine particulate material (for example 1 - 100 pm) is carried in the upward flow of water in the first tank to pass over the overflow weir 14 defined by the upper edge of the outer wall of the first tank 2 and into the first collection chamber 16, from which it is removed as a first cut via the drain outlet 18 of the first collection chamber 16. Due to the pressure differential between the ends of the transfer pipe 6, water and heavier entrained particulate material passes through the transfer pipe 6 from a lower region of the first tank 2 and is delivered into a central region of the second tank 4 through an outlet region of the transfer pipe 6 in an upwards direction, avoiding the creation of turbulence within the second tank 4. At the same time water is supplied to the water outlets 12 in the lower region of the second tank 4, creating an upwards flow of water within the second tank 4. Heavier particulate material (for example 200pm to 2mm) falls against the flow of water under the action of gravity to settle in a lower region of the second tank 4. At the same time, lighter particulate material (for example 100pm to 200pm) is carried in the upward flow of water in the second tank 4 to pass over the overflow weir 24 defined by the upper edge of the outer wall of the second tank 4 to pass into the second collection chamber 26 surrounding an upper end of the second tank 4 to drain therefrom via the drain outlet 28 thereof as a second cut.

Control means may be provided for controlling the flow rate of material through the transfer passage 6. Such control means may include a valve within the or each transfer passage of a drain outlet in the first tank.

The heavier particulate material collected in the lower region of the second tank 4, defining a third cut, is removed from the second tank 4 via the drain outlets 32 extending from lower wall 34 of the second tank 4 as a slurry, under the control of a respective modulating plug valve in each drain outlet 32. The modulating plug valves may be adapted to control the flow rate of the slurry passing through each drain outlet 32.

The drain outlets 32 extend vertically into an upper side of a horizontally extending suction pipe 40 extending between a reservoir 42 and a pump 44, whereby the pump 44 draws water from the reservoir 42 through the suction pipe 40 and draws the slurry passing into the suction pipe 40 from the drain outlets 32 into the flow of water before the water and slurry is pumped via the pump 44 to one or more subsequent processes, for example to one or more hydrocyclones for reducing the water content of the slurry and removing fine contaminants before passing the slurry onto the deck of a dewatering screen (not shown). The water supplied to the reservoir 42 (which may comprise a sump) coupled to the suction line 40 may be received from a further process integrated into the overall plant, such as the underflow of one or more hydrocyclones (not shown). A sand product may be entrained into the suction line 40 along with the water, enabling such sand product to be added to the slurry from the drain outlets 32 of the classification tanks 2,4.

As best shown in Figure 3, a flow control device in the form of a dart valve 46, is provided in each drain outlet 32 for controlling the flow of slurry from the bottom of the second classification tank 4 into the suction line 40. Each dart valve 46 comprises an axially moveable double ended frustoconical valve member 48 located within a tapered seat region 50 of the respective discharge outlet 32 wherein axial such that axial movement of the valve member 48 facilitates adjustment of the flow rate therethrough. Each valve member 48 is mounted on a vertically extending guide rod coupled to a respective actuator to facilitate vertical displacement of the valve member 48 in its respective seat region 50. A further shut off valve 49 may be provided in each discharge outlet 42, preferably below each dart valve. In the embodiment shown, each shut off valve 49 comprises a respective gate valve.

The use of a pump and suction line to transfer the material from the bottom of the classification tank to a subsequent process allows the classification tank to be located at a much lower position than required for known systems where the material is transferred from the classification under gravity. This provides much improved maintenance access to the classification tank as well as greater flexibility in the arrangement of the various parts of the overall material processing plant. The use of a water reservoir to supply water into the suction line into which material from the discharge outlets of the classification tank enables particulate material from a further process to be blended with the underflow of the classification tank before being passed to a further process. The invention is not limited to the embodiment described herein but can be amended or modified without departing from the scope of the present invention as defined in the appended claims.