APPARATUS AND METHOD OF FEEDING A FEED SLURRY INTO A SEPARATING DEVICE

Abstract

The present invention provides an apparatus and method for feeding a feed slurry into a device for separating low density particles from the feed slurry. The apparatus comprises a conduit having a slurry inlet, a gas feed inlet, a plurality of hollow tubes and an outlet. The hollow tubes are configured to combine the feed slurry from the slurry inlet and gas from the gas feed inlet. The hollow tubes comprise a porous section to generate bubbles of substantially uniform size into the slurry for adhering to the low density particles. Slurry flows in axially aligned hollow tubes as gas is introduced through the porous sections into the slurry. Alternatively, slurry flows around hollow tubes arranged perpendicular to the conduit longitudinal axis as gas is discharged through the porous sections into the slurry.

Claims

1-24. (canceled)

25. An apparatus for feeding a feed slurry into a device for separating low density particles from the feed slurry, the apparatus comprising: a conduit having a slurry inlet for receiving the feed slurry, a gas feed inlet for receiving a gas and an outlet for discharging the gas and feed slurry; and a plurality of hollow tubes within the conduit for combining the feed slurry and gas from the slurry and gas feed inlets; wherein one or more of the hollow tubes comprise a non-porous section for directing the flow of the feed slurry and gas and a porous section to generate bubbles of substantially uniform size into the feed slurry flowing within the conduit.

26. The apparatus of claim 25, wherein the one or more hollow tubes comprise a porous surface.

27. The apparatus of claim 25, wherein the porous section is formed at a lower portion of the one or more hollow tubes.

28. The apparatus of claim 25, wherein the porous section is formed in the sidewalls of the one or more hollow tubes.

29. The apparatus of claim 25, wherein the porous section comprises pores or perforations having an average diameter of less than 1 mm to 0.1 microns.

30. The apparatus of claim 25, wherein the porous section has a porosity of between 1% to 90%, preferably 10% and 80%.

31. The apparatus of claim 25, wherein the porous section is in fluid communication with the gas feed inlet to receive gas from the gas feed inlet and generate the bubbles of substantially uniform size into the slurry flowing in the one or more hollow tubes.

32. An apparatus for feeding a feed slurry into a device for separating low density particles from the feed slurry, the apparatus comprising: a conduit having a slurry inlet for receiving the feed slurry, a gas feed inlet for receiving a gas and an outlet for discharging the gas and feed slurry; a plurality of hollow tubes within the conduit for combining the feed slurry and gas from the slurry and gas feed inlets, wherein the hollow tubes are positioned substantially perpendicular to a longitudinal axis of the conduit and arranged in one or more rows; and a plurality of channels located above and below the hollow tubes, the channels being positioned axially within the conduit; wherein the hollow tubes each comprise a porous section to generate bubbles of substantially uniform size into the feed slurry flowing within the conduit.

33. The apparatus of claim 32, wherein the one or more hollow tubes each have an open end in fluid communication with the gas feed inlet, the open end receiving the gas from the gas feed inlet so that the porous section of each of the one or more hollow tubes receives the gas from the one or more hollow tubes and generates the bubbles of substantially uniform size into the feed slurry flowing within the conduit.

34. The apparatus of claim 32, wherein the channels are defined by a plurality of parallel plates.

35. The apparatus of claim 32, wherein the hollow tubes comprise a porous surface.

36. The apparatus of claim 32, wherein the porous section is formed in the sidewalls of the one or more hollow tubes.

37. The apparatus of claim 32, wherein the porous section comprises pores or perforations having an average diameter of less than 1 mm to 0.1 microns.

38. The apparatus of claim 32, wherein the porous section has a porosity of between 1% to 90%, preferably 10% and 80%.

39. The apparatus of claim 25, wherein the one or more hollow tubes each comprise an inner conduit, tube or pipe to define an annulus between the hollow tube and the inner conduit, tube or pipe.

40. The apparatus of claim 39, wherein the inner conduit, tube or pipe comprises a porous section for generating the bubbles of substantially uniform size into the feed slurry.

41. The apparatus claim 25, wherein the one or more hollow tubes comprise at least one of (a) an expanded portion having a cross-sectional area greater than the cross-sectional area of the remainder of the one or more hollow tubes; and (b) a contracted portion having a cross-sectional area less than the cross-sectional area of the remainder of the one or more hollow tubes.

42. An apparatus for separating low density particles from a feed slurry, comprising: a chamber having a plurality of inclined channels; a slurry feeder arranged to feed the feed slurry into the feed apparatus of claim 25; and a gas feeder arranged to feed gas into the feed apparatus; wherein the outlet of the feed apparatus is arranged to feed the gas and slurry into the chamber.

43. A method of feeding gas and a feed slurry into a device for separation low density particles from the feed slurry, comprising: introducing the feed slurry into a slurry inlet of a conduit; introducing gas into a gas feed inlet of the conduit; conveying the feed slurry and gas into a plurality of hollow tubes so that the feed slurry and gas is discharged from an outlet of the conduit into the separation device; and providing one of more of the hollow tubes with a non-porous section for directing the flow of the feed slurry and gas and a porous section or surface to generate bubbles of substantially uniform size into the feed slurry flowing within the conduit.

44. The method of claim 43, comprising forming the porous section or surface at a lower portion of the one or more hollow tubes.

45. The method of claim 43, comprising introducing the gas from the gas feed inlet into the one of more hollow tubes through the porous section or surface to generate bubbles of substantially uniform size into the feed slurry flowing the slurry flowing along the one of more hollow tubes.

46. A method of feeding gas and a feed slurry into a device for separation low density particles from the feed slurry, comprising: introducing the feed slurry into a slurry inlet of a conduit; introducing gas into a gas feed inlet of the conduit; positioning a plurality of hollow tubes substantially perpendicular to a longitudinal axis of the conduit and arranged in one or more rows; positioning a plurality of channels located above and below the hollow tubes, the channels being positioned axially within the conduit; conveying the feed slurry and gas into a plurality of hollow tubes so that the feed slurry and gas is discharged from an outlet of the conduit into the separation device; and providing the hollow tubes with a porous section or surface to generate bubbles of substantially uniform size into the feed slurry flowing within the conduit.

47. The method of claim 46, comprising introducing the gas from the gas feed inlet into the hollow tubes and discharging the gas through the porous section or surface in the form of the bubbles of substantially uniform size into the feed slurry flowing within the conduit.

48. A method of separating low density particles from a feed slurry containing such particles, comprising: introducing the feed slurry and a gas into a device for separating the low density particles from the feed slurry according to the method of claim 43, wherein the separating device comprises a chamber having plurality of inclined channels; allowing the slurry to flow downwardly through the inclined channels such that the low density particles escape the flow by sliding up the inclined channels while the denser particles in the slurry slide down the channels; and removing the low density particles from the chamber.

49. A method of separating low density particles from a feed slurry containing such particles, comprising: introducing the feed slurry and a gas into a device for separating the low density particles from the feed slurry according to the method of claim 46, wherein the separating device comprises a chamber having plurality of inclined channels; allowing the slurry to flow downwardly through the inclined channels such that the low density particles escape the flow by sliding up the inclined channels while the denser particles in the slurry slide down the channels; and removing the low density particles from the chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0070] FIG. 1 is a perspective view of an apparatus according to one embodiment of the invention;

[0071] FIG. 2 is a partial cut-away view of the apparatus of FIG. 1;

[0072] FIG. 3 is a bottom view of the apparatus of FIG. 1; and

[0073] FIG. 4 is a partial cut-away view of the apparatus of FIG. 1 mounted or fitted to a separation device.

[0074] FIG. 5 are top views of other embodiments of the invention;

[0075] FIG. 6 are end views of other embodiments of the hollow tubes employed in embodiments of the invention;

[0076] FIG. 7 is a top view of a further embodiment of the invention;

[0077] FIG. 8 is a side view of the embodiment of FIG. 7;

[0078] FIG. 9 is a top view of yet another embodiment of the invention; and

[0079] FIG. 10 is a side view of the embodiment of FIG. 9.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0080] The present invention will now be described with reference to the following examples which should be considered in all respects as illustrative and non-restrictive. In the Figures, corresponding features within the same embodiment or common to different embodiments have been given the same reference numerals.

[0081] The preferred forms of the invention as described below relate to the method and apparatus being used for froth flotation, as typically applied to fine particles of coal and mineral matter and used to concentrate hydrophobic particles of coal or minerals.

[0082] These hydrophobic particles selectively adhere to the surface of air bubbles, leaving hydrophilic particles in suspension between the bubbles. Thus, once the hydrophobic particles become attached to the air bubbles a new hybrid particle is formed which is of an overall density much less than the density of the water. The attached hydrophobic particle then has a segregation velocity in the upwards direction which is very high compared to the downward superficial velocity of the suspension of denser particles.

[0083] In most flotation situations certain reagents need to be added to promote flotation. A collector may be added to promote the hydrophobicity of the hydrophobic coal particles. In particular, a surfactant (sometimes called a frother) is added to stabilise the bubbles and hence the foam formed as the bubbles seek to exit the bulk liquid. Surfactant adsorbs at the surface of the bubble helping to prevent bubble coalescence, and hence preserving the low density particles. This is especially important when the bubbles are forced through the top valve.

[0084] In the described embodiment shown in FIGS. 1 to 4, a more efficient and convenient arrangement is provided to feed the feed slurry and gas into a separating device for separating low density particles from a feed slurry containing the low density particles and denser particles and/or matter. In particular, the described embodiment has been developed to feed the feed slurry and gas into a reflux classifier or inverted reflux classifier, as described in International Patent Application Numbers PCT/AU2007/001817 and PCT/AU2011/000682, respectively.

[0085] Referring FIG. 1, the feed apparatus 1 according to the embodiment of the invention comprising a conduit or chamber 2 having a slurry inlet 3 located in an upper portion 4 of the apparatus 1, a gas feed inlet 5 located in a middle portion 6 of the apparatus and a discharge outlet 7 located at one end of a lower portion 8 of the apparatus.

[0086] The conduit 2 also comprises a plurality of hollow tubes 10, shown in FIG. 2, with open entry ends 12 for receiving the feed slurry from the slurry inlet 3 and open exit ends 14 for discharging the slurry and gas from the conduit. The hollow tubes 10 also comprise a porous section 16 to enable gas from the gas feed inlet 5 to enter the hollow tubes and generate bubbles of substantially uniform size that flow with the incoming feed slurry from the entry ends 12. Mounting holes 18 are provided for mounting the feed apparatus 1 onto a device 30 for separating low density particles from the feed slurry (as best shown in FIGS. 3 and 4), such as a reflux or inverted reflux classifier.

[0087] The upper portion 4 of the conduit has a frusto-conical shape to facilitate distribution of the feed slurry into the entry ends 12 of the hollow tubes 10. Similarly, the lower portion 8 of the conduit has a frusto-conical section 31 to direct and concentrate the gas and slurry into a cylindrical section 32 before discharging through the outlet 7. The cylindrical section 32 effectively acts like a downcomer to deliver the bubbly flow to a chamber of the separating device 30.

[0088] The feed slurry is introduced via the slurry feed inlet 3 and passes through the entry end 12 of each hollow tube 10 and flows downwardly along the length of the hollow tubes in the vertical channels formed by the hollow tube walls. Gas (typically in the form of air) is introduced via the gas inlet 5 and passes through the porous section 16 of each hollow tube 10, generating bubbles of substantially uniform size that flow with the feed slurry and adhere to low density hydrophobic particles in the feed slurry. Generally, the gas is fed through the gas inlet 5 in a controlled manner so that fine bubbles preferably in the order of 0.3 mm diameter will emerge from the porous sections 16 of each hollow tube 10 and interact with the hydrophobic particles (which tend to be the low density particles) in the feed slurry passes through the length of the hollow tubes. Hydrophobic particles attached to the air bubbles are entrained downwards through the vertical channels and then discharge from the exit ends 14 of the hollow tubes 10.

[0089] The porous section 16 ensures formation of relatively uniformly sized bubbles that flow as part of the slurry suspension and collide with the solid particles, producing adhesion between the hydrophobic particles and the air bubbles to achieve separation. The uniformity in the geometry of the porous section 16 ensures that the strong and consistent shear rate in the flowing slurry suspension causes the air flow through the pores of the porous section 16 to break off and form bubbles of substantially uniform size. Generally, the average pore diameter of the pores or perforations in the porous section may range from 1 mm down to 0.2 microns, depending on the grade of material chosen for the application. In some embodiments, the pores or perforations have an average pore diameter of less than 0.1 mm. In other embodiments, the average pore diameter is 10 microns. In another embodiment, the average pore diameter is 2 microns. In a further embodiment, the average pore diameter is 100 microns.

[0090] The feed slurry from the slurry inlet 3 and air via the gas inlet 5 into the hollow tubes 10 leave together through the exit ends 14 into the conduit 2 for discharge from the discharge outlet 7 as a bubbly flow. As best shown in FIG. 4, this bubbly flow enters the chamber 33 of the separating device 30 at an upper end 35 and above a plurality of inclined channels 37, preferably formed by a set of inclined surfaces or ideally by an array of parallel inclined plates. The bubbly flow separates into gas/bubble and slurry components and the rising gas bubbles with attached low density hydrophobic particles rise upwardly on either side of the feed apparatus 1 until they flow into an outlet 40 for recovery. The denser matter and particles descend through the inclined channels towards a discharge outlet (not shown) for removing the denser matter from the chamber 33.

[0091] The separating device 30 thus operates in substantially the same manner as described in the above cited international patent application numbers where the separating device 30 is in the form of a reflux classifier or an inverted reflux classifier. However, it will be appreciated that the feed apparatus 1 may be used with other types of separating devices using froth flotation.

[0092] The feed apparatus 1 thus provides an alternative configuration to the feed box described in International Patent Application Number PCT/AU2011/000682. Hence, the feed apparatus 1 also has the primary advantage of producing a precise laminar flow field in each channel of the hollow tubes 10. This laminar flow field has a high sheer rate in the range 10 s.sup.1 to 1000 s.sup.1. This high sheer rate is achieved by laminar flow created by the array of hollow tubes 10, which enables a high flow rate of bubbly flow to be achieved at the outlet 7 from the feed apparatus 1. It is appreciated that in practical operations, the feed slurry flow may range from transitional to turbulent, as required.

[0093] The feed apparatus 1 also provides the benefits of: [0094] providing an increased surface area for the gas to enter the tubes 10 via the porous sections 16this, in effect, maximises the surface area of the permeable interface at the porous sections 16 between the air phase and the flowing slurry suspension over a given vertical height (for the vertically arranged hollow tubes 10), as well as presenting this permeable interface to the flowing suspension with a uniform geometry; [0095] providing a confined area for the gas bubbles and slurry to interact, improving the probability of the gas and low density particles attaching; [0096] allowing for scalability (either up or down) in the total surface area through the addition of more tubes 10 or the subtraction of existing tubes 10; [0097] creating a single gas inlet point or multiple gas inlet points with a controlled volume and pressure of gas to all hollow tubes 10; [0098] providing a high shear and a precise laminar flow field being applied to the gas and slurry, resulting in a high flow rate of the bubbly flow into the separating device; and [0099] ensuring that the slurry has a laminar flow before the gas is added to the slurry suspension.

[0100] The conduit 2, comprising a plurality of hollow tubes, also has improved scalability through the inverted arrangement of air being supplied on the outside of the feed apparatus 1 through gas inlet 5. Hence, a single feed apparatus 1 is only required in the separating device 30 to accommodate higher flow rates, and the number of hollow tubes 10 can be readily scaled with the cross-sectional area of the separating device 30 without a loss in performance. In some embodiments, there may be reason to include more than one feed apparatus 1. For instance, in other types of separating devices using froth flotation.

[0101] While the embodiment has been described as having hollow tubes 10 of circular cross-section, it will be appreciated that in other embodiments, the tubes may have a rectangular, square, oval or any other polygonal cross-section. Also, the hollow tubes 10 may each have one or more portions that have a greater or lesser cross-sectional area than other portions, rather than being uniform in cross-sectional areas as shown in the illustrated embodiments. For example, a hollow tube 10 may have an enlarged open end (i.e. the open end has a larger cross-sectional area than the rest of the hollow tube). Alternatively, the hollow tube may have a contracted open end (i.e. the open end has a smaller cross-sectional area than the rest of the hollow tube). A change in the exit diameter (i.e. the open end) in the feed apparatus 1 can alter the hydrodynamics underpinning the kinetic rate of flotation within the separating apparatus by improving the local combining of the gas into the feed slurry under a variation in the rate of shear. Similarly, a change in the entrance diameter in the feed apparatus 1 may also improve the local combining of the gas with the feed slurry for the same reason.

[0102] Similarly, the conduit in the form of downcomer 2 has a circular cross-section, but in other embodiments, the conduit may have a rectangular, square, oval or any other polygonal cross-section. FIG. 5 illustrates the top views of different embodiments employing combinations of hollow tubes 10 and conduits 2. In FIG. 5(i), the conduit 2 and hollow tubes 10 both have circular cross-sections. In FIG. 5(ii), the conduit 50 has a rectangular or square cross-section while the hollow tubes 10 are arranged substantially perpendicular to the longitudinal axis of the conduit. In most cases, the hollow tubes 10 will lie generally in the horizontal direction relative to the vertical orientation of the conduit 50. In FIG. 5(iii), there is a plurality of conduits 50 with substantially perpendicular hollow tubes 10 arranged into a conduit housing or array 55. The rectangular cross-section of the conduit 50, array 55, in combination with parallel channels above and/or below the hollow tubes 10 (as described in more detail below in relation to FIGS. 7 to 10) has the advantages of providing a well-defined flow field within the channels, and reducing the risk for particle blockages by providing a second dimension, perpendicular to the direction of flow, for particle movement. Hence, the reduced risk for blockage within a channel provides additional oversized-particle blockage protection, permitting larger sized particles to be processed, and increasing the effective maximum particle diameter by up to a factor of 2 compared to the maximum particle size permitted in hollow tubes 10. However, it will be appreciated that in other embodiments, the conduit 50 and array 55 can be provided without parallel channels. Also, the conduit 2, 50 and array 55 may also have one or more portions that vary in cross-sectional area, as discussed in relation to the hollow tubes 10 above.

[0103] In some embodiments, the porous section 16 may comprise a perforated section of the hollow tube 10, a porous surface, an open section covered by a porous material or a membrane.

[0104] In some embodiments, the porous section 16 may comprise internally located conduits, tubes or pipes 60, as best shown in FIG. 6, to form an annulus 63 (with a corresponding annular cross-section) or other similar geometries. Generally, the internal conduits 60 are co-axial to the hollow tubes 10 but may simply lie parallel to the longitudinal axis 65 of the hollow tube 10. FIG. 6 shows end views of combinations of hollow tubes 10 with internal conduits 60. FIG. 6(i) illustrates a porous hollow tube 10 and a porous internal tube 60a; FIG. 6(ii) illustrates a porous hollow tube 10 and non-porous internal tube 60b; and FIG. 6 (iii) illustrates a non-porous hollow tube 10 and porous internal tube 60c. In each illustrated configuration, the annulus 63 that is formed permits the gas and feed slurry to combine and flow through the hollow tube 10. The benefits of the annulus 63 include providing a second dimension perpendicular to the direction of flow and a further factor of 2 in particle size, therefore reducing the likelihood of particle blockages. The annulus 63 provides a significant increased shear rate by changing the hydraulic diameter at the cost of a small loss of flow area. For example, a 10% loss in flow area through the porous section 16 will provide a factor of 2 increase in shear rate. In addition, in other embodiments, the inner tube 60 may comprise a perforated section of the inner tube, a porous surface, an open section covered by a porous material or a membrane.

[0105] Referring to FIGS. 7 and 8, a further embodiment of the invention is shown. In this embodiment, the conduit in the form of a downcomer 70 comprises an upper section 72, a gas delivery section 75 and a lower section 77 that is longer than the upper section 72. Each section has flanges 78 for mounting to each other and a feed slurry inlet assembly (not shown). A first array 80 of generally parallel channels 82 defined by parallel plates 85 is located in the upper section 72 above the gas delivery section 75. A second array 88 of generally parallel channels 82 defined by parallel plates 85 is located in the lower section below the gas delivery section 75.

[0106] The gas delivery section 75 comprises a plurality of hollow tubes in the form of tubular spargers 90 arranged substantially perpendicular to a longitudinal axis 92 of the downcomer 70. Preferably, there is one sparger 90 for every one or two parallel channels 82. A plurality of gas inlets 95 are arranged to deliver a gas in the form of air along an air chamber 96 into one end 97 of the spargers 90. The air flows out the other end 98 into another air chamber 96 and exits via gas outlets 99. The air may be fed to the spargers 90 via a common manifold (not shown) connected to either ends 97, 98 of the spargers.

[0107] In the operation of this embodiment, the feed slurry enters through the upper section 72 of the downcomer 70 to flow downwardly through the channels 82, as indicated by arrows 100, and around the spargers 90. Air is delivered to the spargers 90 by the gas inlets 95 and air chamber 96. As the air travels along the length of the spargers 90, a portion of the air discharges through the sidewalls of the spargers to form air bubbles that flow with the downward flow of feed slurry and commence adhesion to the hydrophobic low density particles in the suspension. The substantially perpendicular arrangement of the spargers 90 means that the feed slurry is able to flow over the outer surfaces of the spargers (instead of through the hollow tubes 10 as in the previous embodiments) at high shear rates to achieve effective bubble-particle collisions. Generally, there is a high shear zone and shear gradients around the sparger radius.

[0108] Referring to FIGS. 9 and 10, a further embodiment of the invention is illustrated. In this embodiment, the conduit 105 is substantially the same as the conduit 70 of FIGS. 7 and 8. However, the gas delivery section 75 comprises tubular spargers 90 arranged in multiple rows 110 that are vertically aligned. In some embodiments, the spargers 90 may be arranged in stacks.

[0109] It is contemplated that the use of parallel channels 82 provides better scale up options over the use of hollow tubes 10 in the previous embodiments and may lower the pressure drop and/or energy requirements for the apparatus. A further advantage of using parallel channels 82 is that they provide a well-defined flow field within the channels and reduce the risk for particle blockage within the channel by providing a second dimension, perpendicular to the direction of flow, for particle movement. This provides additional oversized-particle blockage protection, permitting larger sized particles to be processed, and increasing the effective maximum particle diameter by up to a factor of 2 compared to the maximum particle size permitted in hollow tubes 10.

[0110] In some embodiments, the parallel plates 85 do not extend along the full length of the lower section 77. However, it is preferred that the parallel plates 85 extend along the full length of the lower section 77 to improve bubble-particle collisions.

[0111] In some embodiments, the downcomers 70, 105 may be sheathed in a circular tube. While the embodiments shown in FIGS. 7 to 10 have downcomers 70, 105 with square cross sections (i.e. the downcomers are symmetrical), it will be appreciated that the downcomers 70, 105 in other embodiments may have rectangular, circular, oval, hexagonal or any other polygonal cross-section.

[0112] The embodiment of FIGS. 7 to 10 has the same technical advantages of the embodiment of FIGS. 1 to 4, as discussed above. Moreover, the connectivity between all the elements of the slurry suspension flow can be maintained by subdividing the air flow through the hollow tubes and associated porous sections (as exemplified by FIGS. 1 to 4), or the connectivity between all the elements of our air/gas flow can be maintained by subdividing the slurry suspension flow through the hollow tubes and associate porous sections (as exemplified by FIGS. 7 to 10). In addition, a large permeable surface area between the gas and slurry phases is achieved with porous sections 16 in a manner that achieves geometrical uniformity. The geometrical length scale is best measured via the so-called hydraulic diameter defined as 4 flow area of the suspension in total divided by the wetted perimeter, the wetted perimeter being the perimeter of the porous surface/section 16. This hydraulic diameter and suspension flow velocity then governs the shear rate. Thus, in effect, the subdivision of either the air/gas flow or the slurry suspension flow results in creating a larger interface area between the gas and liquid phases, through which the gas phase enters the liquid phase for the purpose of forming bubbles at the interface (the porous section 16), via shear from the flowing feed slurry suspension. The substantially uniform bubble size of the relatively fine air bubbles is effective in recovering hydrophobic (low density) particles of a relatively fine size by flotation. Also, the uniform geometry of the porous section assists in producing a distinct shear rate to promote bubble-particle collisions and attachment.

[0113] In other embodiments, the discharge outlet 7 of the feed apparatus 1 need not extend into the upper end 35 of the chamber 33 but may instead be located at the top of the chamber 33 or extend further towards or at a mid-point or middle portion of the chamber 33. Ideally, the discharge outlet 7 is located above the plurality of the inclined channels 37. Hence, there could be a configuration where the discharge outlet 7 is located toward or at a lower end of the chamber 33. In addition, the plurality of inclined channels 37 may be located anywhere in the chamber 33, where desired, including the upper end 35, the middle portion or lower end of the chamber 33.

[0114] In some embodiments, the hollow tubes 10 may be inclined, if desired, within the conduit 2 instead of being arranged to extend vertically. In addition, the hollow tubes 10 may simply extend axially within the conduit substantially parallel to the conduit walls (and hence the feed apparatus 1 may have an inclined conduit 2 with inclined hollow tubes 10).

[0115] In other embodiments, the hollow tubes 10 extend further along the length of the conduit 2 past the middle portion 6 and into the lower portion 8 to discharge the feed slurry and gas from their respective exit ends 14 closer to the conduit outlet 7. In another embodiment, the exit end 14 of each hollow tube 10 is adjacent to the conduit outlet 7.

[0116] In some embodiments, the shape of the conduit 2 may vary as desired. Hence, the upper portion 4 and the section 31 of the lower portion 8 need not be frusto-conical in shape.

[0117] It is also contemplated that the feed apparatus 1 is particularly suitable for high volumetric feed rates and low solids concentrations or low feed grades, and may be used with wash water being added to the bubbly flow in the chamber 33 of the separating device 30 from above. In this regard, it should be noted that the separating device 30 illustrated in FIG. 4 does not use wash water.

[0118] The objective of this embodiment is to recover all of the hydrophobic particles and, in this case, some entrained hydrophilic particles in the final product can be anticipated. In this arrangement it is not essential for foam to form. There are benefits in not having to maintain or control foam because foams can be highly variable in their stability.

[0119] It is further noted that the vast majority of the volumetric flow would normally tend to discharge out the bottom of the vessel. Hence the system would operate effectively under dilute conditions, and hence there would be good distribution of this flow down all of the inclined channels. Higher system concentrations could still be used.

[0120] It is further noted that the device would operate effectively at feed and gas rates higher than used in a conventional froth flotation device and would operate with higher wash water rates. These higher rates are made possible by the powerful effect of the inclined channels in the lower part of the system. These channels provide for an increase in the effective vessel area allowing gas bubbles that might otherwise be entrained downwards to the underflow to rise upwards towards the overflow.

[0121] It will further be appreciated that any of the features in the preferred embodiments of the invention can be combined together and are not necessarily applied in isolation from each other. For example, the feature of inclined hollow tubes 10 and the feature of a rectangular upper portion may be combined into the same feed apparatus 1. Similar combinations of two or more features from the above described embodiments of the invention can be readily made by one skilled in the art.

[0122] By providing the feed apparatus with hollow tubes each having a porous section, a useful alternative configuration for feeding the slurry into a separating device is provided that has the same benefits of high shear and a precise laminar flow field being applied, resulting in a high flow rate of the bubbly flow into the separating device. Consequently, the feed slurry is delivered quickly and efficiently, and is conditioned (due to being combined with the gas generated bubbles) for separation of the low density particles. Furthermore, the porous section maximises the surface area of the permeable interface between the air phase and the flowing slurry suspension, increasing the amount of substantially uniform bubble generation. The porous section also ensures that the permeable interface has a uniform geometry. In all these respects, the invention represents a practical and commercially significant improvement over the prior art.

[0123] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.