WO1997000728A1

WO1997000728A1 - Centrifugal separator having fluid injection openings in the peripheral wall

Info

Publication number: WO1997000728A1
Application number: PCT/CA1996/000426
Authority: WO
Inventors: Benjamin Knelson
Original assignee: Benjamin Knelson
Priority date: 1995-06-23
Filing date: 1996-06-24
Publication date: 1997-01-09
Also published as: AU6120096A; CA2195762A1

Abstract

In a centrifuge bowl (10) of the type including a plurality of axially spaced recesses (15) and a surrounding jacket (21) which communicates fluidizing water through holes (30) in the peripheral wall of the bowl communicating with the recesses. Each recess (15) defines a band at the peripheral wall through which the holes pass. The wall (11) of the bowl and the surrounding wall (20) of the jacket (21) are both conical. The number of holes (30) is selected in the bands so that those initial bands at the base of the bowl where the feed occurs have the minimum number of holes, the maximum number of holes are provided at the bands immediately above the initial bands and the number of holes gradually decreases from the maximum to the uppermost band even though the diameter of the bands is also increasing.

Description

CENTRIFUGAL SEPARATOR HAVING FLUID INJECTION OPENINGS IN THE PERIPHERAL WALL

This invention relates to a centrifugal concentrator of the type comprising a bowl having a generally conical concentrator wall extending from a base at one end and diverging outwardly to a mouth at the opposed end with a plurality of axially spaced recesses arranged around the wall for receiving concentrated material therein. Outside the conical wall is provided an outer housing defining a chamber containing fluidizing water which is injected through injection openings in the conical wall of the bowl into the recesses for fluidizing the material therein.

One example of a centrifugal concentrator of this type is shown in United States patent 4,608,040 of the present inventor. A more recent design of the same concentrator principal is shown in United States patent 4,776,833 of the present inventor. The more recent patent shows improvements in relation to the structure and arrangement of the recess itself.

It is important for the operation of the concentrator of this type that the heavier material within the recesses be maintained fluidized to effect the proper transfer between the lighter materials to be discharged from the open mouth and the heavier materials to be collected within the recesses. For this reason, the arrangement of the recesses and the fluid therein is important to maintain the required fluidization of the materials in the recess. The only prior patent which has been found to disclose information relating to the number of injection holes in the recesses is prior patent 4,608,040 of the present inventor which discloses in column 8 lines 44 through 68 that the number of holes (assuming the holes are all the same size) must increase from the lowermost recess which is the smallest diameter to the uppermost recess which is of largest diameter so that there are more holes per unit area in the uppermost recess than there are holes per unit area in the lowermost recess.

In the above examples of the concentrator of the present inventor, the concentrate is collected in the recesses and discharged therefrom when the processing is temporarily halted thus forming a batch processing situation. However the present invention also relates to a continuous concentrator of the type shown in United States patent 5,338,284 of the present inventor.

It is one object of the present invention therefore to provide an improved concentrator of the above type in which the fluidization of the material within the recesses is enhanced.

According to the present invention there is provided an apparatus for separating intermixed materials of different specific gravity comprising: a centrifuge bowl having a base end and a peripheral wall surrounding an axis passing through the base end and generally upstanding from the base end to an open mouth, means mounting the bowl for rotation about the axis; feed means for feeding the materials into the bowl so that during rotation of the bowl the materials flow over the peripheral wall for discharge from the open mouth; first guide means for collecting the discharged materials; a plurality of axially spaced, inwardly projecting rings carried on the peripheral wall and extending therefrom generally towards the axis and defining therebetween a plurality of axially spaced, annular recesses over which the materials pass so that heavier material collects in the recesses between the inwardly projecting rings and lighter material passes thereover to the mouth for discharge therefrom; the annular recesses including a primary recess and a secondary recess arranged closer to the mouth than said primary recess so that said feed materials pass firstly over the primary recess and later over the secondary recess, the peripheral wall being shaped such that said primary recess has a diameter less than that of said secondary recess; fluidizing means for fluidizing said heavier material in said primary and secondary recesses comprising a plurality of injection openings through the peripheral wall at said at least one primary recess and said at least one secondary recess and fluid injection means outside the peripheral wall for injecting fluid through the injection openings, each said injection opening defining an opening area at the peripheral wall; and second guide means for collecting the heavier materials from said annular recesses; each of said annular recesses defining a substantially cylindrical band of the peripheral wall through which the injection openings pass with each opening defining an area at the band; the sum of the opening areas of the openings per unit area of said at primary recess being greater than the sum of the opening areas of the openings per unit area of said secondary recess.

On embodiment of the invention is herein described by reference to the accompanying drawings, in which:

Figure 1 is a vertical cross-sectional view through a centrifugal concentrator to show the type of device to which the present invention relates, the drawings being taken from Figure 1 of patent 4,608,040 mentioned above.

Figures 2 to 5 show schematically hole patterns related to tables 1 and 3 hereinafter, according to the present invention.

The concentrator shown in Figure 1 is of the type shown and described in more detail in the above patents of the present inventor and particularly United States patent 4,608,040. The present description will therefore only concentrate upon those areas of the concentrator which are important to the present invention and the above patents are incorporated herein by reference for any further details not described herein. The concentrator therefore comprises an inner bowl or rotor 10 having a peripheral wall 11 which is fustro-conical in shape extending from a base 12 to an open mouth 13. Upon the inner surface of the wall 11 is provided a plurality of ribs 14 defining therebetween recesses 15. As the wall 1 1 is conical, each recess is of an increased diameter relative to the next previous recess from a lowest one of the recesses indicated at 15A to an uppermost or largest one of the recesses indicated at 15B. Each recess has a flat band of generally cylindrical shape at a base of the recess as indicated at 16. In the band is a plurality of openings 30 passing through the wall. Outside the peripheral wall of the bowl is provided a peripheral wall 20 of a housing generally indicated at 21. The housing 21 includes a base 22 through which water is injected from a shaft 23 so as to provide pressurized fluid between the outer surface of the bowl 10 and the inner surface of the housing 21. This pressurized water is injected through the openings in the recesses 15. Both the peripheral wall 1 1 of the bowl and the surrounding wall 20 of the housing 21 are conical so as to increase gradually in diameter from the base end to the open mouth end. The wall 11 is connected to the wall 20 by a flange arrangement. A first guide 40 is arranged to collect wate materials discharging from the open mouth 13. A second guide 50 is arranged to collect materials collecting in the recesses. The bowl is mounted in bearings 60 for rotation about an axis 61 and is driven by a drive assembly 62.

The openings in the bands 16 are arranged in two rows and are shown only schematically in Figure 1 as the specific arrangement of these openings is more fully shown in Figures 2 to 5.

The openings 30 are those arranged in the two rows at each band 16 with the rows being spaced axially and the holes in the rows being offset angularly so that the holes in the upper row lie intermediate the holes in the Iower row. In these figures the holes which are crosshatched are 1/16 inch in diameter and the holes which are unmarked are 3/32 inch in diameter. The pattern of holes as shown is selected in order to maintain the predetermined pattern and to use holes of the above sizes but in an arrangement which does not have these limitations on the selection of holes pattern and hole sizes the holes may be of all the same size in each band.

In two examples the number of holes in each band is arranged in the following tables. In the table the bands are numbered consecutively from the lowermost band indicated at #1 to the uppermost band (#10 in Table 1 and #14 in Table 2) at the base of the bowl. In one of the examples there are 10 such bands, in the second example there are 14 such bands with the difference being dependent upon the diameter of the bowl at its widest. In the first example, the diameter of the uppermost band is 30 inches. In the second example the diameter of the uppermost band is 48 inches. Table 1 and Table 2 include a first column which indicates the total hole area that is the sum of the areas of the holes in that ring. A second column indicates the total hole area per unit area of the ring.

It will be noted that band #1 of the base has a total hole area which is less than the hole area in band #3 which is third from the bottom of the bowl. More particularly the total hole area gradually decreases from a maximum at band #8 which is third, fourth or fifth from the bottom to the uppermost band #10 or #14 even though the diameter of the bands is gradually increasing. Thus the total hole area per unit area follows the same pattern in that the total hole area per unit area of band #1 is less than the maximum at band #4 (Table 1 ) or at band #5 (Table 2) and then the total hole area per unit area decreases gradually from the maximum to the uppermost band. -o-

This is totally contrary to previous procedures in machines of this type and is totally contrary to previous analysis of the matter. Simplistically, one would believe that the number of holes per unit area would be constant so that (if the holes are all of the same size) the number of holes in each band would increase as the diameter of the band increases.

The above previous patent 4,608,040 states that the number of holes should be yet further increased as the diameter increases to accommodate the increase of G-forces which occur in the materials within the recess as the band of the diameter increases. Thus in the prior patent, the total hole area per unit area increases as the diameter increases.

To the contrary, in the present arrangement the total hole area in the bands decreases from the maximum as the diameter increases so that the total hole area per unit area yet further decreases as the diameter increases.

It will be noted that the lowermost two bands have a total hole area which is significantly reduced relative to the total hole area at the maximum holes in the band which is fourth or fifth from bottom. This reduction in the total hole area in the two initial bands is provided in view of the increased amount of water which is carried in the slurry from the feed at the base of the bowl into the two initial bands.

Tables 1 and 2 hereinafter show the parameters of two examples of bowl according to the present invention.

Table 3 provides a calculation of the factors as set out hereinafter in relation to the example of the bowl shown in Table 1. Table 4 provides a calculation of the same factors in relation to the example of the bowl from Table 2.

The column identified at "voiume" refers to the total amount of concentrate that the ring or band identified will hold. The "G-force" for that band is calculated at the outside wall diameter.

The "fluidization water flow" is calculated by taking the fluidization hole size and the water pressure, calculating a flow through each hole and then multiplying it by the number of holes of that size in the ring. The water pressure is estimated at each band based upon the G-force, thus as the band diameter increases, so does the water pressure.

The column indicated at "fluid ratio" is the concentrate volume divided by the water flow.

The column indicated at "G-force/fluidization" is the G-force divided by the fluid ratio.

The objective of the present invention is to establish for the rings 3 through 10 a G-force/fluidization ratio which is substantially constant. It is believed that this will provide a constant through the bands for the fluidization water requirement. The first and second bands are located at the bottom directly in the impact area where the feed material intercepts the concentrating wall. This area has a great deal of turbulence and since the feed material is in slurry form (containing water), the band is prevented from packing and allowing concentration to take place, thus less fluidization water is required. The amount of fluidization water in ring 1 is therefore reduced by 50% and in ring 2 by 30%.

The example shown utilize holes or openings which are of the two selected diameters. However it will be appreciated that it is not necessary to form all of the holes with the same diameters of hole since the diameter can be modified particularly wherein an increased total hole area is required. The more proper technique set forth above for determining the requirement for holes is therefore to calculate the total hole area in a band. Thus for example the band with the maximum number of holes could have a reduced number of holes of larger diameter so that the total hole area in the band or the total hole area per unit area in the band is increased. Thus it will be noted that the total hole area in the band which is ar the maximum is significantly greater than the total hole area in the top band and the total hole area per unit area of the same band is even larger than the total hole area per unit area of the top band.

The reason for calculating the number of holes as set forth in Tables above is that is has been determined that the increasing pressure in the water as it moves along the conical surrounding wall 20 from the Iower end thereof to the upper end thereof overcomes the increasing G-forces in the material within the recess so that the amount of fluidizing water which actually passes through the openings is significantly larger at the upper bands thus reducing the requirement for the number of holes in those bands.

In the example shown in Table 4, the G-force/fluidization ratio has a larger spread between the rings than in the first example. However this is within acceptable tolerances. The use of holes of 1/16 inch is not preferred due to the possibility of blockage but it would be preferred to redesign the hole pattern to utilize holes of constant diameter.

Claims

CLAIMS:

1. An apparatus for separating intermixed materials of different specific gravity comprising: a centrifuge bowl having a base end and a peripheral wall surrounding an axis passing through the base end and generally upstanding from the base end to an open mouth, means mounting the bowl for rotation about the axis; feed means for feeding the materials into the bowl so that during rotation of the bowl the materials flow over the peripheral wall for discharge from the open mouth; first guide means for collecting the discharged materials; a plurality of axially spaced, inwardly projecting rings carried on the peripheral wall and extending therefrom generally towards the axis and defining therebetween a plurality of axially spaced, annular recesses over which the materials pass so that heavier material collects in the recesses between the inwardly projecting rings and lighter material passes thereover to the mouth for discharge therefrom; the annular recesses including at least one primary recess and at least one secondary recess arranged closer to the mouth than said at least one primary recess so that said feed materials pass firstly over said at least one primary recess and later over said at least one secondary recess, the peripheral wall being shaped such that said at least one primary recess has a diameter less than that of said at least one secondary recess; fluidizing means for fluidizing said heavier material in said at least one primary and said at least one secondary recesses comprising a plurality of injection openings through the peripheral wall at said at least one primary recess and said at least one secondary recess and fluid injection means outside the peripheral wall for injecting fluid through the injection openings, each said injection opening defining an opening area at the peripheral wall; and second guide means for collecting the heavier materials from said annular recesses; each of said annular recesses defining a substantially cylindrical band of the peripheral wall through which the injection openings pass with each opening defining an area at the band; the sum of the opening areas of the openings per unit area of said at least one primary recess being greater than the sum of the opening areas of the openings per unit area of said at least one secondary recess.

2. The apparatus according to Claim 1 wherein the sum of the opening areas of the openings of said at least one primary recess is greater than the sum of the opening areas of the openings of said at least one secondary recess.

3. The apparatus according to Claim 1 wherein the fluid injection means includes an outer housing having a wall surrounding the peripheral wall and defining therebetween an annular channel, the wall of the outer housing increasing in diameter from said at least one primary recess to said at least one secondary recess^.

4. The apparatus according to Claim 1 wherein the sum of the opening areas in a recess is arranged relative to the diameter of that recess such that the G-force/fluidization ratio as defined herein is substantially equal for each of a plurality of the recesses.

5. An apparatus for separating intermixed materials of different specific gravity comprising: a centrifuge bowl having a base end and a peripheral wall surrounding an axis passing through the base end and generally upstanding from the base end to an open mouth, means mounting the bowl for rotation about the axis; feed means for feeding the materials into the bowl so that during rotation of the bowl the materials flow over the peripheral wall for discharge from the open mouth; first guide means for collecting the discharged materials; a plurality of axially spaced, inwardly projecting rings carried on the peripheral wall and extending therefrom generally towards the axis and defining therebetween a plurality of axially spaced, annular recesses over which the materials pass so that heavier material collects in the recesses between the inwardly projecting rings and lighter material passes thereover to the mouth for discharge therefrom; the annular recesses including a primary recess and a secondary recess arranged closer to the mouth than said primary recess so that said feed materials pass firstly over said primary recess and later over said secondary recess, the peripheral wall being shaped such that said primary recess has a diameter less than that of said secondary recess and a series of recesses from said primary recess to said secondary recess in which the diameter of each recess increases from each recess to the next recess; fluidizing means for fluidizing said heavier material in said recesses comprising a plurality of injection openings through the peripheral wall at said recesses and fluid injection means outside the peripheral wall for injecting fluid through the injection openings, each said injection opening defining an opening area at the peripheral wall; and second guide means for collecting the heavier materials from said annular recesses; each of said annular recesses defining a substantially cylindrical band of the peripheral wall through which the injection openings pass with each opening defining an area at the band; the sum of the opening areas of the openings per unit area of said primary recess being greater than the sum of the opening areas of the openings per unit area of said secondary recess and the sum of the opening areas of the openings per unit area decreasing from each recess to the next recess.

6. The apparatus according to Claim 5 wherein the sum of the opening areas of the openings of said primary recess is greater than the sum of the opening areas of the openings of said secondary recess.

7. The apparatus according to Claim 5 wherein the fluid injection means includes an outer housing having a wall surrounding the peripheral wall and defining therebetween an annular channel, the wall of the outer housing increasing in diameter from said primary recess to said secondary recess^.

8. The apparatus according to Claim 5 wherein the sum of the opening areas in a recess is arranged relative to the diameter of that recess such that the G-force/fluidization ratio as defined herein is substantially equal for each of a plurality of the recesses.

9. An apparatus for separating intermixed materials of different specific gravity comprising: a centrifuge bowl having a base end and a peripheral wall surrounding an axis passing through the base end and generally upstanding from the base end to an open mouth, means mounting the bowl for rotation about the axis; feed means for feeding the materials into the bowl so that during rotation of the bowl the materials flow over the peripheral wall for discharge from the open mouth; first guide means for collecting the discharged materials; a plurality of axially spaced, inwardly projecting rings carried on the peripheral wall and extending therefrom generally towards the axis and defining therebetween a plurality of axially spaced, annular recesses over which the materials pass so that heavier material collects in the recesses between the inwardly projecting rings and lighter material passes thereover to the mouth for discharge therefrom; the annular recesses including at least one initial recess, at least one primary recess and at least one secondary recess, said at least one initial recess being arranged closer to the base than said at least one primary recess and said at least one secondary recess being arranged closer to the mouth than the primary recess so that said feed materials pass firstly over said at least one initial recess and subsequently over said at least one primary recess and said at least one secondary recess, the peripheral wall being shaped such that said at least one intiial recess has a diameter lee than that of said at least one primary recess which has a diameter less than that of said at least one secondary recess; fluidizing means for fluidizing said heavier material in said recesses comprising a plurality of injection openings through the peripheral wall at said recesses and fluid injection means outside the peripheral wall for injecting fluid through the injection openings, each said injection opening defining an opening area at the peripheral wall; and second guide means for collecting the heavier materials from said annular recesses; each of said annular recesses defining a substantially cylindrical band of the peripheral wall through which the injection openings pass with each opening defining an area at the band; the sum of the opening areas of the openings per unit area of said at least one primary recess being greater than the sum of the opening areas of the openings per unit area of said at least one secondary recess and being greater than the sum of the opening areas of the openings per unit area of said at least one initial recess.

10. The apparatus according to Claim 9 wherein the sum of the opening areas of the openings of said at least one primary recess is greater than the sum of the opening areas of the openings of said at least one secondary recess and is greater than the sum of the opening areas of the openings of said at least one initial recess.

11. The apparatus according to Claim 9 wherein the fluid injection means includes an outer housing having a wall surrounding the peripheral wall and defining therebetween an annular channel, the wall of the outer housing increasing in diameter from said at least one primary recess to said at least one secondary recess^

12. The apparatus according to Claim 9 wherein the sum of the opening areas in a recess is arranged relative to the diameter of that recess such that the G-force/fluidization ratio as defined herein is substantially equal for each of a plurality of the recesses.