GB2160445A

GB2160445A - Hydraulic separating method and apparatus

Info

Publication number: GB2160445A
Application number: GB08415902A
Authority: GB
Inventors: Clinton A Hollingsworth
Original assignee: CH Development and Sales Inc
Current assignee: CH Development and Sales Inc
Priority date: 1984-01-27
Filing date: 1984-06-21
Publication date: 1985-12-24
Also published as: CA1215942A; AU567347B2; GB8415895D0; GB2153261B; ZA844362B; GB2153261A; GB2160445B; GB8415902D0; AU2919884A

Abstract

In an apparatus for the separation of solid particles from hydrous slurries having particles of different settling velocities, such as slurries containing minerals including ore solids, coal and sands, the slurry solids are subjected to the jetting action of water discharged through openings in a perforated barrier plate mounted in a tauls to effect separation between particles of greater settling velocity, which progress downwardly through the openings and are discharged in an underflow, and particles of lower velocity that progress upwardly and are discharged in an overflow.

Description

SPECIFICATION Hydraulic Separating Method and Apparatus This invention relates generally to methods and apparatus for separating the solid particles of hydrous slurries or pulps into two or more fractions containing particles of different settling velocities.

The invention is applicable to various slurries, such as those containing minerals like ore solids, coal and sands This application is a continuation-in-part of my copending applications Serial No. 543,975 filed September 22, 1983, Serial No. 368,625 filed April 15, 1982, and Serial No. 338,341 filed January 11, 1982, now abandoned.

Many sizing and classifying methods employ gravity separation of solid particles of a hydrous slurry, the separation being dependent on the differences in the settling rates or settling velocities of the particles in a relatively quiescent body of water. The apparatus may consist of a settling tank having means for introducing the slurry, an upper overflow weir and launder for receiving an overlfow and means for removing an underflow from a lower portion of the tank. In operation, water may be continuously introduced into the lower portion of the tank to provide an upward flow of water such as to create the condition of 'teeter' whereby solids of greater settling velocity progress downwardly to be discharged in the underflow and particles of lesser settling rate progress upwardly to be discharged in the overflow.The different settling velocities of the solid particles of the slurry may be by virtue of particles differing in size, particles of different substances differing in their densities, or both. In some instances (e.g. U.S. Patent Evans et al 2,967,617, January 10, 1961) the tank is provided with a perforated barrier commonly known as a constriction barrier or plate which divides the interior of the tank into a main upper chamber and a lower space below the barrier.

Water introduced into the lower space flows upwardly through the barrier. Particles of greater settling velocities that settle into the region adjacent the upper side of the constriction plate are removed in the underflow, as by means of a siphon.

When such apparatus and methods make use of a teeter zone, maintenance of this zone is relied upon to effect the principal separating action.

Methods and apparatus of the above type are subject to certain disadvantages and limitations.

For example, the separation may not be as sharp as desired, particularly for certain types of slurries Also the apparatus may be excessively elaborate in structural detail and size for the capacity or the sharpness of separation desired. In addition, the sharpness of separation tends to be subject to variations, particularly when a teeter zone is relied upon to effect the primary separation. Such varia fions may occur when there are changes in the solids content of the feed or in the relative amounts of the solids in the feed having different settling velocities.

A further object is to improve upon hydraulic separating methods and apparatus, particularly with respect to providing a desired sharpness of separation.

Another object is to provide a separating method and apparatus which facilitates maintenance of optimum separating conditions and does not depend upon a teeter zone.

In general the present invention makes use of apparatus comprising an upright tank having overflow discharge means at its upper end, and special baffle means located between the upper main separating chamber of the tank and the space in the lower portion of the tank below the baffle means.

Means is provided for introducing a feed slurry into the upper chamber and also means for introducing water into the space below the baffle means. Additional means is provided for withdrawing an underflow fraction containing solid particles of greater settling velocity. The special baffle means has openings that are of a diameter sufficient to pass the heavier underflow particles. The method carried out with such apparatus includes introducing a feed slurry into the chamber above the baffle means to form a body of material therein extending from the overflow to the baffle means.

Water is continuously introduced into the space below the baffle means, whereby it flows upwardly through the openings in the baffle means to merge with the body of material. The body of material in the upper chamber is maintained substantially quiescent. Water introduced below the baffle means flows upwardly through the openings in the baffle and is caused to creat a jetting action which extends upwardly from the openings, and which effects separation between particles of different settling velocities, the action being such that particles of greater settling velocities pass downwardly by gravity through the openings, and particles of lower settling velocities are carried upwardly and eventually are discharged as an overflow from the upper end of the tank. The particles passing downwardly through the openings are collected and discharged as the underflow.

Additional objects and features of the invention will appear from the following description in which the preferred embodiments are set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing Figure 1 is a side elevational view illustrating apparatus in accordance with the present invention.

Figure 2 is a detail in section showing a portion of the barrier means and the openings through the same.

Figure 3 is a detail in section illustrating inclined openings for the baffle means.

Figure 4 is a detail in section of a portion of the baffle means, illustrating inserts for providing the desired openings in the baffle means.

Figure 5 is an enlarged detail in section graphically illustrating the separating action provided by the water flowing upwardly through the openings of the baffle means with jetting action extending above the baffle.

Figure 6 is a detail in side elevation illustrating an installation of the invention together with slurry feed means.

Figure 7 is a side elevational view showing an embodiment having more than one velocity plate.

The apparatus shown in Figure 1 consists of a tank 10 which, in this instance, has a cylindrical section 10a and a lower conical section 10b. At the upper end of the tank there is a saw tooth type of overflow weir 11 which delivers the overflow material into the surrounding launder 12. Mounted within the lower part of the cylindrical section 10a there is a perforated barrier 13, which may be in the form of a plate. Preferably an imperforate cone 14 is positioned upon the barrier 13 and is aligned with the central axis of the tank. The base of this cone is dimensioned whereby a substantial annular portion of the barrier plate extends between the side walls of the tank and the base of the cone. As shown particularly in Figure 2, the barrier plate may be provided with two rows of openings 15.

For example, when the feed material is a natural sand comprising both coarse and fine sand particles, the openings 15 may have a diameter of the order of 34 inch. This is in contrast with standard constriction plate practice, where the openings in a typical constriction plate are of relatively small diameter (e.g. 1/4 inch), for operation with a comparable teed slurry.

As illustrated in Figure 3, the openings 15a in the barrier may be inclined, as indicated at 15a in Figure 3. Such construction serves to aid swirling movement of material above the barrier.

As shown in Figure 4 the barrier plate may be fitted with the removable plastic inserts 19, which provide the openings 15b. Such fittings may be replaceable to adjust the diameter of the openings The feed slurry is fed into section 10a of the tank through conduit 16. Preferably this conduit connects tangentially with the tank as shown in Figure 1. The region of connection is located intermediate the upper end of the tank and the barrier 13.

In operation the particles of higher settling velocities pass downwardly through the openings 15 and are collected in the lower portion of the tank.

A conduit or pipe 17 serves to introduce water into the space below the baffle means, and may connect tangentially through one side wall of the tank below the level of the baffle. It is shown connected to pumping means 17a which serves to deliver water into the space below the baffle means at a substantially constant flow rate. The heavier material, constituting the underflow material, may be removed from the tank through the valve 18.

The method of the present invention, making use of the apparatus described above, is as follows. It is assumed that the slurry consists of a natural sand having solid particles of different sizes and settling velocities. The coarser particles of the sand are silica, and the finer particles are likewise silica, together with some clay or other fine solids. The solids content of the slurry may be of the order of 22%. In a start-up operation slurry is introduced into the tank through pipe 16 and at the same time water is supplied through pipe 17 to the space below the barrier 13. When the tank is completely filled, the sand slurry is continuously supplied through pipe 16 at a substantially constant head, and assuming that this pipe connects tangentially with the tank, the main body of material above the barrier is caused to swirl about the central axis of the tank.Water is continuously supplied through the pipe 17 into the space below the barrier, and at a substantially constant flow rate. This water is caused to flow upwardly through the openings 15 in the barrier, thereby creating a jetting action which extends with diminishing velocity a substanial distance above the barrier. While some swirling of the water below the barrier is not essential, it tends to cause better distribution of flow through the openings.

Figure 5, which is exaggerated as to scale, serves schematically to illustrate the jetting and separating action which takes place. Slurry particles in the vicinity of each opening 15 tend to be drawn into the water jetting upwardly from the opening, as indicated by the arrows in Figure 5, and the larger particles 21, which are presumed to have the greater settling velocities, progress downwardly through the jetting water, through the openings 15, and into the space below the barrier.

The finer particles 22 of the slurry which have the lower settling velocities, are carried upwardly into the main body of material above the barrier, and eventually are discharged in the overflow.

Effective separating action is dependent upon a proper rate of flow of water through the openings 15. if the flow rate is excessive, none of the particles of the slurry may progress downwardly through the openings 15. On the other hand, if the flow is of insufficient velocity, then both coarse and some fine particles may progress downwardly through the openings. When the flow rate of water is properly adjusted, the separating action described above is obtained. Proper flow rates for the feed slurry, the water introduced through pipe 17 and the upward rate of flow through openings 15 will vary for different feed slurries and operating conditions, but can be readily adjusted for optimum operation by a few simple trial tests.With proper adjustment, the rate of flow through each opening 15 is less than the settling velocity of the coarser or heavier particles and greater than the settling velocity of the finer or lighter particles.

A feature of the invention is that it does not depend upon the maintenance of a teeter zone in the upper body of material for effective separating action. However, some preliminary gravity separation may take place in the tank portion 10a as the material progresses downwardly into the active separating regions of the jetting water.

The swirling action of the slurry and water in tank portion 10a promotes effective separation by the jetting action because it causes continuous motion about the axis of the tank in the region above the barrier plate where the jetting action is effective. Such motion aids in carrying particles of the slurry into the active regions of the upwardly jetting water.

Figure 6 schematically illustrates an installation of the apparatus. A feed hopper 26 is shown con nected to the feed pipe 16, through a suitable control valve 27, and the feed slurry is discharged upon the screen 28, which overlies hopper 26. The screen serves to remove oversized material.

Figure 7 illustrates another embodiment of the invention in which two barrier plates of the velocity jet type are employed, in place of the single plate shown in Figure 1. The two plates 29a and 29b, are spaced vertically by an amount sufficient to prevent the upper plate from interfering with jetting action extending upwardly from the lower plate. The cone 14 shown in Figure 1 is omitted in this instance. The holes in the upper plate 29a are preferably somewhat larger in diameter than the holes in plate 29b. By way of example, in effecting separation between coarse and fine particles of sand, the holes in the upper plate may be about 3/ 4 inch in diameter, and the holes in the lower plate about 11/16 inch in diameter. 'Alater is applied at a constant rate through pipe 17 into the space below the lower plate 29b.This water flows upwardly through the holes in the lower plate 29b, and from thence through the holes in the upper plate 29a.

The coarser and heavier material passing through the holes in the lower plate 29b are removed in an underflow through the valve 18. This valve can be operated manually to discharge the underflow material, or it may be automatically controlled.

The arrangement shown in Figure 7 makes possible a sharper separation than the use of a single velocity plate as disclosed in Figure 1. This is because the separating action produced by the water jets operates as two separating stages, thereby reducing the percentage of finds remaining with the coarse material passing through the openings in the lower plate 29b.

Examples of the invention are as follows.

Example I Laboratory tests were made to determine data for the construction and operation of commercial equipment. The laboratory apparatus consisted of a cylindrical vessel made of transparent plastic, forming a chamber having an internal diameter of 3.25 inches and a height of about 24 inches. The top of the vessel formed an overflow weir and a collecting launder. At the lower end of the vessel there was a conical extension. A barrier plate was removably mounted near the lower end of the cylindrical portion of the vessel. The lower end of the conical extension was closed by a valve, which could be opened for the discharge of underflow material. The feed was introduced tangentially into the chamber intermediate the top of the chamber and the barrier plate, and water was introduced into the space below the barrier. The barrier plate was constructed to operate as a velocity plate.It was provided with three openings, each 5/8 inch in diameter, which were not sloped. The underflow draw-off pipe connected with the bottom of the vessel below the plate, and the plate was located 15.5 inches below the top of the vessel. The hole area was about 11.1% of the total exposed barrier plate area. Water was introduced below the barier plate at a pressure of about 3.5 psi. A feed slurry of natual sand was introduced at the rate of about 2.7 gallons per minute. Water was introduced into the bottom of the vessel below the velocity plate at a rate of about 2.7 gallons per minute. The feed slurry contained 18.2% solid particles and was introduced at the rate of about 300 Ibs. per hour. After a period of operation, a screen analysis was made of the solids in the underflow and overflow.It was found that 97.3% of the solids of the underflow were plus 48 mesh )Tyler Standard screen). Only 0.7% of the solid particles of the overflow were plus 28 mesh.

Example 2 The apparatus was generally the same as in Example 1 with modifications as follows. Two velocity plates were used, vertically spaced about four inches apart. The upper plate was located about 15.5 inches from the top of the vessel. The upper plate had three holes, each 11/16 inches in diamater. The lower plate had three holes, each 5/8 inches in diameter.The open hole area of the upper plate was 13.4% of the total plate area, and for the lower plate 11.1%. Water was introduced below the lower plate at a pressure of 2.25 psi and at the rate of 3.1 gallons per minute. The feed slurry contained the same sand as in Example 1 and had solids content of about 33.3%. It was introduced at a rate of about 475 Ibs. per hour.A screen analysis of the solids in the underflow and overflow was as follows.About 97.9% of the solids in the underflow were plus 48 mesh and 0.6% of the solids in the overflow were plus 28%.

Example 3 This Example is with respect to apparatus made substantially as shown in Figure 1, and suitable for commercial operation. The barrier 13 is of the velocity plate type, making use of jetting action through openings in the barrier to effect separation between the coarse and finer particles. The barrier also is provided with an imperforate cone 14. The cylindrical portion 10a of the tank had a weight of about 5.75 feet, and an internal diameter of 4.5 feet. The velocity barrier was located about 4.5 feet from the top of the tank. A typical slurry that may be processed for sizing, is a natural sand having coarse particles the bulk of which are plus 48 mesh, and relatively finer particles Typical operating conditions for effecting separation between the coarse and fine particles of such a feed slurry, are as follows. The slurry is prepared to have an optimum solids content of about 33%, although in practice this may vary during operation. The feed slurry is fed through the pipe 16 under a hydrostatic head of the order of 18 inches. Assuming that the slurry is supplied to the tank through pipe 16 at the rate of 1,500 gallons per minute, water is supplied through pipe 17 into the space below the barrier plate at the rate of about 600 gallons per minute. The barrier plate may have three rows of openings disposed on different diameters, wich each opening 3/4 inches in diameter. The exposed annular area of the barrier, namely that annular portion between the side walls of the tank and the base of the cone 14, may be about 1,230 square inches. The open hole area may be 92.3 inches.

The valve 18 for discharge of the underflow may be manually controlled. Assuming construction and operating conditions as described above, there is affected separation between coarser and finer sand particles, whereby 94% of the coarse particles in the underflow may be plus 48 mesh, and only 0.4% of the solids in the overflow may be plus 28 mesh.

Claims

1. Apparatus for the separation of solid particles in a hydrous slurry, the particles having different settling velocities, comprising a tank having means for discharge of an overflow from an upper region of the tank and a means for discharge of an underflow from a lower region of the tank, baffle means disposed between the upper and lower regions of the tank for separating the same, said baffle means having openings communicating between the regions, means for supplying a hydrous slurry to the upper tank region, and means for introducing a liquid under pressure into the lower tank region below the baffle means to cause a jet-like flow of liquid to be discharged upwardly through the openings of the baffle into the upper region, such jet-like flow being of such velocity that a separation is carried out between the solid particles of the pulp having different settling velocities, with the particles of lower settling velocity being retained in a region above the separating means for discharge from the upper region as an overflow and particles of greater settling rate passing downwardly through the openings for discharge from the lower tank region as an underflow.

2. Apparatus as in Claim 1 in which two vertically spaced baffle means are disposed within the tank between the upper tank region and the lower tank region, each of said baffle means having openings through the same through which liquid is caused to flow, the flow through each of the openings in the lower baffle means and the flow of liquid through the openings in the upper baffle means being in each instance of such velocity that a separation is carried out between solid particles of the slurry having different settling velocities, the separation being carried out in two stages, initially by the action of liquid flowing through the openings of the upper baffle means, and subsequently by the action of liquid flowing through the openings of the lower baffle means.

3. Apparatus as in Claim 2 in which the openings in the upper baffle means are of a diameter greater than the openings in the lower baffle means.

4. A method for the separation of solid particles of a hydrous slurry into fractions containing particles of different settling velocities, the method making use of an upright tank having means for the discharge of an overflow from an upper tank region, means for discharge of an underflow from a lower tank region, and baffle means located between the upper and lower tank regions, the method comprising delivering the slurry into the upper tank region, delivering liquid under pressure into the lower tank region, and causing liquid from the lower region to be discharged upwardly through openings in the baffle means and into the upper tank region, the velocity of flow of liquid through the openings being such that it prevents downward passage of particles of lower settling velocity through the openings, and permits passage of particles of higher settling velocity into the lower tank region and causing the particles of lower settling velocity to be discharged from the upper tank region in an overflow by way of the overflow means,and causing the particles passing through said openings to be discharged from the lower region in an underflow by way of the underflow means.

5. The method of Claim 4 in which the body of material in the upper tank region is caused to swirl about the central axis of the tank to promote movement of particles of the slurry into the active regions of the water flowing through the openings.

6. The method as in Claim 4 making use of apparatus as in Claim 4 having, however, two vertically spaced baffle means, in which method the liquid introduced into the lower tank region is caused to flow upwardly successively through openings in the lower baffle means and then opening through the upper baffle means, the rate of flow through openings of each baffle means being such that particles of the slurry are subjected to two successive separating stages, one being carried out by the action of liquid flowing through the openings in the upper baffle means, and the second being carried out by flow of liquid through the openings in the lower baffle means.

7. The method as in Claim 6 in which the flow velocity of the liquid through the openings of the lower baffle means is greater than the flow velocity of liquid through the openings in the upper baffle means.

8. Separation apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

9. A separation method substantially as hereinbefore described with reference to the accompanying drawings.