US3438501A - Washing arrangement for screen centrifuge - Google Patents

Description

A l 15 1969 H. c. F. OYEN 3,438,501

WASHING ARRANGEMENT FOR SCREEN CENTRIFUGE Original Filed Sept. 29, 1966 Sheet of 4 INVENTOR.

HAAKON C. F- OYEN AGENT.

April 15, 1969 H. c. F. OYEN WASHING ARRANGEMENT FOR SCREEN CENTRIFUGE Original Filed Sept. 29, 1966 Sheet FIG. 2

INVENTOR.

HAAKON C. F. OYEN AGENT.

Sheet 3 of 4 A il 15, 1969 H. c. F. OYEN WASHING ARRANGEMENT FOR" SCREEN CENTRIFUGE Original Filed Sept. 29, 1966 INVENTOR.

April 15, 1969 OYEN 3,438,501

WASHING ARRANGEMENT FOR SCREEN CENTRIFUGE Original Filed Sept. 29, 196$ Sheet 4 0f 4 INVENTOR.

HAAKON C.F. OYEN United States Patent 0 3,438,501 WASHING ARRANGEMENT FOR SCREEN CENTRIFUGE Haakon C. F. Oyen, Stamford, Conn., assignor to Dorr- Oliver Incorporated, Stamford, Conn., a corporation of Delaware Continuation of application Ser. No. 583,051, Sept. 29, 1966. This application Oct. 4, 1967, Ser. No. 675,008

Int. Cl. B01d 33/00 US. Cl. 210-213 9 Claims ABSTRACT OF THE DISCLOSURE A screening centrifuge wherein the wash liquid discharge openings are oriented parallel to the helical vanes of the conveyor. A sloped wedge-shaped section is cut from the interior surface of the conveyor to provide an equi-radius weir for the inside edge of the wash liquid discharge openings.

The present application is a continuation of copending application Ser. No. 583,051 filed Sept. 29, 1966, and now abandoned.

The present invention relates to screening centrifuges of the type having a screen and a conveyor concentric therewith to move solids along the screen. More particularly, the present invention-relates to an improved washing apparatus for use in conjunction with such screening centrifuges.

In such devices the feed material is introduced at one end of the screen. Rapid rotation of the screen creates a centrifugal force which urges the feed material radially outward against the screen, causing a separation of the feed material into fractions. If, for example, a sugar crystal carrying liquor is to be separated, the liquid or mother liquor will pass through the screen while the crystals or solids will be retained on the screen.

The conveyor of the centrifuge has helical vanes and is positioned Within the screen and concentric therewith, with a predetermined clearance therebetween. The helical conveyor is also rotated but at a slightly different speed. In this manner the helical vanes effect an apparent traverse of the screen, from the feed end to the discharge end and thus control the axial movement of the solids along the screen.

After the initial separation of the feed liquor and solids, the solids are moved under the control of the helical conveyor into a series of wash zones. A washing liquid is applied and any remaining mother liquor or impurities are removed.

A problem has arisen in this area because the solids are being continuously moved downward along the screen and thus only a limited amount of time is spent in the washing zones. The effectiveness of this treatment therefore has previously been largely dependent upon the amount of wash liquid applied. Any increase in the amount of wash liquid, however, not only increases the chance that some solids may be redissolved, thereby lowering efiiciency and increasing process costs, but it also increases wash liquid consumption and the load upon wash-liquid recovery equipment.

Another and even more serious problem which has evolved in the application of a wasing liquid is that a significant amount of the washing liquid never comes in contact with the solids to be washed. Prior art devices 3,438,501 Patented Apr. 15, 1969 disclose discharge portals for the washing liquid disposed in a transverse plane relative to the axis of rotation of the screen. The solids retained on the screen, however, tend to congregate along the lower or leading face of the helical vane which is transporting them axially along the screen. Since the helical vanes are at an angle relative to the transverse plane defined by the prior art washing liquid discharge openings, a large percentage of the liquid never came into contact with the solids to be washed. It was only at those points where the transverse plane defined by the washing liquid discharge openings and the helical vanes intersect that the solids in the prior art devices were scrubbed and the washing zones effectively fulfilled their function.

With these prior art problems in mind, applicant broke with convention and positioned the wash discharge openings in a plane parallel to the inclination of the helical vanes. In this manner, applicant theorized he could place the discharge openings adjacent to the leading face of: the helical vane and thus produce the most efiicient washin g with the least expenditure of wash liquid.

When applicant attempted to incorporate this novel structural arrangement in screening centrifuges having conically shaped screens and conveyors, he had to overcome the problem that the wash liquid would seek egress from the discharge opening, or a portion thereof, having the greatest radial distance from the axis of rotation. To prevent the resulting uneven distribution of wash liquid in such conical conveyors, applicant provided for a generally annular reservoir of wash liquid overflowing an equal radius weir or surface into the discharge openings. For example, in one specific conveyor having a conical wall, a circumferentially-extending notch is provided on the internal surface to form a constant radius cylindrical surface in the conical wall along the line of intersection defined by the discharge openings and the internal surface of the helical conveyor. In this manner, the inner end of the wash liquid discharge ports are positioned at a constant radial distance from the axis of rotation even through the outer end of the discharge ports in following the inclination of the helical vanes are at different distances from the axis of rotation.

Applicant has further improved upon the efiicient utilization of the Wash liquid by changing the configuration of the cage which supports the rotating screen. Instead of having an unbroken series of slotted openings to permit free passage of separated liquid, applicant provides a solid imperforated band directly opposite the wash liquid egress. In this manner the wash liquid is momentarily retained on the screen in the zone of the imperferate band to permit a more thorough mixing and contact with the solids passing through the wash zone. The wash liquid is then drained from the scrubbed solids when they are conveyed out of the zone of the imperforate band. Applicant thereby increases efficiency, further lowers wash liquid consumption, and further reduces operating costs.

Accordingly, it is a primary object of the present invention to improve the washing eificiency of screening centrifuges.

It is a further object of the present invention to position the wash liquid discharge ports in a plane parallel to the inclined vanes of the helical conveyors of screening centrifuges.

It is still a further object of the present invention to provide means for maintaining an equal rate of discharge from all the wash liquid ports even though the wash liq- 3 uid ports are not all equally spaced from the axis of rotation.

In conjunction with the foregoing objects, a still further object of the present invention is to provide means on the centrifuge cage which will allow for retention and more thorough use of the wash liquid immediately after it is discharged from the helix.

The subject matter which applicant regards as his invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention, however, as to its organization and method of operation together with further objects and advantages thereof will best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is an elevational cross-section of the screening centrifuge that incorporates the instant invention;

FIGURE 2 is an enlarged elevational cross-section showing in detail the upper portion of FIGURE 1;

FIGURE 3 is an enlarged perspective view partly in section of the helical conveyor screen and cage incorporating the instant invention, parts being removed for clarity of showing;

FIGURE 4 is an elevational cross-sectional view of the helical conveyor and screen incorporating the instant invention;

FIGURE 5 is a vertical perspective view of a helical conveyor incorporating the instant invention with one embodiment of a wash liquid discharge portal; and

FIGURE 6 is an elevational perspective view of a helical conveyor incorporating the instant invention with another embodiment of a wash liquid discharge portal.

Referring now to the drawings wherein like numerals indicate like parts there is shown in FIGURE 1 a screening centrifuge 10 which includes a rotor 12 having an inlet opening 14 for feeding materials to be separated to the rotor as indicated by arrows 16. The feed material passes to an annular conical space 18 in the rotor 12 between a frusto-conical screen 20, which is carried on the interior surface of a rapidly rotating perforated cage or screen support 22, and a concentric rotating conveyor or helix 24 having vanes 25. Rotation of the cage 22 and screen subjects the process material to centrifugal forces, urging the material up against the screen and thereby causing the separation of the various components that make up the process material. The screen retains one of the components, for example, solids, while the other portion of the feed material, for example a liquid, is pushed through the screen by the centrifugal force as indicated by arrows 26. Most of the liquid, or mother liquor separated passes through the screen into an initial receiving chamber 28 where it is discharged through a pipe 30.

Following the separation of the mother liquor, the solids on the screen are moved under the control of the helical conveyor from the first treatment zone defined by the initial receiving chamber 28 sequentially through the next two treatment Zones defined by respective receiving chambers 32 and 34 which surround the rotor 12.

A first wash liquid enters conical space 18 through wash liquid discharge port 36 and intercepts the axial path of the solids to thoroughly scrub them and remove any remaining mother liquor and/or impurities. The resulting first wash solution centrifugally passes through screen 20 where it is collected in receiving chamber 32 and subsequently discharged through conduit 38.

As the solids continue their downward path along the screen, under the control of the helical conveyor, they are intercepted by a second and final Wash, to insure the purity of the final product. Wash liquid for this operation is pumped into the device through conduit 40, recovered in chamber 34 and discharged through conduit 42.

The separated solids are then discharged by the helical conveyor through exits 44 into hopper 46.

A drive head assembly 48 is provided to rotatably support and drive the cage and the helical conveyor of the rotor. Drive head assembly 48 includes a fixed support housing 50 and bearing assemblies 52. An annular outer shaft assembly 54, which drives cage 22, is mounted to rotate Within these bearings. A co-axial inner shaft assembly 56, which drives helical conveyor 24, is mounted by bearing assembly 58 to rotate within outer shaft assembly 54.

The lower ends of shaft assemblies 54 and 56 are driven at relatively differential speeds by a suitable drive arrangement such as transmission 60 powered by pulley 62, driven by a belt or belts 64 which extends from a power source such as a motor (not shown).

As can be seen from an inspection of FIGURE 2, the shaft 56 rotatably supports the helical conveyor 24 by means of a series of keys (not shown), each of which extends radially from shaft 56 and is accepted in a corresponding pocket (not shown) in the conveyor. The top end of the conveyor is formed with an axially directed cup-shaped recess into which a wash liquid distributor 70 is fixedly attached. The wash liquid distributor has a conically shaped bottom portion 72 having a neck 74 and a conically shaped top portion 76 having a neck 78. The top portion 76 and the bottom portion 72 are interconnected by means of .a cylindrically shaped body portion. Thus, when in position, the wash liquid distributor 70 provides a lower or second wash liquid chamber 82 and an upper or first wash liquid chamber 84. Acceleration vanes 86 and 88 are provided in the respective wash chambers.

Wash liquid supply conduit 40 extends through upper chamber 84 and feeds wash liquid into lower chamber 82. Conduit 43 feeds into conduit 90 which is concentric with inflow pipe 40 and feeds into upper chamber 84.

As shown in FIGURE 1 the first wash liquid from upper chamber 84 is fed through channel 92 to discharge ports 36 and the second wash liquid from lower chamber 82 is fed through channel 94 to discharge ports 96. Channel 92 is formed between the inner surface of helix 24 and concentric conical wall 93.

FIGURES 3, 4 and 5 depict the structural interrelationship between the screen 20, the cage 22, the helical con veyor 24 and one embodiment of the wash liquid discharge arrangement. Only the second wash liquid discharge arrangements will be described herein in detail, it being understood that the first wash discharge arrangement may also be constructed in the same manner.

Channels 94 are formed between the inner surface of helix 24 and a concentric wall 101 (FIGURES 1 and 4) disposed within the helix. Radial vanes 98, extend between the inner wall of the helix 24 and concentric wall 101 to form the side walls of channels 94; vanes 98, 100 also serve as strengthening ribs for helix 24.

The wash liquid is fed into channel 94 and exits through outlets 102, 104 provided in vanes 98, 100. These outlets are located at a greater radial distance from the axis of rotation than are discharge ports 96. Wash liquid, therefore, pours out of outlets 102, 104 and begins to fill the area 108 between the inner surface of helix 24 and concentric inner wall 101. The area 108 acts as a reservoir, the wash liquid building up to surface level 110 and then overflowing through discharge ports on slots 96.

Discharge slots 96 are intermittently cut into the helix 24 at a desired level below the leading face of the helical vanes at such an angle that they follow the inclination of helical vanes 25. In order to insure an even distribution of wash liquid along the entire length of each of the slots, a notch 114 is cut into the inner surface of the helix 24 to provide a constant radius weir or surface across which the liquid in reservoir 108 overflows. In this manner each point along the inner end 118 of inclined slot 96 has the same radial distance from the axis of rotation as every other point even though the exit end 120 of the slot follows the contour of the helical vanes 25 and therefore varies in radial distance from the rotational axis. Although as shown in FIGURE 3 point B on slot 96 is below point A on slot 96, and therefore theoretically should have the larger radial distance vis-avis the axis of rotation, point A is recessed into the internal surface of the helix, behind point B, a sufiicient distance such that both points have the same radial distance vis-a-vis the axis of rotation. Triangular notch 114 is so designed that each point, going from A to B along the slope of slot 96, even though above the preceding point, is sufficiently behind it such that the radial distance from the axis of rotation is kept a constant.

To further insure an equal distribution of the wash liquid all along discharge slot 96, a series of distribution ribs 106 are provided. These ribs extend from a point well below liquid level 110 to a point closely adjacent discharge slot 96 and follow the contour of the inner surface of helix 24 and notch 114. A comparison of the distance that each rib 106 travels into notch 114 (see FIGURE 3) gives an indication of how the radial distance of each point along the inner end of slot 96 is kept constant by notch 114.

The arrows in FIGURES 3 and 4 trace the path of the wash liquid from its introduction into channel 94 to its discharge through slots 96.

Applicants wash liquid, because it is fed down channel 94 to a reservoir below the discharge ports 96, builds up to the overflow weir or surface and overflows into the inner end 118 of the discharge slot. Ribs 106, positioned in this area and extending from the bottom of the reservoir up to the overflow surface (see FIGURE 4), channelize the liquid and ensure an even distribution throughout the entire circumferential length of discharge port 96. Therefore due to the interaction of the notch 114, which keeps the inlet end of port 96 at a constant radius and the channelizing ribs just discussed, applicants wash mechanism discharges the wash liquid evenly and equally all along discharge port 96.

In the embodiment depicted in FIGURE 3, discharge slots 96 are positioned immediately adjacent the leading face of the helical vane 25. The wash liquid will centrifugally discharge radially across chamber 18 and contact the solids which collected just below the leading face of vane 25.

Thus, because of the inclination and location of the wash slots, all of the wash liquid comes in contact with the solids. Therefore, the greatest scrubbing effect can be accomplished with the least quantity of wash liquid.

To further increase the efliciency of the washing operation of his device, applicant has included a specially designed cage which allows for a retention of wash liquid immediately after it is discharged from the helix. As can be seen from FIGURES 1 and 3 the cage includes an imperforate band 124 directly opposite the wash liquid discharge slots. The wash liquid, after it is discharged from the helix, has its path of forward progress blocked by solid band 124. In this manner the wash liquid is momentarily retained in the solids being rolled along in front of the vane. During this retention period the wash liquid is thoroughly mixed with the solids and, thus, a more eflicient utilization of the washing liquid results.

FIGURE 6 shows a modified embodiment of the present invention wherein the wash liquid discharge ports on helical conveyor 24 are defined by a plurality of openings 140 arranged in a circumferentially elongated pattern which is oriented parallel to the inclination of the helical vanes 25.

I claim:

1. A screening centrifuge comprising:

(a) a trunco-conically shaped screening means to separate material being treated in said centrifuge into a fraction retained on said screening means and a fraction centrifugally forced therethrough;

(b) a hollow conveyor having at least one helical vane positioned coaxially within said screening means and a conically shaped interior wall;

(c) differential drive means connected to said screening means and said conveyor such that said conveyor can be rotated at a different speed than said screening means to move the retained fraction axially along said screening means; and,

(d) wash means in said conveyor to discharge a wash liquid against the fraction retained on said screening means, said wash means having at least one circumferentially-elongated discharge means oriented in a plane parallel to the inclined helical vane of the conveyor to hydraulically connect the interior and exterior surfaces of said conveyor and a corresponding circumferentially disposed wedge shaped section cut into the conically shaped interior surface of said conveyor in a complementary plane relative to the axis of said conveyor and substantially along the inner edge of said elongated discharge means, said section being positioned relative to the inner edge of said elongated discharge means such that every point along said inner edge is equally spaced from the axis of rotation of said conveyor so as to form an equiradius weir.

2. Apparatus as defined in claim 1, wherein said wash means further comprises a chamber having a reservoir portion extending axially from said elongated discharge means and at least one conduit to supply wash liquid to said reservoir portion, the wash liquid overflowing from said reservoir into the wedge shaped section cut into the interior surface of said conveyor and over the equi-radius weir formed by said Wedge shaped section to discharge from said conveyor through said elongated discharge means.

3. Apparatus as defined in claim 2, wherein said chamber has a plurality of guides spaced along said discharge means and extending axially therefrom, said guides providing a plurality of overflow channels for wash liquid as it enters said discharge means.

4. Apparatus as defined in claim 1, wherein said discharge means comprises an array of spaced apertures.

5. Apparatus as defined in claim 2, wherein said conveyor has a concentric inner wall attached thereto extending axially from a point before to a point beyond said discharge means, said concentric inner wall cooperating with said conveyor to form the reservoir portion of said chamber.

6. Apparatus as defined in claim 5, wherein said at least one conduit comprises a pair of axially extending spaced apart channel members interposed between said concentric inner wall and said conveyor, the wash liquid flowing in the space defined between said channel members, and at least one opening in at least one of said channel members to provide hydraulic communication to said reservoir portion.

7. A conveyor comprising:

(a) a hollow trunco-conically shaped central body member;

(b) at least one inclined helical vane on said central body member;

(c) at least one circumferentially elongated slot oriented in a plane substantially parallel to said inclined vane providing hydraulic communication between the interior and exterior surfaces of said central body member; and,

(d) a corresponding circumferentially elongated wedge cut into the interior surface of said central body member extending substantially in a complementary plane relative to the axis of said central body member and encompassing at least a major portion of said corresponding slot, said slot transversing the surface of said cut substantially along a diagonal from one end thereof to the other end thereof.

8. Apparatus as defined in claim 7, wherein said central body member has a chamber therein having a reservoir portion which communicates at one end thereof with said elongated slot and at least one conduit to supply a fluid to the reservoir portion of said chamber, the fluid build- 7 ing up in said reservoir and overflowing out of said central body member through said slot.

9. Apparatus as defined in claim 8, wherein said chamber has a plurality of guides spaced along said discharge means and extending axially therefrom, said guides providing a series of overflow channels for said fluid as it rises in said reservoir and flows through said slot.

References Cited 8 1,903,795 4/1933 Rigler 210374 X 2,283,457 5/1942 Pecker 210- -374 3,289,843 12/1966 Nyrop 2102 15 X FOREIGN PATENTS 859,429 12/ 1952 Germany.

US. Cl. X.R.

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