US3228595A

US3228595A - Centrifuge discharge means

Info

Publication number: US3228595A
Application number: US285819A
Authority: US
Inventors: Thomas D Sharples
Original assignee: Pennsalt Chemical Corp
Current assignee: Pennwalt Corp
Priority date: 1963-06-05
Filing date: 1963-06-05
Publication date: 1966-01-11
Anticipated expiration: 1983-01-11
Also published as: DE1657658A1

Description

Jan. 11, 1966 D. SHARPLES CENTRIFUGE DISCHARGE MEANS 2 Sheets-Sheet 1 Filed June 5, 1963 INVENTOR.

THOMAS [EHARPLES BY ATTORNEY Jan. 11, 1966 D. SHARPLES 3,228,595

' CENTRIFUGE DISCHARGE MEANS Filed June 5, 1963 2 Sheets-Sheet 2 INVENTOR. THOMAS D. HARPLES BYEM L ATTORNEY United States Patent 3,228,595 CENTRIFUGE DISCHARGE MEANS Thomas D. Sharples, Lansdale, Pa., 'assignor to Pennsalt Chemicals Corporation, a corporation of Pennsylvania Filed June 5, 1963, Ser. No. 285,819 14 Claims. (Cl. 233-21) This invention relates to a centrifuge discharge means. More specifically this invention relates to a skimming tube or skimmer by which a liquid discharge is extracted from a centrifuge bowl. The device of the invention is especially adapt-ed for use with liquids which have a tendency to foam, that is, form a mixture of gas with the liquid discharge when they are extracted by conventional skimmers.

It is well known in the prior art to discharge a liquid from a rotating centrifuge bowl by means of a stationary skimming tube. Such a skimmer often comprises a tube held in the bowl in such a position that its open front end faces the oncoming rotating liquid in the bowl and is partly submerged therein. A great variety of such skimmers have been developed and many include means for mounting them so that they may be adjusted to the desired radius with respect to the axis of the bowl.

In the centrifugal treatment of many liquids using a centrifuge bowl having a skimming device there is noted a marked tendency for the liquid to create a foam, that is, a mixture of gas, usually air, with the liquid. Such foaming is to be avoided for it not only makes the liquid more difficult to handle, may cause overflow from the centrifuge chamber, etc., but also in many cases has a detrimental elfect on the quality of the liquid itself. For instance, many food liquids, such as orange juice, when foamed with air exhibit a considerable degradation in flavor. Some chemicals-almost any reducing agent, such as a photographic developing solutionupon being mixed with air, will lose much of their efficacy.

The cause of foaming of liquids being discharged by a skimming device has been found to be directly associated with the degree of turbulence present in the fast-moving liquid in the area of the stationary skimming tube mouth. It can readily be imagined that when this liquid which may be travelling at a surface speed of 12,000 feet per minute meets the periphery of the conventional stationary skimming tube mouth as well as the normal back pressure within the skimmer itself, there will be considerable splashing. The result is an exposure of the liquid to the surrounding gas and a consequent foaming of the liquid in the bowl and in the tube. The result is also increased power required to drive the centrifuge.

Many attempts have been made in the prior art to design a skimming tube which will eliminate as much as possible the conditions which cause turbulence and foaming. The essence of the thought in designing these prior art devices has been to streamline the skimmer as much as possible so that a minimum of turbulence will result. None of these prior attempts have been suflicient and the processor has had to be content with the considerable foam produced.

After much experimentation I have developed a skimming discharge structure which eliminates or avoids to .a remarkable degree the foaming ordinarily produced by a skimming tube operating in foamable liquids. My invention has been developed through an understanding of various skimmer types. I have noted that a completely submerged skimming tube because of the inaccessibility of gas will discharge a gas-free liquid although wild surface disturbance takes place at the liquid level in the bowl above the skimming tube mouth as well as around the skimming tube riser. The disturbance at the mouth of the submerged skimmer will be in the form of a defiection or bow wave which even in a small machine may shoot the liquid out a distance of twenty or thirty feet. At the riser of the submerged skimmer tube a comparably violent bow wave will be formed unless the skimmer is a streamlined airfoil. In the latter case the disturbance will be in the form of strong secondary flows or rooster tails from the sides of the riser. I have also found that a skimming tube when only partially submerged will operate quite smoothly with a minimum of foaming if its discharge is returned to the bowl such that there is little or no back pressure at the mouth of the skimming tube due to friction of the liquid with the walls of the tube, etc. With these thoughts in mind I have developed the present invention.

It is a feature of the present invention, therefore, to provide a skimming tube which reduces to a remarkable extent manifestations of a foaming tendency in liquid which possess them.

It is a further feature of my invention to provide a skimming tube which requires a minimum amount of additional power to drive the machine.

Further features of my invention will become apparent to those skilled in the art upon reference to the following description including the drawings which present preferred forms of the invention. In the drawings:

FIGURE 1 is a fragmentary perspective view of a skimmer embodying the invention;

FIGURE 2 is a side elevation of a skimmer embodying the invention;

FIGURE 3 is a sectional view taken on the line 33 of FIGURE 4;

FIGURE 4 is an elevational view in the front plane of a skimmer embodying my invention;

FIGURE 5 is a sectional view taken on the line 5-5 of FIGURE 3;

FIGURE 6 is a sectional view taken on the line 6-6 of FIGURE 3;

FIGURE 7 is a fragmentary perspective view partly in section, of a separator embodying the invent-ion;

FIGURE 8 is a front elevation of a modified form of a skimmer embodying the invention;

FIGURE 9 is a sectional view taken on the line 99 of FIGURE 8; and

FIGURE 10 is a sectional view taken on the line 1010 of FIGURE 9.

Referring more specifically to the drawings, a skimmer embodying the invention is shown in FIGURE 1 and generally designated 10. It comprises an elongate body portion 12 which in operation is partly immersed in the liquid. At the front or leading end the body presents an upper opening 14 and a lower opening 16 defined by knife edge walls to minimize turbulence. The lower opening which is completely submerged in the liquid during operation has a passage 18 which extends rearwardly (FIG. 3) in the body to communicate with an outlet conduit 20 by which the skimmer may be supported. To convert velocity into pressure, the cross-section of passage 18 may increase as the distance from the mouth 16 increases. The upper opening 14 communicates with a passage 22 which is partitioned from passage 18 and extends rearwardly in the body to an outlet opening 24 which is adapted in a form of the invention to discharge into the centrifuge rearwardly of the elongate body. In order for the surface liquid to flow smoothly through the upper passage, it is important that the passage and discharge 24 be ample so as not to fill with liquid and cause back pressure.

Preferably, as shown in FIGURES 2 and 3, the upper wall of passage 22 protrudes forward of the front end of the partition between the

passages

18 and 22 to catch as much as possible of the bow wave.

As shown especially in FIGURES l, 2, 4 and 5 the elongate body in the preferred embodiment is equipped on its opposite sides with outwardly and downwardly extending deflectors 26. As shown in FIGURE 5 the deflectors are made to blend smoothly into the structure of the side walls of the body so that the easy return of this liquid to the liquid level is possible. These deflectors are for the purpose of returning back to the surface of the liquid as much as possible of the secondary flow or rooster tail of liquid that moves upward on the sides of the body. This upward movement-due to the pressure differential of the liquid immediately adjacent the sides of the body which theoretically is stationary with the skimmer and the liquid outward from it which is moving at bowl speeds-is designated the secondary flow. To keep to a minimum the secondary flow, the leading end of the skimmer projects into the water to as shallow a depth as possible making as small as possible the pressure differential created, and still assuring that the opening 16 will be completely submerged. For this purpose the opening 16 is made fiat and wide.

In operation, the elongate skimmer body 12 is held by appropriate and conventional means in approximately the disposition with respect to the liquid line LL as shown in FIGURE 1. The leading end of the elongate body is disposed with the liquid line somewhere in the cross-sectional area of the opening 14 so that the surface skimmings flow through the passage 22 and discharge through opening 24. These skimmings include a major portion of the bow wave above the opening 16, as well as any splash or foam on the surface. The skimmings also include the layer of air above the liquid which is induced into movement by the movement of the liquid and which will mix with the turbulent liquid and foam it. The upper passage 22 confines and limits the air and liquid it conducts and keeps it from splashing out of control and from further foaming. It gently diverts the liquid to one side of the passage20 riser, impact with which would otherwise cause splashing and other foam-inducing turbulences. It finally discharges the liquid through opening 24, gently laying it as smoothly as possible on the surface of the liquid to the rear of the skimmer.

FIGURE 5 illustrates the condition of the liquid in the two

passages

18 and 22. The liquid in the passage 18 having been drawn from a submerged location contains no foam even with the most foamable of material, while the liquid in the passage 22 may contain some.

In most cases the discharge of material containing very small amounts of foam from opening 24 back into the centrifuge is tolerable for the small amount of foam resolves itself back into gas and liquid. In unusual instances it is desirable to segregate the foamed liquid discharging out the opening 24 from the non-foamed liquid in the chamber. This may be done by providing an extension 28 (FIGURE 7) connected with opening 24 and leading the foamed liquid to a partitioned zone A, the surface of which is cut off by an annular bafile B from the zone C. In the zone A the foamed material is allowed to break up in the centrifugal field and flow back into the zone C under the baffle B.

In the usual installation of a skimmer embodying the invention there will be no intention to use it to controI the liquid level in the centrifuge. The liquid level is normally maintained by precise control of the feed rate and perhaps some control of the back pressure at submerged opening 16 for instance by a throttle valve in the line 20. It should be understood that for optimum results the back pressure in line 20 should be kept to a minimum so as to avoid unnecessary turbulence at the opening 16.

A modified form of the invention is shown in FIG- URES 8, 9 and and generally designated 38. This form may comprise a unitary body 40, the front end of which carries a lower opening 42 and an upper opening 44. As shown by the phantom liquid level line in FIG- URES 8 and 9, the opening 42 is normally submerged. It communicates with a passage 46 in the upward liquid lead-off conduit 48 by which the body is supported. The upper opening 44 through which the surface skimming enters the body communicates with the passage 50, which is bifurcated to cause the skimmings to travel on either side of the walls enclosing the passage 46 (FIGURE 10). The bifurcations recombine toward the trailing end of the body and terminate in the discharge opening 52.

The sides of the body 40 are provided with outwardly and downwardly extending curved deflectors 54 which smoothly return the secondary flow to the level of the liquid.

In operation, as with the first disclosed embodiment, the body is disposed at the liquid level substantially as shown in FIGURES 8 and 9 so that opening 44 is partly submerged. The liquid discharge which is drawn from a submerged position through opening 42 contains no foam while the walls of passage 50 contain and confine the secondary flow about the walls of passage 46 and return the liquid undisturbed to the liquid level from discharge opening 52. Secondary flow from the outer walls of the passage 50 is smoothly turned back into the liquid level by the deflectors 54.

In the specification the terms above and below have been used for simplicity in place of inward toward the axis and outward from the axis or at a lesser radius and at a greater radius, respectively.

It should be understood that a skimmer embodying the invention may be used on any of a variety of types of centrifuges. For instance it may be used in simple conventional solid bowl centrifuge, positioned in the main separating zone itself, or it may be disposed in a stationary annular discharge pocket about the axis of any kind of centrifuge such as a worm-type centrifuge, a frusto-conical basket centrifuge.

Therefore, variations of the apparatus shown are possible within the scope of the appended claims. Hence while I have explained my invention with the aid of particular embodiments thereof, it is to be understood that I do not wish to be limited to the specific structural details illustrated and described from which departure can be made without departing from the spirit and scope of the invention as defined by the following claims.

I claim:

1. For a centrifugal separator a skimmer comprising an elongate body having an upper and a lower wall and opposite side walls and a leading end and a trailing end, the leading end having upper and lower openings with passages segregated by a partition wall, the passages extending rearwardly toward the trailing end, the lower opening passage having a lead-01f adapted to be connected to a liquid discharge conduit for .the separator, and the upper opening passage terminating rearwardly in an opening adapted to direct its discharge into the separator rearwardly of the elongate body.

2. The skimmer of claim 1 wherein the side walls have outward deflectors at a level spaced above the lower opening, the outward deflectors extending rearwardly along the elongate body toward its trailing end.

3. The skimmer of claim 2 wherein the deflectors extend outwardly and downwardly.

4. The skimmer of claim 1 wherein the lower opening passage extends rearwardly toward the trailing end of the elongate body and then upward, and the upper opening passage is bifurcated about the upwardly extending portion of the lower opening passage.

5. The skimmer of claim 4 wherein the side walls have outward deflectors at a level spaced above the lower opening, the outward deflector-s extending rearwardly toward the trailing end of the elongate body.

6. The skimmer of claim 1 wherein the upper wall protrudes forward of the partition wall and the lower wall.

7. A centrifuge comprising a rotatable bowl having a peripheral wall and end walls, and a skimmer comprising an elongate body having an upper wall and a lower wall and opposite side walls and a leading end and a trailing end, the leading end having upper and lower openings with passages segregated by a partition wall and extending rearward-1y toward the trailing end, the lower opening being connected to a liquid discharge conduit for the centrifuge, the elongate body being disposed substantially in a radial plane of the separator in a posture substantially parallel to the peripheral wall, the bowl having an inward baffle dividing it into two portions, the batfle being formed with an opening adjacent the wall of the bowl, and the upper opening passage extending rearwardly from the elongate body and inward over the baffle to terminate in an outlet directing its discharge into the portion of the bowl segregated from the portion in which the elongate body is disposed.

8. A centrifuge as described in claim 7 wherein the opposite side walls of the elongate body have outward deflectors at a level spaced above the lower opening, the outward deflectors extending rearwardly toward the trailing end of the elongate body.

9. The centrifuge of claim 8 wherein the deflectors extend outwardly and downwardly.

10. The centrifuge of claim 7 wherein the lower opening passage extends rearwardly toward the trailing end of the elongate body and then upward, and the upper opening passage is bifurcated about the upwardly extending portion of the lower opening passage.

11. The centrifuge of claim 10 wherein the opposite side walls of the elongate body have outward deflectors at a level spaced above the lower opening, the outward deflectors extending rearwardly toward the trailing end of the elongate body.

12. The centrifuge of claim 11 wherein the deflectors extend outwardly and downwardly.

13. The centrifuge of claim 7 wherein the upper wall of the skimmer protrudes forward of the partition wall and the lower Wall.

14. A process for discharging liquid from a rotating centrifuge bowl comprising the steps of withdrawing the liquid through a first conduit having an open end completely submerged in and facing the oncoming liquid, flowing a portion of the surface liquid including liquid splashed up from the open end of the first conduit immediately above the open end through a second conduit having an open end only partially submerged in the oncoming liquid, the second conduit extending to one side of the first conduit and terminating in an opening rearward of the first conduit, and returning the surface liquid to the body of liquid through the rearward opening.

References Cited by the Examiner UNITED STATES PATENTS 536,444 3/1895 Reid 23322 585,552 6/1897 Bushby 233-22 779,986 1/1905 Arnberg 233-22 904,533 11/1908 Haufi 23322 MARTIN P. SCHWADRON, Acting Primary Examiner.

HENRY T. KLINKSIEK, Examiner.

Claims

1. FOR A CENTRIFUGAL SEPARATOR A SKIMMER COMPRISING AN ELONGATE BODY HAVING AN UPPER AND A LOWER WALL AND OPPOSITE SIDE WALLS AND A LEADING END AND A TRAILING END, THE LEADING END HAVING UPPER AND LOWER OPENINGS WITH PASSAGES SEGREGATED BY A PARTITION WALL, THE PASSAGES EXTENDING REARWARDLY TOWARD THE TRAILING END, THE LOWER OPENING PASSAGE HAVING A LEAD-OFF ADAPTED TO BE CONNECTED TO A LIQUID DISCHARGE CONDUIT FOR THE SEPARATOR, AND THE UPPER OPENING PASSAGE TERMINATING REARWARDLY IN AN OPENING ADAPTED TO DIRECT ITS DISCHARGE INTO THE SEPARATOR REARWARDLY OF THE ELONGATE BODY.