US3365066A - Centrifuge - Google Patents

Description

Jan. 23, 1968 .1. HOWELL CENTRIFUGE 2 Sheets-Sheet 1 Filed March 7, 1967 /NVENTOR JOHN D. HOWELL J. D. HOWELL Jan. 23, 1968 CENTRIFUGE 2 Sheets-Sheet 2 Filed March '7, 1967 INVENTOR JOHN .D. HOWELL United States Patent Ofiice 3,365,066 CENTRIFUGE John D. Howell, 140 Red Hill Road, New City, N.Y. 16956 Filed Mar. 7, 1967, Ser. No. 621,224 3 Claims. (Cl. 210-374) ABSTRACT F THE DISCLOSURE A centrifuge having a basket surrounded by a housing with a transverse Wall therein spaced from the basket and dividing the housing into a liquid receiving section and a solids receiving section. Opposed screw threads on the outer edge of the wall and on the periphery of the basket adjacent the wall cooperate to counter the tendency of the basket to blow air or gases from the liquid receiving section to the soiids receiving section.

The present invention relates to centrifuges, and partic ularly to centrifuges of the type employed for the separation of solids from liquids.

Centrifuges designed for liquid-solid separation may be of various shapes and mechanical designs. The centrifuge bowl may, for example, be of the basket type and may have a perforate or an internal scroll or screw mechanism which serves to advance the separated solids toward the discharge outlet of the bowl.

As another design feature of the conventional centrifuge, means have often been provided for washing the separated solids. The wash liquid employed may, for example, be introduced into the hollow area of the scroll and be directed, through one or more openings in the wall of the scroll, onto the separated solids.

When such a centrifuge is employed for the separation of ice (or other light solids) from a highly viscous mother liquor of greater density, there is a tendency for the centrifuge to act as a fan blowing vapor or gas from the inside of the basket through the screen and cake to the outside. The gas in the inside of the basket is drawn in through the ice discharge hopper. The air on the outside of the basket leaves through the liquor discharge outlets. Some also take a shorter route back to the inside of the basket by passing through space between the rotating basket and the baffle. This gas movement is undesirable from several viewpoints: (1) because of its high velocity, it causes the liquor to foam as it leaves the basket. The gas passing out the liquor outlet may also cause foaming in the liquor tank; (2) the passage of gas through the coffee liquor in the cake and through the mist of coffee liquor outside the basket may cause oxidation of the extract and adversely affect the flavor this foam can eventually plug the discharge parts of the centrifuge; (3) because recirculated gas is warmer than the ice, it causes ice crystals to melt; (4) because the ice plugging up part of the annular space between the rotating basket and partition periodically breaks away, the flow of gas varies with time. This causes alternate thawing and refreezing of crystals in the cake. Thi results in a pronounced reduction in liquor handling capacity.

It is therefore an object of the present invention to provide an improved centrifuge.

Another object of the invention is to provide a centrifuge of improved design for liquid-solid separation.

A further object of the present invention is to provide, for the purpose of liquid-solid separation, a centrifuge in which the tendency for viscous mother liquor to form foam is held to a minimum.

These and other objects and advantages of the present invention will become more apparent from the following description thereof.

3,365,066 Patented Jan. 23, 1968 FIG. 1 is a side elevation, being partly in section, of a centrifuge constructed in accordance with the invention;

FIG. 2 is a vertical section taken along the lines 2-2 of FIG. 1;

FIG. 3 is an enlarged, partial vertical section, illustrating the invention.

Referring to the drawings, and particularly to FIG. 1, a centrifuge 10 is shown, being designed for the separation of solids from liquids. The centrifuge 10 is equipped with a cylindrical bowl, or basket, 12, which is rotatably mounted with a housing 14, and provides a centrifuge chamber 16. Positioned Within the chamber 16 is a scroll 13. The scroll 18 is mounted coaxially with, and is rotatable with respect to, the basket 12 The basket 12 is rotated by a belt 20, which is driven by conventional means (not shown), such as a motor. The belt 20 serves to drive a pulley 22, which is mounted on a supporting shaft structure 24 for the basket 12.

The scroll 18 is similarly rotated by a belt 26, which drives a pulley 28 mounted on supporting shaft structure In for the scroll 18. However, the belt 26 is driven at a speed slightly greater than that of the belt 20. The driving mechanism (not shown) for the belt 26 may be of any conventional design. For example, the belt 26 may be driven, through use of a differential gear mechanism, by the same drive means as employed for driving the belt 20.

The basket 12, is provided with a cylindrical side wall 32, and is closed at one end by a wall 34. An opening 35 is cut through the wall 34, for receipt therethrough of the respective inner ends 36 and 37 of the supporting shaft structures 24 and 39. At its end opposite the wall 34, the basket 12 is open, as seen at 38. The side wall 32 is formed at the open end 38, with a circumferentially extending lip 39. The side wall 32 of the basket 12 is provided. over a portion 41) thereof, with perforations 43.

A cylindrical lining screen 44 lies within the chamber 16, and in contact with the side wall 32. The screen 44 is formed, so as to provide a ratio of open area to total area, which is as high as possible. The openings in the screen should each have at least one dimension which is slightly smaller than the size of the solid particles to be separated in the centrifuge 10. It has been found advantageous in many instances to employ a screen having openings in the form of rectangular slots. In the case of the separation of ice crystals from a slurry thereof in brine, a minimum dimension of .008 inch is preferred for each opening.

The scroll 18 is of generally hollow cylindrical shape, and is closed at one end by a wall 56. At its opposite end, the scroll 18 is open, as seen at 58. The side wall of the scroll 18 at its outer circumferential surface 61, is provided with a continuously extending helical impeller blade 62. The latter is of such pitch diameter,

' that the distal edge 64 thereof is located closely adjacent the screen 44. The rearward end of the blade 62 is located generally in alignment with the end Wall 56. The forward end 68 of the blade 62 is located adjacent the open end 58 of the scroll 18. The scroll 18 is positioned, so that the wall 56 and the rearward end of the blade 62 lie closely adjacent the end wall 34 of the basket 12.

The scroll 18 is of abbreviated length, as compared to the length of the chamber 16. Thus, the open end 58 of the scroll 18 is spaced from the open end 38 of the basket 12. At the same time, the forward end 68 of the blade 62 is spaced from the lip 39 of the side wall 32 of basket 12. It will thus be seen that only the rearward portion 17 of the chamber 16, located adjacent to the end wall 34, is occupied by the scroll 18. The latter does 0 not extend through the remaining portion 19 of chamber 16, located adjacent to theopen end 38 of basket 12.

The blade 62 overlies only that portion 45 of the screen 44 which is coextensive with the chamber portion 17. The remaining screen portion 46, lying adjacent the lip 39, provides a washing zone for separated solids, as will be made clear hereinbelow.

A feed conduit 71 extends through the open end 38 of the basket 12. At its inner end 72, the conduit 70 extends through the open end 58 of the scroll 18.

A conically-shaped baffle member 74 is mounted within the scroll 18. The bafile member 74, at its inner or constricted end 76, is located at the open end 58 of the scroll 18, and there receives the inner end '72 of the feed conduit 70. A washer is provided to assure a fluid tight joint between the baflle inner end 76, and the conduit inner end 72. At its outer, or flared end 80, the bafile member 74 is secured in conventional manner to the scroll side wall 6t), and at a short distance from the end wall 56. A number of discharge ports 82 are spaced about the scroll wall 60. The discharge ports 82 are each located between end wall 56 of the scroll 18 and the flared end 80 of the bathe member 74.

A conduit 84 for conducting wash liquid extends through the open end 38 of the basket 12, and into the chamber 16. The conduit 84 at its outer end is provided with a nozzle 86. The nozzle 86 is positioned so as to be close to the upper surface of the cake of solids advanced across the portion 46 of the screen 44.

The housing 14 is made up of two sections, 13 and 15. The first housing section 13 generally serves to enclose the basket 12. The housing section 13 is formed of a circumferentially-extending wall 92, and two oppositelypositioned side walls 93 and 94. The latter two walls each extend generally radially with respect to the axis of the housing 13. The side wall 93 is provided with a central, circular opening 95, which is designed to permit the passage therethrough of the shaft structure 24 of the basket 12 and the shaft structure 30 of the scroll 18. The wall 94 is provided with a circular opening 96, within which the lip 39 of the basket 12 is situated.

The housing section 13 is divided by a radially-extending divider plate 97 into two chambers 98 and 99. The chamber 98 is situated to receive liquid which has been separated from solids, in the operation of the centrifuge 10. Such separated liquid is received from the chamber portion 17 and through the screen portion 45 and adjacently located perforations 42 in the basket side wall 32. Located in the chamber 98 and mounted on the circumferential wall portion 92 of the housing section 13 are a plurality of circumferentially spaced spray nozzles 100 (one being shown). Each nozzle is connected through a conduit 102 to a distributor head (not shown). The nozzles 100 are positioned to direct wash liquid, such as water, onto the exterior surface 104 of the basket wall 32. Such wash liquid serves to maintain the perforations 42 clear, for free flow therethrough of the liquid separated from the solids.

An outlet pipe 106 serves to conduct the separated liquid from the chamber 98. The outlet pipe 106 extends horizontally from a lower portion of the chamber 98, and terminates in a downwardly-directed discharge end 107.

The chamber 99 is situated to receive wash liquor which has been formed by washing of the separated solids by wash liquid from the nozzle 86. Such wash liquor is received from the chamber portion 19, and through the screen portion 46 and adjacently located perforations 42. A horizontal outlet pipe 198, having a downwardly directed outer end 109, extends from a bottom portion of the chamber 99, for the discharge of the wash liquor.

The housing section is formed by the wall 94; a circumferentially-extending wall 110; and an outer wall 111. The section 15 provides therewithin a generally cylindrical chamber 112 (see also FIG. 2) situated to receive washed solids which pass from the chamber 19. Mounted on an upper portion of the wall 110 and located at op posite sides of the chamber 112 are two water inlet couplings 114 and 116 connected to water inlet conduits 118 and 120 respectively. A spray pipe 122, having perforations 123 in the wall thereof, is connected at its opposite ends 124 and 126 to the couplings 114 and 116 respectively. The spray pipe 122 serves to spray liquid, such as water, onto the solids received in the chamber 112. Such liquid carries the solids from the chamber 112 and through a discharge outlet 128.

In the operation of the centrifuge 10, feed slurry, constituted of a mixture of solids and liquid to be separated, is fed through the feed conduit 78 and from the inner end 72 thereof into the scroll 18. The feed slurry proceeds along the inner surface of the baffle member 74, through the discharge ports 82 and onto the screen portion 45. Here, solids and liquid are separated by the centrifugal forces. The separated liquid passes through the screen portion 45, through the adjacent wall perforations 42, and into the chamber 98. Such separated liquid is then withdrawn from the chamber 98 through the discharge pipe 106. The separated solids, possibly retaining some adherent liquid, remain on the screen portion 45.

As previously indicated, the scroll 18 is rotated during the centrifuge operation at a speed somewhat faster than that of the basket 12. The rotating helical blade 62 engages the solids which remain on the screen portion 45 after the separation of the liquid. The blade 62 impels such solids along the screen portion 45, and onto the screen portion 46. As the solids pass along the screen portion 46, wash liquid is directed onto such solids through the conduit 84, and the nozzle 86 at the lower end thereof. The solids are thus washed for the removal therefrom of any adherent liquid. The wash liquor passes through the screen portion 46, through the adjacent wall perforations 42, and into the chamber 99. From the chamber 99, the wash liquor is withdrawn through the discharge pipe 193.

The washed solids pass from the screen portion 46 over the lip 39, and into the chamber 112. From the chamber 112 the solids are discharged through the outlet 128. Such discharge is aided by liquid from the spray pipe 122.

The basket 12 is preferably rotated at a speed that will provide a force of 1,000-1,500 gs. The scroll 18 is, as has been indicated, rotated at a speed slightly greater than that of the basket 12. The preferred speed difference is about 2 to 10 r.p.m. As a result of the speed of rotation of the basket, adequate dewatering of the solids is assured. At the same time, the rotation of the scroll 18 relative to the basket 12 provides for advancement of the separated solids by the blade 62 along the screen portions 45 and 46, and over the lip 39.

The length of the screen portion 46 is preferably about one-half that of the screen portion 45. However, in the case of separations in which the viscosity of the adherent liquid is unusually low, a washing zone which is about onehalf the length of the basket 12 may be desired.

It will be noted that the housing 14 is designed to permit rotation therewithin of the basket 12. Thus, a small clearance is provided between the shaft structure 24 for the basket 12, and the circumferential surface 130 defining the opening 95 in the side wall 93 of the housing 14. A small clearance is likewise provided between the outer circumferential surface 132 of the lip 39 and the circumferential surface 134 defining the opening 96 in the side wall 94 of the housing 14.

It is preferred that the clearance between the surfaces 132 and 134 be maintained at a minimum so as to minimize the amount of flow of air through the annular space between the basket 12 and housing 14, as such air flowing over the basket 12 and in the chambers 98 and 99 tends to produce foam from the liquid being separated from the solids. This foam may eventually fill the chambcrs 98 and 99 and prevent the centrifuge from performing an efiicient separation of solids from carrier liquid. This is particularly true when the material being separated is a slurry of ice in a concentrated, high viscous, comestible extract such as coffee extract containing from 20 to 45 percent by weight of coffee solids.

Referring to FIGURE 3, the invention is illustrated with respect to the placement of the lip 39 of the basket 12 within the opening 96 in the side wall 94 of the housing 14 to minimize or prevent such foaming. Here, the outer circumferential surface 132' of the lip 3% of the basket side wall 32 is formed with a right-hand screw thread 136. A left-hand screw thread 138 is formed in the circumferential surface 134 defining the opening 95. A small clearance 140 is provided between the threading 136 and the threading 138.

The structure of FIG. 3 serves to prevent foaming which is otherwise produced by circulation of air through the basket 12. Referring to FIG. 1, there is some tendency of air to flow from the wash liquor chamber 99 through the clearance between the surfaces 132 a d 134, through the chamber 112, into the basket 12 through thc open end 38 thereof, and back to the chamber 99 through the screen portion 46 and the wall perforations 42. The structure of FIG. 3 is constructed somewhat in the manner of a conventional labyrinth seal. However, as has been pointed out, screw threads 136 and 138 are provided as the opposed elements. Also, the clearance 140 is provided between the threads 136 and 138. The maintenance of such clearance is desirable as a safety factor in view of the risk present that the cake of solids passing over the lip 39 might become unbalanced. Any air which tends to pass through the clearance 1% from the chamber 99 is met by a counter-current of air which is produced in the clearance 140. When the basket 12 is rotated in a clock-wise direction, the screw thread 136 on the rotating lip 3? in cooperation with the screw thread 138 on the stationary wall 94 provides a pumping action. Such action tends to produce movement of air from the chamber 112 and into the chamber 99 As a result, the undesirable circulation of air from the chamber 95 and into the chamber 112 is prevented.

Also, it is desirable that a wear ring of polytetrafiuoroethylene or other slippery material be installed on the basket rim or on the edge of the bafiie. Then, in the event that the basket wobbles due to uneven ice load, the resulting rub will not cause serious galling and damage to basket or baffle.

In accordance with the present invention, a number of modifications may be effected with respect to the structure and operation of the centrifuge 19. Thus, the basket 12 and the scroll 13 may be designed of a shape other than cylindrical, e.g., conical. Also, the basket 12 may be formed with a solid, rather than perforated, side wall 32. In this case, suitable ports, as are Well known in the art, would be provided for the passage of the mother liquor from the chamber 16.

Although the invention has been described with reference to particular embodiments thereof, it is to be understood that various changes may be made without departing from the spirit of the invention as defined by the scope of the appended claims.

What is claimed is:

1. In a centrifuge for separating crystals from an adhering mother liquor, said centrifuge having a basket with a closed rear end and an open front end, said basket containing small openings for the passage of liquid therethrough, means rotating said basket, means introducing crystals and an adhering mother liquor into the rear end of said basket, means advancing said crystals toward the open front end of said basket, and a housing having a first section extending about said basket to catch liquid passing through the small openings of said basket and a second section disposed beyond the open front end of said basket to catch crystals advanced within said basket; the improvement comprising, in combination, means preventing said rotating basket from acting as a fan to blow air or gases from said first section of said housing into said second section of said housing, said means being a transverse wall containing an opening having an inner annular surface, said transverse wall being disposed between the first and second sections of said housing, a lip on the open front end of said basket having an annular outer surface, said lip extending within said opening with a small clearance between the inner annular surface of said opening and the outer annular surface of said lip, and right and left hand opposed screw threads formed on the inner and outer annular surfaces of said opening and said lip, said opposed screw threads pumping air or gases from said second section of said housing into said first section countering the tendency of said basket to blow air or gases from said first section of said housing to said sec ond section.

2. The combination according to claim 1 wherein said basket has a rear wall and a cylindrical outer wall containing said openings.

3. The combination according to claim 2 wherein said means advancing said crystals toward the open front end of said basket comprises a helical scroll Within said hasket rotated with said basket at a slightly different rate of speed than said basket.

References Cited UNITED STATES PATENTS 3,307,703 3/1967 Trojan 210-378 X REUBEN FRTEDMAN, Primary Examiner. J. L. DECESARE, Assistant Examiner.

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