US3108067A

US3108067A - Centrifugal apparatus

Info

Publication number: US3108067A
Application number: US137775A
Authority: US
Inventors: Dietzel Walter; Hillebrand Heinrich
Original assignee: BMA Braunschweigische Maschinenbauanstalt AG
Current assignee: BMA Braunschweigische Maschinenbauanstalt AG
Priority date: 1960-10-14
Filing date: 1961-09-13
Publication date: 1963-10-22
Anticipated expiration: 1980-10-22
Also published as: DE1144192B

Description

of the height of the first centrifuge means.

United States Patent many Filed Sept. 13, 196i, er. No. 137,775 Claims priority, application Germany Get. 14, 1969 2 Claims. (Cl. 210-330) This invention relates to centrifugal apparatus, and more particularly to centrifugal apparatus for continuous separation of the components of mixtures of solids and liquids. In such continuous centrifugal separators, both the solid components and the liquid are con dnuously and separately discharged while the centrifuge runs at full speed.

The primary object of the present invention is to generally improve centrifugal apparatus of the referred to type.

Centrifugal apparatus for automatically and continuously separating solids and liquids of a mass of material containing these and using an upwardly widening centrifuge basket and a vessel underneath that basket are known. Such vessels which have an imperforate side wall may be referred to as acceleration vessels. in these known apparatus, the mixtures to be treated are centrally charged. The mass is subjected in the acceleration vessel, in a gradually increasing manner, to the separating infiu ences of the forces due to rotation. For instance, a mass of concentrated sugar syrup separates in sugar and molasses. Both sugar and molasses are whirled off, but the specifically heavier sugar crystals reach the imperforate side wall of the acceleration vessel before the molasses does. When working with centrifuges of this type it has been observed that the sugar, before reaching the circumferential speed of the acceleration vessel, slides along the metallic side wall of the vessel, and this has been found to have the great disadvantage of causing sugar crystals as well as grains of other solid particles to be abraded, to break, and disintegrate.

Important objects of our invention center about a centrifugal separator which does away with the disadvantages of the referred to known apparatus and offers advantages which so far could not be secured.

Other objects of this invention will appear from the following description.

In accordance with one aspect of the invention, the objects of the invention are achieved by providing a centrifugal apparatus which comprises a support, a shaft mounted on the support for rotation about a substantially vertical axis, and first and second centrifuge means mounted to be operated by the shaft, whereby the second centrifuge means are disposed under the first centrifuge means. Each of the two centrifuge means has a certain height and a side wall. The second or lower arranged centrifuge means has a height of no more than substantially a fifth The centrifu gal apparatus of the invention further comprises means for charging the mixture to be treated into the second centrifuge means closely adjacent the side wall thereof.

The first or upper centrifuge means are generally constituted by what will be referred to hereinafter as a centrifuge basket or basket, and the second or lower centrifuge means are generally constituted by what will be referred to as a centrifuge bowl or bowl.

Due to the provision that the material to be treated is charged closely adjacent the side wall of the centrifuge bowl, the energy with which the material under treatment strikes the side wall of the bowl is relatively small,

Eddhfid? Patented Get. 22, 1.963

ice

this being due to the small radial distance between the point at which the material impinges upon the bottom of the bowl and the side Wall of the bowl. This small distance and thus the small energy of the material whirled against the side wall of the bowl make it possible for separated solids, for instance, sugar crystals, to be gently moved onto the side wall of the bowl.

The invention enhances in a high degree the aforesaid advantage which results from charging the material to be treated closely adjacent the side wall of the bowl by providing the bowl with a perforate side wall and by further providing that the height of the bowl is not greater than substantially a fifth of the height of the basket. The centrifugation which takes place in the bowl causes a liquid film to form between the perforate side wall of the bowl and separated solid particles, which liquid film forms constantly and moves on and greatly decreases abrasion of the solid particles. By height of the basket and bowl, respectively, is meant the vertical distance that material has to ascend during the operation.

According to another aspect of our present invention, we provide two screening media, Wtih one of these media lining the inside of the side wall of the basket and the other screening medium lining the inside of the side wall of the bowl. Best results have been achieved, that is, the most tender treatment of solids separated in the bowl has been ensured by providing an effective screening surface in the bowl, that is less than substantially 10% of the effective screening surface in the basket.

' In order that the present invention may be fully understood, illustrative embodiments are hereinafter described and shown in the accompanying drawing, by way of example, the drawing forming a part hereof and wherein:

FIG. 1 is a section taken in elevation through a centrifugal apparatus embodying features of the invention; and

FIG. 2 is a sectioned elevation of a modified centrifuge basket and centrifuge bowl.

Referring to the drawing in greater detail, and initially to FIG. 1, a shaft it) is vertically supported for rotation in a bearing assembly generally designated 11. The shaft carries a drive pulley 12 at the lower end thereof and a centrifuge bowl 13 at the upper end. The bowl has a bottom 14 and a perforated side wall =15. Seated upon the bowl is a centrifuge basket 16. The bowl is cylindrical and the basket is of upwardly widening conical shape. The basket has a perforated side wall 17 which forms an angular upward continuation of the side wall 15. However, the bowl and basket are separate parts and either of the two parts can be exchanged by a differently shaped but corresponding part.

Both the side wall of the bowl and the side wall of the basket are interiorly lined with a

screening medium

13 and 19*, respectively, each of the screening media being of a mesh size such as to permit passage of the liquid component of a mixture to be separated but to retain the solid component thereon. Both screening media are preferably provided with hard chromium plating.

Conduits are provided above the centrifugal apparatus for charging the centrifuge bowl with the mixture to be treated. A conduit 26' has an axial opening which is downwardly directed and faces a portion of the bottom 14 of the bowl, that is closely adjacent the side wall 15 of the bowl. Thus, the mixture is discharged onto the bottom wall of the bowl closely adjacent the side wall thereof. Centrifugal forces exerted on the mixture have a separating influence upon the solids and the liquid phase of the mixture and force the components against the side wall of the bowl. 'The distance between the charging point and the side wall of the bowl is so small that the momentum gained by separated solid particles during their radially outward movement should cause no serious damage to the structure of the solid particles, if it were not for the fact that the solid particles when they reach the side wall of the bowl have not had time also to reach the circumferential speed of the side wall of the bowl. The solid particles slide along the metallic side wall of the bowl at speeds lower than the circumferential speed, which would have a damaging effect upon the solid particles.

The present invention counteracts any abrading and disintegrating effect caused by the sliding of solid particles on a metallic side wall of a centrifuge by providing a centrifuge bowl, that is, a bowl having a perforated side wall, underneath a centrifuge basket and by giving the bowl a height of no more than substantially a fifth of the height of the basket. As shown in FIG. 1, the basket 16 has a height a, whereas the bowl 13 has a height 17, that is,

or less. By height, as has been indicated hereinbefore, is meant the vertical distance which the components of a mixture have to move upwardly in the bowl and basket, respectively. It has been found that the referred to height relation is conducive to the formation of a liquid film between the screening medium in the bowl and separated solid particles. Such film decreases the friction relative to the side wall of the bowl. The solid particles, while still within the centrifuge bowl, contain the highest amount of liquid and have therefore the lowest coefficient of both internal friction and friction relative to the side wall 15, and this condition is strongly helped by the formation of the referred to liquid film, making it safe for separated solid particles to be in contact with a steep side wall, such as the wall 15 of cylindrical shape.

A different requisite of an effective separation and at the same time of a gentle treatment of separated solid particles, according to our invention, is a certain relation between the areas of the screening media of bowl and basket. The invention provides that the effective screening surface of the bowl is less than substantially of the effective screening surface of the basket.

The liquid passes through the

screening media

18 and 19 and the perforations of the side walls and 17 and enters a collector space 21 defined by the side walls 15, 1'7, a deflector 22, and an intermediate housing wall 23 which coaxially surrounds the bowl 13 and basket 16. The liquid collected in the space 21 is withdrawn therefrom through a tube 24 communicating with the space 21 near the bottom thereof.

The solids retained on the screens 18 and 19' are gradually moved upwardly by the axial component of the centrifugal force until they are discharged over the upper rim of the side wall 17 and drop into a compartment 25 formed between the intermediate housing wall 23 and an outer housing wall 26 of the apparatus.

The apparatus is covered by a cover member 27.

Important to the proper functioning of the apparatus is a steep side wall of the bowl. No upward forcing of the mass to be treated is needed or desired as long as the liquid amount is large. When the mass becomes increasingly viscous, as the moisture is progressively ejected, provision must be made for increasing the upward forcing tendency. Thus, the side wall of the basket which is generally of upwardly widening conical shape is given a greater angle of inclination with respect to the shaft or the vertical axis of the apparatus than the side wall of the bowl.

To provide for smooth discharge of the solid material separated from the liquid, the side wall of the basket may be composed of a plurality of frustoconical sections arranged axially adjacent to each other, with the side walls of the frusta defining angles with the axis of the basket,

which increase from one section to the next in direction from the bottom toward the top of the basket. By such an arrangement, the solids containing the smallest amount of liquid and thus having the highest coefficient of friction are in contact with a wall section which makes the largest angle with the axis of the basket or the smallest angle with a horizontal plane. In the construction of FIG. 2, a bowl 13 of cylindrical shape, as illustrated in FIG. 1, is shown to be associated with a two-sectioned basket 16b.

It is believed that the construction and operation of the forms of apparatus for practicing the invention, as shown and described, will be understood from the foregoing detailed description. Some of the features and advantages of the invention are reviewed hereinafter. The invention makes use of a bowl of relatively small diameter having a side wall which forms the steepest portion of the bowl-basket combination, and it provides that the side wall of the bowl is perforated. Although the centrifugal force exerted on separated solids in the bowl is relatively small, it has been found that the difference in circumferential speeds of the side wall of the bowl and the solids has a harmful effect on the solid particles. The present invention overcomes this disadvantage by giving the bowl a height of no more than substantially a fifth of the height of the basket or by providing an effective screening surface in the bowl, that is less than substantially 10% of the effective screening surface of the basket. The provision of bowl and basket as different units offers the advantage of a wide range of adjustment possibilities. While the requirements of the invention for the height and effective screening surface relation, as far as bowl and basket are concerned, must be satisfied, it remains possible to combine less or more steep bowls with the same basket or kind of basket, or the same kind of bowl with different shapes of baskets.

It will be apparent that although we have shown and described our invention in a few forms only many changes and modifications may be made without departing from the spirit of the invention defined in the following claims.

We claim:

1. Centrifugal apparatus for continuous separation of the components of a mixture, comprising a support, a shaft mounted on said support for rotation about a substantially vertical axis, a centrifuge basket and a centrifuge bowl mounted to be operated by said shaft, and two screening media, said bowl being disposed under said basket and having a height of no more than substantially a fifth of the heighth of said basket, each of said basket and bowl having an at least partly perforated side wall, both of said side Walls being coaxial with said shaft, the side wall of said bowl being of substantially cylindrical shape, the side wall of said basket having a generally upwardly widening conical shape and constituting an angular upward continuation of the side wall of said bowl, a first of said screening media lining the inside of the side wall of said basket, the second of said media lining the inside of the side wall of said bowl, the effective screening surface of said second screening medium being less than substantially 10% of the effective screening surface of said first screening medium.

2. In the apparatus according to claim 1, said bowl having a bottom, said apparatus further comprising means for charging said mixture onto said bottom closely adjacent the side wall of said bowl.

References Cited in the file of this patent UNITED STATES PATENTS 1,634,868 Elmore July 5, 1927 3,050,190 Siepe Aug. 21, 1962 FOREIGN PATENTS 210,846 Austria Aug. 25, 1960