Imperforate bowl: centrifugal separators – Rotatable bowl – Including housing for bowl
Reexamination Certificate
2000-08-10
2001-12-04
Cooley, Charles E. (Department: 1723)
Imperforate bowl: centrifugal separators
Rotatable bowl
Including housing for bowl
Reexamination Certificate
active
06325751
ABSTRACT:
FIELD OF THE INVENTION
The present invention refers to a centrifugal separator comprising: a centrifuge rotor, which is rotatable about an essentially vertical axis of rotation and which around the periphery has at least one outlet being openable during operation and being arranged to discharge intermittently a certain quantity of a separated product; a casing, which encloses the centrifuge rotor; a space, which is delimited by the centrifuge rotor and by an inner surface of a wall extending around the centrifuge rotor and forming a part of the casing, wherein the space is arranged to receive said product from said openable outlet; and an outlet passage, which extends from the space and is arranged to convey said product from the space, wherein the inner surface comprises a first surface portion, located at the level of said openable outlet and extending around the centrifuge rotor and upwardly and inwardly with respect to said axis of rotation from a second surface portion of the inner surface, the second surface portion being located below the first surface portion. Such a centrifugal separator is disclosed in SE-B-447 544.
BACKGROUND OF THE INVENTION
In such centrifugal separators, the separated product, which is discharged through the intermittently openable outlets, has a considerable kinetic energy, which results in a large impulse, when the product impacts on the wall. The discharge takes place very quickly and the separated product impacts on the receiving parts of the casing at the same time as the product is broken and forms spatter distributed in the space within the casing in a plurality of directions which are frequently not controllable. Although a part of the kinetic energy of the separated product is utilized for feeding the separated product from the centrifuge rotor through the outlet passage, the main part of the kinetic energy has to be removed from the product before it finally leaves the centrifugal separator, i.e. the velocity of the separated product has to be reduced. By the technique available today, it is not possible to provide a sufficient velocity reduction to the separated product in the space within the casing. Therefore, the necessary velocity reduction frequently is obtained by means of a so-called sludge cyclone, which is located outside the centrifugal separator proper in connection to the outlet passage. Such sludge cyclones are expensive and result in a complicated and spacious centrifugal separator. SE-447 544 mentioned above discloses for instance a chute provided in the space and extending around almost the whole centrifuge rotor and being intended to convey the separated product to an outlet extending into a tube. This known chute is, however, insufficient for reducing the velocity of the separated product and thus a sludge cyclone is required downstream of the outlet disclosed.
WO-A-95/21697 discloses a centrifugal separator for separating solid particles from a liquid and having a centrifuge rotor which is designed as a basket having a perforated wall and which widens conically in an upward direction. At the upper end of the conical centrifuge basket, there is a lip over which the solid particles leave the centrifuge basket in a direction outwardly towards a curved deflection plate. When the particles impact on the deflection plate, their velocity is reduced and their direction of movement is changed towards a collecting chamber from which they may be discharged through an outlet. Due to the feeding of the solid particles upwardly, it is necessary that the particles rotate at the upper edge of the centrifuge rotor in order to be able to be discharged from the centrifuge rotor.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a centrifugal separator, which makes it possible to discharge a separated product from a centrifuge rotor and out of the centrifugal separator in a more controlled manner than up to now.
This object is obtained by the centrifugal separator initially defined, which is characterized in that the second surface portion is essentially rotary symmetric and extends around the centrifuge rotor and downwardly and inwardly with respect to said axis of rotation and that the outlet passage is located below the maximum diameter of the second surface portion with respect to said axis of rotation. By such a centrifugal separator, the main part of the separated product discharged through the openable outlet will be caught by the first surface portion and its velocity in the radial direction of movement will be reduced. The main part of the separated product will rotate along the first surface portion and move towards and reach the second rotary symmetric surface portion along which it continues to rotate at a high velocity. Due to the friction against the second surface portion, the velocity of the separated product will decrease, which means that the rotative effect of the gravitation increases. When the effect of the gravitation exceeds the effect of the centrifugal force in a vertical direction, the separated product will move downwardly along the second surface portion and be conveyed out through the outlet passage. Thereby, the velocity of the separated product has been reduced to such an extent that it may be taken care of in an easy manner outside the centrifugal separator without first passing a sludge cyclone. By the fact that the second surface portion inclines downwardly and radially inwardly, the downwardly directed effect of the gravitation to the separated product is delayed, i.e. the friction against the second surface portion, which contributes to the reduction of velocity, may act during a longer time period than if the second surface portion would have been extended vertically. Thanks to the fact that the second surface portion is rotary symmetrical, i.e. the surface is even without any parts, projecting inwardly from the surface and hindering the product from flowing in the peripheral direction along the second surface portion, the separated product will move downwardly in a controlled manner.
Further advantages of the invention are obtained by the different embodiments, which are defined in the dependent claims and the following description.
According to an embodiment of the invention, a first connection line, extending in an axial plane between a radially outermost point and a radially innermost point of the first surface portion, forms a first angle, which is less than 90° and greater than 30°, to said axis of rotation. According to a particular embodiment, the first surface portion may be essentially conical.
According to a third embodiment of the invention, the second surface portion and the outlet passage form an edge, which defines at least a part of an orifice of the outlet passage. Thereby, a second connection line, extending in an axial plane between a radially outermost point of the second surface portion and a radially outermost point of said edge, may form a second angle, which is greater than 0° and less than 45°, to said axis of rotation. By such an angle of inclination of the second surface portion, the velocity of the separated product will be reduced against the surface portion during the downward movement of the product. The second angle may, by a man skilled in the art, in an easy manner be adapted to different properties of the separated product, in the first place its viscosity, i.e. a high viscosity requires a relatively small second angle, whereas a low viscosity requires a relatively great second angle. Thereby, said second angle may, according to a further embodiment, be less than or equal to 35°, furthermore greater than or equal to 2°. According to a special embodiment, the second surface portion may be essentially conical.
According to a further embodiment of the invention, the lowest point of the orifice, with respect to said axis of rotation, coincides essentially with the lowest point of the space. Thereby, it is ensured that all separated products also will be discharged from the centrifugal separator, i.e. from the space within the casing.
According
Klintenstedt Kjell
Szepessy Stefan
Alfa Laval AB
Cooley Charles E.
Fish & Richardson P.C.
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