Imperforate bowl: centrifugal separators – Rotatable bowl – Including driven material-moving means therein
Reexamination Certificate
1999-12-29
2003-01-21
Cooley, Charles E. (Department: 1723)
Imperforate bowl: centrifugal separators
Rotatable bowl
Including driven material-moving means therein
C494S053000, C494S070000, C494S084000
Reexamination Certificate
active
06508752
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a centrifugal separator for freeing a liquid from solid particles suspended therein and having a density larger than that of the liquid.
BACKGROUND OF THE INVENTION
Several different types of centrifugal separators for this purpose are known, being arranged during operation to discharge continuously or intermittently sludge, which contains separated solid particles. Each one of the various types is intended for treatment of liquid containing particles in a certain amount and/or of a certain kind.
Thus, there are so called decanter centrifuges for treatment of liquids containing a relatively large amount of particles. An ordinary decanter centrifuge has a normally elongated rotor, in the separation chamber of which only one single conveyor screw is arranged to rotate around the same rotational axis as the rotor but with a different speed than that. Separated particles in this way may be transported by the conveyor screw axially within the rotor up to normally constantly open so-called sludge outlets. A decanter centrifuge of this kind is shown for instance in U.S. Pat. No. 4,245,777.
A decanter centrifuge of a somewhat different kind is shown in U.S. Pat. No. 3,685,721. This decanter centrifuge has several conveyor screws arranged in the centrifuge rotor separation chamber evenly distributed around the rotational axis of the centrifugal rotor. Each of the conveyor screws is arranged to transport separated particles to and out through a sludge outlet at one end of the separation chamber.
A centrifugal separator reminding of an ordinary decanter centrifuge, i.e. having only one conveyor screw, but having an intermittently openable so called sludge outlet, is shown in U.S. Pat. No. 4,508,530. In this centrifugal separator, which is intended for freeing a liquid from both solid particles heavier than the liquid and from liquid drops dispersed/emulgated in the liquid and being lighter than the carrying liquid, there is used for the separation also a set of conical separation discs which are arranged in the separation chamber radially inside the conveyor screw.
A decanter centrifuge as a rule has a large rotor volume and, thereby, a relatively large capacity, i.e. a large flow of a liquid containing a large amount of solid particles can be treated. The elongated rotor is normally journalled at both its ends and is adapted to rotate about a horizontal rotational axis. This means that a decanter centrifuge requires a relatively large floor area for its rotor, its driving means and its gear box, the last mentioned being needed for operation of the sludge transportation device within the rotor. Decanter centrifuges having centrifugal rotors rotatable around vertical axes are also known, however, for instance through U.S. Pat. No. 2,862,658. The rotor of such a decanter centrifuge is journalled either at its lower end or at its upper end.
Centrifugal separators of the kinds described so far are, as mentioned before, intended above all for treatment of large flows of liquid containing relatively large amounts of particles. For this purpose they have been given a construction which does not make large rotational speeds of the centrifugal rotor possible and which, therefore, are not suitable when there are requirements of substantial cleanliness of the separated liquid.
For such requirements of substantial cleanliness of the separated liquid there are other types of centrifugal separators. These are so formed, however, that they are not suitable for treating large flows of liquid having a large content of solid particles. Thus, there are so called nozzle separators of a kind shown for instance in U.S. Pat. No. 2,321,918. The rotor of a centrifugal separator of this type normally has a set of conical separation discs in its separation chamber and a rotor body the radial extension of which is in the same order as its axial extension. The reason for this form of the rotor body is that particles being separated from a liquid in the separation chamber should be able to move by themselves, i.e. slide on the surrounding wall of the separation chamber, without assistance from separate sludge transportation means, to sludge outlet nozzles situated at the surrounding wall of the rotor and being open or intermittently openable. The surrounding wall of the separation chamber in this case is constituted mainly by two conical rotor end walls, which are united with each other along their surrounding edges. A rotor having a design like this is expensive to produce and gets by necessity a rather large diameter without for this reason being usable for treatment of large amounts of sludge.
There are also centrifugal separators the centrifugal rotors of which in addition to conical separation discs in the separation chamber have equipment for intermittent discharge of particles from the separation chamber through separate openings or a slot extending all around the rotational axis of the rotor. The rotors for centrifugal separators of this kind are even more expensive to produce than rotors for nozzle separators and are even less suitable for freeing of liquids from large amounts of particles suspended therein. One example of a centrifugal separator of the last mentioned type is shown in U.S. Pat. No. 4,698,053.
SUMMARY OF THE INVENTION
The purpose of the present invention is to accomplish a construction for a centrifugal separator, which makes possible a design for the centrifugal rotor such that it gets a large separation efficiency, can be subjected to a large rotational speed, i.e. a large centrifugal force, and can be used for treatment of liquids containing small as well as large amounts of particles. The construction also should be such that the centrifugal rotor becomes relatively cheap to produce.
According to the invention this object can be achieved by means of a centrifugal separator which has a rotor having a center axis around which it is rotatable, the rotor comprising two axially spaced end walls and a surrounding wall arranged axially between the end walls and surrounding together therewith a separation chamber, the axial extension of which is substantially larger than the radial extension thereof, the end walls being adapted to be subjected to axially directed forces as a consequence of centrifugally generated pressure of liquid in the separation chamber, which forces strive to push the end walls away from each other; inlet means forming an inlet for introducing said liquid and particles suspended therein into the separation chamber; separation discs arranged in the separation chamber for creating small separation distances for the particles to be separated from the liquid; first outlet means forming a first outlet for discharging liquid having been freed from particles; second outlet means forming a second outlet for discharging particles having been separated from the liquid; transportation means comprising at least one transportation member which is situated within the separation chamber and is rotatable relative to the rotor, while this is rotating, for the transportation of separated particles axially in the separation chamber; transmission means for driving of the transportation means; and a central member extending between said end walls through the separation chamber and being dimensioned and connected with the two end walls in a way such that it will take up a substantial part of the forces acting axially on the end walls during the operation of the rotor.
In a centrifugal separator of this kind the centrifugal rotor may be given an axial extension which is large in relation to the diameter of the rotor, since separate transportation means is arranged for axial transportation of solid particles separated from the liquid. As a consequence of the force transferring connection between the rotor end walls and the central member the surrounding wall of the rotor need not transfer large axial forces caused by the pressure against the rotor end walls of the liquid present in the separation chamber during the operation of the centrifuga
Hällgren Ingvar
Martin Hans
Nyström Berndt
Alfa Laval AB
Cooley Charles E.
Fish & Richardson P.C.
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