Imperforate bowl: centrifugal separators – Rotatable bowl – Including driven material-moving means therein
Reexamination Certificate
2000-11-22
2003-03-25
Cooley, Charles E. (Department: 1723)
Imperforate bowl: centrifugal separators
Rotatable bowl
Including driven material-moving means therein
C494S064000, C494S070000, C494S084000
Reexamination Certificate
active
06537191
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a centrifugal separator for separation of solids from a liquid mixture, in which particles of this kind are suspended in a liquid having a density smaller than that of the particles. Particularly, the invention concerns a so-called decanter centrifuge, which includes a rotor having a center axis around which it is rotatable at a first speed, a screw conveyor, which is arranged in the rotor and is rotatable around said center axis at a second speed differing from said first speed, and a driving device adapted for rotation of the rotor at said first speed and the screw conveyor at said second speed.
BACKGROUND OF THE INVENTION
Decanter centrifuges of this kind are used in many different applications, especially where the mixture to be treated has a relatively large content of solids. Decanter centrifuges are used also in applications where the particles to be separated have a greatly varying size and/or where the content of particles in the mixture varies greatly. Furthermore, it is common to use decanter centrifuges in applications where relatively large volumes of liquid are treated, which means that decanter centrifuges as a rule are relatively large, so that they may give a satisfactory separation result despite large flows per unit of time of a supplied mixture.
Irrespective of the amount of mixture supplied per unit of time it is a desire for each centrifugal separator, independent of type, that it should provide a satisfactory separation result independently of whether the supplied liquid mixture has a relatively large or a relatively small content of solids. Thus, it is desirable that a centrifugal separator dimensioned for a certain through flow of liquid to be treated may be used under different conditions, i.e. both in conditions where the content of solids is large and under conditions where the content of solids is small. If the centrifugal separator has to be modified in order to give a satisfactory separation result in one condition or another, it should have a construction making such a modification possible in an inexpensive and simple way.
This is a problem with previously known decanter centrifuges, i.e. they have a construction which does not make a simple and inexpensive modification possible so the centrifuge becomes efficient, i.e. gives a satisfactory separation result, under different conditions.
It has become a consequence of this problem that, instead of decanter centrifuges, centrifugal separators of other kinds have been used under conditions where the mixture to be treated has had a relatively small flow per unit of time and an although relatively small but still not insignificant content of solids. Then, in certain cases, it has been possible to use so-called nozzle separators, but if the content of particles in the mixture, or the size of the particles, has varied heavily, nozzle separators have not been suitable. Instead, for this kind of separation cases, it has been necessary to use centrifugal separators, which are adapted for intermittent discharge of separated particles. However, other problems have then arisen, since centrifugal separators of this kind have a very limited ability to discharge separated solids during operation. Thus, it has either been necessary to perform sludge discharge operations at a very large frequency during the operation of the centrifugal separator, which has made an effective separation difficult, or it has been necessary to reduce the amount of mixture supplied to the centrifugal separator per unit of time, which has rendered the capacity of the centrifugal separator to be much too small. In both cases it has often been necessary to overdimension the centrifugal separator to obtain an acceptable separation efficiency, i.e. a satisfactory separation result, or an acceptable separation capacity.
In other connections, where a liquid to be treated has had a relatively large flow per unit of time and a relatively small content of solids, decanter centrifuges have been used, since use of centrifugal separators of a different kind has not been possible from a cost point of view. In these cases it has been necessary, however, to overdimension the decanter centrifuges so that they would give a desired separation result. Thus, it has not been possible to design a decanter centrifuge in an optimum way for treatment of a mixture having a relatively small content of solids.
Based on the foregoing, it is the general object of the present invention to provide a design or construction for decanter centrifuges which overcomes the problems and drawbacks of the prior art.
A primary object of the present invention is to provide a design or construction for decanter centrifuges, which is of a kind such that a decanter centrifuge relatively simply and inexpensively may be adapted for operation in connections where the mixture to be treated has a large content of solids as well as in connections where this content is small, so that a desired separation result is achieved.
Another object of the invention is that the design in question should make possible production of decanter centrifuges at a low cost.
SUMMARY OF THE INVENTION
The above defined objects may be obtained according to the invention by a design for a centrifugal separator of the initially defined kind, which is characterised by the combination that
the rotor is rotatably supported only at its one end through a rotor shaft, which is arranged such that the center axis of the rotor extends substantially vertically,
the rotor has an inlet for said mixture in the form of at least one inlet channel, which extends into the rotor at its said one end, a liquid outlet for separated liquid in the form of at least one outlet channel, which extends out of the rotor at its said one end, and a sludge outlet for separated solids situated at the opposite other end of the rotor,
the rotor includes a conical portion, at the apex of which the said sludge outlet is situated,
the screw conveyor is formed for transportation of the separated solids through said conical portion of the rotor towards the sludge outlet, and
the screw conveyor has or is connected with a conveyor shaft, which extends axially through the rotor shaft and is coupled to said driving device.
Thanks to this combination according to the invention said sludge outlet may be positioned at any desired distance from the rotor center axis all the way into this center axis.
A first advantage of the present invention is that it makes possible a dimensioning of a decanter centrifuge outgoing from the amount of solids to be discharged through the sludge outlet per unit of time. This means that a decanter centrifuge according to the invention, which is intended for a certain flow per unit of time of the mixture to be treated, may be given a desired separation ability without being overdimensioned, independently of the content of solids of the mixture.
A second advantage of the invention is that the sludge outlet of the rotor may be moved by simple means towards or away from the rotor center axis for adaptation of the decanter centrifuge to different needs or in connection with investigations for determination of the most suitable location of the sludge outlet in a special separation case.
A third advantage of the invention is that is suitable for relatively small decanter centrifuges, i.e. decanter centrifuges which may be used for treatment of liquid mixtures having a relatively small flow per unit of time. In small decanter centrifuges of this kind the sludge outlet may be formed as a very small opening at the apex of the conical rotor portion, i.e. at the innermost part of it at the rotor center axis, whereby the surrounding wall of the rotor may be given the smallest possible diameter. Hereby, the invention may be used in flow areas where conventional decanter centrifuges have not previously been used.
Small decanter centrifuges designed according to the invention may be produced very inexpensively, because many parts thereof may be produced for instance of plastics or light m
Ridderstråle Rolf
Stroucken Klaus
Alfa Laval AB
Cooley Charles E.
McCormick Paulding & Huber LLP
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