Imperforate bowl: centrifugal separators – With means for furnishing auxiliary fluid to material or... – Liquid
Reexamination Certificate
2000-03-29
2001-11-20
Cooley, Charles E. (Department: 1723)
Imperforate bowl: centrifugal separators
With means for furnishing auxiliary fluid to material or...
Liquid
C494S037000, C494S070000
Reexamination Certificate
active
06319186
ABSTRACT:
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,311,270 describes a centrifugal separator intended for dividing a solids containing liquid mixture into one liquid phase, which is substantially free of solids and has a relatively low viscosity, and one concentrate phase, which is rich in solids and has a relatively high viscosity. The centrifugal separator comprises a rotor, which is rotatable around a central rotational axis and which has an inlet for said mixture, an outlet for said liquid phase and an outlet for said concentrate phase. Characteristic of the centrifugal separator according to U.S. Pat. No. 4,311,270 is that its rotor has in its outlet for the concentrate phase a vortex device, which has the property that it can maintain the viscosity substantially constant of the concentrate phase flowing therethrough and out of the rotor. Thus, if the viscosity of the outflowing concentrate phase tends to increase, the vortex device automatically lets out a larger flow of the concentrate phase, and if the viscosity tends to decrease, a smaller flow of the concentrate phase is let out of the rotor. Thereby, the vortex device can be formed in a way such that a desired viscosity is always obtained of the concentrate phase separated in and leaving the rotor.
One embodiment of the centrifugal separator according to U.S. Pat. No. 4,311,270, which has been used in practice, is the one shown in FIG. 3 of said U.S. Pat. No. 4,311,270. This is used for instance for separation of yeast. In a centrifugal separator of this kind the radially outermost part of the rotor separation chamber, the so-called concentrate space, where separated yeast is accumulated during operation of the rotor, constantly communicates with a central chamber in the rotor, the so-called concentrate chamber, from where the yeast is discharged out of the rotor through a so-called paring member. At least one so-called concentrate tube connects the concentrate space with the concentrate chamber and at the radially innermost part of the concentrate tube a vortex device of the previously described kind is placed, so that the yeast may pass therethrough before entering the concentrate chamber.
A problem which has been noticed in connection with a centrifugal separator of this kind is that parts of the rotor and certain process conduits outside the rotor downstream thereof have not been sufficiently clean upon a conventionally performed cleaning of the centrifugal separator during rotation of the rotor. During a cleaning of this kind cleaning liquid is continuously supplied through the rotor inlet for mixture to be treated within the rotor, the cleaning liquid being discharged from the rotor through the ordinary rotor outlets for separated liquid phase and separated concentrate phase, respectively. The problem having been noticed is concerned with the flow paths for separated concentrate phase, which have not been cleaned to a desired extent neither within the rotor nor downstream thereof.
The reason for the problem is that said vortex device has the property—which is desirable during normal separation but not in connection with cleaning of the centrifugal separator—that it reduces a through flow of liquid if the viscosity of the liquid decreases. Since cleaning liquid has a substantially lower viscosity than the concentrate phase normally passing through the vortex device, the resulting flow of cleaning liquid in the flow paths for the concentrate phase becomes undesirably low, which leads to an insufficient cleaning of these flow paths. It has been noticed in some cases that the flow of cleaning liquid through the relevant flow paths has only been about 30% of the normal flow of concentrate phase during separation.
The problem here concerned does not arise, of course, only in connection with the embodiment of a centrifugal separator as discussed above. In any centrifugal separator, the rotor of which has a vortex device of one kind or another placed in the flow path for a liquid concentrate phase between a so-called concentrate space and a so-called concentrate chamber, the problem will arise, thus, also for instance in a rotor provided with a vortex device of the kind which can be seen from DE 36 13 335 C1 or DE 36 35 059 C1.
SUMMARY OF THE INVENTION
The object of the present invention is to resolve the problem of insufficient cleaning of a centrifugal separator intended for division of a liquid mixture containing solids into one liquid phase, which is substantially free of solids and has a relatively low viscosity, and one concentrate phase, which is rich in solids and has a relatively high viscosity and a larger density than the liquid phase, which centrifugal separator comprises a rotor, which is rotatable around a central rotational axis and has an inlet for said mixture, an outlet for said liquid phase and an outlet for said concentrate phase, and in which centrifugal separator
the rotor delimits a process liquid space comprising at least one separation chamber, which has a liquid space for separated liquid phase and a concentrate space for separated concentrate phase, a liquid outlet chamber, which communicates with said liquid space, and a concentrate outlet chamber, which through at least one concentrate passage communicates with said concentrate space,
said concentrate passage extends through a vortex device which is adapted upon unchanged pressure drop across the same to admit a larger through flow of concentrate phase having a relatively high viscosity than of concentrate phase having a relatively low viscosity, and
a concentrate outlet member, which is adapted not to rotate together with the rotor, extends into the concentrate outlet chamber for discharge of separated concentrate phase from the rotor.
The object of the present invention can be achieved in that
cleaning liquid is introduced into the rotor to a part of said process liquid space of the rotor other than said concentrate outlet chamber,
the cleaning liquid is transferred from said other part of the process liquid space of the rotor to the concentrate outlet chamber a way other than through said vortex device, and
the cleaning liquid is removed from the concentrate outlet chamber and is discharged out of the rotor through said concentrate outlet member.
In this way cleaning liquid in a sufficient amount per unit of time may be supplied to the concentrate outlet chamber and from there be pumped further out through the concentrate outlet member to the flow paths for the concentrate phase downstream of the centrifugal separator.
If desired, cleaning liquid may be introduced into the rotor by means of a particular supply member, but preferably the normal centrifugal separator inlet for mixture to be treated in the rotor is used for this purpose.
The cleaning liquid may be transferred to the concentrate outlet chamber from said other part of the process liquid space in the rotor in different ways. For instance, a paring member or the like, which is placed centrally in the rotor and is radially movable, may be used to be moved during a cleaning operation to contact with cleaning liquid having been introduced into said other part of the rotor process liquid space. An outlet from a paring member of this kind may be adapted to conduct cleaning liquid thus pared out into the concentrate outlet chamber. Alternatively, a paring member may be used for the transfer of cleaning liquid, which is placed within the rotor but which is not radially movable, the free liquid surface of the cleaning liquid in said other part of the rotor process liquid space instead being moved radially inwardly in the rotor to a level radially inside that at which process liquid is present during normal operation of the centrifugal separator, i.e. during a separating operation.
If the free liquid surface of cleaning liquid is moved radially inwardly in the way just mentioned, it is not sure that a paring member need to be used for the transfer of cleaning liquid to the concentrate outlet chamber. Instead, with advantage, a transferring passage may be formed in the rotor itself, adapted t
Alfa Laval AB
Cooley Charles E.
Fish & Richardson P.C.
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