Imperforate bowl: centrifugal separators – Rotatable bowl – Including means for imparting other movement to bowl in...
Reexamination Certificate
2000-03-02
2001-06-19
Cooley, Charles E. (Department: 1723)
Imperforate bowl: centrifugal separators
Rotatable bowl
Including means for imparting other movement to bowl in...
C494S056000, C494S076000
Reexamination Certificate
active
06248053
ABSTRACT:
BACKGROUND
The present invention relates to a device for discontinuous separation of solid particles from a liquid by centrifugal sedimentation thereof, comprising a vessel rotatable about a vertical axis, said vessel having an inlet for the liquid which is to be separated, a separation zone with sedimentation surface elements, upper and lower collection chambers communicating with the separation zone, an outlet for liquid which has been freed of particles in the separation zone, and an outlet which can be opened and closed, for particle sediment collected on the sedimentation surface elements. Centrifugal separators are used for among other things:
separation and extraction of yeast, starch, kaolin and the like
separation of oil, grease and the like from a liquid mixture
purification and clarification of high value liquids such as beer, wine, oils etc
purification of waste flows.
One method of making separation more effective is to increase the area of the separation surface elements and reduce the liquid depth as much as possible, which can be done by various methods. The most common method is to provide the rotor rotating about a vertical axis with conical plates provided with so-called staples, i.e. spacer elements, which guarantee a predetermined relatively small spacing between the plates, thus shortening the sedimentation distance.
Such centrifugal separators are, however, expensive to manufacture, since strict safety standards are required to prevent breakdowns which can be violent due to the large amounts of energy stored in the high-speed rotors, which generate thousands of g's. Furthermore, they consume great amounts of energy during operation. A risk of turbulent flow and breaking apart of particles is present at the inlet when the liquid is to be accelerated. Also in the gaps between the surface multiplying separation plates there is a risk of turbulent flow, which decreases the quality of separation. Emptying of sediment at the high rotational speeds disturbs the separation, and emptying is often incomplete. The emptying of sediment also uses great amounts of energy and there is the risk of clogging. Finally, the sediment can be damaged during emptying.
A major purpose of the present invention is to suggest a centrifugal separation device which eliminates in any case most of the above mentioned deficiencies in known centrifugal separators and which can fulfill the following requirements of efficient separation of both process and waste flows:
should be able to separate small solid particles with a density close to the continuous liquid phase at moderate speeds, i.e. g-numbers below 100
lower investment requirements than for current centrifuges with similar capacity
lower energy requirements than for present machines with similar capacity
must be reliable and not cause stoppages due to clogging for example, i.e. must have a high accessibility
should be compact and simple to install
the sediment should have high dry substance ratio
should be able to withstand relatively aggressive liquids
should be able to be pasteurized at temperatures slightly below 100° C.
should be able to be washed without dismantling.
Thus, a separator is sought which has the ordered laminar flow of the static separator and which, in combination with a reasonable g-number, provides a greater separation capacity at a more efficient smaller installation volume.
SUMMARY
In order to achieve this, the device described by way of introduction is characterized according to the invention in that the sedimentation surface elements are formed by a plurality of adjacent tubular elements which are oriented axially and arranged to form a ring about the center axis of the rotatable vessel and which are open at both ends. By thus arranging a very large number of axially directed tubes in the separation chamber, which have a relatively small diameter and wall thickness, a very large separation area can be obtained at the same time as an essentially laminar flow is assured through the flow channels in the tubes, where the sedimentation distance to the tube wall is short, which means that the sediment will precipitate efficiently on the walls even at a relatively reasonable rpm (g-number).
U.S. Pat. No. 3,695,509 reveals as previously known a centrifugal separator device, the separation zone of which—similar to that according to the present invention—is formed by a plurality of adjacent tube elements oriented axially and in annular formation but there is here a substantial principal difference both in the separation processes and in the structures of the devices. The device according to U.S. Pat. No. 3,695,509 is a device for continuous centrifugal separation of mixtures of liquids containing a heavy and a relatively light liquid phase, for example an emulsion of oil and water or the like, and—in accordance with FIG.
2
—the liquid phases are separated by conducting the liquid mixture into an upper collection chamber, whereafter the mixture is allowed to flow through tubular channels under a high g-number of about 900-1250, so that the heavier liquid phase (e.g. water) during its transport through the tubes ends up radially outermost therein, while the lighter liquid phase (e.g. drops of oil) are pressed radially inwards. The liquid phases separated in the tubular channels are then removed continuously from the separator at different radial distances from the center axis of the rotating container.
The process and the device according to the present invention, however, deal with separating from a liquid relatively difficultly separated particles, such as solid particles, with a density close to that of a liquid, by sedimentation of the particles in a separation zone with the aid of moderate centrifugal forces. The process according to the present invention is thus a discontinuous separation process, where the separated particles are to be collected and precipitated on the tube channel walls in the separation zone, while the liquid (the effluent) which is freed from particles will flow out of the separator. When the particle concentration in the effluent begins to increase and exceeds a predetermined value as a result of clogging of the tube channels with precipitated particle sediment, the inflow of the liquid particle mixture and the rotation of the container is halted to remove the sediment from the tube walls by gravity, with or without rinsing, and thereafter emptying the sediment via a separate openable sludge outlet. The separator according to U.S. Pat. No. 3,695,509 (
FIG. 2
) is not intended for and is in no way suitable for separation of particles by sedimentation thereof in the tubular channel walls shown. There is no emptying and outlet arrangement which would function for the present process. Furthermore, the high g-numbers (rpm) at which the known device operates would create excessively high compression and break-up of the particle sediment.
Suitably, the tube elements in the device according to the present invention are made of plastic, such as polypropylene or the like. Thus, the entire set of particle separating separation surface elements can be made extremely inexpensively and easily, since in principle tubular elements of simple, inexpensive suction tube type can be used in an efficient manner.
Alternatively, it is possible within the scope of the invention to replace the tubular elements with a body of rotation, where the separation surface elements are formed by the walls of a plurality of adjacent, axially oriented channels or holes in the body of rotation, which are open at both their ends.
The invention also relates to a process for discontinuous separation of solid particles from a liquid by centrifugal sedimentation thereof in which a liquid-particle mixture, which is to be separated, is conducted into an inlet chamber of a rotating separator container, where the liquid-particle mixture is caused to rotate together with the container. The particular characteristic of the process is that the liquid mixture is thereafter caused to flow with essentially laminar flow through a plural
Ehnstrom Lars
Lee Hyosong
Burns Doane Swecker & Mathis L.L.P.
Cooley Charles E.
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