Liquid purification or separation – Processes – Separating
Reexamination Certificate
1999-05-13
2001-05-29
Reifsnyder, David A. (Department: 1723)
Liquid purification or separation
Processes
Separating
C210S512100, C210S512200, C209S715000, C209S717000, C209S719000, C209S720000, C209S722000, C209S723000, C209S725000, C209S728000, C209S729000, C209S733000, C209S734000, C209S720000, C055S459100, C055S459200, C055S459300, C055S459400, C055S459500
Reexamination Certificate
active
06238579
ABSTRACT:
BACKGROUND
1. Field of Invention
This invention relates to devices that are used to separate solid materials having some differing physical characteristic, e.g., density, especially to those devices which separate respective different divided solids having some corresponding different physical characteristic when suspended in a transporting fluid under the influence of centrifugal force disposed within a containment (a vortex body) transporting the fluid between inlet(s) and outlet(s).
2. Description of Prior Art
Numerous methods have been employed for separating divided solids suspended in moving fluids (fluid streams). Many methods take advantage of the hydrostatic forces acting on buoyant solids when placed in a liquid medium. This “buoyant” force can be imparted by natal gravitational force or by centrifugal force. In general, the methods that employ centrifugal force have higher throughput rates and/or perform more accurate separations than those that rely on gravity alone.
Some devices that separate solids by the use of centrifugal force use motors or other physical means of supplying energy to impart a centrifugal motion to the fluid. Devices of this sort have traditionally been referred to as “centrifuges”, a typical example of which is described by Brandrup et al. These devices are, in general, effective at separating solids, however they usually have many moving parts, and therefore are subject to mechanical failure and require routine maintenance. They are also usually difficult to manufacture and therefore expensive.
Many devices that separate solids by the use of centrifugal force consist of a stationary cylindrical or conical body into which a moving slurry of a liquid medium having divided solids (solid particles) suspended therein is admitted or introduced. The moving slurry may be brought in to a separating (vortex) body through a fluid entrance or inlet from a container at a higher elevation, taking advantage of the pressure ‘head’ or be introduced from a source driven by a pump.
The fluid inlet may be oriented tangentially to the vortex axis of the separator body, so the momentum of the inlet fluid imparts or adds to a rotational flow to the rotating fluid contained in the device The oldest and most traditional of these devices is called a hydrocyclone. The first hydrocyclone was described by U.S. Pat. No. 453,105 to Bretney. Although the hydrocyclone was originally patented for the use of removing water from dense solids (“dewatering’), the fundamental shape of the device has stayed the same. Hydrocyclones were first applied to the separation of solids in the field of “coal benefaction”, and one of the first patents for this application was awarded by U.K. Patent 528,590 to the Directie van de Staatsmijnen.
Hydrocyclones have high throughput rates, require very little maintenance, and are inexpensive to construct and operate. However, they do not effectively separate solids that have small differences in density. This is due to the fact that a substantial amount of turbulence is generated inside the hydrocyclone. This turbulence is primarily due to the fact that the two exit ports are at different (opposing) ends of the device.
To understand why exit ports at different ends of the device negatively affect the separation, it is useful to analyze the flow inside a device in terms of its directional components. Using the parlance of cylindrical coordinate systems, these components are angular (or “rotational”), radial, and axial with respect to an axis defining the circulating fluid (the vortex). The centrifugal forces that separate particles from each other are imparted by the rotational component of the flow field, but the other components of flow, the radial and axial, tend to disrupt the separating effects of the rotational flow. Devices that have the two outlet ports at different ends of the device generate excessive radial and axial flows that disrupt the separating effects imparted by the rotational component of the flow.
Numerous other variations of the hydrocyclone have been invented. For example, U.S. Pat. No. 3,802,570 to Dehne claims a novel exit port and U.S. Pat. No. 4,838,434 to Miller et al claims an air-sparged hydrocyclone. (An “air-sparged” hydrocyclone is one with a fritted porous wall through which compressed air is injected. The air typically aids in separating “fines” from coarse particles or hydrophobic particles form hydrophilic particles.) However, all of the hydrocyclone variations still incorporate exit ports that are on opposite ends of the device.
Other devices have been used for separating particles in a liquid medium. One of the more useful is referred to as the “Dyna-Whirlpool” separator, described by Goldberger and Robbins (1984). This device is predominantly cylindrical and has both an entrance port and an exit port at both ends of the device. A liquid feed enters at one end and a slurry feed at the other. The separated particles exit from tangential and axial ports at opposite ends of the device. This device is similar in principal to a hydrocyclone but is more complicated to operate because two streams need to be supplied to the unit, and therefore two pumps need to be employed.
There are a few patents that describe devices having both outlet ports on the same end. A first is U.K. Patent 537,771 by Alexander in 1940 “Improvements in Centrifugal Separators for Extracting Solids from Liquids” (the Alexander patent). Alexander distinguishes his improved centrifugal separator (
FIGS. 1-6
) from the then existing prior art separator devices which have fluid inlet (‘admission’) and fluid outlet (‘discharge’) at the same one end of the ‘vortex’ chamber. In column 1 lines 48-57 he describes the improved separator as having:
“the inlet (reference number
7
in the Figures) is at or near the circumference at one end and the outlet (reference number
4
) is of less diameter and centrally situated, or nearly so, at the other end of the vortex. The said inlet being of single or multiple tangential type, or vaned or vaneless type, and the said outlet being of plan circular or annular section and the flow in which is in a direction away from the inlet”
Alexander thus shows and describes one or more inlets
7
at one end of the “vortex” separating chamber and a single fluid outlet
4
at the other. The inlets
7
are shown having inlet steam(s) directed along various orientations with respect to the vortex axis; e.g., tangential to the chamber outer circumference and perpendicular, oblique or askew to the vortex axis, or parallel to or coaxial with the vortex axis.
Alexander also shows a closed “receptacle or hopper”
8
situated in spaced apart relationship to the inlet(s) in
FIGS. 1
,
4
,
5
, and
6
. The ‘hopper’
8
is described as positioned so that it “receives the extracted comparatively dense material.” (columns 3, line 33, 34). The hopper
8
is shown variously as parallel to the outlet axis or coaxial therewith at the same end of the ‘vortex chamber’ as the outlet. Alternatively the hopper is shown at right angles to the chamber vortex axis and also perpendicular to either or both the inlet and outlet.
Alexander's claim 1 refers to “an admission passage or passages for admitting the liquid with a tangential component of motion to the vortical chamber” and “another passage or passages—through which the said extracted material is transferred to the receptacle;” (column 4, lines 118-124).
Thus it is clear that Alexander's device is restricted to separators with a single fluid outlet that provides a single outlet stream. Also the separators of Alexander's patent are not restricted to having tangential inlets, but include inward projecting inclined vanes for producing ‘vortical’ separator flow.
Alexander's devices, it is clear, were designed and patented specifically for the application of removing solids from a single liquid stream (i.e. “dewatering”) and depositing them in a fixed, closed receptacle while directing the liquid to be discharged at a single exit or port.
Alexander's devices would not facili
Allen Laurence E.
Heald Larry G.
Paxton Blaine K.
Fish & Richardson P.C.
MBA Polymers, Inc.
Reifsnyder David A.
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