Liquid purification or separation – Processes – Separating
Reexamination Certificate
1998-07-13
2001-11-06
Reifsnyder, David A. (Department: 1723)
Liquid purification or separation
Processes
Separating
C210S360100, C210S377000, C210S378000, C210S380100, C494S037000, C494S044000, C494S056000, C494S080000, C095S269000
Reexamination Certificate
active
06312610
ABSTRACT:
BACKGROUND—FIELD OF INVENTION
The field of the invention is the “imperforate bowl,” related to prior art under “fluid separation”—“tubal centrifuges,” “nozzle centrifuges,” and “decanting centrifuges.”
BACKGROUND—DESCRIPTION OF PRIOR ART
Prior art contains three predominant methods for removing and separating, also called “transporting,” the heavy particles thrown outwards by centrifugal force from a column of fluid or gas being spun within centrifugal separation devices. Each of these three transport methods is historically tied to particular types or classes of centrifugal devices, notably, tubal centrifuges, decanting centrifuges and cone centrifuges (cone type devices include Split Cone, Stacked Cone and Nozzle centrifuges).
Tubal Centrifuges include devices used in medicine and in pharmaceutical production, as well as ultra centrifuges, found notably in U.S. Patent classes 494 and 210. This type of centrifuge includes numerous variations on the single theme of a long solid core tube placed within a larger cylinder. Fluid enters one end of the device and flows longitudinally to opposite end, passing through the fluid work area, an elongated torroidal space formed between the core and the outer wall. During the duration of its passage through this elongated fluid work area, said fluid is spun, usually at high revolutions per minute, producing centrifugal forces as great as 10,000 gravities.
Heavier materials in the fluid, which is simultaneously moving lengthwise down the device and also rotating centrifugally, are thrown to the outside of the moving fluid column and impact the outer wall. Up to this point the device is separating materials in the fluid by their weight or density, but not yet transporting the heavy materials away. To do the transport work, most tubal centrifuges rely on manual or semi-automated material removal. This is done by draining the device, stopping its spin, and then mechanically scraping the impacted heavy particles from the outer wall.
Because nearly all tubal centrifuges are physically small and designed for processing low volumes of materials, they can attain comparatively high rates of spin and can thus create a comparatively large weight differential between materials of even quite similar densities. This large differential means that tubal devices can remove extremely small particles (down to one half micron or smaller) from a fluid flow.
Because of material bursting strength limitations at the required very high revolutions per minute (RPM's), however, tubal centrifuges are not expected to separate large volumes of fluid; and, because of their batch operating mode (they must be shut down to transport the heavy materials away from the device), they are also not satisfactory for continuous operation applications. The chief advantage of tubal centrifuges is their capacity for high spin speed, albeit with only small volumes, and their shape, long and narrow, which permits fluid to be held under gravitational spin for the entire length of travel down a device. Their shape permits what is thus called long “residence time” (the comparatively long time that the fluid is “in residence” inside the device and thus being acted on by centrifugal force).
Decanting centrifuges are a workhorse of high volume applications such as wastewater treatment and oil platform fluid recycling. Like Tubal centrifuges, decanters are long and narrow, again offering the advantage of long residence time. The transport method used in decanting centrifuges, however, means that unlike tubal devices, decanters can provide continuous operation, at least for periods of time.
The transport solution in such devices is to use a tight-fitting helical screw fitted against the inside of the outer wall, which scrapes out heavy materials being thrown and held against that outer wall. Among the numerous examples of decanting centrifuge prior art, including decades of improvement patents for various forms of multi-speed transmissions, wear-surface improvements and the like, are: U.S. Pat. Nos. 3,937,317, 3,960,318, 3,967,778, 3,977,515, 4,070,290, 4,251,023, 4,298,162, 4,379,976, 4,381,849, 4,504,262, 4,519,496, 4,581,896, 4,978,331, 5,197,939, 5,374,234, 5,380,434, 5,397,471 and 5,429,581. The foregoing is a representative, but by no means exhaustive, list of such prior work.
While the mechanical screw or conveyor transport system affords decanting centrifuges the advantage of continuous operation, such a system also brings with it complex problems, including the need for a complex multi-speed transmission to permit the outer cylinder to rotate at a slightly different speed from the scraper screw, as well as extremely high energy use, scraper friction and noise. The latter problems result in frequent downtime and maintenance cycles. Some decanting centrifuges are quite large, such that their main advantage is to combine both relatively high processing volumes and continuous transport (in between breakdowns or maintenance shutdowns).
In addition to the noise, vibration, high wear and energy use and high maintenance costs of decanting centrifuges, however, is another limitation, which is the upper limit of their commercial gravity production capacity, which lies between 2,500 and 3,500 gravities and which is thus insufficient to create the density differential required between materials of similar weights, required for the removal of particles smaller than about five microns from a fluid mix.
In theory, increasing the rotational speed of a decanting centrifuge could create gravities in the 5,000 to 8,000 range. However this gravity increase would enormously increase the weight of the heavy particles needing to be laboriously scraped along the entire length of the spinning decanter outer wall, such that the torsional strength of the screw conveyor would quickly be exceeded. And, even if a practical, torsionally stronger screw conveyor could be designed, the far heavier spun weight of the materials being thrown to the outer wall of such a device would unacceptably increase already high noise, energy use, wear and maintenance factors.
Cone Centrifuges. The third class of centrifuges approaches high volume in continuous operation in a more design-elegant way, through the use of the pure geometry in the form of the shape of the device's outer walls, in order to effect transport of the thrown, heavy materials. These devices are variously called Stacked Cone, Split Cone and Nozzle centrifuges, depending on the details of their inner core and of their heavy particle collection and ejection mechanisms. From within the large field of prior art for these centrifugal devices, notable are U.S. Pat. Nos. 4,005,817, 4,015,773, 4,067, 494, 4,103,822, 4,311,270, 4,343,431, 4,375,870, 4,505,697, 4,629,564, 4,643,709, 4,698,053, 4,701,158, 4,710,159, 4,721,505, 4,729,759, 4,759,744, 4,813,923, 4,820,256, 4,840,612, 4,861,329, 5,045,049, 5,052,996, 5,202,024, and 5,362,292. Again, the preceding list is not intended to be exhaustive, but rather illustrative of the cone centrifuge approach and some of the many attempts by numerous inventors and manufacturers to improve it over the years.
The key to the transport solution in all these cone centrifuge variants is their use of sloped surfaces which lead outwards in the direction of spin, at or greater than the 37 degree angle of repose, and which thus guide heavy materials thrown from the fluid in the device core to fall and slide gravitationally “downhill” into an outward bulging, annular or beltline valley. Such a valley uses slope shape and gravity alone to receive the heavy particles and then to guide them to ejection at the apex of said valley, either through nozzles or via the rhythmic opening and closing of the top and bottom conical outer shells which form the valley. For illustrations of this classical industry “collector valley approach,” see the examples in
FIG. 24
, Drawings Section, which reprint the
FIG. 1
, respectively, from U.S. Pat. Nos. 3,986,663 (1976), 4,430,071 (1984), 4,861,329 (1989) and 5,052,996 (1991).
Most of these devices
Fuller Berkeley F.
Kirker Curtis
Phase Inc.
Reifsnyder David A.
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