Liquid purification or separation – Filter – Movable medium
Reexamination Certificate
2000-05-26
2002-01-08
Reifsnyder, David A. (Department: 1723)
Liquid purification or separation
Filter
Movable medium
C210S402000, C210S406000, C210S416100
Reexamination Certificate
active
06336561
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally directed to rotary drum filters, and more specifically, to disposable rotary drum filters for batch processing.
BACKGROUND OF THE INVENTION
In the pharmaceutical, fine chemical, hazardous material, beverage, juice, wine, and beer industries, most of the production processes are inherently batch processes. Batch processing, rather than continuous flow processing, is advantageous when a limited volume of material is to be processed, when there is a need for traceable “lots” of product, and/or when the intrinsic value of the product is high. A common process step in both batch and continuous flow processing is the separation of solids from liquids.
Traditionally, solid-liquid separation for batch processing has been carried out using centrifuges, gravity filtration, vacuum filtration, and/or pressure filtration equipment. Although such equipment has been used for years, there are inherent disadvantages to its use, especially when employed in laboratory, pilot plant, or other small volume applications where time and resources are limited, and for processes in which it is critical that the materials be isolated from the outside environment.
For example, centrifuges are often relatively expensive, require significant maintenance, and are labor intensive to operate under aseptic or “clean” conditions. Other types of conventional batch type filtration equipment can also be expensive and similarly require a high degree of operator attendance. A further inherent problem with prior art batch filtration units is that the designs of small batch volume filtration units are often radically different than the designs of larger batch volume equipment, making the results of scaling up from laboratory or pilot plant volume production to industrial scale production less predictable.
An additional drawback with the use of centrifuges and other batch filtration units in the laboratory and pilot plant environments is that cleaning these units between batches requires considerable time and labor. Frequently, time and technical manpower resources in laboratory and pilot plant environments are at a premium, and such cleaning operations can become an unacceptable bottleneck. These cleaning operations also introduce an element of risk, both in terms of exposing personnel to potentially hazardous materials, and in terms of introducing contaminates into the processing equipment that may degrade the quality of, or even completely ruin, the next batch to be processed.
Thus, it would be desirable to provide efficient means to separate solids and liquids that is usable in batch processing, and which does not require time consuming cleaning procedures between processing batches. To eliminate the requirement for cleaning, it would be preferable if such means were sufficiently low cost as to be disposable, so that a new unit could be used for each batch of material processed.
A common non-disposable device used for solid-liquid phase separation for continuous flow processing is the rotary drum filtration unit. In fact, the rotary drum vacuum filter is considered to be the workhorse of the chemical process industry. In this type of filter, a drum that is partially submerged in a trough of suspended solids rotates slowly at only a few revolutions per minute (RPM). Solids adhere to the outer surface of the drum, which may be coated to aid in the collection of the solids. The slow rotational speed of the drum, as well as air flow over the portion of the drum that is not submerged, help to dry the solids adhering to the drum. This solid filtrate is then removed from the rotating drum, often by a blade that scrapes the collected solids from the drum. While efficient, such units are generally quite large and expensive. Consequently, they have been used primarily in association with large-scale continuous flow processing, such as for wastewater treatment. In view of the operating efficiencies of this type of device, it would be desirable to provide a much smaller and substantially lower cost disposable filtration unit that operates according to the principles of rotary drum filtration, but which can be used for batch processing in place of the traditional centrifuges and other batch filtering units.
Preferably, such a batch filtration disposable rotary drum filter should be capable of running continuously, in a steady state fashion for a period of time sufficient to process a batch of product, enabling the device to be very small as compared to conventional types of batch equipment that would normally be employed to handle the same amount of material. It would also be desirable to provide a unit that is enclosed, to minimize the risk of product and personnel contamination. It would further be desirable to fabricate such a unit from inexpensive plastic materials that can be sterilized if a process requires that sterile equipment be used. Disposability offers the advantages of eliminating clean up, containing any hazardous materials used within the disposed device, reducing the chances of product contamination, and enhancing reliability and reproducibility.
Typical conventional rotary drum filters do not provide these desirable features. Prior art rotary drum filters are relatively complicated mechanical constructions and not readily adaptable to be mass produced in quantity and at low cost for use as a disposable unit. Specifically, prior art rotary drum filters often include complicated float valves to control the level of slurry in the trough in which the drum rotates, as well as complicated valves to control pressure in the system to ensure the proper flow of fluid into the filter unit. Because of the relatively large size of prior art rotary drum filters, and the fact that such units are designed to have very substantial service lives, such units have often incorporated relatively expensive bearing and seal components. In contrast, it would be desirable to provide a disposable rotary drum filter that replaces these mechanically complicated float control and pressure control schemes in the prior art with control means that are similarly effective, yet much simpler, lower cost, and more appropriate for a disposable unit. It would further be desirable to provide a disposable rotary drum filter that does not require expensive bearing and seal components.
Examples of prior art designs of a typical rotary drum filter include those described in U.S. Pat. Nos. 3,794,178; 3,837,499; 4,157,301; 4,346,008; 5,055,205; 5,244,572; 5,262,069; and 5,308,488. The configurations shown in these patents typically were created to optimize high production rates, to provide long service life, and with minimal concern about product loss due to retention of the product in the filters. While plastic and fiberglass have been used in the design of rotary drum filters (see U.S. Pat. Nos. 3,894,899; 4,419,165; and 4,515,693) to enable the processing of corrosive products, such rotary drum filters are not suitable for use in a single batch process as a disposable unit.
It would be therefore desirable to provide a rotary drum filter unit designed to process a batch of material, and then be replaced with a new unit for the next batch. Preferably, such a rotary drum filter would be engineered such that its fabrication costs are low and its operation is very simple. It would be desirable to provide a rotary drum filter made from plastic and encased in a plastic housing. Preferably, the unit should be relatively small, especially as compared with traditional rotary drum filters, and made from relatively inexpensive materials, such that it is practical for a single-use, and can be economically considered a disposable unit.
A desirable feature of such a single-use device would be the elimination of traditional seals and other isolation mechanisms. To further simplify the disposable unit, it would be desirable to eliminate internal prime movers and to instead rotate the inner drum using an external prime mover that is not part of the disposable component. In addition, seals associated with a drive
Delys Jeff F.
Kossik John Michael
LandOfFree
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