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Systems and methods for filtration

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Systems and methods for filtration


Systems for filtration are disclosed. A feed mixture including at least one liquid component and at least one solid component and a flow of gas may be directed to a filter element and filtrate and gas may be passed through a filter medium from a feed fluid side to a filtrate side.

Browse recent Pall Corporation patents - Port Washington, NY, US
Inventors: Toru UMEDA, Steven C. CHISOLM
USPTO Applicaton #: #20120279917 - Class: 210409 (USPTO) - 11/08/12 - Class 210 
Liquid Purification Or Separation > Filter >With Residue Removing Means Or Agitation Of Liquid >Fluid Cleaning

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The Patent Description & Claims data below is from USPTO Patent Application 20120279917, Systems and methods for filtration.

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DISCLOSURE OF THE INVENTION

The present invention relates to systems and methods for filtering mixtures of liquids and solids by passing the mixtures through porous filter media. In particular, the present invention is directed to systems and methods for filtering mixtures of liquids and solids and maintaining the permeability of the filter media. For example, systems and methods embodying the invention may be used to remove foulant materials, such as solids, deposited on or within the filter media while filtering the mixture.

In accordance with one aspect of the invention, methods of filtration comprise directing a feed mixture including at least one liquid component and at least one solid component to a filter medium, directing a flow of gas along a feed fluid side of the filter medium, and passing filtrate and at least a portion of the gas through the filter medium from the feed fluid side to the filtrate side to filter the feed mixture and remove accumulated material from the filter medium.

In accordance with another aspect of the invention, systems for filtration comprise a filter assembly including a feed inlet for introducing a liquid-solid feed mixture, a gas inlet for introducing a gas, and a filter element. The filter element may have a feed fluid side communicating with the feed and gas inlets and a filtrate side. The filter element may also include a filter medium positioned across a flow path for gas and filtrate through the filter element from the feed fluid side to the filtrate side, wherein filtrate passes through the filter medium. The gas inlet supplies a sweep of gas along at least 50% of the feed side of the filter element, at least 50% of the introduced gas passing with the filtrate through the filter medium to the filtrate side of the filter element.

Filtration systems and methods in accordance with the present invention offer many advantages. For example, systems and methods embodying the invention effectively reduce or prevent the accumulation of solids, e.g., foulants, on a filter element and prevent solids which may accumulate, e.g., a “filter cake”, from densely packing against the filter element. By directing gas along and through the filter medium as the fluid being filtered passes through the medium, systems and methods embodying the invention effectively disrupt the accumulation of solids on or within the filter medium, for example, by loosening, lifting and/or dislodging the solids material. By reducing the accumulation of solids and preventing solids from densely packing against the filter element, systems and methods embodying the invention prevent the solids from substantially altering the filtration characteristics of the element so that the desired level of filtration can be achieved. Additionally, systems and methods embodying the invention prevent an accumulation of solids which make it harder to force filtrate through the element, e.g., a densely packed filter cake, so that the fluid to be filtered more easily passes through the filter element, enhancing the performance of the filtration system. In addition, the systems and methods effectively obtain this result without damaging delicate filter media and with low levels of energy consumption. Accordingly, filtration systems and methods in accordance with the present invention may be operated for extended periods of time without fouling. Systems and methods embodying the invention may also be effectively utilized in combination with other fluid regeneration methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a filtration system.

FIG. 2 is a cross-sectional view of a filter assembly.

FIG. 3 is a plot of pressure drop through a filter versus time.

DESCRIPTION OF EMBODIMENTS

While many different filtration methods and systems may embody the invention, in one example, a feed mixture, including at least one liquid component and at least one solid component, and a gas stream are directed to flow through a filter element which includes a filter medium. The feed mixture may include any type of liquid-solid mixture and the present invention is particularly advantageous for filtering mixtures having a high solids content, e.g., slurries, such as polishing slurries, polymer toner dispersions, and metal powder dispersions. The gas stream may comprise any gas or mixture of gases compatible with the feed mixture. Exemplary gases include inert gases, such as argon and nitrogen, as well as other gases, including air and oxygen.

Using the exemplary filtration system 10 illustrated in FIG. 1 for reference, the method may include directing a feed mixture from a feed source 12 to a filter assembly 14 including one or more filter elements 16 each having a filter medium 18. The feed mixture may be directed through a feed inlet 20 of the assembly 14 and the feed mixture may flow outside-in or inside-out through each filter element 16. In the illustrated embodiment, fluid flows from the outside-in through the filter element 16. The feed mixture preferably contacts the outside, e.g., the upstream side, of the filter element 16 and filtrate preferably flows through the filter medium 18 from a feed side 22 to a filtrate side 24 along a filtrate flow path. As the filtrate flows through the filter medium 18, material, e.g., foulants, may accumulate on or within the filter medium 18.

Continuously or periodically, the gas may be directed from a gas source 26 to the filter assembly 14 through a gas inlet 28 while the feed mixture is being directed to the filter assembly 14. For example, gas may be directed to the filter assembly 14 for substantially the entire time filtration is being performed or intermittently, e.g., every 5, 10, 15, 30 or 60 minutes, twice-daily, daily, etc. The gas may be introduced in a pulsed manner, e.g., as short bursts, for longer durations or as a continuous stream.

In some embodiments, the gas may be introduced to the filter assembly along with the feed mixture, e.g., at substantially the same time as the feed mixture. The filtration system may include a valve arrangement coupled to the filter assembly to facilitate the introduction of the gas along with the feed mixture. The valve arrangement may have any suitable configuration. For example, the valve arrangement may couple a feed inlet valve and a gas inlet valve. In some embodiments, a valve arrangement may also include a controller 31, as seen in the exemplary filter assembly illustrated in FIG. 2.

The gas preferably flows and distributes along the upstream side of the filter element 16, e.g., along the upstream surface of the filter element. For example, the gas may flow along about 50% or more or about 75% or more or about 90% or more or about 99% or more of the upstream surface of the filter element 16. Higher percentages may be more advantageous. As the gas flows and distributes along the upstream side of the filter element, the gas may loosen and/or dislodge solids material adhering to the filter medium and/or inhibit the accumulation of solids material on or within the filter medium. For example, the gas may scour the surface of the filter element, lifting solids from the surface of the element and disrupting the formation of a “filter cake”. In some embodiments, the gas at the surface of the filter element may not completely prevent solids from accumulating, but may reduce the accumulation and/or may prevent any accumulated solids from densely packing against the filter element, yielding a loose, more porous filter cake. The fluid to be filtered may more readily pass through this loose, porous filter cake, increasing fluid flow and decreasing the pressure drop through the filter assembly. Thus, as the gas sweeps more of the surface of the filter element, the performance of the filter assembly may be even further enhanced.

The gas may also pass through the filter element, e.g., along a gas flow path through the filter medium 18, from the feed side 22 to the filtrate side 24. A substantial portion of the volume of gas, for example, about 50% of the volume or more or about 70% of the volume or more or about 85% of the volume or more or about 90% of the volume or more or about 95% of the volume or more or about 99% of the volume or more of the gas introduced into the filter assembly may flow from the upstream side of the filter element 16 through the filter medium 18 to the filtrate side of the element 16. Again, higher percentages may be more advantageous. The gas passing along the gas flow path through the filter medium, may more effectively lift solids from the surface of the filter element, inhibit their accumulation on or 15 within the filter element, and loosen any solids that do accumulate. Gas flowing along a gas flow path through the filter medium may achieve more intimate contact with the surface of a filter element than gas merely flowing along one side, e.g., an upstream side, of a filter element. For example, the gas passing into the filter medium may more effectively infiltrate accumulated solids at the surface of the element, lifting, dislodging, and loosening otherwise difficult to remove foulants. Additionally, as the gas flows along a gas flow path through the filter element, the gas may loosen and/or dislodge some solids material that may be trapped within the filter medium, for example, solids material intended to pass through the filter medium, but which has become lodged within the medium. Furthermore, the flow of gas both along the filter element and through the filter medium may cause the filter medium to vibrate, further facilitating the prevention of and removal of accumulated foulants. Thus, as more of the gas passes through the filter medium, the performance of the filter assembly may be even further enhanced.

The gas may be directed to flow into the filter medium 18 in any suitable manner. For example, in some embodiments, a housing 30 may fit closely around the exterior of the filter element 16, e.g., only a small gap may be present between the exterior of the filter element 16 and an interior wall of the housing 30. This small gap may help to direct the gas to flow into the filter medium 18 and along the gas flow path. In some embodiments, the gas may be directed to flow into to the filter element 16 by a gas distributor. A gas distributor may have a variety of suitable configurations. A gas distributor may comprise a pipe or tube with one or more openings that may be positioned in the filter assembly 14 to distribute gas to one or more regions of the filter element 16. The gas distributor may distribute gas only near the bottom of the filter element. Alternatively, the gas distributor may distribute gas to multiple regions of a filter element 16, such as a first region near a lower end of the element and one or more additional regions spaced upwardly from the first region. Additionally or alternatively, a gas distributor may distribute gas to multiple filter elements disposed in a filter assembly. For example, the gas distributor may distribute gas to multiple filter elements arranged in a single housing or in multiple housings. An exemplary filter assembly 14 including multiple filter elements 16a, 16b, 16c distributed in a single housing 30 and a gas distributor 32 is illustrated in FIG. 2.

In some embodiments, gas may accumulate in the filter assembly, e.g., on the feed side of the filter element 16, for example, above a gas-liquid interface. Gas above and below the gas-liquid interface may pass through the filter element as the filtrate passes through the filter element. The position of the gas-liquid interface and/or the volume of accumulated gas may be affected by a variety of factors, including for example, the inlet flow rate of the gas. Gas on the feed fluid side of the filter element may be removed from the filter assembly, for example, through a vent. The vent may allow gas to be removed continuously or intermittently. In some embodiments, it may be preferable to vent the gas only periodically to prevent an excess of gas from exiting through the vent rather than flowing through the filter medium. For many embodiments, the gas is not vented from the feed fluid side of the filter assembly.

After passing through the filter medium to the filtrate side, the filtrate and the gas may be separated from one another. The filtrate and the gas may be separated from one another prior to or after being removed from the filter assembly. For example, the filter assembly may include a filtrate chamber having a filtrate outlet, a separate gas outlet, e.g., a vent, each communicating with the filtrate side of the filter element. The two outlets may be arranged to facilitate the removal of gas through the vent and filtrate through the filtrate outlet. For example, the vent may be disposed in the top of the assembly so that as gas rises, it passes through the filtrate and exits through the vent. Alternatively, the filter assembly 14 may include a single outlet 40 for both the gas and the filtrate, and the gas and the filtrate may be separated after exiting the filter assembly. As seen in FIG. 1, a liquid-gas separator 44 may be disposed downstream of the outlet 40. The liquid-gas separator 44 may separate the filtrate and gas in any suitable manner. For example, the liquid-gas separator may separate the gas from the liquid based on the buoyancy of the gas, allowing the gas to rise through liquid or by centrifugal force, e.g., centrifugal force generated by the flow of fluid through the separator inlet. Other methods of separating liquids and gases are known in the art and may include, for example, coalescing.

The inventive methods may also include additional cleaning regimes, including fluid regeneration methods such as backwash, blowback or scouring arrangements. For example, backwashing may be performed periodically or recurrently, or as needed, based on the measured pressure drop through the filter assembly. In operation, the flow of feed mixture through the filter medium may be halted and a cleaning fluid, such as water, a chemical cleaning agent, a gas or even filtrate, may be directed to flow through the filter medium from the filtrate side to the feed side. The backwash fluid may drive foulants from within the filter medium and/or from the upstream surface of the filter medium. The foulants may then be expelled from the filter assembly with the backwash fluid, for example through a drain or outlet. Alternatively, in some embodiments flow may be stopped and the liquid drained from the assembly and a gas stream may be directed in reverse through the filter medium to dislodge foulants. Sluicing or scraping or other means known in the art may also be utilized.

While many different systems may embody the invention, the exemplary filtration system 10 illustrated in FIG. 1 comprises a dead-end system which generally includes a filter assembly 12 which may be coupled to a source of feed mixture 12, a source of gas 26, and a separator 44. The filter assembly may be variously configured. The filter assembly 14 may include two or more ports for communicating with the feed and gas sources and the separator. For example, the filter assembly may include an inlet port for the feed mixture 20, an inlet port for the gas mixture 28, and an outlet port for the filtrate 40. The filter assembly may also include a vent 42 communicating with the feed side of the filter medium for removing accumulated gas from the assembly 14. The filter assembly may include fewer ports or more ports than illustrated in FIG. 1. For example, the filter assembly 14 may include only one inlet port and one outlet port, the feed inlet and gas inlet being configured as a single port. Alternatively, the filter assembly 14 may include additional ports, such as additional outlet ports, vents, backwashing ports, and/or a drain.

The filter assembly 14 may include one or more filter elements 16. For example, a filter assembly may include one or more filter elements disposed in one or more housings. In an embodiment illustrated in FIG. 1, the filter assembly 14 includes a single filter element 16 surrounded by a housing 30. In other embodiments, multiple filter elements may be disposed in a single housing or multiple filter elements may be disposed in multiple housings. Multiple elements within a housing or within a filter assembly may be the same or different from one another and may be arranged in any suitable configuration, e.g., serially or in parallel. An exemplary filter assembly including multiple filter elements is illustrated in FIG. 2. The filter assembly 14 illustrated in FIG. 2 includes a housing 30 surrounding three filter elements 16a, 16b, 16c arranged in parallel. Although three filter elements are shown, the filter assembly 14 may include any number of filter elements, for example, two, 15 four, five or even more filter elements.



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stats Patent Info
Application #
US 20120279917 A1
Publish Date
11/08/2012
Document #
13550679
File Date
07/17/2012
USPTO Class
210409
Other USPTO Classes
International Class
01D29/66
Drawings
4



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