Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2000-01-26
2001-07-31
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S321690, C210S321870, C210S402000, C210S650000, C210S770000, C210S784000
Reexamination Certificate
active
06267889
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a drum filter which uses a membrane or very fine filtration media and an improved filtering method for producing a substantially solids free filtrate and/or a paste-like filter cake without the use of filter aids.
BACKGROUND
Environmental concerns and economics encourage the collection and reuse of many materials which once were thought to be of little or no value. In some industries a large volume of liquids or solvents are used for producing valuable products. These ho liquids and solvents often times become contaminated with fines or particulates which pose environmental hazards or which may have significant value if they could be recovered from the liquids in an economical manner. Recovery of fine or very fine particles having an average diameter of less than about 20 microns represents one such need. In some industries, production of a high solids filter cake containing valuable product is desirable. It is also desirable to recover such filter cake products without the use of filter aids which have to be removed from the filter cake product in a subsequent step. In other industries, the solids are collected and disposed of and a substantially solids free filtrate or permeate is collected and reused. Whether it is the liquid portion or the solid portion which is desired to be recovered, there continues to be a need for a means for recovering difficult to recover solids and for producing substantially solids free liquids from large volumes of liquid streams in a cost efficient manner.
SUMMARY OF THE INVENTION
With regard to the above, the invention provides a filter assembly for treating a mixture of solids and liquid to yield a paste-like filter cake and/or a substantially suspended solids free filtrate or permeate. The filter assembly includes a substantially cylindrical member having an exterior foraminous surface, the cylindrical member being mounted on an elongate shaft for rotating the exterior foraminous surface about an axis defined by the shaft. The exterior foraminous surface is preferably covered by a microporous filter media, such as a membrane filter or very fine woven filter cloth. A stationary housing is positioned adjacent at least a portion of the exterior surface of the cylindrical member. The stationary housing includes a filter feed inlet and a sealing device. The housing is spaced from the exterior surface of the cylindrical member a distance sufficient to enable cross flow relative to the cylindrical surface. Unique filter seal members operatively associated with the housing and cylindrical member define a filtration area and promote retention of fluid to be filtered under pressure in the filtration area adjacent the filter media. As the cylindrical member is rotated about the axis, a cake removal and/or membrane cleaning device removes filter cake from the filter media.
In another aspect, the invention provides method for producing a paste-like filter cake from a mixture of liquid and solids using a filter system which includes a substantially cylindrical member having an exterior foraminous surface. The cylindrical member is mounted on an elongate shaft for rotating the exterior foraminous surface about an axis defined by the shaft. A microporous filter media such as a membrane filter or very fine woven filter cloth preferably covers the exterior foraminous surface. At least one stationary housing is positioned adjacent at least a portion of the exterior surface of the cylindrical member, each of the stationary housings including a filter feed inlet and a sealing device. The housing is spaced from the exterior surface of the cylindrical member a distance sufficient to enable cross flow and/or flooding of the space between the housing and cylindrical member. The filtration system also includes one or more filter seal members which are operatively associated with the housing and cylindrical member and define a filtration area between the housing and cylindrical member for promoting retention of fluid to be filtered in the filtration area. A drive is provided for rotating the cylindrical member about the axis and a cake removal and/or membrane cleaning device external to the one or more housings is provided adjacent the exterior surface of the cylindrical member for removing filter cake therefrom as the cylindrical member rotates. A liquid containing solids is fed through the filter feed inlet at a pressure and a rate sufficient to form a filter cake having a solids content including bound water above about 65 percent by weight on the filter media while rotating the cylindrical member relative to the housing. A relatively even filter cake height is maintained during filtering, and the filter cake is dried and removed from the filter media external to the housing. The filter media may also be cleaned for reuse.
The filtration device of the invention provides significant operational and cost advantages over conventional membrane filtration devices and over conventional belt or drum filters. Pressurized, cross-flow and/or puddle filtration can be conducted with the filter system according to the invention to provide substantially continuous removal of unbound water from solids and substantially continuous cleaning of the filter media. The unbound water removal is substantially greater than obtainable by use of conventional membrane filters or ultrafiltration processes.
Use of unique filter seal members enables use of a rotating cylindrical member containing a microporous filter media which is not abraded or otherwise significantly damaged by the seal member. According to the invention, the filtration surface moves relative to a housing member so as to enter and exit the housing member thereby providing a filtration zone between the housing and filtration surface which may be pressurized. As the filtration surface moves relative to the housing member, the surface undergoes periodic filtration and product removal. The unique design of the filtration device provides high solids production similar to a drum or belt filter without the use of filter aids and provides fine particle removal from a liquid similar to a membrane filter, however with a higher solids content than conventional membrane filters.
For the purposes of this invention, the term “solids” means suspended particulates and dissolved polymers and excludes dissolved salts. The term “bound water” means water which is trapped within the pores or interstices of the solids and which cannot be easily removed from the solids by mechanical techniques. The term “microporous” means having an average pore size ranging from about 0.01 to about 10 microns in diameter.
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JP 08 309 160 “Structure of Filter Plate of Rotary Membrane Separator” Published Nov. 26, 1996 (Abstract only).
JP 08 243 363 “Rotary Membrance Separation Filter Capable of Maintaining High Filtration Rate” Published Sep. 24, 1996 (Abstract only).
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Drodge Joseph W.
Luedeka, Neeley & Graham, P.C.
MDF, LLC
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