Disposable rotary drum filter

Abstract

A disposable rotary drum filter for processing batches of slurry. The device includes an outer housing in which is disposed a rotatable inner drum that is covered with a filter material. Preferably the device is fabricated from a plastic material that is sterilizable. The inner drum is preferably magnetically coupled to an external drive unit, eliminating seals required if it were necessary for a drive shaft to pass through the housing. The inner drum rotates through a slurry. The filtrate outlet is connected to a vacuum source that draws the slurry through the filter material. Solids in the slurry are thus deposited as a filter cake on the outer surface of the filter material, while liquid from the slurry passes through the filter material to be collected as a filtrate. Air drawn into the housing through an inlet passes through the filter material and partially dries the filter cake that has been rotated out of the slurry. As the inner drum rotates, an edge formed on the housing scrapes away a portion of the filter cake, which falls into a filter cake receiver. A simple overflow outlet level limits the slurry level to a defined maximum, and an orifice formed in a fixed plate disposed in a cavity at one end of the inner drum controls pressure conditions within the device to ensure optimal fluid flow. The device is thus useful for solid-liquid separations in batch processing of many types of slurries and can be sterilized, if required.

The invention in which an exclusive right is claimed is defined by the following:  
     
         1 . A disposable rotary drum filter for separating a slurry into a liquid filtrate and a solid filter cake, comprising: 
 (a) a housing defining a slurry reservoir and including: 
 (i) a slurry inlet adapted to receive a slurry into the slurry reservoir;  
 (ii) a gas inlet adapted to receive gas into the housing;  
 (iii) a filtrate outlet adapted to convey filtrate from the housing after the filtrate has been separated from the filter cake;  
 (iv) a filter cake outlet adapted to convey the filter cake from the housing; and  
 (v) an overflow outlet disposed within the housing and having an opening disposed at an elevation within the housing that is selected to determine a maximum level of a slurry within the slurry reservoir;  
   (b) an inner drum rotatably mounted within said housing, said inner drum comprising: 
 (i) a generally cylindrical frame;  
 (ii) a filter extending around said generally cylindrical frame, the inner drum being disposed within the housing such that said filter is partially below the level determined by the opening of the overflow outlet, said filter being adapted to receive a filter cake deposited on an outer surface of said filter as the filtrate separated from the filter cake is drawn through the filter and the filtrate outlet;  
 (iii) a portion of said generally cylindrical frame providing fluid communication between an interior surface of said filter and said filtrate outlet and thereby adapted to convey the filtrate from said inner drum after the filtrate has passed though said filter; and  
 (iv) a driven member connected to said generally cylindrical frame and adapted to be drivingly coupled to an external prime mover to rotate the inner drum, exposing the filter cake deposited on the filter to gas that is drawn through the filter into the inner drum from inside the housing, to at least partially dry the filter cake; and  
   (c) means for removing at least a portion of said filter cake deposited on said filter after the filter cake has been at least partially dried by the gas so that the filter cake that is thus removed passes through said filter cake outlet.    
     
     
         2 . The disposable rotary drum filter of  claim 1 , wherein the slurry inlet is disposed at a bottom of the housing and is adapted to couple to a fluid line that conveys the slurry from an outlet of a slurry pump.  
     
     
         3 . The disposable rotary drum filter of  claim 1 , wherein the slurry reservoir is disposed in a lower portion of the housing, such that said inner drum is partially disposed within the slurry reservoir.  
     
     
         4 . The disposable rotary drum filter of  claim 1 , wherein said housing further includes a journal that supports said inner drum so as to enable the internal drum to freely rotate about a longitudinal axis of the inner drum.  
     
     
         5 . The disposable rotary drum filter of  claim 4 , further comprising a spring that exerts a biasing force to position said inner drum at a desired position along the longitudinal axis of the inner drum within said housing.  
     
     
         6 . The disposable rotary drum filter of  claim 5 , wherein said spring is disposed between said driven member and said housing.  
     
     
         7 . The disposable rotary drum filter of  claim 1 , wherein said filter cake outlet is oriented vertically, such that a gravitational force facilitates the removal of said filter cake from the housing.  
     
     
         8 . The disposable rotary drum filter of  claim 1 , wherein said filter cake outlet is elongate and is disposed along one side of the housing, extending generally in alignment with the outer surface of the filter.  
     
     
         9 . The disposable rotary drum filter of  claim 1 , wherein the means for removing at least the portion of said filter cake comprises an elongate edge formed in said housing and extending adjacent to the outer surface of the filter.  
     
     
         10 . The disposable rotary drum filter of  claim 1 , wherein said filtrate outlet is adapted to couple to a fluid line connected with a vacuum source.  
     
     
         11 . The disposable rotary drum filter of  claim 1 , wherein said filter comprises a porous material having a plurality of openings sized to enable the filtrate to pass therethrough, while blocking passage of the filter cake.  
     
     
         12 . The disposable rotary drum filter of  claim 11 , wherein said porous material comprises a porous plastic.  
     
     
         13 . The disposable rotary drum filter of  claim 1 , wherein said gas inlet is disposed in an upper part of the housing.  
     
     
         14 . The disposable rotary drum filter of  claim 13 , further comprising pressure control means for equalizing a pressure drop within said housing as the gas within the housing is drawn into the inner drum through the filter.  
     
     
         15 . The disposable rotary drum filter of  claim 14 , wherein said pressure control means comprises an orifice through which gas flowing through the filtrate outlet is drawn.  
     
     
         16 . The disposable rotary drum filter of  claim 15 , wherein the orifice is formed in a plate disposed adjacent to the filtrate outlet; and wherein a fluid flow through said filter is optimized by selecting an appropriate size of said orifice in said plate.  
     
     
         17 . The disposable rotary drum filter of  claim 1 , wherein said inner drum further comprises a plurality of fluid channels in fluid communication with said filtrate outlet.  
     
     
         18 . The disposable rotary drum filter of  claim 1 , wherein the inner drum further comprises a plurality of orifices in fluid communication with said filtrate outlet.  
     
     
         19 . The disposable rotary drum filter of  claim 1 , wherein the inner drum further comprises a plurality of filtrate tubes in fluid communication with said filtrate outlet.  
     
     
         20 . The disposable rotary drum filter of  claim 1 , wherein the inner drum further comprises: 
 (a) a plurality of fluid channels disposed between said filter and said generally cylindrical frame and extending longitudinally along the generally cylindrical frame;    (b) a cavity in fluid communication with said filtrate outlet; said cavity being disposed proximate a center of said inner drum and adjacent to an end of said inner drum; and    (c) a plurality of filtrate tubes connecting said longitudinal fluid channels in fluid communication with said cavity, thereby establishing a fluid path between said longitudinal channels and said filtrate outlet.    
     
     
         21 . The disposable rotary drum filter of  claim 20 , further comprising a plate that separates said cavity into an upper portion and a lower portion, said plate being fixedly attached to said housing with said inner drum being free to rotate about said plate.  
     
     
         22 . The disposable rotary drum filter of  claim 20 , wherein said plate includes an orifice that controls a gas flow between said upper portion and said lower portion of the cavity and thereby control gas flow through the filter from inside the housing.  
     
     
         23 . The disposable rotary drum filter of  claim 22 , wherein said generally cylindrical frame adds structural integrity to said inner drum.  
     
     
         24 . The disposable rotary drum filter of  claim 23 , wherein said plurality of fluid channels have a cross-sectional shape that is one of a rectangular shape, a triangular shape, and a sigmoid shape.  
     
     
         25 . The disposable rotary drum filter of  claim 1 , wherein said driven member comprises a shaft.  
     
     
         26 . The disposable rotary drum filter of  claim 25 , wherein said shaft is adapted to magnetically couple to an external prime mover.  
     
     
         27 . The disposable rotary drum filter of  claim 26 , wherein said shaft includes a magnet.  
     
     
         28 . The disposable rotary drum filter of  claim 26 , wherein a plurality of permanent magnets are disposed in a spaced-apart array around an end of the shaft.  
     
     
         29 . The disposable rotary drum filter of  claim 1 , further comprising an external coupling hub adapted to be drivingly connected to a prime mover.  
     
     
         30 . The disposable rotary drum filter of  claim 29 , wherein said driven member is magnetically coupled to said external hub.  
     
     
         31 . The disposable rotary drum filter of  claim 30 , wherein said external hub comprises at least one magnet.  
     
     
         32 . The disposable rotary drum filter of  claim 30 , wherein said external hub comprises at least one electromagnet.  
     
     
         33 . The disposable rotary drum filter of  claim 1 , wherein said means to remove said filter cake comprises an edge of a material extending adjacent to and spaced apart from the filter.  
     
     
         34 . The disposable rotary drum filter of  claim 33 , wherein said edge has a length that is at least one of substantially equal to that of said inner drum, and substantially equal to a length of said housing.  
     
     
         35 . The disposable rotary drum filter of  claim 34 , wherein said edge is formed as an integral part of said housing.  
     
     
         36 . The disposable rotary drum filter of  claim 1 , wherein the filter is generally cylindrical in shape and extends generally between opposite ends of the generally cylindrical frame.  
     
     
         37 . The disposable rotary drum filter of  claim 1 , wherein said housing is fabricated from a material that can be readily sterilized.  
     
     
         38 . The disposable rotary drum filter of  claim 1 , wherein said housing is fabricated from a material that can be readily sterilized by one of ethylene oxide, steam, gamma radiation, electron beam radiation, and light.  
     
     
         39 . A disposable vacuum type rotary drum filter for separating a liquid containing suspended solids into a filtrate fraction and a filter cake fraction, comprising: 
 (a) a housing, said housing including: 
 (i) a liquid inlet;  
 (ii) a liquid overflow disposed so as to determine a maximum level of the liquid in the housing;  
 (iii) a gas inlet;  
 (iv) a filter cake outlet; and  
 (v) a filtrate outlet adapted to couple to a vacuum source;  
   (b) a rotatable filter element rotatably mounted within the housing to rotate through a liquid and through gas contained within the housing, and comprising: 
 (i) a filter membrane covering an outer surface of said filter element, said filter membrane being of a porosity selected to prevent said suspended solids from passing through said filter membrane, thereby forming the filter cake on an outer surface of said filter membrane, while enabling said filtrate fraction to pass through said filter membrane, rotation of the rotatable filter element causing the filter cake just deposited on the filter membrane to be exposed to a gas as the filter cake is rotated out of the liquid, gas passing through the filter cake and the filter membrane tending to dry the filter cake; and  
 (ii) a plurality of fluid channels in fluid communication with said filtrate outlet and disposed behind the filter membrane to receive the filtrate fraction and gas that has passed therethrough and to convey the filtrate fraction and gas toward said filtrate outlet;  
   (c) a driven member connected to the rotatable filter element and adapted to be drivingly coupled to an external prime mover; said driven member causing said rotatable filter element to rotate; and    (d) means for removing said filter cake from said outer surface of said filter membrane, and to direct any filter cake removed into said filter cake outlet.    
     
     
         40 . The disposable vacuum type rotary drum filter of  claim 39 , wherein said liquid inlet, said liquid overflow, said gas inlet, said filtrate outlet, and said filter cake discharge are integral integrally formed within said housing.  
     
     
         41 . The disposable vacuum type rotary drum filter of  claim 39 , wherein said housing is formed of a material that is chemically compatible with said liquid.  
     
     
         42 . The disposable vacuum type rotary drum filter of  claim 41 , wherein said housing is fabricated from a plurality of parts formed from a plastic material.  
     
     
         43 . The disposable vacuum type rotary drum filter of  claim 39 , wherein said housing further comprises a journal, said journal rotatably supporting said rotatable filter element.  
     
     
         44 . The disposable vacuum type rotary drum filter of  claim 39 , wherein said driven member is integral to said rotatable filter element.  
     
     
         45 . The disposable vacuum type rotary drum filter of  claim 39 , wherein said means to remove said filter cake from said surface of said filter comprises an elongate edge extending adjacent to and spaced apart from said surface of said filter.  
     
     
         46 . The disposable vacuum type rotary drum filter of  claim 45 , wherein said edge is integral to said housing.  
     
     
         47 . The disposable vacuum type rotary drum filter of  claim 39 , wherein said driven member is adapted to magnetically couple with an external prime mover.  
     
     
         48 . The disposable vacuum type rotary drum filter of  claim 39 , wherein said rotatable filter element is generally cylindrical in shape and rotates about its longitudinal axis.  
     
     
         49 . The disposable vacuum type rotary drum filter of  claim 48 , wherein said plurality of fluid channels extend along the rotatable filter element immediately under the filter membrane; and wherein said rotatable filter element further comprises: 
 (a) a cavity in fluid communication with said filtrate outlet, said cavity being disposed proximate a center of an end of said rotatable filter element; and    (b) a plurality of filtrate tubes connecting said plurality of fluid channels in fluid communication with said cavity, thereby conveying the filtrate fraction to said filtrate outlet.    
     
     
         50 . The disposable vacuum type rotary drum filter of  claim 49 , further comprising a plate that separates said cavity into an upper portion and a lower portion, said plate being attached to said housing so that said rotatable filter element is free to rotate about said plate.  
     
     
         51 . The disposable vacuum type rotary drum filter of  claim 50 , further comprising an orifice, said orifice controlling a gas flow through said filter membrane by controlling a pressure differential between said upper portion and said lower portion of said cavity.  
     
     
         52 . The disposable vacuum type rotary drum filter of  claim 51 , wherein gas flows into the housing through the gas inlet to replace gas exiting said housing through said filtrate outlet.  
     
     
         53 . The disposable vacuum type rotary drum filter of  claim 52 , wherein the orifice comprises a pressure control that limits a volume of gas flowing out of the housing to ensure that the filtrate fraction flows out the filtrate outlet.  
     
     
         54 . The disposable vacuum type rotary drum filter of  claim 53 , wherein the plurality of filtrate tubes extend radially, between the cavity and the plurality of fluid channels, around the longitudinal axis of the rotatable filter element.  
     
     
         55 . The disposable vacuum type rotary drum filter of  claim 54 , wherein changing a size of said orifice changes a flow of the filtrate fraction through the filtrate outlet.  
     
     
         56 . A batch processing method for separating a slurry comprised of a liquid material and a solid material suspended in said liquid material, comprising the steps of: 
 (a) providing a disposable rotary drum filter and a batch of said slurry;    (b) causing said slurry to flow into said disposable rotary drum filter;    (c) operating said disposable rotary drum filter to separate said slurry into a solid portion and a liquid portion, for a time sufficient to process said batch of said slurry, thereby separating said solid material from said liquid material;    (d) separately collecting a separated solid material and a separated liquid material; and    (e) discarding said disposable rotary drum filter.    
     
     
         57 . A processing method for separating a slurry comprised of a liquid material and a solid material into a liquid filtrate and a substantially solid filter cake, comprising the steps of: 
 (a) providing a disposable vacuum type rotary drum filter and a source of slurry to be processed;    (b) causing a liquid filtrate outlet of said disposable vacuum type rotary drum filter to be in fluid communication with a vacuum source;    (c) causing a slurry inlet of said disposable vacuum type rotary drum filter to be in fluid communication with said source of slurry;    (d) positioning a filter cake receiver such that filter cake exiting said disposable vacuum type rotary drum filter is collected in said filter cake receiver;    (e) rotating said disposable vacuum type rotary drum filter so as to separate said slurry into said filter cake and said liquid filtrate; and    (f) stopping said disposable vacuum type rotary drum filter from rotating once a desired volume of slurry has been processed.    
     
     
         58 . The processing method of  claim 57 , further comprising the step of discarding said disposable vacuum type rotary drum filter once said desired volume of slurry has been processed.  
     
     
         59 . The processing method of  claim 57 , wherein the step of rotating said disposable vacuum type rotary drum filter comprises the steps of: 
 (a) providing a prime mover adapted to be drivingly coupled with said disposable vacuum type rotary drum filter;    (b) magnetically drivingly coupling said prime mover to said disposable vacuum type rotary drum filter; and    (c) energizing said prime mover.    
     
     
         60 . The processing method of  claim 59 , wherein the step of rotating said disposable vacuum type rotary drum filter further comprises the step of rotating an inner drum of said disposable vacuum type rotary drum filter at a rotational velocity within a range of one to ten revolutions per minute.  
     
     
         61 . The processing method of  claim 57 , further comprising the step of controlling a flow of liquid filtrate from within said disposable vacuum type rotary drum filter, the step of controlling a flow of fluid comprising: 
 (a) providing a plate that separates an internal volume of said disposable vacuum type rotary drum filter into a first portion having a low flow resistance, and a second portion having a higher flow resistance, said plate including an orifice that controls a pressure differential between said first portion and said second portion; and    (b) selecting a size of said orifice to produce a desired flow of filtrate liquid from the disposable vacuum type rotary drum filter.