Abstract:
Processing of a bulk liquid including particles, including use of a rotating strainer surface with openings disposed on a circumference thereof, the openings allowing an extracted liquid in the bulk liquid to pass through the strainer surface while preventing particles from passing through the strainer surface, such that a concentration of particles in the extracted liquid is less than in the bulk liquid; an extracted liquid outflow port which outputs the extracted liquid from an interior region of the rotating strainer surface; and a motor configured to rotate the strainer surface at a speed sufficient to generate a centrifugal force or turbulence at the openings sufficient to prevent the particles from clogging the openings, wherein the strainer surface is rotated and the extracted liquid is output through the extracted liquid outflow port when the strainer surface is fully submerged in the bulk liquid.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure generally relates to a submerged rotating strainer device useful for extracting a liquid from a bulk liquid containing particles, where the device is self-cleaning while performing the extracting. 
       BACKGROUND 
       [0002]    A curdmaking process is used to transform cheese milk into quality cheese curd with the highest possible yield. In use, this cheese vat is filled with cheese milk (optionally pre-acidified), and then caused to coagulate by addition of enzyme and acid, acid alone, or a composite coagulant to the cheese milk. Various types of cheese have respective production procedures. Once the cheese milk has coagulated to form a curd, it is important to handle the curd gently as it is still soft. A portion of whey is drained. As the whey is removed, the cheese mass turns harder. After whey is removed, the curd and remaining whey are then transferred for subsequent processing, such as processing over a slotted conveyor or such to further drain whey from the curd. 
         [0003]    One issue in separating the curd and whey is that small curd particles that often leave the vat together with drained whey. This loss of curd can significantly reduce yield, and processing techniques have been developed which seek to reclaim these curd particles from the whey stream and reincorporate them into the cheese mass. Reductions in yield resulting from these curd particles can be reduced or avoided by continuously stirring the curd and whey while draining the whey. However, simple strainers, such as meshes, quickly become clogged with curd particles. U.S. Pat. No. 6,050,179, herein incorporated by reference in its entirety, describes a strainer disc device for draining whey while stirring the curd and whey. The disclosed strainer has a circularly shaped strainer disc rotatably arranged flat against a wall of a cheese vat. It is intended that the rotation of the strainer disc is sufficient to prevent the accumulation of curd particles and associated clogging of the strainer disc. Additionally, rotation of the agitator during stirring is also intended to help remove any curd particles which manage to adhere to the strainer disc by performing mechanical scraping of the strainer disc. 
         [0004]    However, the inventors have recognized a number of issues with this strainer disc. First, the curd is extremely fragile in the beginning of the cheese-making process. Shear stress created by the rotating strainer disc damages the curd and crease small curd particles which escape through the strainer disc with the whey, which reduces yield. Second, limitations to the size of the disc limit the capacity of the strainer. Third, there are inconsistent flow characteristics on the surface of the strainer disc, which make it difficult to determine and maintain optimal settings for its operation from batch to batch or unit to unit. 
       BRIEF SUMMARY 
       [0005]    The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
         [0006]    The subject matter described in this application, in comparison to the above-mentioned strainer disc, ensures gentler treatment of curd, improved production yield by reducing the generation of additional curd particles, greater flow capacity, and more consistent flow characteristics. In particular, embodiments of the disclosed subject matter demonstrate outstanding anti clogging performance when the rotated as prescribed. It has been observed, for example, that as soon as rotation of a strainer according to the disclosed subject matter is stopped, strainer flow capacity goes down to only 1% of the flow capacity observed during rotation. The disclosed subject matter is useful for cheese production in particular, but is also applicable more generally for extracting a liquid component from a bulk liquid containing particles. 
         [0007]    In an embodiment of the disclosed subject matter, there is a device for processing a bulk liquid comprising particles, the particles in the bulk liquid being at a first concentration, and the device comprising: a rotating strainer surface with one or more openings disposed on a circumference thereof, the openings configured to allow an extracted liquid included in the bulk liquid to pass through the strainer surface while preventing particles from passing through the strainer surface, such that a concentration of particles in the extracted liquid is less than 10% of the first concentration; an extracted liquid outflow port which outputs the extracted liquid from an interior region of the rotating strainer surface; and a motor configured to rotate the strainer surface at a speed sufficient to generate a centrifugal force or turbulence at the openings sufficient to prevent the particles from clogging the openings, wherein the device is configured to rotate the strainer surface and output the extracted liquid through the extracted liquid outflow port when the strainer surface is fully submerged in the bulk liquid. 
         [0008]    In another embodiment of the disclosed subject matter, there is a method for processing a bulk liquid comprising particles, the particles in the bulk liquid being at a first concentration, and the method comprising: providing a strainer surface with one or more openings disposed on a circumference thereof, the openings configured to allow an extracted liquid included in the bulk liquid to pass through the strainer surface while preventing particles from passing through the strainer surface, such that a concentration of particles in the extracted liquid is less than 10% of the first concentration; outputting the extracted liquid from an interior region of the rotating strainer surface; and rotating the strainer surface at a speed sufficient to generate a centrifugal force or turbulence at the openings sufficient to prevent the particles from clogging the openings, wherein the rotating and outputting are performed when the strainer surface is fully submerged in the bulk liquid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The accompanying figures, in which like reference numerals refer to identical or functionally similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the present invention and, together with the above background of the disclosed subject matter, brief summary of the disclosed subject matter, and detailed description of the disclosed subject matter, serve to explain the principles of the disclosed subject matter. Other features and advantages of the disclosed subject matter will become more apparent from this disclosure, which serves as a nonlimiting illustration of the disclosed subject matter. 
           [0010]      FIG. 1  illustrates a vessel  100  which includes a strainer  200  for separating a liquid from a bulk liquid containing particles stored within a liquid-bearing portion of vessel  100 . 
           [0011]      FIG. 2  illustrates a cross-sectional view of strainer  200 . 
           [0012]      FIG. 3  shows experimental results observed with an embodiment of the disclosed subject matter. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate embodiments and are not intended to limit the scope of the disclosed subject matter. 
         [0014]      FIG. 1  illustrates a vessel  100 , such as the closed cheese vats discussed above, which includes strainer  200 , which is illustrated in more detail in  FIG. 2 . Vessel  100  is configured to receive materials, whether liquid and/or solid, and store a bulk liquid containing particles (not illustrated) comprising a liquid component and a particulate component. Although  FIG. 1  illustrates a vertical vessel, horizontal or other vessel configurations are also suitable. 
         [0015]    Within a liquid-bearing portion of vessel  100  is agitator  110 , which may be selectively rotated in order to stir the bulk liquid containing particles by rotation of agitator  110 . In some embodiments, agitator  110  may be selectively rotated in either a clockwise or counterclockwise direction. In some embodiments, agitator  110  may be rotated at varying speeds. In some uses of the disclosed subject matter, particles included in the bulk liquid containing particles may settle out of the bulk liquid, and agitator  110  may be actuated in order to ensure the particles remain suspended or are again suspended in the bulk liquid. Although  FIG. 1  illustrates an agitator  110  comprising 4 paddles at the lower portion of the liquid-bearing portion of vessel  100 , many other agitator configurations are known to those of ordinary skill in the art. For example, U.S. Pat. No. 6,050,179, which is discussed above, describes use of a frame which serves to cut a cheese curd when rotated in a first direction, and stir the curd when rotated in an opposite direction. In some embodiments, pumping of the bulk liquid containing particles may be more appropriate for ensuring the particles are suspended in the bulk liquid, in which case pumps (not illustrated) may be used instead or, or in conjunction with, rotating agitator  110 . In some embodiments, there may be multiple agitators included in vessel  100 . 
         [0016]    In some embodiments, vessel  100  may be configured to receive a plurality of materials which are mixed and/or reacted therein. As one example, in a cheese-making procedure a cheese milk and a coagulant may be combined in order to produce curd and whey. In some embodiments, vessel  100  may serve as a holding or processing vessel which receives from another processing unit a bulk liquid containing particles from which a liquid component is to be extracted using strainer  200 . 
         [0017]    As illustrated in  FIG. 1 , strainer  200  protrudes from a wall of vessel  100  into the liquid-bearing portion of vessel  100 . In some embodiments, a wall of vessel  100  may protrude outward in order to position strainer  200  away from agitator  110 . In some embodiments, more than one strainer  200  may be included in vessel  100  in order to increase the total straining capacity, or to provide strainers with different characteristics, such as different gap sizes, which may be used at different times during production cycle. Strainer  200  is positioned so as to be submerged, preferably entirely, within a liquid containing particles within the liquid-bearing portion of vessel  100  while rotating and performing liquid extraction. Although  FIGS. 1 and 2  illustrate strainer  200  with a horizontal axis of rotation, strainer  200  may be in other orientations. 
         [0018]      FIG. 2  illustrates a cross-sectional view of strainer  200  in more detail. Strainer  200  is mounted in wall  120  of vessel  100 . As illustrated in  FIG. 2 , strainer  200  is inserted through a hole in wall  120 , and base plate  225  of strainer  200  is removably attached to wall  120  using bolts or other fasteners. By being removably attached, strainer  200  may be more easily removed from vessel  100  for cleaning, inspection, maintenance, repair, or replacement. 
         [0019]    Shaft  215 , which is driven by motor  220 , passes through base plate  225 . Motor  220  may be configured to rotate shaft  215  in either direction, and at variable speed. Inside vessel  100 , shaft  215  supports and rotates a cylindrical screen  205 . Although  FIG. 2  illustrates a cylindrical screen, other configurations, such as a cone or dome shape by way of example, may be used. Screen  205  is further supported by support rods  210 , which extend parallel to shaft  215 . 
         [0020]    In some embodiments, screen  205  comprises a wedge wire mesh screen, in which one or more lengths of wire with a wedge-shaped cross section are wound around and attached to support rods  210 . The wedge-shaped cross section is helpful in avoiding clogging of screen  205 , although other cross sectional shapes may be used. Depending upon the properties of the liquid containing particles to be filtered by strainer  200 , different wire diameters may be employed, and a gap between neighboring windings of the wedge wire may be varied. As an example, wedge wire mesh screens having a nominal gap size of 0.01 mm are readily available, with smaller gap sizes available depending upon the application and materials used. A gap size is selected such that most particles contained in the bulk liquid will not pass through the selected gap size, while an extracted liquid to be extracted from the bulk liquid does pass through the gap. An amount of particles present in the extracted liquid is affected by the gap size. A concentration of particles in the extracted liquid is less than in the bulk liquid. In some embodiments, a concentration of particles in the extracted liquid is less than 50% of a concentration of particles in the bulk liquid. In some embodiments, a concentration of particles in the extracted liquid is less than 25% of a concentration of particles in the bulk liquid. In some embodiments, a concentration of particles in the extracted liquid is less than 10% of a concentration of particles in the bulk liquid. In some embodiments, a concentration of particles in the extracted liquid is less than 5% of a concentration of particles in the bulk liquid. In some embodiments, a concentration of particles in the extracted liquid is less than 1% of a concentration of particles in the bulk liquid. Additionally, the overall length and diameter of screen  205  may also be varied. The length, diameter, and gap size for screen  205  each contribute to the flow rate capacity for strainer  200 , and each may be varied to optimize flow characteristics for a particular application. The screen has been tested in a number of practical full scale experiments with gap sizes from 0.15 mm to 0.40 mm, lengths from 20 to 35 cm, a diameter of 20 cm, and maximum flow rate capacity of 22.5 L/h, exhibiting retention of cheese curd particles of more than 95% (i.e., the particulate concentration in the extracted liquid was less than 5% of the particulate concentration of the bulk fluid). 
         [0021]      FIG. 3  shows experimental results observed with an embodiment of the disclosed subject matter. Specifically, a test of anti clogging performance of an embodiment of the disclosed subject matter was performed on cheese whey. The test confirmed the anti clogging performance of the disclosed techniques, as when the strainer was rotating as prescribed, the strainer flow capacity was stable at approximately 39000 liters per hour, and when rotation of the strainer was stopped, the strainer flow capacity quickly dropped down to approximately 200 liters per hour, which is only 0.5% of the normal strainer flow capacity observed while rotating the strainer. The test results are summarized in the following table: 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Observed flow 
                   
               
               
                 Time of day 
                   
                 capacity 
                 Percent 
               
               
                 (hour:minute) 
                 Strainer status 
                 (liters per hour) 
                 maximum flow 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10:15 
                 Rotating 
                 39400 
                  100% 
               
               
                 10:17 
                 Rotating 
                 39210 
                 99.5% 
               
               
                 10:20 
                 Rotating 
                 39025 
                 99.0% 
               
               
                 10:21 
                 Stopped 
                 200 
                  0.5% 
               
               
                 10:23 
                 Stopped 
                 200 
                  0.5% 
               
               
                   
               
             
          
         
       
     
         [0022]    Those skilled in the art will appreciate that other effective embodiments for screen  205  are known in the art, including, for example, a standard wire mesh comprising perpendicularly oriented rows and columns of wires, and a sheet of material with apertures arranged thereon for allowing liquid to pass through. The size of apertures may be adjusted to accommodate the properties of the liquid and particulate components of the bulk liquid being separated. 
         [0023]    During separation of a liquid containing particles stored in vessel  100 , during which time liquid from the liquid containing particles is filtered into the interior of strainer  200 , screen  205  is rotated. This rotation creates sufficient turbulence and/or centrifugal force at the surface of screen  205  so as to prevent the gaps through which the extracted liquid passes from being clogged. As a result, a mechanical scraper device is not needed to prevent strainer  200  from becoming clogged. In some embodiments, such as the separation of curd and whey discussed above, screen  205  is rotated at a relatively low speed in order to minimize damage to the curd particles. In some cases, by increasing the surface area of screen  205 , the pressure across screen  205  may be reduced, and consequently slower rates of rotation may be effective in preventing clogging of screen  205 . 
         [0024]    Upper tube  230  serves two primary functions. First, it is filled with liquid during operation of vessel  100  in order to prevent air from intruding into vessel  100 . Second, upper tube  230  has a corresponding hole in base plate  225 . In this hole is positioned a spray nozzle  235 , which is used to flush and clean the interior of screen  205  between each batch produced in vessel  100 . Spray nozzle  235  may be configured so as to spray the entire interior length of screen  205  and shaft  215 , so as to require only a single spray nozzle  235 . During flushing and cleaning of screen  205  with spray nozzle  235 , motor  220  is operated so as to rotate screen  205  to ensure complete coverage and to provide centrifugal force to expel cleaning fluid. In this manner, strainer  200  is able to execute clean-in-place procedures which better ensure sanitary conditions in vessel  100  and more rapid turnaround time between batches. 
         [0025]    The primary function of lower tube  240  is to provide an outward port for liquid filtered by screen  205 . In some embodiments, there may be a pump (not illustrated), which may be used to increase the pressure by which the liquid is pulled through screen  205 . In some embodiments, lower tube  240  may be operated so as to control a differential pressure across screen  205 , in order to better reduce clogging of screen  205 , reduce damage to particles in the bulk liquid, and control a flow rate of filtered liquid output through lower tube  240 . In some uses of the disclosed strainer  200 , the filtered liquid may be considered waste liquid. In other uses, the filtered liquid may be considered a useful product, and accordingly directed for further processing. 
         [0026]    Reference numeral  245  illustrates a seal between the rotating portion of strainer  200  within vessel  100  and base plate  225 . In some embodiments, rather than using a gasket or interlocking components in order to produce a tight seal, there is a gap. In one example, this gap is approximately 0.8 mm. Although such a gap may be larger than the particles in the liquid containing particles, when screen  205  is rotated the gap functions as a low flow pump as a result of centrifugal force, whereby a small portion of the liquid which has passed through screen  205  is pumped back into the liquid-bearing portion of vessel  100 . With the flow in this gap running counter to the direction of the separating flow through screen  205 , only a minimal quantity of particles pass through the gap while strainer  200  is being used for separation of the liquid containing particles. In some embodiments, this gap may be sealed in order to ensure particles from the liquid containing particles do not pass into the interior of strainer  200 . 
         [0027]    Strainer  200  can be installed in a batch process where a bulk liquid containing particles is filled into a vessel via a bulk liquid inflow port and a volume of liquid is extracted for further processing though the rotating strainer  200 , leaving a concentrated bulk liquid with particles in the vessel which is output via a bulk liquid outflow port for further processing. 
         [0028]    Also, strainer  200  be installed as part of a continuous process where a bulk liquid with a first concentration of particles is continuously supplied through an inflow port to strainer  200 , liquid is extracted continuously from the bulk liquid though the rotating strainer  200  for further processing, allowing a remaining concentrated bulk liquid, with a second concentration of particles greater than the first concentration, to be removed through an outflow port by continuous flow from the process for further processing. 
         [0029]    Although portions of the above description are made with reference to the production of cheese, and the separation of curd and whey produced during this process, the disclosed subject matter is not limited to this particular application. The disclosed subject matter may also be used for other foodmaking processes. For example, the disclosed subject matter can be used to extract milk or any milk-based product from a bulk milk or milk-based product containing particles originating from milk or any other source retaining the concentrated bulk milk or milk-based product with particles in the vessel or in a continuous downstream flow. As another example, the disclosed subject matter can be used to extract juices of fruit or vegetable origin or similar products from juices containing particles originating from fruits or vegetables or any other source retaining the concentrated juices with particles in the vessel or in the continuous downstream flow. 
         [0030]    In another example, the disclosed subject matter can be used to extract liquids of animal origin e.g. waste water or blood from a liquid containing particles originating from animals or any other source retaining the concentrated liquid with particles in the vessel or in the continuous downstream out flow. 
         [0031]    In another example, the disclosed subject matter can be used to extract liquid product or by product from a fermenter or bioreactor vessel containing a liquid product or by product with particles consisting of any chemically or biochemically active substances that is to be retained in the vessel or in the continuous downstream out flow such as microorganisms, catalysts, or a substance immobilized by a carrier matrix to obtain a certain minimum size. 
         [0032]    In some embodiments, a processing device including strainer  200  is operated under the control of a programmed computer, according to a set of instructions for the computer. The computer controls a sequence of operations performed by the processing device, including, for example, filling vessel  100  with a bulk liquid including particles, rotation of screen  205 , supplying filtered liquid for further processing, and supplying the remaining concentrated bulk liquid for further processing. 
         [0033]    The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated. 
         [0034]    It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. It will also be appreciated that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims. Unless specifically recited in a claim, steps or components of claims should not be implied or imported from the specification or any other claims as to any particular order, number, position, size, shape, angle, color, or material.