Abstract:
The method of forming a filter cake from a slurry comprising the steps of feeding the slurry into a filter housing, wherein the filter housing includes a plurality of vertical filter elements; pressing the slurry into the filter housing against the filter elements resulting in i) a filtrate passing through the filter elements and exiting out an exhaust port of the filter housing; ii) forming a solid cake on the filter elements; feeding a wash liquid into the filter housing while draining out the slurry by opening the slurry drain valve; closing the slurry drain valve and then continually feeding wash liquid through the cake and into the filter tube of the filter housing; stopping the feed of wash liquid; introducing a gas into the filter housing and draining out the wash liquid by opening a bottom drain valve; stopping the gas flow and opening a drain to exit most of the gas and remaining wash liquid; opening the bottom cake discharge valve; and back pulsing by a gas to break and to release the filter cake from the filter elements of the filter housing.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a filter system to separate a solid phase from a liquid phase in a slurry. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present invention relates to a method of forming a filter cake from a slurry comprising the steps of: feeding the slurry into a filter housing, wherein the filter housing includes a plurality of vertical filter elements; pressing the slurry into the filter housing against the filter elements resulting in a i) a filtrate passing through the filter elements and exiting out an exhaust port of the filter housing; ii) forming a solid cake on the filter elements; feeding a wash liquid into the filter housing while draining out the slurry by opening the slurry drain valve; closing the slurry drain valve and then continually feeding wash liquid through the cake and into the filter tube of the filter housing; stopping the feed of wash liquid; introducing a gas into the filter housing and draining out the wash liquid by opening a bottom drain valve; stopping the gas flow and opening a drain to exit most of the gas and remaining wash liquid; opening the bottom cake discharge valve; and back pulsing by a gas to break and to release the filter cake from the filter elements of the filter housing. 
     In another embodiment, the present invention relates to a cake filtration device having a filter housing: wherein the filter housing having a top and bottom portion; wherein the filter housing includes a plurality of vertical filter elements; and wherein the bottom of the filter housing has a flange that contains a cake discharge valve that has an internal diameter which is at least 70% of an internal diameter of the filter housing. 
     In another embodiment, the present invention relates to a cake filtration device wherein the cake discharge valve has at least one drain port sufficiently designed to allow for substantial removal of liquid held within the discharge valve. 
     In another embodiment, the present invention relates to a cake filtration device having a filter housing: wherein the filter housing having a top and bottom portion; wherein the filter housing includes a plurality of vertical filter elements; wherein the top portion of the filter housing has at least one process connection for a wash liquid and the bottom portion of the filter housing has at least one process connection for a slurry drain. 
     In another embodiment, the present invention relates to a cake filtration device having a filter housing: wherein the filter housing having a top and bottom portion wherein the filter housing includes a plurality of vertical filter elements; wherein the bottom portion of the filter housing has at least one process connection for a wash liquid and the top portion of the filter housing has at least one process connection for a slurry drain. 
     In another embodiment, the present invention relates to a cake filtration device having a filter housing: wherein the filter housing having a top and bottom portion; wherein the filter housing includes a plurality of vertical filter elements; wherein the bottom of the filter housing has a flange that contains a cake discharge valve that has an internal diameter which is at least 70% of an internal diameter of the filter housing; and wherein the top portion of the filter housing has at least one process connection for a wash liquid and the bottom portion of the filter housing has at least one process connection for a slurry drain. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The present invention will be further explained with reference to the attached drawings, wherein like structures are referred to by like numerals throughout the several views. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention. 
         FIG. 1  illustrates a cross section of an embodiment of the filter system in accordance with the present invention. 
         FIG. 2  shows a vertical cross section through a component of the filter system in accordance with the present invention. 
         FIG. 3  shows a horizontal cross section through a component of the filter system in accordance with the present invention. 
         FIG. 4  shows a cross section of an embodiment of components of the filter system in accordance with the present invention. 
         FIG. 5  shows a top view of an embodiment of a component of the filter system during practicing the present invention. 
         FIG. 6  shows a top view of an embodiment of a component of the filter system in accordance with the present invention. 
         FIG. 7  shows a cross section of a portion of an embodiment of the filter system in accordance with the present invention. 
         FIG. 8  shows a cross section of a bottom portion of an embodiment of the filter system in accordance with the present invention. 
         FIGS. 9A and 9B  illustrate flow charts of embodiments of a process utilizing the filter system in accordance with the present invention. 
         FIG. 10  illustrates a cross section of an embodiment of the filter system in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that is embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention is intended to be illustrative, and not restrictive. Further, the figures are not necessarily to scale, some features are exaggerated to show details of particular components. In addition, any measurements, specifications and the like shown in the figures are intended to be illustrative, and not restrictive. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     The present invention relates to a filter cake device having a filter housing. In one specific embodiment, the filter housing is a vertical round filter housing. Suitable examples of dimensions of filter housings include, but are not limited to, 6″, 16″, 24″, or 26″ diameter. In one embodiment, the filter housing contains at least one filter element. In an embodiment, the filter element has a tube shape. In another embodiment, the filter housings may contain a plurality of filter elements e.g. 3, 7, 15, or 19 elements, and a full system may contain several filter housings to achieve the desired solids rate. In an embodiment, the filter element is a tube shape. In one embodiment, the filter elements are made of porous stainless steel sintered metal. Suitable filter elements material include, but are not, limited to sintered metal, woven metal mesh, porous ceramic, porous polymer membranes, or woven polymer cloth. In one example, the sintered metal membrane elements have a porosity sized for the material being filtered to minimize solids loss and maximize flow through the membrane. Different products may require different filter porosity depending on particle size. In one specific example, the micron rating of the filter elements used to filter corn starch can be in the range of about 1-5 microns. Suitable porosity sizes include, but are not limited to, 0.5-micron to 20-micron. 
     In another embodiment, the filter elements are suspended vertically from the top. In another embodiment, the elements are suspended vertically from a fixed top flange or plate that allows flow from the center of the filter element through the plate and to a filtrate collection header. An example of the filter element is a filter tube that is about 50 mm outside diameter and 1500 mm length. Suitable filter tubes sizes include, but are not limited to, 25-75 mm outside diameter (OD) and 500-2000 mm long. 
     In yet another embodiment, this filtrate collection header has one or more process connections for back-pulse air, exhaust, and/or clean-in-place (CIP) fluid. 
     In another embodiment, the bottom of the filter housing has a flange that contains a valve that is substantially the same inside diameter (ID) as the filter housing. In one embodiment, the valve comprises a means that allows for draining at least some of a liquid from the housing prior to opening the valve. For example, the valve housing may contain one or more outlets to accommodate controlled drainage flow rates. Suitable valves include, but are not limited to, a slide gate valve with flush/drain ports and a high performance butterfly valve with drain ports in the housing. In another embodiment, the bottom of the housing includes connections for slurry, wash liquid, and/or draining. In one embodiment, the bottom drain ports combine into a header. In one embodiment, the bottom drain header has a slurry drain process connection and a water drain process connection. 
     In yet another embodiment, the housing includes one or more process connections for slurry, air, wash liquid, drain, and/or CIP fluid. The top of the housing may include a connection for drying air process, wash liquid, and/or slurry feed. In another embodiment, the process connections may have one or more common manifolds external to the housing. On one example, the metal membranes may foul over time, so in one embodiment, a cleaning system is provided to regenerate the membranes. For corn starch filtration, one example includes a hot, dilute caustic solution to remove the membrane fouling. 
     The cake filtration device of the present invention is used in conjunction with a slurry. For purposes of the present invention, a slurry is a liquid containing suspended solids. Examples of suitable slurries include, but are not limited to, starch in water. In one embodiment, the slurry concentrations range from about 5% to about 40% solids, more particularly, about 10% to about 30%. The method of the present invention results is a “filter cake” having a thickness that can vary from about ⅛″ to over 2″. The thickness of the filter cake can vary depending on variables such as, e.g., the product being filtered, the pressure used during slurry feed, and the time during the slurry feed phase. The maximum cake thickness is determined by the distance between filter elements, filter tubes, and/or the distance between the filter element and the housing wall. 
     The following is an illustrative example of one embodiment of a method of operating the cake forming filtration device. First, slurry is fed into the filter housing through the slurry process connection. Based on the pumping capacity, the pressure inside the filter housing increases and thus, causes liquid to be squeezed through the filter element, for example the filter tube, into the filtrate housing and out the exhaust port. Suitable pressures include, but are not, limited to 30-150 psi. As liquid is pushed through the filter, solids are left behind to form a “filter cake” around the filter tube. 
     Once filtration is deemed complete and thus the slurry flow is stopped, air may be introduced into the filter housing through an air process connection to drain the slurry out of the filter housing either by way of the slurry process connection or through the drain ports. In one embodiment, at least one drain port is located at the bottom of the filter hosing. 
     Wash liquid (e.g. water, acetone, ethanol) can then be fed into the filter housing through the wash liquid process connection. In one embodiment, the wash water inlet is located at the top of the filter housing. The wash liquid is pushed through the cake built up on the filter tubes, displacing the liquid still around the cake into the filtrate collection header. The wash liquid is sent out the exhaust port. 
     Once washing is complete, the air drying is performed. Air may again be introduced into the housing through the air process connection to either push the wash liquid through the cake and/or push the wash liquid out of the housing through the drain port. Air continues to be fed into the filter housing through the air process connection. The air displaces some of the liquid surrounding and within the cake, reducing the cake moisture. Air and liquid are pushed through the filter tubes, into the filtrate collection header, and out the exhaust port. The drain valve is open part of the time to remove all liquid from the housing. 
     When air drying is considered completed (e.g., the desired cake moisture has been achieved), the air valve and exhaust port are closed. Once the housing pressure has been reduced to only slightly above ambient (e.g. less than 5 psi), the bottom cake discharge valve is opened (e.g. a valve that is substantially the same ID as the filter housing; please consider in view of  FIG. 1  in which the discharge valve looks bigger than the housing) and air is introduced into the filtrate header from the back-pulse air connection. Consequently, the cake is dislodged from the filter tubes, falls through the bottom valve, and the cake is recovered. 
       FIG. 1  illustrates a cross section of an embodiment of the filter system in accordance with the present invention. Specifically,  FIG. 1  shows the embodiment having a housing  100  which holds one or more filter elements  101 . In an embodiment, the filter elements  101  are vertically suspended from a header plate  103 . In an embodiment, the filter element  101  is made from a porous sintered metal material. In an embodiment, the header plate  103  allows a flow from a center of the filter element  101  to a filtrate collection header  104 . In an embodiment, the filtrate collection header  104  has at least one process connection  109  for back-pulse air, clean-in-place fluid, and/or filtrate exhaust. These ports may be separate or part of an external manifold. In an embodiment, top flange  102  seals the filtrate collection and allows access to the filter elements. 
     In an embodiment, the housing  100  is connected to a bottom flange  107 . In an embodiment, the bottom flange  107  includes a cake discharge valve  106 . In an embodiment, the housing  100  is a round housing, and a part of the cake discharge valve  106  that opens to the insides of the housing  100  has the same or substantially the same inside diameter as the internal diameter of the housing  100  In an embodiment, a part of the cake discharge valve  106  that opens to the insides of the housing  100  has a diameter which is at least 70% of an internal diameter of the housing  100 . In an embodiment, the cake discharge valve  106  has one or more drain ports  108  drilled into the side of the valve housing to drain substantially all liquid from the housing  100  before the valve  106  is opened. In an embodiment, the valve  106  is a slide gate valve with flush/drain ports. In an embodiment, the valve  106  is a high performance butterfly valve with added drain ports. 
     In an embodiment, the housing  100  further has at least one or more process connections  105  to deliver a feed, for example slurry, air, wash fluid, and clean-in-place fluid and/or to drain the housing  100 . In an embodiment, the housing  100  further has at least one or more process connections  110  to deliver a feed, for example slurry, wash fluid, and clean-in-place fluid, and/or to drain the housing  100 . In an embodiment, process connections  105 ,  108 ,  110  are connected to an external manifold. In an embodiment, housing  100  has additional wall penetrations  111 , for example, pressure gauges, level detectors, and/or sightglasses. 
       FIG. 2  shows a vertical cross section through a filter element  200  used in the present invention. In an embodiment, a ferrule  201  is part of the top part of the filter element.  FIG. 3  shows a cross section of an embodiment of a top plate  303  that separates a housing and a filtrate collection header. The top plate  303  includes holes to pass through portions of filter elements suspended in the housing. In an embodiment, the portions of the filter elements which are above the top plate are substantially designed to allow the filter elements to hang from the top plate within the body of the housing. In an embodiment, the ferrules  312  are attached to the top plate and clamp to the top portions of the filter elements. In an embodiment, the ferrules  312  are welded to the corresponding holes on the top plate. 
       FIG. 4  shows an expanded view of how  FIG. 2  and  FIG. 3  can be combined. The filter element  401  is inserted through top plate  403  and ferrule  412 . Clamp  406  and gasket  405  are used to seal the filter element  401  to ferrule  412 . 
       FIG. 5  shows a horizontal cross section through an embodiment of a housing  500  during practice of the present invention.  FIG. 5  shows filter elements  501  surrounded with a filtrand  502 , a residue remaining in the housing  500  following removal of a filtrate in accordance with the present invention. For example, in an embodiment the filtrand  502  is a filter cake formed when a liquid portion of slurry, the filtrate, is removed from slurry in accordance with the present invention. 
       FIG. 6  shows a top view of an embodiment of a top plate  603  of the filter system in accordance with the present invention. In an embodiment, the top plate  603  contains holes  614  designed to allow portions of filter elements to pass through the top plate  603 . In an embodiment, ferrules  612  are attached to the top plate  603  and clamp the top portions of the filter elements. 
       FIG. 7  shows a cross section of a portion of an embodiment of the filter system in accordance with the present invention. In an embodiment, bottom cake discharge valve  702  is a high performance butterfly valve. In an embodiment, discharge valve  702  is flanged and bolted to the bottom of the housing. In an embodiment, butterfly valve wafer  700  provides the opening to discharge cake from the invention. In an embodiment, there are 4 drain ports drilled into the housing of cake discharge valve  702 . In an embodiment, the 4 drain ports connect to a header  715 . 
       FIG. 8  shows a cross section of a bottom portion of an embodiment of the filter system in accordance with the present invention. In an embodiment, the bottom portion of the filter system includes a high performance butterfly valve  806 , connected to the bottom of a housing. In an embodiment, the high performance butterfly valve  806  has at least one or more drain ports  819  to drain the filter system. In an embodiment, the drain ports  819  are gathered into a common manifold, a drain header  820 . 
       FIGS. 9A and 9B  illustrate flow charts of embodiments of processes utilizing the filter system in accordance with the present invention. In an embodiment, slurry, a liquid containing suspended solids, is fed into a housing  900  of the filter system through the slurry process connection  902 . In an embodiment, the pressure inside the housing  900  causes the liquid portion of the slurry to be squeezed through filter elements  901  into a filtrate header  904  and out of the exhaust port  909 . In an embodiment, as the liquid portion is squeezed through the filter system, a filtrand, e.g. solids, are left behind to form a filter cake around the filter elements  901 . In an embodiment, once filtration is deemed complete, air is introduced in to the housing  900  through an air process connection  922  to push the slurry out of the housing  900  back through the slurry drain connection  903 .  FIGS. 9A and 9B  illustrate two embodiments.  FIG. 9A  has slurry/water being fed from the top and all draining out the bottom.  FIG. 9B  has slurry/water being fed from the bottom, slurry draining from top, and water draining out bottom. 
     In an embodiment, a wash liquid, typically water, is fed into the housing  900  through a wash liquid process connection  908 . In an embodiment, the wash liquid is pushed through the cake built up on the filter elements  901 , displacing the liquid portion still around the cake into the filtrate collection header  904  and into the exhaust port  909 . In an embodiment, once washing is complete, air is introduced in to the housing  900  through an air process connection  922  to either push the wash liquid through the filter cake or push the wash liquid out of the housing  900  through the wash drain connection  905 . 
     In an embodiment, air continues to be fed into the housing  900  through the air process connection  922 . In an embodiment, the air displaces some of the liquid surrounding and/or within the filter cake, reducing the cake&#39;s moisture. In an embodiment, air and liquid are pushed through the filter elements  901  into the filtrate header  904  and out the exhaust port  909 . In an embodiment, a wash liquid drain valve  905  is opened part of the time to remove all liquid from the housing  900 . 
     In an embodiment, when air drying is completed, an air valve  922  is closed. In an embodiment, once a pressure in the housing  900  is reduced to less than 5 psig, the exhaust port  909  is closed and the cake discharge valve  923  is opened. In an embodiment, air is introduced into the filtrate header  904  from a back-pulse air connection  906 . In an embodiment, the filter cake is dislodged from the filter elements  901 , falls through the slide gate  923 , and leaves the filter system. 
       FIG. 10  illustrates the cross section of a modified high performance butterfly valve in accordance with the current invention. In an embodiment, the valve body  1000  is placed with the main disc  1001  as the lowest part of the valve. In a typical high performance ball valve, the seat ring  1002  is fitted into the housing  1000  and held in place by seat retainer  1003 . In an embodiment, one or more holes  1004  are drilled into the housing at or slightly below the level of the main disc  1001 . In an embodiment, connection piping  1005  is welded to the valve housing  1000 . 
     In embodiments, the housing of the filter system is assembled from a broad range of materials from piping to custom fabricated material. In embodiments, all process connections to the housing have valves. In embodiments, the use of the back-pulse of air allows for a gravity discharge. 
     The present invention can be used for various applications where a solid needs to be separated from a liquid portion of slurries into a cake. For example, in an embodiment, the filter system is used to dewater and wash filter corn starch slurries to produce a starch cake. For example, corn starch slurry has a nominal particle size of 8-10 microns. In an embodiment for the corn starch that has solids of this size, the filter element with a porosity of 5 microns allows less than 100 ppm start solids into the filtrate.