Patent Publication Number: US-4580732-A

Title: Filter cake processing method and mechanism

Description:
This application is a continuation of application Ser. No. 354,833, filed Mar. 4, 1982, now abandoned. 
    
    
     TECHNICAL FIELD 
     This invention relates to a method and mechanism for shredding a filter cake which has a pasty consistency, and transporting shredded filter cake particles to a drier mechanism. 
     BACKGROUND ART 
     The prior art systems used for transfering a filter cake from a filter press to a dryer typically involved shoveling of the filter cake mass onto pan and drying the mass. In the case of a great number of materials, the shoveling operation can easily be an all day project because the filter cake mass has a pasty or peanut butter like consistency. The filter cake tends to stick to the shovel, making the operation extremely inefficient. The drying operation must be continued until the filter cake is totally dry and could require a full week in the dryer because of the difficulty of drying the center of the mass of the filter cake. The drying time is directly related to the amount of exposed surface area, and therefore great efforts have been made to convert the filter cake mass into relatively small particles. Among the systems employed for converting the filter cake mass into particles is a mechanism which required a large, expensive, high energy consuming hydraulic ram. Attempts to use a blender type of mechanism have proven to be unsuccessful because the wiper blades of the blender tend to work the filter cake mass for an extended period and produce a liquified product. The pasty consistency of the filter cake has proven to render the granulating or pulverizing of the filter cake extremely difficult. 
     SUMMARY OF THE INVENTION 
     It has now been found that the problems encountered with the prior art systems can be overcome through the use of a wiper blade in combination with a shredding screen. In accordance with the present invention, a wiper blade of a resilient though stiff material is drawn across a shredding screen which is formed of a first set of spaced parallel bars and a second set of parallel spaced bars. The second set of spaced parallel bars are at a right angle to the first set of spaced parallel bars. The wiper blade is a semi-rigid member formed of a material such as a hard urethane or rubber. The lower end of the wiper blade is positioned for firm contact with the spaced parallel bars of the shredding screen. The upper section of the wiper blade is supported for limited oscillatory movement in order to act on the filter cake during the shredding operation. The process involves dumping the filter cake into a hopper which sits over the shredding screen. The shredding screen is moved relative to the wiper blade thereby forcing the filter cake mass through the shredding screen as descrete particles. The descrete particles can be collected in a pan and conveyed to a dryer. 
     The system of the instant invention provides among its advantages, the rapid production of descrete particles with a relatively low energy requirement for the particle forming operation and the increase in speed of the drying operation with a concomittent decrease in the energy requirement of the drying operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and advantages of the invention will become more apparent and more readily understood when the following detailed description of the invention is read in conjunction with the drawings wherein: 
     FIG. 1 is a schematic cross-sectional side view of a shredding and collecting assembly of the instant invention; 
     FIG. 2 is a side view of a shredder assembly showing the shredding screen in a first position relative to the wiper blade; 
     FIG. 3 is a side view of a shredder assembly showing the shredding screen in a second position relative to the wiper blade; 
     FIG. 4 is a side view of a shredder assembly showing the shredding screen in a third position relative to the wiper blade; 
     FIG. 5 is a side view of a shredder assembly showing the shredding screen in a fourth position relative to the wiper blade; 
     FIG. 6 is a schematic cross-sectional end view of a shredding and collecting assembly of FIG. 1, and 
     FIG. 7 is a perspective view of a wiper blade rotational carrier bar. 
    
    
     MODE OR MODES FOR CARRYING OUT THE INVENTION INCLUDING THE BEST MODE 
     The device of the present invention is a filter cake shredder for dryer pan loading or loading in drums for bulk sale. The filter cake shredder and pan loader assembly 100 employs a live bottom and can be positioned directly under the filter or can receive filter cake from filter cake pans or other containers. 
     As shown in FIG. 1, a filter cake shredder and pan loader assembly 100 is provided for receiving filter cake from a filter (not shown). The filter can be a pressure filter such as a plate and frame press, a vacuum, centrifugal or gravity filter. The type of filtration employed and the material of the filter cake are not narrowly critical with respect to the present invention. 
     However, the apparatus and methods of the invention have particular utility in connection with filter cakes which are of a pasty or dough-like consistency and which can be as thick and viscous as peanut butter, or can have a consistency characteristic of putty or clay. The material which is being processed can be any wet product such as a pigment, food stuff such as beet-sugar, paper pulp or other product of the filter. These types of filter cakes are particularly difficult to handle because of their tendency to stick to processing tools such as shovels, thereby rendering the transferring of the material quite difficult. Moreover, it is extremely difficult to force the material through extrusion orifices and ram devices employed for this type of operation are high in cost and power comsumption. During drying operations, the exposed surfaces lose water quite rapidly, but the interior regions are slow to dry. Since the drying operation must continue until the entire mass is completely dry, drying of a pasty filter cake can require a full week. Similarly, the transferring of the material from the filter to the dryer can be a full day project. By way of contrast, the instant system can reduce the transferring operation to a continuous operation or at least an extremely fast process. 
     The filter cake 104 is dumped into the filter cake shredder and pan loader assembly 100 from a filter cake box or can be received directly from a filter located directly above the filter cake shredder and pan loader assembly 100. The filter cake shredder and pan loader assembly 100 is fitted with a live bottom mechanism or shuttle bar assembly indicated generally as 101. The shuttle bar assembly 101 includes shredder bars 102 and complementary cutter bars 103 which are moved in the direction of arrow 110. The shuttle bar assembly 101 is connected to a reciprocating drive mechanism, not shown, by means of the shuttle drive means 109. The filter cake 104 is forced through the space between the crossed bars 102 and 103, by the weight of the material, and most significantly by the relative movement between the shuttle bar assembly 101, the walls of the hopper 115 and the wiper blade assembly 108 with a shearing effect. The most significant and critical driving force is achieved by means of the interaction between the wiper blade lower end and the shredder bar 102. The filter cake 104 is prevented from accumulating or hanging up by virtue of the reciprocating motion of the wiper blade upper end 105. This motion is limited by wiper blade stop 106 and wiper blade stop 107. Since the wiper blade assembly 108 rotates or oscillates about the wiper blade rotational carrier bar 708, the limiting of motion of the upper end also confines the degree of movement of wiper blade lower end. The wiper blade assembly 108 is formed of a material which has a spring steel-like quality. A urethane polymer having a Durometer hardness of at least 90 (A scale) has been found to provide the combination of durability, corrosion resistance and resiliency. 
     The interaction between the wiper blade lower end and the filter cake 104 to form shredded particles 111 and fill pan 113 is explained in greater detail hereinafter, in association with FIGS. 2, 3, 4 and 5. The filter cake 104 passes through the shuttle bar assembly 101, as indicated by reference numeral 117 to form individual particles 111 of a predetermined size, dependent upon the size of the opening between the crossed bars of the shredder assembly 101, as well as the position of the wiper blade assembly 108 relative to the shuttle bar assembly 101, the speed of shuttle bar assembly 101 and the properties of filter cake 104. The collection of shredded particles 112 in the pan 113 can be transported by means of conveyor mechanism 114 to the desired destination. In certain circumstances the collection of shredded particles 112 is collected in drums for shipping, or for many applications is transported directly to a dryer. 
     The shuttle bar assembly 101 is referred to as a live bottom because it moves relative to the housing. The wiper blade assembly 108 is not indepenently powered, but rather moves in response to movement of shuttle bar assembly 101. The wiper blade assembly 108 oscillates about the fulcrum point provided by wiper blade rotational carrier bar 708. The wiper blade lower end rides up and over the shredder bar 102 as shown in FIG. 2. The wiper blade resiliency can best be compared to spring steel. The wiper blade lower end 116 deforms initially, due to the force exerted on the wiper blade 108 by virtue of the blade being compressed between the wiper blade rotational carrier bar 708 and the shredder bar 102 or complemtary cutter bars 103. The lower end 116 of the plastic spring like wiper blade, as shown in FIG. 3, rides on the complementary cutter bar 103 as it moves between adjacent bars 102, unless the bottom of the wiper blade is notched so as to permit the wiper blade to extend below the lower bar. 
     The trailing end 130 of the wiper blade 108 can be notched so as to permit the wiper blade trailing end 130 to project through the upper bars 102 to a point below the bottom of the complemtary cutter bars 103. 
     During this stage of the process, filter cake is extruded through the openings formed by the shredder bar 102 and complemtary cutter bars 103. The wiper blade lower end drops off the shredder bar 102 onto or past the complemtary cutter bars 103 with a snapping action and punches filter cake through the openings. The trailing edge of the wiper blade lower end shears the extruded filter cake as the forward portion of the wiper blade lower end extrudes additional filter cake. 
     As indicated in FIGS. 2 through 5 by arrows 303, 403 and 503, the live bottom travels first in one direction. It then reverses its direction of travel and transverse the bottom of the filter cake shredder and pan loader assembly 100 in the other direction. 
     The filter cake can be confined within the hopper region of the filter cake shredder and pan loader assembly 100 by the lower end of the side walls of the hopper, or alternatively, wiper blades 306 can be used. The use of wiper blades 306 at the housing ends eliminates the need to provide a clearance space 120 between the hopper 115 and the shuttle bar assembly 101. 
     The entire wiper blade and shuttle bar assembly can be remove for ease of cleaning or replacement with an alternate unit to satisfy the requirements of a different material. 
     It is evident from FIG. 6 that the wiper blade upper end 105 extends across the full width of the shuttle bar assembly 101 and oscillates about the wiper blade rotational carrier bar 708 to the extent permitted by the wiper blade stop 106 and wiper blade stop 107 which engage the wiper blade upper end 105. The wiper blade rotational carrier bar 708 can be provided with a wiper blade receiving slot 701 for receiving the wiper blade upper end 105. The wiper blade upper end 105 can be fixed in place by means of set screws located at spaced positions in set screw receiving openings 702. The wiper blade rotational carrier bar 708 is mounted in place for oscillating movement by means of retaining pins 609. Each end of the wiper blade rotational carrier bar 708 is provided with rotation pin receiving openings 703 for the mounting pins 609. 
     The interaction between the wiper blades 105, the filter cake 104 and the shredder assembly 101 can be controlled by raising or lowering the wiper blade with respect to the shuttle bar assembly 101. This can conveniently be achieved by providing a vertical adjusting mechanism for the carrier bar 708. The vertical adjusting mechanism thus increase or decrease the force exerted on the filter cake by the wiper blades. 
     The live bottom 610 can be formed of complementary cutter bars 603 which are preferably welded to the shredder bar 102 at a plurality of cross points. The shuttle supports 602 are suported by shuttle guide 602 which are fixed to the filter cake shredder and pan loader assembly 100 end walls 615. 
     In another aspect of the invention, the shredder can be employed to particlize friable material which can be either wet or dry. Thus, while the mechanism of the instant invention works with materials as pasty as peanut butter, it can convert blocks of material such as rigid, expanded polystyrene blocks into small particles. 
     In accordance with the process of the invention a wiper blade of a flexible material is drawn across a shredding screen which is formed of a first set of spaced parallel bars and a second set of parallel spaced bars. The second set of spaced parallel bars are at a right angle to the first set of spaced parallel bars. The wiper blade is a semi-rigid member formed of a material such as a hard urethane or rubber. The lower end of the wiper blade is positioned for firm contact with the spaced parallel bars of the shredding screen. The upper section of the wiper blade is supported for limited oscillatory movement in order to act on the filter cake during the shredding operation. It should be understood that the wiper blades can be fixed in place, depending upon system requirements. The process involves dumping the filter cake into a hopper which sits over the shredding screen. The shredding screen is moved relative to the wiper blade thereby forcing the filter cake mass through the shredding screen as descrete particles. The descrete particles are collected in a pan and conveyed to a dryer. The system of the instant invention provides among its advantages, the rapid production of descrete particles with a relatively low energy requirement for the particle forming operation and the increase in speed of the drying operation with a concomittent decrease in the energy requirement of the drying operation. 
     The number of wiper blades and the space between the blades is not critical, but rather can be selected depending upon the desired results and the rheology of the filter 
     
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GLOSSARY                                                                  
Reference                                                                 
Number     Description                                                    
______________________________________                                    
100        filter cake shredder and pan loader assembly                   
101        shuttler bar assembly                                          
102        shredder bar                                                   
103        complemtary cutter bars                                        
104        filter cake                                                    
105        wiper blade upper end                                          
106        wiper blade stop                                               
107        wiper blade stop                                               
108        wiper blade assembly                                           
109        shuttle drive means                                            
110        arrow                                                          
111        shredded particles                                             
112        collection of shredded particles                               
113        pan                                                            
114        conveyor mechanism                                             
115        hopper                                                         
116        wiper blade lower end                                          
117        extruding filter cake                                          
120        clearance between the hopper and the                           
           shuttle bar assembly 101                                       
201        arrow                                                          
301        arrow                                                          
501        arrow                                                          
601        shuttle support                                                
602        shuttle guide                                                  
603        shredder cross bar                                             
609        mounting pins                                                  
610        live bottom                                                    
615        end walls                                                      
701        wiper blade receiving slot                                     
702        set screw receiving opening                                    
703        rotation pin receiving opening                                 
708        wiper blade rotational carrier bar                             
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