Abstract:
Separating a mixture comprising at least two solid materials comprises transporting the mixture into a plenum, introducing air into the plenum, removing a heavier fraction of the solid materials from the plenum, removing air having a lighter fraction of the solid materials entrained therein from the plenum, removing the lighter fraction of the solid materials from the air that is removed from the plenum, filtering the remaining air, and re-circulating the air back to the plenum. Valves at the locations where material is introduced to and removed from the system can prevent air flow therethrough while allowing the materials to pass. The air can be introduced into the plenum at an angle with respect to the pathway in which the heavier fraction of the materials falls through the plenum, thereby avoiding damage to a screen that diffuses the air being introduced into the plenum.

Description:
RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application No. 61/214,794 filed Apr. 28, 2009 and entitled “Apparatus For Separating Recycled Materials Using Air.” The complete disclosure of the above-identified priority application is hereby fully incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to an apparatus for sorting materials. More particularly, the invention relates to an apparatus that employs closed-system air separation to sort and recover materials from recyclable materials. 
     BACKGROUND 
     Recycling of waste materials is highly desirable from many viewpoints, not the least of which are financial and ecological. Properly sorted recyclable materials often can be sold for significant revenue. Many of the more valuable recyclable materials do not biodegrade within a short period. Therefore, recycling such materials significantly reduces the strain on local landfills and ultimately the environment. 
     Typically, waste streams are composed of a variety of types of waste materials. One such waste stream is generated from the recovery and recycling of automobiles or other large machinery and appliances. For example, at the end of its useful life, an automobile will be shredded. This shredded material can be processed to recover ferrous metals. The remaining materials, referred to as automobile shredder residue (ASR) typically would be disposed in a landfill. Recently, efforts have been made to recover additional materials from ASR, such as plastics and non-ferrous metals. Similar efforts have been made to recover materials from whitegood shredder residue (WSR), which are the waste materials left over after recovering ferrous metals from shredded machinery or large appliances. Other waste streams may include electronic components, building components, retrieved landfill material, or other industrial waste streams. These materials generally are of value only when they have been separated into like-type materials. However, in many instances, cost-effective methods are not available to effectively sort waste streams that contain diverse materials. This deficiency has been particularly true for non-ferrous materials, and particularly for non-metallic materials, such as high density plastics, and non-ferrous metals, including copper wiring. For example, one approach to recycling plastics has been to station a number of laborers along a sorting line, each of whom manually sorts through shredded waste and manually selects the desired recyclables from the sorting line. This approach is not sustainable in most economies because the labor cost component is too high. Also, while ferrous recycling has been automated for some time, mainly through the use of magnets, this technique is ineffective for sorting non-ferrous materials. Again, labor-intensive manual processing has been employed to recover wiring and other non-ferrous metal materials. Because of the cost of labor, many of these manual processes are conducted in other countries and transporting the materials to and from these countries adds to the cost. 
     Copper wiring and other valuable non-ferrous metals can be recovered and recycled. However, waste materials, including ASR and WSR, must be separated from a concentrated mass of recoverable materials. Typically, the waste materials will include wood, rubber, plastics, glass, fabric, and copper wiring and other non-ferrous metals. The fabric includes carpet materials from the shredded automobiles. Often, the fabric includes embedded ferrous materials accumulated during the shredding process. Methods are known for separating the non-ferrous metals from these other materials. These methods may include a “pre-concentration” process that roughly separates the materials for further processing. However, these methods typically involve density separation processes. These processes typically involve expensive chemicals or other separation media and are almost always a “wet” process. These wet processes are inefficient for a number of reasons. After separation, often the separation medium must be collected to be reused. Also, these wet processes typically are batch processes, and they cannot process a continuous flow of material. 
     Another known system uses an air aspirator, or separator, to separate a light fraction of materials, which typically contains the waste materials that are not worth recovering (that is, the wood, rubber, and fabric), from a heavy fraction of materials, which typically includes the metals to be recovered. These types of separators are known in other industries as well, such as the agricultural industry, which uses air separators to separate materials of differing densities. However, these known systems usually employ open systems, where air is moved through the system and then released to the atmosphere. One problem with these systems is that they need air permits to operate, which adds cost to the system. 
     Conventional systems also force air directly up from a bottom of the plenum, and the material being separated falls on top of a screen at the bottom of the plenum. Accordingly, such systems cannot process heavy materials because the heavy materials will damage the screen when those materials fall on top of the screen. 
     Accordingly, a need exists in the art for a system and method that processes materials to be separated while recycling air in a closed system. Additionally, a need exists for a system and method that can separate heavier materials without damaging the system. 
     SUMMARY 
     The invention relates to a closed air system for separating materials. A fan directs air into a plenum in which the materials are separated. A heavier fraction of the materials falls through the air in the plenum to the bottom of the plenum. A stream of air carrying a lighter fraction of the materials exits the plenum and is directed to an expansion chamber. In the expansion chamber, the lighter fraction of the materials falls to the bottom as the velocity of the air slows. The air then flows from the expansion chamber to a centrifugal filter, which removes remaining material from the air. The air then returns to the fan where it is re-circulated through the system. 
     The separated materials can be removed from the system at the bottom of the plenum, the bottom of the expansion chamber, and the bottom of the centrifugal filter. Rotary Valves (“Air Locks”) at these locations prevent air from flowing therethrough while allowing the materials to pass. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 ,  2 , and  3  are perspective, side, and top views, respectively, of an air separation classifier according to an exemplary embodiment. 
         FIG. 4  is a perspective view of certain components of the classifier illustrated in  FIGS. 1-3 . 
         FIG. 5  is a cross sectional view of an air reducer according to an exemplary embodiment. 
         FIG. 6  is a side view of an expansion chamber according to an exemplary embodiment. 
         FIG. 7  is a side view of a lower air plenum according to an exemplary embodiment. 
         FIG. 8  is a perspective view of a rotary valve according to an exemplary embodiment. 
         FIGS. 9 and 10  are perspective and end views, respectively, of an exemplary vane of the rotary valve depicted in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Referring to the drawings, in which like numerals represent like elements, aspects of the exemplary embodiments will be described. 
     With reference to  FIGS. 1-4 , an exemplary air separation classifier system  100  will be described.  FIGS. 1 ,  2 , and  3  are perspective, side, and top views, respectively, of an air separation classifier system  100  according to an exemplary embodiment.  FIG. 4  is a perspective view of certain components of the system  100  illustrated in  FIGS. 1-3 . The system  100  implements a closed air system to process solid materials. 
     An air flow producing device  102  produces air flow in the system  100  in the direction of the arrows illustrated in  FIGS. 1-3  by drawing air from a return side of the air flow producing device  102  and pushing air through a supply side of the air flow producing device  102 . The size of the air flow producing device can be adjusted to provide the desired air flow and pressures throughout the system  100 . In an exemplary embodiment, the air flow producing device  102  is a 50-75 horsepower fan. The air flow producing device  102  can have a variable speed control to control the air flow created by the air flow producing device  102 . 
     The air flow producing device  102  pushes air into the air intake  104 . The air then flows from the air intake  104  through a lower transition  106 , through an air reducer  107 , and into a plenum  108 . The air reducer  107  comprises a butterfly valve  502  ( FIG. 5 ) that can be rotated around a shaft  504  ( FIG. 5 ) to obstruct or unobstruct air flow through the air reducer  107 , thereby controlling the air flow and velocity through the air reducer  107  and into the plenum  108 . 
     The plenum  108  includes two sections, a lower plenum  108   a  and an upper plenum  108   b . The air enters the lower plenum  108   a  via a lower entrance  108   c  in the lower plenum  108   a.    
     Material to be separated is introduced into the system  100  at location A via an intake feeder (not shown). The material to be separated is fed into a first rotary valve  110  (A), which allows the material to fall into the upper plenum  108   b  via an upper entrance  108   d  in the upper plenum  108   b . The first rotary valve  110  (A) also prevents all or a substantial amount of air from exiting the system  100  via the upper entrance  108   d  in the upper plenum  108   b . The rotary valve  110  (A) prevents a sufficient amount of, in some cases all, air from exiting the system  100  to maintain the desired static pressures and air flows therein. 
     The air flows through the air intake  104 , into the plenum  108 , and up the plenum  108 , where it interacts with the material to be separated as the material to be separated falls through the plenum  108  via the force of gravity. 
     The movement of air through the material to be separated causes lighter material to be entrained in the air flow while heavier material falls through the plenum  108 . The heavier material falls through a lower exit  108   f  in the lower plenum  108   a  and exits the system  100  at location B via a second rotary valve  110  (B) attached to the lower exit  108   f  in the lower plenum  108   a . The second rotary valve  110  (B) also prevents air from exiting the system  100  via the lower exit  108   f  in the lower plenum  108   a , similarly to the operation of the first rotary valve  110  (A). 
     Some light material could remain with the heavy material, as the light material is physically entwined with the heavy material and the force of the air is insufficient to entrain the light material. The system  100  can minimize the amount of light material that is not entrained in the air by optimizing the residence time of the material to be separated in the plenum  108 . By optimizing the residence time, the chances are increased that the air flow will separate the heavy and light fractions of material and that the light fractions will be entrained in the air. This optimization allows for the separation of materials that have relatively close densities. 
     Residence time of the material to be separated in the plenum  108  can be optimized in a number of ways. This optimization allows for highly efficient separation of the materials—the residence time is such that the material to be separated that falls through the plenum  108  under gravity is mixed with the moving air to maximize the amount of light materials that are entrained in the air as it moves up through the plenum  108 . This process, in turn, maximizes the amount of heavy material, including, for example, copper wire, that falls out of the plenum  108 . In other words, this increased residence time allows for a more complete separation of the light and heavy fractions of materials. 
     The material to be separated can be sized, such as in a granulator or other size reducing equipment, prior to entering the plenum  108 . In exemplary embodiments, this step can be omitted, and the system  100  can process the material to be separated directly from a shredder or other process equipment without sizing. 
     In one exemplary embodiment, the residence time in the plenum  108  is increased by matching the required air flow with the size of the material to be separated. An air diffuser plate  602  ( FIG. 6 ) is added between the location where the air flow leaves the air flow producing device  102  and the location where the air flow enters the plenum  108 . As illustrated in the exemplary embodiment of  FIG. 7 , the diffuser plate is disposed at the lower inlet in the plenum  108 . The diffuser plate  602  creates minor back pressure and distributes the air flow evenly throughout the width of the plenum  108 . The diffuser plate  602  can be a perforated metal plate and can have openings sized to maximize the residence time of the material to be separated based on the size of the material to be separated and the size of the air flow producing device  102 . Examples for configurations for this plate range from a plate with one-half inch holes to a mesh screen, with many fine holes. For example, for material to be separated with a nominal size of 0-4 millimeters, the diffuser plate can have one-quarter inch holes. For larger size particles, a plate with larger holes may be used. 
     In the exemplary embodiment illustrated in  FIGS. 1 ,  2 ,  4 , and  7 , the lower inlet in the plenum  108  is angled with respect to a vertical pathway through which the mixture and the heavy fraction of materials pass. In this manner, the heavy fraction of materials can fall through the plenum  108  to the lower exit  108   f  of the plenum  108  without falling onto and/or damaging the screen  602 , which is positioned at the lower inlet in the plenum  108 . 
     Alternatively or additionally, a depth of the plenum chamber can be optimized to achieve the maximum residence time for the waste material to be separated in the chamber. For example, the depth can be between 10 inches and 16 inches. The smaller depth can be used for smaller particle sizes. For example, the 10 inch depth can be matched to particles with a size range of 0-1 inch. In exemplary embodiments, a volume of the plenum  108 , including a particular depth, width, height, and shape can be selected to obtain the desired static pressures and air flows in the plenum  108  and the system  100  and to process the desired type and size/density of materials. 
     In one exemplary embodiment, the following static pressures and air flow volumes for different particle size ranges are used: 
     
       
         
               
               
               
             
           
               
                   
               
               
                   
                 Static Pressure 
                 Air Flow 
               
               
                 Particle Size 
                 (in. of water) 
                 (cubic feet per minute) 
               
               
                   
               
             
             
               
                 4 millimeters to ⅝ inches 
                 8 to 12 
                  8,000 to 12,000 
               
               
                 ⅝ inches to 1.25 inches 
                 12 
                 15,000 to 22,000 
               
               
                 1.25 inches to 5 inches 
                 9 to 13 
                 12,000 to 15,000 
               
               
                   
               
             
          
         
       
     
     The sizes of the air flow producing device  102 , the passageways and transitions through which the air flows, the plenum  108 , the air reducer  107 , the expansion chamber  114 , and other components can be selected to obtain the desired static pressures and air flows throughout the system  100  and to process the desired type and size/density of materials. 
     As illustrated in  FIGS. 1 ,  2 , and  4 , the lower plenum  108   a  can comprise an access door  126  to gain entry into an interior of the plenum  108 . 
     The air with the entrained light fraction of materials moves up and out of the plenum  108 , through an upper transition  112 , and into an expansion chamber  114  via an entrance  114   a  in the expansion chamber  114 . In the expansion chamber  114 , the air and entrained light fraction of materials contact a redirecting plate  702  ( FIG. 7 ), which redirects the path of the air and entrained light fraction of materials. As the velocity of the air slows in the expansion chamber  114 , the entrained light fraction of materials falls to the bottom of the expansion chamber  114  and exits the system  100  at location C via a third rotary valve  110  (C) attached to a lower exit  114   b  in the expansion chamber  114 . The third rotary valve  110  (C) also prevents air from exiting the system  100  via the lower exit  114   f  in the expansion chamber  114 , similarly to the operation of rotary valves  110  (A, B). 
     The air then flows from an upper exit  114   c  of the expansion chamber  114 , through ducting  116 , and into a centrifugal filtering device  118 . 
     The air flow producing device  102  pushes the air through the expansion chamber  114  and also draws the air from the centrifugal filtering device  118 , which in turn draws air from the expansion chamber  114 . The expansion chamber  114  can comprise a make-up air vent to allow air into the expansion chamber  114  to maintain the desired air flow and static pressure throughout the system  100 . In exemplary embodiments, the make-up air vent can comprise a butterfly-type vent, a pressure actuated vent, or other suitable vent. 
     Referring to  FIG. 7 , the plate  702  prevents the air and entrained light fraction of materials from flowing directly through the expansion chamber  114 , from the entrance  114   a  to the upper exit  114   c . With the plate  702 , the air flows through the expansion chamber in the general direction of the dashed arrows illustrated in  FIG. 7 , allowing time for the air flow to slow and for the light fraction of materials to fall to the bottom of the expansion chamber  114 . The exemplary plate  702  includes two sections oriented and positioned to deflect the air flow in the desired direction. However, any suitable shape and position of the plate  702  can be used to redirect the air flow in the desired direction. Additionally, the shape and position of the plate  702  can be controlled to optimize the air flow based on the materials included in the light fraction of materials entrained in the air flow. 
     In exemplary embodiments, a volume of the expansion chamber  114 , including a particular depth, width, height, and shape can be selected to obtain the desired static pressures and air flows in the expansion chamber  114  and the system  100  and to process the desired type and size/density of materials. 
     Referring back to  FIGS. 1-3 , the centrifugal filtering device  118  removes additional solid material that remains entrained in the air. In operation, the centrifugal filtering device  118  directs the flow of the air in a circular (cyclone) manner, which forces the remaining material to the outside of the centrifugal filtering device  118 . The remaining material then falls to the bottom of the centrifugal filtering device  118  and exits the system  100  at location D via a fourth rotary valve  110  (D) attached to the centrifugal filtering device  118 . The fourth rotary valve  110  (D) prevents air from entering the system  100  via the centrifugal filtering device  118  so air can only be drawn from the expansion chamber  114 , similarly to the operation of rotary valves  110  (A, B, C) which prevent air from exiting the system  100 . 
     Additionally or alternatively, other devices can be used to filter the air and/or recover materials from the air that is flowing through the system  100 . For example, an inline filter can be used in the ducting  116 . Any suitable device that further cleans the air returning to the fan while maintaining the desired air flow and static pressures in the system  100  can be used. 
     Alternatively, in a non-closed loop system embodiment, the filter can filter the air as it exits the expansion chamber  114  into the atmosphere. 
     In the exemplary embodiment illustrated in  FIGS. 1-3 , transitions  120  direct the air flow from the ducting  116  into the centrifugal filtering device  118  and from the centrifugal filtering device  118  into the ducting  116 . 
     The air is then cycled back to the air intake  104 . More specifically, the air flows from the centrifugal filtering device  118  through ducting  116  and returns to the air flow producing device  102 . The air flow producing device  102  draws the air from the ducting  116  and pushes the air towards the plenum  108 , thereby reusing the air throughout the system  100 . 
     In this way, the process air loops through the system  100  and is not released to the atmosphere. The air path from the fan to the plenum  108  to the expansion chamber  114  to the centrifugal filter device  118  and back to the fan is closed. Valves (such as the rotary valves  110 ) and duct connections prevent the bleeding of air into the atmosphere. 
     The system  100  can comprise brackets  122  at various external locations to attach the system  100  to a support structure  124  that holds the components of the system  100  in place. 
     Materials separated via the system  100  can be usable materials or waste materials. In one exemplary embodiment, all of the materials can be waste materials that are separated and removed from the system  100  at locations A-D for proper disposal. In another exemplary embodiment, all of the materials can be recyclable materials that are separated and removed from the system  100  at locations A-D for recycling. In yet another exemplary embodiment, the materials can comprise both waste materials and recyclable materials that are separated and removed from the system  100  at locations A-D for proper disposal and recycling, respectively. 
     The rotary valves  110  described with reference to  FIGS. 1-3  are exemplary “airlocks,” which maintain a suitable air seal while allowing materials to enter or exit the system  100 . However, other suitable types of airlocks can be used which maintain a suitable air seal while allowing materials to enter or exit the system  100 . 
     An exemplary rotary valve  110  will now be described with reference to  FIGS. 8-10 .  FIG. 8  is a perspective view of a rotary valve  110  according to an exemplary embodiment.  FIGS. 9 and 10  are perspective and end views, respectively, of an exemplary vane of the rotary valve  110  depicted in  FIG. 8 . 
     The rotary valve  110  comprises in inlet  801  through which material enters the rotary valve  110  and an exit  803  through which material exits the rotary valve  110 . An interior of the rotary valve  110  houses multiple vanes  804  supported on a shaft  806 . The vanes  804  are sizes to contact the interior of the rotary valve  110  during operation such that air does not pass through the rotary valve  110 . In operation, a motor  802  turns the shaft  806 , thereby turning the vanes  804 . As the vanes  804  turn, material disposed between the vanes  804  is transferred from the inlet  801  to the exit  803 . 
     The vanes  804  can comprise a material that creates a suitable seal with the interior of the rotary valve  110  to prevent air flow through the rotary valve  110 . 
       FIG. 10  illustrates an exemplary embodiment comprising five vanes  804  disposed seventy-two degrees apart. Other configurations utilizing more or less vanes that prevent an air path through the rotary valve  110  are within the scope of the invention. 
     The description above uses the terms heavy fraction and light fraction to describe the two streams of material to be separated. One of ordinary skill in the art would understand that these terms are relative. In one exemplary embodiment, the light fraction can include fabric, rubber, and insulated wire, and the heavy fraction can include wet wood and heavier metals, such as non-ferrous metals including aluminum, zinc, and brass. In another exemplary embodiment, the light fraction can include fabric (“fluff”), and the heavy fraction can include insulated wire. Indeed, the apparatus of the present invention can be optimized to separate material within a narrow range of densities. As such, the processed material can range from raw shredder residue to a light fraction that was separated by a different separator technology, such as a Z-box air separator or sink/float separator. 
     One of ordinary skill in the art also would understand that the separator described above may be one step in a multi-step process that concentrates and recovers recyclable materials, such as copper wire from ASR and WSR. 
     Although specific embodiments of the present invention have been described in this application in detail, the description is merely for purposes of illustration. It should be appreciated, therefore, that many aspects of the invention were described above by way of example only and are not intended as required or essential elements of the invention unless explicitly stated otherwise. Certain steps and components in the exemplary processing methods and systems described herein may be omitted, performed and a different order, and/or combined with other steps or components. Various modifications of, and equivalent components corresponding to, the disclosed aspects of the exemplary embodiments, in addition to those described herein, can be made by those having ordinary skill in the art without departing from the scope and spirit of the present invention described herein and defined in the following claims, the scope of which is to be accorded the broadest interpretation so as to encompass such modifications and equivalent structures.