Patent Application
20090188842
The present invention relates to an improved method and apparatus for separating materials from shredder residue and other waste streams. More specifically, this invention relates to an improved method and apparatus for separating elastomeric materials from mixed material streams.
The usage of elastomer including rubber products in automobiles continues to increase. Additionally, more shredder yards in the United States are shredding vehicles with tires remaining on them. This increases the amount of rubber found in shredder residue. When the polymers are separated from the shredder residue in processes such as provided at a mechanical separation plant at Argonne National Laboratory, almost all of the rubber reports to the polymer concentrate fraction. In some residues, rubber constituted over 50% of the polymer concentrate by weight.
A need exists for an effective method and mechanism to recover polymers from shredder residue, which are currently disposed of in landfills. Known sink float processes, including froth flotation, separate the polymer concentrate into potentially recyclable plastics streams. These streams typically are contaminated with different amounts of elastomeric materials. These materials can reduce the quality and value of the recovered plastics. In addition, an elastomeric stream could prove to be a product of value. Therefore, it would be advantageous to find a method to separate these materials from the recovered plastics.
It is desirable to provide such a process that can be installed to separate the rubber from the polymer concentrate before it is fed to the flotation system or used to purify individual products. If the former is used, less material will enter the flotation system reducing the size and cost of the flotation process.
U.S. Pat. No. 7,255,233, issued to Daniels et al. on Aug. 14, 2007 and assigned to the present assignee, discloses a method and apparatus for separating mixed plastics using flotation techniques including a first stage initial washing tank for washing of incoming plastics and providing a first separation process and at least one separation module. The first stage initial washing tank includes a perforated basket to hold heavy materials, such as metals, glass, and the like. Each separation module includes a separation tank, a feeding section for feeding of mixed stream into the separation tank; and a collecting section for collecting of the separated mixed plastics including floaters and sinkers from the separation tank. The separation tank has no moving parts. Each separation tank and the first stage initial washing tank is a standard off-the-shelf circular tank with a flat bottom. Washing and drying steps are eliminated between separation stages. Batch processing is replaced with generally continuous operation. An integrated vibrating screen and air classification system is provided.
U.S. Pat. No. 5,653,867, issued to Jody et al. on Aug. 5, 1997 and assigned to the present assignee, discloses an improved method for separating acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS) plastics from each other. The ABS and HIPS plastics are shredded to provide a selected particle size. The shredded particles of the ABS and HIPS plastics are applied to a solution having a solution density in a predefined range between 1.055 gm/cm.sup.3 and 1.07 gm/cm.sup.3, a predefined surface tension in a range between 22 dynes/cm to 40 dynes/cm and a pH in the range of 1.77 and 2.05. The disclosed method separates ABS and HIPS, two solid thermoplastics which have similar densities, by selectively modifying the effective density of the HIPS using a binary solution with the appropriate properties, such as pH, density and surface tension, such as a solution of acetic acid and water or a quaternary solution having the appropriate density, surface tension, and pH.
U.S. Pat. No. 6,599,950, issued to Jody et al. on Jul. 29, 2003 and assigned to the present assignee, discloses a method of separating a portion of acrylonitrile-butadiene-styrene (ABS) from a mixture containing ABS and for separating a portion of ABS and polycarbonate (PC) from a mixture of plastics containing ABS and PC. The method includes shredding and/or granulating the mixture of plastics containing ABS and PC to provide a selected particle size; sequentially dispersing the shredded mixture of plastics in a series of aqueous solutions having different specific gravities and separating the floating fraction until the desired separation is obtained. Surface tension and pH are also variables to be controlled.
Principal objects of the present invention are to provide an improved method and apparatus for separating elastomeric materials from mixed material streams.
Other objects of the present invention are to provide an improved method and apparatus for separating elastomeric materials from mixed material streams based upon frictional and elastic material characteristics.
Important aspects of the present invention are to provide a dry method and apparatus for separating elastomeric materials from mixed material streams substantially without negative effect and that overcome some of the disadvantages of prior art arrangements.
In brief, a method and apparatus are provided for separating elastomeric materials from mixed material streams, such as polymeric rich waste streams. A separator includes a bank of parallel rollers extending longitudinally between a first end and a second. The bank of parallel rollers having a predefined inclination with the first end elevated higher than the second end. Mixed material streams are fed onto a top surface of the high end of the inclined parallel rollers. A material having less friction and elasticity slides down the inclined roller bank top surface is collected into a collection bin positioned adjacent the second, lower end of the roller bank. Other materials having a higher friction coefficient grip the rollers more are lifted out of the valley due to friction and migrate in a perpendicular direction to the rotating rollers and are collected in a collection bin positioned adjacent one side, or at the end of the roller bank next to, and in the direction of elastomeric migration, the other collection bin, of the roller bank parallel to the longitudinal roller axis.
In accordance with features of the invention, the rollers are formed of carbon steel. Differing deck geometry of the bank of parallel rollers is provided to change material flow characteristics for certain mixed material streams. The bank of parallel rollers has a predefined roller diameter and spacing between the rollers determined based on the geometry of the particles that are being separated. An optimum length of the rollers is predetermined based on the properties of the material in the stream that is to be separated. Changing the deck speed is selectively provided to affect the material separation. The rollers typically are closely spaced so the materials cannot fall between the rollers; or alternatively small thin objects are allowed to fall through.
The present invention together with the above and other objects and advantages may best be understood from the following detailed description of the preferred embodiments of the invention illustrated in the drawings, wherein:
In accordance with features of the invention, a dry mechanical process using a separator including a bank of rollers has been invented to reduce the cost of separating the elastomers from the non-elastomers. After unsuccessfully searching for off-the-shelf roller-type machinery that would accomplish this task, a separator developed by the inventors has been tested on a bench scale apparatus having a capacity of 250 pounds/hour.
While the separator or rollers generally are not effective in separating the wood from the plastics, a color sorter can be used to remove the wood; currently removing the majority of the rubber and wood from the polyolefin product stream is through a wet process. For example, this wet process produces a 95% Polypropylene (PP)/Polyethylene (PE) product with about 5% rubber in it. This wet process contributes significant cost to the overall recovery of this product stream.
In accordance with features of the invention, the separator or roller system advantageously separates rubber from mixed material streams at significantly less cost. Mixed material streams contain various amounts of elastomeric materials, which typically reduce the quality, and value of a conventional recovered stream. The recovered plastics and recyclable polymer materials generally have improved quality and increased value, and also the recovered elastomeric materials may prove to be a valuable product.
Having reference now to the drawings, in
Separator 100 includes a bank 102 of parallel rollers 104 extending longitudinally between a first end 106 and a second end 108. The bank of parallel rollers having a predefined inclination indicated by arrow 110 in
Separator 100 includes a drive motor 116 with a drive belt 118 or associated drive gear 118 cooperatively rotating the parallel rollers 104. The rollers 104 are closely spaced so that the mixed stream materials generally cannot fall between the rollers 104.
In accordance with features of the invention, separator 100 separates material based on frictional and elastic characteristics. The mixed stream materials are fed onto the high end 106 of the inclined parallel rollers 104 and a material having less friction and elasticity with the roller surface material is more likely to remain in the valley of two adjacent rollers 104. These pieces of material slide down the incline top surface 114 and eventually fall off of the second, lower end 108 of the roller bank 102 into a collection bin 120 positioned adjacent the second end 108. The collection bin 120 should be understood to broadly include a conveyor and other collection device. Other materials that grip the rollers 104 more are lifted out of the valley due to friction and migrate in the same direction as the rotating rollers 104 and are collected in a collection bin 122 positioned adjacent a first side 124 of the roller bank 102. An opposing second side 126 of the roller bank is located near the feed supply 112.
To test the mechanical rubber separation process we developed a limited parametric experimental matrix to determine the impact of three major parameters on the performance of the process. These parameters are: the roller diameter, roller tip speed and inclination angle. A roller diameter for the bank of cooperatively rotated parallel rollers is selectively provided to affect material separation by inherently changing the dimension of the valley between the rollers. Also in general the effect of selectively using different roller materials is to provide a way to change the frictional characteristics between the material and the roller. Two roller diameters (1 and 1⅜ inches) and three roller tip speeds (110 ft/min, 210 ft/min and 340 ft/min) were tested. The performance of the roller system was also evaluated at four inclination angles (2½, 5, 7½ and 10 degrees). The test matrix used a typical polymer concentrate derived from shredder residue containing approximately 30% rubber. Tests were also conducted using the following fractions produced by the froth flotation process.
Testing was performed using mixed material streams having a particle size between about ⅛ inch and ½ inch; however, it should be understood that materials of almost any size could be separated by operating the separator 100 with different hardware and configuration and at different operating conditions.
The performance is determined based on percent of total rubber removed and percent of total loss of the targeted plastics (PP/PE, ABS, PS and ABS/PC) with the separated rubber. Performance when targeting rubber as a product is based on purity of the rubber product and the amount of rubber loss.
The equipment used for testing had a pre-selected spacing between the rollers. This gap is selected such that it allows a quantity of small and thin material to fall through. In some instances this material is undesirable and can be discarded, however some of the thin material would be considered a loss. The gap width used for the 1⅜″ roller deck incorporated a 0.070-inch gap width, which resulted in an average of about 7% material loss on the first pass of material. The gap width used for the 1″ roller deck used a 0.040-inch gap width, which led to only a 2% loss on the first pass. This fine material is roughly 50% plastic and 10% each of rubber, metal, wood, foam, and other material. This shows that a smaller gap width is desirable.
The experimental results are summarized in Appendix A. The roller system has not yet been optimized. The results obtained when the rollers were used to separate rubber from the polymer concentrate proved that:
It should be understood that an optimum inclination angle and roller speed combination advantageously is selectively provided as to be determined for particular mixed material streams.
Preliminary tests using the roller separation system as a purification step for the PP/PE concentrate has shown the following results after a single pass over the rollers:
Preliminary tests using the roller separation system as a means to recover a rubber concentrate from the wet PP/PE purification reject stream has shown the following results:
Preliminary tests using the roller separation system as a purification step for the PC-ABS/PC concentrate has shown the following results after a single pass over the rollers:
In conclusion, tests conducted so far proved the technical feasibility of using rollers to separate rubber from polymer concentrates derived from shredder residue or from plastics derived from polymer concentrates. The use of this equipment can minimize the equipment size required downstream, upgrade current product streams to contain less rubber contamination, and produce new rubber product streams which do not currently exist in the base process. Over 70% of the rubber can be separated from the polymer concentrate in a single pass. The plastic product streams can be upgraded to contain less than 10% rubber. The rubber rich streams can also be upgraded using the rollers to produce a potential rubber product fraction containing less than 10% non-rubber material.
With respect to
While the present invention has been described with reference to the details of the embodiments of the invention shown in the drawing, these details are not intended to limit the scope of the invention as claimed in the appended claims.
This application claims the benefit of U.S. Provisional Application No. 61/024,618 filed on Jan. 30, 2008.
The United States Government has rights in this invention pursuant to Contract No. W-31-109-ENG-38 between the United States Government and The University of Chicago and/or pursuant to Contract No. DE-AC02-06CH11357 between the United States Government and UChicago Argonne, LLC representing Argonne National Laboratory.
| Number | Date | Country | |
|---|---|---|---|
| 61024618 | Jan 2008 | US |
