The invention relates to systems and processes for recycling glass, and more particularly relates, in one embodiment, to an apparatus and process for producing clean glass aggregate from recycled glass articles.
Recycled materials can provide many benefits. Many common household materials, including paper, cardboard, metal cans, glass containers and other glass items can be recycled for use by industry and consumers. The cost of recycling such materials, however, varies depending upon the particular recycled material.
Most industries that use recycled glass require the glass to be substantially free of contaminants. In addition, many industries require glass materials that have a particular composition, color, or purity. Unfortunately, municipal household waste recycling programs generally do not discriminate between glass articles having various colors or compositions. Accordingly, glass items collected by recyclers often include a mixture of different glasses. In addition, collected glass items typically include a substantial amount of contaminants, such as paper and foil labels, bottle caps and lids, food waste, and other non-recyclable refuse that often accompanies recycled glass items into recycling bins.
Recycled container glass, mirror glass, tempered glass, and window glass have significant potential as aggregate in asphalt and concrete, as abrasive media, and as filter media, if the glass aggregate can be effectively cleaned of food residue, label paper and foil, and other non-glass contaminants. Though contaminated glass aggregate may have some value as a substandard filler, significant values can be achieved if the glass can be effectively freed of contaminants.
Contamination presents a substantial obstacle to the use of glass aggregate in asphalt and concrete, as refined abrasives, and as filter media. Paper fibers tend to clog asphalt bag houses when contaminated glass is used as asphalt aggregate. Paper and food residues can clog the nozzles of pneumatic air guns when contaminated glass is used as a sandblasting abrasive. Sugar and oil residue are believed by some to significantly retard and weaken concrete when contaminated glass is used as an aggregate in cement. Furthermore, organic residues and paper fiber contaniments can prevent the use of recycled glass as aggregate as a high end filter media.
Historically, grinding, screening, and cleaning recycled glass has been costly. Prior systems and methods typically have used ball, flail, and/or hammer mills to crush recycled glass articles. Such systems and methods characteristically excessively shred label paper and undesirably incorporate paper fibers into the final glass aggregate product. In order to remove the unwanted paper, label glue, dried sugar, food contaminants, and the like from the crushed glass particles, others have employed expensive fluid bed dryers to bum away the contaminants. Others have employed water cleaning tanks that are substantially ineffective at removing adhered contaminants such as label glue, dried sugars, or coagulated lipids from the glass.
Known systems and methods for producing clean glass aggregate are plagued by high capital costs, high maintenance costs, low throughput, high energy costs, high labor costs, and excessively shredded label paper content. Initial capital costs for a system that produces glass aggregate that is less than one-half inch in size at a rate of 18-20 tons per hour may be as high as $160,000. Such a system may require two employees for operation. The cost of a fluid bed dryer for burning away paper and other contaminants may be as high as about $450,000-$700,000. The cost of an alternative cleaning system such as a water bubble tank may be as high as about $135,000, though such systems are ineffective at removing many types of contaminants. Such systems also typically include on-site bulk storage facilities for storing and staging recycled glass before processing, and various types of glass crushing and screening equipment. The total cost of such known glass recycling systems typically is about $500,000 to about $1,000,000 for a capacity of about 15-20 tons per hour. Energy costs to operate such a glass recycling system may range from about $8 to $16 per ton, depending on present fuel and electricity costs.
As a result of these prohibitively high costs to produce clean glass aggregate, known glass crushing systems predominately have been used to produce recycled glass for use as a low margin filler or substandard additive for asphalt. Due to the resultant underutilization of stockpiled recycled glass since the 1990's, a surplus of recycled glass has accumulated, and recycled glass commodity prices have plummeted.
Accordingly, there is a need for a system and method that cost-effectively transforms recycled glass into clean glass aggregate. More specifically, there is a need for a glass recovery system and method that has substantially lower capital costs than known systems and methods, and is capable of producing clean glass aggregate that includes less than about one percent contaminants by weight. Preferably, such a system should be capable of producing clean glass aggregate that includes not more than about 0.1 percent contaminants by weight. In addition, such a system should be capable of producing glass aggregate of about 0.5 inch or smaller at a rate of about 20 tons per hour or greater.
The invention includes an apparatus for removing contaminants from a plurality of particles. The apparatus includes a basin for receiving the plurality of particles. The basin is configured to retain a volume of liquid. The apparatus further includes a rotating auger in the basin for mechanically agitating the plurality of particles in the basin. The apparatus also includes at least one inlet configured to direct a current of the liquid onto at least a portion of the plurality of particles as the particles are mechanically agitated in the basin.
The invention also includes an apparatus for producing clean glass aggregate from glass particles that include at least one contaminant. The apparatus includes an inclined housing having a lower end and an upper end. An auger having a first end and a second end is rotatably mounted in the housing, and substantially extends between the lower end and the upper end of the housing. A basin in the lower end of the housing is configured to retain a volume of cleaning solution, such that the first end of the auger is at least partially submersed in the volume of cleaning solution. The apparatus further includes at least one inlet configured to inject a substantially upwardly directed current of cleaning solution into the basin. Crushed glass particles received in the basin are mechanically agitated by the rotating screw auger and are impinged upon by the current of cleaning solution, thereby separating at least a portion of the contaminant from the glass particles. Cleaned glass particles are transferred to the upper end of the housing by the rotating auger.
The invention also includes a method of removing a contaminant from crushed glass particles. The method includes mechanically agitating the glass particles in a volume of liquid, and simultaneously directing at least one substantially upward stream of the liquid onto a portion of the particles.
These and other aspects of the invention will be understood from a reading of the following detailed description together with the drawings.
a and 1b are a schematic diagram showing one embodiment of a recycled glass recovery system according to the invention.
One embodiment of a crushing apparatus 10 for recovering recycled glass according to the invention is shown in
When the hopper 20 is in the fully raised delivery position, glass articles are transferred from the hopper 20 to an intake conveyor belt 30 at point “A” in
In one embodiment, the crushing unit 40 is a triple roll crusher 41 like that shown in
The glass shards are directed from the primary roller 42 to a passive secondary roller 46 and an opposed powered secondary roller 48. The triple roll crusher 41 may include a 35 horsepower electric motor or a larger motor to drive the primary roller 42 and the powered secondary roller 48. The opposed secondary rollers 46, 48 may cooperatively rotate at about 300 rpm or greater. The outer surfaces 57 of the secondary rollers 46, 48 may each include a plurality of cooperating spaced teeth that are about 0.25 inches or shorter in length. The spacing between the secondary rollers 46, 48 may be selectively adjusted to produce a desired size of glass aggregate. As the glass shards pass between the oppositely rotating secondary rollers 46, 48, the shards are compressively crushed into smaller glass particles. A triple roll crusher 41 suitable for use in the system 10 has been specially produced for the applicant by McLanahan Corp. of Hollidaysburg, Pa. As shown in
The second conveyor 58 carries the glass particles from the crusher 40 to a screening or sizing device 60 at point “C” in
In one embodiment, the screening device 60 is a multi-deck vibratory screener 61 like that shown in
As shown in
A screw auger 94 is rotatably mounted in the housing 98 such that a lower end of the auger 94 is substantially submersed in the volume of water 96 in the basin 112. In one embodiment, the auger has a diameter of about 20 inches or greater, and is spaced from the bottom 104 and sidewalls 102 of the housing 98 by a gap of about 2 inches or more. A motor 100 causes the auger 94 to rotate in the housing 98. In one embodiment, the motor 100 is rated at about 10 horsepower or higher. A screw washer 81 that is suitable for use in the system 10 has been specially produced for the applicant by McLanahan Corp. of Hollidaysburg, Pa.
In operation, a mixture of glass particles and various contaminants is introduced into the screw washer 80 through the feed opening 82. As shown in
Accordingly, the combination of the mechanical abrasive action of the rotating screw auger 94 and the impinging water jets, currents, or streams from the inlets 92 effectively separates adhered contaminants from the glass particles. Once thus cleaned, the glass particles are carried upward in the housing 98 by the rotating auger 94. Once the particles are carried out of the water 96 in the basin 112 by the auger 94, the continued agitation of the particles by the auger 94 facilitates air drying of the particles as they approach the upper end 86 of the housing 98. The dried glass particles or cleaned glass aggregate exits the screw washer 81 through the discharge opening 88. As shown in
The system 10 described above has been demonstrated to produce glass aggregate of a size less than 0.5 inch, and having less than about one percent contaminants by weight. In addition, the system 10 has been demonstrated to produce clean glass aggregate containing less than about 0.1 percent contaminants by weight. Such clean glass aggregate is desirable for use in many applications, such as aggregate for use in asphalt and cement, as an abrasive suitable for use in sandblasting operations, and as filter media. In addition, a system like that shown in
As shown in
The above descriptions of various embodiments of the invention are intended to describe and illustrate various aspects of the invention, and are not intended to limit the invention thereto. Persons of ordinary skill in the art will understand that various modifications may be made to the described embodiments without departing from the invention. All such modifications are intended to be within the scope of the appended claims.