Patent Application
20130307172
The present invention relates to a process of recovering the available bitumen, fibers, aggregate, and inert materials contained in used asphalt shingles and creating useful articles therefrom.
The ever-growing waste stream of asphalt shingles that have been removed from existing roofs is putting an increasing burden on waste management resources. Contained within this waste stream are finitely available reusable products like asphalt, fibers, aggregate and other inert materials. The need to protect the ecosystem by recovering tons of useful materials that would normally be discarded into landfills is one object of this invention. The ecosystem is also benefited by the process of this invention by initially removing hazardous materials, such as asbestos, from the shingles being processed.
Waste shingle material is normally available from two sources. The largest and most conveniently available source is shingles removed from old or damaged roofs, referred to as “tear-off.” The second source, “Prompt scrap,” is the trimming produced during new shingle manufacture.
The idea to recover materials contained in tear-off shingles and prompt scrap is not new. A number of U.S. patents exist which disclose methods of extracting the bituminous materials for reuse in manufacturing new shingles or providing material for roadway pavement or making new products.
U.S. Pat. No. 2,128,191 relates to the use of recycled asphalt shingles (RAS) as an additive to the process of manufacturing new shingles.
U.S. Pat. Nos. 4,325,641 and 4,706,893, among others, described uses for RAS in roadway construction and repair.
RAS material is separated into its constituent parts using various methods, as those are described in U.S. Pat. Nos. 4,222,851 and 5,098,025 which use either a solvent or water to disassociate the component parts of the shingle. The process of the present invention intentionally leaves the constituent parts of the shingles in the final mix.
Some prior patents, including U.S. Pat. No. 5,221,702, suggest adding other materials like rubber from tires, polyethylene from plastic bottles, crushed brick and minerals such as limestone, basalt, quartz or granite to refine the aggregate ratio or to impose a color on the final product. The present process does not change the mechanical qualities of the final product by using aggregate additives.
Referring first to
The second phase of the conversion process begins at 20 with the removal from the RAS of foreign materials such as aluminum, steel, plastic and construction debris. This material is collected and sent to an appropriate recycling center 21. Unusable debris is directed to a land fill 22. Preferably, the output of the separation step contains less than one percent by weight of deleterious material.
The “clean” RAS may, if necessary, be stored for processing at a later time at step 23. Whether taken from storage or directly from the separation stage, a charge of the clean RAS is placed into a grinder 24 where the charge of tear-off and/or prompt scrap is comminuted to a mix of small sized particles, preferably of less than one half inch in width 25. The grinder can be any one of many commercially available grinders that incorporate an exit conveyor having an electro-magnetic final roller 26 that attracts and redirects the small steel particles and roofing nails that may remain in the mix.
The charge of comminuted shingles 25 is transferred to a heating and mixing vessel where the amount of tap water 27 necessary to form slurry is added. In addition to the water, a quantity of aluminosilicate (zeolite) that is approximately two percent (2%) by weight is added to the slurry at 28. At step 29 the slurry is heated to a temperature of between 225 and 275 degrees Fahrenheit, while at the same time being physically agitated by a stirring or mixing device.
The formation of the slurry and the heating and mixing functions 29 are significant steps in achieving the ecosystem protection objectives of the invention. Avoiding high temperature in the slurry precludes the release of polycyclic aromatic hydrocarbons (PAH) and volatile organic compounds (VOC) that are known to be hazardous to health.
As the bitumen melts in the heating step 29 with increased temperature, the solids (aggregate/ceramic) contained in the RAS are mechanically released from the paper or fiberglass matting. Gravity causes the heavier solids to settle out due to sedimentation and the asphalt's increased viscosity which requires mechanical agitation to distribute the solids homogeneously throughout the slurry. The heat added to the closed system also induces a measure of thermodynamic entropy which, when controlled, increases the tendency of the process reaction to become entropically favored to proceed in a particular direction.
The goal of the process is to change the RAS and zeolite mixture from its initial condition to a homogeneous mixture with a uniform dispersion of the base materials which can be acted on by pressure in the third phase to change the state of the slurry material into a useful article.
The zeolite creates a catalysis effect on the chemical reaction in the bituminous slurry (which is basically an ion exchange) because the cations are free to migrate in and out of the zeolite structures which are tiny channels formed by eight tetrahedrally coordinated silicon or aluminum atoms and eight oxygen atoms which measure around six angstroms. This structure mechanically sets the maximum size of the molecular or ionic species that can enter the pores and limits the absorption to water molecules which can then evaporate with continued heating and provide a micro-stirring effect on the RAS slurry. The zeolite thus provides a mechanism for the reaction to successfully occur with lower activation energy. The end result of the heating and mixing step is a homogeneous mixture of the constituent parts of the recovered asphaltic shingles comprising approximately 97% recovered and reclaimed materials after deducting 2% for the aluminosilicate minerals added and the 1% inert deleterious materials contained in the mixture.
The third phase of the process begins with loading the homogenous slurry into molds 30 for shaping the final product. Pressure on the slurry in the molds, in excess of 4000 pounds per square inch, with a dwell time of at least three seconds at 31, serves to stabilize and fix the solids within the slurry. The pressure on the slurry in the molds increases the kinetic energy of the its particles which in turn increases the number of collisions between reactants in the slurry. This increases the possibility of successful molecular collisions and shortens the time for all of the material to have been acted upon by the reaction. This feature contributes to lowering the amount of heat necessary to obtain the same chemical reaction.
Following the application of pressure on the contents of the mold, the article is discharged from the mold at step 32. The resultant solid homogeneous material created after the material is cooled at step 33 is mechanically stronger due to the absence of gas pockets that reduce the final material's mechanical strength.
The final steps of the process are washing the cooled product at 36 and applying the desired finish or coating to the article at 38.
