Shredding and grinding tires:
By shredding, the volume of scrap tires can be reduced to about ¼, thus reducing space requirement and shipping costs. Tire shredding can be considered a mature technology now in North America.
Products: Rubber Crumb (sellable product – serves as raw material to many many industries) Finer synthetic and natural rubber (obviously after treatments) which can be used in Tiles and tile adhesives, mixing with asphalt, sports surfaces, carpet underlay, noise and vibration insulation, playgrounds and matting. Rubber crumb is also used in new tyres, devulcanisation for low-tech pressed or extruded rubber products, commercial flooring, traffic control products and plenty more.
Ambient Scrap Tire processing
The process is called ambient, because all size reduction steps take place at or near ambient temperatures, i.e. no cooling is applied to make the rubber brittle.
The tires are first processed into chips of 2” (50 mm) in size in a preliminary shredder (A). The tire chips then enter a granulator (B). In this processing step the chips are reduced to a size of smaller than 3/8” (10 mm), while liberating most of the steel and fiber from the rubber granules. After exiting the granulator, steel is removed magnetically and the fiber fraction is removed by a combination of shaking screens and wind sifters (C). While there is some demand for 3/8” rubber granules, most applications call for finer mesh material, mostly in the range of 10 to 30 mesh. For this reason, most ambient grinding plants have a number of consecutive grinding steps (D). The machines most commonly used for fine grinding in ambient plants are: • Secondary granulators
• High speed rotary mills
• Extruders or screw presses
• Cracker mills
Ambient grinding can be operated safely and economically if the bulk of the rubber output needs to be relatively coarse material, i.e., down to approximately 20 mesh material. Products: Rubber Crumb of different sizes. It’s a further refined process and this crumb is more valuable and useful.
whole tires or tire chips are cooled down to a temperature of below –80 C (-112 F). Below this “glass transition temperature”, rubber becomes nearly as brittle and glass and size reduction can be accomplished by crushing and breaking.
This type of size reduction requires less energy and fewer pieces of machinery when compared to ambient size reduction. Another advantage of the cryogenic process is that steel and fiber liberation, is much easier, leading to a cleaner end product. The drawback, of course, is the cost for liquid nitrogen (LN2).
Products: Rubber crumb. Its only economical if clean, fine mesh rubber powder is required.
The pyrolysis process is the thermal degradation of waste in the absence of oxygen at elevated temperatures and pressures. The process is carried out at temperatures typically upwards of 430°C. In practice, it is not possible to achieve a completely oxygen-free enviroment and so a small amount of oxidation occurs. The products of pyrolysis (from organic waste) are gases, small quantities of liquid, and a solid residue containing carbon and ash. The gases produced in the process can then be used to provide the heating energy for continuing the process. The tyre pyrolysis process essentially returns the high heating value of the rubber and oils that were initially used in the manufacture of the tyres. By carefully controlling the temperature, pressure and oxygen level more pyrolysis oil and charcoal is encouraged. This pyrolysis oil can then be used as a replacement diesel fuel. Since the tyres used in the pyrolysis process were originally produced from rubbers and oils extracted from fossil oil then this fuel can not be described as renewable nor can it provide saving on carbon emissions or other green house gases. It does however provide...
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