by Yelena BORISOVA, expert, "Technology and Science" LLC
The problem of disposal of used automobile tyres is as old as these articles themselves.
Dumping used tyres at junkyards is impractical because of the truly huge volumes involved and because of economic considerations too. With the steadily swelling numbers of automobiles in the world the problem of used tyre disposal is now of global significance.
There are two basic solutions of this problem at the present stage. In one waste tyres are mechanically crushed and used as a raw for producing various technical articles. This reprocessing can occur either at room temperature or with the tyres being cooled down to - 70-80C. The drawbacks of this method: high electricity consumption, rapid wear of the cutting tools and low output.
The second disposal technique involves altering the chemical structure of rubber by means of what is known as a destruction method. In this case, however, raw rubber from processed tyres is not preserved, and the reprocessing products obtained are of far smaller practical value-they can be employed only for the making of rust-proof coatings and certain lubricants.
But the main common drawback of both these methods is a relatively high cost of the end product and, accordingly, the wasteful nature of production because of the slow and time- consuming processes involved. With all that in mind, building such tyre reprocessing factories runs into a host of ecological problems which calls for financial backing by the state. What is more, in cases such as reprocessing of some very large tyres from trucks used at open-cut mines, no practicable technical solutions have been found so far.
A transition from any and all of such wasteful and ecologically
unsafe technologies and methods called for a real breakthrough. This has now been achieved on the basis of the latest discoveries by Russian experts in the theory and technical methods of what they call the localization of explosion energy. The research was launched back in 1993 at the "Kriokonsul" R&D Center of the Bauman Moscow State University of Technology, and the project was headed by Dr. A. Nabok, Cand. Sc. (Tech.). The scientists developed a unit for directional channelling of blast energy. This energy, together with crushed bits of tyres, is circulated within a closed loop.
The authors named their brainchild vzryvotsirkulator which can be literally translated as "blastcirculator". Its body is in the shape of an armored chamber of special geometry to which an external duct is attached. It forms a closed circular system sealed from the environment to prevent noise and gas pollution. A pack of used tyres with an explosive change inside is cooled down to -70-80C before it is placed into the chamber. The blast destroys the tyres producing a mix of fine rubber powder (grain size from 0.1 to 1.0 mm), granulate (from 3 to 10 mm), bits of metal wire (50-100 mm long) and shreds of textile cord. The powder volume amounts to about 50 percent of the rubber mass.
The shock wave produced by the initial blast carries the bits and pieces of the demolished tyres which are broken up into some even finer fractions as they hit special grids installed inside the duct. And since the whole process occurs within milliseconds, the shreds of the granulate do not heat up or burn, which saves their elasticity and other useful properties of the "input" product.
Since the shock wave and "debris" of the blast are propagating parallel to the chamber walls and the annular duct, their pressure on the walls of the reactor is much smaller than in all the previous units of this kind (spherical, cylindrical or other configurations). This being so, it is possible to use
much less expensive armored chambers of minimal size, close to the dimensions of the tyres.
The explosives used include inexpensive and safe mixtures based on ammonium nitrate with the addition of either diesel fuel or trotyl.
As for the preparation of a package of tyres for reprocessing, the authors of this invention have developed a special "mini technology" and a machine tool, or stand. It cuts out from tyres the metallic side rings, then makes a cut across the tyre and twists it into a spiral. After that these pre-processed tyres (from 4 to 10 pieces) are wound upon a drum one often the other, producing a compact package. This method can be used for tyres of all shapes and sizes, including big ones from heavy dump trucks.
When the blastcirculator is discharged the product mix is cleaned from metal wires and textile cord in separators, and then separated into fractions (if need be, larger granules are additionally processed in rotor crushers).
At the present stage several models of blastcirculators are produced. Units with the capacity of 4,000, 8,000, 12,000 and 18,000 tyres a year have the following parameters: diameter-2.5, 3.0, 3.5 and 4.0 m; height-5.5, 7.0, 8.5 and 10.5 m; weight-12, 40, 80 and 100 t; charge mass-3.6, 12.5, 22 and 26.4 kg. The work cycle (interval between blasts) is 10-12 min, and the power consumption is only 20, 30, 40 and 60 kW.
On the basis of the blastcirculator, experts from the "Kriokonsul" R&D Center have pioneered a reprocessing line for junk tyres. Besides the main unit it includes some new elements like a machine for cutting and batching, a cooling chamber and a gas cleaning unit. The standard equipment includes
a magnetic separator, air separator, rotary dispergator and classifier, or sorter. The line can be manned by 6 to 8 operators only and the most powerful of such units will have an annual capacity of 20 to 30 thousand tyres depending on their size as compared with not more than 10 thousand reprocessed on earlier models.
The new junk tyre reprocessing technique can cut down by half to two-thirds the cost of rubber crumb as compared with the traditional methods thanks to a reduced energy consumption and thanks to increased productivity.
The capital investments and running costs are also substantially reduced. And last but not least, the new technology meets all of the environmental safety standards because it uses no organic solvents or ozonizing agents, does not discharge liquid wastes and has a high ratio of waste gas purification-of up to 98 or 99.9 percent.
The basic principle of forming a directed blast energy flux and its products circulating within a closed circuit and the appropriate equipment have been patented in Russia and also Canada, the United States, West European countries, Japan, South Korea, Brazil, Australia and other countries. A Russian patent has also been obtained on the original method of tyre compaction.
Prepared by Arkady MALTSEV
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