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The advanced technology of modified bitumen
Introduction
Modified petroleum bitumen — is bitumen, which quality is improved by the additives of polymers, rubber crumb, substances with adhesion properties, sulfur, etc.
Petroleum bitumen with rubber additives called bitumen-rubber binders (BRB). Bitumen with crumb rubber additives called Resin astringent (ABR).
Modified bitumen is widely used for the manufacture of a variety of coatings that are resistant to temperature changes, mechanical strains and for preparation of asphalt mixtures.
The quality of road asphalt coatings and its durability are significantly determined by the quality and properties of bitumen. Numerous researches have shown that the most promising areas for modification of petroleum bitumen are addition of the rubber crumb. Rubber crumb is significantly cheaper than rubber and various polymer additives (5−9 times). At the same time, the quality of bitumen modified with technical rubber, is comparable to the quality of bitumen which are modified by new synthetic rubber. In addition for the bitumen modification one can used rubber crumb, which is produced by the processing of used tires of all types of transport and various rubber waste.
1. The known technologies for modified bitumen production
Two main technologies for bitumen modification:
«Dry» technology, which comprises addition to the bitumen of the crushed crumb rubber (0.3−0.6 mm size) in an amount 1.5−3.0%;
«Wet» technology — the rubber is converted into a soluble state inside bitumen.
«Wet» technology allows receiving various types of bitumen: asphalt binder (AB) and bitumen, modified chemically by rubber crumb (MCRC). Existing technologies for both types of bitumen provide the mixing of rubber crumb (30% by weight) with bitumen (tar, asphalt) at temperatures of 150−250°C. The quality of modified bitumen is influenced by temperature, mixing duration, the chemical and fractional composition of crumb rubber, type and chemical composition of the bitumen, the type of plasticizer. Parameters of the process of bitumen modification depend on the type of rubber, which part of the crumb rubber and the type of plasticizer. Thus, in the bitumen modification is carried out the de-vulcanization of rubber crumb.
Especially noticeable decline in the quality of modified bitumen during addition of rubber crumb, produced from the used tires. This is due to tire construction and method of its recycling. The tire contains 9−10 constructive elements. These elements made of natural or synthetic rubber, butyl rubber, high-strength steel wire and nylon. For example, the truck tires have 28% natural rubber and 13% synthetic rubber, and car tires contain 28% of synthetic rubber and 13% natural rubber. All other components of tires material and its rubber composition are approximately the same.
The composition of the tire material produced by different companies varies quite widely. But it is obvious that the crumb from tire recycling is a complex composition, which cannot be used for bitumen modification without careful pre-separation.
Currently, recycling of used tires is carried out mainly by mechanical grinding in chipping machines or shredders. After grinding steel wire and thread are separated from rubber the chips. The energy consumption in mechanical method of tires processing is more than 940−1100 kWh per ton of recycled tires. In addition, the rubber crumb is contaminated by synthetic thread and small pieces of wire, which is extremely negative impact to the quality of bitumen modified by rubber crumb.
2. The main differences of the proposed technology
2.1. Complete technological cycle for producing of modified bitumen consists of three production lines arranged in series: a line for destruction of tire shell and separating of rubber composition from the cord; installation for de-vulcanization of rubber crumb and chips; installation for bitumen modification by de-vulcanized rubber crumb;
2.2. For bitumen modification are using rubber crumb and chips, obtained separately from the processing of: trucks, or cars, or light trucks and SUVs;
2.3. Pure rubber crumb and chips (without wire and nylon threads) obtained by the technology of the ozone destruction of tire shell;
2.4. To restore the properties of the rubber which contains in the crumb and chips, they are subjected to thermo mechanical de-vulcanization in simple rolls;
2.5. The process of the de-vulcanization of rubber crumb and chips made using the modifier, which must correspond to the type of tire, which is obtained from rubber crumb and chips
2.6. Modification of bitumen by rubber crumb is produced in a reactor, whose design provides an equable temperature in the volume of stirred substance;
2.7. In a reactor for bitumen modification and in other installations, for heating the mixture and bitumen are using heat transfer elements operating on the principle of heat pipes.
3. The main advantages of the technology and installation for bitumen modification
3.1. The main advantages of advanced technology and equipment are the reactor for the bitumen modification and special installations for tire recycling and for de-vulcanization of rubber crumb and chips;
3.2. The temperature in the reactor for bitumen modification is maintained at 5−6°C above the melting point of the using bitumen (tar). It guarantees to reduce the heat consumption by 35−40% in comparison with known technology;
3.3. Electricity consumption per ton of recycled waste tires using ozone technology and followed de-vulcanization of rubber crumb and chips is 220−250 kW • h;
3.4. Using of de-vulcanized rubber crumb greatly simplifies technological scheme of the installation for bitumen modification. It reduced the number of processing units, and power consumption for the drives of agitating devices;
4. The economic feasibility of the advanced technology
4.1. For the developer of technology and equipment manufacturer’s the cost-effectiveness is defined as follows:
4.1.1. For the plant with capacity of 4 tons per hour of modified bitumen necessary to obtain 400 kg/hour de-vulcanized rubber crumb, which corresponds to the installation which use 450−500 kg/hour of recycling tires.
4.2. For a company that buys advanced technology and equipment, economic efficiency is made up of the following positions:
4.2.4. The payback period of the plant for processing waste tires (productivity 360−500 kg/hour) and modifying bitumen (4 t/h) - 2.5−3.2 years;
4.2.6. Company revenue can be increased if payment will be made for the acceptance of old tires for recycling.
5. Specialists of Scientific-Engineering Center in cooperation with the manufacturer of specialized equipment are ready:
1) To prepare a feasibility study for the plant construction;
2) To produce the technological scheme;
3) To produce the design documentation for specific types of machines and apparatus;
4) To organize the production and selection of the entire set of equipment for the plant for processing used tires of vehicles;
5) To exercise the control during installation and commissioning works.
6. There are various options for cooperation in the development of new machines and apparatuses for all known technologies of bitumen modification and processing used tires and waste of the industrial rubber article.