Code No: TMS122 Price: Rs1900/- Category: Environment: Recycling
With the phenomenal increase in number of automobiles in India during recent years the demand of tyres as original equipment and as replacement has also increased from 22,846 thousand tyres in the year 1990-91 to 31,213 thousand tyres in the year 1994-95. As every tyre is destined to go to waste stream for disposal/recycling/reclamation, despite its passage through retreading process, the number of used tyres being discarded is going to increase significantly. Timely action regarding recycling of used tyres is necessary in view to solve the problem of disposal of used tyres keeping in view the increasing cost of raw material, resource constraints and environmental problems including fire and health hazards associated with the stockpiles of the used tyres. The problem has drawn attention of planners, environmentalists, consumers and industry in the developed countries in Western Europe, USA, Japan, Australia etc. where billions of used tyres are stock piled. These stockpiles are also direct loss of energy and resources in addition to fire & health hazard and other environmental issues.
Objective of the Study
Technology Information, Forecasting and Assessment Council (TIFAC) commissions’ techno-market survey studies with multiple objectives given below:
- Identification of technology areas for further development
- Identification of optimum technologies for the country in selected areas
- Development of implementation action plan including identification of agencies
- Development of technology assessment capabilities in the country.
Scope of Work
The scope and coverage of the study, as given by TIFAC is :
1. Relationship and the importance the specific topic to the broad area to which it belongs.
2. The current status of the technology in the world and in the country. Market sizes and their potentials.
3. Assessment of the technology, resources parameters such as energy, raw materials, infrastructure, manpower etc. to arrive at the preferred technology options available to the country.
4. Short term and long term economic aspects of preferred options along with their feasibilities.
5. Impact of the preferred option(s) by itself and its spinoffs
i) For implementations of preferred technology option(s) identify critical inputs such as raw material, capital goods and human resources required and their availability, investments required to commercialize, and benefits/returns expected. Maximum possible quantification is required.
ii) For R&D / Technology development identify the requirement of inputs and expected benefits.
7. Action Plan for implementation of recommendations alongwith identification of:
a) List of available technologies for Indian industry and
b) The agencies/groups/individuals for implementation.
8. Expected impact of recommendations, if implemented
The study has been conducted through intensive literature survey and market survey covering a number of relevant institutes/agencies, users and government agencies. Some of the details being:
i) In-depth Literature survey has been undertaken. List of literature scanned /referred are given a “Reference” and “Bibliography”.
ii) International database ‘DIALOG’ has been scanned for technologies.
iii) Number of agencies have been contacted during field survey. It covered academic institutes, R&D Agencies, Govt. bodies, industry etc. The list of the agencies contacted during the study is enclosed as Appendix A VI. Various modes used for the field survey are:
- Structured questionnaire
- Open ended questionnaire
- Personal Interviews
- Literature request
- Brain storming etc.
iv) The information has been processed, analyzed and complied under desired sub-groups. The sub-groups are inline with the various aspects to be covered as per scope w and objectives given by TIFAC.
v) Drat report has been discussed with experts in the field.
Survey of Indian scenario & International scenario regarding recycling of used tyres was conduced to cover various agencies e.g. academic institutes, R&D Agencies Government bodies manufactures of tyres, tyre recycling agencies, reclaim/crumb producers/dealers, retreaders, machinery manufactures etc. in India & abroad. The information received from abroad is base don correspondence only & non of the foreign country was visited/ in Indian efforts were made to contact maximum possible agencies through correspondences and to visit in person. Out lines of various processes & methods have been given in the report. Further details can be collected from relevant agencies on commercial terms.
Recycling of waste has drawn attention of society based on the slogan “There is gold in our garbage” on hand and growing concern about the environmental protection on the other hand. The main constituent of a tyre is rubber and the largest single application of rubber is vehicle tyres. Also the requirement of tyre is directly related to growth of automobile. The production of automobiles is forecast to continue to rise and is indicative of buoyant economic conditions for tyre industry, but at the same time guarantee and annual discarded scrap tyre volume growing at the same rate as new tyre manufacture. This discarded volume of scrap tyres would around was more than 75 million cubic meter in 1993.
The tyre production and recycle is closely related to rubber and automobiles, therefore to have the good appreciation of the subject details regarding production of automobiles, the construction design of tyre and rubber have been given in Annexures A-I, A-II & A-III respectively.
In India sale of automobile tyres was 8.8 million units in 1982 which had increased to 17.7 millions in the year 1991, representing growth rate of more than 100% in ten years there are more than twenty large & medium tyre producing units manufacturing cross ply tyres in India. Radial tyres are also being manufactured. During he next five years the production of passenger cars is forecast to be doubled. In addition to increase in number of automobiles, the kilometer coverage by the vehicles is also increasing with the change in living style & attitude of people. All this resulting in increased demand of tyres. Every new tyre produced is destined to the scrap yard (with or without passing through retreading cycle). The problem of scrap auto tyres had assumed serious proportions in developed countries where hundreds f million of auto tyres are added to waste stream every year. The stock piles of used tyres are fir hazards and health hazards. The Hagersville fire in USA continued for seventeen days causing environmental pollution and put a financial burden on public exchequer. The rain-water collected in improperly stored tyres become breeding habitat for disease carrying mosquitoes, pose a health hazard. Tyres are not easily degradable and occupy large space. If disposed in open field, create spongy ground and represent loss of material and energy rubber, steel, nylon cord, carbon black etc. can be recovered by recycling the used tyres. If it s carcass is good the old tyre can be reused after retreading. The crumb rubber obtained can be used as asphalt modifier, rubber modifier, soil conditioner, for land filling etc. Whole used tyre can also be used for sea defence and civil engineering works. Pyrolysis & incineration of tyres helps in recovery of materials and energy. USA, Japan, UK, Germany, Belgium etc. are the countries leading in reuse/recovery of values of used tyres RAPRA, EPA, BIPAVER etc. are the agencies working in the field of recycling of used tyres.
Retreading of tyre is being practiced to extend the life of a tyre by replacing worn tread of the used tyre. The tyre is to be scraped only if it is not suitable for retreading. Retreading saves material energy and reduces tyres to be disposed off in waste stream. Hot cap process is conventional method and cold method (procured process) are the two methods being practiced for retreading of tyres. As name implies, in the ‘hot’ method un-vulcanized rubber strip also known as Camel-Back is applied on the buffed surface using natural rubber gum film and vulcanized in an autoclave. In the ‘cold’ method a procured strip of tread rubber is used and a thin strip of un-vulcanized rubber is used as boding agent between precured strip and buffed tyre surface and cured in a mould at low temperature. The precured rubber is being manufactured in India by six manufactures. Only two of these films have technical collaborations with foreign manufacturers where as four firms have developed the technology indigenously, and is technically as good as the imported technology. The plant and machinery is also available indigenously. The precured rubber is supplied by the main units to their retreading centre and franchise units. The available capacity for procured tyres retreading is approx 4.8 million truck and bus tyres and 4.5 million car and jeep tyres per year.
The sequence followed for retreading includes inspection of casing, buffing, cementing, repairing, treat preparation, tread building, balancing, enveloping, vulcanization and final inspection. The broad comparison between the ‘Hot’ & ‘Cold’ methods include that the basic raw material in cold method is a moulded and vulcanized strip where as in the hot method the rubber strip is un-vulcanized. The quality & performance of cold process is consistent and gives life to the extent of 85% at a cost of approx 50% of new tyre where as in ‘hot’ method the quality and performance is not consistent and depends on the skill/experience of artisan and material selected and gives life to the extant of 40% at a cost of approx 25% of new tyre. The ‘hot’ method requires less investment and has been always in small scale sector, spread all over the country and can be adopted for various kinds of tyres easily.
The tyre retreading is being practiced in all the developed countries including USA, Japan, Germany, France, UK, Italy, Sweden Austria etc. but with the advent of radial tyres, which have longer life and are more susceptible to sustain side wall damage during careless use, the percentage of tyre being retreated now had dropped as compared to ten years ago in most of the developed countries. Also in car tyre, the customer sees an image factor and there is a ‘fashion’ element also which dissuades potential purchaser to buy a retreated tyre. But with fixing of retreading target by EC Commission and increase in the cost of rubber are expected to result in increased retreading activity in these countries.
Bureau of Indian Standard is preparing standards for retreaded tyres. European Standards issued by BIPAVER & extracts of America code if regulations for retreaded tyres are given as annexure to this report. The carcass of tyre, if damaged and is not suitable for retreading, forms part of waste stream for recycling/recovery of values. In tyre, rubber-compound consisting of Carbon black, sulphur, process oil, zinc oxide and other compounds are in vulcanized stage and their reclamation is not possible simple physical methods. With physical method steel, cord and rubber compared in form of crumb can be separated by grinding tyre at ambient temperature or by cryogenic grinding. Tyre crumb is also obtained as by-product of retreading operation; the old tread of tyre is buffed producing crumb, before applying new rubber. Crumb is classified based on size. In cryogenic grinding the tyre is cooled below the glass transition temperature making it brittle thus fine crumb is produced. The crumb can be used as rubber extender, asphalt modifier for road surfacing, modifier in plastics, making sports surfaces, safety surfaces, soil treatment etc. a study conducted on behaviour of cryogenic ground tyre crumb at Rubber Technology Centre, IIT-Kharagpur revealed that properties of vulcanizates containing crumb rubber depend on size, loading, hardness, cross links and nature of polymer matrix of the crumb.
By application of heat and chemical agents to the crumb rubber a substantial regeneration of rubber compound to its original plastic state is effected, yielding a product known as reclaim. The reclaim can be processed, compounded, and re-vulcanized. The ‘reclaim’ is a de-vulcanized rubber available in sheet form and is suitable for blending with new rubber upto 40%. Addition of reclaim in rubber compound offer economic as well as processing advantages. However a balance between cost and quality should be maintained by optimizing the level of reclaimed rubber in rubber compound. The reclaim process is not environmentally friendly unless expensive scrubbers and effluent treatment plants are installed.
The reclaim rubber can be obtained using mechanical, mechnochemical or chemical methods. The conventional processes used for reclaim of rubber include Digester Reclamator, Pan, Engelke etc. the commercial scale production of rubber reclaim from used tyres in China, Germany Holland, Australia etc. are also covered in this report. The products include rubber tiles for surfacing (pedestrian concrete areas school play grounds, roof terraces etc.), animal mats, insulation tiles, rubber slabs known as ‘strail’ for railway crossings in Germany & other rubber products
Rubber is also used to modify plastics e.g. polypropylene, polystyrene, polyethylene, polyurethane etc. addition of rubber increases toughness, impact strength but reduces tensile strength of plastics. Polyurethane and tyre granules have been used for laying sports surfaces. The sport surface can be made from factory made tiles or can be applied in situation using the wet lay method. The other minor uses of crumb as plastic modifier include porous hoses, soles of boots, exercise mats, paving stones etc. Tyre crumb is also used for carpet underly soil treatment, to prepare safe play fields, to manufacture mattresses for use in cow sheds etc. Crumb is being used as compounding ingredient in rubber since long. The recycled rubber is also used as sound insulator, vibration absorber rubber mats etc.
The most promising field of utilization of scrap tyres is use of tyre crumb as asphalt modifier. 8-15% of crumb can be used for construction and maintenance of roads. It improves visco-elastic properties of bituminous mixes. Various advantages include improved skid resistance, better crack reflection control increased flexibility, toughness, tenacity of road surface, reduced noise level of traffic, improved performance under extreme temperature conditions etc. much work has been done in the field in US, Canada, France, Belgium Australia. In India the use of crumb as asphalt modifier is in experimental stage. Study has been carried out a CRRI to find out effect of particle size and percentage of crumb on various properties of crumb modified bitumen concrete. A trial track has also been laid near Allahabad. The extra cost of blending the crumb is offset by the improved durability of track surface. In USA, regulatory support has been provided in many states for use of tyre crumb as modifier of asphalt for road constriction. In USA various studies have been carried out in this field. The construction of road surfaces using crumb modified asphalt, uses techniques of wet process and dry process. The uses include construction of road surface, joint and crack sealant. The various techniques being used are McDonald Technology, Plus Ride Technology Tak system etc. Major barriers to wide spread use of rubber asphalt are requirement of specialized equipments, unique aggregate gradation, specialized mix designs, cost of crumb, use of patented processes etc. the development of storable asphalt rubber binder has overcome a major barrier for its use. Now it is not necessary to prepare rubber binder just before the use, it can be prepared in advance to match the requirement of laying the road surface. Field experiences of using crumb rubber in Florida and Texas USA have also been discussed in the report. Effect of use of crumb on construction and performance of pavement, estimated uses and cost have also been covered. Specifications for ground tyre rubber and asphalt rubber binder have been prepared by the state material office, Florida Department of Transportation.
Apart from recovery of material i.e. crumb rubber/reclaim rubber, nylon cord, steel etc. from the used tyre various uses have been developed to utilized whole/halves/shredded tyres e.g. for tyre faced retaining walls for narrow hill roads, along drainage channels for control of erosion, barrier reef in coastal area, crash acoustic barriers, earth filling in Civil Engineering works etc. most of these uses are low technological options but help in mitigating the problem of disposal of sued tyres. Along the 1500 km of Atlantic coast in USA a range of barriers made of used tyres have been put up for soil protection. The tyres are tied together in pyramidal honey comb structure, for stability 20% of bottom layer is filled with cement concrete in Austria ‘Ecowalls’ have been constructed for noise protection and acoustic –barriers have been built in France using tyre halves. By removing one side wall the tyres have also been converted to flower pots. Two tyres coupled together & filled with concrete are being developed as replacement of rail sleepers. Shoe soles, gaskets, “Scale-belt”, continuous conveyor belt etc. are the other uses of cuttings from used tyres.
The shredded tyres can replace sand and gravel to fill the areas or used as bulking agent in sludge composting and septic tanks. Tyre shredding are also used to prepare protective surface for equestrian activities. Rubberized concrete is also being developed by replacing tyre shredding with aggregate or tyre crumb with sand.
The used tyres are also pyrolysed for recovery of chemicals fuel oil, fuel gases and carbon black) in addition to steel. Pyrolysis is also known as destructive distillation. The products of Pyrolysis are influenced by process temperature, residence time, particle size of the feed and atmosphere. Pyrolysis is an endothermic process. The Pyrolysis reactors of various types are used e.g. vertical shaft reactor, rotary kiln reactor, fluidized bed reactor etc. Pyrolysis of tyres was first attempted by US Bureau of Mines Coal Research Centre and in excess of sixty components were identified in the yield consisting of solids, liquid and gases of high calorific value. Electrostatic precipitators and acidic/caustic scrubbers were also used in the process. Since then various efforts have been made world over to pyrolyse used tyres and the various products have been obtained which include benzene, fuel oil, carbon black fuel gas, activated carbon, steel etc. In Japan a simple economical method of thermal decomposition of used tyres for their ultimate disposal have been developed. In the process supersonic jet flame is used and the tyres are crushed by huge kinetic and thermal energy of jet flame into fine carbon powder and oil and both of the products having good calorific value, are good fuel for cement kiln and boilers. No pollution control equipment is required in this plant if cement kiln are located at same place for direct use of products from jet flame plant for the cement kiln. Many of the Pyrolysis plants installed in the wake of oil crises have closed down in Europe. However commercial scale tyre-Pyrolysis plants are being operated in South Korea, USA, Germany, Belgium, UK etc. American Tire Reclamation Inc. have obtained a version of carbon black and oil produced by Pyrolysis of used tyres and have termed it as ATR 33. this is being formulated to act as asphalt modifier. Activated carbon is also produced by Pyrolysis of used tyres. Hydrogenation of waste tyres is done to obtain carbon black. Gasification of waste tyres produce fuel gas which is being used for generation of Electricity in Japan.
Incineration is yet another option for ultimate disposal of used tyres. The heat generated can be used for raising steam in the boiler or used in cement/lime kilns. The tyres are largely hydrocarbons having high calorific value. The uncontrolled fire in the stockpile of tyres results in highly toxic gases in atmosphere and oils in ground due to incomplete combustion. Where as when tyres alone or with fossil fuel is burnt in an incinerator/boiler with excess air for its compete combustion the extent of air pollution is significantly reduces and even lower ten the air pollution caused by some of the fossil fuels e.g. coal. However scrubbers & electrostatic precipitators are provided to clean the flue gases. As tyres have high calorific value these re incinerated in specially designed incinerators to avoid internal damages. The various method of incineration include cyclonic furnaces, direct kiln burning, fluidized bed combustion, starved air incineration, conventional tube boiler (modified). In cyclonic furnace & modified boilers whole tyres can be burnt where as shredded tyres are burnt in other processes. Steel Zinc and gypsum are the useful by-products of the incineration process.
A substance containing lime can bind sulphur and zinc oxides. Tyre burning produces sulphur and zinc oxides and these can be bound by burning the tyres as fuel in cement and lime kilns. Tyre when use fuel in shredded form is also termed as tyre derived fuel (TDF). At times it is used along with the fossil fuel with the added advantage of increased thermal output and reduced emissions. TDF is being widely used in USA by cement kilns, industrial units, pulp and paper mills, power utilities as fuel/supplementary fuel. Tyres can also be gasified and the fuel gas thus obtained also being used in cement kilns. Some of the cement plants and power generating plants using tyres as fuel, which are under commercial operation in USA, UK, Germany, Japan, Italy, Belgium, France, Canada etc. have been discussed in the report. Various efforts are being made world over to effectively utilize the used tyres and the crumb/reclaim for more useful purposes and some of such efforts are listed in the chapter “Emerging Treads: Waste Tyre Recycling”.
With the increased rate of production of automobile which is expected to more than treble in next yeas as per latest indications. Efforts are required to be made for recycling of used/scrap tyres to avoid the problems regarding disposal of scrap tyres presently being faced by developed world. The recommendations include:
1. Removal of prejudice to look at retreaded tyres and products of recycled material as inferior. Recommend use of recycled products in various field of life.
2. To educate people through mass media about the salient points for taking care of tyres by optimum inflation, loading of tyres. To ensure proper suspension & alignment of vehicle. These will have effect on fuel economy and increase tyre life. Thus reducing the number of tyres to be replaced & scrapped.
3. Retreading of old tyres before its tread worn out beyond the limits and renders tyre to be scrapped. This is essential for safe driving and also prevents untimely scrapping of tyre; a conservation of resources and energy. Procured or ‘cold’ process of retreading is capable of increasing life of tyre to about 85-90% of life a new tyre and costs less than 50% cost of new tyre.
4. Tyres not suitable for retreading may be subject to
a) Use as whole tyres for erosion control, use as tree guards etc. (minor uses)
b) Shredding and crumbing of scrap tyres
- To use crumb as asphalt modifier for road construction. This field has lot of potential to utilize tyre crumb. Regulatory support is required in India in line with being provided in USA. Suitable amendment in specifications for construction of asphalted roads are required to be incorporated in the schedules of items of works prepared by various Govt. Agencies e.g. Ministry of Surface transport, Indian Roads congress, CPWD, PWDs, MES, Directorate General Boarder Roads Organization, International Air port Authority of India etc. to use crumb as asphalt modifier.
- To use tyre crumb for preparation of sports fields using rubber as modifier of polyurethane.
- To use tyre shedding as tyre derived fuel in cement kilns and boilers. By products include steel, zinc oxide etc.
- To use tyre shredding/crumb for reclaiming the “reclaim” rubber. Reclaim of rubber from whole tyres also produce cord and steel.
- To pyrolyse the tyre shredding to obtain end products including fuel gas, fuel oil, carbon black, steel etc.
- Tyre shredding can be used as low density constructive landfills.
c) Other minor uses of tyre e.g. shoe soles gaskets, tyres for wheels of tonga, hand cart etc.
5. Initiate R&D activities in the field for useful recycling and disposal of scrap tyres by Industry and Government.
6. Government Departments to fix targets for use of retreaded tyres for vehicles not being operated regularly on highways e.g. vehicle pertaining to municipal corporations, water supply)/electric supply services official jeep (excluding defence services) etc.