Published on 31/03/2014
First Update 15/03/2017
The automobile industry across the globe is exploding due to the modernization of the society. This is leading to a rapid growth in production of rubber. In India, the production of tyres is of the order of a billion and is third highest in the world; the Government of India has allowed their import as cut pieces for certified industrial end users. This, in effect, is leading to creation of scrap tyre piles. It is estimated that the annual availability of scrap tyres is about a million tons and this figure is increasing as the number of vehicle in the passenger, commercial and industrial sectors is catching up to the western levels. Scrap tyre pickers and scrap dealers collect thousands of tons of scrap tyres at economically viable rates.
Disposing the scrap tyres
These scrap tyres, due to their large volumes and 75 per cent void space, quickly consume valuable space and are thus are not desired at landfills. Tyres can trap methane gases, leading to the property of buoyancy or bubbling to the surface. This ‘bubbling’ effect can damage landfill liners, which are installed to help keep landfill contaminants from polluting ground water as well as the local surface.
Shredded tires are replacing other construction materials and are now being used in landfills, leachate collection systems, for a lightweight backfill in gas venting systems and operational liners. Shredded tire material can also be utilized to cap, close or cover landfill sites. These scrap tyres are very difficult to decompose which is why it is called as Black contamination; these cannot be burnt due to pollution problems. There is no other use of these waste tyres.
Scrap tyre as an energy source
As the world economy is progressing by leaps and bounds, the tendency of petroleum scarcity is growing day by day. The availability of energy has become the primary factor that controls various developments across the globe; the research says that the available petroleum will be exhausted within 15 years. The identification of alternative sources of energy has become the matter of concern for various countries.
In a country like India with large population, massive land, rapidly growing auto and machinery industry and market economy, the requirement of oil market will keep on rising; the country has transformed from an exporter to an importer of petroleum. The pyrolysis of tyre gives tyre oil, which can act as a substitution for furnace oil that is derived from crude. Thus, it creates the valuable things out of waste.
What is Pyrolysis?
Pyrolysis is a thermo chemical decomposition of organic material in the absence of oxygen at elevated temperatures. Pyrolysis typically occurs at operating temperatures about 430 degree Celsius (800 °F) and under pressure. Pyrolysis is a special case of thermolysis and is usually used for organic materials, being, therefore, one of the processes involved in charring. In general, pyrolysis of organic substances results in production of gaseous and liquid products and leaves behind a solid residue, which is richer in carbon content. Extreme pyrolysis, which mostly leaves carbon as the residue, is called carbonization. The chemical industry heavily utilizes this process to produce, for example, charcoal, activated carbon, methanol and other chemicals from wood, to produce coke from coal, to convert ethylene dichloride into vinyl chloride to make PVC, to turn waste into safely disposable substances, to convert biomass into syngas and for converting medium-weight hydrocarbons from oil into lighter ones like gasoline.
Pyrolysis of scrap tyre
If a waste tyre is heated in an anaerobic environment at temperatures of about 400 – 450 degree Celsius, it melts down, but does not burn. After it has melted, it starts to boil which brings about molecular restructuring of rubber and converts it into vapors and gases; when these vapors are passed through a cooling device and cooled, most of the vapors condense to a liquid while some of the vapors with shorter hydrocarbon lengths will pass through as a gas (similar to propane). The gas coming out of the cooling device is then passed through a bubbler containing water to capture the remaining liquid forms of fuel. If we provide enough cooling to the cooling tube, there will be no fuel in the bubbler, but if not, the water will capture all the remaining fuel that will float above the water and can be poured off the water. The bottom of the cooling device is a reservoir that collects all of the liquid and it has a release valve on the bottom to empty the fuel.
The period for which the process of pyrolysis needs to be performed depends on the quantity and size of tyre; the typical period is about 4 to 12 hours. During the process different vacuum values are applied in predetermined temperatures and in different phases. Different gases are obtained and the condensed gas is stored as a fuel-oil in tanks.
The main products of the process of pyrolysis are:
- 1. Fuel oil
The main oil product produced by this recycling application is the fuel oil, which is widely used for industrial and commercial purposes as a substitute for industrial diesel or furnace oil. The oil has 40 per cent to 45 per cent of the amount of recycled scrap tyres and can be carried by licensed tanker trucks.
Typical industrial applications of pyrolysis oil as a fuel are mentioned below:
- Hot Water Generators
- Hot Air Generators
- Thermic Fluid Heater
- Electric Generators (mixed with 50 per cent diesel)
- Diesel Pumps (mixed with 50 per cent diesel)
- 2. Carbon Black
Carbon Black is the also a major product recycled by Pyrolysis technology. The amount of recycled carbon black depends on the type of tyres but varies in the range of 30 per cent to 35 per cent of the total amount of scrap tyres recycled in the system. Carbon black acts as a raw material for many industries as the chemical structure of carbon black increases the endurance, strengthens and improves the coloring features of the materials.
Carbon black finds its application the following industries:
- Steel industries for burning process
- Footwear industries to make rubber souls
- Polish industries
- Ink industries
- Color industries as pigment
- Iron industries
- 3. Steel Wire Scrap
The third product of tyre pyrolysis is steel wire, the quantity of which is in the range of 10 to 15 per cent and depends on the quality of tyre. The steel wire scrap is very easily sold in the local market.
- 4. Pyrolytic Gases
Pyrolytic gases constitute about 10 per cent of the output of the process of pyrolysis of tyre. Methane is the main component of these gases. These gases are used to heat the reactor and for other heating applications.
Advantages of pyrolysis of tyre
- The raw material is cheap and easily accessible.
- The process is applicable to all rubber-based materials.
- The process is environment friendly, as it does not involve the use of chemical ingredients.
- The process leaves no churn left and complete waste tyre recycling is achieved.
- There is no soil, water or air pollution.
- The recycling of each ton of tyres preserves 10 tons of CO2, a major greenhouse gas.
- The process creates industrially valuable products out of wastage tyres.
- The system creates an alternative source of energy to replace petroleum products and natural gas.