The world generates millions of tons of plastic and tire waste every year. Most of this waste is burned or used for landfill. Burning will release harmful gases and pose a threat to the environment. Pyrolysis technology emerged as a solution for breaking down plastic and tire waste. Pyrolysis involves the thermal decomposition of carbonaceous materials in an oxygen-free environment. During this process, the pressure of the system is not limited by the water vapor pressure. In other words, pyrolysis is the process of heating biomass in the absence of oxygen. This approach is thought to help reduce plastic and tire waste. It also allows recovery of some of the useful energy stored in the biomass.
The application of pyrolysis helps to recover energy from plastic waste and tire waste through chemical operations. Recycling plastics through the pyrolysis process consists of several steps. All plastic waste needs to be sorted before it can be disposed of. Mechanical recycling involves shredding of polymers and cryogenic grinding of plastics. Through the process of pyrolysis, the polymer's long-chain molecules are broken into smaller chains with the help of pressure and heat. In fact, this is similar to the Earth's natural process of breaking down carbon and producing oil. This natural process takes millions of years. The plastic pyrolysis process produces three main products: bio-oil, biochar and syngas.
Bio-oil or pyrolysis oil can be considered as an alternative to industrial diesel. After going through the sludge treatment pyrolysis process, pyrolysis oil is also used in boilers, furnaces, generators, diesel pumps, hot air/water generators, heaters, thermal fluids and other equipment. Syngas is reused in pyrolysis plants and biochar or carbon black is used in the plastics/rubber industry as well as inks, paints, etc. High calorific value biomass can only be pyrolyzed to produce bio-oil.
Tire recycling via the pyrolysis process involves heating whole or shredded tires without oxygen in a closed vessel reactor. Rubber polymers break down and form smaller molecules. The vaporized smaller molecules are further burned to produce bio-oil or pyrolysis oil. Solid, liquid and gas properties are obtained from the tire pyrolysis process depending on the process conditions and raw materials used.
A major issue associated with tire pyrolysis is the generation of solids streams, which account for approximately 40% of the total production. The steel is removed from the solids stream with the help of magnets, but the remaining biochar has no value other than as a lower-grade carbon fuel.
The Importance of Waste Tire and Plastic Pyrolysis Plants
The main advantage of the pyrolysis process is that it breaks down waste and produces valuable products. The pyrolysis process uses waste plastics and scrap tires as biomass or feedstock. The pyrolysis process and the output of the process are environmentally friendly. Pyrolysis can produce synthetic diesel fuel, which can reduce dependence on fossil fuels. Bio-oils can be used in pharmaceuticals. Further research could lead to technology that can convert bio-oil, and in the future it could become an alternative fuel for car engines. Biochar or black carbon is considered a useful fertilizer. Therefore, all products from the pyrolysis process are different forms of renewable energy.
Apart from this, the pyrolysis process and technology is economically viable as there will not be any shortage in the supply of waste plastics and waste tires. The technology is modular and more flexible than incineration. The pyrolysis process does not produce any harmful gases or chemicals, and the product provides a better solution for the recycling of natural resources. Improved pyrolysis operations could reduce large amounts of plastic and tire waste.
Challenges of waste tire and plastic pyrolysis
Appropriate measures or steps should be taken to bridge all technical knowledge gaps that exist in the pyrolysis industry. Availability of high-end infrastructure can be considered as another major challenge. The products of this process require long-term storage. Governments should provide support for the development of pyrolysis technology. In addition to technology-related gaps, knowledge industries should address all major challenges related to operational performance. Upgrades and stability are necessary for the proper operation of the pyrolysis unit.
