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Car tires as a source of industrial energy

To transform old and dumped car tires into a source of energy. This is the proposal of a project developed by researchers of the School of Civil Engineering with the support from the area of energy planning of the School of Mechanical Engineering of the State University of Campinas (Unicamp). They have assembled equipment that generates three usable sub-products: carbon black, a raw material used in tire production, methane gas and fuel oil used in industrial furnaces and ovens. Thus, they hope to contribute towards a solution for one of the greatest environmental problems happening today, the destiny of used tires.

When they are no longer of use in the different types of vehicles, a large part of the tires are thrown out in garbage dumps, into vacant lots and into rivers and streams. A small number are burned in industrial furnaces as a source of energy. Besides being large scale pollutants by their size and by not being bio-degradable – it would take hundreds of years for a tire to decompose – they accumulate water and serve as sites for mosquitoes that are the transmitter of sicknesses such as dengue fever.

The idea to transform the tires into energy originated during the decade of the 70’s with the first global oil crisis. “When the first oil shock occurred, we got to test the use of energy from tires in a small industrial company that recycled iron.” recalls professor Carlos Alberto Mariotoni, the coordinator of the project. He told us that he had come up against problems of the most diverse type during that period. The main one also referred to the environment. “The process resulted in a curtain of black smoke going into the atmosphere without any treatment.” he remembers.

The choice, at that time, fell upon the tire because it is an alternative energy product whose cost is practically zero. Each tire contains the energy equivalent of 9.4 liters of petrol, according to the Business Commitment towards Recycling (Cempre), an organization maintained by fifteen large companies such as Ambev, Coca-Cola, Mercedes-Benz, Paraibuna Packaging and Gessy Lever. It has been estimated that in Brazil close to 500,000 tires per month are available for use as a fuel. This figure would be equivalent to a saving of 4.7 million liters of crude oil (petroleum).

Brazil throws away each year close to 20 million tires. Close to 70%, mainly in the area of passenger and cargo transport which go on for retreading. In the United States there are 242 million tires thrown away per year, 25 million in the United Kingdom and 10 million in Australia. In these countries, a large quantity of the tires are fragmented and placed in landfills and the remainder are mixed in with asphalt or used in furnaces for the making of cement.

An obligatory destination
Another factor that today brings a greater importance to the work of professor Mariotoni is the law which will be effective in January of 2002 and forces manufacturers, retailers or importers of tires to recall a certain amount of units for recycling. In the beginning, for every four tire manufactured here or imported, the company must provide the destination of one used tire. From 2003, for every four tires manufactured, two used tires must be collected, and in 2005, for every four manufactured, five must be collected.

Today there are few companies that carry out the recycling of tires. The technology used is pulverization and de-vulcanization with chemical products that result in a paste used in the manufacture of the rubber carpets for cars, soles for shoes and industrial flooring. The objective of professor Mariotoni, who took up again the research in 1997, more than 20 years after his first initiatives, was to recover the raw materials for the manufacturing of new tires as well as obtaining higher quality products that have energetic qualities.

“We began by working on a new project and the setting up of equipment that would be adequate for the present environmental reality.” he says. Today, the project is ready and is going through dimensions studies to be used on an industrial scale. The equipment has a reactor that receives, before the fragments of rubber, compressed air at a high pressure and a layer of alumina, an inert material (aluminum oxide) which serves as a reaction site for the process. The compressed air forces the expansion of the alumina from a thickness of 40 cm to 1.5m and it is centrifuged while the internal temperature of the reactor reaches 700°C. At this point, liquid petroleum gas (LPG) is injected and the temperature reaches 1000ºC. “The material transforms itself into a large incandescent mass.” reports professor Mariotoni. Then it is time to introduce into the reactor the tire fragments, which in this way quickly absorb the heat. When the rubber gets to this state it enters into decomposition. In this phase, various original rubber molecules come up as well as a series of compounds. These compounds break down and form even smaller particles. In the end, the process produces gaseous, liquid and solid compounds.

The separation of the gas from the liquid happens in the condenser. “It forces the gas to pass through a series of coils (with various layers and water).” explains the professor. This gas is cooled from 350°C to 32°C. During this fall in temperature, a lot of what was vapor becomes liquid again and is separated in a recipient. In the end, we obtain three by-products (around 30% for each), carbonized ashes known as carbon black, the oil and methane gas, these last two possessing energetic qualities. “If equipment like this was installed in the plant of a small or medium industry, it would be possible to use the resulting fuels from the process in its production.” says professor Mariotoni.

The system developed by the researchers uses the method of pyrolysis. Or that is to say, everything is done without the presence of oxygen. This way, it gives priority towards the formation of the liquid part (oil). “Various processes were tested and in this one the occurrence of problems such as smoke doesn’t exist.” states Eduardo Antônio Goulart, who prepared his doctorate thesis on the theme in the Area of Planning of Energetic Systems at Unicamp.

Alternative energy
“The problem of used tires has worrying dimensions, and there will have to be various initiatives to solve it.” says Dr. Goulart. For him, the project is one of the solutions because on its own it will not solve the question. “In the 70’s, our main goal was to find an energy alternative. Today it is not possible to speak of energy without taking into consideration the question of the environment.” points out professor Mariotoni.

The project
The Energetic Recycling of Discarded Tires via a Fluidized Reactor Bed: a Contribution to The Environment Question (nº 97/02312-5); Modality
Regular line of research assistance; Coordinator Professor Carlos Alberto Mariotoni – Faculty of Civil Engineering of Unicamp; Investment
R$ 21,000.00