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Environmental Engineering

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Plasma-based equipment for recycling aluminum guarantees economic and environmental gains

Cans of beer and soft drinks have gained a new process for recycling that is going to make it more efficient, with less spending on energy and without leaving waste, to bring these products back to the aluminum alloy used in the production of new cans. The novelty is based on a furnace heated by plasma, a gas produced at high temperatures, better known as the fourth state of matter. It is different, because the ionization (losing or gaining electrons) of its particles, molecules and atoms is significant, guaranteeing physical and chemical qualities that are distinct from those of the other existing states, the solid, liquid and gaseous ones. Accordingly, plasma acquires a peculiar characteristic, which is its capacity for conducting electricity, in a way very similar to metals.

The equipment, which is going to recycle every kind of aluminum object, besides industrial swarf and sludge, is at the final stage of development at the Technological Researches Institute (IPT) of the State of São Paulo. It is part of a project of FAPESP’s Partnership for Technological Innovation (PITE) program, in conjunction with the Brazilian Aluminum Association (Abal), which brings together companies that produce and transform this metal.

Built in the IPT’s Mechanics and Electricity Division, where it is already in operation, the furnace shows a low consumption of energy as its most evident advantage. The use of plasma makes possible savings of 97% in electricity, compared with the production of primary aluminum, produced from the mineral extraction of bauxite. Even when compared with the most advanced stage of the conventional method for recycling – which makes use of combustion with the presence of pure oxygen for heating the furnace (oxycombustion) -, the plasma process is more economical. Experiments carried out in the prototype built at the IPT indicate that, to produce 1 tons of recycled material, depending on its composition, the new furnace needs something like 400 to 500 kilowatt-hours (kWh), against the 750 kWh or so of the conventional method.

The efficiency of the equipment makes another welcome gain possible, now in the environmental area: the total elimination of industrial waste at the end of the process. In the conventional method for recycling, the use of salts is an environmentally problematic factor. They are used to coat the aluminum, avoiding the losses of metal through oxidation, a situation that occurs through the presence of oxygen in the process. The material used is a mixture of sodium chloride (NaCl) and potassium chloride (KCl), in a composition of from 10% to 40% of the load of metal to be processed in the old furnace.

At the end, after being separated from the metal, they cannot be reused, and they become a risk factor for contaminating rivers and water tables. That is why the saltsused are intended to be kept in specific deposits, in the form of industrial landfills, which cost the companies dear. The use of plasma solves this problem completely, because it does not need these products in the recycling process. Being of recent technological use and having such distinct properties from the more common states of matter, plasma is apparently something that it is difficult to handle.

But researcher Antônio Carlos da Cruz, the coordinator of the project in the IPT, explains that the technique is relatively simple: when heated, the argon (Ar) – a gas chosen because it does not show any reaction with aluminum – transforms electrical energy into thermal energy (heat), without the use of any other element, besides the gas itself. At the entrance of the furnace, the plasma torch is installed, which, maintained by an electrical discharge, makes the gas reach temperatures between 5,000° C and 12,000° C, far higher figures than those obtained in the conventional process.

Industrial secret
Cruz prefers not to disclose further details about the new process. “The technology is at the stage of registering the patent”, says the researcher. Secrets aside, the furnace developed at the IPT is of the rotary type, with a drum that, when loaded, continuously shakes the material that is inside it. “This characteristic is important, because every object of aluminum has a layer of oxide, which needs to be broken for the molten material to join up and be transformed into liquid metal”, he explains. In this way, the aluminum will be taken by small channels to the molds, where the metal will solidify and be transformed into ingots.

The current Plasma Furnace for Recycling Aluminum prototype offers a variable capacity for operation, according to the kind of material. For aluminum sludge, which is a waste from primary production, it can take a load of up to 200 kilos. With more noble materials, such as aluminum parts and cans, its capacity is 550 kilos, in a complete operational procedure that lasts around two hours. In total, about 50 tons of material have now been processed, between sludge and scrap, under a condition of industrial simulation, which is the same as the equipment’s monthly processing capacity.

To demonstrate better the application of the plasma furnace on an industrial scale, materials in similar conditions of composition and quantity are to be processed, at the same time, in a conventional furnace, so as to get a more precise comparison, including under the heading of consumption of energy. The way to make, with greater effectiveness, these comparisons between furnaces, according to Cruz, is to set up pilot equipment, of an industrial conception, with a greater capacity for recycling, and which can be operated in a system of two shifts a day, because it can work non-stop for 24 hours. On the premises of the IPT, the operation of the prototype furnace covers just one shift.

Industrial operation will put Brazil in the group of countries that are already using plasma in the recycling of aluminum. “In Canada, in France, and in South Africa, companies are now using plasma for recycling aluminum sludge, but the process we have developed here is innovative, because it widens the range of possibilities of materials for recycling by the new technique, such as parts in cast aluminum, laminates, sections, sheets and cans”, explains Cruz, mentioning that for being totally clean, the implantation of the technology employed in the furnace tends to be more expensive. “But, at the same time, it is just as competitive operationally as the processes with oxycombustion”, he adds.

Joint effort
Following the consortium organized by Abal, an entity that brings together Brazil’s producers of aluminum, companies like Alcoa, Tomra-Latasa, Metalur, Servibrás and Sulina de Metais have taken an active part in the IPT’s project, with training of personnel and funding of part of the R$ 800,000 or so spent on carrying out the research. The material for recycling is also supplied by these companies, which are given back the recycled aluminum – in the form of ingots – resulting from the process.

Alongside the economic question, the importance of developing technologies that do not harm the environment was what most motivated Abal and the companies to take part in the program, according to Ayrton Filleti, the coordinator of the association’s technical commission. “The plasma process is environmentally more suitable, because it eliminates the toxic waste that comes from the recycling of aluminum and, as a consequence, generates savings for the companies, with the reduction in the consumption of electricity, and it does away with the need for special industrial landfills, which are very expensive”, he avers.

“The plasma technology interests the industries, but there is not yet a definitive time limit for it to be implanted”, says Filleti. “The furnace developed at the IPT, besides being cheaper than the similar ones that there are abroad, is more efficient, and, in the future, the companies will have to resort to this recourse. For the first time, Abal took part in a project that resulted in a novel technology, developed in Brazil, which we need to value”, he points out, recalling that, in Europe, the lack of space for industrial landfills has even pushed companies to look into recycling the saline waste from the conventional process, something that is very expensive, and this is something that may generate international interest in using the Brazilian furnace.

According to Abal, Brazil, with 1.5 million tons a year, is currently the sixth largest producer of aluminum in the world. Of this total, 1.3 million tons are obtained from mining, and 253,500 tons are the result of recycling. The production of primary aluminum, besides needing a large quantity of electricity and interfering with the environment, generates between three and four times more waste than recycling.

In a way that is different from what happens with other materials, the recycling of aluminum boasts surprising levels in Brazil, with the list of items headed up by beer cans, with a remarkable rate of 87% being totally recycled, according to the most recent figures released by the entity. At the moment, the recycling of aluminum in the country accounts for 35.3% of the domestic consumption of this metal – a total of 717,700 tons a year -, a percentage higher than the world average, at the 33% level.

If we take into consideration just the recycling of aluminum cans, the average cycle for which is 46 days, between filling, consumption, and returning back to the industry, Brazil is today the largest recycler among the countries in which the practice is not mandatory, with 121,100 tons a year, ahead of Japan and the United States. This accounts for 50% of the total of aluminum recycled in the country. It is also worth recalling that for each ton of aluminum recycled, 5 tons of crude ore are saved.

Of the total of cans recycled in Brazil, 70% is processed in Pindamonhangaba (SP), a city in the region of the Paraíba Valley, which Abal gave the titleof Brazilian Capital of Aluminum Recycling, because it is there that the scrap processing factories are installed. Besides a rapid cycle of consumption, cans are very much linked to society’s daily life. Some companies that produce aluminum have now implemented recycling programs, promoting awareness in schools, with incentives like using the material collected as trade-in for computers.

Distribution of scrap
Another important factor in recycling of cans is the diligence of the collectors, scattered all over the country, who account for a major part of the selective collection of materials, passing on the results of their work to the scrap deposits. These centers handle the distribution of the material to the processing industry, in large quantities. With the increase in the demand for and production of secondary aluminum – cheaper and easier to get -, the industry is now facing the possibility of the Brazilian market running out of scrap. With this, Brazil, which buys only 98,700 tons of aluminum a year from the foreign market, may shortly need to import scrap for recycling.

Even if there is a significant increase in the quantity of aluminum recycled, primary production will continue to be a necessity, because the demand for this metal is growing. The most important thing is that it can be recycled countless times. This characteristic, besides economizing energy and saving the environment, guarantees a healthy economic activity that, even without being legally mandatory or getting official incentives, is amongst those that is growing most in the country.

Long life in recycling

Almost invisible to the consumers, inside the long-life packaging that today, besides milk, holds juices and even coconut milk, there is a fine layer of aluminum in the form of a plastic and paper sandwich. The same as in the cans, this material could be recycled and go back into the productive system. To put this process into effect, TSL Engenharia Ambiental – a company that specializes in the treatment of waste – has been researching for three years the use of plasma for recycling the aluminum of the long-life cartons.

The resulting process, different from the one developed at the Technological Researches Institute (IPT) for recycling the aluminum from cans, was presented by the company in December 2003. “In the case of TSL’s process, the IPT was contacted only to test and corroborate the efficiency of the new system”, says Roberto Szente, from the Plasma Laboratory of the IPT’s Mechanics and Electricity Division, who supervised the tests. The process will be implanted in a partnership between Tetra Pak, a company that produces long-life packaging, Klabin, a paper manufacturer, and Alcoa, which produces aluminum.

Using thermal plasma as one of the components of the recycling process, the new technology – a novelty in the world – will be used to separate the plastic from the aluminum that is present in the cartons, after separating the paper, which is done beforehand on specific machines. The system developed by TSL uses a plasma torch for heating the plastic and aluminum mixture up to 15,000° C.

This process transforms the plastic into paraffin, and the aluminum is totally recovered, with the same characteristics of the metal used by Tetra Pak in producing the packaging. The new system will be installed in an industrial unit of Klabin in Piracicaba (SP), and it should be ready in October this year. The company is going to receive the collected material, separate the paper, and forward the plastic and aluminum to TSL. In turn, this company will separate these two products and send the aluminum to Alcoa, which will transform this metal into extremely thin sheets for Tetra Pak, which at present does not use any recycled material in the composition of its packaging.

The investment in the construction of the plasma unit will be R$ 10.5 million, financed in equal parts by the four companies involved. One year after its implantation, the intention is to export the technology to other Tetra Pak units round the world. According to Fernando von Zuben, the company’s director for the environment, the gain will be above all for the environment, since the plasma unit will have the capacity for processing 8,000 tons of plastic and aluminum a year, equivalent to recycling 32,000 tons of long-life cartons. Besides the process coming to be part of a chain of sustainable development, the expectation is for a 30% increase in the value of the cartons collected, generating more earnings for the collectors, the companies and the city halls that work with the selective collection of garbage.

The Project
Recycling of Aluminum: Development of Technological Innovations (nº 99/06282-9); Modality Partnership for Technological Innovation Program (PITE); Coordinator Antônio Carlos da Cruz – IPT; Investment R$ 397,730.16 and US$ 25,307.89 (FAPESP) and R$ 355,952.00 (Abal)

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