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Steel mills

Sustainable charcoal

New system produces raw material cleanly within eucalyptus plantation

073_Carvao Sustentavel_189Better known for being used at barbecues, charcoal in Brazil is also responsible for the production of 30% of the pig iron, the metal alloy used for producing the steel used in vehicles, machines, ships, trains, cables and other products. Worldwide, this percentage is less than 1%. Thus, part of the steel made in the country is renewable, unlike the use of coal, which requires the exploration of finite mines, often underground, and in the case of Brazil is almost all imported. Charcoal or coal is essential for supplying the carbon in pig iron. The problem is that around 50% of Brazilian charcoal production, whether for barbecues or for producing steel, is also carried out in a rudimentary way, in a brick-oven, which is highly polluting and looks like an oca [Indian hut] or igloo, called a meda or raboquente [hot tail], and often uses native wood. The solutions, including the social solution because the industry often employs children and slave labor, are beginning to appear as a result of research by companies and universities and also the need  for technological advances in the production of charcoal.

One of the solutions comes from the more than 20 years of persistence by production engineer Nilton Nunes Toledo, a retired professor from the Polytechnic School (Poli) of the University of São Paulo (USP). He has developed a more advanced and environmentally correct system for producing charcoal with the generation of electricity during the gasification process of wood chips and sawdust, for example. Furthermore, the system does away with the use of trucks in the production, cutting and transporting of eucalyptus, the reforestation crop most indicated for charcoal-making, although it can also be produced from elephant grass, orange and sugarcane bagasse, rice husks and other waste.

“The charcoal plant must be set up in the eucalyptus forest and the focus has to cover everything, including the way it is planted, harvested, handled and made into charcoal. Heat consumption and a new, rapid cooling system have to be optimized and all by-products must take advantage of this, including bio-oil, tar and pyroligneous acid, which is used in the chemical and cosmetics industries and which can be worth more than the charcoal itself,” says Nilton, who is currently the CEO of the Foundation for the Technological Development of Engineering (FDTE), an entity formed by Poli engineers and that is responsible for coordinating the project. He started studying the subject in the 1980s when he was a co-owner, with other businessmen, of a farm producing wood in the Ribeira Valley region in São Paulo State.

“We started selling wood for packaging, while at the same time studying what it is to make charcoal and building several types of oven that were heated by blow-torches. But the system was disappointing because of problems with the process, like the huge amount of time it took for the wood to turn into charcoal.” Since the 1980s, he has been thinking about developing a second version, which was recently finished. “Now I don’t think about using brick cells, but a tunnel made from the same material that functions as an oven. The wood must be heated within cylindrical metallic boxes, called retorts, which are hermetically sealed, in the absence of oxygen that can change the charcoal yield.” They roll into the oven and in around 10 hours, on average, at a temperature of around 400°C, the wood is transformed into charcoal.

The manufacture of chemical products that can substitute the congeners obtained from oil is carried out by condensing steam. It is taken to separation towers set up alongside the oven where the combustible gases coming from the charcoal-making process mix with the gases produced in the gasification boiler and help the plant to be self-sufficient in energy. “Condensation is divided into two parts, an oily phase from which come the vegetable tar and bio-oil, a complex mixture of many products, and the aqueous phase that produces pyroligneous acid, which can be transformed into methanol and acetic acid,” explains Nilton. Bio-oil, which can be employed for generating electricity, is a dark liquid used both for burning in boilers and in the chemical industry in the manufacture of resins, for example. Tar, another type of fuel, is also the raw material for disinfectants. Methanol is widely used in producing biodiesel and acetic acid in the manufacture of solvents and paints. “Producing these compounds in the plant is difficult, but feasible because they are classic processes.” The production system and the oven that receives the retorts and has a mechanism designed for separating the by-products and heating gases for the wood drying oven are two of the three patent applications submitted to the National Institute of Industrial Property (INPI). The third has to do with the transportation of the wood, which is done using a system called a monorail, similar to a cable car. The wood travels from where it is cut to the plant on supports that move throughout the eucalyptus plantation on steel cables attached to two meter high posts fixed to the trees themselves. “This system avoids the use of tractors or trucks for transporting logs to the plant,” he explains. He estimates that daily production of charcoal with the new system, which is called silvo-chemistry, will be 40 tons on a 5000 hectare farm and should employ 300 people.

Compared with the raboquente ovens, the new one has the advantage of using 432 kg less wood for each ton of charcoal produced. From the same amount of charcoal it is possible to obtain 333 kg of chemical by-products. Having been well-assessed in the laboratory phase, the project needs a pilot plant, which is likely to cost around R$ 2 million, in order to check the efficiency of all stages. “We’re looking to business for funds for this phase,” he says. The final setting up of the plant is likely to cost R$ 10 million. “This type of industrial model is used in other countries and in Brazil is has already been tried in the past, in the 1970s and 1980s, when charcoal was only made from native timber, which was abundant,” says Professor José Otávio Brito, from USP’s Higher School of Agriculture “Luiz de Queiroz” (Esalq).

“After a certain stagnation of technology  in the 1990s, there has been a growing return by the steel industry in Brazil to charcoal because the country has the potential to be a large global competitor in the so-called “green steel,” that is obtained from pig iron produced using charcoal,” says Brito. With regard to  technology, some companies, such as Bricarbras, from Paraná, and Ondatec, from Uberaba (MG), are examples of investment in the development of ovens for transforming wood into charcoal. In the late 1990s the former began developing a charcoal-making system that takes place in cylindrical containers and has had good results, with a reduction in gas emissions, by means of an incinerator, when compared with ovens made from clay or brickwork. “But this system is very expensive for medium size and small owners,” says Professor Benedito Vital, from the Department of Forestry Engineering at the Federal University of Viçosa (UFV), in Minas Gerais. Focusing on these companies, Vital and Professor Angélica de Cássia Carneiro, developed a system that is similar to the one used in large steel mills, which in addition to doing the carbonization work more efficiently than charcoal made by hand, burns off the process gases. “The smoke is burned off in jets of hot air at temperatures of more than 1000°C. Using heat exchangers we’ve managed to cool the charcoal quickly to sell the product in a shorter period of time,” says Vital. “This system is ready to be passed on to companies.”

Wilson Dias / ABRBrickwork ovens in Pará: rudimentary system that pollutes and often uses slave and child laborWilson Dias / ABR

Another novelty for the sector is still surrounded by secrecy. Ondatec, which originated in the Technology and Business Incubator at the University of Uberaba (Uniube), in Minas Gerais, is ready to launch a new carbonization oven. The brainchild of Professor Ricardo Naufel from the electrical engineering course, who is also the company’s technical director, the difference about this oven is the mathematical modeling used in the carbonization control system, which will be very precise. “It will be an intelligent oven,” Naufel guarantees. According to the professor, R$ 10 million was invested by private investors, whose names cannot be revealed before the launch. “We installed a pilot unit in Uberaba and for a year we observed the system. Now we’ve installed the first industrial unit in Tietê, in São Paulo State to produce barbecue charcoal first. Afterwards, we’re going to produce bigger units for steel mills.”

Many of the problems related to current charcoal making plants concern some of the pig iron makers, which produce it independently from the major steel mills to sell to foundries and steelworks. The wood often comes from native timber. Productivity is low and control conditions are ineffective. At the other extreme of the sector are some of the country’s steel-makers, such Vallourec & Mannesmann and Aperam, formerly ArcelorMittal, both in Minas Gerais, and Votorantim Siderurgia, in Rio de Janeiro, which use charcoal and have their own production systems for this raw material. Other mills use coal for the same function. To supply this, Brazil, the world’s ninth biggest steel producer, imported 15.9 million tons of coal in 2010, according to the World Steel Association, at a cost of US$ 1.6 billion.

“Charcoal is a peculiarity of the Brazilian steel-making industry,” reveals the technical document, Siderurgia no Brasil 2010-2025, [Steel-making in Brazil, 2010-2025], a study published in 2010 by the Center for Strategic Management and Studies (CGEE), an organization linked to the Ministry of Science and Technology. The document points out that charcoal is a type of biomass that can be produced from several plants, like a renewable mine. According to the researcher José Dilcio Rocha, from Embrapa Agroenergia [Embrapa Agroenergy] in Brasília, “green steel” has an environmental appeal because of the reduction of greenhouse gas emissions in the steel sector. “We lack public policies and good projects, like Professor Nilton’s one, which could raise the charcoal production sector to a level equal to that of the production of ethanol,” says Rocha.