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Agricultural Engineering

Quality Bagasse

Researchers at Unicamp develop equipment that makes it easier to obtain ethanol cellulose

EDUARDO CESARSugarcane residue: vegetable biomass to produce electricity and fuelEDUARDO CESAR

Sugarcane bagasse is mainly burnt in mills to generate power. However, researchers are developing new uses for this type of waste, which is regarded as the most important residue of the sugar and alcohol industry. One alternative is the generation of fuel, the so-called second-generation ethanol. The potential is huge, largely because of raw material availability. The volume of this subproduct is equal to about one third of Brazil’s sugarcane production, which has reached record highs year after year. The 2009 crop announced in December by the Ministry of Agriculture exceeded 600 million tonnes of sugarcane, which yielded some 200 million tonnes of bagasse. Laboratory developed genetic improvements may also help to increase the plant’s biomass. This will result in larger plants and, consequently, more bagasse at the end of the conventional sugar and ethanol production processes.

It was while thinking about treating such waste on a preliminary basis that researchers from the Agricultural Engineering School at the State University of Campinas (Feagri-Unicamp), under the coordination of Professor Luis Augusto Barbosa Cortez, developed equipment that can separate this heterogeneous material into similar parts. After the last sugarcane crusher, the bagasse turns essentially into a powder consisting of particles and fibers of various sizes. The hardest portion of this mix is rich in lignin and comes from the external portion of the plan’s stems. It is almost dry. As for the moister and softer material, it comes from within the stem. This is the best portion for ethanol production, thanks to its high cellulose content. “Lignin is harder to degrade, which is why the internal part, with less lignin, is ideal for submitting to hydrolysis,”  explained Cortez, referring to the process that breaks down cellulose sugar and transforms it into alcohol.

“Lignin is an aggregator that offers resistance when it comes to breaking down molecules. The less lignin in the material, the easier the process of getting cellulose alcohol from it,”  he explained. Therefore, the classification of bagasse obtained through the technology developed by the Feagri group will tend to become increasingly important as research into new forms of ethanol generation advance. Creating a technology to classify, continuously and automatically, these different parts of sugarcane bagasse was the challenge that the researchers faced. To meet it, the group had the support of FAPESP, through its Regular Research Awards program, and the involvement of Professor Guillermo Roca, from Cuba’s University of Oriente, who came to Brazil to take part in the project. It was Roca’s work that established the general principles for the construction of the invention, a sort of pneumatic classifier. In it, the bagasse is inserted though a diagonal orifice in the device’s upper section, and pushed by a rotating valve over a constant air flow. “The thick particles are then deposited in the bottom; the medium-sized ones go into a collector in the device’s medium level and the smaller, lighter ones are conveyed by air along a curved tube into a higher collector section,” explained Cortez. “It isn’t necessary to prepare the bagasse before putting it in the machine,” he highlighted. This makes its operating cost interesting to industry. Even before starting to produce cellulose ethanol, the separation of bagasse can improve bagasse quality for the several uses to which it will be put. The dry portion, for instance, burns more uniformly and efficiently, to produce thermoelectric power.

Other applications
For as long as the technology is not ready for industrial use, bagasse will continue to be used to produce animal feed and fertilizer, but, above all, as burning fuel for power generating boilers within mills. It is not treated in any way to be used in this way. “It isn’t even dried before it is burnt, which causes it to burn less efficiently,” says Cortez.

When second generation ethanol comes into being, the most valued part of the bagasse will be removed from the lower collector of the classifier developed by Unicamp. Through analyses, the group found that the thicker fraction has higher pulp and lower lignin content, being therefore more suitable for making alcohol. Besides the sugar and alcohol industry, the invention may be useful in any field of endeavor that needs to separate heterogeneous granulated solid materials. For instance, the milled grain in the food industry, hydrated lime in the mining area, and the powder resulting from grinding stones in the civil construction industry. The efficiency and versatility of the equipment led Unicamp’s Inova innovation agency to file a patent for it.

The Project
Development of a technology for continuous segregation of biomass particles using a new type of pneumatic classifier: sugarcane bagasse and other solid biomass residues (nº 07/01888-4); Type Regular Research Awards; Coordinator Luís Augusto Barbosa Cortez – Unicamp; Investment R$ 73.013,50 (FAPESP)