EDUARDO CESARTo be self-sufficient in terms of water, sugar mills must recover steam and dry-wash sugarcane EDUARDO CESAR
Many sugar and alcohol mills produce electric power in boilers and generators as a by-product of the burning of sugarcane bagasse. They become self-sufficient and can also sell part of the electricity produced in the countryside to the power distribution companies. Soon they will be able to supply not only power, but water as well, according to two new sugar mill projects designed by the company Dedini, a traditional equipment manufacturer that specializes in setting up sugar and alcohol mills as well as plants for other industrial sectors. Mills based on these projects will no longer need to draw water from springs or wells for production. According to the company’s vice-president of technology and development, José Luiz Olivério, the water that they will use is in the sugarcane itself. One can obtain 700 liters of liquid from 1 ton (t) of sugarcane.
There are two projects, one for a plant that is self-sufficient in terms of water and the other where the industrial unit, besides having the same characteristics as the aforementioned project, will generate extra water for the plant itself, for irrigation, for instance, or for other companies, thus making the plant a water supplier. Based on the average consumption figures for the state of Sao Paulo, sugar mills consume 1,830 kilos (kg) – equal to 1,830 liters (L) of water – per ton of sugarcane, according to figures for 2005 from the Sugarcane Technology Center (CTC), an association funded by sugar mill owners and sugar producer associations. “Besides this volume, production also uses the 700 liters for each ton of sugarcane bringing the total to 2,530 liters of water. Thanks to the change in the processes throughout the alcohol or sugar production system, we not only avoid using pure water but we also recover much of the liquid used in the process. In the case of the supplying mill, we used just 400 liters of the sugarcane liquid, with the result that 300 liters were left over as surplus,” says Olivério.
To eliminate the capture of water by the sugar mills, as water is ever scarcer and more valued worldwide, the company’s R&D group reviewed the current projects in sectors where there is integration with water, so as to bring these areas closer to a position of total sustainability. “We adopted other types of technology, such as replacing the traditional washing of the sugarcane with water by a dry-wash system based on existing technology,” says Olivério. For each ton of sugarcane, on average 694 liters is used. The strategy goes as far as recovering the water vapor from various pieces of equipment such as sugarcane ovens. “The new system recovers and condenses evaporated water. The condensation work is efficient in this case because we are using more advanced concepts in the fermentation that result in a must, the fermented sugarcane broth, to which yeast is added to produce more concentrated alcohol, with less water and more sucrose,” explains the company’s vice-president. Just from evaporation, traditional sugar mills lose an average of 1,052 liters of water. “It is impossible to recover all of this; there are always losses.” Still, according to the company’s calculations, evaporation losses dropped markedly, to 136 liters, under the new system. Olivério believes that the self-sufficient system, which took two years of studying at the company, is unprecedented anywhere in the world, at least in the sugarcane sector. “It’s hard to say the same for other industries.”
The new system of sugar mills presented by Dedini comes with two options, one for the installation of plants that are self-sufficient in terms of water and another for those that can also produce it, which are called exporters. The difference between the two lies in the use of vinasse, i.e., the slops produced by the distillation of alcohol in the form of a foul-smelling, liquid pollutant, generally discarded into rivers and lakes, but which is used by sugar mills to make fertilizers, often for their own use, because it is rich in mineral salts, such as potassium. In the self-sufficient system the evaporation process produces vinasse with a solid content of 8% to 9%, while the comparable figure in the traditional system is around 3% to 4%. In the so-called export process, the vinasse has a solid content of 65% by evaporation and generates more fresh water. According to Olivério, in the case of a sugar mill that can process 12 thousand tons of sugarcane a day, one can produce a surplus of 3.6 million liters a day of drinking water. Purification systems can also be linked to the mill.
With the concentrated vinasse at 65%, one can produce an organo-mineral biofertilizer that the company has labeled Biofom. The preparation of the fertilizer includes the concentrated vinasse along with other waste from the sugar mill, such as ash from the boilers that burn the bagasse, and also the residues from the filters, left after the treatment of the fermented sugarcane broth. For each ton of sugarcane one can get 4.66 kg of Biofom. The main advantage of the product, according to the company, lies in the increase in agricultural productivity, since it has a 90% fertilizer content, whereas unprocessed or even concentrated liquid vinasse only has 10%. Other Biofom benefits include the possibility of using it for other types of crops, its capacity to lose less nutrients to rain, penetrate the soil and reach the water table, and the partial replacement of traditional mineral fertilizers, as well as not having the nasty vinasse smell. An agricultural analysis of Biofom regarding the increase in the productivity of sugarcane is being carried out by USP’s Luiz de Queiroz School of Agriculture (Esalq – USP) and should be concluded by early October this year.
A macro-machine
The new projects for sugar mills that Dedini presented will enable these plants to be set up in the state of Sao Paulo. “In order to set up and build a sugar and alcohol mill, one needs to show that there is water available and how water will be captured in the area,” says Olivério. The current plants can be adapted, but the process is more complicated, because the installations and equipment are older. The cost of a new plant, totally set up, ranges from R$300 million to R$360 million, using traditional processes, depending on whether or not it will produce just ethanol or sugar as well. According to Olivério, in the self-sufficient system, the investments required will cost 10% more while, in the case of the water export system, it will cost an additional 15% to 20%. Launched in July of this year at the Sugar and Alcohol Agroindustry’s Technology Symposium and Show (Simtec 2008), there was no need to set up a pilot plant for the new projects because, according to Olivério, they were drawn up based on true and tried engineering know-how that is already in use. Up until August, no new mill had been set up nor had any construction contracts been signed. But just the possibility that these projects can be built strengthens the idea that a sugar and alcohol plant is a macro-machine that is increasingly capable of transforming sugarcane into other products.
