Abstract
Centrifugation is a fundamental step for the competitiveness of Brazilian ethanol plants, since it allows the mass of yeasts of interest to be propagated only once, and then reused by yeast recycling process, avoiding the sugar consumption for this purpose. The fermentation process in the mills is not a clean process from the asepsis aspects. In addition to the yeast of interest, there are wild yeasts and bacterial contaminants in the fermentation process. In most cases, in addition to consuming sugars in larger proportions and generating diverse products, these contaminants give the yeast a flocculating characteristic, extremely undesirable, because it decreases the performance of the process and causes several operational problems. In addition, in the yeast recycling by conventional centrifugation, the flocculating characteristic is systematically favored, since the larger diameter particles are preferably kept in the process. Currently, it has been demonstrated that flocculation may be due to bacterial contamination or the presence of wild yeast strains with flocculent characteristics. Flocculation, when caused by bacterial contamination, can be reversed through acid treatment and antibiotic application - a corrective measure with financial and environmental costs. On the other hand, when flocculation originates from wild yeasts, it is necessary to replace yeast with one with industrial characteristics of interest - an action difficult to apply during the season. Therefore, the inclusion of a selective centrifugation step in the fermentation process is of great industrial interest since it will allow a preventive control of the contamination by separating the undesirable floculante yeast from the yeast of interest, isolated and non-flocculant. Another advantage of selective centrifugation is that the flocculated fraction can then be subjected to acid treatment and antibiotic application in a smaller volume if the flocculation is due to contamination of bacterial origin, or, eliminated of the process by purging in case the contamination is caused by wild yeast. Therefore, the main objective of this project is to use the virtual prototyping technique, through simulation with computational fluid dynamics and discrete elements method, to the development of the selective centrifugation process, by means of minimum and precise modifications in the internal of the existing centrifuge, so it can separate flocculated yeast fraction from non-flocculated yeast fraction. The technique would also aid the optimization (using DOE) of the operating parameters of the equipment for the new application, which would be validated in a proof of concept to be carried out on a pilot scale with subsequent economic viability analysis and the elaboration of business plan. Selective centrifugation can be inserted into new process configurations at the ethanol production plants, performing a preventive control of contaminants and increasing the overall performance of the conversion of sugars into ethanol. The selective centrifugation will act preventively in the control of contaminations by bacteria and by wild yeasts and can be considered a "physical vaccine" for the process. (AU)