Estudo da influência das variáveis de hidrociclonagem e de secagem por Spray Dryer em propriedades de bentonita da Paraíba

Abstract

The state of Paraiba is one of the largest producers of bentonite, which is intended to various technological uses, among which, as thixotropic agent of oil well drilling fluids. However, these are sensitive to the presence of contaminants, give origin to fluids that do not meet Petrobras' specification EP-1EP-00011-A. Thus, the separation of coarser fractions of finer fractions by a hydrocyclone enables obtaining a material with improved rheological behavior, which can also be favored by the time and stirring speed of the samples, since these parameters influence the dispersion, delamination and clay hydration process. So, the first stage of this study proposes evaluate, using a factorial design 23 plus three central points, the influence of parameters stirring speed, stirring time and hydrocycloning pressure in the percentage of the accumulated mass with average diameter below 2 μm and the rheological properties of dispersions prepared with clay Verde-Lodo extracted from Juá II mine, Boa Vista, PB, aiming to optimize these properties and enhance the technological use of this clay in aqueous fluids of oil well drilling. After this stage, it chose the best combination of factors to proceed with the second stage of the study, which consists of a factorial design 23 plus three central points to evaluate the influence of the factors compressed air pressure, blower flow and drying temperature by spray dryer in the percentage of the accumulated mass with average diameter below 2 μm and the rheological properties of dispersions. For the response variables of the hydrocyclone and drying operations, variance analysis and Tukey Test were performed, aiming to verify in which cases occur differences between the means of the levels of each factor. From the hydrocyclone operation, it was observed that it was not possible to determine values for rheological properties from the mathematical models proposed at the 90.0% confidence level. Thus, these properties were analyzed point by point, observing that the best experimental combination of the input variables is with disperser stirring speed of 2000rpm for 24h and hydrocyclone pressure of 2.5bar. Thus, this combination was chosen to proceed to the study of the variation of drying parameters by spray dryer. From this, it is observed that the experimental data do not fit the proposed mathematical models for the response variables at the 90.0% confidence level. Therefore, these responses were analyzed point by point, observing that the best value for the rheological properties of the dispersions of the clay minerals concentrates resulted when drying with compressed air pressure of 4.0bar, blower flow of 2.5m3/min and drying temperature of 50°C, since it is the best combination for the apparent and plastic viscosities, which have been in accordance with the regulatory requirements, and provides reasonable value for filtrate volume.