Avaliação de diferentes condições geométricas e operacionais de precipitadores eletrostáticos na coleta de nanopartículas

Abstract

The development and optimization of equipment aimed at removing nanoparticles from atmospheric air have been gaining importance in the current scenario. The adverse effects of these ultrafine particles on human health and the environment motivate the development of techniques for their removal, both for the processes’ sustainability and the mitigation of pollutants. Among the commonly used equipment, electrostatic precipitators stand out for their versatility and, for certain configurations, efficiencies are up to 99.9% in a wide size range. The recent literature has employed wet precipitators with good performance. However, the formation of a new liquid effluent and the difficulty of recovering particles with added value encourages the search for other alternatives. With this, dry operation stands out for the correction of these problems and the lower operating costs. Thus, the present work aims to evaluate the influence of the electric field, velocity, and the following geometric parameters: plate spacing (4 and 6.5 cm) and wire spacing (4, 6, and 12 cm). For this, a scan will be performed between the electric fields of 0.0 kV/cm and 5.0 kV/cm for different air velocities (1.9, 2.9, and 3.9 cm/s). Two electrostatic precipitators with different plate spacing were used, both with single stage wire-plate type, with two collecting plates with length and height of 30 and 10 cm, respectively, with three discharge electrodes with a diameter of 0.4 mm. The results showed the efficiency of the precipitator in removing nanoparticles, with efficiencies above 99.9% for electric fields of 5.0 kV/cm in both precipitators. The increase in velocity did not present a well-defined behavior, with increased efficiency by increasing the velocity in some conditions. In general, the use of 4 cm wire spacing showed a decrease in the efficiency of nanoparticle collection with the reduction of residence time. In the scanning of the electric field to verify the influence of plate spacing, greater variations in the collection efficiency occurred between the fields of 3.1 and 3.4 kV/cm for the precipitator with spacing between plates of 6.5 cm, and between fields of 4.0 and 4.5 kV/cm for the precipitator with a spacing of 4 cm. For the same electric field, the precipitator with a plate spacing of 6.5 cm presented better collection capacity. Efficiencies above 99% were obtained with electric fields above 3.4 kV/cm and 4.5 kV/cm for spacings between 6.5 cm and 4 cm, respectively. It should be noted that higher efficiencies are obtained with a lower voltage applied in the precipitator with less plate spacing. Therefore, even though the precipitator with the spacing of 6.5 cm presented better efficiencies based on the electric field, the energy cost is higher due to the higher voltage applied. In the evaluation of the wire spacing, the increase in the values of this parameter provided greater current and, in general, better collection efficiencies. However, few significant differences were obtained by increasing the electric field, with removals of 99.9% for all spacings at 5.0 kV/cm. The overall efficiency curves by the electric field showed sigmoid behavior, with a higher rate of efficiency increase near the beginning of the corona. By statistical analysis, it was possible to verify the significant effect of plate spacing and wire spacing. Also, statistically, the plate spacing and electric field are more influential than the velocity and wire spacing.