Transporte pneumático horizontal de partículas de baixa densidade: proposta de um sistema de alimentação e estudos de fluidodinâmica

Abstract

The diluted phase pneumatic conveying system offers many advantages for industrial applications, among which stand out the simplicity of operation, maintenance and control. Compared to dense phase conveying, the risk of pipe clogging is reduced when well designed. For this, one should be aware of the properties of the particles, as they significantly affect the performance of the feed system and the pressure drop in the line. In this work, a pneumatic conveying loop was constructed for diluted phase operation in order to study an efficient feeding system for four different particles. The studied materials were divided in two groups: the powders (MDF and sugar cane bagasse fines - BCA) and the grains (malt pilsen and wheat), chosen according to the different classifications in the Geldart diagram. As this is an experimental positive pneumatic conveying unit, the feed takes place after the compressor through a rotary valve. Due to backpressure in the line, materials with low bulk density (MDF and BCA) showed discontinuity during feeding, disrupting the performance of the pneumatic conveying system. Thus, it was tested a feeding system that operated with the closed silo, two vibrators electric motors and a feeding Tee to guarantee a homogenous feeding. The study showed that for the particles of MDF and BCA the air velocity in the line affected the feed rate considerably. A nonlinear empirical correlation was developed, capable of predicting the feeding rate efficiency of the pneumatic conveying system with precision, with a coefficient of determination of 88.73%. Also in the feeding system, an empirical model was proposed to predict the pressure drop in the feed tee, with the correlation coefficient of the model being 98.25%. As a complementary tool to the experimental studies of feeding Tee, numerical simulations in CFD (Computational Fluid Dynamic) were carried out to the prediction of the pressure drop. The model used was the Eulerian Granular Multiphase and the results contributed in the understanding of the dispersion of the particles in the mixing chamber, being possible to evaluate the influence of the geometry of the Tee in the feed rate of solids. Considering the pressure loss an important variable in the design of the pneumatic conveying systems, we also evaluated the models available in the literature to predict the pressure drop in horizontal stretches. According to the particles and experimental conditions studied, the model developed by Yang (1974) is the closest to the experimental results, with mean deviations of 7,13% for MDF and 14,57% for BCA.