Revisão nos métodos de dimensionamento de espessadores e comparação dos modelos industriais

Abstract

The operations of thickening take a place for the necessary recovery of water and for adjustments in the pulp density, aiming at the subsequent operations. Several models of thickening had appeared, throughout time, to minimize the use of noble waters and high cost capitation in favor of the use of one with less operational cost. Some developmentshad occurred throughout history when it comes to the sizing of thickeners, with the creation of a series of tools capable to generate projects with low percentage of errors. Some of the oldest methods, however, still have his place due to simplicity in the collecting of data and in the treatment of the numbers and a great amount of them possess excellent degree of proximity. For a good modeling of a solid-liquid separation equipment, some cares are necessary, like the use of more than one type of sizingmethod as a comparative effect, and the introduction of operational effects that the mathematics of the thickening does not contemplate. In this work, will be reveal the sizing methods differ from each other for equivalent tests of sedimentation and the influence of operational events, such the ascending flow of water, the particle size and the interference of the viscosity of the fluid way, used in batch tests for the calculationof thickening necessary area. Still will be shown a comparison between the three most used methods in practical for the sizing of thickeners and its impreciseness, had the compressibilities of materials. The methods of Coe and Clevenger, Talmage and Fitch and Oltmann produce consistent results, however divergent between itself because hadthe diverse factors there are not considered in the assays. The simplicity of execution of the batch test favors the use of these methods. Viscosity can cause interferences in the sizing, therefore each pulp is different and its behavior is characteristic of its physicistchemistries properties. The ascending water flow can give an important element for solving the problems in the thickening the pulp with lamas, therefore, if the ascending flow to exert a superior force to the terminal speed of particles, the material will float, being make the process water becomes unusable. As a second goal, this work has the intension to show how particles of bigger size help in the sedimentation of ultra-fines materials.