Estudo da secagem da polpa de celulose branqueada Study of cellulose pulp drying

Pulp extracted from wood is used as the raw material for the production of various products. Generally, there are two types of trees used for the extraction, those of long and short fiber, that provide different physical characteristics to the final product. Brazil is the largest producer of short fiber pulp in the world, thus being a key sector for the country's economy. A fundamental part of the process and economic viability of pulp and paper production is the drying operation where, after extraction, purification and bleaching, the cellulose is concentrated by removing the solvent until a consistency of approximately 90%. The objective of this work was to investigate the kinetics of the drying phenomenon when applied to short fiber pulp extracted from eucalyptus wood. In order to verify the influence of these in the time and in the drying rate, and others in wind tunnel with drying agent under different conditions-speed and temperature, coherent with which was performed in the greenhouse experiment, with the aim of scrutinizing the process sensitivity to forced convection. The influence of sample thickness and its initial moisture on time and process rate were also evaluated. Subsequently, the data collected were adjusted to the semi-theoretical and empirical models for the drying of the cellulose samples, obtaining the constants of each equation for each situation. One of the constants obtained from the semi-theoretical models is the drying constant k (s-1), which considers all the external factors that influence the transfer of the wet from the solid medium to the drying medium. The coefficients of effective moisture diffusivity were obtained from the theoretical equation, derived from the second Fick law. It was observed the variation of the diffusive coefficient as a function of the drying process time, and its behavior was also evaluated as a function of the temperature and relative velocity of the drying air.