Acúmulo, elutriação e recuperação do produto na secagem de pasta em leito de jorro

Abstract

One of the equipment that has been highlighting mainly in the drying of pastes and solutions is the spouted bed. In this type of equipment some factors that can make it impossible to use are operational problems caused by the process of agglomeration and accumulation of material inside the bed. In this way, the main objective of this work was to quantify the percentage of mass accumulated in the bed (Ac), recovered in the cyclone (R) and elutriated to the filter (E). As a secondary objective, we investigated the effect of the addition of the filter on the drop in pressure in the bed and identified how the powder granulometry modifies as a function of the process operating conditions. In order to reach the proposed objectives, drying experiments were carried out in a conventional spouted bed, and the paste feed was made with calcium carbonate suspension (5%).Changing the operating conditions of the paste feed flow (10, 20 or 30 mL.min-1) and air temperature (80, 90 or 100ºC), data were collected to perform a global mass balance in the drying. Initial results showed that the use of the filter in the drying system did not lead to significant changes in the characteristic curve of the spouted bed, but caused an increase in the initial and in the course of the process. For paste drying it was evident that the increase in paste feed flow resulted in increased bed instability, with the maximum capacity reached 30 mL.min-1, being able to operate at 90 and 100ºC. But it was surpassed to 80ºC due to the low recovery of product in the cyclone, high humidity of the product and great variation in the obtained data. The accumulated material was around 23 to 34% and the elutriate presented values between 2 to 8%, while the recovered product was 11 to 53%. The proposed experimental design (FCC) showed that both the incoming air temperature and the paste feed flow directly influenced the process, but only for the accumulation was the temperature significant. The results showed that the increase in paste feed flow has a negative effect on R (%) and E (%), while the increase in temperature had a positive effect. The grain size of the powder was strongly influenced by the paste flow, increasing the particle size with the increase of the paste feed flow, covering sizes throughout the analyzed range (0.05 to 550 μm). As expected, larger particles were accumulated in the bed, the intermediate recovered in the cyclone and the smaller ones retained in the filter. With the results of this work it was possible to have a better understanding of the drying in the spouted bed, both for the efficiency and losses of the process, and for the granulometry of the product that changes with the agglomeration process.