Análise do efeito das condições operacionais e características geométricas do leito de jorro na secagem de pastas

Abstract

In this present work, the fluidynamic and drying process of paste in a spouted bed was analyzed. The experiments were conducted using polyethylene particles of 4.38 mm of diameter and 930.5 ± 0.3 kg/m3 of specific mass as inert particles, different loads of inert particles (1.50, 3.00 and 4.50 kg) and a fixed static bed height (23.50 cm). The spouted bed consisted of a cylindrical vessel, with 120 cm of height, 30 cm of diameter, 3 cm of inlet diameter, three lower cone angles (45, 60 and 75º) and two geometric factors of inlet nozzle (Venture and straight pipe). Distilled water and skimmed milk were employed as pastes. Bed pressure, inlet air temperature and velocity, exhaust temperature and dry and wet bulb temperature were measured during the experiments. Results have shown that the bed geometry had influence on the bed fluidynamic and drying process. With respect to fluidynamics, it was found that for fixed particles loads, increasing the cone angle from 45º to 75º decreased the minimum spouting velocity and the pressure drop. However, for a fixed cone angle, increasing the particles loads increased the fluidynamics parameters. The correlations used to predict the values of umj, ΔPmáx and ΔPmj showed a limitation on their application with the operating conditions studied. As regards the drying of skimmed milk, the results showed that the drying process is favored by the cone angles 45º and 75º. This was attributed to the high number of particles collisions and agitation inside the drying chamber , by the bed configurations. Finally, it was found that the Venturi nozzle provided a greater bed stability during drying of skimmed milk over the nozzle type straight pipe.