Análise do desempenho do leito vibrofluidizado na secagem de pasta

Abstract

The agitation promoted by the vibrofluidized bed allows the incorporation of several unitary operations such as granulation, coating of particle, drying of grains, and the drying of pasty materials. However, it is necessary more studies about the drying of paste in this equipment, since according to the work of Daleffe (2005) and Meili (2009) it was verified that a same dimensionless vibration number (Γ) presented different dynamics behaviors and influenced in distinct ways in the process. To understand more about the interference that the vibrational parameters may exert in this type of operation, that the goal of this present work was to develop a more detailed study on the drying of skimmed milk in vibrofluidized bed, varying the intensities of agitation imposed to the bed, two Amplitude (A) from 0.003m and 0.015m combined at frequencies (f) ranging from 100 to 1100 RPM. Thus, firstly, it was analyzed the influence that the vibrational parameters exercised on the characteristic curves of the pressure drop and the standard deviation of pressure drop in function of the superficial velocity of the fluid (Us), when the bed was constituted with glass beads with the diameters of 0.00119m, 0.00219m, and 0.00319m. Thereafter, water evaporation tests were performed to determine the size of the inert material and the experimental conditions that would be used in the paste drying trials. For the drying of the skimmed milk has been used glass beads with 0.00319m of average diameter, air temperature of 100 ° C, surface velocity of 20% higher than minimum fluidization velocity (Umf), different agitation intensities and different paste feed rates. During the experiments, the influence of agitation on the dimensionless pressure drop, air temperature at the bed outlet, relative air humidity at the bed outlet, powder moisture content, powder production rates and powder accumulation rates were analyzed. Analyzing the obtained results, it may be verified in the two amplitudes that the increase of the agitation intensity, through the increase of the frequency, allowed the use of higher maximum feeds rates of skimmed milk in the equipment. It was also observed, for the values of Γ almost constant with different combinations of A and f, that the agitation with amplitude of 0.015m resulted in the greatest variations of pressure drop during the process, in the lower relative humidity levels, in the higher powder production rate and higher powder accumulation rates at the exit of the cyclone. In this way emphasizing the importance to inform A and f to characterize the implemented vibration in the vibrofuidized bed. From these experimental data was designed a hybrid CST / Neural to describe the heat and mass transfer phenomena that occurred during the drying of skim milk. The results showed that the proposed model presented a great agreement with the experimental data, assuming that the vibrofluidized bed behaved as a perfectly stirred tank.