Análise fluidodinâmica e de estabilidade térmica de leito fluidizado de sílica

Abstract

Fluidized beds are known for their wide application and efficiency, however some fluid dynamic phenomena applying binary solid phase beds are not yet well characterized in the sense of a compatibility between theoretical analysis and operating bed behavior. In addition, the fluidized bed in thermal combustion systems such as burners and / or boilers does not have well-known temperature distribution profiles depending on operating conditions. In this sense, the present work analyzes fluidodynamic aspects of the prototype of a bubbling fluidized bed combustion reactor designed for biogas / sludge hybrid combustion and sterilization of contaminated sand from a Wastewater Treatment Plant (WWTP). For better understanding of the fluidization, preliminary fluid bench tests were performed with acrylic tubes. The proper working range for gas flow was studied from the pressure drop curves varying the L / D ratio of the static bed. Dimensions with a ratio lower than 2 were not prone to sand piston formation. Increasing the height of the static bed has been observed to increase the value of the minimum fluidization velocity and reduce the velocity where the "empistonamento" occurs, thus, for beds with an L / D ratio greater than 2, the working range is reduced. . To estimate the expansion and disintegration height of the bed particles in the reactor, correlations proposed in the literature were used to determine the equivalent bubble diameter and the bed bubble fraction. The results obtained were compared with the experimental data and considering that the correlations presented low errors (coefficient of adjustment R² equal to 0.9998 with L / D ratio equal to 5.28), they were applied to estimate the expansion and the disintegration height. of lithium particles in the reactor prototype at room temperature. For thermal evaluation of heat loss, boiler operating data at constant temperature were used. The results showed the increase of the firing fraction between 56.5% to 82% for surface velocities between 1.25 and 1.35Umf, respectively, pointing that the burning is favored with the bed movement. By varying the gas velocity from 1.18Umf to 1.64Umf and the equivalence ratio between 0.45 and 1.42, the extraction efficiency was maintained around 85%.