Hidrodinámica de un secador multietapas de lecho fluidizado continuo con vertederos
Hydrodynamic study of a continuous multistage fluidized bed dryer with downcomers
L.A. Verduzco-Mora, C. Martínez-Vera y M.G. Vizcarra-Mendoza*
Universidad Autónoma Metropolitana - Iztapalapa, Av. San Rafael Atlixco No. 186, C.P. 09340, México D.F., México. *Autor para la correspondencia. E-mail: mgvm@xanum.uam.mx Tel. +52 5558 044648.
]]>Recibido 24 de octubre de 2014
Aceptado May 28, 2015
Resumen
Se caracterizó hidrodinámicamente una columna multietapas de lecho fluidizado continua con vertederos, que se utilizará como secador de partículas de gel de sílice. Experimentalmente, se determinaron, la zona de operación estable (ZOE) y la distribución de tiempos de residencia (DTR) de los sólidos en la columna y se observó que la ZOE disminuye con el aumento en el flujo de sólidos y de aire y que para valores de entre 34 y 45 % del área libre de la reducción cónica empleada en la parte inferior de los vertederos, la velocidad crítica de operación, prácticamente es constante. El análisis de la DTR determinó que el patrón de flujo de los sólidos se ajusta al modelo de tanques en serie y que al aumentar el número de etapas, se tiende al flujo pistón. A partir del diseño factorial 33 y un análisis de superficies de respuesta se generó un modelo estadístico tomando como variable de respuesta la caída de presión total en la columna (ΔPtotal) y como variables independientes, el número de etapas (N), la temperatura de alimentación (T) y la relación altura a diámetro de la columna (L/D). El modelo explica adecuadamente la variabilidad de la caída de presión total.
Palabras clave: hidrodinámica, vertederos, fluidizacion, secador multietapas, distribución de tiempos de residencia.
Abstract
In this work a multistage continuous fluidized bed drier provided with downcomers with a conical reduction at their bottom was characterized hydrodynamically. The solids to be dried were silica gel particles. The stable operation zone (SOZ) and the solid's residence time distribution (RTD) were determined. The SOZ is a function of the solids and air flows and the free area in the conical reduction. The range of values of these variables for which the column operation lies in the SOZ was determined. It was found from the analysis of the RTD of the solids in the column that the solid's flow pattern in it can be represented adequately by the series of perfectly stirred tanks model and that this pattern tends to piston flow as the number of stages increases. A statistical model for the total pressure drop (ΔPtotal) in the multistage dryer was obtained employing the surface response technique and taking as variables the number of stages (N), the ratio of the downcomer length to column diameter (L/D) and the temperature of the air fed to the dryer (T). This model represents adequately the observed variability of the total pressure drop and can be employed as a predictive tool.
]]> Key words: hydrodynamics, downcomers, fluidization, multistage drier, residence time distribution.
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