Drying Sawdust in a Pulsed Fluidized Bed

The objective of this work was the experimental and theoretical study of sawdust drying, in batch and continuous experiences, using a pulsed fluidized bed dryer. In the batch experiences, a 23 factorial design was used to determine the kinetics of drying, the critical moisture content, and the effective coefficients of both diffusivity and heat transfer, all of them as a function of the velocity and temperature of the air, the speed of turning of the slotted plate that generates the air pulses in the dryer, using sawdust with 65% moisture in each run. In the continuous operation, a 23 factorial design was used to study the effect of the solid flow and the velocity and temperature of the air on both the product moisture and the distribution of residence times. In order to determine these last ones, digital image processing was used, utilizing sawdust colored by a solution of methylene blue as tracer. The statistically significant factors were the velocity and the temperature of the heating air, for both the continuous and batch operations. Although the speed of turn of the slotted plate was not significant, it was observed that the air pulses increased the movement of particles, facilitating its fluidization, especially at the beginning of drying. The heat transfer coefficients were adjusted according to the equation Nu = 0.0014 Re p 1.52, whose standard deviation of fit is 0.145. The period of decreasing rate was adjusted to several diffusivity models, giving the best fit the simplified variable diffusivity model (SVDM). The curve of distribution of residence times was adjusted using the model of tanks in series, with values between 2.6 and 5 tanks.

[1]  Arun S. Mujumdar,et al.  Advances in drying , 1980 .

[2]  Tadeusz Kudra,et al.  Drying: Principles, Applications and Design , 1987 .

[3]  A. Reyes,et al.  Drying of Turnip Seeds with Microwaves in Fixed and Pulsed Fluidized Beds , 2006 .

[4]  A. Reyes,et al.  ANALYSIS OF MECHANICALLY AGITATED FLUID-PARTICLE CONTACT DRYERS , 2001 .

[5]  Alejandro Reyes,et al.  Drying Characteristics of Forest Biomass Particles of Pinus radiata , 2004 .

[6]  A. D. Martin,et al.  Interpretation of residence time distribution data , 2000 .

[7]  Pedro I. Alvarez,et al.  A SEMI-THEORETICAL MODEL FOR THE DRYING OF THUMPSON SEEDLESS GRAPES , 1986 .

[8]  O. Taranto,et al.  The drying of solids in a modified fluidized bed , 2002 .

[9]  G. Antolín,et al.  Thermal behaviour of forest biomass drying in a mechanically agitated fluidized bed , 2007 .

[10]  Alejandro Reyes,et al.  Drying Suspensions in a Pulsed Fluidized Bed of Inert Particles , 2007 .

[11]  Jules Thibault,et al.  INFLUENCE OF SOLIDS MOISTURE CONTENT ON THE AVERAGE RESIDENCE TIME IN A ROTARY DRYER , 2001 .

[12]  Arun S. Mujumdar,et al.  Drying Technology in Agriculture and Food Sciences , 2000 .

[13]  T. Kudra,et al.  DRYING OF POWDERY MATERIALS IN A PULSED FLUID BED DRYER , 1999 .

[14]  M. Gray,et al.  Pyrolysis of a wood-derived material. Effects of moisture and ash content , 1985 .

[15]  Osvaldir Pereira Taranto,et al.  Drying of beans in a pulsed fluid bed dryer : Drying kinetics, fluid-dynamic study and comparisons with conventional fluidization , 2007 .

[16]  Javier Herguido,et al.  Steam gasification of lignocellulosic residues in a fluidized bed at a small pilot scale. Effect of the type of feedstock , 1992 .

[17]  Z. Gawrzyński,et al.  Drying in a Pulsed-Fluid Bed with Relocated Gas Stream , 1996 .

[18]  J. Westwater,et al.  The Mathematics of Diffusion. , 1957 .

[19]  V. Weekman,et al.  Chemical Reaction Engineering , 1974 .

[20]  Arun S. Mujumdar,et al.  Innovation in Drying , 1996 .

[21]  Jonas Berghel,et al.  DRYING OF SAWDUST IN AN ATMOSPHERIC PRESSURE SPOUTED BED STEAM DRYER , 2002 .

[22]  M. L. Passos,et al.  Spouted Beds of Inert Particles for Drying Suspension , 2006 .

[23]  Javier Bilbao,et al.  Pyrolysis of sawdust in a conical spouted‐bed reactor with a HZSM‐5 catalyst , 2000 .

[24]  A. Reyes,et al.  SLURRY DRYING IN GAS-PARTICLE CONTACTORS: FLUID-DYNAMICS AND CAPACITY ANALYSIS , 1998 .

[25]  M. Mazza,et al.  Characterization of the Residence Time Distribution in Spray Dryers , 2003 .

[26]  José Corella,et al.  Steam gasification of cellulosic wastes in a fluidized bed with downstream vessels. , 1991 .

[27]  A. Mujumdar,et al.  Advanced drying technologies , 2001 .