ENGINEERING STUDY ON THE DRYING OF WOOD PARTICLES IN A FLUIDIZED BED (HEAT TRANSFER, MINIMUM FLUIDIZATION VELOCITY, EFFICIENCY)

Fluidized bed dryers are commonly employed for the industrial drying of granular materials. In the forest products industry there exists a potential to dry particulate wood in fluidized beds. This study investigated the engineering parameters necessary to design an industrial fluidized bed dryer and compared various fluidized bed drying arrangements to commercial rotary dryers in terms of energy efficiency.; A 0.2 m square bed was constructed to fluidize processed wood particles and sawdust. The minimum fluidization velocities (u(,mf)), voidages, and elutriation constants were determined for a bed at room temperature. Emulsion-to-surface heat transfer coefficients were determined with a copper tube in both a cold and hot bed. Batch and batch simulated continuous (BSC) drying trials were done with inlet temperatures ranging from 127 to 290(DEGREES)C. BSC drying was done to collect data for designing a continuous dryer.; For the unscreened material (dust to 7 mm), u(,mf) was 0.66 m/s for the sawdust and 1.03 m/s for the processed particles. These values increased with increasing moisture content, decreasing sphericity, and increasing particle diameter. An operating range of 1.3 to 2.0 times u(,mf) was found to give acceptable fluidization without excessive entrainment. Some channeling and agglomeration occurred at average bed moisture contents greater than 80 percent (dry weight basis). Surface-to-emulsion heat transfer coefficients of 80 to 130 W/m('2)K were low for a fluidized system when compared to other materials.; Drying curves were presented for batch and BSC drying and a method was presented for adjusting these curves to account for the bed temperature, gas flow rate, and bed weight. Using this method, an isothermal inlet drying curve can be used to either obtain an isothermal bed drying curve or adjust drying curves to predict the performance of an industrial design.; Single and two stage fluidized bed drying arrangements were compared to two commercial rotary dryers. The fluidized bed designs are competitive in terms of energy efficiency. The information presented in this study indicates that wood particles can be fluidized to make this type of dryer practical.