Drying sago pith waste in a fluidized bed dryer

Abstract

Sago pith waste produced in largely during the manufacturing process of sago flour and causes serious environmental pollution. Once SPW is dried, it can be stored and further exploited for its high starch content. SPW has an original moisture content of 90% wet basis but can be dried to 10% wet basis. This study evaluated the effects of the bulk and tapped densities on the moisture content of SPW and used the compressibility index and Hausner ratio to characterize the flow of SPW in a fluidized bed dryer at wet basis. The temperature (50–80 °C) and velocity (1.5–2.1 m/s) of the air supplied into the fluidized bed dryer were considered in terms of the loss of moisture content, drying rate, and fluidization profile of the drying process. The effective moisture diffusivity were estimated to determine the optimum drying condition. The experimental results showed that the drying process took less time and reached a higher drying rate as the air temperature and velocity increased. Increasing the air temperature increased the heat transfer between SPW and dry air and accelerated the movement of moisture to the surface. The air velocity had a less significant effect on the drying process and was more important for fluidization of the SPW. The profile showed a fixed bed during early fluidization, followed by a bubbling state and then turbulent condition. Increasing the air temperature reduced the time for SPW to reach turbulent situation. Increasing the air velocity increased the bubbling fluidization density and accelerated the turbulent fluidization. Based on the effective moisture diffusivity analysis, it showed that the optimum drying process of SPW could be achieved at air velocity of 1.50 m/s with 80 °C of air temperature and at air temperature of 70 °C with 2.10 m/s of air velocity. Meanwhile, dry sieve analysis was performed to obtain the particle size distribution and percentage of fines in SPW with the sieve sizes of 3.35, 2.00, 1.70, 1.00, 0.85, 0.60, and 0.43 mm. Then, SPW was classified and characterized according to each particle size range. Visually, SPW was found to have three categories of particles: sand, gravel, and fibrous wood.