Simulation of a Fluidized Bed Dryer for the Drying of Sago Waste

Abstract

The large amount of sago waste produced by sago processing industries can cause serious environmental problems. When dried, these residues usually have a high starch content (around 58%) and have many potential applications. In this study, the drying of sago waste using a fluidized bed dryer (FBD), which offers more advantages than other drying methods, is analyzed via computational fluid dynamics (CFD) modeling. A two-dimensional (2D) FBD model is also developed and a mesh independency test is conducted immediately afterwards. A fine mesh is selected for the CFD model and a simulation is conducted using ANSYS Fluent 17.1 software (Ansys Inc., version 17.1, Canonsburg, PA, USA). The governing and discretized algebraic equations are solved by applying the phase-coupled semi-implicit method for pressure-linked equations. Both the Eulerian–Eulerian multiphase model approach and the turbulence model are applied in the simulation due to the turbulent flow in the dryer. A velocity of 1.30 m/s and temperature of 50 °C are selected as boundary conditions based on the optimum parameter values from previous experiments. The final moisture content that we aim to achieve is 10% or a moisture ratio of 0.25 in sago waste for the purpose of animal feed, so as to prevent bacterial growth and for packaging purposes based on common industrial practice. Both the drying rate and fluidization profile are examined at air velocities of 0.6, 1.0, 1.3, 1.8, and 2.2 m/s. Based on the results, the velocity range of 1.0 m/s to 2.2 m/s is deemed suitable for the fluidization and drying of sago waste with a particle size of 2000 μm for a drying simulation of 1 h. The drying rate is further examined at air temperatures of 50 °C, 60 °C, 70 °C, and 80 °C, whereas the fluidization profile is examined at particle sizes of 200, 500, 1000, and 2000 μm. The results reveal excellent fluidization at a particle size range of 500 μm to 2000 μm and a velocity of 1.3 m/s.

Keywords

• fluidized bed dryer
• sago waste
• computational fluid dynamic
• multiphase model
• fluidization