Effects of spiral and cone angles on drying characteristics and energy consumption of fluidized bed paddy dryer

Abstract

The demand for energy has been increasing all over the world, necessitating the introduction of novel devices to work with lower energy consumption. Modern technologies used for paddy drying are one of such processes which consumes a substantial amount of energy. The present work introduces a device (passive spiral) to be incorporated in fluidized bed dryers which could considerably reduce energy consumption and enhance drying characteristics while providing better nutritional values and quality end product in terms of paddy drying. Two conical fluidized bed with various cone angles (5° and 10°) and a columnar fluidized bed (0° cone angle) are used for the study to investigate the performance of dryers with and without spiral which shows that energy consumptions could be considerably reduced with the incorporation of a spiral inside the conical fluidized dryer and least with 10° cone angle. The pressure drop across the dryers, drying characteristics, the total energy consumptions such as blower and thermal energy consumption, nutritional values and milling quality of drying products are investigated for these three dryers with and without spiral and results are compared. The experiments are performed with two different inlet air velocities (1.1 and 1.6 m/s), and three different inlet air temperatures (55, 60, and 65 °C) with 1–3 kg batch size of paddy as a bed inventory. It is observed that the time taken to reduce the moisture content in conical bubbling fluidized dryer having cone angle 10° is lesser than the other two dryers. The drying rate is also found to be faster with the use of a spiral inside the three dryers than without the spiral. Incorporation of spiral exhibits better drying characteristics in terms of milling quality. Conical fluidized bed dryer having larger cone angle (10°) consumes less energy than the conical fluidized bed dryer having smaller cone angle (5°) and conventional fluidized bed dryer (0°). A total of around 40% less energy of blower and heater was consumed when spiral was used.