Energetic and exergetic analyses of Barnyard millet drying　using continuous multistage fluidized bed dryer

摘要

Most of the exergy studies reported were in batch fluidized bed drying process. The continuous dryer plays a pivotal role in industrial usage. In this study, exergy and energy analyses of multistage fluidized bed drying of Barnyard millet with stages connected externally were examined. The dryer was operated by changing wall temperature of stages (313-328 K), air inlet velocity (1.01-1.3 m/s), downcomer height (50-70 mm), and flow rate of solids (5-10 kg/h). Drying characteristics of Barnyard millet by changing process operating conditions of the dryer, were reported and the energy utilization ratio, exergy loss and exergy efficiency of dryer were also reported. The EUR of dryer at steady state has been found to be in the range of 0.25-0.46 and the maximum exergy efficiency of dryer was observed as 0.64 and lowest as 0.371 in the continuous drying process. Practical Applications Fluidized beds offer many distinct features and advantages for processing of particulate food materials. To decrease the drying time than that for single stage dryers, continuous multistage fluidized bed dryer was introduced. Reducing moisture content from feed materials in continuous dryers while discharging continuously, helps to process large quantity of solid materials with good quality of product. Several dryers with different modifications and designs have been suggested by many earlier investigators but continuous dryers play significant role in particulate industry. The multistage dryer is designed by connecting two or more fluidized beds internally or externally, where each bed is termed as a stage. Advantages of the multistage dryer are improvement in gas-solid axial mixing, which results in good quality of product. Due to stage-wise contact of solids with gas, dried product with uniform moisture content can be obtained.