OPTIMIZATION AND ANALYSIS OF FLUIDIZED BED DRYER FOR IMPROVED THERMAL EFFICIENCY IN TEA FACTORIES

Abstract

Drying is a vital process in most agricultural industries to increase finished product shelf life and storage. This thesis focused on optimization of thermal energy consumption in black tea drying process using a fluidized bed dryer (FBD) in tea factories. The research also covered laboratory practical experiment and drying simulation using computational fluid dynamics (CFD). A quantitatively evaluation and examination of laboratory drying was done by means of computational fluid dynamics in ANYS Fluent. Tea drying input variables considered in the study were hot air temperature, velocity and time. Energy utilization (EU), energy utilization ratio (EUR), exergetic efficiency were investigated under the same dryer input parameters to determine the dryer’s performance. The response variables in the experiment were the black tea moisture content and thermal energy utilization. The velocity of hot air was varied between 0.21 m/s and 0.55 m/s while the dryer hot air temperature was varied between 70 °C and 130 °C. The drying time varied between 0 minute to 20 minutes. Box Behnken methodology under response surface design was used to design experimental models. The Resulting fifteen (15) experimental models guided in conducting black tea drying experiments in the macerated tea laboratory at Sotik Tea Company Limited using the miniature fluidized bed dryer Sherwood Tornado model 501. From the experiment results, it took 20 minutes to lower the dhool moisture content from 72 % to 3.5 %. The data obtained from the drying experiment was used to develop black tea drying curve and black tea drying rate. The Box Behnken design under response surface design methodology in Minitab software was used to analyse and optimize the black tea drying variables. The optimum variables were found to be hot air temperature of 100 °C, hot air velocity of 0.38 m/s and drying time of 12.9 minutes. The optimal drying variables above, resulted in a more acceptable moisture content in the final black tea of 3.5 % db which falls between the acceptable black tea moisture content of 3 % to 4 % . From the energy and exergy results, EU and EUR increased with increase of drying air temperature also EU and EUR decreased with increase of drying time. Similarly, exergy utilization decreased with increase in drying time likewise exergy loss increased by increasing drying air temperature.