A Study on fluidization behaviour of orthodox-rotorvane teas

Abstract

Orthodox-Rotor-vane teas dried in liquidized bed driers in tea factories at present have, on average, smaller size particles than that of teas produced a decade ago. Further particles are distributed over a wide size range. As a result, achieving desired fluidization was found to be difficult in the drier and that affected quality of the product. Therefore, a detailed study was conducted to understand the fluidizing behaviour of tea particles. Fluidization behaviour of drier-mouth teas from a commonly used drier called TRICCC FBD was studied using six different bedplates having varying opening area percentages and number of perforations. The study was conducted using a pilot scale fluidized bed unit. Desired bubbling phase in tea-bed was observed with three different bedplates: bedplate with perforations of 0.5 mm wide, opening area percentage of 4 and 2,217 perforations per square meter, bedplate with perforations of 0.5 mm wide, opening area percentage of 5 and 2,779 perforations per square meter and bedplate with perforations of 0.6 mm wide, opening area percentage of 5 and 2,269 perforations per square meter. These bedplates could be used in the drier to dry and improve the quality of the teas produced at present. A statistical analysis conducted on the data of bed pressure drop with varying loading rates of teas indicates that desired bubbling phase in tea-bed is achievable using these bedplates. This was confirmed bystudying change in bed pressure drop and fluidization velocity when airflow for fluidization of teas varied. The bedplate with perforations of 0.5 mm wide, opening area percentage of 4 and 2,217 perforations per square meter was found to be most suitable for the drier as desired bubbling phase in tea-bed could be achieved at lowest fluidization velocity for a wide range of loading rates, 21 - 29 kg/ m2. Low fluidization velocity may lead to a reduction in energy consumption for drying the teas in the drier.

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