Study on bedplate configuration for fluidizing orthodox broken type tea

Abstract

Orthodox broken type tea produced in Sri Lanka is popular for its distinct characteristics. Fluid bed dryers which are widely used in manufacturing of tea has been changed over the years and consequently, drying the tea with required fluidizing condition with co-existence of continuous phase and bubble phase in the conventional fluid bed dryers became difficult. In this study, fluidization behavior of Orthodox broken type tea was examined in a pilot-scale fluid bed dryer. Six different bedplate configurations were evaluated against the conventional bedplate. Bedplate of 36 mm × 0.6 mm with 5 % opening area facilitated a stable fluidized tea-bed with coexistence of continuous phase and bubble phase without stagnation and entrainment. Higher loadings of 44.5 – 50.5 kg/m2 than the conventional loading of 38.5 kg/m2 was achieved. Mean particle size was found to reduce from 1801 to 462 μm and particle density increased from 1336 to 1600 kg/m3 during drying. Minimum fluidization velocity was varied between 0.74 and 1.0 m/s and an empirical model relating the moisture ratio to the tea-bed temperature was proposed and validated for fluidized bed drying of dhool using air at 124 ± 1 °C and for loadings in the range of 44.5 – 50.5 kg/m2.