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.
