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Drying Tea in a Kilburn Vibro Fluid Bed Dryer

M. Akhtaruzzaman
Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

M. R. Ali
Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

M. M. Rahman
Department of Food Engineering & Tea Technology, Shahjalal University of Science & Technology, Sylhet, Bangladesh

M. S. Ahamed
Department of Farm Power and Machinery, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Abstract/ Executive Summary:

The fluidized bed drying principles for drying of tea in Bangladesh is thoroughly studied. The experiments were conducted to determine the drying curve, drying time, drying constant and dynamic equilibrium moisture contents of tea at the Bangladesh Tea Research Institute. Drying of tea in a fluidized bed dryer (Kilburn Vibro Fluid Bed Dryer) takes only 20 min for drying from an initial moisture content of 69.1% to a final moisture content of 2.8%. Temperatures of drying air were recorded to be 130°C at the inlet and 90°C at the outlet. The drying constant was found to be 31.05 h^-1 and the dynamic equilibrium moisture contents were in the range of 18.3 to 2.0%. Finally the principle of fluidized bed drying was compared with the principle of conventional endless chain pressure type drying.

Keywords: Tea, Moisture content, Drying, Fluidized bed dryer, Drying rate constant

Location: Bangladesh Tea Research Institute (BTRI),Srimangal , Moulavibazar

Start Date:

End Date:

Program Area: Postharvest and Agro-processing

Commodity: Tea

Objectives:

i) To obtain primary knowledge on fluidized bed drying of tea

ii) To determine drying curve, drying rate and drying rate constant of tea on fluidized bed dryer

iii) To determine dynamic equilibrium moisture contents of tea.

Methodology:

The experimental study of fluidized bed drying of tea was conducted at Bangladesh Tea Research Institute (BTRI) located at Srimangal under the district of Moulavibazar, the tea growing area at the North- Eastern part of Bangladesh. A fluidized bed dryer (Kilburn Vibro Fluid Bed Dryer -KVD-A-1333) of BTRI was used for the experiment.It consisted of a heater system, a centrifugal type hot air blower, outlet hot air duct, a feed system, drive and excitation system, plenum chamber, drying chamber, exhaust and de-dusting systems and a cyclone system. The feed system enabled to regulate the feed of fermented leaf to the dryer and breaking up of lumps in the leaf. The plenum chamber consisted of galvanized steel and fully insulated chamber with the provision of two-temperature drying, where the first portion supplied hot air between 100-140^°C while the second portion supplied cold air between 90-120°C. Drying of tea took place in one pass across the closed drying chamber comprising of two perforated stainless steel plates, longitudinal plates, discharge weir plate, and discharge hopper. The duplex cyclone system is capable to separate tea dust and fibers from air before exhaust. The recommended operating temperatures of the dryer were as: Inlet1 T₁ 130-140^oC Refers to inlet air in zone I, Inlet 2 T₂ 100-108^oC Refers to inlet air in zone II, Exhaust 1 T₃ 43-47^oC Refers to feed rate and Exhaust 2 T₄ 85-90^oC Refers to moisture of made tea. Moisture content of tea was determined by infrared lamp method and expressed in dry basis. Samples were collected manually from 0, 0.61, 1.22, 1.83, 2.44, 3.05, 3.66, 4.27, and 4.88 m distances of the dryer bed. Measurements were replicated four times and the average value was taken as the test data. The retention time was 20 min as the tea passes through 4.88 m bed. It was assumed that tea flows over the dryer bed and feeding rate was uniform. So it is required 2.5 min to pass a distance of 0.6 m along the bed of the dryer. The dry bulb and wet bulb temperatures were also determined by a laboratory psychrometer.

Source of Information: J. Bangladesh Agril. Univ. 11(1): 153–158, 2013 ISSN 1810-3030

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Drying of tea in a fluidized bed dryer (Kilburn Vibro Fluid Bed Dryer) takes only 20 min for drying from an initial moisture content of 69.1% to a final moisture content of 2.8%. Temperatures of drying air were recorded to be 130°C at the inlet and 90°C at the outlet. The drying constant was found to be 31.05 h-1 and the dynamic equilibrium moisture contents were in the range of 18.3 to 2.0%. Finally the principle of fluidized bed drying was compared with the principle of conventional endless chain pressure type drying.

Knowledge Management: Journal