The Endless Chain Pressure (ECP) driers consist of two or three individual tray circuits. When the leaf is fed into the feeding circuit, the spreader spreads the leaf uniformly on the tray. As soon as the leaf completes the run on the top circuit, the tray carrying the leaf are automatically tilted at the end of the circuit and the leaf falls on the mid circuit where the direction of tray movement is opposite that of the top circuit. Thus, the leaf is subjected to gradual high temperature from top to bottom circuit and drying is completed when the leaf reaches the bottom circuit. The total drying time is 20-22 minutes. The output of the drier is 200-250 kg made tea with feeding moisture level of 55%. The inlet and exhaust temperature may be maintained at 1000C and 550C, respectively.
Fluid Bed Drier
A fluid bed drier consists of drying chamber, plenum chamber, air flow damper and dust collector. The drying chamber is separated by perforated grid plate through which high pressure hot air from the plenum chamber gets into the drying chamber for fluidization. The plenum chamber is divided into four zones which have individual air control valves. These valves control the quantity of air to the individual zone and the direction of hot air entering the control dampers. At the top of the drying chamber, two centrifugal exhaust fans are fitted with cyclone, one for refiring and the other for dust extraction. When the fermented leaves are fed into the drying chamber in the first zone they get fluidised. With the help of pressurised hot air, water is removed by evaporation. The inlet and exhaust temperature in FBD may be maintained at 2500F to 2600F and 150-1600F respectively for achieving better quality.
Vibro Fluid Bed Drier
This type of tea drier works on the principle of ‘vibrating fluidised bed’. It works on pneumatic and mechanical power. The fermented leaves are fed through a feed system into the drying chamber. Hot air from the heater is passed from underneath to the drying chamber through the perforated tray carrying wet leaves. The tea leaves are effectively fluidised by a combination of air pressure and mechanical vibration.
Tempest drier is a combination of conventional and fluid bed drier. In the tempest drier on the top of the drying chamber i.e., above the fluidisation zone there is a tray moving inside which carries the fermented leaf from the drum where surface moisture is removed by exhaust temperature. Since certain percentage of moisture is removed from the leaf before entering into the fluidisation zone, the out put of the drier is higher than conventional FBD.