Table of Contents
(A) Batch Type fluidized bed dryer
(i) Reverse turning bed type: In this FBD, by turning the air dispersion plate (the reverse turning bed) in 90° direction with the control motor, all the dried material can be discharged at once.
(ii) Rotating discharge type: Dried material is discharged by opening the discharge gate equipped at the side of the dryer. Since the perforated plate is used as the air dispersion plate, the air inside the equipment whirls and pushes the dried material out from the discharge gate.
Example: Vertical FBD with granulating option
Characteristics of batch fluidized bed dryer
i) The residence period of the dried material can be controlled which results in uniform drying.
(ii) It is most suitable in case where an accurate control of the residence period is required at the decreasing rate drying zone.
(iii) Small destruction of particle occurs therefore suitable for granular or crystallized material.
(iv) Easy operation can be achieved by an automatic control of material feeding, drying discharging etc.
(v) When multiple stage system is adopted, the exhaust air heat can be used efficiently.
(B) Continuous Type fluidized bed dryer
Residence time in any drying zone is dependent on length of the zone, the frequency and the amplitude of the vibration and use of dams. Heat transfer units such as tube or plate are built inside the equipment. These units supply 60-80 % heat necessary for drying.
Example: Horizontal vibrating conveyor fluid bed dryer
Characteristics of continuous FBD
(i) The materials with relative high moisture content can be dried.
(ii) At and after a second drying chamber piston flowability can be achieved by arranging numbers of the partition plates as per the required residence period.
(iii) The perforated plate at the fixed direction ensures easy discharging.
(iv) It causes small destruction of particles and thus are suitable for drying granules or crystalline materials.
(v) In multiple zone, fluid bed dryers heating and cooling occurs in same unit.
(vi) Each zone has independent control for temperature, dew point and velocity of air.
(vii) By adjusting the weir height for each zone, residence time can vary up to four fold in the unit.