SHMT, Chemical Engineering

2. Topic
FLUIDIZED BED DRYER
Group Members
Awais Hafiz (034)
Hafiz Luqman (032)

3. What is Drying?
Drying is a unit operation in which a liquid is
separated from a solid by other than
mechanical means.
This generally requires supplying heat and
resulting in evaporation of liquid.
Drying Principle
Migration of moisture from the interior of a
material to its surface
Evaporation of moisture from surface to the
surrounding air
Basic Mechanism

4. DryerFeed Dry Solid
Heat
Moisture
Drying Process

5. Purpose of Solid Drying
 Increasing shelf life
 Enhancing calorific value of fuel
 Reduction of transportation cost
 To improve or keep good properties of
materials like flow ability, compressibility
 To make the material easy and more suitable
for handling
 Preservation

6. Feed Stock for Drying Process
 Wet Solids
 Slurry
 Solution
 Suspension

7. Types of Dryers on the basis of
Heating Mode
 Convective/Direct Dryers
 Conductive/Indirect Dryers
 Dryers by Radiant Energy

8.  Continuous Dryers
•Continuous-Tray Dryers, Continuous
Sheeting Dryers, Pneumatic Conveying
Dryers, Rotary Dryers, Spray Dryers,
Through - Circulation Dryers, Tunnel
Dryers, Fluid Bed Dryers
 Batch Dryers
•Batch - Through Circulation Dryers,
Tray and Compartment Dryers, Fluid
Batch Dryers
 Continuous Dryers
•Cylinder Dryers, Drum Dryers,
Screw-Conveyor Dryers, Steam-
Tube Rotary Dryers, Vibrating - Tray
Dryers
 Batch Dryers
•Agitated Pan Dryers, Freeze
Dryers, Vacuum Rotary Dryers,
Vacuum Tray Dryers
Direct Contact Indirect Contact

9. Types of Dryers on the basis of feed
 Tray Dryer
 Screen-Conveyor Dryer
 Fluid Bed Dryer
 Rotary Dryer
 Tower Dryer
 Screw-Conveyor Dryer
 Flash Dryer
 Spray Dryer
 Thin Film Dryer
 Drum Dryer
Dryers for Solids Dryers for Liquids/slurries

10. Selection of Drying Equipment
It depends upon;
 Physical/Chemical properties of materials
 Production capacity (Kg/hr)
 Initial moisture content & final moisture
content required
 Particle size distribution
 Temperature & drying characteristics
 Explosion & Texicological characteristics

11. General Consideration for
Selection of Dryer
 Dryer must operate reliably, safely &
economically
 Operating & maintenance must not be
excessive
 Pollution must be controlled
 Energy consumption must be minimized

12. Koncept Learning Center
klcenter@gmail.com
Industrial Dryers

13. Fluidized Bed Dryer
13

14. What is Fluidization?
 Fluidization (or fluidization) is a process similar to liquefaction
whereby a granular material is converted from a static solid-
like state to a dynamic fluid-like state. This process occurs
when a fluid (liquid or gas) is passed up through the granular
material.
 Different types of fluidized beds are formed depending upon
the velocity of fluid.

15. Status of approach fluid velocity
(V 0 )
Type of bed formed
V 0 < V mf Fixed Bed
V mf ≥ Vo < U t Fluidized Bed
V 0 ≥ U t Mobilized Bed
Where
Vo is approach velocity or superficial velocity,
Vmf is the minimized fluidized velocity,
Ut is particle terminal velocity.

16. Different Fluidized Bed Formation

17. Fluidized Bed Dryer
1)INTRODUCTION
 Fluid bed drying is most widely used technique for drying pharmaceutical powders
and granulation.
 The direct contact between particles and air/gas is possible in fluid bed system.
 Here any type of inert gas or air is used.
 They can be designed in either batch or continuous type fluid bed dryer.
2)PRINCIPLE
 In fluidized bed dryer, hot air is passed at high pressure through a perforated bottom
of the container containing granules to be dried.
 The granules are lifted from the bottom and suspended in the stream of air.
 This condition is called fluidized state.

18. PARAMETERS TO BE CONTROLLED
IN FLUIDIZED BED SYSTEMS
1) Apparatus Parameters
1) Air distribution plate Position influences the
airflow pattern inside the body.
2) Shape of instrument body Annular base gives better
product and fluidization
3) Nozzle height in case of coater and granulator. It
plays vital role as in coating, the atomized coating
solution should not get dried before reaching the tablet
surface.
4) Positive and negative pressure operation.

19. 2)Process Parameters
The following inlet air parameters are critical
i) Temperature
 As the inlet air temperature increases the rate of drying increases and
vice versa.
 This approach to increase the rate of drying can not be used always
because some materials are harmed by high temperature, e.g.
Ibuprofen liquefies above 60°C temperature of inlet air should be
optimized without any impact on product quality.
 If temperature is high, it leads to blistering. If temperature is low, soft
spot can be formed.
ii) Humidity
 Humidity in the inlet air should be as low as possible and ideally
dehumidified air should be used for faster drying rate because as the
humidity of inlet air decreases the rate of drying increases.

20. iii) Air Flow Rate
 Air flow rate should be controlled properly in order
to get efficient use of drying air. Air flow rate
should not be too fast or too slow but optimized to
have efficient drying.
3) Product Parameters:
 Initial moisture content of material.
It should not be high otherwise it increases
drying time.
 Batch size.
It should be small and optimized based on
feasibility.

21. CONSTRUCTION
The construction of a vertical fluidized bed dryer
 The dryer is made of stainless steel or plastic.
 A detachable bowl is placed at the bottom of the dryer,
which is used for charging and discharging.
 The bowl has a perforated bottom with a wire mesh support
for placing materials to be dried.
 A fan is mounted in the upper part for circulating hot air.
 Fresh air inlet, pre-filter and heat exchanger are connected
serially to heat the air to the required temperatures.
 The temperature of hot air and exit are monitored.
 Bag filters are placed above the drying bowl for recovery
of fines.

23. WORKING
 When the velocity of the air is greater than the settling
velocity of granules, the granules remain partially
suspended in the gas stream.
 After some time, a point of pressure is reached at which
frictional drag in the particles is equal to the force of
gravity.
 The granules rise in the container because of high
velocity gas and fell back in a random boiling motion.
 This condition is said to be fluidized state.
 Drying is achieved at constant rate and falling rate
period is very short.

24. Solids Drying
T, Time
dw/dT
Drying
Rate A
B C
D
AB - Warming up period
BC - Constant Rate Period
‘C’ - Critical Moisture Content
CD - Falling Rate Period

25. ADVANTAGES
 It requires less time to complete drying i.e., 20 to 40
minutes compared
 To 24 hrs of tray dryer. Handling time is also short. It is 15
times faster than tray dryer.
 Hot spots are not observed in the dryer, because of its
excellent mixing and drying capacities.
 It facilitates the drying of thermo labile substances, since
the contact time is short.
 It can be used either as batch type or continuous type.
 The free movement of individual particles eliminates the
risk of soluble material migrating as may occur in static

26. TYPES OF FLUID BED DRYER
A)Batch Type Vertical Fluid Bed Dryer With
Granulating Option.
I. Reverse Turning Bed Type
In this equipment, by turning the gas 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. As the perforated plate is
used as the gas dispersion plate, the gas inside the equipment
whirls and pushes the dried material out from the discharge
gate.

27. Batch Type Fluid Bed Dryer

28. Characteristics Of Batch Type Fluidized Bed Dryer
 The residence period of the dried material can be controlled which
results in uniform drying.
 It is most suitable in case where an accurate control of the
residence period is required at the decreasing rate drying zone.
 Small destruction of particle occurs therefore suitable for granular
or crystallized material.
 Easy operation can be achieved by an automatic control of material
feeding, drying discharging etc. When multiple stage system us
adopted, the exhaust gas heat can be used efficiently.

29. Continous Fluid Bed Dryer

30. B) Continuous Type Horizontal Vibrating Conveyor Fluid
Bed Dryer
 Residence time in any drying zone is dependent on
(1) Length of the zone
(2) The frequency and the amplitude of the vibration
(3) Use of dams
 Heat transfer units such as tube or plate, are built inside
the equipment.
 These unit supplies 60-80 % heat necessary for drying.

31. Characteristics Of Continuous Fluidized Bed Dryer
 The materials with relative high moisture content can also be dried.
 At and after a second drying chamber, piston flow ability can be
achieved by arranging numbers of the partition plates as per the
required residence period.
 The perforated plate at the fixed direction ensures easy discharging.
 Small destruction of particles, so suitable for granules or crystalline
materials.
 In multiple zones fluid bed dryers, heating and cooling occurs in
same unit.
 Each zone has independent control for temperature, dewpoint and
velocity of air/gas.
 By adjusting the weir height for each zone, residence time can vary
up to four fold in the unit.

32. Troubleshooting
Problem Cause Solution
 Material
Degrades
 High Drying
Time
 Reduced
particle Size
 High moisture
Contents in
dried Solids
 Material not
Fluidizing
 Surface
Shrinkage
 Very High
Temperature
 Material contains
high moisture
contents
 High residence time
 Due to internal
diffusion of particles
 Powders develop
electrostatic charge
 High temperature
 Low down the
temperature or
distribute the particles
 Prefer using twice drying
 Reduce resistance time
 Reduce residence time
 Use efficient electrical
earthing of Drying
chamber
 Optimize temperature

33. Applications
 Instant Tea/Coffee
 Milk Powder
 Ceram Slurry
 Magnesium Chloride
 Molasses
 Poly Aluminium Chloride
 Enzymes
 Catalysts
 Calcium Chloride
 Pastes
 Zeolites
 Resins
 Fruit Juice Powder
 Polyvinyl Acetate
 Dyes
 Detergent Powder
 Herbal Products
 Polymers (PVC, PP)