Embed Size (px)
Citation preview
TopicFLUIDIZED BED DRYER
Group Members
Awais Hafiz (034)
Hafiz Luqman (032)
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
DryerFeed Dry Solid
Heat
Moisture
Drying Process
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
Feed Stock for Drying Process
Wet Solids
Slurry
Solution
Suspension
Types of Dryers on the basis of Heating Mode
Convective/Direct Dryers
Conductive/Indirect Dryers
Dryers by Radiant Energy
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
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
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
General Consideration forSelection of Dryer
Dryer must operate reliably, safely & economically
Operating & maintenance must not be excessive
Pollution must be controlled
Energy consumption must be minimized
Fluidized Bed Dryer
13
What is Fluidization?
Fluidization (or fluidization) is a process similar to liquefactionwhereby a granular material is converted from a static solid-like state to a dynamic fluid-like state. This process occurswhen a fluid (liquid or gas) is passed up through the granularmaterial.
Different types of fluidized beds are formed depending uponthe velocity of fluid.
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.
Different Fluidized Bed Formation
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.
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.
2)Process ParametersThe 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.
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.
CONSTRUCTIONThe 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.
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.
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
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
bed.
TYPES OF FLUID BED DRYERA)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.
Batch Type Fluid Bed Dryer
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.
Continous Fluid Bed Dryer
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.
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.
TroubleshootingProblem 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
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)
