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What is Fluid Bed
Processing?
Fast and gentle drying of particles and powders
The most common use of Fluid bed is to dry wet granulated powders. The
product to be dried is fluidized by passing hot air through it. The process achieves
rapid heat transfer thus making it very efficient method to dry powders.
Besides drying, Fluid Bed Processors can also be used in the following processes:
- Granulating/Agglomerating
- Air Suspension Coating
- Coating
- Rotary Pelletization
For over 40 years fluid bed processors have been the standard method for
producing a wide variety of products. The success of the technology is due to its
fast and accurate processing, which can be executed in vary large batches.
From instant ice tea, to candy and pharmaceutical products, the technology is
superior.
As the name suggests, a fluid bed fluidizes a bed of particles (wet or
dry) by passing gas (air) through the bottom of the bed at a speed great enough to
lift the bed and fluidize it.
Fluidization (or
fluidisation) is a process 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. When a gas
flow is introduced through the bottom of a bed of solid particles, it will move upwards through the
bed via the empty spaces between the particles. At low gas velocities,
aerodynamic drag on each particle is also low, and thus the bed remains in a fixed state.
Increasing the velocity, the aerodynamic drag forces will begin to
counteract the gravitational forces, causing the bed to expand in volume as the particles move away
from each other. Further increasing the velocity, it will reach a
critical value at which the upward drag forces will exactly equal the downward gravitational
forces, causing the particles to become suspended within the fluid. At
this critical value, the bed is said to be fluidized and will exhibit fluidic behavior. By
further increasing gas velocity, the bulk density of the bed will
continue to decrease, and its fluidization becomes more violent, until the particles no longer
form a bed and are “conveyed” upwards by the gas flow.
Thus the fluid bed can used in many different ways to effect different
properties on products such as: Drying wet products, instantizing product, coating
particles for controlled pharmaceutical active release, agglomerating powders
or simply improving a materials flow properties.
Explosion Protection in Diosna Fluid Beds
The interior of a fluid bed is filled with fine particles/dust that are in
a state that can ignite providing there is an ignition source. Oftentimes solvents are also used in
processing, which obviously presents a danger of explosion. As there are no moving parts in
the fluid bed, ignition can only be caused by static charge. To solve this problem Diosna has
designed their fluid bed system to safely withstand any internal explosion by making the apparatus
12 bar shock proof. It is widely accepted that a 10 bar shock proof system is adaquite protection,
thus the 12 bar is total piece of mind. The Diosna fluid bed is also grounded and can be provided
with a grounding monitoring system built into the controls. The Diosna 12 bar system is a totally
enclosed design meaning that you do not have to make an explosion pathway/vent to the exterior of
your facility. This greatly simplifies the installation of the machine.
In cases where the fluid bed is connected to a High Shear Granulator,
Diosna can provide the entire system in 12 bar design.
Diosna Air-handling unit
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Diosna Air Handler
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Generally process air is drawn from the outside of the building as the
system uses vast amounts of air. Depending on your installation region, the air handler is equipped
with frost protection or extra humidity handling capabilities (like a desiccant wheel). The air
handler is the actual processor of the machine, and is therefore the most important mechanical part
of the system. Reproducible, consistent control of the air humidity, temperature, purity and
velocity is paramount to validate the process. Diosna provides the finest air handlers available
for this application and offers every possible configuration to suit all environments and
processes.
Air Inlet and Bowl Plate (Air Distributor)
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Diosna Air Distributor Plate
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The product being processed is held in a bowl, which can be
hinged/swinging off the fluid bed or removable on a trolley. The bottom of the bowl is covered with
the air distribution plate, this uniformly distributes the air to the bowl fluidizing the product.
Additionally the inlet air is lead tangentially into the lower part of the fluid bed (below the
bowl) creating a vortex like air movement. To further this circular movement of air, Diosna employs
a special air distributor plate design which guides the air in a circular movement through the
product. the two combined systems are very effective in producing a uniform flow and also aid the
unloading of product using the Diosna vacuum emptying system.
Fluid Bed Process Filters & Single Chamber/Double Chamber
Design
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Double Chamber Filters
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The top inside of the fluid bed is covered in filters. These are required
to stop product from escaping the fluid bed system. The top chamber of the fluid bed can
be provided in two variations: Single Chamber and Double Chamber. The single chamber design
has one large filter spanning the entire outlet of the machine, this is not advantageous for
processing as the filters must be constantly shaken to release the particles that clog it. Thus the
process air must be slowed down to reduce pressure on the filter surface - resulting in
intermittent processing. To solve intermittent processing we can supply the machine with two
chambers, and cycle between the two for cleaning e.g., one chamber is closed and the filters
cleaned while the other is in full air-flow operation. The two chamber system is the most popular
design we sell, however, it does cost more.
Diosna offers a wide arrangement of filters to cover all
applications. General filter configurations are as follows:
- Standard fabric high surface area filter ("cow udder" style). This is
the most widely used
- Separate cartridge filers with fabric filters
- Stainless Steel cartridge filters
- Patented CIP cartridge filters
In all cases the filters automatically lower out of the upper machine part
and are easily removed for washing.
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