| Special
Applications & Considerations - Swirl Fluidizer
Swirl Fluidizer
Drying of filter cakes, pastes, and sludges
When producing powders of fine size from aqueous
suspensions, it is a distinct advantage to first mechanically dewater so
as to reduce the plant installation and operating costs of the final
drying stage.
During dewatering, suspensions are converted to either
filter cakes, pastes or thick viscous liquids, sometimes in the form of
sludges.
Drying of such materials is ideal in the Nitro Swirl Fluidizer. This is a continuous one stage drying plant that can produce
a fine particled powder without the need for back-mixing powder with
feed material, a feature of more conventional technology, i.e. flash
drying. The Swirl Fluidizer operates with very short product and air
residence times and thus permits high production rates in small compact
units.
There is an extensive range of materials suitable for Swirl Fluidizer drying, and further details are given below. Plants can
be supplied in pilot or industrial size, both of which meet
environmental and safety requirements. The Swirl Fluidizer process can
be demonstrated at Niro's comprehensive test station facilities. Here
feed and powder properties can be investigated and industrial plant
specifications determined. The Swirl Fluidizer has already been proven
over long periods of operation – a clear sign of Niro's unique drying
experience and dedication to solving specific drying needs with
customers.
| Drying
Process
Process advantages
The Swirl Fluidizer offers a number of important advantages when
viscous liquids, sludges, pastes and filter cakes must be
converted into powders:
- Continuous operation
- One stage drying
- Compact layout – robust design
- Effective heat and mass transfer – short
drying times
- Negligible heat loss – high thermal
efficiency
- Easy access and cleaning
Drying chamber
The heart of the drying process is a cylindrical drying chamber
consisting of three important components: an air disperser, a
rotating disintegrator, and a drying section.
The hot drying air enters the air disperser
tangentially, and with the use of an advanced guide vane
arrangement is introduced into the drying section as an intense,
controlled swirling air flow. The rotating disintegrator is
mounted at the base of the drying section. Under the influence
of the disintegrator operation and swirling air flow, a feed
comminution and drying process takes place, and the resulting
dry fine particles pass out with the exhaust air for collection
in a bag filter.
Disintegrator speed controls the degree of
comminution, and hence particle size.
As the air residence time in the drying
section is very short, typically 1-2 seconds, the Swirl
Fluidizer is always a compact unit.
Feed system
Feed enters the feed tank under level control. The tank is
fitted with a slowly rotating impeller which provides the base
mounted dosing unit with a constant feed supply.
The rheological properties of the feed
determine the design of the dosing unit. This can be a screw
feeder or pump. The dosing rate to the dryer controls the outlet
air temperature at a fixed level, which in turn ensures that the
powder collected from the bag filter has a constant residual
moisture content.
Hot air system
The drying air is heated either directly or indirectly,
depending upon the feed material, the specified powder
properties, and available fuel source. The heat sensitivity of
the product determines the drying air temperature. The highest
possible value is used in the interest of optimizing thermal
efficiency
Powder discharge and exhaust air system
A bag filter is usually recommended for collecting the fine
particles produced. The exhaust fan maintains a slight vacuum in
the dryer, thus preventing powder leakage into the surroundings. |
Typical
Products Dried
Catalysts
Ceramics
Dyestuffs
Pigments
Inorganic chemicals
Organic chemicals
Zeolites
Kaolin |
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| Dryer
Selection
NIRO offers a range of dryer designs.
The selection of the most suitable dryer depends upon
feed solids, the rheology of the feed material, and
desired powder properties, but any dust explosion and
oxidation hazard can be handled, irrespective of dryer
type. Testwork on the given feedstock is always
recommended to confirm plant design.
Swirl Fluidizer
Solids properties: Insoluble, amorphous or
crystalline fine particles
Feed characteristics: Viscous liquid, sludge,
paste, filter cake, semi-dry powder Solids consisting of
small particles insoluable in water or solvent
Powder characteristics: Fine particles of average
size < 20 microns
Spray Dryer (Special
literature available)
Solids properties:
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