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The '''Dispersion Dryers''' are used for drying applications of wet cakes, pastes, sludges and production of powders from aqueous suspension. Due to the dewatering mechanism, these dryers provide effective solutions and converted to either filter cakes, pastes or sludges. These air dispersion dryers are chosen on the basis of wet deed cake particle size distribution of final powder and drying curve. The range of air dispersion dryers generally includes spray dryers, rotary dryers, flash dryers, spin flash dryers, vibrated fluid bed dryers and fluid bed dryer. | |||
===Features=== | |||
* Smooth functionality | |||
* Easy operation | |||
* Durable performance | |||
==Spin Flash Dryers== | |||
If the wet cake is a paste or sludge, the [[Spin Flash Dryers]] are the most suited for drying application. The dryer is fitted with a mechanical agitator which helps to disperse the wet cake without any need for back mixing of the dry powder. the feeding system includes a feed tank with agitator and a screw feeder for feeding into the drying unit. The heart of drying process is cylindrical drying chamber, where the drying air enters the air distributor. The tangential air distributor of special design introduces the air as an intense swirl flow. the simple spin flash dryer is designed to handle materials that can be suspended directly in air. The drying process usually is completed in 0. 5 - 2 sees, and the final moisture is generally in the constant rate drying zone. Various types of spin flash dryers designs are available based on uniform / non uniform particle size of the feed / product. the feeding of cake is through specially designed paddle mixer / screw conveyor with / without rotary injector depending on rheology of feed material. For difficult to handle feed materials part of dried powder can be re-cycled. Spin flash dryers are suited for filter cakes, semi dried powders. | |||
==Rotary Dryers== | |||
The [[Rotary Dryers]] that are classified as direct or indirect (air heating method), current or counter current (material air contact). While using the dryers the material should be dried and uniformly dispersed over the entire cross-section. These dyers can also be customized based on the properties of the material. | |||
===Features=== | |||
* Material is Passage through heated air | |||
* Dryer is driven through a girth gear and tyre arrangement | |||
* Minimum air leakage | |||
===Advantages=== | |||
* Low operating costs* Low maintenance costs | |||
* Ideally suited for high volumes | |||
* High thermal efficiency | |||
'''These dryers are used to handle following material''' | |||
* Sand | |||
* Clays | |||
* Maize germs | |||
* Coal | |||
* Ore | |||
* Industrial sludge | |||
==Fluid Bed Dryers== | |||
The [[Fluid Bed Dryers]] are known for single stage operation and extensively used to convert solutions, suspensions, and slurries into dry powder within a few seconds without any intermediate handling. The high speed of the process and controlled temperature ensure the optimum efficiency of the process. | |||
===Feature=== | |||
* Easy to install | |||
* High functionality | |||
* Optimum performance | |||
* Smooth operation | |||
==Spray Dryers== | |||
The [[Spray Dryers]] offer an effective and efficient method of removal of surface or on bound moisture from a feed product. Spray dryers are pneumatic driers having very low residence time within the equipment, thus flashing off the moisture from the feed. They are used for efficient drying of moist powders. Slurry, filter cakes, granules, etc. They operate on varying throughput rates from few hundred kilograms per hour to hundreds of tons per hour. Low temperature dehumidified air could be used for heat sensitive products to hot gases with temperature up to 500 - 600 deg. C. for temperature resistant products. spray drying equipment comprises of the feeding section normally a screw feeder, rotary valve, vibratory feeder, etc. Which feeds the wet product in a controlled fashion into the throat of the flash drier, where it is mixed with hot air produced by a hot air generator or heat exchanger | |||
==Flash Dryers== | |||
The [[Flash Dryers]] offer an effective and efficient method of removal of surface or on bound moisture from a feed product. Flash dryers are pneumatic driers having very low residence time within the equipment, thus flashing off the moisture from the feed. They are used for efficient drying of moist powders. Slurry, filter cakes, granules, etc. They operate on varying throughput rates from few hundred kilograms per hour to hundreds of tons per hour. Low temperature dehumidified air could be used for heat sensitive products to hot gases with temperature up to 500 - 600 deg. C. For temperature resistant products. Flash dryers comprises of the feeding section normally a screw feeder, rotary valve, vibratory feeder, etc. Which feeds the wet product in a controlled fashion into the throat of the flash drier, where it is mixed with hot air produced by a hot air generator or heat exchanger. | |||
==Vibrating Fluid Bed Dryers== | |||
The [[Vibrating Fluid Bed Dryers]] are used for fluidization of materials which are difficult to handle in a static fluid bed dryer. | |||
===Physical Properties=== | |||
These materials are often characterized by having one or more of the following physical properties: | |||
* Wide particle size distribution | |||
* Low strength of wet or dry particles | |||
* Stickiness or thermo plasticity of the particles | |||
* Pasty properties of the wet feed | |||
In the vibrated fluid bed dryer, the material is easily transported through the dryer by the combined effect of fluidization and vibration. The fluidization velocity can be judiciously selected, to minimize entertainment of the smaller particles, to avoid gas bubbling m the fluid bed thereby minimizing attrition. The residence time can be adjusted, by varying the bed height, through the overflow weir position. A cooling section can also be provided, by partitioning of the plenum chamber. | |||
'''Typical products handled:''' | |||
* Salt | |||
* Milk products (used as a secondary dyer) | |||
* Chemicals | |||
* Tea | |||
Fluid bed dryer is suited for powder, granules with average particle size 50 - 2000 microns. If the feed material is sticky and having wide particle size distribution. Vibro fluid bed dryer is the most suited, where vibration helps the movement of solids and drying. | |||
===Operation=== | |||
* Material is easily transported through the dryer due to fluidization and vibration | |||
* Fluidization velocity can be judiciously selected to minimize entertainment of the smaller :particles | |||
* Minimize entertainment avoid gas bubbling m the fluid bed thereby minimizing attrition. | |||
* Residence time can be adjusted by varying the bed height, through the overflow weir position. | |||
* Provided with cooling section by partitioning of the plenum chamber. | |||
===Advantage=== | |||
* Well suited for constant | |||
* Well suited for failing rate drying | |||
* By preheating the air, the residual moisture can be reduced | |||
* Can fluidized well the solids having a well defined particle size | |||
==Laboratory Spray Dryer== | |||
The [[Laboratory Spray Dryers]] follow some basic principles. | |||
===Principle=== | |||
A peristaltic pump delivers liquid from the sample container to the 2 fluid nozzle mounted on the drying chamber. Compressed air from the inbuilt compressor is also supplied to the nozzle, resulting in atomization of the liquid into a fine spray. Air from the blower is heated by an electrical air heater and blown through the drying chamber. Due to the large surface area, drying is very rapid, resulting in a sharp drop in temperature. The dry powder particles are separated from the air in the cyclone separator and collected in the glass collection bottle. The exhaust air is directed through a flexible ss hose into the atmosphere. A bag filter can be provided for secondary powder collection. | |||
===Construction=== | |||
* The blower, electrical air heater, air compressor and the pump are placed in a stainless steel panel, with free and easy access | |||
* The air entering the panel is filtered through a fine cloth filter | |||
* The chamber and cyclone are of borosilicate glass with clamp fillings, designed for easy assembly and removal | |||
* The peristaltic pump is mounted on the front of the panel with easy accessibility | |||
===Operation=== | |||
The dryer has ease of operations. The inlet air temperature is precisely controlled by the inlet temperature pid controller. The panel includes: | |||
* Inlet temperature controller | |||
* Outlet temperature indicator | |||
* On/off switch and indicator for blower | |||
* On/off switch and indicator for heater | |||
* On/off switch and indicator for air compressor | |||
* On/off switch and indicator for feed pump | |||
* Pump speed control with lcd display | |||
* Compressed air pressure control with lcd display of air pressure. | |||