Pneumatic dryers are the systems in which the drying particles are entrained and conveyed in a high velocity gas stream.
The pneumatic drying technologies allow to atomize slurry and liquid compounds with different degree of viscosity, producing fine powders with precise particle size.
Furthermore, the obtained powders have a high degree of fluidity and solubility, thanks to the perfect distribution of the shape and of the particle size that is obtained by the atomizing process.
This system further improved on fluidized bed. Ex: Spray dryer.
A spray dryer is a drying machine used to process solutions, suspensions, or materials in a slurry state.
A spray dryer is a kind of continuous atmospheric dryer which can be used to dry materials such as fuel, intermediates, soap powder, or inorganic salts, etc.
Drying of the material in spray dryer involves 3 stages:
1- Atomization of liquid from liquid droplets.
2- Drying of the liquid droplets.
3- Recovery of the dried product
A spray dryer uses the spray method to transform the material into fog droplets in order to be dispersed into the hot gas stream.
The material connects with the hot air in a co-current, counter-current, or mixed flow manner so that the water can evaporate quickly to achieve the drying effect.
Advantages of Spray Drying
• The droplets are small, giving a large surface area for heat and mass transfer so that evaporation is very rapid.
• It can be used for drying heat sensitive or oxidized materials without degradation.
• It can be designed for drying under sterile conditions.
• The dried powder will have a uniform particle size and shape.
• Because of good flow properties, the spray-dried powder can be easily compressed into the form of tablets.
• It is useful in the coating and encapsulation of both solids and liquids.
• Labor cost is low since the material is dried in a single operation with no handling.
• Produce powders with a specific particle size and moisture content
• Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas.
• Preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals.
• A consistent particle size distribution is a reason for spray drying some industrial products such as catalysts.
• Air is the heated drying medium:
However, if the liquid is a flammable solvent such as Ethanol or the product is oxygen –sensitive then nitrogen is used.
• Spray dryers are used for the drying of liquid materials like emulsion, suspension, solution, slurries, thin pastes, etc.
• Spray drying can be used to dry materials that are sensitive to heat or oxidation without degrading them, even when high temperature air is employed.
• The liquid feed is dispersed into droplets, which are dried in seconds because of their high surface area and intimate contact with the drying gas.
• The product is kept cool by the vaporization of the enveloping liquid, and the dried product is kept from overheating by rapid removal from the drying zone.
• The improvement in flow and reduction of air entrapment make the spray-dried material suitable for use in the manufacturing of tablets and capsules.
• The Spray Drying is a very important process that allows to obtain high quality engineered powders for various industries (Food, Pharmaceutical, Ceramic, Environment, etc.).