Exploring the Spray Dryer Diagram, Principle, Construction, Working and other details

A spray dryer diagram is a device used in various industries to convert liquid or slurry feed into a dried powder form. The process involves spraying the liquid feed into a hot gas stream, usually through a nozzle, creating fine droplets. The hot gas evaporates the moisture from the droplets, leaving behind the dry particles.

Principle of Spray Dryer

• The fluids to be dried are atomized into fine droplets.
• The droplets are thrown radially into a moving stream of hot gas.
• The temperature of the droplet increases rapidly and gets converted into dried spherical particles.
• This process completes in a few seconds before the droplet reaches the wall of the dryer.

Construction of Spray Dryer

• Spray dryer diagram consists of a large cylindrical drying chamber with a short conical bottom
  • ~ material: stainless steel
  • ~ Diameter:2.5-9 M
  • Height:25 m or more
• Air inlet present in the roof of the chamber
• An additional inlet-carrying spray disk atomizer strategically positioned in the roof
• Spray disk atomizer :
  • – Diameter — 300 mm
  • — Speed – 3000-50,000 pm
• The bottom of the dryer is connected to a cyclone separator

Working on Spray Dryer

 It occurs in 3 stages:

1. Atomization of the liquid
2. Drying of the liquid droplet
3. Recovery of the dried product

1. ATOMIZATION OF THE LIQUID TO FORM DROPLETS

• The introduction of the feed occurs via the atomizer mechanism.
• It forms fine droplets
• The selection of the type of atomizer is essential because the properties of the final product depend on the nature of the droplet formed

Types of atomizers:

1. Pneumatic atomizer
2. Pressure nozzle atomizer
3. Spinning disc atomizer

• The feed rate is adjusted, so the droplets should be dried entirely before reaching the walls of the drying chamber; the product should not be overheated.

2. Drying of the liquid droplet

• Hot air is introduced through the hot air inlet
• The fine droplet is introduced into this air stream.
• It absorbs heat from the hot air and gets dried in the drying chamber
• The liquid droplet’s surface undergoes instantaneous drying, resulting in the formation of a resilient outer shell.
• The liquid from the inner side of the shell diffuses out through the shell at a particular rate
• At the same time, heat transfer takes place at a rate more significant than the liquid diffusion rate
• As a result, heat inside mounts up
• This allows the liquid to evaporate at a faster rate so that vapor will be produced inside the shell
• As a result, the internal pressure rises, leading to the expansion of the droplet.
• The vapor within the shell begins to permeate through its surface.
• So the thickness of the shell decreases, and finally, it ruptures and releases the internal pressure
• The feed rate and the temperature of the air are adjusted in such a way that the droplets should be dried entirely before reaching the wall of the drying chamber

3. Recovery of the dried product

• The centrifugal force generated by the atomizer propels the droplets to trace a helical path.
• During their trajectory, these particles undergo drying and eventually descend to settle at the conical bottom.
• The entirety of these processes is accomplished within a matter of seconds.
• The final product exhibits a particle size ranging from 2 to 500 mm.

Application of Spray Dryer

• In the realm of dairy farming and the processing of milk.
• The manufacturing of powdered milk, skimmed milk, and whole milk.
• Processing Egg‐based products.
• Production of sweets and ordinary edible acids.
• Processing Coffee/ Tea whiteners.
• Wheat and corn-based products in the bakery.
• Spray dryers have applications in tablet production for drying liquid to powder.
• Used in the production of dye color, food colors, and paint pigments.
• Soap and detergent manufacturing processes utilize spray dryers.
• Spray dryers find a place in fertilizer production like nitrates, ammonium salts,
  phosphates, etc.
• Spray dryers are handy in drying citric acid, borax, sodium phosphate,
  hexamine, gelatine, and extracts.

Advantages of Spray Dryers

• Spray drying is a continuous process
• Drying is very rapid(completes within 3-30 seconds)
• Labor costs are low
• Fine droplets formed to provide a large surface area for heat and mass transfer, so the product shows excellent solubility
• It is applicable for dehydrating sterile products.

Disadvantages of spray dryers

• The spray dryer is both large in size and comes with a substantial installation cost.
• It isn’t easy to clean after use.
• It has a low thermal efficiency, which means a lot of heat is wasted during operation.
• Spray dryers are not suitable for drying solid materials.
• Product degradation or fire hazard may result from product deposit in the drying
  chamber.

Uses of Spray Dryer

• The quantity of the material to be dried is large
• Thermolabile, hygroscopic materials can be handled

Conclusion

In conclusion, the spray dryer is no ordinary machine; it’s a transformative force in manufacturing. From its intriguing diagram to the efficient, cost-effective operation, we’ve unveiled the secrets behind this magical apparatus.

FAQs About Spray Dryers