The Process of Spray Drying
The process of spray drying is way older than it is assumed commonly among people. The first design that was patented goes back in a record to 1872 and earliest descriptions date back in 1860. The whole idea of spray drying comes from the emitting of powder that is dispersed from a liquid that evaporates the solvent. This is only possible when the heated gases are mixed with fluids that are atomized at a high surface to mass ratio of drops, ideal equal size, in a drying chamber, helping the mixture to uniformly and quickly evaporate by coming in direct contact with each other.
There are a number of applications where these spray drying techniques are put to use and the free-flowing powder is used for production. This method has proven to be extremely successful in multiple areas and few them to name are these:-
- Soaps and detergents
- Beverages
- Milk and egg products
- Bone and tooth amalgams
- Pharmaceuticals
- Textiles and much more
- Flavours, colorings, and plant extracts
- Plastics, polymers, and resins
All the other methods that are used for drying, that may also include rotary evaporators or freeze dryers, use the age of ovens, manufactures a mass of material that is required to process further for example for grinding and filtering. And further manufacturing irregularly shaped particles of different shapes and sizes. On the contrary, if you choose spray drying, it will power you with a very flexible control over the properties of particles like its size, density, flow characteristics, or content of moisture.
Design and Control
The challenges that are faced by every designer or user are to command more production, improve the quality of the powder and comprehension of the necessary control and process of the implementation.
There are two phases of spray drying
Feed preparation
This can be anything from being a solution that is free from impurities, homogenous mix, suspension or paste.
Atomization (changing the feed into droplets)
The most important step to follow in the process is the control of atoms and at what degree and also the dryer size.
Pressure nozzle atomization
The spray turned into the fluid is then pushed through an orifice. This is considered to be an energy efficient method that’ll also offer the narrowest particle size distribution.
Two-fluid nozzle atomization
Compressed gas is mixed with the feed in this process. It is the least energy efficient method and is only useful for grinding extremely fine particles.
Centrifugal atomization
Spray created by passing the feed through or across a rotating disk. Most resistant to wear and can generally be run for longer periods of time.
Drying
If there is a constant rate phase, it will ensure that the moisture does evaporate quickly from the surface of the particle. This is also further followed by a dropping rate period where the drying is taken care of by the diffusion of water to the surface of the particle.
Separation of powder from moist gas:
This is one more thing that should be done in a pollution free environment in an economical manner. The finer particles are strained generally by the cyclones, scrubbers and bag filters.
Cooling and packaging:
A lot of researches have been conducted in recent times and have suggested mainly that the use of spray drying techniques may be a very effective and significant alternative method for crystallization of amorphous powders during the process of drying.