Spray drying can be used for a wide range of applications requiring the production of free-flowing powders. This method of dehydration has become one of the most successful in the following areas: Pharmaceuticals, Bone and Dental Fillings, Beverages, Flavors, Colors and Plant Extracts, Milk and Egg Products, Plastics, Polymers and Resins, Soaps and Detergents, Textiles and more.
Almost all other drying methods are used, including the use of ovens, freeze dryers or rotary evaporators, to produce large quantities of material that require further processing (such as grinding and screening) and therefore, produce irregular particle sizes and shapes . Spray drying, on the other hand, offers a very flexible control over powder particle properties such as density, size, flow characteristics and moisture content.
design and control
The challenges facing designers and users are to increase production, improve powder quality and reduce costs. This requires a process understanding and a robust control implementation.
Spray drying involves the following stages:
Preparation: This may be a homogeneous, pumpable, impurity-free solution, suspended or pasted.
Atomization (converting the feed into water droplets): The most critical step in the process. The degree of atomization controls the drying rate and therefore the size of the spray dryer. The most commonly used atomization techniques are:
1. Pressure nozzle atomization: The spray is made by forcing the fluid through a hole. This is an energy efficient method that also provides a narrow particle size distribution.
2. Two-fluid nozzle atomization: the spray is fed by the mixed feed of compressed gas. ^Method of saving energy. For the manufacture of very fine particles.
3. The feed is created by centrifugal atomization: spray or on a rotating disk. ^Resistant to wear and generally lasts longer.
Drying: The constant speed stage ensures rapid evaporation of moisture from the particles on the surface. This is followed by a period of decreasing rate of drying at the surface which is controlled by the diffusion of water particles. Separation of powders from moist gases: carried out in an economical (eg recovery of drying medium) and free manner. Particulates are usually removed with cyclones, bag filters, dust collectors or scrubbers.
The control system must provide the flexibility, accurate and repeatable control to achieve spray drying and will include the following functions:
1. Loop control and anchor point profile programming
2. Simple parameterization of formula management system
3. Sequence control complex control strategy
4. Online data analysis and evidence from system security
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