Spray Dryer Process

The Spray Drying Process is far older than people's imagination. The earliest description dates back to 1860, and the earliest record of design patents is 1872. The basic principle of spray drying is to produce highly dispersible powder products by evaporating the solvent contained in the liquid feed. It is achieved by mixing the heating gas with a mist (spray) stream with a high surface mass ratio in a container (drying chamber), and direct contact to make the solvent evaporate uniformly and quickly. The size of the mist droplets are preferably the same.

Spray drying is widely used in the production of fluid powders. The dehydration method has been successfully applied in the following fields:

Pharmaceutical
Bone and tooth amalgam
Drink
Spices, dyes and plant extracts
Milk and egg products
Plastics, polymers and resins
Soap and detergent
Textiles and many other products
Almost all other drying methods, including the use of ovens, freeze-drying and rotary evaporators, will cause a large amount of materials to be further processed (such as grinding and screening), resulting in uneven particle size and shape. On the contrary, spray drying can more flexibly control the characteristics of powder particles such as density, size, fluid characteristics and humidity.

Design and control
The challenge faced by designers and users is to increase output, improve the quality of powder products, and reduce costs. This requires a deep understanding of the production process and efficient implementation of production control.

Spray drying consists of the following stages:

Supply preparation: it can be homogeneous, pumpable, impurity-free liquid, suspended solids, or viscous materials.
Atomization (converting the feed into droplets): This is the most critical step of the process. The degree of atomization determines the drying rate, which in turn affects the size of the Dryer. The most commonly used atomization techniques are:
1. Pressure nozzle atomization: the liquid is forced out of the nozzle to produce spray. This method saves energy, and the particle size obtained is the most uniform.

2. Two-channel airflow nozzle atomization: mix the feed and compressed air to form atomization. This method has the worst energy saving effect. Can be used to produce fine particles

3. Centrifugal atomization: make the feed flow through the turntable to produce atomization. The most wear-resistant, so it can generally run for a long time.

Drying: The isokinetic stage allows moisture to quickly evaporate from the surface of the particles. The drying speed of the subsequent deceleration phase depends on the speed at which the moisture diffuses from the inside of the particles to the surface.
Separate powder from moisture: The treatment method (such as the recycling of dry media) is economical and pollution-free. Fine particles are generally removed by cyclones, bag filters, settlers or scrubbers.
Cooling and packaging.
Therefore, the control system must be flexible to achieve precise and repeatable control of spray drying, and has the following characteristics:

Precise loop control with set point curve programming
Easy to parameterize recipe management system
Sequence control suitable for complex control strategies
System real-time security data recording for analysis and evidence
Local operator station, with clear graphical interface monitoring and parameter control access authority management