Spray Drying Granulation Technology
The spray drying granulation technology is far older than people think. The earliest description can be traced back to 1860, while the earliest design patent record is 1872. The basic principle of spray drying granulation technology is to produce highly dispersed powder products by evaporating the solvent contained in the liquid. This is achieved by mixing the heated gas with a mist (spray) liquid stream (which has a high surface-to-mass ratio) in a container (drying chamber) and evaporating the solvent uniformly and quickly through direct contact. The droplet size is preferably the same.
Spray drying granulation technology is widely used in the production of fluid powders. The dehydration method has been successfully applied in the following fields:
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 result in a large number of materials that need to be further processed (such as grinding and screening), and further lead to uneven particle sizes and uneven shapes. On the contrary, spray drying granulation technology can keep the characteristics of powder particles such as density, size, and humidity, etc.
The challenges faced by designers and users are to increase output, improve the quality of powder products, and reduce costs. This requires a deep understanding of the production process and the efficient implementation of production control.
Spray drying granulation technology consists of the following stages:
Feed preparation: it can be homogeneous, free of impurities, suspended solids, or viscous materials, and materials that can be transferred by pumps.
Atomization (transforming the feedstock into droplets): it is the most critical step in the process of spray drying granulation technology. The degree of atomization determines the drying rate, which in turn affects the size of the dryer. The most commonly used atomization technologies are:
1. Pressure nozzle atomization: the liquid is forced out of the nozzle to produce a spray. This method is energy-saving and the particle size obtained is the most uniform.
2. Double-channel airstream nozzle atomization: mixing the feed and compressed air to form atomization. This spray drying granulation technology can be used to produce fine particles.
3. Centrifugal atomization: atomize the feed flow through the turntable. This atomization method is the most resistant, so it can generally run for a long time. Hawach’s industrial spray dryer is just this centrifugal atomization type.
Drying: The constant velocity stage allows moisture to evaporate quickly from the particle surface. The rate of drying in the subsequent deceleration phase depends on the rate at which moisture diffuses from the interior of the particles to the surface.
Separate the powder from the moisture: the treatment(such as recycling the drying medium) is economical and pollution-free. Fine particles are generally removed using cyclones, bag filters, precipitation, or scrubbers.
Cool and pack.
Therefore, the control system must have the flexibility to achieve precise and repeatable control of the spray drying granulation technology, and should have the following characteristics:
a.Precise loop control with set-point curve programming.
b.Sequential control suitable for complex control strategies.
c.Real-time data recording for analysis.
d.Local operator station with clear graphical interface monitoring and parameter control/access rights management.