There are many types of spray dryers, which can be divided into open type, closed cycle type, self idling cycle type and semi closed cycle type according to the process; According to the direction of spray and gas flow, it can be divided into: parallel flow, counter flow and mixed flow; According to the atomization method, it can be divided into centrifugal type, pressure type and air flow type. Among them, atomization method classification is a common visible method. The following points are about atomizers.

It is the boring heart of the whole spray, which directly affects the product quality and economic indicators. The higher the dispersion of atomizer, the greater the dry power; The more uniform the atomization, the smaller the change of water content of the product. Therefore, the atomizer should not only ensure the dispersion of the feed liquid, but also control the particle size change to a very small extent.

Features of atomizer

(1) Centrifugal atomizer

Centrifugal atomization: the material liquid is thrown out from the edge of the disc by centrifugal force in the high-speed rotary table (peripheral speed 90~160m/s). It uses the effect of high-speed rotating disk. When the liquid is injected into the disk surface, the liquid is subject to two force effects: one is accelerated under centrifugal force and gravity effect and split atomization; Second, there is friction at the contact surface between the liquid and the surrounding air to promote the formation of fog drops. The former is centrifugal atomization and the latter is velocity atomization. In fact, the two exist together. The atomization effect of centrifugal atomizer is directly related to the characteristics of feed liquid, flow rate, disc shape, diameter and speed.

(2) The pressure atomizer uses a high-pressure pump to obtain high pressure for the liquid. When the high-pressure liquid passes through the nozzle, it will convert the pressure energy into kinetic energy and disperse into droplets when it is sprayed at high speed. When the liquid is atomized after being pressurized from a single hole, it is due to the external force effect. The liquid is separated from the nozzle outlet by a short distance, overcoming the surface tension, and is cut into thin lines from the liquid film. In addition, the influence of the turbulent radial velocity and the relative velocity of the surrounding air causes the liquid line to be cut into droplets of different sizes. The pressure atomizer also starts from this principle.

(3) Air flow atomizer

Air flow atomization (also known as two fluid spray) uses compressed air to spray from the nozzle at a very high speed (≥ 300 m/s). Depending on the friction generated by the speed difference between gas and liquid, the feed liquid is separated into droplets. It uses the high-speed movement of steam or compressed air to make the feed liquid meet at the nozzle outlet and the liquid film is cut and atomized. Because the feed liquid velocity is not large, but the air velocity is very high, the relative velocity of the two fluids exists. The liquid film is pulled into a wire, and then cut into fine droplets. The size of the droplets depends on the relative velocity and the viscosity of the feed liquid.