Spray drying is a better method for fluidized technology for drying liquid materials. The basic principle is that air passes through the filter and heater, into the air distributor at the top of the drying tower, and the hot air passing through the hot air distributor enters the drying chamber in a spiral shape uniformly. The liquid is sent from the liquid storage tank through the filter to the atomizer at the top of the drying tower through the pump or compressed air, so that the liquid is sprayed into extremely small mist droplets, and the liquid is in parallel contact with the hot air, and the contact surface area is greatly increased. The water evaporates quickly and is dried to a finished product in a very short period of time. The finished product is discharged from the bottom of the drying tower and the cyclone separator, and the collection bottle is recovered. The exhaust gas is collected by the filter bag and collected by the fan.
One of the parts of the spray dryer that relies mainly on the parts during the drying process is the atomizer. For the atomizer, there are several kinds of atomization methods. Let's take a look at the small series:
Airflow nozzle atomization
The airflow nozzle atomization is performed by using compressed air to be ejected from the nozzle at a high speed, and the liquid is dispersed into droplets by the frictional force generated by the difference in relative speed between the air and the liquid and the liquid. Although the airflow atomizer can atomize high viscosity materials, and the corresponding processing ratio
It's simpler. However, because the compressed air conversion function is very inefficient, the specific energy consumption of atomization is larger than that of the other two atomizing devices, and the atomization particle size distribution is not uniform enough, so the research focus is later transferred to the centrifugal atomizer. .
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2. High-speed centrifugal rotary atomization
According to reports, the rotational speed of the turntable is inversely proportional to the diameter of the droplet, and after the rotational speed is increased, the spray distance of the droplet is shortened, and the droplet distribution tends to be uniform. Therefore, the diameter of the drying tower can be made smaller, the degree of heat of the material to be treated is reduced, the ubiquitous sticking phenomenon is eliminated, and the speed of rotation becomes a trend of drying devices in various countries.
At present, the maximum spray volume of rotary atomizers in China is 10000 kg/h. It was successfully developed by the Institute of Chemical Industry of Forest Products of the Chinese Academy of Forestry. The motor power is 90 kW, the rotational speed is 12 000 r/min, and the model is RW10T. Its overall performance has reached the performance index of similar products of NiRo Company of Denmark.
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3. Pressure atomization
The pressure atomizer is based on a device that directly compresses a solution with a high pressure pump and depressurizes the pores to atomize the solution. Its specific energy consumption is relatively low, and the droplets ejected in the low pressure range (P ≤ 2.5 MPa) are coarser and the particle size distribution is wider. The height of the drying tower can be correspondingly reduced by the process of spraying down. In recent years, such devices have been widely used in the special ceramic (electrical ceramics) industry to prepare, for example, alumina, ferrite oxide, and the like. The development of these new materials has also contributed to the development of pressure spray dryers. At present, the maximum tower diameter has reached 7 m and the evaporation capacity can reach 1 t/h. Due to the use of the lower spray model (water fountain type), and because of the coarse particle size, the device has a solvent drying strength that is more than twice as high as that of the high-speed rotary atomization device.
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