Introduction to Centrifugal Spray Dryer
Centrifugal spray dryer is an ideal drying process, featuring fast drying speed, increased surface area of the material liquid after atomization, and the ability to instantly evaporate 95% to 98% of the moisture. The drying process only takes 5 to 15 seconds and features instantaneous drying. The centrifugal spray dryer reduces equipment resistance through a special air distribution device and effectively provides the processing air volume of the dryer, thus being suitable for most drying requirements. The following will introduce the advantages and disadvantages of centrifugal spray dryers as well as the inspection items before use.
I. Introduction to Centrifugal Spray Dryer
Centrifugal spray dryers are widely used processes in the liquid process forming and drying industry. It is applicable to generating powder, granular or block solids from liquid raw materials such as solutions, emulsions, suspensions and pumpable pasty liquids. Therefore, when the particle size distribution, residual moisture content, bulk density and particle shape of the finished product must meet specific standards, a centrifugal spray dryer is an ideal choice.
Ii. Advantages of Centrifugal Spray Dryers
Centrifugal spray dryers do not require strict filtration equipment. Unless there is fibrous liquid in the material liquid, it basically will not clog the material liquid channel.
It can adapt to liquid materials with higher viscosity and has more advantages than pressure spray dryers.
Because the adjustment of the atomizer's rotational speed is relatively easy, the particle size of the product can be controlled relatively easily, and the particle size distribution is relatively narrow.
When adjusting the processing capacity, there is no need to change the working state of the atomizer. Only the feed rate needs to be adjusted to achieve the same product quality.
The droplets produced by the centrifugal atomizer are almost on the same horizontal plane, moving along the radial and tangential directions, with almost no axial initial velocity. Therefore, the diameter of the dryer can be relatively large and its length relatively small, maximizing the utilization of the space in the drying chamber.
Iii. Disadvantages of Centrifugal Spray Dryers
When the feed volume of the material liquid is relatively small, the centrifugal spray dryer will cause the material liquid to be subjected to the effect of centrifugal force and rapidly move towards the edge of the dispersion disc, forming a hemispherical liquid ring. When the centrifugal force is greater than the surface tension, the hemispherical droplets at the edge of the dispersion disc will be immediately thrown out and split into fog droplets, which may contain a small number of larger droplets.
When the flow rate of the feed liquid continues to increase, the number and diameter of the liquid filaments no longer increase but instead adhere to each other to form a liquid film. After the centrifugal force throws the liquid film out of the periphery of the dispersion disc for a certain distance, it will split into widely distributed droplets. If the rotational speed is further increased, the liquid film will contract towards the periphery of the dispersion disc, and the liquid film band will narrow. If the sliding energy of the liquid on the surface of the dispersion disc is reduced to a minimum, the liquid will be ejected at a high speed, rubbing against the air around the dispersion disc and splitting into droplets.
When the flow rate of the material liquid is large and the rotational speed increases, the hemispherical material liquid will be pulled into many liquid threads. As the flow rate increases, the number of liquid threads around the dispersion disc will also increase. When the quantity reaches a certain value, the liquid thread will become thicker, but the quantity will no longer increase, and the liquid thread thrown out will also be unstable. The fluctuations and unevenness of the liquid filament movement will cause the liquid filament to break near the edge of the dispersion disc, and form spherical shapes under the effect of surface tension.
Iv. Inspection of the Centrifugal Spray Dryer Before Use
Check the lubricating oil condition of each mechanical part of the centrifugal spray dryer, as well as whether the valve ports of each water, air and slurry pipe are in the required positions. Also, check whether the connection points of the bearings and sealing parts of each device of the centrifugal spray dryer are loose.
Check whether the joints of the lubricating oil cooling pipes of the atomizer in the centrifugal spray dryer are well connected and whether the cooling water is turned on. Then, connect the power supply of the centrifugal spray dryer and check whether the voltage and instruments are normal. Finally, check the amount and concentration of the slurry in the slurry mixing tank and other conditions. If there are any problems, they should be solved in time.
Check whether the connecting pipes of the feed pump of the centrifugal spray dryer are well connected and whether the rotation directions of the motor and the pump are correct.
Check whether the position where the spray head is installed on the top of the drying chamber is properly covered to prevent air leakage.
Check whether the regulating butterfly valve at the outlet of the centrifugal fan of the centrifugal spray dryer is open. Do not close the butterfly valve too tightly, otherwise it will damage the electric heater and the air inlet pipe. This point must be paid special attention to.
Check whether sealing materials are installed at the pipe connections and then connect them to ensure that unheated air does not enter the drying chamber. Check whether the door and the observation window holes are closed and there is no air leakage. Check whether the rotation direction of the centrifugal fan of the centrifugal spray dryer is correct.
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