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2 Equipment structure The micro-powder dryer is mainly composed of a feeder, a stirrer, a classifier, a transmission device and a drying chamber. The specific introduction is as follows.
2.1 Feeder Micro-powder dryer is generally fed with a screw conveyor. For paste viscous materials, the conveyor is specially designed to prevent material blockage and bridging. For slurry materials, the feed can be fed using a positive displacement pump.
2.2 The function of the agitator is to break up the mass of material and fluidize the material under the action of hot air. Different types of agitators can be designed for different materials such as paste, viscous and bulk. Different from the rotary flash dryer, the mixer of the micro-powder dryer can be designed as a stand-alone or horizontal structure, which is suitable for different occasions. The horizontal structure can greatly reduce the height of the equipment and is easy to maintain and inspect.
2.3 Classifier Rotary flash dryer is generally used for materials that do not have strict requirements on the particle size of the product. The classification structure is a fixed elution ring at the top of the dryer. The top of the micro-powder dryer is equipped with a grading wheel, and its rotation speed is adjustable, which is suitable for materials with strict requirements such as ultra-fine and nano-scale. For materials with very strict particle size range (such as d90 ≥ 2μm), multiple grading wheels can be used if necessary.
2.4 Transmission Rotary Desiccant Dryer generally adopts belt vertical transmission. The motor is generally fixed on the frame at the bottom of the cylinder to increase the stability of the equipment. The transmission of the micro-powder dryer is fixed to the integral frame with almost no vibration. Corresponding to vertical and horizontal mixers, the transmissions are available in both vertical and horizontal versions.
The design of the transmission has a great influence on the stability of the equipment. The 10 type rotary flash dryer produced by a domestic manufacturer by Lanhua Company has a very large vibration due to the unreasonable design of the transmission device.
2.5 Drying chamber The micropowder dryer is basically the same as the drying chamber of the rotary flash dryer. The difference is that the air inlet sections of the cylinder are different due to different air intake modes. Micron dryers do not require complex inlet volutes and distributors.
3 The process of designing and calculating the micro-powder dryer is similar to that of the rotary flash dryer. The cylinder diameter is generally determined by reference to the calculation method of the rotary flash dryer. Here we mainly introduce the design method of the agitator and classifier.
3.1 Design of the agitator The form and structure of the agitator and the rotational speed have a great influence on the drying process. The agitator of the rotary flash dryer adopts vertical structures such as anchor type, paddle type and rotary vane type, and the structure is multi-layered to ensure the dispersion of materials.
The agitator of the micro-powder dryer has been developed from the vertical structure of Zui to the horizontal. The rotor is designed with multiple reference grinder structures, and the crushing and dispersing ability is very strong. The speed of the agitator can be between 1000 and 4500 rpm, and the specific value is determined according to the diameter and physical properties of the drying chamber. When the diameter of the drying chamber is large, take a small value, and when the diameter is large, take a small value. The peripheral speed of the outer edge of the agitator is between about 50 and 80 m/s. Due to the high speed of the stirrer of the micronized dryer, a dynamic balance test must be carried out after processing. The force of the rotor is more complicated. At present, the required power is mainly selected by experience.
3.2 Design of classifier The classifier of the micro-powder dryer is a centrifugal flow classifier, which separates the fine powder from the coarse powder by the action between the centrifugal force generated by the high-speed rotation of the impeller and the centripetal force of the airflow. The speed of the classifier can be between 1000 and 2000 rpm, and the peripheral speed of the outer edge of the impeller is between 20 and 30 m/s. When designing the classifier, according to the air volume required for drying, the diameter of the impeller corresponding to the diameter of the cylinder and the impeller speed of the large Zui are determined to ensure the large classification ability of the Zui. In the production process, the impeller speed and air volume can be adjusted to meet the particle size requirements of the finished dust.
4 Application Situation After years of research and development, Tianhua Chemical Machinery and Automation Research and Design Institute developed the φ350 and vertical φ1100 vertical micro-powder dryers in 2000. In 2003, the φ800 horizontal and φ1100 horizontal micro-powder dryers were successfully developed. The dryer has been patented and successfully applied to industrial installations. The micronized dryer is very suitable for the drying of paste-like viscous materials. When used to dry high-viscosity viscous materials, if the moisture content of the final product is very low, the micro-powder dryer alone has a small output and consumes a large amount of energy. At this time, it is advantageous to use two-stage drying.
For materials that are loose or not very viscous, any material that can be used in a rotary flash dryer can be dried by a micro-powder dryer. Moreover, the micronized dryer is more effective when applied to these materials. By modifying the rotor structure, the micronized dryer can be applied to the drying of organic materials such as nitrile rubber. In the wet state, the nano-materials have great viscosity due to the strong surface bonding, which leads to agglomeration of the materials, poor mobility, difficulty in transportation, and difficulty in drying. In the drying process, this combination of forces causes material reunion and affects product performance. Therefore, the material should be bridged during the drying process and the reunion material should be effectively dispersed. In addition, nanomaterials generally contain modifiers, both organic and inorganic, which are easily decomposed by heat. Therefore, the heat sensitiveness of the material needs to be considered when drying the nanomaterial.
The mixing of the micro-powder dryer has a strong crushing ability and dispersing ability, and can disperse the reunion material and classify it by the classifier, which can fully meet the particle size requirement. At the same time, the residence time of the material in the micro-powder dryer is very short, and the material does not deteriorate. The micro-powder dryer developed by Tianhua Institute has been successfully applied to the drying of materials such as nano calcium carbonate, nano aluminum hydroxide, fine powder aluminum hydroxide and nano magnesium hydroxide.
The nano-calcium carbonate production line of a factory in Inner Mongolia has exceeded the standard large particles due to the use of a rotary flash dryer, which cannot meet the requirements. In January 2002, the manufacturer and the hospital were transformed. Later, the manufacturer adopted the micro-powder dryer developed by our institute, and the product performance was greatly improved, which fully met the requirements of the manufacturer. This fully demonstrates the superiority of the micronized dryer.
In addition, the micronized powder dryer can also directly dry the slurry material such as molecular sieves and the like.
5 Conclusion The micro-powder dryer is a new type of dryer developed on the basis of rotary flash dryer. However, the structure of the micro-powder dryer is more advanced and the performance is superior, especially suitable for the drying of ultra-fine materials. The manufacturing cost of the micronized dryer is much higher than that of the rotary flash dryer. Today, with the development of nanotechnology, the application range of micro-powder dryers will become wider and wider.
Development of a new type of micro-powder dryer
1 Working principle The working principle of the micro-powder dryer is basically the same as that of the rotary flash dryer. Both of them use the principle that the rotating airflow and the material particles generate a large relative motion, thereby enhancing the heat and mass transfer to complete the drying of the material. The difference is: the micro-powder dryer has stronger crushing and dispersing ability, which is very suitable for the drying of ultra-fine materials; the micro-powder dryer has an adjustable classifier, which can conveniently control the particle size of the product; the structure of the micro-powder dryer is more Advanced, inspection and maintenance is more convenient. The micro-powder dryer is a multi-functional dryer that combines drying, crushing and grading.
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