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What are the spray methods for fluidized bed coating machines?

From:ChangZhou Zhiyang Machinery Equipment Co.,LTD.  Time:2019-1-18 16:27:46  Hits:

     In fluidized bed granulation or pellets and coating process, spray method should be selected according to material properties and product quality in the plan. At present, there are three kinds of fluidized bed spray methods, namely, top type spray, tangential spray and bottom type spray.

      (1) top spray  
          Most products agglomerated in fluidization use this method. The granules produced are characterized by porous surface and interstitial voids. The bulk density is small. It is an effective method to increase the dissolution rate of insoluble drugs because the granules or pellets are easy to absorb liquid and disintegrate quickly, such as drying and granulation of Chinese medicine leachate.
        (2) tangential spray  
          It utilizes centrifugal force produced by rotating disc to obtain high-strength mixing effect and combines with drying efficiency of fluidized bed to produce products with high bulk density, but with a small number of gaps and voids. Particle hardness is high, it is not easy to break, and it is close to spherical. It is a common method to prepare pellets.
        (3) bottom type spray  
          The nozzle is arranged in the draft tube at the center of the air distribution plate, and the fluidized particles, pellets or tablets receive adhesive or coating solution in the draft tube. At present, the most commonly used pellet coating method has the advantages of high coating efficiency, and pellets are not easy to adhere. Xinyi has developed a modified fluidized bed which can adjust the internal and external air volume of the draft tube online, and the spray device can be cleaned online, greatly improving the controllability of pellets coated in fluidized beds.
        The above three spray methods can be used to prepare pellets and pellets for fluidized beds, but the coating is limited to bottom injection. The core of fluidized bed granulation is the spray system of liquid. In almost all fluidized bed equipment, the function of the nozzle is twofold, namely granulation and coating. The liquid is ejected through a hole at low pressure and atomized by the airflow. This nozzle can produce smaller droplets, which is an advantage for pellets or pellets to coat, but with the increase of evaporation surface, small droplets rapidly change into solid concentrates during the forward movement, and the viscosity also increases. If the degree of coordination is not appropriate, some droplets can not spread evenly when contacting with the surface of particles or pellets, forming incomplete film or making the formation of particles and pellets uneven, or even forming binder or coating material itself to dry into particles or pellets, resulting in unstable or unqualified product quality. If the evaporation heat of the solvent in the atomized solution is low, the problem will become more serious. Some spray commonly used solvents and their evaporation heat are shown in tabular form.
Evaporation heat of common solvents
 

        In the top spray granulation and coating, the flow of pellets and pellets is the most chaotic, and the spraying of adhesive or coating liquid is directed towards the evaporating medium. The dripping itself is the most serious, the loss is also large, the granulation and coating effect is poor, and the product quality is not stable. This is because it has two advantages: one is that the production scale is much larger than other methods; the other is that the structure is relatively simple and the operation is convenient. A production scale of top spray granulation and coating equipment requires only one nozzle and one pump. Compared with the other two spray methods, there are usually multiple nozzles and pumps. In this way, the variable parameters of the former need to be taken into account in production operation are much less, and the cleaning cycle is also short.


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