What are the spray methods of fluidized bed coater

      In the fluidized bed granulation or pelletizing and coating process, the spray method should be selected according to the properties of the materials and the product quality in the plan. There are currently three methods of fluidized bed spraying, namely top spray, tangential spray and bottom spray, as shown in the figure.

 

       (1) Tip spray

       Most products condensed during fluidization use this method. The granules produced are characterized by porous surfaces and interstitial voids, and have a small bulk density, which is an effective method to increase the dissolution rate of poorly soluble drugs, because granules or pellets It absorbs liquid easily and disintegrates quickly, such as drying and granulating of Chinese medicine extract.

       (2) Tangential spray

       It uses the centrifugal force generated by the rotation of the turntable to obtain a high-intensity mixing effect, which is combined with the drying efficiency of the fluidized bed to produce a product with a high bulk density, but still a small amount of gaps and voids. The particles have a large hardness and are not easy to break. , And close to spherical, is a common method for preparing pellets.

       (3) Bottom spray

       The nozzle is set in the baffle at the center of the air distribution plate, and the fluidized particles, pellets or tablets receive the adhesive or coating solution in the baffle. It is currently the most commonly used coating method for pellets, which has the advantages of high coating efficiency and the pellets are not easy to stick. Xinyite has developed an on-line adjustment of the inside and outside air flow of the deflector, and an improved fluidized bed with on-line cleaning of the spray device, which greatly improves the controllability of the fluidized bed pellet coating.

 

       The above three spray methods can be used for granulation, pellet preparation and coating in a fluidized bed. However, tablet coating is limited to the bottom spray type. The core of the fluidized bed granulation and coating process is a liquid spray system. In almost all fluidized bed equipment, the role of the nozzle is dual, namely granulation and coating. The liquid is ejected through an orifice under low pressure and atomized by the air flow. This nozzle can produce smaller droplets, which is an advantage for the coating of particles or pellets, but it also brings It is because the evaporation surface increases, and the small droplets quickly transform into solid concentrates during the forward movement process, and their viscosity also increases. If the spray speed, solution concentration and fluidization temperature are not properly matched, some small droplets When in contact with the surface of granules or pellets, it cannot spread evenly, form a less complete film or make the granules and pellets unevenly formed, and even form an adhesive or coating material that itself dries into granules or pellets, resulting in The quality is unstable or substandard. This problem is exacerbated if the heat of solvent evaporation of the atomized solution is low. Some common solvents for spraying and their evaporation heat are shown in the table.

Evaporation heat of common solvents

 

       In top-type spray granulation and coating, the flow of granules and pellets is the most chaotic, and the spray direction of the adhesive or coating liquid is facing the evaporation medium. The self-drying of the droplet is also the most serious, and the loss is also large. The coating effect is poor and the product quality is not stable enough. Nevertheless, a considerable amount of granulation, pelleting and coating processes are still carried out by top spraying. This is due to its two major advantages. One is that the production scale is much larger than other The second method is simple structure and convenient operation. For a production scale top spray granulation and coating equipment, only one nozzle and one pump are required. In contrast, the remaining two spray methods generally use multiple nozzles and pumps. In this way, the former needs to consider much less variable parameters in the production operation, and the cleaning cycle is short.