What are the spray methods of the fluidized bed coating machine?

In fluidized bed granulation or pelleting and coating, the spray method should be selected based on the properties of the material and the quality of the product being planned. There are currently three fluidized bed spray methods, namely top spray, tangential spray and bottom spray, see figure.

(1) Top-type spray Most of the products condensed in fluidization use this method. The produced particles are characterized by porous surface and interstitial voids, and the bulk density is small, which is an effective method for increasing the dissolution of poorly soluble drugs. Because the particles or pellets are easy to absorb liquid, disintegration is faster, such as drying and granulation of Chinese medicine leachate.

(2) Tangential spray It uses the centrifugal force generated by the rotation of the turntable to obtain a high-strength mixing effect, 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. It has a large hardness, is not easily broken, and is close to a spherical shape, and is a common method for preparing pellets.

(3) Bottom spray A nozzle is placed in the guide tube at the center of the gas flow distribution plate, and the fluidized particles, pellets or tablets receive the binder or coating solution in the draft tube. It is a commonly used micropellet coating method, which has the advantages of high coating efficiency and low adhesion of pellets. Xinyi Special has developed an improved fluidized bed in which the air volume inside and outside the guide tube can be adjusted online, and the spray device can be cleaned online, which greatly improves the controllability of the fluidized bed pellet coating.

The above three spray methods are all available for the preparation of granules, pellets and coatings in a fluidized bed, however, the tablet coating is limited to the bottom spray type. At the heart of the fluidized bed granulation coating process is a liquid spray system. In almost all fluidized bed equipment, the nozzle functions in a dual manner, namely granulation and coating. The liquid is ejected through an orifice at low pressure and atomized by a gas stream. This nozzle produces smaller droplets, which is an advantage for the coating of pellets or pellets, but with the consequent The evaporation surface increases, and the small droplets rapidly change into a solid concentrate during the forward movement, and the viscosity thereof also increases. If the spray speed, the solution concentration, and the fluidization temperature are improperly matched, some small droplets are formed. When in contact with the surface of the granules or pellets, it may not spread evenly, forming a less complete film or making the granules, pellets unevenly formed, or even forming the binder or coating material itself to dry into granules or pellets, resulting in a product The quality is unstable or unqualified. This problem becomes more serious if the solvent evaporating heat of the atomized solution is low. Some solvents commonly used for spraying and their heat of evaporation are shown in the table.

Evaporation heat of common solvents

In top-end spray granulation and coating, the flow of granules and pellets is disorganized, and the direction of spraying of the binder or coating liquid is opposite to the evaporation medium. The droplets themselves are also very dry and the loss is also large. The coating effect is poor and the product quality is not stable enough. However, a considerable amount of granulation, pelleting and coating processes are still carried out by top spray, which is due to its two advantages, one of which is much larger than other The second method is simple structure and convenient operation. A production-scale top-jet granulation and coating equipment requires only one nozzle and one pump. In contrast, the other two spray methods generally use multiple nozzles and pumps. In this way, the variable parameters that the former needs to consider in the production operation are much less, and the cleaning cycle is also short.