2001 Volume 3 Issue 1 Pages 20-27
Spray drying is used as a very convenient means for drying liquid into powder instantly, continuously and economically in laboratory use and large production, but at high temperature, e.g. over 100°C as inlet air temperature. Freeze-drying is a typical drying technology for drying heat-sensitive products at 20-50°C during desorption drying, but for several hours. Due to invention of Four Fluid Nozzle (patented in USA, Europe and Japan), spray drying at low temperature closer to atmospheric temperature below 80°C as hot air temperature is possible and therefore a new drying technology as low temperature spray drying has been realized based on the principle of quicker drying speed by huge heating surface area of droplets minimized below abt. 10 μm by the new nozzle. The Four Fluid Nozzle, which was developed by the design concept of minimization and uniformity of droplet size for quicker drying speed and elimination of wet deposits on chamber wall, has a special acceleration zone on it for forming thin film of liquid just before atomization in addition to a focusing point of compressed air as a newly designed structure for removing loss of atomization energy. Thus, the droplet size distribution is in a very narrow range resulting in the uniform particle size distribution of dry powder all in a single micron. The smaller and uniform droplet size makes heating surface area bigger by abt. 10 times compared with conventional atomization systems and so such smaller droplets are dried quickly and completely before reaching chamber wall even at low temperature without wet deposits on chamber wall. The geometry of the new nozzle is quite the same even in smaller or larger types of the nozzles and so the quality of dried product is also the same even in case of the so-called circle nozzle for larger production scale, for example having the atomization capacity of max. 1000 Itr/h. There is a possibility that conventional low temperature drying technology like freeze-drying, vacuum drying, etc. can probably be replaced by the low temperature spray drying technology. Drying of parenteral drugs will also be possible by the new drying technology with Four Fluid Nozzle using CIP/SIP systems, powder recovery system with metal mesh cartridge filter and isolation technology as a validatable system in the near future.