- Dec 22, 2018 -
An important advantage of spray drying process is that the material can actually be any form. Solutions, slurry, pastes, gels, and suspensions can be successfully dried. The initial process of spray drying is optimizing temperature, concentration, viscosity, or other characteristics to produce materials.
Temperature of raw material
The temperature of the material affects viscosity and heat transfer from the dry air in the chamber to the droplets. When selecting nozzle sealing material, the temperature of raw material and the temperature of chamber air should be considered.
Temperature of melting point
Some raw materials are solid at room temperature and need to be melted to be atomized. Granulation or spray cooling produces particles or crystals by injecting molten material into a chamber through which cooling air flows.
When selecting the material for the internal nozzle assembled, the abrasion property of the material should be considered. Tungsten carbide is the preferred material for swirl and orifice plates for most applications. For most raw materials, tungsten carbide has excellent wear resistance and good corrosion resistance.
For some materials, erosion of nozzle components is a worse problem than abrasion.
For these cases, 316 stainless steel may be a good choice.
Solid content is the percentage of raw materials made up of solids. Most raw materials have about 50% solids, but the range is from about 20% to 70%. Increasing the solid content can reduce the amount of water removed during spray drying. As the solid content increases, the material becomes more difficult to pump and atomize.
Surface tension is the force acting on liquid surface and tends to minimize its surface area. Reducing surface tension makes the material more easily atomized.
Viscosity is the resistance of a fluid to flow. The usual unit is centipoise. Increasing viscosity tends to increase droplet size. For some nozzle designs, increasing viscosity tends to increase velocity.