What are fluid bed dryers?
Fluid bed dryers are designed to dry powder particles, where the residual moisture content is higher than what is wanted in the final powder. Hot drying air is distributed through specially designed perforated plates, on which the powder particles/agglomerates are resting.
The velocity of the drying air makes the powder ‘fluidize’, i.e. the particles get airborne; however, to the extent that only the finest/smallest particles leave the fluid bed with the air, while the bigger particles/agglomerates are conveyed/transported with the upward and forward directed flow of air (due to the perforation technique of the plate) into the subsequent section. Here cold and/or dehumidified is introduced to cool the powder to the wanted temperature.
Fluid bed drying is suited for powders, granules, agglomerates and pellets with an average particle size between 50 microns and 5 mm.
What does GEA Niro offer?
GEA Niro offers two types of basic fluid bed designs, both individually designed to the solids flow pattern in the dryer.
- The integrated fluid bed is a back-mix fluid bed – typically connected directly below the drying chamber - from where moist powder, which is non-fluidizable, enters. It is used in the MSD™/FSD™ , the IFD™ and in a COMPACT DRYER™. The moisture content of the already fluidizing powder is lower than the powder that enters. The product temperature and moisture remain uniform throughout the fluidized layer. By controlling the powder layer in the back-mix fluid bed, the residence time can be controlled.
- The VIBRO-FLUIDIZER™ is a plug-flow fluid bed applied for powders that are directly fluidizable. The design of this type of fluid bed is important for achieving a narrow and controlled residence time distribution. The powder passes through the VIBRO-FLUIDIZER™, while coming close to equilibrium with the incoming drying air.
To facilitate the fluidization the powder is vibrated on the air distributor plate (patented), welded on to the fluid bed house. The effect of this vibration combined with the upward and forward directed flow of air through the plate creates ideal processing conditions and powder transport. The unit operates with a powder layer of approx. 200 mm. This gives a much more lenient powder treatment, since powder residence times are shorter than in non-vibrating fluid beds, which operate at much deeper powder layers.
The VIBRO-FLUIDIZER™ from GEA Niro
The VIBRO-FLUIDIZER™ is successfully used on all types of powders, agglomerates, and granulates; especially those with a broad particle size distribution or highly irregular shape, or which require relatively low fluidization velocities to prevent attrition. The VIBRO-FLUIDIZER™ is typically used as after-dryer/cooler in MSD™FSD™ plants or directly connected to conventional dryers or a TALL FORM DRYER™.
The VIBRO-FLUIDIZER™ can be operated as a separate drying or cooling unit. It is often associ-ated with a spray drying system to produce agglomerated instant powder or act as a powder con-ditioning plant for special coating operations.