Spray Drying & Encapsulation
 | NozzleThe two-fluid nozzle disperses the liquid into fine droplets, which are dried quickly and gently in the drying chamber. |
Spray drying involves evaporation of moisture from an atomised feed by mixing the spray and the drying medium. The drying medium is typically air. The drying proceeds until the desired moisture content is reached in the sprayed particles and the product is then separated from the air. The mixture being sprayed can be a solvent, emulsion, suspension or dispersion.
Here all the detail are brougth together - the functional principle of the Mini Spray Dryer B-290
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The B-290 two fluid nozzle
The intelligent design of the B-290 reduces preparation and cleaning times to a minimum! That means more productivity and efficiency in the current development process. The details of the innovative nozzle are:
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Example:
100 ml of a solution are sprayed, resulting in approx. 8 x 108 = 800,000,000 drops (25 microns) representing approx. 12 m2 of surface area. This clearly demonstrates that the solvent (mainly water) is vaporized extremely quickly.
Cyclone technology
The glass cyclone used as a separator is a dust collection device widely used in industry for more than a century. The main advantages are its simple construction and absence of moving parts. Separation is based on the inertial deposition of the particles from the gas stream. In the reverse flow cyclone, the gas is made to spin by introducing it tangentially. This produces centrifugal forces up to hundred to thousand times greater than gravitational force. The particles move towards the wall and the base of the cyclone, while the gas spirals upwards to the gas outlet at the top of the cyclone.
BUCHI Labortechnik offers a bench-top Spray Dryer with glass cyclone incorporating an electrically conductive layer to prevent electrostatic binding and thus product loss in the cyclone. The effect of this coating strongly depends on the material properties, e.g. for proteins, no difference can be detected, whereas for lactose as a typical matrix substace in pharmaceutical applications, the difference in separation performance is obvious.
BUCHI offers two diferent kinds of cyclones. The standard cyclone for standard applications with particles in the range of 3 µm to 25 µm and a high performance cyclone for small sample amounts and better yields also for smaller particles down to 1 µm.
Dependance of inlet and outlet temperature
Inlet temperature is understood as being the temperature of the heated drying air. The drying air is sucked or blowed in over a heater by the aspirator. The heated air temperature is measured prior to flowing into the drying chamber. When spray drying a solution, emulsion or dispersion the solvent is removed by vaporization.
The temperature of the air flow does not have to be higher than the boiling point of water to evaporate the individual drops during the short residence time. The gradient between wet surface and not saturated gas leads to an evaporation at low temperatures. The final product is separated and has no further thermal load.
The temperature of the air with the solid particles before entering the cyclone is designated as the outlet temperature. This temperature is the resultig temperature of the heat and mass balance in the drying cylinder and thus cannot be regulated. Due to the intese heat and mass transfer and the loss of humidity, the particles can be regarded to have the same temperature as the gas. Thus, as a rule of thumb is: outlet temperature = max. product temperature. Due to this fact spray drying is a very gentle methode to dry powders.