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C. Neugebauer et al.
the influence of drying conditions on layer formation and properties with meso-scale
information of particle flow and recirculation between process chambers separated by
weirs. On the macro-scale, population balance modeling is used to describe the overall process dynamics taking into account apparatus design and process conditions.
New process regime maps are presented along with control concepts to guarantee
stable and safe operation as well as desired particle properties.
1 Introduction
Spray layering (granulation) is a particle formulation process in which a solid containing liquid is sprayed onto a collection of core particles. The droplets collide with
the cores and wet their surface. Supplying a heated gas flow, the liquid evaporates and
the solid remains on the core particle surface. By continued spraying and evaporation,
full layers can be obtained. As a consequence, the particles grow in size.
Horizontal fluidized beds are a key technology in spray layering, with widespread
application in the areas of food, feed, fine chemicals and pharmaceuticals. They
can be used to combine more than one operation in a single apparatus, for example
layering of particles with a solid-containing liquid, followed by drying and cooling.
For this, the apparatus can be compartmentalized along the apparatus length, by
installation of weirs, creating different process chambers (Fig. 1).
Installation of weirs generates a residence time distribution (RTD) of the particles
in the apparatus, as the passing of a weir by an individual particle depends on the
particle properties, for example mass density, sphericity, as well as the fluidization
conditions. Residence time distributions are known to cause product property distributions, for example differences in particle size in granulation, or product moisture
content in drying operation.
The knowledge of the effect of an individual weir, parameterized with respect to
particle properties and fluidization conditions, would allow answering a number of
important design questions, for example how many weirs are required in an apparatus
to obtain a desired spread of the residence time distribution, and therefore guide the
design and operation of horizontal fluidized beds.
Furthermore, thermal conditions influence the dynamics of the evaporation process and thereby the dynamics of layer formation and layer properties, for instance
layer thickness and porosity. These in turn influence the evolution of the particle size
distribution.
Product classification in continuous operation can be performed internally and
externally, for example by a screen-mill cycle. Here, the particle size distribution in
the horizontal fluidized bed determines the dynamics of the process including the
classification, for example the magnitude and time-scale of recycle flows or loads on
screens and mill, influencing their efficiency.
Due to the multi-scale interaction, starting with single-particle layer formation
dynamics over particle flows between adjacent process chambers to large-scale pro-
C. Neugebauer et al.
the influence of drying conditions on layer formation and properties with meso-scale
information of particle flow and recirculation between process chambers separated by
weirs. On the macro-scale, population balance modeling is used to describe the overall process dynamics taking into account apparatus design and process conditions.
New process regime maps are presented along with control concepts to guarantee
stable and safe operation as well as desired particle properties.
1 Introduction
Spray layering (granulation) is a particle formulation process in which a solid containing liquid is sprayed onto a collection of core particles. The droplets collide with
the cores and wet their surface. Supplying a heated gas flow, the liquid evaporates and
the solid remains on the core particle surface. By continued spraying and evaporation,
full layers can be obtained. As a consequence, the particles grow in size.
Horizontal fluidized beds are a key technology in spray layering, with widespread
application in the areas of food, feed, fine chemicals and pharmaceuticals. They
can be used to combine more than one operation in a single apparatus, for example
layering of particles with a solid-containing liquid, followed by drying and cooling.
For this, the apparatus can be compartmentalized along the apparatus length, by
installation of weirs, creating different process chambers (Fig. 1).
Installation of weirs generates a residence time distribution (RTD) of the particles
in the apparatus, as the passing of a weir by an individual particle depends on the
particle properties, for example mass density, sphericity, as well as the fluidization
conditions. Residence time distributions are known to cause product property distributions, for example differences in particle size in granulation, or product moisture
content in drying operation.
The knowledge of the effect of an individual weir, parameterized with respect to
particle properties and fluidization conditions, would allow answering a number of
important design questions, for example how many weirs are required in an apparatus
to obtain a desired spread of the residence time distribution, and therefore guide the
design and operation of horizontal fluidized beds.
Furthermore, thermal conditions influence the dynamics of the evaporation process and thereby the dynamics of layer formation and layer properties, for instance
layer thickness and porosity. These in turn influence the evolution of the particle size
distribution.
Product classification in continuous operation can be performed internally and
externally, for example by a screen-mill cycle. Here, the particle size distribution in
the horizontal fluidized bed determines the dynamics of the process including the
classification, for example the magnitude and time-scale of recycle flows or loads on
screens and mill, influencing their efficiency.
Due to the multi-scale interaction, starting with single-particle layer formation
dynamics over particle flows between adjacent process chambers to large-scale pro-