Spray Drying Tower process
Spray-drying plant for the production of detergent powders of low and medium
density, covering the full range of commercial formulations including a post
addition of thermosensible components, up to powder packaging.
The slurry is pumped to a spray nozzles circuit installed in the upper part of
the spray tower.
The size and number of nozzles depends on the plant capacity and required
The spray is generally of the hollow cone type and nozzle size generally varies
in diameter from 3 to 5 mm with a spray angle in a range of 50-70°.
In the spray tower the special design of the hot air distribution chamber allows
operation with high differential temperatures i.e.: hot air inlet temperature up
to 400-450°C, exhaust air outlet temperature down to 85-90°C with consequent
optimum thermal efficiency.
The optimization of the design of hot-air inlet ducts and the design and
positioning of slurry distribution nozzles result in overall improvement of the
drying path through the Spray-Tower.
This fact, together with the increase of solid matter content in the slurry and
the increase of hot-air temperature, results in increased evaporation efficiency
of the Spray-Tower.
All the operating conditions are automatically adjusted by setting the proper
parameters of fuel feeding, air flow, slurry concentration and all
pressures/temperatures at the required optimum value, for controlled heat and
mass balance of the process.
The characteristics of the powder beads are largely determined by direction,
velocity and temperature of the hot air stream.
The hot air is generated in furnaces purposely designed to obtain smokeless
The most commonly available fuels (ranging from natural gas to heavy fuel oils),
can be utilized without causing inconveniences nor affecting the whiteness of
the finished products.
The hot air is conveyed to the lower part of the spraying tower. Two fans,
determining the pressure conditions of the air circuit, are installed for
regulation of the air-flow passing through the tower. By means of this circuit
the hot air is conveyed via a special distribution ring located at the bottom
and from there up to the top of the tower coming into contact countercurrently
with the slurry spray falling down from the top.
The detergent powder with bulk density in the range of 200-450 g/l, is
discharged from the tower at a temperature of 60-70°C and is transferred by
means of a belt, to a continuous crystallization unit (air-lift), where it is
conveyed upward by a flow of ambient air that cools it down so completing the
drying and initiating the particles surface crystallization.
By this way the product is also lifted up to such a height as to allow the next
operations by a gentle gravity-discharge avoiding as much as possible any
breaking of the hollow beads.
Both the drying and transport air are sucked through sleeve filters before being
discharged to the atmosphere.
The separated fines are reblown into the spray tower, close to the slurry
spraying zone, so as to fully recover them by agglomeration with the slurry
The detergent powder finally collected in the air-lift bottom cone are
discharged into a sieve to remove any coarse agglomerated/wet material before
eventual post addition, perfuming and packaging. The coarse material from the
sieve is reprocessed via a separate dry or wet mixing/milling directly into the
slurry preparation step.
The base powder obtained by the steps of spray-drying and subsequent product
conditioning doesn’t contain those components that, due to their chemical
characteristics, are sensitive to increased temperatures and consequently have
to be incorporated into the powder recipe in a way that preserves their chemical
and physical structure.
The step of Post-Addition of these components is performed in a special Rotary
Blender where the base powder and the thermosensitive component (both solids and
liquids), are gently and intimately mixed and agglomerated, so resulting in a
final product having characteristics of regular shape, high flowability and
chemical stability / homogeneity. The configuration of the post-addition unit
can be very different according to the specific requirements of the final powder
formulation and plant capacity.
For high production rates a continuous unit is recommended, which can be
configured similarly to what is foreseen for the COMBEX section (Spray-Drying
SABIZ process control
The SABIZ plant is operated by a Computer Control System “CCS” specifically
designed for reliable and performing operations with an easy to use and friendly
The computer control system ensures a trouble free plant operation with the
automatic control of all the critical process parameters. It also guarantees a
high dosing accuracy and therefore the accuracy and consistency of the product
formulations. Moreover, the computer control system reduces to a minimum labour
requirements for plant operation.
Up to 100 different preset formulations can be stored in the computer memory and
the system automatically adjusts all process parameters and dosing devices to
achieve the final formulation selected by the operator.
The CCS is built using the most advanced architecture that includes a PLC for
process and production data control. The PLC is foreseen for digital and analog
signals handling and it is provided with one or more CPU, designed to make all
controls (PID loops, data acquisition, alarming, interlocks, sequences, etc.) by
The supervisory system based on PC establishes a “friendly interface” with the
operator, through an animated process video screen-layout, diagrams, trends,
list of process variable figures, operators entry windows, etc.
The PC will run the Windows NT Workstation operating system and Logoview NT HMI/SCADA