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 product granulometry.
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 combustion.
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 droplets.
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 plus Agglomeration)
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 operator interface.
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 programmable logic.
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 package.