The Spray-drying plant allows the production of low and medium density detergent powders, covering the full range of commercial formulations including the post-addition of thermosensitive components, up to powder packaging.
Solid raw materials pneumatic transport
Solid raw materials can reach the detergents production plant in bags, big-bags or even in bulk, and from their storage shall be transferred the daily silos in the process plant.
Desmet Ballestra can offer diluted phase and dense phase pneumatic transport systems suitable to convey solid raw materials by means of transport air supplied by blowers, whose characteristics are selected according to the type of transfer and the relevant duty.
Sieving devices, as well as dedusting solutions, ensure smooth operation and cleanness of the working environment.
Insoluble solid raw materials and liquid ingredients shall be intimately mixed to produce a concentrated and homogeneous slurry suitable for spray-drying.
In the most updated configuration, slurry preparation is performed batchwise, by means of automatic raw materials dosing directly in the crutcher, which is provided with a special high turbulence stirrer that prevents lumps formation.
Each production recipe has a pre-set dosing sequence in the Control System, which allows to weigh each raw material without manual activities of the operators.
On/off valves, mass flowmeters and load cells ensure accurate dosing of the raw materials, granting constant composition of the product, compliance to the desired formulation and control of the ingredients consumption.
LABS neutralisation with caustic soda is also performed in the crutcher, during the slurry preparation sequence.
The slurry is mixed and finally discharged into the ageing vessel, where itis further homogenised. The ageing vessel acts also as a buffer volume, as all the downstream operations are continuously performed.
The main advantages of Desmet Ballestra's design for the slurry preparation system are:
- homogeneous slurry composition and constant physical characteristics;
- slurry preparator with high‑efficiency heat control;
- high concentration of solids in the slurry, thus obtaining a high capacity with low fuel consumption.
After ageing, the slurry passes through a self‑cleaning filter to break lumps eventually present in the slurry; then a booster pump feeds the slurry to the High Pressure Pump at an automatically controlled pressure.
The proprietary Desmet Ballestra High Pressure Pump has been specifically designed to handle viscous and abrasive slurries at a pressure up to 70 bar.
It is an alternating pump with single‑acting plungers. Pump delivery flowrate is continuously adjusted according to the plant capacity, by regulating the rotation speed.
The constant high pressure and the regular pumping, achieved also with highly concentrated slurry, allow to obtain a final product of strictly constant characteristics.
From the High Pressure Pump, the slurry is fed to the spray-drying tower.
The washing waters of slurry preparation/pumping line, and water of mechanical seals are collected in a pit and recycled to the process.
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 optimization of the design of hot-air inlet ducts and the design and positioning of slurry distribution nozzles, achieved through Computational Fluid-Dynamics simulation, result in overall improvement of the drying path through the Spray-Tower, granting operation with high differential temperatures and consequent optimum thermal efficiency.
All the operating conditions are automatically adjusted by setting the proper parameters at the required optimum value, for controlled heat and mass balance of the process.
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, via a special distribution ring, and from there flows up to the top of the tower coming into contact with the slurry spray falling down from the top.
The detergent powder is discharged from the tower 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.
The detergent powder finally collected in the air-lift bottom cone is 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.
Post-addition and perfuming
The base powder obtained by the steps of spray-drying and subsequent product conditioning does not contain those components that, due to their chemical characteristics, are sensitive to temperature 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.
Heat Recovery System (HRS)
Special care is given to energy saving and to reduce the overall fuel and electric power requirements.
The thermal recovery is based on a recirculating water closed loop whose principles are:
- The exhaust hot air coming from the dedusting filter passes through a special plate heat exchanger and is cooled down by means of the recirculating water (pumped by centrifugal pump) which flows in the exchanger countercurrent to the air.
- The exchanger is equipped with a dedicated nozzle for special cleaning in place (CIP), designed to spray process water on the plates and keep them clean.
- The recirculating water, now heated-up, is then cooled down in the pre-heater, heating up the combustion air which is sent to the burner.
- The unit is completed by the expansion tank, for the volume compensation inside the water recirculating circuit.
Main Characteristics of the Heat Recovery System
- The HRS allows the heat recovery of the exhaust air discharged from the spray tower, which otherwise is lost
- The Heat Exchanger installed on the hot air line is designed to deal with dust loaded air and includes integrated CIP system
- Compact heat exchanger enabling an easy installation in all existing plants
- The HRS offers a substantial energy savings as it allows to save, depending on the ambient conditions, 10% to 18% fuel consumption
- Good thermal operating efficiency, due to high heat transfer coefficients
- Heat recovery with constant condensation.
- Investment with short pay-back period
- Significant reduction of CO2 emissions
- Compact design and simple installation
- Low maintenance cost
- Long life due to stable and durable corrosion resistant materials
- No expensive interruptions since the cleaning takes place during production.
For large plants capacities, whenever required by local conditions, Desmet Ballestra has also studied and implemented co-generation systems based on the use of gas turbines to produce electric power, and on the use of relevant hot exhaust gases in the spray-drying tower to substantially increase the overall plant efficiency.
SABIZ process control
The SABIZ plant is monitored 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 minimizes the labour requirements for plant operation.
Many different pre-set 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 analogic 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.