Spray drying foodstuffs
All the leading food processing companies use spray dryers to produce powdered products. Spray drying has the ability to handle heat sensitive foods with maximum retention of their nutritive content. The flexibility of spray dryer design enables powders to be produced in the various forms required by consumer and industry. This includes agglomerated and non-agglomerated powders having precise particles size distribution, residual moisture content, and bulk density.
The spray drying process
Spray drying transforms a liquid foodstuff into dry powder. The process involves the atomization of liquid into a spray using either rotary or nozzle atomizers. The spray is contacted with hot air entering the drying chamber through a roof air disperser. Evaporation of moisture, particle formation, and drying proceed under controlled conditions of low product temperature processing. The product is discharged continuously from the drying chamber and fines entrained in the exhaust air are recovered in cyclones. Operating temperatures and spray dyer designs are selected according to the powder specification and drying characteristics. Spray dryers for food products often feature vibrating fluid bed attachments for powder moisture content adjustment, agglomeration or cooling. These fluids beds conform to 3A standards.
Foodstuffs in powder or agglomerated form
The desired powder characteristics and operating economy decide the choice.
The basic system is a co-current spray dryer featuring rotary or nozzle atomization. Fines entrained in the exhaust air are recovered in cyclones. Bagfilters can be installed to meet extra low environmental emission levels. This system is used, where drying can be completed in the drying chamber alone, and powder on discharge meets the quality specification. Standard non-agglomerated powders are produced.
The two-stage system involves attaching to the drying chamber base a vibrating fluid bed for product after-drying, agglomeration and cooling.
The compact system is a co-current integrated fluid bed spray dryer. The location of the fluid bed within the drying chamber permits drying to be achieved at lower temperature levels resulting in higher thermal efficiencies and more lenient powder handling. The chamber can be equipped with pneumatic transport system for non-agglomerated powders and with a vibrating fluid bed for agglomerating or cooling powders.
The fluidized spray dryer system is mixed-flow integrated fluid bed unit and offers excellent product flexibility and thermal efficiency. The product is sprayed down on the fluid bed, and the drying air is exhausted through the roof creating a high airborne powder loading in the drying chamber. Free-flowing, readily dispersible powders in instant, agglomerated or standard form can be produced. Hygroscopic and sticky products that cannot be handled in other systems can be successfully dried. The fluidized spray dryer can be equipped with a vibrating fluid bed for powder conditioning or cooling.
The tall form system is a co-current, parallel-flow nozzle tower with fines return capability. The atomized spray dries while gently falling down the tower, and the resulting powder is effectively separated in the enlarged chamber cone section. A vibrated fluid bed can be mounted under the cone section, where after-drying or cooling is necessary. This system is recommended for products with high fat and carbohydrate content.
The coffee tower is a special tall form system with an air disperser for drying foodstuffs of high aroma.
All spray dryer designs are supplied with a semi- or fully automatic cleaning-in-place (CIP) system featuring special retractable CIP-nozzles (positioning by water pressure only) and water-tight dampers that isolate wet washing areas from equipment containing powder.
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