US JUICE ® SPRAY DRYING

Spray Drying Systems (Open and Closed). The essential elements of the spray dryer: atomizer, air disperser, drying chamber, inlet and exhaust air handling are combined into a system that meets individual operational safety, environmental protection, and powder handling requirements. All spray drying systems can be provided with post-treatment equipment: fluid bed dryer/cooler, agglomerator, de-duster and conveyor.

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Open Spray Drying System. Featuring once-through airflow with exhaust to atmosphere. The majority of industrial spray drying systems handle aqueous feedstocks and use this system. Both direct and indirect air heating are applicable. Exhaust air cleaning in cyclones, bag filters, electrostatic precipitators, and scrubbers.

Closed Spray Drying System. Featuring once-through airflow with exhaust to atmosphere. The majority of industrial spray drying systems handle aqueous feedstocks and use this system. Both direct and indirect air heating are applicable. Exhaust air cleaning in cyclones, bag filters, electrostatic precipitators, and scrubbers.

Spray Drying Technology- Process Principles. Spray drying is the most widely used industrial process involving particle formation and drying. It is highly suited for the continuous production of dry solids in either powder, granulate or agglomerate form from liquid feedstocks as solutions, emulsions and pumpable suspensions. Therefore, spray drying is an ideal process where the end-product must comply with precise quality standards regarding particle size distribution, residual moisture content, bulk density, and particle shape. Spray drying involves the atomization of a liquid feedstock into a spray of droplets and contacting the droplets with hot air in a drying chamber. The sprays are produced by either rotary (wheel) or nozzle atomizers. Evaporation of moisture from the droplets and formation of dry particles proceed under controlled temperature and airflow conditions. Powder is discharged continuously from the drying chamber. Operating conditions and dryer design are selected according to the drying characteristics of the product and powder specification.

Principles. Every spray dryer consists of feed pump, atomizer, air heater, air disperser, drying chamber, and systems for exhaust air cleaning and powder recovery.

Widely varying drying characteristics and quality requirements of the thousands of products spray dried determine the selection of the atomizer, the most suitable airflow pattern, and the drying chamber design.

Atomization. The formation of sprays having the required droplet size distribution is vital to any successful spray dryer operation so that powder specifications can be met. Atomization is a high technology area employing the development and use of nozzles and rotary atomizers in spray drying.

Airflow. The initial contact between spray droplets and drying air controls evaporation rates and product temperatures in the dryer. There are three modes of contact:

Co-current Airflow. Drying air and particles move through the drying chamber in the same direction. Product temperatures on discharge from the dryer are lower than the exhaust air temperature, and hence this is an ideal mode for drying heat sensitive products. When operating with rotary atomizer, the air disperser creates a high degree of air rotation, giving uniform temperatures throughout the drying chamber. However, an alternative non-rotating airflow is often used in tower or Filter mat-type spray dryers using nozzle atomizers with equal success.

Counter-current Airflow. Drying air and particles move through the drying chamber in opposite directions. This mode is suitable for products which require a degree of heat treatment during drying. The temperature of the powder leaving the dryer is usually higher than the exhaust air temperature.

Mixed flow Airflow. Particle movement through the drying chamber experiences both co-current and counter-current phases. This mode is suitable for heat stable products where coarse powder requirements necessitate the use of nozzle atomizers, spraying upwards into an incoming airflow, or for heat sensitive products where the atomizer sprays droplets downwards towards an integrated fluid bed and the air inlet and outlet are located at the top of the drying chamber.

Atomizers. Three types of atomizers are used in industrial drying:

• Rotary Atomization by Centrifugal Energy
• Pressure Nozzle Atomization by Pressure Energy
• Two - fluid nozzle Atomization by Kinetic Energy

The choice of atomizer depends upon the properties of the feed and the dried product specification. In cases where more than one atomizer type is suitable, the rotary atomizer is generally preferred due to its greater flexibility and ease of operation. The advantages include: handling of high feed rates without need for atomizer duplication, handling of abrasive feeds, no blockage problems, low pressure feed system, and ease of droplet size control through wheel speed adjustment.

A range of rotary atomizers, including the worlds largest, covering feed rates up to 200 t/h. Power requirements up to 800 kW.

Food product spray dryers are designed specially for integration into batch or continuous operations under sanitary or aseptic conditions to produce in powder or agglomerated form include the following: coffee/coffee substitutes, food colors, fruit and vegetable juice powders and maltodextrin, soup mixes and teas, and spices and herbs.