140 120 100 80 60 40 Design evaporation (%)

Figure 17. Variation of efficiency with dryer turndown.

While demands for energy efficient drying may have become somewhat relaxed recently with the stabilizing of energy costs, the fact remains that spray dryers and evaporators are among the most energy-intensive processing systems and the future of energy costs is still uncertain.

The extra functionality that may be required of the powders is to a large extent determined by the drying conditions, including pre- and posttreatment of the concentrate and final powder. Desirable characteristics are dust-free and good reconstitution properties that involve carefully controlled drying conditions, often with added agglomeration and lecithination steps.

The interest in the production of high-value specialty dried products instead of straight commodity products has been accentuated by the government's reduced support to dairy producers, whereby there will be less milk solids available. Processors naturally are looking into ways to better use these available supplies by producing products with improved functional, nutritional, and handling properties and, coincidentally, products with higher profit margins.

This is particularly noticeable in the utilization of whey and whey product derivatives. A larger percentage of the total whey produced today is handled and processed so that it will be suitable as food ingredients for human consumption. It also is finding new applications by being refined into whey protein concentrate and lactose through crystallization, hydrolyzation, and separation by ultrafiltration.

To handle the increase in plant size and complexity and to meet demands for closer adherence to exact product specifications, dryer instrumentation has been improved and operation gradually has evolved from manual to fully automated. Today, it is normal for milk drying plants to be controlled by such microprocessor-based systems as the APV ACCOS, with automation covering the increasingly complex startup, shutdown, and CIP procedures as well as sophisticated automatic adjustment of the dryer operating parameters to variations in ambient-air conditions.

Finally, more stringent demands governing environmental aspects of plant operations have resulted in that virtually all spray dryers today have to be equipped with exhaust air pollution control devices such as wet scrubbers or bag filters.

Principle and Approaches

Spray drying basically is accomplished in a specially designed chamber by atomizing feed liquid into a hot-air stream. Evaporation of water from the droplets takes place almost instantaneously, resulting in dried particles being carried with the spent drying air. The powder is subsequently separated from the air in cyclone separators or bag filters and collected for packaging. The powder particles being protected during the drying phase by the evaporative cooling effect results in very low heat exposure to the product, and the process is thus suitable also for heat-sensitive materials.

A number of different spray dryer configurations are available, distinguished by the type of feed atomization device and the drying chamber design.

Homemade Pet Food Secrets

Homemade Pet Food Secrets

It is a well known fact that homemade food is always a healthier option for pets when compared to the market packed food. The increasing hazards to the health of the pets have made pet owners stick to containment of commercial pet food. The basic fundamentals of health for human beings are applicable for pets also.

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