SPECIFICS OF POWDERED FOOD PRODUCTS’ DRYING IN A FLUIDIZED MODE
Abstract
The main methods of drying food powders are considered. One of these, since viewed as the
most important stage in starch production, is selected and its model is considered in detail. In the
food industry various dryers are used. Construction of a dryer should first of all provide uniform
heating and drying of a product and reliable monitoring of its temperature and humidity. Dryers
should have rather high performance, but at the same time they should be cost effective with regard
to specific expenditures of heat and electric power, and should probably have smaller content
of metal. Methods of drying differ by heat input methods. Drying technique uses convective,
conductive (or contact), thermoradiation (by means of infrared rays) methods, and the method of
using high- and super-high frequency currents. The convective method of drying materials is
widely adopted. The drying agent (heated air, superheated steam or a mixture of furnace gases)
performs functions of a heat carrier and moisture absorber. Simplicity, and possibility of regulation
of material temperature are the advantages of this method. But in this method the temperature
gradient is directed to the side opposite to moisture content gradient, what slows down removing
of moisture from material. Another drawback of the convective method of drying are relatively
small values of coefficient of heat transmission from the drying agent to the surface of
material. The possibility of intensification of convective drying are caused by the increase in
heat-mass exchange between material and drying agent by means of increasing speed and temperature
of the drying agent, or by the reduction of the size of particles. In chamber, beltconveyor,
tunnel and tower drying installations process is carried out in a non-moving layer.
Tunnel drying installations are used for drying fruits. Simplicity of design and reliable operation
are characteristic of these installations. Using a mixture of furnace gases with air content may be
cost effective, but there is a danger of generation of cancerogenic substances. In this regard, in
the modern tunnel drying installations the system of drying agent treatment is changed.
