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CHEMICAL TECHNOLOGY
25
-high intensity of drying.
However, it is not widely used in industry due to its high energy consumption (3 kWh of electricity
can evaporate 1 kg of moisture).
Depending on the layers of grain products, there are several types of combined drying. These are the
following types of drying: conductive, radiation or electrical (high-frequency); convective radiation (high
frequency) [12, 20]. Using these methods of drying cereal products is very beneficial to speed up the drying
process, reduce waste, achieve more flexible process control, and deliver all the beneficial substances of the
dried grain and cereal products to the downstream production process.
In large industrial dryers usually corn located in a dense gravity-moving, fluidized or suspended
state layer [5, 11, 15].
The intensity of drying depends on with the state of the layer, which determines the size of the active
surface of the grain in contact with the drying agent. A stationary dense layer is characterized by a
permanently fixed grain contact.
In this case, a decrease in grain moisture during drying does not occur immediately over the entire
layer thickness, but gradually in zones. There is large difference in moisture content of the upper and lower
layers.
To form a gravitationally moving dense layer, it is necessary to continuously feed grain from above
into the dryer and continuously transfer grain falling to the bottom. The drying surface of the grain product
is constantly renewed. During drying, they always touch, despite the fact that each grain moves in the layer.
During the drying process, the grain layer changes its thickness from 0 to 25 sm. When drying grain with a
gravitationally moving dense layer, a drying temperature of 100-170 °C is more effective. Drying the grain
takes 15-20 minutes [4]. Drying of grain with this layer is carried out in most grain dryers.
When the drying process takes place in a fluidized bed, first, the dense layer is loosened, and then
turns into a fluidized state. Such a layer has the properties of mixing, acquiring the properties of a liquid,
and can "boil" like a liquid. With an increase in external influence (air flow), fluidized the layer gradually
becomes suspended. Loosening of the grain layer leads to a decrease in diffusion and thermal resistance at
the boundary phase separation, which contributes to an increase in heat and moisture exchange [6, 17].
One of the dryers that dry grain in a falling layer is the Tselinnaya dryer. The flow of grain in this
layer is caused by the movement of the gas flow from the bottom up and by aerodynamic drag. The grains
in this layer, which act by gravity, increase their concentration during the drying process. The grain is heated
by the concentration of the dryer as it moves. This layer is used to dry the grain sprinkled on top of the dryer
by spraying the drying agent from the bottom. The time it takes to heat the grain is 1-4 seconds and the
temperature of the drying agent is 300-380 °C [19].
The suspended layer (suspended layer) is fed into the dryer through a belt from the outside with
grain. During drying, the entire surface of the grain is exposed to the drying agent flow. For this, a critical
speed must be reached, i.e. the speed of the dryer must be greater than the flow rate of the grain. Grain does
not remain in the dryer for more than 1-2 seconds, and the temperature is in the range of 300-380 °C [11].
Due to the rapid passage of grain through the dryer, a small amount of moisture is lost. This type of dryer
is used as an integral part of a combination dryer.
In combination drying, the preheating of the grain product is part of the process. When preheating
the grain to prevent overheating of the surface of the grain product, it is effective to use it to quickly remove
strong heat from it [7].
The design of the dryer should be such that the cereal product is heated and dried at a constant
temperature, along with constant control of the temperature and moisture content of the grain during the
grain drying process. Modern dryers need to be flexible (depending on the type of grain) depending on the
drying efficiency of many types of grain grown in agriculture. To do this: expand the drying surface of grain
products during the drying process; the surface of the grain product should be warmed up to the desired
temperature before drying. The efficiency of the grain drying process can be achieved due to: the correct
sequence of technological methods of the grain drying process, an increase in the rate of evaporation of
moisture from the grain and a decrease in energy consumption for the process [16].
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