RU2446013C2 - Method of drying seeds in mixed layer - Google Patents

Abstract

FIELD: agriculture.

SUBSTANCE: invention relates to agriculture, particularly to drying seeds, mainly breeder. According to the method, seeds are loaded, ventilated with drying agent at a temperature of 5 °C lower than accepted at average moisture content, periodically stirred, dried, cooled and unloaded. The rate of drying agent is calculated depending on the properties of the material and drying agent. Time of first and subsequent mixings is determined. Mixing is carried out manually with a frequency of 1-2 times per cycle of mixing.

EFFECT: use of the invention enables to improve effectiveness and safety of drying breeder seeds.

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Description

The invention relates to drying of seeds, mainly breeding and can be used in agriculture.

A known method of drying seeds, in which the wet material is loaded, ventilated with a drying agent when heated to a temperature below the maximum permissible, cooled and unloaded [1].

According to this method, ordinary seeds are dried, but the selection seeds are not dried as the humidity of individual grains can significantly exceed the average batch, by which the maximum permissible temperature is determined.

A known method of drying the seeds, which consists in the fact that the material is loaded with a layer height of 0.4 m, is vented with a drying agent at a temperature 5 ° C lower than the accepted average humidity, with a specific consumption of 1800-1900 m ³ / m ² · h (V ≈0.5 m / s), they begin to mix after 1-2 hours with a duration of intervals between mixing of 1-2 hours, the number of revolutions of the mixer is 3-5 revolutions / cycle of complete mixing, the dried material is cooled and unloaded [2].

This method is by technical essence closest to the claimed one and is selected as a prototype.

The known method provides drying of the seeds to a conditioned humidity while maintaining sowing qualities, however, is energy-consuming due to the increased speed of the drying agent. In addition, seed damage due to overheating or personal injury is possible.

An object of the invention is to increase the efficiency and safety of drying selection seeds.

The stated technical problem is achieved by the fact that in the method of drying seeds in a mixed bed, namely, that the material is loaded, vented with a drying agent at a temperature of 5 ° C lower than the accepted average humidity, it is periodically mixed, dried, cooled and unloaded, according to the invention the speed of the drying agent V is calculated depending on the properties of the material and the drying agent according to the formula

and the time of the first and subsequent seed mixing is determined by the ratio

where α _m is the diffusion coefficient of moisture in the grain, m ² / s;

ρ, ρ _in - the dry matter density of the grains and drying agent, kg / m ³ ;

U ₀ , U ₁ , U ₂ - moisture content of the original seeds, drying agent at the inlet and outlet of the layer, respectively, kg / kg;

C is the heat capacity of seeds, kJ / kg ° C;

Θ ₀ ; Θ ₁ ; Θ _cf - initial, final and average temperature of seeds, ° С;

Ko is the Kossovich number;

α is the heat transfer coefficient from the drying agent to seeds, W / m ² ° C;

f is the coefficient of the specific surface of the seeds, m ² / kg;

ε _n - porosity of a thin layer;

t ₁ - temperature of the drying agent, ° C,

while mixing is carried out manually with a frequency of 1-2 times per cycle of mixing.

Comparison of the claimed method with the prototype shows that the new method is that the speed of the drying agent V is calculated depending on the drying mode and the properties of the material and drying agent according to the formula

and the time of the first and subsequent seed mixing is determined by the ratio

where α _m is the diffusion coefficient of moisture in the grain, m ² / s;

ρ, ρ _in - the dry matter density of the grains and drying agent, kg / m ³ ;

U ₀ , U ₁ , U ₂ - moisture content of the original seeds, drying agent at the inlet and outlet of the layer, respectively, kg / kg;

C is the heat capacity of seeds, kJ / kg ° C;

Θ ₀ ; Θ ₁ ; Θ _cf - initial, final and average temperature of seeds, ° С;

Ko is the Kossovich number;

α is the heat transfer coefficient from the drying agent to seeds, W / m ² ° C;

f is the coefficient of the specific surface of the seeds, m ² / kg;

ε _n - porosity of a thin layer;

t ₁ - temperature of the drying agent, ° C, while mixing is carried out with a frequency of 1-2 times per cycle of mixing.

Thus, the claimed method meets the criterion of "novelty."

The invention meets the criterion of "inventive step", as a result can be achieved that satisfies the existing need, namely: improving the efficiency and safety of drying selection seeds.

The invention is "industrially applicable", as it can be used in agriculture.

The invention is illustrated by drawings.

Figure 1 shows a diagram of the device (breeding dryer SL-0.3 × 2), figure 2 is a fragment of a layer with a rotary mixer; a thin layer (shading) and the removed part of this layer (painted over) per revolution of the mixer are highlighted.

The device includes a heater 1, a fan 2, a damper 3, an air channel 4, a spreading agent for drying into two chambers 5, a grill 6, a partition 7, discharge openings 8 and a seed layer 9.

The device operates as follows.

Manually or by mobile means, the seeds are loaded into chambers 5, which are divided into sections by partitions 7.

Turn on fan 2, air heater 1, set the desired temperature and speed of the drying agent and ventilate the seeds. The dried seeds are cooled with outside air after turning off the heater 1 and unload. Unloading is carried out by turning the chambers 5 relative to the horizontal axis so that the seeds spill out into bags fixed below the windows 8 on the sections of the chambers 5.

The method is as follows.

The seeds are loaded, vented with a drying agent, cooled and unloaded, mixing is carried out manually. The set speed and temperature of the drying agent are maintained. Control the temperature of the seeds in a thin layer (border with the grid). The time of the first and subsequent mixing is calculated by the ratio

.

.

To justify the energy-saving speed of the drying agent V, we consider a mathematical model of moisture transfer in the grain. We take the shape of the caryopsis in the form of a bounded cylinder of radius R, length 1 = 5R, and shell thickness δ≈0.1 R, in which most of the moisture, including free moisture, is concentrated. Under the action of concentration diffusion, moisture moves from the shell to the flow of the drying agent, as well as from the central regions of the grains to the shell. We neglect the last transfer, since its speed is much lower than the first, we also neglect the transfer of moisture through the end surfaces of the grain. Then the moisture flow can be written

where α _m is the diffusion coefficient of moisture in the grain, m ² / s;

ρ is the dry matter density of the grain, kg / m;

U ₀ , U - moisture content of seeds and drying agent, respectively, kg / kg

The value of 0.1 R represents the shell thickness δ, and the expression (U ₀ -U) / 0.1R is the transfer gradient.

This moisture stream, evaporated from the surface of the grain, can also be represented as

where dG is the consumption of the drying agent, kg / s;

F is the surface of the grain, m ² .

The value of dG can be expressed in terms of

where V is the air velocity, m / s;

F is the surface of the grain, m ² ;

ρ _in - the density of air.

Equating the right sides of expressions (1) and (2) and after integration from 0 to V and from U ₁ to U ₂ we get

In practice, for the economic and safe drying of selection seeds, the actual value of V _f <V.

Expression (4) does not directly include the temperature of heating the seeds, but it is indirectly given through α _m , ρ _in and U ₂ .

α_m=60·10^-10 м²/с (оболочка) [3]; ρ=1200 кг/м³, ρ_в=1,1 кг/м³, R=2·10^-3 м. Получим V=0,27 м/с ≈0,3 м/с.Example 1. We calculate the speed of the drying agent V for the following case: seed temperature - 35 ° C, seed moisture 25% (U ₀ = 0.33 kg / kg), moisture content of the drying agent U ₁ = 0.008 kg / kg, U ₂ = 0 , 0115 kg / kg, then

α _m = 60 · 10 ^-10 m ² / s (shell) [3]; ρ = 1200 kg / m ³ , ρ _в = 1.1 kg / m ³ , R = 2 · 10 ^-3 m. We get V = 0.27 m / s ≈0.3 m / s.

A speed of V = 0.3 m / s is sufficient for effective and safe drying of selection seeds, and a speed of V = 0.4 m / s in the prototype is somewhat overestimated and should be reduced, which will provide not only safe, but also economical drying.

Mixing is primarily necessary to prevent overheating of the seeds in a thin layer bordering the grate. The seeds in this layer are affected by the convective and conductive components of heat transfer. Based on the accepted mathematical model, the periods between the first and subsequent mixing should differ, since with the humidity of the seeds, the ratio of the heat consumption that goes to the evaporation of moisture to the heat that goes to heat, determined by the Kossovich number (Ko), simultaneously decreases (see table )

The value of Ko at a temperature of the drying agent of 35 ° C and its speed V = 0.5 m / s [3]. The initial moisture content of the seeds,% Duration of drying, min 45 135 thirty 9.5 12.5 25 5 8 twenty four 6 eighteen 3.8 5,0

To justify the duration of the dryer until the first and subsequent mixing, we will make a heat balance. The heat flux from the drying agent to the seeds in a thin layer can be recorded.

α _e ≈1.4α;

; Nu=0,106 Re (20<Re<200),

; Nu = 0.106 Re (20 <Re <200),

where α _e is the effective heat transfer coefficient, taking into account the convective and conductive components, W / m ² ° C;

Nu - Reynolds criterion;

λ - thermal conductivity of seeds, kJ / m · h;

d _e - the equivalent diameter of the grain, m;

t ₁ is the temperature of the drying agent, ° C;

Θ ₀ - initial seed temperature, ° С.

The amount of heat absorbed by the seeds in a thin layer is

where G is the mass of seeds in a thin layer, kg;

C is the heat capacity of seeds, kJ / kg ° C;

;

;

- предельно допустимая температура нагрева семян, °С;

- the maximum allowable temperature for heating seeds, ° C;

C is the heat capacity of grain, ≈2.05 kJ / kg ° C.

Equating the right-hand sides of (5) and (6) we write

where f is the specific surface coefficient (m ² / kg) is effective and equal to

f = f ₀ (1-ε),

where f ₀ is the geometric coefficient of the specific surface (for wheat, f ₀ ≈ 1.0), ε is the porosity of the thin layer (ε ≈ 0.55).

The use of the effective coefficient is due to the structure of the thin layer, in which part of the drying agent does not come into contact with the surface of the material.

After simplifications we get

t₁=40°C; W₀=23% (исходная влажность). По таблице примем Ko≈8, найдем α≈15 Вт/м² °С. Получим решением (8) τ≈0,7 ч.Example 2. We determine after what time it is necessary to mix the layer of wheat seeds for conditions: V = 0.30 m / s;

t ₁ = 40 ° C; W ₀ = 23% (initial humidity). According to the table we take Ko≈8, we find α≈15 W / m ² ° С. We obtain the solution of (8) τ≈0.7 hours

Let us compare the efficiency and safety of mechanical and manual mixing of selection seeds. In the first case, mixing is carried out with a rotary mixer, in the second - with a wooden shovel or dustpan. Consider that seeds with a moisture content of more than 22% are at increased risk of injury, so the mechanical impact on them should be minimized.

A rotary mixer with plates picks up dried seeds of the lower layer and moves them to the free surface, wet seeds arrive at the places of the displaced. Studies [2] found that with the number of revolutions of the mixer n = 3-5 rpm / cycle, the minimum values of drying non-uniformity δ were achieved. Other parameters of the device and process are also given: initial seed moisture of 20-30%, number of blades - 6, blade width 0.25 m, tilt angle -90 °, unevenness of drying by average samples does not exceed ± 0.5 ... 1.0% and does not decrease with increasing n.

Obviously, for 3 ... 5 rpm, the dried seeds of the lower layer will not only be moved up, but also mixed with wetter ones, which will allow us to achieve a minimum value of δ. A similar effect with manual stirring with a wooden shovel (slider) or scoop can be achieved in 1-2 cycles of mixing (1 - with a grate area of up to 2 ... 4 m ² , 2 - with a larger area, as there may be unmixed places on the grate )

Indeed, if we take as a first approximation that the main task of mixing is to move up the boundary layer of seeds having the lowest humidity, the thickness of which is approximately 2-3 grains, then only a small part of this layer is removed in one pass of the mixer (approximately 0.15-0 , 25) the mass of everything in the mixer. The remaining seeds of the boundary layer will shift to the place of the removed ones, and only after 3-5 cycles will the value of δ not decrease, i.e. the seeds will be mixed.

While using a shovel or scoop, 1-2 cycles of mixing are sufficient, and a decrease in the mechanical effect on the seeds is obvious.

Information sources

1. S.D. Ptitsyn. Grain dryers. M .: Mashgiz, 1962, p. 49-53.

2. P.M. Galikhoshvili. Justification of technological and structural parameters and the development of a universal installation for drying breeding seeds of agricultural crops. Author. thesis. for the degree of candidate of technical. sciences. M., 1975, pp. 20-21.

3. V.F. Sorochinsky. Improving the efficiency of convective drying and cooling of grain based on the intensification of heat and mass transfer processes. Dissert. scientist. step. Doct. tech. sciences. M., 2003, p. 161-162.

Claims (1)

The method of drying seeds in a mixed bed, namely, that the material is loaded, vented with a drying agent at a temperature of 5 ° C lower than the average humidity, periodically mixed, dried, cooled and unloaded, characterized in that the speed of the drying agent V is calculated as from the properties of the material and the drying agent according to the formula

and the time of the first and subsequent seed mixing is determined by the ratio

where α _m is the diffusion coefficient of moisture in the grain, m ² / s;
ρ, ρ _in - the dry matter density of the grains and drying agent, kg / m ³ ;
U ₀ , U ₁ , U ₂ - moisture content of the original seeds, drying agent at the inlet and outlet of the layer, respectively, kg / kg;
C is the heat capacity of seeds, kJ / kg · ° C;
Θ ₀ , Θ ₁ ; Θ _cf - initial, final and average temperature of seeds, ° С;
Ko is the Kossovich number;
α is the heat transfer coefficient from the drying agent to seeds, W / m ² · ° C;
f is the coefficient of the specific surface of the seeds, m ² / kg;
ε _n - porosity of a thin layer;
t ₁ - temperature of the drying agent, ° C,
while mixing is carried out manually with a frequency of 1-2 times per cycle of mixing.

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