RU2489656C1 - Method of drying seeds in fixed bed - Google Patents

Abstract

FIELD: agriculture.

SUBSTANCE: method of drying seeds in a fixed bed consists in the fact that the material is charged, ventilated by the drying agent, the dried material is cooled and discharged. The new in the method is that the dried material is mixed and rested for at least 2 h, and the critical height of seed layer h_k, not exceeding the actual bed height h, is determined by the formula $$h_k=\frac{\nu d_e{\rho }_B}{8\epsilon \beta \rho }\ln \frac{U_1-U_0}{U_2-U_0},\text{ m}\text{,}$$

where v is the rate of the drying agent, m/s; ρ_B, ρ is density of the drying agent and the material, respectively, kg/m³; d_e is equivalent diameter of the corn seed, m; ε is pore space of the layer; β is mass transfer coefficient, m/s, where U₀ is moisture content of the drying agent at the inlet to the bed, kg/kg; U₁, U₂ is moisture content of the air-vapor film of the seeds at the outlet and inlet of the layer, kg/kg.

EFFECT: use of the method enables to reduce costs on drying due to reducing its duration and to provide safe storage.

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Description

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

There is a known method of drying seeds, in which wet material is loaded, vented with a drying agent when heated to a temperature below the maximum permissible, the dried material is cooled and unloaded (S.D. Ptitsyn. Grain dryers, Mashgiz, M., 1962, p. 49-53.) .

According to the known method, ordinary seeds are dried, but the selection seeds are not dried, since the moisture content of individual grains can significantly exceed the average humidity of the seed lot, which determines the maximum allowable heating temperature.

A known method of drying selection seeds in a fixed bed, according to which the material is loaded with a layer with a height of 0.4-0.45 m, and ventilated with a drying agent with a temperature of 35 ° C and a specific flow rate of 1800-1900 m ³ / m ² · h (agent speed drying 0.5-0.53 m / s), the dried material is cooled and unloaded (R. M. Gamkhashvili. Justification of technological and design parameters and the development of a universal installation for drying selection seeds of agricultural crops, author. Thesis for the degree of candidate Engineering Sciences, M., 1975, p.16).

The known method in technical essence is closest to the claimed one and is selected as a prototype.

Drying the seeds in a layer with a critical height h _to ≤0.4-0.45 m by this method provides the initial requirements for uneven drying (± 1.5%) when the seeds reach average standard humidity.

The disadvantage of this method is that it is inefficient and expensive, since at such a low temperature of the drying agent, the drying time is 6 ... 10 hours at the initial seed moisture of more than 21 ... 22%, and does not satisfy the requirements for uneven drying in relation to individual kernels.

The technical task of this invention is to increase efficiency, reduce the cost and unevenness of drying (not more than δ ± 1.5%) not only in average humidity, but also in individual grains.

The stated technical problem is achieved by the fact that in the method of drying seeds in a fixed bed, namely, the material is loaded, vented with a drying agent, the dried material is cooled and unloaded, according to the invention, the dried material is mixed and traced for at least 2 hours, and the critical height of the seed layer h _to not exceeding the actual height of the layer h, is determined by the formula

м, $$h_{\mathrm{to}}=\frac{\nu d_{\mathrm{uh}}{\rho }_{\mathrm{at}}}{8\epsilon \beta \rho }\ell n\frac{U_{\mathrm{one}}-U_0}{U_2-U_0}$$

m

where ν is the speed of the drying agent, m / s;

ρ _in , ρ is the density of the drying agent and the material, respectively, kg / m ³ ;

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

ε is the porosity of the layer;

β - mass transfer coefficient, m / s

where U ₀ is the moisture content of the drying agent at the entrance to the layer, kg / kg;

U ₁ , U ₂ - moisture content of the vapor-air film of seeds at the outlet and inlet of the layer, kg / kg

Comparison of the claimed method with the prototype shows that the new method is that the dried material is mixed and traced for at least 2 hours, and the critical seed layer height h _k , not exceeding the actual layer height h, is determined by the formula.

м, $$h_{\mathrm{to}}=\frac{\nu d_{\mathrm{uh}}{\rho }_{\mathrm{at}}}{8\epsilon \beta \rho }\ell n\frac{U_{\mathrm{one}}-U_0}{U_2-U_0}$$

m

where ν is the speed of the drying agent, m / s;

ρ _in , ρ is the density of the drying agent and the material, respectively, kg / m ³ ;

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

ε is the porosity of the layer;

β - mass transfer coefficient, m / s;

where U ₀ is the moisture content of the drying agent at the entrance to the layer, kg / kg;

U ₁ , U ₂ - moisture content of the vapor-air film of seeds at the outlet and inlet of the layer, kg / kg

The invention meets the criterion of "inventive step", since a result can be achieved that satisfies an existing need, namely, increasing efficiency and reducing the cost of drying.

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

The invention is illustrated in the drawing.

Figure 1 shows a diagram of a device (selection dryer SL-0.3 × 2).

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, and discharge openings 8.

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 the fan 2, air heater 1, set the desired temperature of the drying agent and ventilate the seeds. The dried seeds are cooled with outside air after turning off the heater 1 and unload. The unloading of the seed layer 9 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.

Seeds are loaded, ventilated with a drying agent, mixed, traced, cooled and unloaded. The control of the drying process, including the size of the non-uniformity of drying δ, can be carried out in the following ways - periodically select samples of seeds from the layer bordering the grate and on the surface with subsequent comparison, or by controlling the relative humidity of the drying drying agent. At δ> ± 1.5% at the end of drying, in several consecutive samples, the drying mode is adjusted (lower the temperature or increase the speed of the drying agent).

To justify the value of the critical layer height h _k , which should not exceed the actual h, we consider a simplified mathematical model of moisture transfer in the seed layer.

Suppose that the moisture content in the grains is equalized, then after ventilation, a difference in the potentials of moisture content occurs in them, due to which moisture from the surface of the grains evaporates, the steam moves into the flow of the drying agent and is removed from the layer. In turn, a stream of moisture rushes from the central areas of the grains to peripheral ones, in the first drying period in the form of a liquid, then in the form of steam. We restrict ourselves to considering the flow of moisture from the surface of the grains to the flow of the drying agent, since the second stream is of little importance. The mass of moisture carried out from the layer can be written as

$$dM=\beta \rho dF\left(U_{\mathrm{one}}-U_0\right),\left(\mathrm{one}\right)$$

where β is the mass transfer coefficient from the grains to the drying agent, m / s;

ρ is the density of dry matter of seeds, kg / m ³ ;

dF is the area from which moisture evaporates, m;

U is the moisture content of seeds, kg / kg;

U ₀ - moisture content of the drying agent at the entrance to the layer.

The same flow of moisture can be represented as

$$dM=GdU,\left(2\right)$$

where G is the mass of moisture removed from the layer, kg / s.

Equating the right sides of expressions (1) and (2), we obtain

$$\beta \rho dF\left(U_0-U\right)=GdU\left(3\right)$$

Having considered a separate elementary channel with a diameter of d _to in the embankment, from the inner surface of which moisture evaporates, we obtain

$$dF=\pi d_{\mathrm{to}}dl,\left(\mathrm{four}\right)$$

where dl is the length of the channel through which the drying agent passes. The mass of moisture removed from the layer can be written as

$$G={\rho }_{\mathrm{at}}{\nu }_0\frac{\pi d_{\mathrm{to}}^2}{\mathrm{four}}\left(5\right)$$

После интегрирования (3) от 0 до 1 и упрощений (l≈h_к), 2d_к=d_э получимwhere ρ _in - the density of the drying agent, kg / m ³ ; v ₀ is the speed of the drying agent in the channel, m / s; the value of d _k can be written d _k = 2d _e ε / 3 (l-ε), ε is the porosity of the layer, d _e is the equivalent diameter of the grain, m. Velocity V _{0 is} expressed through the porosity of the layer ε and the air velocity above the layer $$V_0=\frac{V}{\epsilon }.$$

After integrating (3) from 0 to 1 and simplifications (l≈h _a), 2d _to obtain _e = d

$$h_{\mathrm{to}}=\frac{\nu d_{\mathrm{uh}}}{8\cdot \epsilon \beta }\frac{{\rho }_{\mathrm{at}}}{\rho }\ell n\frac{U_{\mathrm{one}}-U_0}{U_2-U_0}\left(6\right)$$

where - U ₁ , U ₂ - moisture content of the vapor-air film of seeds at the outlet and entrance of the layer, kg / kg

. Приняв скорость агента сушки V=0,5 м/с, порозность слоя ε=0,42; эквивалентный диаметр d_э=3,0·10^-3 м. ρ_в=1,1 кг/м³, ρ=1200 кг/м³, β=0,3·10^-6 м/с (В.Д. Сорочинский. Повышение эффективности конвективной сушки и охлаждения зерна… Диссертация на соискание ученой степени доктора технических наук. М. 2003 г., с.143-145), получим $$h_{к}=\frac{{\rho }_{в}{d}_{э}\cdot \mathrm{0,28}}{\beta \rho \epsilon }=\mathrm{0,39}\approx \mathrm{0,4}м$$

Example 1: Upon reaching the moisture content of seeds on the grate W ₂ = 13.25% (U ₂ = 0.153 kg / kg), on the free surface of the layer, the moisture content of the seeds will be W ₁ = 16.75% (U ₁ = 0.02 kg / kg ), i.e. the average seed moisture content will be 14% (conditional) and at U ₀ = 0.008 kg / kg, which corresponds to the moisture content of the drying agent $$\ell n=\frac{U_{\mathrm{one}}-U_0}{U_2-U_0}=0.28$$

. Having adopted the speed of the drying agent V = 0.5 m / s, the porosity of the layer ε = 0.42; equivalent diameter d _e = 3.0 · 10 ^-3 m. ρ _в = 1.1 kg / m ³ , ρ = 1200 kg / m ³ , β = 0.3 · 10 ^-6 m / s (V.D. Sorochinsky. Increasing the efficiency of convective drying and cooling of grain ... The dissertation for the degree of Doctor of Technical Sciences. M. 2003, p.143-145), we get $$h_{\mathrm{to}}=\frac{{\rho }_{\mathrm{at}}{d}_{\mathrm{uh}}\cdot 0.28}{\beta \rho \epsilon }=0.39\approx 0.4m$$

Example 2: Investigated the drying efficiency at elevated temperature for the condition δ = ± 1.5%. The experiments were carried out on a laboratory dryer with a chamber capacity of 1 kg. The seeds were dried with an average humidity of 23% at a drying agent speed of V = 0.4 m / s at a temperature of 35 ° C and 45 ° C. In the first case, the layer was h = 0.4 m, in the second of the increase in β by ~ 20%, h = 0.48. In the first case, the drying time was 8.0 hours, and in the second - 5.2 hours and the drying performance increased by 35%.

Subject to the condition at the end of drying, σ≤ ± 1.5% in average humidity, the unevenness in humidity between individual grains can be σ> ± 1.5%, and the difference in humidity between individual grains reaches 4 ... 6%, especially if the initial average seed moisture 25% or more (Aniskin V.I., Okun G.S. Technological basis for evaluating the operation of grain drying plants. M., VIM, 2003, p. 56-63). In order to reduce the unevenness of drying between the individual grains, the dried seeds are mixed and traced, with the redistribution of moisture. Moreover, the higher the temperature of the seeds, the faster the unevenness decreases. According to (S.D. Ptitsyn. Zernosushilki, Mashgiz, M., 1962, p. 39-41) at a temperature of 20 ° C the rate of moisture equalization is 1.05% / h, and at 55 ° C - 3% / h. For breeding seeds at a temperature of 35 ° C, after two hours of curing, the unevenness between the individual grains will decrease by ~ 3%, which will ensure their safety.

Claims (1)

The method of drying seeds in a fixed bed, namely, that the material is loaded, vented with a drying agent, and the dried material is cooled and unloaded, characterized in that the dried material is mixed, tracked for at least 2 hours, and the critical seed layer height h _k , not exceeding the actual layer height h, is determined by the formula
$$h_{\mathrm{to}}=\frac{\nu d_{\mathrm{uh}}{\rho }_{\mathrm{at}}}{8\epsilon \beta \rho }\ln \frac{U_{\mathrm{one}}-U_0}{U_2-U_0},\text{m}\text{,}$$

where ν is the speed of the drying agent, m / s;
ρ _in , ρ is the density of the drying agent and material, respectively, kg / m ³ ;
d _e - the equivalent diameter of the grain, m;
ε is the porosity of the layer;
β - mass transfer coefficient, m / s,
where U ₀ is the moisture content of the drying agent at the entrance to the layer, kg / kg;
U ₁ , U ₂ - moisture content of the vapor-air film of seeds at the outlet and inlet of the layer, kg / kg