JPH06237687A - Method for drying grain - Google Patents

Abstract

PURPOSE:To improve drying efficiency of grain. CONSTITUTION:Whether a dehumidifier 13 is operated or not is judged according to outside air conditions in a dehumidifier operation-judging part 12. When it is judged not to operate the dehumidifier 13, outside air is sucked in large air amounts and the discharge air is discharged. Thereby, consumed electric power of the dehumidifier becomes zero and drying efficiency is raised by large dehydration amount and air amount ratio of safety limit is secured. When it is judged to operate the dehumidifier, whether the grain is safe or not is judged according to discharge conditions in a grain safety judging part 16. When the operation is judged to be safe, whether fed air amount is large or small and discharged air is recycled or not are judged in a recycle and air amount judging part 18. Thereby, quality of grains is guaranteed and dehumidifying efficiency of the dehumidifier are increased and consumed electric power of a blower 7 is reduced by making air amount small to improve drying efficiency. When it is judged that the grain is not safe, air amount is made large and whether discharged air is recycled or not is judged and dehydrating amount is increased while satisfying air amount ratio of safety limit and guaranteeing quality of the grain to improve efficiency of the dehumidifier 13 and drying efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain drying method for maintaining grain quality and improving grain drying efficiency.

[0002]

2. Description of the Related Art Harvested rice will be described below as an example of grain. The harvested rice processing facility must guarantee the quality of the harvested rice during the treatment process of the harvested rice, that is, storage, drying and hulling of the harvested rice. The quality of rice refers to mold, taste, cracking of the harvested rice at the time of storage, skin deviation of brown rice at the time of hulling, and the like. And there is a lot of water in the rice, and
If it is stored for a long period of time, mold will be generated, and if it is overly dried, so-called overdrying will cause deterioration of taste and cracking of the body. Therefore, the water content of rice greatly affects the quality of rice. Also, since rice itself is a living thing, if the temperature is high, the respiration of rice becomes active and the energy inside the rice is consumed (hereinafter referred to as the deterioration of grains), and the quality of rice deteriorates. Since the reproductive activity of rice plants becomes active and causes mold development, which reduces the quality of rice, the temperature of the stored rice itself also has a great influence on the quality of rice.

Therefore, the Ministry of Agriculture, Forestry and Fisheries of the Ministry of Agriculture, Forestry and Fisheries regulates the moisture content of the harvested rice and maintains the quality of the harvested rice as the air flow standard. The air volume per unit weight is fixed. This is called the safety limit air volume ratio. Therefore, if this safety limit air volume ratio is satisfied, for example, the water content is 24%.
It will be judged that it is safe to store 10 tons of harvested rice for 3 days.

Next, the basic technical idea of the present invention will be described. The grain drying efficiency η is the dehydration amount Gkg from the grain per unit total power consumption WH, which is expressed as follows.

Drying efficiency η = dehydration amount Gkg / total power consumption WH ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ And the power of the compressor of the dehumidifier that adjusts the humidity of the drying air, and the total power consumption in (1 set)
WH = Blower power consumption WH1 + Dehumidifier power consumption WH2
It can be expressed as (2 types). Also (1 set)
The amount of dehydration Gkg in is expressed as follows. Dehydration Gkg = (Absolute humidity of exhaust Mx-Absolute humidity of blown air My)
× Ventilation amount V × Specific gravity of blown air γ ... (3 formulas)

Therefore, in order to improve the drying efficiency η, it is necessary to reduce the total power consumption WH and increase the dehydration amount Gkg. Total power consumption in grain drying method
One way to reduce WH is to reduce the air flow to reduce the power consumption WH1 of the blower, and to stop the compressor of the dehumidifier to reduce power consumption WH2 of the dehumidifier.

Next, as a condition for increasing the dehydration amount Gkg, either the value of (absolute humidity Mx of exhaust gas−absolute humidity My of blown air My) is increased or the blown air amount V is increased by the above-mentioned three equations. However, the condition for increasing the value of (Absolute humidity of exhaust air Mx-Absolute humidity of blown air My) is to reduce the absolute humidity My of blown air by removing moisture in the blown air with a dehumidifier as much as possible. Therefore, there is a conflict with reducing the power consumption WH2 of the dehumidifier, and increasing the air flow rate V is also a conflict with reducing the power consumption WH1 of the blower. There is something to do. Therefore, in order to maximize the drying efficiency η, how to adjust the dehydration amount Gkg and the total power consumption WH, which are contradictory to each other, is a key point.

As a method of drying grains, naturally, quality of grains,
That is, the safety limit air volume ratio must be considered. The basic idea of the present invention regarding grain quality is to give priority to grain quality when the moisture content of the grain is very high. That is, at the time of planning, a blower that can blow the amount of air required to maintain the quality of the grain while satisfying the safety margin air volume ratio is selected, and the quality of the grain is maintained by operating this blower at the rated level. In order to improve the drying efficiency, whether the exhaust gas is recycled or not.

In the dehumidifying / drying method, it is generally practiced to recycle the drying air and dry the dehumidifying dryer while gradually lowering the humidity of the blown air in order to efficiently dry the material to be dried. However, the method of drying by recycling differs depending on the type of the material to be dried. For example, when there is a lot of water like medicinal herbs and when the water of medicinal herbs is sufficiently removed to form a powder, a large amount of water is contained in the exhausted air when the water content is high. The exhaust gas is discharged as it is, and when the water content reaches a certain level, the exhaust gas is guided to the dehumidifying dryer again to remove the water content in the exhaust gas and continue to recycle the exhaust gas until the water content of the herbs is sufficiently removed. I try to do it.

Further, when the timber is dried as disclosed in Japanese Patent Publication No. 59-25134, the drying characteristics of the timber,
That is, if only the surface of the timber is dried, the moisture in the core of the timber will be trapped and the drying time will be long, so you can recycle the exhaust or discharge the exhaust as it is so that the surface of the timber does not become overdried. By adjusting the temperature and humidity, the moisture in the core of the timber is efficiently removed and the timber is dried.

Specifically, the wood is dried in four stages. Explaining with reference to FIG. 3, first, in the first stage where the lumber has just been lumbered and the water content is high, the opening degree of the damper 2 is adjusted and a part of the air is supplied to the auxiliary condenser 3
To release outside air, open the damper 5 to take in the outside air, turn off the dehumidifying evaporator 4 condenser 6 and absorb the water content of the wood in the drying chamber 1 to remove the drying air containing a large amount of water. A part of the air is discharged to the outside air through the auxiliary evaporator 3, and the remaining air is mixed with the outside air sucked through the damper 5 in a state where a large amount of water is contained in the dehumidification evaporator 4 without evaporating the contained water. After adjusting the humidity, it passes through the condenser 6 in the OFF state and is recirculated to the drying chamber 1 by the blower 7. This first stage is continued until the absolute humidity of the air in the drying chamber 1 becomes substantially equal to the absolute humidity of the outside air. This promotes drying so that the surface of the wood does not become overdried. Next, in the second to fourth stages, the dampers 2 and 5 are closed, and the dehumidifying evaporator 6 and the condenser 4 are turned on.
In this state, the drying air is circulated in a closed circuit state, and moisture in the circulating drying air is gradually removed by the dehumidifying evaporator 6 and the condenser 4 to suppress overdrying of the surface of the wood. At the same time, the core of the wood is dried evenly.

In the conventional grain drying method shown in FIG. 4 (JP-A-3-87589), when the set humidity is higher than the humidity of the outside air, the damper 9 is closed to stop sucking the outside air and the damper 10 is closed. The drying air is circulated in a closed circuit state, and the humidity of the drying air is gradually lowered to be circulated by the blower 7 so that the grains in the storage tank 1 are prevented from being overdried and the grains are dried. When the set humidity is lower than the humidity of the outside air, the damper 9 and the damper 10 are opened, the outside air is sucked from the damper 9, the dehumidifier 8 dehumidifies, and the grain in the storage tank 1 is dried. The air is exhausted from the ground to prevent the grain from overdrying while drying. Also, the humidity of the outside air is very high,
Alternatively, when the humidity is close to the set humidity, the dampers 9 and 10 are opened halfway to release a part of the air into the atmosphere and circulate the remaining air so as to prevent the grain from overdrying and dry it.

[0013]

The above-mentioned conventional recycling-type drying has problems in terms of drying efficiency. First of all, when drying the herbs, when the water content of the herbs is high, the exhaust air contains a large amount of water, so the exhaust air is discharged as it is, and when the water reaches a certain amount, Since the exhaust gas is guided to the dehumidifying dryer again to remove the water content in the exhaust gas, the exhaust gas is continuously recycled until the water content of the herbs is sufficiently removed. The dehumidifier is operated continuously until the medicinal herbs are completely dried by recycling the exhaust gas,
And, as a result, the blower is also continuously operated in rated operation, and when viewed from the viewpoint of drying the grain that is the subject of the present invention, a large amount of total power consumption is consumed and the drying efficiency is low. is there.

Next, in the conventional example shown in FIG. 3, in the first stage in which the wood has just been lumbered and has a large amount of water, in the first stage, one of the drying air which absorbs the water of the wood in the drying chamber 1 and contains a large amount of water. Part of the air is discharged to the outside air through the auxiliary evaporator 3, and the remaining air is mixed with the outside air sucked through the damper 5 in a state where a large amount of water is contained in the dehumidification evaporator 4 without evaporating the contained water, thereby obtaining an absolute humidity. After adjusting the air conditioner, the air passes through the condenser 6 in the OFF state and is recirculated to the drying chamber 1 by the blower 7, so that the blast humidity becomes high, and as a result, the dehydration amount decreases, and when viewed from the viewpoint of grain drying. There is a problem that the drying efficiency is low. Further, in the second to fourth steps, the drying air is circulated in a closed circuit state, and the moisture in the circulating drying air is gradually removed by the dehumidifying evaporator 6 and the condenser 4 for drying. Therefore, from the viewpoint of drying grains, as in the case of drying the above-mentioned herbs, even when the conditions of the outside air are good, the exhaust gas is recycled without utilizing the outside air. 4 and the blower 7 are continuously in rated operation, resulting in a large total power consumption and a low drying efficiency.

Further, the conventional example shown in FIG. 4 for drying grains has a main purpose of preventing overdrying. Therefore, when the set humidity is higher than the humidity of the outside air (when the conditions of the outside air are good), the humidity Since high air is circulated in a closed circuit state and the humidity of the drying air is gradually lowered by the dehumidifier, the air is circulated by the blower 7, so that the dehydration amount is small and the dehumidifier and the blower must be continuously rated. Therefore, there is a problem that total power consumption increases and drying efficiency is low.

Further, none of the above-mentioned conventional examples describes the control of the air flow rate, and does not disclose the technique of improving the drying efficiency by minimizing the power consumption of the blower related to the drying efficiency.

The present invention has been made in view of the above-mentioned problems, and provides a method for drying a grain in which the drying efficiency is improved by comprehensively examining the dehydration amount, the total power consumption, and the quality of the grain. .

[0018]

Means for Solving the Problems According to the present invention for solving the above-mentioned problems, the grain for drying the grain by introducing the drying air which has passed through the dehumidifier to a storage tank storing the grain by a blower. In the drying method, the moisture content of the grain stored in the storage tank is determined from the relative humidity and temperature of the exhaust gas discharged from the storage tank and the equilibrium moisture content of the grain, and the moisture content of the grain stored in the storage tank is determined according to the determined moisture content. It is characterized in that the amount of air blown into the storage tank is controlled.

[0019]

Since the present invention is constructed in this way, it has the following actions. That is, the drying air that has passed through the dehumidifier is guided by a blower to a storage tank that stores grains to dry the grains, and the relative humidity and temperature of the exhaust gas discharged from the storage tank and the equilibrium moisture content of the grains are used. The water content of the grain stored in the storage tank is determined, and the amount of air blown into the storage tank is controlled according to the determined water content. If it is determined that the water content is high, it is possible to increase the amount of dewatering by increasing the air volume to increase the drying efficiency. It becomes possible to maintain the quality of the grain by setting the moisture judgment standard and the air volume so as to satisfy the limit air volume ratio, and by judging the moisture content of the grain by the exhaust condition,
By comparing the exhaust condition and the outside air condition, it becomes possible to judge whether or not to recycle the exhaust, and it is possible to lower the humidity of the blown air and raise the temperature to improve the drying efficiency.

[0020]

EXAMPLE An example of the present invention will be described below. In FIG. 1, the detector 11 detects the relative humidity mx and the temperature tx of the outside air and inputs it to the dehumidifier operation determination unit 12 to determine whether to operate the dehumidifier 13. In this judgment, from the relationship between the relative humidity and the temperature regarding the equilibrium moisture of the grain shown in FIG. 2, for example, when the outside air temperature is 5 ° C. and the outside air relative humidity is 55%, the outside air temperature is 40 ° C. and the outside air relative humidity is 69% (A If the outside air condition is within the range of), it is possible to dry the grain to a moisture content of 14% or less by the outside air in this condition due to the relationship with the equilibrium moisture content of the grain, so it is sufficient to reduce the humidity of the outside air with the dehumidifier 13. Therefore, the grain can be dried, and it is determined that the dehumidifier 13 is stopped under the above-mentioned outside air condition. As a result, the power consumption WH1 of the dehumidifier 13 becomes zero, and the outside air intake damper 14 is opened to take in the outside air, the exhaust damper 15 is opened and exhausted, and the amount of dehydration G is increased by drying with a large amount of outside air. The drying efficiency can be improved, and since a large air volume is blown under the above-mentioned outside air conditions, the safety limit air volume ratio is satisfied, and it becomes possible to maintain the grain quality regardless of the moisture content of any grain.

On the other hand, when the relative humidity mx and the temperature tx of the outside air detected by the detector 11 are in the ranges of (B) and (C) of FIG. 2, it is judged that the dehumidifier 13 is operated, and at this time, the grain safety. The sex determination unit 16 determines whether or not the grain is safe. The grain safety is judged by detecting the relative humidity Mx and temperature Tx of the exhaust gas by the detector 17 and inputting these signals to the grain safety judging section 16 from the equilibrium moisture relationship shown in FIG. You can know the water content of the grain in 1. For example, if the exhaust humidity Mx is 80% and the exhaust temperature Tx is 20 ° C,
The water content of the grain in the storage tank 1 is determined to be 18%.

When the exhaust conditions are within the range of FIG. 2B, that is, the exhaust temperature is 5 ° C., the exhaust relative humidity is 55%.
From 75% to exhaust temperature 40 ° C and exhaust relative humidity 69% to
When it is 87%, the water content of the grain in the storage tank 1 is in the range of 14% to 18%, and it is judged that it is safe even with a small air volume, and this judgment signal is input to the recycling / air volume judgment section 18. In the recycle / air flow rate determining unit 18, the outside air relative humidity mx and the temperature tx input from the detector 11 and the exhaust air relative humidity Mx and the temperature Tx input from the detector 17 are used to determine the outside air relative humidity mx.
And the relative humidity Mx of the exhaust gas and the outside air temperature tx are compared with the exhaust temperature Tx, and the blower control is performed when the outside air relative humidity mx is equal to or higher than the relative humidity Mx of the exhaust gas, and / or the outside air temperature tx is equal to or lower than the exhaust temperature Tx. The blower 7 is controlled by being output to the small air volume of the part 20, and the air intake damper 14 with a small air volume is provided.
Also, the exhaust damper 15 is closed to recycle the exhaust gas (hereinafter, this condition is referred to as a recycle small air flow condition).

As described above, since the dehumidifier 13 is operated and it is determined that the grain is safe, and the exhaust condition is better for drying the grain, the safety limit air flow amount is small even if the air flow amount is small. The ratio is satisfied and the quality of the grain is guaranteed, and
The air volume is reduced to reduce the power consumption WH1 of the blower 7,
Furthermore, the relative humidity Mx is lower than the outside air, and / or the temperature Tx.
By recycling high exhaust gas and dehumidifying it with the dehumidifier 13, it is possible to further lower the relative humidity my of the air to be blown, increase the dehydration amount G, and improve the drying efficiency.

In addition, when the outside air relative humidity mx is lower than the exhaust relative humidity Mx in the recycle / air flow rate determination unit 18 and / or when the outside air temperature tx is higher than the exhaust temperature Tx, it is input to the large air volume unit of the blower control unit 20. Then, the blower 7 is controlled to open the outside air intake damper 14 and the exhaust damper 15 with a large air volume to discharge the exhaust gas (hereinafter, this condition is referred to as a non-recycled large air volume condition).

That is, the above non-recycled large air volume condition means that the grain is sufficiently dehydrated, the heat of the air is taken away by the heat of evaporation of the moisture of the grain, the exhaust temperature Tx is lowered, and the moisture is absorbed. Since it means that the exhaust gas relative humidity Mx rises, the drying efficiency can be improved by taking in the air in good condition to discharge the exhaust gas with a large amount of water, and by increasing the air volume to increase the dehydration amount G. It will be possible to improve.

Next, when the grain safety determination unit 16 determines that it is not safe, the determination signal is input to the recycle / non-recycle determination unit 19 and the blower control unit 20 gives priority to the safety of the grain. The air blower 7 is controlled by being input to the large air volume part. That is, in FIG. 2, the exhaust temperature Tx is 5 ° C.
When the exhaust relative humidity Mx is 75% or more and the exhaust temperature Tx is 40 ° C and the exhaust relative humidity Mx is 87% or more (C), it is judged that the grains are not safe (high moisture content) and stored at this time. A large amount of air is blown into the tank 1 to meet the safety limit air volume ratio, and the safety of the grain is given first, and the dehumidifier 13 recycles the exhaust having the relative humidity Mx lower than the outside air and / or the temperature Tx higher than the outside air. By dehumidifying, the relative humidity my of the blown air is further lowered to increase the dehydration amount G to improve the drying efficiency, and when the outside air relative humidity mx is lower than the exhaust relative humidity Mx, and / or outside air When the temperature tx is higher than the exhaust temperature Tx, the air volume is large, and the outside air intake damper 14 and the exhaust damper 15 are opened to exhaust the exhaust gas to a large air volume and dehydration amount G
By increasing the amount, it becomes possible to improve the drying efficiency.

In this way, the exhaust condition is detected by the detector 17 and the moisture content of the grain in the storage tank 1 is determined. By using this exhaust condition, it is compared with the outside air condition to determine whether the exhaust gas is recycled. It becomes possible to improve the drying efficiency by judging the air flow rate together with the judgment, and comprehensively considering the dehydration amount, the total power consumption and the grain quality.

In the above description, the relationship between the equilibrium moisture content of the grain, the humidity and the temperature is shown in FIG. 2 as a criterion for the determination of the dehumidifier operation determination unit 12 and the grain safety determination unit 16, but the ranges (A), ( B) and (C) are not limited to this, and this range can be set arbitrarily.

[0029]

As described in detail above, according to the present invention, the moisture content of grains stored in the storage tank is determined from the relative humidity and temperature of the exhaust gas discharged from the distilling tank and the equilibrium moisture content of the grain, Since the amount of air blown into the storage tank is controlled in accordance with the water content thus determined, if the water content is determined to be low, the air flow rate is reduced to reduce the power consumption of the blower. However, if it is determined that the water content is high, a large air volume can be used to increase the dehydration amount to increase the drying efficiency, and the water content judgment criteria and air volume can be set to meet the safety limit air volume ratio. By doing so, the quality of the grain can be maintained, and by judging the moisture content of the grain by the exhaust condition, it becomes possible to compare the exhaust condition with the outside air condition and judge whether to recycle the exhaust. Of the blast air It is possible to reduce the degree by raising the temperature to increase the drying efficiency.

When the dehumidifier operation determination unit determines whether or not to operate the dehumidifier according to the outside air conditions, and when it is determined that the dehumidifier is not operated, the outside air is sucked in with a large air volume and dried, and then the exhaust gas is discharged. This makes it possible to reduce the power consumption of the dehumidifier to zero and reduce the total power consumption, and to dry the grain with a large amount of outside air to increase the dehydration amount and improve the drying efficiency. By blowing air, the safety limit air volume ratio is secured and the grain quality can be maintained.

On the other hand, when it is determined that the dehumidifier is to be operated, the grain safety determination unit determines whether or not the grain is safe based on the exhaust conditions. If it is determined that the grain is safe, the temperature and the relative humidity of the outside air are determined. By comparing the temperature and relative humidity of the exhaust with the relative humidity of the outside air is higher than the relative humidity of the exhaust and / or when the outside air temperature is lower than the exhaust temperature, recycling the exhaust with a small air volume will improve the quality of the grain. Guaranteed and with a relative humidity lower than the outside air and higher than the outside temperature, the exhaust gas is recycled to lower the blast humidity and increase the blast temperature to increase the dehydration amount, and further reduce the air flow to reduce the power consumption of the blower. The drying efficiency can be improved.

On the other hand, when the relative humidity of the outside air is lower than the relative humidity of the exhaust gas and / or the outside air temperature is higher than the exhaust gas temperature, the outside air is sucked and dried with a large air volume, and then the exhaust gas is discharged. , The quality of grain is guaranteed, and the relative humidity is lower than the exhaust gas and higher than the exhaust temperature to reduce the blast humidity by increasing the blast temperature and to increase the blast temperature. And the drying efficiency can be improved.

When it is determined that the grain is not safe, a large air volume is set and the outside air condition and the exhaust condition are compared to determine whether or not the exhaust gas is recycled. It is possible to increase the amount of dehydration while ensuring the above, and determine whether or not to recycle, to lower the blast humidity, raise the blast temperature, and improve the drying efficiency. As a result, it is possible to obtain a grain drying method in which the drying efficiency is improved by comprehensively considering the dehydration amount, the total power consumption, and the grain quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the equilibrium moisture content of grains, the temperature of outside air and the temperature of exhaust gas, and the relative humidity.

FIG. 3 is a flow diagram of a conventional example.

FIG. 4 is a flow diagram of another conventional example.

[Explanation of sign]

 1 Storage tank 7 Blower 11 Detector 12 Dehumidifier operation determination unit 13 Dehumidifier 14 Outside air intake damper 15 Exhaust damper 16 Grain safety determination unit 17 Detector 18 Recycle / air volume determination unit 19 Recycle / non-recycle determination unit mx Ambient air relative humidity tx outside temperature Mx exhaust relative humidity Tx exhaust temperature My blast humidity

Claims (5)

[Claims] 1. A method for drying grains, in which drying air that has passed through a dehumidifier is introduced into a storage tank that stores the grains by a blower to dry the grains, in which relative humidity and temperature of exhaust gas discharged from the storage tanks. And the grain moisture stored in the storage tank from the equilibrium moisture content of the grain and controlling the amount of air blown into the storage tank in accordance with the determined moisture. How to dry. 2. A method for drying a grain, in which drying air that has passed through a dehumidifier is introduced into a storage tank storing the grain by a blower to dry the grain, and the temperature and relative humidity of the outside air and the discharge from the storage tank are used. When the relative humidity of the outside air is higher than the relative humidity of the exhaust air and / or the outside air temperature is lower than the exhaust temperature, the exhaust gas is recycled with a small air volume to determine the relative humidity of the outside air. A method for drying cereals, characterized in that, when the temperature is lower than the relative humidity of exhaust gas and / or the external air temperature is higher than the exhaust gas temperature, the external air is sucked and dried with a large amount of air and then the exhaust gas is discharged. 3. A relative humidity and temperature of exhaust gas discharged from the storage tank in a method of drying a grain by introducing drying air that has passed through a dehumidifier to a storage tank storing the grain by a blower. Determine the water content of the grains in the storage tank by using the
When the temperature and relative humidity of the outside air and the temperature and relative humidity of the exhaust gas discharged from the storage tank are compared, and the relative humidity of the outside air is higher than the relative humidity of the exhaust gas, or when the outside air temperature is lower than the exhaust temperature. Of cereals, characterized by recycling the exhaust and sucking the outside air and drying it after the outside air has a relative humidity lower than the exhaust relative humidity and / or an outside temperature higher than the exhaust temperature. Drying method. 4. A grain drying method in which drying air that has passed through a dehumidifier is introduced by a blower to a storage tank that stores grains to dry the grains, and whether or not the grains are safe in a grain safety determination unit. If it is judged to be safe by comparing the temperature and relative humidity of the outside air with the temperature and relative humidity of the exhaust air, the relative humidity of the outside air is higher than the relative humidity of the exhaust air, and or When the outside air temperature is lower than the exhaust temperature, the exhaust air is recycled with a small air flow, and when the outside air relative humidity is lower than the exhaust air relative temperature or the outside air temperature is higher than the exhaust temperature, the outside air is sucked in with a large air flow rate. It is characterized by discharging the exhaust after drying, and if it is judged that the grain is not safe, make a large air volume and compare the outside air condition with the exhaust condition to judge whether the exhaust gas is recycled or not. How to dry grain. 5. A method for drying a grain, in which drying air that has passed through a dehumidifier is introduced into a storage tank that stores the grain by a blower to dry the grain, and dehumidification is performed depending on the outside air condition. When the dehumidifier operation judgment unit judges that the dehumidifier is not operated, it sucks the outside air with a large air volume to dry it and discharges the exhaust air, and when it is judged that the dehumidifier is operated, the grain safety judgment unit judges that the grain is safe. If it is safe, the temperature and relative humidity of the outside air are compared with the temperature and relative humidity of the exhaust gas, and the relative humidity of the outside air is higher than the relative humidity of the exhaust gas. And / or when the outside air temperature is lower than the exhaust temperature, the exhaust air is recycled with a small air flow, and the relative humidity of the outside air is lower than the relative humidity of the exhaust, and / or the outside air temperature is higher than the exhaust temperature. In addition, after sucking the outside air with a large air volume and drying it, the exhaust air is discharged, and if it is judged that the grain is not safe, make a large air volume and compare the outside air condition with the exhaust condition to recycle the exhaust gas. A method for drying a grain, which comprises judging.