JPH0464885A - Grain drying method - Google Patents

Abstract

PURPOSE:To effect drying treatment within a short period of time without generating any trouble such as overdrying, heat damage or the like by a method wherein an atmospheric humidity is measured during drying treatment and drying by hot air is switched into the drying by natural air when the atmospheric humidity becomes lower than a predetermined value while the drying by the natural air is switched into the drying by hot air when the atmospheric humidity has become higher than the predetermined value. CONSTITUTION:A downflow passage 18, partitioned by a porous bulkhead, is formed in a drying unit 16 to serve to the downflow of grains in a grain tank 14. An air guiding passage 20 and an air discharging passage 22 are formed alternately between neighboring downflow passages 18. A burner 24 is arranged in the suction side of the air guiding passage 20 and a suction type air discharging passage 27 is arranged in the exhaust side of the air discharging passage 22. When an air sucking and air discharging machine 27 is operated, atmosphere is sucked from the suction side of the air guiding passage 20 and is discharged out of the air discharging side. When the burner 24 is operated under a condition that the suction and air discharging machine 27 is operated, atmosphere is heated and hot air is supplied to the grain at the downstream side of the downflow passage 18 to dry them. A temperature sensor 58 is arranged near the burner 24. The temperature sensor 58 detects the temperature of natural air or hot air supplied to the grains in the downflow passage 18. An atmospheric humidity sensor 62, detecting the humidity of the atmosphere, and an atmospheric temperature sensor 64, detecting the temperature of the atmosphere, are attached to the side surface of the body of the machine 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a grain drying method for drying grain by supplying hot air or natural air to the grain.

[Conventional technology]

Grain that has been kept at a constant temperature and humidity for a long time is
It reaches a predetermined moisture content that is in balance with humidity, the so-called equilibrium moisture content.

The grain is dried by supplying the grain with air at a humidity lower than this equilibrium moisture content. Also, the drying speed of grains,
In other words, the drying rate depends on the so-called free moisture content, which is the difference between the moisture content of the grain and the equilibrium moisture content corresponding to the temperature and humidity of the supplied air.If the free moisture content is large, the drying rate of the grain will be large. Become. A conventional grain drying apparatus that dries grain according to outside air humidity dries grain using the following drying method.

That is, the drying process is performed after measuring the outside air humidity and selecting whether to supply hot air or natural air depending on the outside air humidity. When the outside air humidity is high, the equilibrium moisture content of the grain is high relative to the outside air humidity, and drying that supplies natural air to the grain may not be able to dry the grain to the specified moisture content, or it will take a long time, so heating the outside air is necessary. Drying is performed by generating low-humidity hot air and supplying this hot air to grains to lower the equilibrium moisture content. Furthermore, when the outside air humidity is low, the equilibrium moisture content of the grain is low relative to the outside air humidity, and the grain is dried by supplying natural air to reduce fuel consumption. In this way, by selectively supplying natural air or hot air depending on the outside air humidity, drying time is shortened and fuel consumption is reduced.

[Problem to be solved by the invention]

However, the above-mentioned drying method cannot cope with a case where the outside air humidity during the drying process changes from the measured value before the drying process, and it may not be possible to perform the appropriate drying process. For example, if the outside air humidity decreases during drying by supplying hot air, the humidity of the hot air supplied to the grain will decrease, and the equilibrium moisture content will become lower than necessary, increasing the drying rate and causing excessive drying. This may result in dryness, heat damage to many grains, and other problems such as on the trunk side.

In addition, if the outside air humidity increases during drying by supplying natural air, the humidity of the natural air supplied to the grain will increase, so the moisture content of the grain and the equilibrium moisture content of the grain with respect to the natural wind will increase. As the difference became smaller, the drying speed of the grain became slower and the drying time increased, or the grain could not be dried to a predetermined moisture content.

The present invention has been made in consideration of the above-mentioned facts, and an object thereof is to provide a grain drying method that can perform drying treatment in a short time without causing problems such as overdrying or heat damage.

[Means to solve the problem]

The invention described in claim (1) measures outside air humidity, and when the outside air humidity is above a predetermined value, the grains are dried with hot air, and when the outside air humidity is less than a predetermined value, the grains are dried with natural air. In the grain drying method, the outside air humidity is measured during the drying process, and if drying is performed using hot air, when the outside air humidity falls below a predetermined value, the drying is switched to natural air, and drying is performed using natural air. If the outside air humidity exceeds a predetermined value, the drying method switches to hot air drying.

The invention described in claim (2) measures outside air humidity, and when the outside air humidity is above a predetermined value, the grains are dried with hot air, and when the outside air humidity is less than a predetermined value, the grains are dried with natural air. In this grain drying method, the drying loss rate of the grain is calculated during the drying process, and if drying is performed using hot air, after the drying loss rate becomes larger than a predetermined value, the drying rate is switched to natural air drying.
When drying with natural air, the special feature is to switch to drying with hot air after the drying loss rate becomes less than a predetermined value.

The invention described in claim (3) measures the outside air humidity, and when the outside air humidity is above a predetermined value, the grains are dried with hot air, and when the outside air humidity is less than the predetermined value, the grains are dried with natural air. A grain drying method, characterized by calculating the drying loss rate of the grain during drying processing, and switching to rest drying when the drying loss rate becomes larger than a predetermined value when drying by natural wind. There is.

The invention described in claim (4) measures outside air humidity, and when the outside air humidity is above a predetermined value, the grains are dried with hot air, and when the outside air humidity is less than a predetermined value, the grains are dried with natural air. This grain drying method calculates the variation in the moisture content distribution of the grain during the drying process, and if drying is performed using the natural wind, the drying is stopped after the variation in the moisture content distribution exceeds a predetermined value. When drying with hot air is being performed, the drying is switched to drying with natural air after the variation in moisture content distribution exceeds a predetermined value.

The invention described in claim (5) measures the outside air humidity, and when the outside air humidity is above a predetermined value, the grain is dried with hot air at a temperature corresponding to the drying rate of the grain, and when the outside air humidity is less than the predetermined value. In some cases, this is a grain drying method in which grains are dried with natural air, and in the case of drying with hot air, if the temperature of the hot air determined according to the drying loss rate falls below the temperature of the outside air, drying with natural air is performed. It is characterized by switching to

[Effect]

In the invention of claim (1), the outside air humidity is measured during the drying process, and when drying with hot air is being performed, when the outside air humidity is less than a predetermined value, switching to drying with natural air is performed, and drying with natural air is performed. If the outside air humidity exceeds a predetermined value, the drying method switches to hot air drying. Therefore, if the outside air humidity decreases when drying using hot air, the equilibrium moisture content will decrease and the drying speed will become higher than necessary, but the drying process will switch to drying using natural air and the drying speed will be reduced. Therefore, inconveniences such as overdrying and heat damage do not occur, and the amount of fuel consumed by burners and the like for heating natural air into hot air can be reduced. Additionally, when drying using natural wind is performed and the outside air humidity increases, the equilibrium moisture content increases and the drying rate decreases;
Since the drying process is switched to supplying hot air and the drying speed is increased, the drying process can be performed in a short time.

In the invention described in claim (2), the drying loss rate of the grain is calculated during the drying process, and if drying is performed using hot air, the drying rate is switched to natural air drying after the drying loss rate becomes larger than a predetermined value. Therefore, the drying speed is reduced and problems such as overdrying and heat damage do not occur. Further, when drying with natural air is performed, the drying process is switched to hot air after the drying loss rate becomes less than a predetermined value, so that the drying process can be performed in a short time.

In the invention of claim (3), the drying loss rate of the grain is calculated during the drying process, and when drying by natural wind is performed, the drying rate is switched to rest drying after the drying loss rate becomes larger than a predetermined value. Inconveniences such as overdrying and thermal injury do not occur, and the power consumption of a fan and the like that generates natural air and the fuel consumption of a burner and the like that heat the natural air into hot air can be reduced.

In the invention of claim (4), the variation in the moisture content distribution of the grain is calculated during the drying process, and when drying is performed by natural wind, the process is stopped after the variation in the moisture content distribution exceeds a predetermined value. If drying is being performed using hot air, the drying is switched to natural air after the variation in moisture content distribution exceeds a predetermined value. When the moisture content distribution of grains has a large dispersion, the proportion of grains with high moisture content is high, so if drying is performed at a high drying rate, a large number of grains are susceptible to thermal damage. In the invention of claim (4), the drying process is switched so that the drying rate is reduced when the variation in the moisture content distribution is large, so that inconveniences such as thermal injury do not occur.

In the invention of claim (5), when drying with hot air is performed and the temperature of the hot air determined according to the drying loss rate becomes equal to or lower than the temperature of the outside air, the drying is switched to drying with natural air.
It is possible to reduce the amount of fuel consumed by a burner or the like for heating natural air into hot air.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings. In addition,
Although this example will be described using numerical values that do not interfere with the present invention, the present invention is not limited to the numerical values described below.

1 and 2 show a grain drying apparatus 10 to which the grain drying method of the present invention can be applied. Grain drying device 10
The fuselage 12 is shaped like a box that is high up and down and long in the front and back.

The upper inner cavity of the fuselage 12 serves as a grain tank 14, and the lower inner cavity serves as a drying section 16.

A flow path 18 partitioned by a porous stem≠ partition wall is formed in the drying section 16, so that the grains in the grain tank 14 flow down. Air guide passages 20 and air exhaust passages 22 are alternately formed between adjacent flow passages I8. A burner 24 is arranged on the intake side of the air guide path 20, and a suction exhaust fan 27 is arranged on the exhaust side of the air exhaust path 22.

When the suction exhaust fan 27 is operated, outside air is sucked in from the intake side of the air guide path 20, flows from the air guide path 20 through the downstream path 18 to the air exhaust path 22, and is discharged from the exhaust side of the air exhaust path 22. Ru.

Therefore, natural air is supplied to the grains in the flow path 18 and the grains are dried. Furthermore, when the burner 24 is operated while the suction/exhaust fan 27 is operating, the outside air is heated and hot air is supplied to the grains in the flow path 18 to dry them. Also, burner 2
A temperature sensor 58 is disposed near 4. The temperature sensor 58 detects the temperature of the natural air or hot air supplied to the grain in the flow path 18. Further, an outside air humidity sensor 62 for detecting the humidity of outside air and an outside air temperature sensor 64 for detecting the temperature of outside air are attached to the side surface of the body 12.

A shutter drum 30 that is reciprocated by a motor 28 is arranged at the lower end opening of the flow path 18.
The dried grains that have passed through the shutter drum 8 are delivered to a grain harvesting section 31 below the shutter drum 30.

There is a loading port 29 on the side of the grain harvesting section 3I for loading grain into the machine.
is provided.

Further, a lower screw conveyor 34 driven by a synchronous motor 32 is arranged at the lower part of the grain harvesting section 31, and is adapted to convey the grain fed out by the shutter drum 30 to the front side of the machine body 12. A packet conveyor 36 is erected on the front side of the body 12.

The inside of this packet conveyor 36 is comprised of an endless conveyor 39 driven by a synchronous motor 38 and grain conveying packets 41 attached to the endless conveyor 39. This packet conveyor 36 is a lower screw conveyor 3.
The grain sent out from 4 is conveyed to the top of the machine body 12. One end of an upper screw conveyor 40 corresponds to the upper end of the packet conveyor 36, and a rotary equalizer 42 is connected to the other end of the upper screw conveyor 40.

The upper screw conveyor 40 and the rotary equalizer 42 are driven by a motor 38 together with the packet conveyor 36, and distribute the grain lifted and conveyed by the packet conveyor 36 to the grain tank 14 of the machine body 12.

A moisture sensor 44 is arranged at the bottom of the packet conveyor 36 to detect the moisture value (moisture content) of the grain.
When the grain conveying packet 41 of the packet conveyor 36 is reversed, a portion of the scooped up grain flows into the inside.

As shown in FIG. 3, a power switch 50, a drying operation switch 52, a moisture setting dial 53, a grain setting dial 54, and a humidity setting dial 56 are provided on the operation unit 60.
are each connected to a control circuit 48 located inside the fuselage 12. The control circuit 48 also includes the burner 24, suction blower 27, motor 28, motor 32, motor 38, moisture sensor 44, and temperature sensor 58 described above.
, an outside air humidity sensor 62 and an outside air temperature sensor 64 are connected, and an AC power source 51 is also connected via a power switch 50. 60Hz)
AC is now supplied.

Next, the operation of this embodiment will be explained with reference to the flowcharts of FIGS. 4 and 5. The flowchart shown in FIG. 4 is a main routine, which is executed when the power switch 50 is turned on, grain is loaded into the grain drying apparatus 10, and the drying operation switch 52 is turned on.

In step 100, the set moisture content rate stored in advance in the control circuit 48 is determined. Then, the initial value t of the hot air temperature when performing the hot air drying process is read out. In the grain drying device 10, the moisture content of the grain is the set moisture content. Drying process is carried out until . Set moisture content. is determined and stored for each type of grain, and is a set moisture content rate according to the type of grain set with the grain setting dial 54. Read out. For example, the moisture content of paddy. is set to 15%.

In step 102, the motor 28.32.38 is turned on,
Shutter drum 30 and conveyance section (lower screw conveyor 34, packet conveyor 36, upper screw conveyor 4
0, rotate the rotary equalizer 42).

As a result, the grain is delivered from the drying section 16 to the grain harvesting section 31 by the shutter drum 30, and from the grain harvesting section 31, it is sequentially transferred to the packet conveyor 36 by the lower screw conveyor 34.
The packets 41 of the rotating packet conveyor 36 further transport the packets 41 to the side and upwardly. The grain conveyed above the machine body 12 by the packet conveyor 36 is sent to the upper central part of the machine body 12 by the upper screw conveyor 40, and is transferred to the grain bin 1 in the machine body by the rotary equalizer 42.
4 and circulated.

In step 104, a drying process routine is executed to dry the grain. This drying process routine will be explained below with reference to the flowchart shown in FIG.

In step 150, a predetermined amount of grain is supplied to the moisture sensor 44, the moisture content of each grain is measured by the moisture sensor 44, and the average value of the moisture content is calculated.

In step 152, the average value of the grain moisture content calculated in step 150 is determined as the set moisture content. It is determined whether the drying process has been completed, that is, whether the drying process has been completed. If the average moisture content of grains is not the set moisture content Do, the process moves to step 154.

In step 154, the outside air humidity HR is measured by the outside air humidity sensor 62. In step 156, the drying loss rate A is set corresponding to the average moisture content of grains stored in advance. Read out. For example, when the grain to be dried is paddy, the drying loss rate can be set as shown in the table below depending on the moisture content.

In table step 158, the average value of the moisture content determined this time is compared with the average value of the moisture content determined last time to determine the drying loss rate A indicating the degree of dryness from the previous time.

Note that when step 158 is executed for the first time, the moisture content is measured only once, so the drying rate is determined by the set drying rate A read out in step 156.

Substitute.

In step 160, it is determined whether the outside air humidity H2 is equal to or higher than a predetermined humidity α. This predetermined humidity α is such that the equilibrium moisture content corresponding to the predetermined humidity α of grain set by the grain setting dial 54 is the set moisture content. It is set to approximately match the . For example, the moisture content set in paddy grains to be dried. When the humidity is 15%, the predetermined humidity α is set to around 70% as shown in FIG. Therefore, when the outside air humidity H8 is equal to or higher than the predetermined humidity α, the equilibrium moisture content with respect to the outside air humidity H3 is the set moisture content. Even supply natural wind to the grain higher than the set moisture content. Since it is not possible to dry the grains to a certain extent, the process moves to step 162, and after step 162, hot air is supplied to the grains to dry them. Note that the equilibrium moisture content of the outside air is determined by the temperature and humidity of the outside air.
As shown in the figure, the relationship between the outside air humidity and the equilibrium water content, which uses the outside air temperature as a parameter, has a small amount of change with respect to changes in the outside air temperature. Therefore, the equilibrium moisture content of the outside air can be determined by measuring only the outside air humidity.

In step 162, the magnitude of variation in the moisture content distribution of the grains measured in step 150 is determined.

Regarding the magnitude of the variation, for example, the standard deviation value of the measured value of water content can be determined, and it can be determined that the variation is large when the standard deviation value is large, and that the variation is small when the standard deviation value is small.

In step 164, it is determined whether the variation is small.

When the variation in moisture content is large, the proportion of grains with high moisture content, that is, grains with high free moisture content, is larger than when the variation is small. Grain with a high free moisture content may dry at an excessive rate and cause thermal injury.

Therefore, in step 170, a predetermined value β is subtracted from the hot air temperature t.

If the variation in the measured values is small, the process moves to step 166.

In step 166, the drying rate A and the set drying rate A are determined.

Compare with. If the drying rate A is smaller than the set drying rate AO, a predetermined value β is added to the hot air temperature t in step 168 to increase the drying rate, and the process proceeds to step 176. If the drying rate and the set drying rate Ao are equal, the process moves to step 176.

Also, the drying rate is set to drying rate A. If it is larger than , the process moves to step 170, and the predetermined value β is subtracted from the hot air temperature t as described above. In the next step 172, the hot air temperature t
from outside temperature t. The difference Δt (temperature increase due to burner) is calculated by subtracting Δt. In step 174, it is determined whether Δt is greater than 0. If Δt is less than 0, the hot air temperature t is less than the outside air temperature and the outside air is supplied without being heated, so the process moves to step 188 and changes to the ventilation drying process. Note that this ventilation drying process will be described later.

If Δt is greater than O, the process moves to step 176.

In step 176, the suction exhaust fan 27 is operated and the burner 24 is ignited. As a result, a hot air drying process is performed, and the outside air heated by the burner 24 is sucked as hot air by the suction exhaust fan 27 and sent into the air guide path 20.
It is directly fed to the grain in the flow path 18. The hot air after absorbing moisture from the grains is discharged to the outside of the grain drying device 10 through the exhaust passage 22. In the next step 178, it is determined whether a predetermined time has elapsed. If the predetermined time has not elapsed, in step 180, the temperature of the hot air is controlled to control the burner 24 based on the detected value of the temperature sensor 58 so that the hot air supplied to the grain has the hot air temperature t. Note that the hot air drying process is repeated until it is determined in step 178 that a predetermined time has elapsed. After performing the hot air drying process for a predetermined period of time, the process returns to step 150.

Further, if it is determined in step 160 that the outside air humidity HR is smaller than the predetermined humidity α, the equilibrium moisture content with respect to the outside air humidity H3 is the set moisture content. The moisture content is set lower than the moisture content by supplying natural wind to the grain. Can be dried until dry. Therefore, in steps 182 and subsequent steps, a ventilation drying process is performed in which natural air is supplied to the grains.

That is, in step 182, the magnitude of variation in the measured values of moisture content is determined in the same way as step 162, and step 1
In 84, it is determined whether the variation is small. If the variation is small, use the drying rate A and the set drying rate A. Compare with. Drying rate is set to drying rate A. If it is smaller than , the process moves to step 168 to increase the drying rate, and the hot air drying process described above is performed. Therefore, drying time can be shortened. Drying rate A and set drying rate A. If they are equal, the suction exhaust fan 27 is activated and the burner 24 is extinguished in step 188. As a result, the ventilation drying process is performed, and the outside air is drawn as natural air by the suction/exhaust fan 27 without being heated, is sent into the air guide path 20, and is directly supplied to the grains in the flow path 18. The natural wind after absorbing moisture from the grains is discharged to the outside of the grain drying device 10 through the exhaust passage 22. In step 190, it is determined whether a predetermined time has elapsed or not, and the ventilation drying process is performed until the predetermined time has elapsed. After performing the ventilation drying process for a predetermined period of time, the process returns to step 150.

Further, if it is determined in step 184 that the variation in moisture content is large, or if it is determined in step 186 that the drying loss rate A is the set drying loss rate A. If it is determined that it is larger than , the ventilation drying process may cause problems such as overdrying or thermal injury, so in step 194 the operation of the suction/exhaust fan 27 is stopped and the burner 24 is extinguished. As a result, the drying process is temporarily stopped, and the grain is suspended for drying (tempering). In step 196, it is determined whether or not a predetermined time has elapsed, and the drying process is maintained in a stopped state until the predetermined time has elapsed. After the predetermined time has elapsed, the process returns to step 150.

In this way, in the drying routine, the average moisture content is equal to the set moisture content. Until this happens, hot air drying, ventilation drying, or rest drying are repeatedly performed depending on the outside air humidity Ha and the drying loss rate Δ.

In step 152, the average moisture content of the grain is determined as the set moisture content. If it is determined that this has occurred, the operation of the suction/exhaust fan 27 is stopped in step 198, and the burner 24 is extinguished to complete the process of the drying process routine, and the process returns to step 106 of the main routine shown in FIG. .

In step 106, the motors 28, 32, and 38 are turned off to stop the shack drum 30 and the conveyance section (lower screw conveyor 34, packet conveyor 36, upper screw conveyor 40, rotary equalizer 42), and the drying work is completed.

In this way, in this embodiment, the average value of the moisture content is the set moisture content. Until then, hot air drying, ventilation drying, or pause drying are repeated depending on the outside air humidity HR and the drying loss rate A, so if the outside air humidity decreases during hot air drying, the ventilation Since the drying process is changed and the drying speed is reduced, there will be no inconvenience on the shell side due to heat damage. Further, if the outside air humidity increases during the ventilation drying process, the drying process is changed to hot air drying process and the drying speed is increased, so that the drying process can be performed in a short time.

In addition, in this example, the degree of variation in the measured values of moisture content was determined, and if the variation was large, the drying rate was controlled to be small. No inconvenience will occur on the torso side, etc.

In this example, the predetermined value β is a constant, but the drying rate A
and set drying rate A. It may be increased or decreased depending on the size of the difference between the two.

In addition, in this example, the standard deviation value of the distribution of grains was used to find the size of the dispersion of the distribution of the measured values of moisture content. If it is spreading, the drying rate may be controlled to be low.

〔Effect of the invention〕

In the invention of claim (1), when drying is performed using hot air, the drying is switched to natural air when the outside air humidity becomes less than a predetermined value, so that problems such as overdrying and thermal injury do not occur. Energy saving can be achieved without any problems. Also,
If drying is performed using natural air, the drying process is switched to hot air when the outside air humidity reaches a predetermined value or higher, so that the drying process can be performed in a short time.

In the invention of claim (2), when drying is performed using hot air, drying is switched to natural air after the drying loss rate becomes larger than a predetermined value, so that inconveniences such as overdrying and thermal injury may occur. energy savings can be achieved without Also,
When drying with natural air, the drying process is switched to hot air after the drying loss rate becomes less than a predetermined value, so that the drying process can be performed in a short time.

In the invention of claim (3), when drying with natural air is performed, the drying is switched to rest drying after the drying loss rate becomes larger than a predetermined value, so that problems such as overdrying and heat damage do not occur. Energy saving can be achieved without any problems. Further, it is possible to perform a drying process that is closer to natural drying.

In the invention of claim (4), when drying is performed using natural air, the mode is switched to idle drying after the variation in the moisture content distribution reaches a predetermined value or more, and when drying is performed using hot air, the moisture content Since drying is switched to natural wind after the distribution variation exceeds a predetermined value, energy saving can be achieved without causing inconveniences such as thermal injury.

In the invention of claim (5), when drying with hot air is performed and the temperature of the hot air determined according to the drying loss rate becomes equal to or lower than the temperature of the outside air, the drying is switched to drying with natural air.
The amount of fuel consumed by burners, etc. can be reduced, and energy savings can be achieved.

[Brief explanation of the drawing]

is a block diagram of the circuit of the control device of the grain drying apparatus of this embodiment, FIGS. 4 and 5 are flowcharts explaining the operation of this embodiment, and FIG. 6 shows the relationship between outside air humidity and equilibrium moisture content. It is a line diagram. DESCRIPTION OF SYMBOLS 10... Grain drying device, 24... Burner, 27... Suction exhaust fan, 48... Control circuit, 58... Temperature sensor, 62... Outside air humidity sensor, 64... Outside air temperature sensor.

Claims (5)

[Claims] (1) A grain drying method in which outside air humidity is measured, and if the outside air humidity is above a predetermined value, the grain is dried with hot air, and when the outside air humidity is less than a predetermined value, the grain is dried with natural air, The outside air humidity is measured during the drying process, and if the outside air humidity is below a predetermined value when drying with hot air, the system switches to natural air drying. A grain drying method characterized by switching to drying using hot air when the temperature exceeds a predetermined value. (2) A grain drying method in which outside air humidity is measured, and if the outside air humidity is above a predetermined value, the grain is dried with hot air, and when the outside air humidity is less than a predetermined value, the grain is dried with natural air, The drying rate of the grain is calculated during the drying process, and if drying is performed using hot air, the drying rate is switched to natural air after the drying rate becomes greater than a predetermined value; if drying is performed using natural air. is a grain drying method characterized by switching to drying using hot air after the drying loss rate becomes less than a predetermined value. (3) A grain drying method in which outside air humidity is measured, and if the outside air humidity is above a predetermined value, the grain is dried with hot air, and when the outside air humidity is less than a predetermined value, the grain is dried with natural wind, A grain drying method characterized in that the drying loss rate of the grain is calculated during the drying process, and when drying by natural wind is performed, switching to rest drying is performed after the drying loss rate becomes larger than a predetermined value. (4) A grain drying method in which outside air humidity is measured, and when the outside air humidity is above a predetermined value, the grain is dried with hot air, and when the outside air humidity is less than the predetermined value, the grain is dried with natural wind, During the drying process, the variation in the moisture content distribution of the grains is calculated, and if the drying is performed using the natural air, after the variation in the moisture content distribution reaches a predetermined value or more, the drying is switched to rest drying, and the drying is performed using the hot air. A grain drying method characterized by switching to natural wind drying after the variation in moisture content distribution exceeds a predetermined value. (5) Measure the outside air humidity, and if the outside air humidity is above a predetermined value, dry the grain with hot air at a temperature that corresponds to the drying rate of the grain, and if the outside air humidity is less than a predetermined value, dry the grain with natural wind. A grain drying method for drying grains, which is characterized by switching to natural air drying when the temperature of the hot air, determined according to the drying loss rate, falls below the outside air temperature when drying with hot air is being carried out. Grain drying method.