JPH05223450A - Drying control system for grain drier - Google Patents

Abstract

PURPOSE:To shorten a drying time of grains, to reduce a cost, and to improve a drying speed by a method wherein drying is performed after unriped grains are removed by a grain size selecting device according to an amount of unriped grains mixed in grains intended to be dried and a drying mode when the moisture content of the grains is high. CONSTITUTION:A grain drier 1 is formed such that a transfer bucket 12 and a ceiling plate 13 are disposed to the upper part of a machine wall 11 and a grain storing chamber 14 is formed below the ceiling plate 13. A grain drying chamber 15 is disposed below the grain storing chamber 14 and between discharge chambers 16 on both sides and a blast chamber 11. Further, a delivery valve 18 and a grain collecting bucket 19 are disposed below the grain drying chamber 14. A grain side selecting device 3 is disposed to the outside part of the machine wall 11. In this constitution, when a quantity of mixed unriped grains is high and a dehumidified air drying mode or a low temperature constant hot blast drying mode is selected, unriped grains are removed for disposal by the grain size selecting device 3 when a grain moisture content is high. Meanwhile, when mixture of unriped grains is low, the grain side selecting device 3 is brought into a stop.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drying control system for a grain dryer.

[0002]

2. Description of the Related Art Conventionally, while feeding and flowing down the grains from the grain storage chamber to the grain drying chamber, hot air or dehumidifying air is passed through the drying chamber to allow the grains flowing down the drying chamber. Is exposed to these hot air or dehumidified air and dried. After the completion of the drying, the dried grain was supplied to a grain size sorting device and passed through the grain size sorting device to sort into large grain grain and immature grain.

[0003]

The grains stored in the grain storage chamber of the grain dryer are fed from the storage chamber into the grain drying chamber and flowed down while hot air or dehumidified air blows through the drying chamber. By passing, the grains flowing down in the drying chamber,
When exposed to these hot air or dehumidified air and dried, and when the moisture content of the grain being dried reaches the finishing target moisture content, it is determined that the drying is completed, the dryer is stopped, and the drying of the grain is stopped. ..

After the completion of the drying, the dried grains are supplied to a grain size sorting device and passed through the grain size sorting device to be sorted into large grain grains and immature grains. At the time of this drying, a part of the grains is supplied to the particle size selection device while drying the grains by a dehumidification drying mode using dehumidifying air, or a drying mode such as a low temperature constant hot air drying mode using low temperature constant hot air. It is intended that large grains having a large grain size and immature grains are sorted, the sorted immature grains are discharged to the outside of the machine, and the sorted large grain grains are circulated and dried.

[0005]

According to the present invention, hot air or dehumidified air is ventilated into the drying chamber 15 while feeding and flowing down the grains from the upper grain storage chamber 14 to the lower grain drying chamber 15. In a grain dryer that supplies a part of the grain that is being circulated and dried while being dried to the grain size selection device 3 and sorts it into a large grain size grain and an immature grain, when there is much immature grain mixing, When selecting a dehumidifying air drying mode by dehumidifying air, or selecting a low temperature constant hot air drying mode by low temperature constant hot air, immature grains are removed by the grain size selection device 3 when the grain moisture is in a high moisture state, When the mixture of the immature particles is small, the particle size selecting device 3 is stopped and controlled, and the drying control method is adopted.

[0006]

The grains stored in the grain storage chamber 14 of the grain dryer are fed out from the storage chamber 14 into the grain drying chamber 15 and flow down, depending on the taste and quality of the grains. The generated dry air is controlled to generate dehumidified air or hot air, which is exposed to the dehumidified air or hot air and dried, and when the moisture content of the grain during drying reaches the finishing target moisture content, the drying is completed. As a result, the dryer is stopped and the drying of the grain is stopped.

At the time of this drying, when the amount of immature grains mixed in the grain being dried is large, and in the dehumidifying air drying mode by dehumidifying air and the low temperature constant hot air drying mode by low temperature constant hot air, the grain is When the grain water content is high, a part of the grain being dried is supplied to the grain size sorting device 3, and by passing through the grain size sorting device 3, it is sorted into a large grain grain and an immature grain. The sorted immature grains are discharged to the outside of the machine, and the sorted large grain grains are circulated and dried.

When the amount of the immature grains mixed is small, the grain size selecting device 3 is controlled to stop even in the dehumidifying drying mode or the low temperature constant hot air drying mode, and the grains are large grain size grains. It is dried without being sorted into grains and immature grains. Also, in the low temperature step drying mode other than the dehumidifying drying mode and the low temperature constant hot air drying mode, and the overhang amount hot air drying mode, the grain size selection device 3 is stopped and controlled, and the grains are large grain grains and immature grains. It is dried without being sorted.

[0009]

[Effects of the Invention] When the moisture content of the grain is high depending on the mixing amount of the immature grains mixed in the dried grain and the drying mode,
Even in the dehumidifying and drying mode and the low temperature constant hot air drying mode, which require a long drying time and high drying cost, because the immature particles are removed and dried by the particle size selection device 3,
The drying time is shortened, the cost can be reduced, and the drying speed is improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The illustrated example is a circulation type grain dryer 1 for drying grains.
A moisture sensor 2 for detecting the moisture of the grain, a particle size sorting device 3 for sorting the grain, a drying device 4 for drying the sample grain,
The hulling device 5 for hulling the sample grains, the drum split quality detecting device 6 for detecting the barrel split of the grains, the external quality detecting device 7 for detecting the external grade, the taste detecting device 8 for detecting the taste, and the hot air are It shows a state in which a hot air device 9 or the like for generating is installed and a dehumidifying device 10 for generating dehumidified air is provided.

The dryer 1 has a rectangular shape that is long in the front-rear direction and has a transfer gutter 12 and a ceiling plate 13 in which a transfer spiral is rotatably installed in the upper part of the machine wall 11. Below the ceiling plate 13, grains are provided. A grain storage chamber 14 for storing grains is formed. The grain drying chambers 15 and 15 are provided below the storage chamber 14 between the left and right air exhaust chambers 16 and 16 and the central air blowing chamber 17, and the grain drying chambers 15 and 15 have lower grains. The pay-out valves 18 for paying-out and paying off are respectively rotatably supported.

The grain collecting trough 19 rotatably supports a transfer spiral and is provided below the drying chambers 15 and 15 to communicate with each other. The hot air device 9 includes a burner 20 and a burner case 21.
The burner case 21 is installed in the interior of the machine wall 1
1 On the front side, it is detachably provided on the outer side of the hot air passage chamber 22 formed on the outer side of the machine wall 11 so as to correspond to the inlet side of the blower chamber 17, and the dryer 1 and the like are installed, dried and discharged. An operation device 23 for starting and stopping each work is detachably provided on the machine wall 11 on the front side.

The blower 24 is a machine wall 11 on the rear side,
The exhaust passage chamber 25 provided to communicate with the left and right exhaust chambers 16, 16 is provided in the central rear side exhaust cylinder 26, and the exhaust wall 24 on the rear side of the exhaust passage rotates the exhaust fan 24. A fan motor 27 is provided. A valve motor 28 rotationally drives the delivery valves 18, 18 via a speed reduction mechanism.

The particle size selecting device 3 includes the lateral machine wall 11
Of the immature grain that leaks through the sorting net is rotatably rotatably supported by a sorting net that is rotatably driven by a particle size sorting motor that sorts large-grained grains and immature grains in the inside. Grains are collected on one side of the downflow funnel 29. An immature grain opening / closing valve 30 that can be opened and closed is provided below the downflow funnel 29, and in the opened state of the immature grain opening / closing valve 30, the immature grains are supplied into the immature grain tank 32 through the immature grain downflow cylinder 31. When the immature grain opening / closing valve 30 is closed, the immature grains are supplied through the immature grain flow-down cylinder 33 into the squeeze hopper 35 provided below the grain raising machine 34 of the dryer 1.
At the time of sorting at the initial stage of the start of drying, the rotation of the sorting net is accelerated or inclined to remove a large amount of immature grains early.

The immature grain weighing machine 36 is provided in the immature grain tank 32.
The weight of the immature grains provided on the lower side and supplied to and stored in the immature grain tank 32 is measured. The large particle size grains that are sorted and transferred in the sorting net are supplied into the large particle size funnel 37 from the terminal end of the sorting net, and the large particle size funnel 37 is supplied.
A large particle size opening / closing valve 38 that can be opened and closed is provided in the lower portion, and when the large particle size opening / closing valve 38 is in a half-opened state, a part of the large particle size grain is sampled to the drying device 4 via the large particle size downflow tube 39. The grain is supplied as the grain, and the rest is passed through the large grain size falling pipe 40 and the grain raising machine 3
4 is fed into the tensioning hopper 35. Further, when the large particle size opening / closing valve 38 is closed, all the large particle size grains are supplied into the hopper 35 of the grain raising machine 34 through the large particle size downflow cylinder 40. Either one of these is done.

The drying device 4 is provided with a sample drying chamber 41 for drying a part of the supplied large-sized grains in a central portion,
A transfer spiral is provided in the lower portion of the sample drying chamber 41, a sample hot air device having a far infrared heater 42 therein is provided on one side of the sample drying chamber 41, and a sample exhaust device 43 for sucking and exhausting hot air is provided on the other side. Is provided. A large particle size measuring machine 44 for measuring the weight of the large particle size grains in the sample drying chamber 41 is provided below the drying device 4.

The hulling device 5 is provided below the drying device 4, and the large grain grains supplied from the transfer spiral of the sample drying chamber 41 are hulled by an internal transfer hulling spiral. The rice is separated into brown rice and rice husk, the rice husk is discharged to the outside of the machine, and the brown rice is supplied to the brown rice funnel 45. A brown rice switching valve 46 is provided below the brown rice funnel 45, and when the brown rice switching valve 46 is in a half-opened state, it is supplied to the taste detecting device 8 on the lower side through a brown rice falling tube 47, and the lower splitting quality is detected. It is supplied to the apparatus 6 through the brown rice falling tube 48, and is further supplied to the appearance quality detecting apparatus 7 on the lower side.

The taste detecting device 8 comprises a near-infrared spectroscopic analysis device emitted from a light source and a storage device for storing the coefficient for calculating the taste evaluation value. By these, the brown rice for the sample supplied through the brown rice lowering cylinder 47 is received and the taste is detected in three stages, for example, good, normal and bad, and the detected brown rice is passed through the brown rice discharging cylinder 49 and the grain refiner. It is supplied to the tension hopper 35 of 34.

The quality detecting devices 6 and 7 include the body split quality detecting device 6 and the appearance quality detecting device 7. Of these, the body split quality detection device 6 includes a transmitted light detection unit, and the presence or extent of the body crack can be determined by detecting the amount of transmitted light. On the other hand, the appearance quality detecting device 7 receives the brown rice for the sample supplied through the brown rice flow down tube 48 based on the data obtained by irradiating the transmitted light amount, the reflected light amount, etc., and damages that are mixed into the brown rice. Grain, heterogeneous grain, foreign matter, dead rice, colored grain, etc. are detected and the quality is detected in three stages, for example, good, normal and bad.
It is supplied to the grain collecting trough 19 through the brown rice discharging cylinder 50.

The fuel pump 51 has a fuel valve,
The fuel pump 51 is provided outside the lower plate of the burner case 21, and by opening and closing the fuel valve, the fuel in the fuel tank 52 is sucked by the fuel pump 51 and supplied to the burner 20.
The blower 53 is provided on the outer side of the upper plate, is rotationally driven at a variable speed by a blower motor 54 for shifting, and blows the combustion air corresponding to the supplied fuel amount to the burner 20 by the blower 53.

The dehumidifying device 10 is arranged at the front part of the dryer 1, and in order to convert the outside air sucked from the suction port into dehumidified wind, the low temperature low pressure gas which is a refrigerant is high temperature high pressure in the compressor. When it is adiabatically compressed to gas, it is deprived of heat when it passes through the condenser and changes to a high-temperature high-pressure liquid, after which it is reduced in pressure to a low-temperature low-pressure liquid by an expansion valve, and then absorbs heat when it passes through the evaporator. Is changed to low-temperature low-pressure gas, and the refrigerant is sequentially repeated in this cycle.
The outside air passing through the inside is dehumidified and converted into dehumidified air, and the dehumidified air passes from the hot air passage chamber 25, the blower chamber 17, and the drying chambers 15, 15.

The diffusion board 55 is provided at the center of the bottom plate of the transfer gutter 12 in the front-rear direction, below the supply port for supplying the transfer grains to the storage chamber 14, and evenly diffusing the grains into the storage chamber 14. I'm giving back. The discharge funnel 55 'is provided on the bottom plate portion of the starting end of the transfer gutter 12, and a discharge switching valve 59 that can be opened and closed is provided on the bottom plate portion. A discharge on-off valve 56 that can be opened and closed is provided below the discharge funnel 55'. During the installation and discharge operation, the dried grains are discharged to the outside of the machine through the discharge cylinder 57 by the opened state of the discharge opening / closing valve 56 and the fully opened state of the discharge switching valve 59. During the drying operation, the discharge opening / closing valve 56 is closed and the discharge switching valve 59 is half-opened so that the grains are circulated and supplied into the storage chamber 14 through the transfer gutter 12 and the discharge cylinder 58.
Some of the grains are supplied to the particle size selection device 3 through the above or the discharge switching valve 59 is closed, so that the grains only pass through the transfer gutter 12 into the storage chamber 14. Either circulation supply or one of these is performed. In addition, during the staking operation, the discharge switching valve 59 is closed, so that the grains are stretched into the storage chamber 14 through the transfer gutter 12.

The grain raising machine 34 is provided outside the front side of the machine wall 11 and has a belt with a bucket conveyor 60 stretched inside. The upper end portion is thrown between the transfer gutter 12 and the starting end portion. An outlet pipe 61 is provided for communication, and a lower end portion thereof is provided with a supply gutter 62 between the terminal end portion of the grain collecting trough 19 for communication. 63 is a sublimator motor, the belt with the bucket conveyor 60, the transfer spiral in the transfer gutter 12,
The moving spiral and the like in the diffusion board 55 and the grain collecting trough 19 are rotationally driven.

The moisture sensor 2 is provided substantially vertically in the center of the grain raising machine 34. The moisture sensor 2 is rotated by a moisture motor 64 when an electric measurement signal is transmitted from the operating device 23. Each part of the moisture sensor 2 is rotationally driven, and receives the grains falling while being conveyed to the upper portion by the bucket conveyor 60. While crushing the grains by pressure, the moisture of the crushed grains is detected.

The operating device 23 has a box shape, and the drier 1, the moisture sensor 2, the hot air device 9, the dehumidifying device 10, etc. are put on the surface plate of the box for drying, discharging. Each start switch 65 for starting operation for each work, stop switch 66 for stopping operation, moisture setting picker 67 for setting target finishing moisture of grain by operation position, hot air device 9 or hot air generated from dehumidifying device 10 There are provided a grain type setting knob 68 for setting the temperature or the dehumidifying air temperature according to the operation position, a sticking amount setting knob 69, a display section 70 for digitally displaying various display items, a monitor display and the like.

The control device 71 is provided in the operation device 23, and the detection values detected by the moisture sensor 2, the immature grain weighing machine 36, the large grain size weighing machine 44, and the hot air temperature sensor 72 and the respective switches. The operation of 65 and 66 and the operation of the setting keys 67, 68 and 69, etc. are inputted, and the CPU 73, etc. for arithmetic and logical operation and comparison operation of these inputs,
The CPU 73 controls the motors 27, 28, 54, 6
3, 64, the fuel valve, the fuel pump 51, etc. are started, stopped and controlled, and the on-off valves 30, 3
The motors for fully opening and closing 8, 46, 56, 59 are controlled to rotate and stop. Each setting selection 6
7, 68 and 69 are rotary switch systems, and predetermined numerical values and types are set according to the operation position.

The drying control of the grain by the control unit 71 is configured as follows. That is, the operation of the start switch 65 for starting the drying operation is input to the CPU 73, and by this input, the dehumidifier 10 is temporarily operated.
Is started and the drying operation by dehumidifying air is started (step 101), and some grains are supplied to the grain size selection device 3 to be sorted into large grain size grains and immature grain size, and have been sorted. Part of the grain-size grains is supplied to the drying device 4 and the hulling device 5, and a part of the hulled brown rice that has been hulled is transferred to the body splitting quality detection device 6 and the appearance quality detection device 7. As shown in FIG. 4, the quality according to the mixing ratio of damaged grains, colored grains, different grains and foreign substances other than the amount of dead rice is detected as good, normal and bad, and there is no dead rice mixed. Is detected.

The remaining hulled brown rice is supplied to the taste detecting device 8 and the taste is detected to be good, normal or bad. Based on these detection results of quality, amount of dead rice, and taste, the drying mode is, for example, from the outside temperature of the dehumidifying and drying mode by the dehumidifying air from the dehumidifying device 10 and the hot air drying by the hot air from the hot air device 9, A low temperature constant hot air drying mode by a low temperature constant hot air of 10 ° C. higher, a low temperature step drying mode in which a predetermined temperature is sequentially increased from a low temperature of 10 ° C. higher than the outside air temperature, or a predetermined temperature increases every predetermined moisture,
And the hot air temperature is selected according to the amount of grain to be inflated, and is classified into four modes of the infiltration amount hot air drying mode. From these four modes, the drying mode is selected (step 102), and the selected drying mode is provisionally set. The dehumidification / drying mode is switched or continuously controlled (step 103).

When the dehumidifying and drying mode and the low temperature constant hot air drying mode are set, the selected large grain size grains supplied to the drying device 4 out of the predetermined grain amount supplied to the grain size selecting device 3. Is weighed by the large grain size measuring machine 44, and the weight of the sorted immature grains discharged to the immature grain tank 32 is weighed by the immature grain weighing machine 36. Whether the amount of immature grains is large or small is detected based on the grain weight and the immature grain weight (step 10).
4).

When it is detected that a large amount of immature grains are mixed, a part of the grains is supplied to the grain size selection device 3, and the grains are continuously sorted into large grain grains and immature grains. While being dried (step 105). When it is detected that the amount of immature grains is small, the grain size sorting device 3 is stopped and the grain is stopped from being fed to the grain size sorting device 3 and sorted into large grain grains and immature grains. Not dried but only dried (step 1
06).

In addition, the control device 71 has the following functions. When the moisture sensor 2 detects the same grain moisture as the finishing target moisture set by operating the moisture setting scoop 67, it is detected that the drying of the grain has ended, and the dryer 1
Automatic stop control. When the taste detected by the taste detecting device 8 is standard and below standard, and the quality detected by the body splitting quality detecting device 6 and the appearance quality detecting device 7 is below standard and standard, from the hot air device 9 The hot air temperature is set according to the amount of the hot-air kernels, and the hot-air temperature is set to the hot-air drying mode to dry the hot-air kernels. Further, at this time, the grain size selection device 3 is stopped, the supply of grains to the grain size selection device 3 is stopped, and only the large grain grain and immature grain are not sorted but only dried. Also in the low temperature step drying mode, only large-sized grains and immature grains are not sorted but only dried.

The dehumidifying device 10 is temporarily started to start drying with dehumidifying air (step 201), and the drying mode is selected according to the quality of the grain, the amount of dead rice mixed and the taste (step 202), and the low temperature is selected. A low temperature constant hot air drying mode with constant hot air is selected and switched to this mode (step 203), it is detected whether the amount of immature grains mixed is large (step 204), and if NO is detected, the particle size selection is performed. The operation of the apparatus 3 is stopped (step 205), and the low temperature constant hot air drying mode allows the immature grains to be dried without being sorted (step 206).

When YES is detected in (step 204), it is detected whether the particle size selecting device 3 is operated (step 207), and when YES is detected, the particle size selecting device 3 is operated ( Step 208), while the immature grains are sorted in the low temperature constant hot air drying mode, the grains are dried (step 209). When NO is detected in (Step 207), it is detected whether or not the drying mode is changed (Step 2
10) If NO is detected, the grains are dried in the low temperature constant hot air drying mode without selecting the immature grains (step 211). If YES is detected, the low temperature step drying mode is used to dry the grains without selecting the immature grains (step 212).

The operation of the above embodiment will be described below. By operating the setting scoops 67, 68, 69 of the operating device 23 to predetermined positions and operating the start switch 65 for starting the drying operation, each part of the grain dryer 1 and the dehumidifying device 1 are operated.
0, the moisture sensor 2 and the like are started, dehumidifying hot air is generated from the dehumidifying device 10, and the dehumidifying hot air passes from the hot air duct chamber 22 and the air blowing chamber 17 through the grain drying chambers 15 and 15 and exhausts air. Room 1
The exhaust air is sucked and exhausted by the air exhaust device 24 through the exhaust air duct chambers 6, 16 and the exhaust air passage chamber 25.

The grains stored in the grain storage chamber 14 are exposed to the dehumidified hot air while they are flowing down from the storage chamber 14 into the drying chambers 15 and 15 to be dried, and the feeding valves 18 and 1 are fed.
At 8 it is fed to the lower part and flows down, and is fed from the grain collecting trough 19 through the supply gutter 62 into the grain raising machine 34 by the lower transfer spiral and is conveyed to the upper part by the bucket conveyor 60 and is ejected from the ejecting cylinder 6
1 is supplied into the transfer gutter 12 and is then supplied from the transfer gutter 12 onto the diffusion plate 55 by an upper transfer spiral, and is uniformly diffused and reduced into the storage chamber 14 by the diffusion plate 55 and circulated and dried. It

A part of the grain which is being dried has a particle size selection device 3
And is sorted into large grain size grains and immature grain size in the grain size sorting device 3, and the sorted immature grain size is discharged from the downflow funnel 29 through the immature grain flow down cylinder 31 into the immature grain tank 32. Be stored. The sorted large grain grain is supplied from the large grain funnel 37 through the large grain downflow tube 39 to the drying device 4 and dried, and the dried large grain grain is supplied to the hulling device 5 and paddy. Some hulled brown rice has been removed from the brown rice funnel 45 and the brown rice flow down cylinder 4
After being supplied to the taste detecting device 8 through 7, the taste of brown rice is
It is detected as good, normal and bad, and a part of the other hulled brown rice is supplied from the brown rice funnel 45 through the brown rice flow lowering cylinder 48 to the splitting quality detecting device 6 and further to the appearance quality detecting device 7. Then, the quality of brown rice is detected as good, normal and bad, and at the same time, it is detected that dead rice is not mixed in or is present.

Dehumidifying hot air generated from the dehumidifying device 10 due to the detected taste, quality and dead rice mixture,
The dehumidifying / drying mode for drying is continued, or the temperature is controlled to be switched between a low temperature constant hot air drying mode for drying hot air with hot air generated from the hot air device 9, a low temperature step drying mode, and a stake amount hot air drying mode for drying. At the time of this drying,
When the dehumidifying and drying mode and the low temperature constant hot air drying mode are selected to dry the grain, the weight of the sorted large grain size grain supplied into the drying device 4 is measured before the drying. The weight of the sorted immature grains weighed by the machine 44 and fed into the immature grain tank 32 is weighed by the immature grain weighing machine 36, and it is detected whether the amount of the immature grains mixed is large or small. When detected, the grain size sorting device 3 continues to sort, and the grain is dried while being sorted. Further, when it is detected that the amount is small and in a drying mode other than the above, the particle size selection device 3 is stopped and controlled, the supply of grains to the particle size selection device 3 is stopped, and the grain size is increased. It is dried without being sorted into large grains and immature grains.

When the grain moisture detected by the moisture sensor 2 is the same as the finishing target moisture set by operating the moisture setting scoop 67, it is determined that the drying of the grain is completed. It is detected, and is automatically controlled by the control device 71 to automatically stop the dryer 1, and the drying of the grain is stopped.

[Brief description of drawings]

 The figure shows an embodiment of the invention.

FIG. 1 is an overall side view of a grain dryer.

FIG. 2 is an enlarged sectional view taken along line AA of FIG.

FIG. 3 is a block diagram.

FIG. 4 is a diagram showing a relationship between a drying mode and sorting by a particle size sorting device.

FIG. 5 is a flowchart.

FIG. 6 is a flowchart.

FIG. 7 is an enlarged front view in which a part of the grain dryer is partially broken.

[Explanation of symbols]

 3 Grain size selection device 14 Grain storage chamber 15 Grain drying chamber

Claims (1)

[Claims] 1. A circulating drying method in which hot air or dehumidifying air is blown into the drying chamber 15 while it is being flowed down from the upper grain storage chamber 14 to the lower grain drying chamber 15 and is being dried. In a grain dryer that supplies the grain of part of the grain to the grain size sorting device 3 and sorts the grain into the large grain size and the immature grain, when the immature grain is mixed in a large amount, the dehumidifying air drying mode by the dehumidifying air is set. When selecting or selecting the low temperature constant hot air drying mode by the low temperature constant hot air, when grain water is in a high moisture state, immature grains are removed by the particle size selection device 3, and when immature grain mixing is small, A drying control method characterized in that the particle size selecting device 3 is stopped and controlled.