Apparatus for drying granular objects involving pre-heating process

Information

  • Patent Grant
  • 6223451
  • Patent Number
    6,223,451
  • Date Filed
    Thursday, December 30, 1999
    25 years ago
  • Date Issued
    Tuesday, May 1, 2001
    23 years ago
Abstract
An apparatus for drying granular objects comprises, from the top of the apparatus, a holding section; a heating section for heating the granular objects flowing down from the holding section, the heating section being provided beneath the holding section and having a plurality of air ducts to which heated air is introduced; a drying air producing section connected to the air ducts, in which the heated air from the air ducts is mixed with air taken-in from the outside of the apparatus to produce a drying air; and a drying section for drying the granular objects by directly exposing the granular objects to the drying air. The dried granular objects are taken out from a taking-out section and returned to the holding section through a bucket elevator. The apparatus further comprises a detector for detecting the temperature of the drying air. Based on the detected temperature, a control device controls the temperature of the heated air so as to keep the temperature of the drying air to a predetermined temperature. The temperature of the drying air can be set to a desirable temperature while the heated air for the heating is kept at a high temperature. The drying operation is performed speedily and safely.
Description




BACKGROUND OF THE INVENTION




(1) Field of the Invention




The present invention relates to a method and an apparatus for drying granular objects in which the granular objects are dried by being exposed to drying air, and more particularly to a method and an apparatus for drying granular objects which utilize a structure for elevating the temperature of granular objects in advance to their exposure to the drying air.




(2) Description of the Related Art




As a conventional method for drying granular objects by exposing them to drying air, a common method was one in which a high temperature drying air was produced by a burner and a fan and the granular objects were repeatedly exposed to such drying air. However, for purposes of reducing the drying time and of preventing the quality change of the granular objects caused during the drying, a method involving pre-heating process of the granular objects, that is, a method with which the internal temperature of the granular objects is raised in advance before they are exposed to the drying air, has attracted attention as an improved method. One example of a drying apparatus which utilizes far infrared radiation for purposes of the pre-heating is found in Japanese Patent Publication No. 2789279.




The drying method and apparatus equipped with the far infrared radiation means disclosed in the above patent publication seemingly has achieved as far as the above objects are concerned. However, since the structure is such that the far infrared radiation generator should be installed within the drying chamber, the size of the apparatus inevitably became larger by the installation space of the far infrared radiation generator, and thus the apparatus itself unavoidably became large-sized. That is, basically, in order to obtain the effects of radiant heat by providing the far infrared radiation generator within the drying apparatus, it is obvious that a correspondingly large space is required. Since the recent trend of the drying apparatus has been to make its size small and the improvement has been underway by reducing the drying chamber for exposing drying air to grains, the introduction of a far infrared radiation generator is against the trend of reducing the entire size of the drying apparatus.




Conventional methods with which granular objects are pre-heated without utilizing a far infrared radiation generator have been disclosed in Japanese Patent Application Kokai Publication No. Sho 58-187779, Japanese Patent Application Kokoku Publication No. Sho 60-8434, Japanese Patent Application Kokai Publication No. Sho 62-9174, etc. The technique disclosed in each of Patent Application Kokai Publication No. Sho 58-187779 and Patent Application Kokoku Publication No. Sho 60-8434 relates to an arrangement in which a heated air path and a drying chamber are provided with separate heat sources, respectively. Because of this arrangement, these separate heat sources are required to be separately controlled. With use of a plurality of heat sources and need of controlling them separately, the apparatus will inevitably be costly.




Further, the technique disclosed in Patent Application Kokai Publication No. Sho 62-9174 relates to a system in which the heated air produced by a burner and sucked by an air exhausting means is supplied directly to a heated air path chamber thus enabling to pre-heat the grains, and the heated air is supplied from the heated air path chamber to a drying chamber through a heated air guide path. In this system, not only is it made possible to produce both the heated air and the drying air by one heat source (one burner), but also it is made possible to pre-heat the grains immediately below a tank chamber, so that an advantage in this system over the above described drying apparatus, of U.S. Pat. No. 2,789,279 is that, unlike said apparatus, the system does not become large-sized.




However, as to the temperature control in the above system, the drying air temperature (approximately 40° C.) in the drying chamber at which grains are dried should be made as a reference temperature and, since the heated air path chamber communicates to the drying chamber simply through the heated air guide path, even by taking into account the fact that the temperature of the heated air drops due to a heat loss to occur at the heated air guide path, the temperature of the heated air never drops to the extent that it is suitable for drying the granular objects and, thus, it is necessary that the temperature of the heated air itself generated by the heat source of the burner must be substantially lowered. As a result, it will be impossible to raise the temperature of the air at the heated air path chamber, which is to raise the temperature of grains by being in contact with the grains, to the extent sufficient to contribute to the pre-heating.




It has become evident that, in drying granular objects, it is essential, for safely and speedily drying the granular objects, to pre-heat the granular objects and to maintain the predetermined temperature of the granular objects themselves prior to the exposure to drying air and, toward this end, various technical researches and developments have been made but so far without success. The object of the present invention is to provide a drying method and an apparatus which enable to meet the demand for a small-sized drying apparatus, and to achieving a desired drying air temperature with a high pre-heated temperature being maintained, thereby enabling the provision and manufacture of low cost drying method and apparatus with which it is possible to conduct the drying of granular objects safely and speedily.




SUMMARY OF THE INVENTION




According to one aspect of the present invention, there is provided a method for drying granular objects until their water content reaches a predetermined water content value, the method comprising the steps of:




holding the granular objects;




pre-heating the granular objects flowing down through the holding step by causing the granular objects to be in contact with outside walls of air ducts into which heated air is introduced;




producing drying air by mixing the heated air from the air ducts with air taken-in from the outside;




drying the granular objects with their water content being taken away, the granular objects flowing down after having been pre-heated by the pre-heating step, by directly exposing the granular objects to the drying air; and




taking out the granular objects flowing down after having been dried by the drying step.




According to another aspect of the invention, there is also provided an apparatus for drying granular objects until their water content reaches a predetermined water content value, the apparatus comprising:




a holding means for holding therein the granular objects;




a heated air generating means for generating a heated air;




a pre-heating means for heating the granular objects flowing down from the holding means, the pre-heating means being provided beneath the holding means and having a plurality of air ducts horizontally arranged therein, the heated air generated by the heated air generating means being introduced to each of one ends of the plurality of air ducts;




a drying air producing means connected to the other ends of the plurality of air ducts, in which the heated air from the air ducts is mixed with air taken-in from the outside of the apparatus so as to produce a drying air;




a drying means for drying the granular objects by directly exposing the granular objects to the drying air, the drying means having a drying chamber to which the granular objects after having been pre-heated at the pre-heating means are supplied and to one end of which the drying air produced by the drying air producing means is introduced;




an exhausting means connected to the other end of the drying chamber of the drying means, for exhausting the drying air involving humidity to the outside of the apparatus; and




a taking-out means arranged beneath the drying means, for taking out the dried granular objects.




For drying the granular objects, as there is provided the heating process between the holding process and the drying process, the temperature from the center portion to the surface portion within the grain can be made uniform and, thus, distortion hardly occurs in the granular objects when they are exposed to the heated air for drying. As a result, not only it is possible to reduce damages of the granular objects caused by the drying, but also it is possible to make the drying more speedily. Further, since it is possible to introduce into the drying process, as a drying air, a heated air whose temperature has been lowered by mixing the outside air to the heated air forwarded from the heating process, even if the temperature of the heated air at the heating process is comparatively high, the heated air can be sufficiently lowered in its temperature by the introduction of the outside air to the extent that it is suitable for the drying operation. Further, the above heating process can be provided at the holding process, no additional space for installing the heating process is necessary, thereby realizing a compact size apparatus.




For the purpose of maintaining the temperature of the drying air at a predetermined one, there is provided means for detecting a temperature of the drying process and, for controlling, based on the detected temperature, the temperature of the heated air at the heating process. With this construction, when the heated air is converted to the drying air suitable for the drying with the outside air being taken-in, even if there occurs any changes in the external conditions such as the rising of the circumference temperature of the apparatus, which may cause the drying air temperature high otherwise, it is possible to keep the drying air to a stable temperature by the control of the temperature of the heated air itself.




In the heating process, a part of the heated air is introduced into the granular objects that are falling down, and the granular objects are exposed to the heated air. In this way, the raising of the temperature of the granular objects to an appropriate temperature is further accelerated, so that the temperature of the granular objects are raised from the starting stage of the drying and the drying speed is advanced. Further, since the heated air is applied to the granular objects at the heating process in addition at the drying process, the positive heating by the heating process in addition to the drying by the conventional drying process, the drying process consisting of the heating process and the drying process can be carried out with high efficiency. In this way, without enlarging the size of the drying apparatus, the drying efficiency is in substance elevated, thus meeting the demand and trend of a smaller sized apparatus.




The above explained drying process in which a part of the heated air is introduced into the flow of the flowing down granular objects includes an outside air adjusting means for increasing or decreasing the amount of in-taking outside air so that the amount of the heated air to be introduced into the granular objects may be changed. Specifically, when the amount of outside air is changed to be reduced by the adjustment of the outside air adjusting means, the amount of the shortage of the air corresponding to the decrease in the amount of the introduced outside air is compensated by the increase in the amount of a part of the heated air introduced into the granular objects in the heating process. This means that the amount of a part of the heated air introduced into the granular objects increases inversely with the decrease in the amount of introduced outside air. Because of this, the heated air introduced into the granular objects during the heating process increases and, accordingly, the temperature of the granular objects subjected to the heating process is raised faster. In order to carry out this more effectively, it is preferable that this process is performed only during the initial stage of the drying, for example, only during the period in which the granular object filled up are heated up through one cycle of all the processes from the heating process to the taking out process. By so doing, the temperature of the entire granular objects can be elevated more quickly to the temperature suitable for the fast drying and, thereafter, by starting the introduction of the outside air in an ordinary way or a steady state, it is possible to dry the entire granular objects more speedily.











BRIEF DESCRIPTION OF THE DRAWINGS




The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention explained with reference to the accompanying drawings, in which:





FIG. 1

is a front view, partly in broken away, of a circulating type grain drying apparatus according to the present invention;





FIG. 2

is a side view, partly in broken away, of the circulating type grain drying apparatus according to the present invention;





FIG. 3

is a plain sectional view of the drying chamber of the circulating type grain drying apparatus according to the present invention;





FIG. 4

is a control block diagram of the grain drying apparatus according to the present invention;





FIG. 5

is a flow-chart of the control means for setting the predetermined temperature based on the filling amount of the grains;





FIG. 6

is a flow-chart of the control means for changing the predetermined temperature based on the water content value of the grains;





FIG. 7

is a flow-chart of the control means for controlling the burner means;





FIG. 8

is a block diagram of the burner means;





FIG. 9

is a flow-chart for the control of the burner means;





FIG. 10

is an enlarged perspective view for showing the internal structure of the air duct;





FIG. 11

is an enlarged perspective view for showing the internal structure of another example of the air duct;





FIG. 12

is an enlarged sectional view showing the outside air intake means; and





FIG. 13

is a perspective view showing the detail of the outside air intake means.











PREFERRED EMBODIMENTS OF THE INVENTION




Now, a preferred embodiment of the invention is explained with reference to

FIGS. 1

to


4


. Here, the explanation is made on one example of a circulating type grain drying apparatus for drying grains as granular objects. A grain drying apparatus


1


is provided with, starting sequentially from the top thereof, a holding tank


2


for holding the grains to be subjected to the drying; a drying chamber


7


having air paths


3


, an air exhaust path


4


and grain flow tubes


5


connected to the holding tank


2


, which are divided by perforated plates


6


extending from a front side A to a rear side B; and a taking-out section


10


from which the dried grains are taken out thereat. The taking-out section


10


includes a rotary valve


8


for intermittently exhausting the grains flowing down on the non-porous slanted plates


5




a


connected to the perforated plates


6


of the drying chamber


7


, and a screw-conveyor


9


for laterally feeding the grains fed from the rotary valve


8


. Further, the taking-out section


10


and the holding tank


2


are connected by a bucket elevator


11


. As a result, a circulating operation is repeated such that the grains forwarded to the drying chamber


7


from the holding tank


2


are again introduced into the holding tank


2


by the bucket elevator


11


via the taking out-section


10


.




The holding tank


2


is equipped with a heating section


13


which is formed under the holding tank


2


and having a plurality of air ducts


12


extending in the front to the rear direction. At the front side A of the drying chamber


7


of the grain drying apparatus


1


, a burner means


14


using a lamp oil as fuel is provided, and a heat path via the front air path


15


is provided so that the heat generated by the burner means


14


is directly introduced as heated air to the starting ends (at the front side A) of the plurality of the air ducts


12


. The finishing ends (at the rear side B) of the air ducts


12


are connected to the air paths


3


of the drying chamber


7


through a rear air path


16


. The rear air path


16


is provided with an outside air in-take opening


17


. At the rear side B of the grain drying apparatus


1


, there is provided an exhausting fan


20


whose air passage is connected to the air exhaust path


4


. At the connecting portion between the rear air path


16


and the drying chamber


7


, there is provided a temperature sensor


21


for measuring the temperature of the drying air. This sensor


21


is connected to the burner means


14


through a control means


22


. In this illustrated example of arrangement, the air ducts


12


are laterally disposed in the front to rear direction. However, the arrangement is not limited to this example as the air ducts


12


may be in the left to right direction, or the heating section


13


may be formed by combining the arrangements in the front to rear direction and the left to right direction.





FIG. 4

is a control block diagram of the control means


22


. The burner means


14


is controlled by the control means


22


such that the drying air introduced into the drying chamber


7


is controlled so as to be a predetermined temperature (approximately 40° C.). To the I/O port


22




a


of the control section


22


, there are respectively inputted signals from an input section


29


equipped with various operating switches, a signal from the temperature sensor


21


for the drying air via an A/D conversion circuit


23


, a signal from a water content detection means


18


via an A/D converter


24


, and a signal from an outside air temperature sensor


41


via an A/D conversion circuit


42


. Also, from the I/O port


22




a,


signals are outputted to the burner means


14


and the motor driving circuit


25


, respectively. The motor driving circuit


25


operates to start and/or stop a driving motor


25




b


of the taking-out section


10


, a driving motor


25




c


of the bucket elevator


11


, a driving motor


25




a


of the air exhausting fan


20


, and a motor


34


for the outside air intake opening. The control means


22


is equipped with an CPU


22




b,


as a main element, for performing the comparison and calculation operation. The control means


22


is further equipped with the I/O port


22




a,


a read-only-memory (here-inafter referred to as “ROM”)


22




c


in which control programs and set values of temperatures and/or water content values are stored, and a random-access-memory (hereinafter referred to as “RAM”)


22




d


in which filling up amount and selected values inputted from the input section


29


, and the results of the calculation are stored. These I/O port


22




a,


ROM


22




c


and RAM


22




d


are all connected to the CPU


22




b.


The CPU


22




b


monitors the respective signals from the input section


29


, the temperature sensor


21


, the water content detection means


18


and the outside air temperature sensor


41


, and outputs control signals, based on the respective signals from the input section


29


, to various sections and means so that the corresponding sections and means operate accordingly.




The input section


29


is equipped with a filling setting switch


29




a


for setting the amount of filling of the grains, a water content setting switch


29




b


for setting the target value of water content at the finishing, a filling button


29




c


for starting the filling up operation, a drying button


29




d


for starting the drying operation, a discharging button


29




e


for discharging grains, etc. Upon receiving the signal generated by operating the filling button


29




c


from the input section


29


, the control means


22


sends out a control signal to the motor driving circuit


25


so as to drive the taking-out section motor


25




b,


the bucket-elevator motor


25




c


and the fan motor


25




a.


Also, upon receiving the signal generated by operating the discharge button


29




e


from the input section


29


, the control means


22


sends out a control signal to the motor driving circuit


25


so as to drive the bucket-elevator motor


25




c,


the taking-out section motor


25




b


and the fan motor


25




a.






In carrying out the actual drying operation, first the amount of filling in the holding tank


2


is set by the filling setting switch


29




a


and the target water content value at the finishing is set by the water content setting switch


29




b.


These values are stored in the RAM


22




d


and, thereafter, the drying starting switch


29




d


is switched on. When the control means


22


receives the drying starting signal, it sends out a control signal to the motor driving circuit


25


so that the taking-out section motor


25




b,


the bucket-elevator motor


25




c


and the fan motor


25




a


are respectively driven in accordance with the programs stored in the ROM


22




c,


and it also sends out a burning signal to the burner means


14


. Then, the programs given hereunder with reference to

FIG. 5

are followed.




As shown in

FIG. 5

, at the starting of the drying operation, the amount N of the filling in the holding tank


2


is stored in the RAM


22




d


in the step


501


. Some initial predetermined temperatures set against the filling amounts N have been stored in the ROM


22




c


in advance so that the predetermined temperature corresponding to the filling amount N at present is selected and then stored in the RAM


22




d.


More specifically, at the step


502


, if the filling amount N is judged as being above 2000 kg, the outside temperature +55° C. against the outside temperature detected by the outside air temperature sensor


41


is stored as the initial predetermined temperature. At the step


503


, if the filling amount N is judged as being below 2000 kg but above 1500 kg, the outside temperature +40° C. is stored as the initial predetermined temperature. Similarly, at the step


504


, if the filling amount N is judged as being below 1500 kg but above 1000 kg, the outside temperature +30° C. is stored as the initial predetermined temperature. At the step


504


, if the same is judged as being below 1000 kg (but above the minimum filling amount), the outside temperature +20° C. is stored as the initial predetermined temperature. Here, an example (A) is shown and explained hereunder in the case where the outside temperature +20° C. is used as the initial predetermined temperature. With respect to other examples (B) to (D), such a temperature as shown in the Table 1 is added to the outside air temperature detected by the outside air temperature sensor


41


and the resulting temperature is used as the initial predetermined temperature T


0


.












TABLE 1











PREDETERMINED TEMPERATURE (° C.)













MEASURED WATER CONTENT














FILLING AMOUNT (kg)




21%




17%




15%




















(D)




2000




+55




+30




+10







(C)




1500




+40




+15




+10







(B)




1000




+30




+15




+5







(A)




below 1000




+20




+7




+5















The drying starts with the initial predetermined temperature being determined as the heated air temperature, but it is so arranged that, as the drying of the grains progresses, the predetermined temperature is caused to be dropped according to the dropping value of the water content of the grains. The water content values and the temperatures are stored in advance in the ROM


22




c


so that, while the water content of the grains is being measured during the drying, the predetermined temperature is caused to fall according to the change in the actual values of water content. Therefore, the values to be selected according to the filling amount N are the first to third water content values for changing the predetermined temperature (outside air temperature +20° C.) and the predetermined temperature shown in the step


505


as well as the predetermined temperature (outside air temperature +α° C.) for making a corresponding change when the water content value is that as shown in

FIG. 6

, and these values are read-out from the ROM


22




c


and stored in the RAM


22




d.


Here, the water content value which corresponds to the third water content value may be made as the finishing water content value which is inputted from the input section


29


and stored in the RAM


22




c.


In this case, the value stored in the ROM


22




c


is tentatively 15% but, when the third water content value read-out from the ROM


22




c


to the RAM


22




d


and the finishing water content value inputted from the input section


29


are compared, and the resulting value is different from the above percentage, the finishing water content value inputted from the input section


29


will have priority and replace the tentative percentage, and this value is stored in the RAM


22




d


as the third water content value.




As above, when the predetermined temperature is set according to the filling amount N from the start of the drying operation, the control as shown in

FIG. 6

takes place according to the predetermined temperature thus set. First, the counter value at the RAM


22




d


is reset to “0”. The signal from the water content detection means


18


obtained through the I/O port


22




a


is measured periodically with an interval of, for example, 10 minutes in the step


601


, and the grain water content value M is compared with the first water content value of 21% in the step


602


. As a result, if the grain water content value M is above 21%, the predetermined temperature T


0


stored in the RAM


22




d


of the control means


22


, the outside air temperature +20° C. is maintained as it is. Further, if the grain water content value M is judged as being below 21% but above 17% in the step


603


, the predetermined temperature T


0


stored in the RAM


22




d


of the control means


22


is changed to the outside temperature +7° C. Also, if the grain water content value M is judged as being below 17% but above 15% in the step


604


, the predetermined temperature T


0


stored in the RAM


22




d


of the control means


22


is changed to the outside temperature +5° C. accordingly.




When the water content value is judged as being below 15% in the step


604


, the counter set in the RAM


22




d


prior to the water content detection in the step


601


is incremented by “1” in the step


605


, and the water content detection is again repeated in the step


601


. In this way, since the predetermined temperature T


0


is changed every time the grain water content value changes, the drying operation can be carried out at the optimum drying air temperature for the grains according to the grain water content value. Finally, at the step


606


, if the value of below 15% is detected three times, it is judged that the drying has been completed and the necessary operation ends. At the ending, the stop signal is sent to the burner means


14


from the control means


22


. And, after a predetermined delay time, a signal is sent to the motor driving circuit


25


for stopping the motor


25




b


of the taking-out section


10


and, also after a further predetermined delay time, a signal is sent to the motor driving circuit


25


for stopping the bucket-elevator motor


25




c


and the fan motor


25




a.


Further, the water content values, the predetermined temperatures, the timing for the ending of drying, the intervals for the setting of water content, etc. set in the programs may be freely changed according to districts and/or conditions at or in which the drying apparatus for the grains is used.




Next, with reference to

FIG. 7

, how the burner means


14


is controlled based on the temperature detected by the temperature sensor


21


is explained. In the ROM


22




c


of the control means


22


, there is stored a control flow as shown in FIG.


7


. By using as reference the predetermined temperature T


0


stored in the RAM


22




d


in the step


701


described above, the comparison is made with respect to the drying air temperature T detected by the temperature detection sensor


21


in the step


702


and, if the drying air temperature T is higher than the predetermined temperature T


0


, a signal is sent from the control means


22


for decreasing the amount of fuel supply to the burner means


14


in the step


703


. To the contrary, when the drying air temperature T is lower than the predetermined temperature T


0


, a signal is sent from the control means


22


for increasing the amount of fuel supply to the burner means


14


in the step


704


. When coincidence of the drying air temperature T with the predetermined temperature T


0


is detected in the step


705


, no signal is sent out, and the detection of the drying air temperature T is repeated. This control is stopped, at the step


706


, by the stopping signal generated in the control means


22


described above.




The signals generated according to the control flow of

FIG. 7

are sent to the driving circuit


26


of the burner means


14


shown in FIG.


8


through the I/O port


22




a


of the control means


22


. As shown in

FIG. 8

, the burner means


14


includes the driving circuit


26


as a main or central component. To the driving circuit


26


, there are connected, a burner fan


28


, an optical detection element


36


, a fuel pump


37


, an opening and shutting valve (hereinafter referred to as “valve”)


38


, and an ignition transformer


39


. On receiving a signal from the control means


22


, the driving circuit


26


drives the burner fan


28


, and causes the fuel pump


37


, the valve


38


and the ignition transformer


39


to act. The fuel pump


37


connected to a fuel tank


40


functions such that a constant amount of the fuel is continually supplied from the fuel tank


40


to the valve


38


and, by changing the opening and shutting time of the valve


38


through the driving circuit


26


, the amount of fuel ejection is increased or decreased accordingly. In the vicinity of the valve


38


, a pair of opposing electrodes connected to the ignition transformer


39


are provided, so that the fuel ejected by the opening and shutting operation of the valve


38


is ignited and burns. The burner fan


28


, by its blowing action, blows out the heated air produced by the burning. In the driving circuit


26


, it is possible to incorporate therein a logic circuit which causes the various elements to be operative or inoperative and the valve


38


to be opened or closed according to the signals inputted from the control means


22


, or a CPU or a ROM may be incorporated in the driving circuit


26


.




The burning in the burner means


14


proceeds according to the control flow which is as shown in FIG.


9


and which is incorporated or programmed in the driving circuit


26


. In the burner means


14


, upon receiving the signal from the control means


22


, in the step


901


, the burner fan


28


is driven according to the logic incorporated in the driving circuit


26


, the fuel pump


37


is driven with the initial value P of the valve, the valve


38


is driven for opening and shutting at the initial value P, and the ignition transformer


39


is driven to ignite. Once the ignition is confirmed by the optical detection element


36


, the operation of the ignition transformer


39


is stopped. When a signal for the fuel decrease or increase is received from the control means


22


in the step


902


after the burner means


14


is ignited as above, the signal for the fuel is judged as to which is of increase or decrease in the step


903


. In the case of the decrease, the amount of fuel is decreased by shortening the opening time P of the valve


38


in the step


904


. In the valve


38


, the opening time P (for example, P=40 ms) of the valve per a unit time may be made short in a stepwise manner by 2 ms per step, thus lowering the heated air temperature by decreasing the amount of burning fuel.




Also, in the burner means


14


, if the fuel signal for the increase or decrease of the fuel is judged as an increase signal in the step


903


, the opening time P for the valve


38


is increased and the amount of the fuel ejection is increased in the step


905


. The heated air temperature may be raised by increasing the amount of fuel supply by increasing the opening time P (=40 ms, for example) of the valve


38


per a unit time by 2 ms per step. In the burner means


14


, in the step


906


, determination as to whether the stopping signal generated in the control means


22


, for example, the drying ending signal, exists or not. If the existence of the stopping signal is detected, the operation of the fuel pump


37


as well as the valve


38


is stopped and, after a lapse of a predetermined delay time, the burner fan


28


is stopped in the step


907


, thereby completing the full stop of the burner means


14


. The range (1 step) of the increase and decrease in the opening time of the valve


38


may be set to any desired value.




Referring back to

FIGS. 1

to


3


, the flow of the heated air and the drying air in the structure described above is explained hereunder. By the action of the burner means


14


and the suction of the air exhausting fan


20


, the heated air produced by the burner means


14


becomes, for example, 100° C. and is directly introduced into the air ducts


12


of the heating section


13


and, thus, the air ducts


12


are heated by the introduced heated air. The heated air passing through the heating section


13


is introduced into the rear air path


16


and, by the suction of the air exhausting fan


20


, the outside air taken-in from the outside air intake hole


17


is mixed in the heated air, and the resulting air becomes the drying air whose temperature is in the order of 40° C. This drying air is then introduced into the air paths


3


from the rear air path


16


and, while passing through from the air paths


3


to the air exhaust path


4


, the drying air takes away the water content of the grains which flow down through the grain flow tubes


5


. The water content taken away passes through the air exhaust path


4


and is exhausted to the outside of the apparatus


1


by the exhausting fan


20


.




While the grains flow down from the holding tank


2


to the drying chamber


7


, they are heated by being in contact directly with the air ducts


12


at the heating section


13


arranged between the holding tank


2


and the drying chamber


7


. The grains thus heated are in turn exposed to the drying air and the water content is taken away while flowing down through the grain flow tubes


5


of the drying chamber


7


, and the dried grains are then discharged from the drying chamber


7


by the operation of the rotary valve


8


of the taking-out section


10


. The grains discharged are laterally conveyed by the screw conveyer


9


and then fed back to the holding tank


2


by the bucket elevator


11


. In this way, the grains are circulated through the series path of the holding tank


2


, the heating section


13


, the drying chamber


7


, and the taking-out section


10


until the set water content value is reached.




As already explained, it is arranged that the outside air is introduced from the outside air intake hole


17


disposed after the heating section


13


so that the heated air produced by the burner means


14


and introduced into the air ducts


12


can be elevated to the temperature in the order of 100° C. independently from the temperature required for the drying air. Thus, since the temperature of the air ducts


12


of the heating section


13


can be raised sufficiently high, the temperature of the grains flowing down through the air ducts


12


and being in contact therewith can be not only heated up to a suitable high temperature, but also the heated air, even being a high temperature, can be adjusted to a suitably low drying air temperature since the high temperature heated air can be mixed with the outside air. That is, at the heating section


13


, the air may be heated up sufficiently without taking the temperature of the drying air into account.




Here, the temperature of the grains is considered. The temperature inside the grain heated at the heating section is such that the temperature at the center portion of the grain and the temperature at the surface portion thereof become uniform. As a result, because there is no distortion in terms of temperature between the center portion and the surface portion of the grain, such defects as a crack will not occur in the grain and the water content thereof is easily and safely taken away by being exposed to the drying air in the drying chamber


7


. The temperature of the drying air in the drying chamber


7


is lowered in accordance with the decrease in the water content value of the grains. The range of the variable temperatures for the drying air is between 40° C. and 30° C., for example.




Although the above explanation has been made such that the drying air flows from the air paths


3


to the air exhaust path


4


through the grain flow tubes


5


, the connection of the rear air path


16


and the air exhausting fan


20


to other components may well be changed so that the air flows from the air exhaust path


4


to the air paths


3


through the grain flow tubes


5


. Importance here is that the grains having been heated at the heating section


13


are exposed to the drying air which is produced by the introduction of the outside air into the heated air forwarded from the heating section


14


. Thus, the flow of the drying air is not limited to the illustrated embodiment.




As shown in

FIG. 10

, on the inner wall of the air duct


12


of the heating section


13


, there are provided a plurality of resistance plates


45


for causing the flow of the heated air to be in a zigzag fashion. The sectional shape of the air duct


12


and the shape of the resistance plate


45


are not limitative to those shown in FIG.


10


. Specifically, the sectional shape of the air duct


12


may well be as shown in

FIG. 11

so long as it causes the grains to flow smoothly and evenly. The shape of the resistance plate


45


may well be any one so long as the entire air duct


12


is uniformly heated.




It is preferable that the air duct


12


at the heating section


13


is provided with air jet openings (holes or slots)


46


for jetting out a part of the heated air (in the order of 1% of the heated air). A part of the heated air is directly jetted into the flow of the grains from the jet openings


46


of the air ducts


12


, whereby the temperature of the grains is further elevated. If the temperature of the heated air is in the order of 80° C. to 100° C., the circumference temperature becomes a temperature in the order of 50° C. to 70° C. by the heating by the air ducts


12


and the heated air jetted from the jet openings


46


. Though an adverse influence on the grains by the jetted heat air may be thought of, as there occurs only small movement of the air in this heating section


13


unlike in the drying chamber


7


, the jetted heated air causes only the temperature of the grains to be elevated and no drying operation occurs here. Therefore, no defect such as a crack caused by the rapid drying occurs.




Further, as already explained, a part of the heated air ejected from the jetting hole or slot


46


towards the flowing down grains results in the raising of the temperature of grains adjacent the air ducts


12


while the grains flow down to the drying chamber


7


. Thus, the substantive drying including the raising of the grain temperature is effected also in between the heating section


13


and also the drying chamber


7


. This means that the effect is the same as that obtained by enlarging the drying chamber


7


. Moreover, although the drying chamber becomes larger, the heating section


13


is provided in the holding tank


2


, so that there is no increase in the overall structure of the holding tank


2


and the drying chamber


7


. In other words, since there is no increase in the size of the apparatus despite the substantial increase in the size of the drying chamber


7


, the arrangement enables the decrease of the drying apparatus in substance and, more over, enables the realization of the faster drying.




Now, with reference to

FIGS. 12 and 13

, an outside air adjusting means, that is, an opening and shutting means


27


for an outside air intake hole


17


is explained. An opening and shutting plate


30


is rotatably mounted on an axis


31


for allowing the plate


30


to be freely opened and shut. On the plate


30


, an arm


32


is provided, and in the vicinity of the arm


32


, there is provided a motor


34


for allowing a shaft


33


thereof to be driven upwardly and downwardly. The shaft


33


carries a supporting member


35


which passes through a slot


43


formed in the supporting arm


32


. The motor


34


drives the supporting member


35


for upward and downward movements so that the arm


32


moves upwardly and downwardly, and by the action of the arm


32


the opening and shutting plate


30


is operated so as to open or shut the outside air intake hole


17


.




A further explanation is made here for the function of the outside air intake hole


17


operated by the opening and shutting means


27


. The opening area of the outside air intake hole


17


is required to be just sufficient to maintain the amount of air to compensate the amount of suction air of the air exhausting fan


20


. The basic operation is to fix the opening area in a constant size and, for doing so, the opening and shutting means


27


for the outside air intake hole


17


is operated so that the total air amount of the amount of output air from the air ducts


12


of the heating section


13


and the amount of absorbed air from the outside air intake hole


17


becomes approximately the same as the amount of the air sucked by the air exhausting fan


20


. This basic opening area is set in advance so that the opening and shutting means


27


is normally not operated.




However, the opening and shutting means


27


is operated in the following case. That is, in order to raise the drying grain temperature speedily in preparing for the drying at the initial stage where the water content is high or during the stage wherein the filling takes place, it is more effective to raise the temperature of the grains by causing them to be in contact with the heated air than to expose them to a large volume of drying air and, for this reason, the outside air intake hole opening and shutting means


27


is operated to rotate the opening and shutting plate


30


so as to shut the outside air intake hole


17


. In this way, the amount of the air introduced from the outside air intake hole


17


becomes short, and this shortage in the amount of air is compensated by introducing into the grains the heated air in the air ducts


12


from the air jet holes or slots


46


provided in the walls of the air ducts


12


. That is, as already explained, into the grains flowing down, the heated air leaks from the heating section


13


and enhances the heating of the surrounding grains. This step is only to raise the grain temperature quickly, and this heated air does not act on the grains for a long period of time. An appropriate time period is for one to two cycles of the grains introduced. It is possible to incorporate in the program of the control means


22


the step by which the opening area of the outside air intake hole


17


is narrowed only by the time period of the above one to two cycles according to the filling amount inputted in the control means


22


at the initial stage of the drying. In this way, the related operations may simply be automated, but of course the operations may be manually carried out.




When the drying signal is inputted from the input section


29


to the control means


22


, in addition to the operation to control the drying as explained above, a signal is outputted to the motor driving circuit


25


so that the air opening and shutting motor


34


is operated to close the outside air intake hole


17


. This signal may be programmed either to be outputted simultaneously with the inputting of the signal for drying, or to be outputted upon the detection of water content value by the water content detection means


18


as being, for example, above 20%, thus the air opening and shutting motor


34


starts to be operated.




As clarified in the foregoing, an advantageous effect of the invention resides in the arrangement that, in line with the trend of making the size of the drying apparatus smaller, the heated air for heating and the drying air for drying are communicated in the same air passage, and the drying air is produced by mixing the introduced outside air with the heated air, thus enabling the maintenance of a high temperature of the heated air for pre-heating.




Irrespective of the temperature of the heated air for pre-heating, it is possible to set the drying air to a predetermined temperature which, with the effect of the pre-heating, makes it possible to carry out the safe and speedy drying. Also, because the heating section at which the pre-heating is effected is provided in the holding tank, it is not necessary to provide a separate or additional space for the heating unlike the case where the far infrared radiation apparatus is used.




Since a part of the heated air is allowed to be in contact directly with the granular objects, the heating is efficiently effected without giving damages to the granular objects, and it is possible to achieve the fast raising of the temperature of both the surface portion and the inside of the granular objects, thus enabling the speedy drying operation.




Since the amount of the outside air introduced can be adjusted, it is possible to control the amount of a part of the heated air directly supplied to the granular objects at the heating section, and to adjust the speed of the heating, thus enabling the change in the amount of heated air introduced depending on the granular objects. Thus, the heating can cope with many different kinds of granular objects.




While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope of the invention as defined by the claims.



Claims
  • 1. An apparatus for drying granular objects until their water content reaches a predetermined water content value, said apparatus comprising:a holding means for holding therein the granular objects; a heated air generating means for generating a heated air; a pre-heating means for heating the granular objects flowing down from said holding means, said pre-heating means being provided beneath said holding means and having a plurality of air ducts horizontally arranged therein, the heated air generated by said heated air generating means being introduced to each of one ends of said plurality of air ducts; a drying air producing means connected to the other ends of said plurality of air ducts, in which the heated air from said air ducts is mixed with air taken-in from the outside of the apparatus so as to produce a drying air; a drying means for drying the granular objects by directly exposing the granular objects to said drying air, said drying means having a drying chamber to which the granular objects after having been pre-heated at said pre-heating means are supplied and to one end of which the drying air produced by said drying air producing means is introduced; an exhausting means connected to the other end of said drying chamber of said drying means, for exhausting the drying air involving humidity to the outside of the apparatus; and a taking-out means arranged beneath said drying means, for taking out the dried granular objects.
  • 2. An apparatus for drying granular objects according to claim 1, said apparatus further comprising a feed-back means for feeding-back the granular objects taken out from said taking-out means to said holding means.
  • 3. An apparatus for drying granular objects according to claim 1, said apparatus further comprising a temperature detection means for detecting a temperature of said drying air produced by said drying air producing means and a control means connected to said temperature detection means, said control means controlling said heated air generating means based on the temperature value detected by said temperature detection means so that a temperature of said drying air produced by said drying air producing means is kept at a predetermined value.
  • 4. An apparatus for drying granular objects according to claim 1, in which each of said air ducts of said pre-heating means has a plurality of resistance plates therein for causing the flow of the heated air therein to be in a zigzag fashion.
  • 5. An apparatus for drying granular objects according to claim 1, in which each of said air ducts of said pre-heating means has a plurality of openings for jetting a part of said introduced heated air to the outside of said air duct.
  • 6. An apparatus for drying granular objects according to claim 1, in which said drying air producing means comprises an outside air adjusting means for adjusting an amount of outside air taken-in from the outside of the apparatus.
Priority Claims (2)
Number Date Country Kind
11-006465 Jan 1999 JP
11-053339 Mar 1999 JP
US Referenced Citations (7)
Number Name Date Kind
3742614 Betterman et al. Jul 1973
4032305 Squires Jun 1977
4686779 Wyatt et al. Aug 1987
4784216 Bracegirdle et al. Nov 1988
5052123 Tischendorf et al. Oct 1991
5305533 Alexander et al. Apr 1994
5685434 Ackerman Nov 1997
Foreign Referenced Citations (4)
Number Date Country
58-187779 Nov 1983 JP
60-8434 Mar 1985 JP
62-9174 Jan 1987 JP
2789279 Jun 1998 JP