JP3981569B2 - Drying equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a drying apparatus for drying freeze-dried foods and the like, and more particularly to a drying apparatus capable of accurately and surely drying a dry state and a drying end point, and capable of being efficiently and reliably dried at a low cost.
[0002]
[Prior art]
In general, a freeze-dried product such as food is dried by storing a frozen object to be dried in a drying chamber, sublimating the frozen water content by evacuating the drying chamber. At this time, normally, in the drying chamber, the object to be dried is placed on a drying shelf, and is heated by radiant heat from a heating plate disposed above each drying shelf, so that the frozen moisture is sublimated. .
[0003]
Ascertaining the dry state of the dried material and determining the time when the target moisture content is reached (i.e., the end point of drying) can be considered, for example, using the weight change of the dried material as an index, but the material is dried under vacuum. It is difficult to measure the weight of the body, and in particular, when many small-volume foods are laid on a drying shelf and freeze-dried, it is not realistic considering the durability of the load cell, the installation position, the number of installations, and the like.
[0004]
Therefore, in the past, the above-described drying state of the object to be dried and the determination of the end point of drying have been estimated by measuring the temperature change of the object to be dried and the drying conditions based on past experience. That is, a material to be dried is selected at random from the materials to be dried placed in the drying chamber, and a temperature sensor is inserted into each of these selected materials to be dried to partially adjust the temperature of the material to be dried. The end of sublimation of the frozen water was judged by measuring the temperature of the material to be dried and observing the rise in the product temperature of the material to be dried.
[0005]
[Problems to be solved by the invention]
However, the apparatus using the temperature sensor has the following problems.
(1) Since a temperature sensor is inserted into the object to be dried, the selected object to be dried becomes a defective product when the temperature sensor is removed after drying. The process yield decreases.
[0006]
(2) The upper part of the object to be dried is radiant heat from the heating plate, and the lower part is transferred by heat from the drying shelf. For this reason, when the insertion position of the temperature sensor deviates from the center of the object to be dried, the temperature measured by the temperature sensor rises even though the drying end point has not yet been reached. There is a possibility that the end point may be grasped by mistake.
[0007]
(3) The drying speed of the above-mentioned body to be dried is theoretically not different between the respective dry bodies if the inside of the drying chamber is uniformly depressurized. Due to the difference in heat conduction from the shelf to the object to be dried, it is possible that differences will occur depending on the position of the drying shelf accommodated in the drying chamber and the position of the object to be dried on each drying shelf. Because of variations in the shape and capacity of the objects to be dried, it is considered that there is a difference in the drying speed between the objects to be dried. The difference in drying speed is not always uniform.For example, the difference in the type of material to be dried differs depending on the type of the material to be dried. The slowest object to be dried is not always selected. For this reason, there exists a possibility of grasping | ascertaining the drying end point of the whole to-be-dried body accidentally.
[0008]
If the above-mentioned drying end point is misunderstood, if the drying process is terminated early, an insufficiently dried defective product is produced, and the yield is lowered. In order to avoid this, conventionally, sufficient drying time has been spent so as not to cause insufficient drying based on experience, and there has been a problem that drying energy is wasted.
[0009]
It is a technical object of the present invention to provide a drying apparatus that solves these problems, accurately grasps the drying state and the drying end point, can efficiently and reliably dry, and can be implemented at low cost.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention is configured as follows, for example, based on FIGS. 1 to 5 showing an embodiment of the present invention. That is, a drying shelf (7) housed in the drying chamber (2) and configured to allow a body to be dried (11) to be placed thereon, and a heating plate (15) disposed above the drying shelf (7) The drying shelf (7) and the heating plate (15) are made of an electrically conductive material, and the object to be dried (11) is housed in a container (12) formed of an insulating material, The drying shelf (7) and the heating plate (15) are electrically connected to the capacitance measuring device (10), and the capacitance between the drying shelf (7) and the heating plate (15) is measured. The drying shelf ( 7 ) and the heating plate (15) are each configured in a multistage manner, and the heating plate (15) is disposed above each drying shelf ( 7 ) .
Then, in the present invention 1, each stage of the drying rack (7), switchably configured into a state of being insulated drying rack (7) and electrically connected state of the other stages, the insulated state static between each drying cabinet (7) measurably constituting the electrostatic capacity between the heating plate in the vicinity (15), a plurality of drying cabinet (7) and the heating plate is in a conducting state and (15) The electric capacity can be measured.
Further, in the present invention 2, the above heating plate each stage (15), the heating plate of the other stages switchably configured into a state of being insulated (15) and an electrically conductive state, each in an insulated state electrostatic between heating plate (15) and measurable configure capacitance between the drying cabinet in the vicinity (7), a plurality of heating plates in a conduction state (15) and a drying cabinet (7) It is characterized in that the capacity can be measured.
[0011]
[Action]
The object to be dried is heated by the radiant heat from the heating plate or the conduction heat from the drying shelf that has been heated by receiving this radiant heat, whereby the contained water vaporizes or the frozen water sublimates, thereby drying the object to be dried.
At this time, when the moisture contained in the object to be dried becomes a gas and comes out of the object to be dried, the capacitance between the drying shelf on which the object to be dried is placed and the heating plate above it becomes small. To go. This capacitance is measured by the above-described capacitance measuring device, and thereby the dry state of the object to be dried is grasped. And since the reduction | decrease of a water | moisture content will stop when a to-be-dried body reaches an equilibrium moisture content, a dry end point is grasped | ascertained because said electrostatic capacitance measured value becomes fixed.
[0012]
The drying shelves accommodated in the drying chamber are usually configured in multiple upper and lower stages in order to increase the number of objects to be dried and increase the drying efficiency. Therefore, the heating plate is also arranged between the drying shelves. It is configured in multiple upper and lower stages to be inserted.
These upper and lower multi-stage drying shelves or heating plates are configured so that each stage can be switched between an electrically conductive state and an insulated state with respect to the other stages , and each stage is insulated from the other stages. In a state, the electrostatic capacity between a specific drying shelf and a heating plate in the vicinity thereof can be measured, and in a state where it is conducted to other stages , the electrostatic capacitance between a plurality of drying shelves and the heating plate can be measured . Therefore, for example, at the initial stage of the drying process, the capacitance between the entire plurality of drying shelves and the heating plate is measured to easily grasp the drying state of the entire object to be dried, and at the end of the drying process. Thus, by measuring the capacitance between each drying shelf and the heating plate in the vicinity thereof, the end point of drying can be accurately grasped.
[0013]
When the above-described drying shelf and heating plate are configured in multiple upper and lower stages, and the capacitance between each drying shelf and the heating plate in the vicinity thereof is measured individually, drying above the heating plate to be measured is performed. The shelf or heating plate and the heating plate or drying shelf in the vicinity of the drying shelf to be measured can be configured as a guard electrode by grounding, respectively. Normally, each drying shelf is formed in substantially the same shape, while the heating plate faces almost the entire surface of this drying shelf. Measurement accuracy can be increased.
[0014]
It is conceivable that the objects to be dried placed on the drying shelf have different drying speeds depending on the place of placement. Therefore, each of the drying shelves and each heating plate is electrically partitioned into a plurality of shelf parts and plate parts, such as a central part and a peripheral part, for example, and each part and the corresponding heating plate or drying shelf It is preferable to be able to measure the capacitance between and the drying state and the drying end point more precisely.
[0015]
In addition, the peripheral wall of the heating chamber is generally formed of a metal material from the viewpoint of pressure resistance and airtightness, but when this peripheral wall is grounded and configured as a guard electrode, the drying shelf accommodated inside and the vicinity thereof are provided. Since the electrostatic capacitance between the heating plates arranged can be accurately measured, it is more preferable.
[0016]
The application of the drying apparatus is not limited to a specific drying method, but the drying state of the object to be dried can be easily grasped even in a state where the drying chamber is sealed. It is particularly suitable when the body is dried under reduced pressure, or when the inside of the drying chamber is vacuumed and freeze-dried.
[0017]
[Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 show an embodiment in which the present invention is applied to a freeze-drying apparatus, FIG. 1 is a schematic configuration diagram of the freeze-drying apparatus, and FIG. 2 is an enlarged cross-sectional view of the main part thereof.
[0018]
As shown in FIG. 1, this freeze-drying device (1) is a device for freeze-drying food such as frozen juice food under vacuum, and the drying chamber (2) is a metal peripheral wall formed in a cylindrical shape. (3) is provided, and the peripheral wall (3) is grounded. A support rail (4) is provided at the upper center of the drying chamber (2), and the drying table (5) is suspended from the support rail (4) and conveyed to the drying chamber (2). Is done.
[0019]
In the drying table (5), a plurality of drying shelves (7) are attached to the left and right sides of the central support frame (6), and the drying shelves (7...) Are both thermally and electrically conductive. It is made of a good metal material, and is fixed to the support frame (6) via insulating materials (8). Each drying shelf (7) is electrically connected to the capacitance measuring device (10) via the wiring (9).
[0020]
As shown in FIGS. 1 and 2, the drying shelf (7) includes a synthetic resin tray (12) in which the frozen food is an insulating material such as polypropylene resin as the body to be dried (11). Each is housed in a large number and mounted.
[0021]
As shown in FIG. 2, each of the drying shelves (7) and the capacitance measuring device (10) are connected via a connection control device (13), and the connection control device (13) is operated. By doing so, switching control is performed between the state where each drying shelf (7) is connected to the capacitance measuring device (10) and the state where it is connected to the ground line (14). At this time, the drying shelf (7) connected to the capacitance measuring device (10) and the drying shelf (7) connected to the ground wire (14) are insulated from each other.
[0022]
On the other hand, as shown in FIGS. 1 and 2, the drying chamber (2) is provided with upper and lower multistage heating plates (15) along the left and right peripheral walls (3). 15) is arranged above each of the drying shelves (7) housed in the drying chamber (2) and at a position separated from these drying shelves (7). That is, the drying shelf (7) and the heating plate (15) are insulated from each other. The left and right heating plates (15) are made of a metal material having good heat conductivity and conductivity, and are electrically connected to the capacitance measuring device (10) via the wiring (16). Further, in the heating plate (15), as shown in FIG. 2, a flow path (17) for circulating a heat transfer fluid such as heating oil is formed.
[0023]
The capacitance measuring device (10) can measure the capacitance between the drying shelf (7) and the heating plate (15) connected via the wirings (9, 16). It is connected to a recording display device (18) so that the measurement result can be recorded and displayed.
[0024]
Next, a procedure for vacuum freeze-drying using the above-described drying apparatus will be described.
First, according to a conventional method, an object to be dried (11) in an unfrozen state is dispensed on a synthetic resin tray (12), placed on each drying shelf (7) of a drying table (5), and then frozen. The drying table (5) is guided by the support rail (4) and carried into the drying chamber (2).
Next, the inside of the drying chamber (2) is sealed, and the degree of vacuum is reduced to 66.6 Pa or less, for example, and the heat medium liquid heated to, for example, 80 ° C. is placed in the flow path (17) in the heating plate (15). It is circulated and the frozen moisture contained in the dried body (11) is sublimated by radiant heat from the heating plate (15).
[0025]
During the drying process, the capacitance between the drying shelf (7) and the heating plate (15) is measured continuously or discontinuously by the capacitance measuring device (10) at a frequency of 100 kHz. The At this time, since the object to be dried (11) is accommodated in the tray (12) formed of a synthetic resin material which is an insulating material, it is disposed between the drying shelf (7) and the heating plate (15). Further, the electrostatic capacity including the object to be dried (11) is measured, and the measured value fluctuates according to the change of moisture (ice content) contained in the object to be dried (11). Since the peripheral wall (3) of the drying chamber (2) is grounded as described above, it constitutes a guard electrode for the above-described capacitance measurement.
[0026]
In the above measurement, in the initial and middle stages of the drying process, each of the drying shelves (7) is electrically connected to the other drying shelves (7) by the connection control device (13). The capacitance between 7) and the heating plate (15) is measured. There are many drying shelves (7) and heating plates (15) at the top and bottom, each forming one electrode as a whole, each electrode has a large area, and the capacitance between them is measured accurately. Is done.
[0027]
At the end of the drying process, by operating the connection control device (13), only the drying shelf (7) to be measured is connected to the capacitance measuring device (10), and the nearby heating plate (15) Is measured. At this time, as shown in FIG. 2, the drying shelves (7b and 7c) located above and below the drying shelf (7a) to be measured are electrically insulated from the drying shelf (7a) to be measured, and are respectively grounded. Connected to the line (14) to be a guard electrode.
[0028]
When the decrease in the capacitance between all the drying shelves (7) and the heating plate (15) stops, it is determined that all the objects to be dried (11) have reached the equilibrium moisture content and have reached the drying end point. . Then, after the circulation of the heat transfer liquid is stopped and the inside of the drying chamber (2) is returned to normal pressure, the drying table (5) is carried out of the drying chamber (2), and the drying process is completed.
[0029]
In the above-described embodiment, each stage of the drying shelf is configured to be switchable between a state where the drying shelf is electrically connected to the other stage and an insulated state, but each stage of the heating plate is replaced with this. Further, it may be configured to be able to be switched to an insulated state when electrically connected to the heating plate of another stage, and configured to be able to measure the capacitance for each stage in the same manner as described above.
[0030]
In the above embodiment, the capacitance can be measured for each stage. For example, as shown in FIG. 3, the drying shelf (7) is further electrically divided into a plurality of shelf portions (19). Thus, the capacitance between each shelf portion (19) and the heating plate in the vicinity thereof may be configured to be measurable. If comprised in this way, since an electrostatic capacitance can be measured separately, for example with the peripheral part and center part of a drying shelf (7), a dry condition and a dry end point can be grasped | ascertained more precisely.
[0031]
Next, a measurement experiment for examining the relationship between the capacitance between the drying shelf and the heating plate in freeze-drying and the weight and temperature change of the object to be dried was performed using the experimental apparatus shown in FIG.
That is, the experimental device (20) is configured such that a drying shelf (23) is placed on a weight measuring device (22) disposed in a drying chamber (21), and a heating plate (24) is placed above the drying shelf (23). The support (26) provided with insulators (25) at the upper and lower ends is supported, and the object to be dried (27) is placed on the polypropylene tray (38) between the drying shelf (23) and the heating plate (24). It is housed and arranged.
[0032]
The weight measuring device (22) is connected to an outdoor weight recording device (28). In addition, the first temperature sensor (29) is fixed to the vicinity of the upper surface corner portion and the second temperature sensor (30) is fixed to the center portion of the above-mentioned body (27) to be dried, and each of these temperature sensors (29, 30) is fixed. ) Are connected to an outdoor temperature measurement recording device (31).
Further, the drying shelf (23) and the heating plate (24) are each connected to a capacitance measuring device (32), and the measurement results of the capacitance measuring device (32) are recorded and displayed on the recording display device (33). ) Can be output.
[0033]
As said to-be-dried body (27), 1300 g of 10% dextrin liquid was dispensed in said tray (38), and what was frozen at -30 degreeC was used.
The drying conditions were such that the inside of the drying chamber (21) was set to a vacuum level of 66.6 Pa or less, and the heating temperature by the heating plate (24) was set to 80 ° C. The capacitance was measured using a frequency of 100 kHz.
[0034]
The results of measurement with the above experimental apparatus are shown in the graph of FIG. The weight measurement result is expressed as the ratio of the amount of ice remaining in the drying process to the amount of ice contained in the object to be dried (27) at the drying start point. Since the drying speed of the object to be dried (27) is represented by the amount of ice sublimated per unit time, the above weight change curve (34) shows the drying curve. According to this drying curve, it is confirmed that the measured weight became a constant value about 930 minutes after the start of drying, and that the material to be dried (27) reached the equilibrium moisture content.
[0035]
On the other hand, the temperature change curves (35, 36) measured by the temperature sensors (29, 30) are different from each other. That is, in the vicinity of the upper surface corner of the object to be dried (27), the rise starts about 80 minutes after the start of drying, and reaches about 60 ° C. after 720 minutes. In the center, the rise starts about 360 minutes after the start of drying. , And reached about 64 ° C. after 870 minutes. From this, it can be seen that the product temperature change of the body to be dried (27) varies depending on the measurement location, and thus it is not easy to accurately grasp the dry state and the end point of drying by the method of measuring the product temperature.
[0036]
In contrast, the capacitance change curve (37) is curved in substantially the same manner as the weight change curve (34), and the change in capacitance between the drying shelf (23) and the heating plate (24) is Good correlation with weight change. Therefore, it can be seen that the dry state and the end point of drying of the body to be dried (27) can be accurately and easily grasped based on the measurement result of the capacitance.
[0037]
In the above embodiment, the case where the drying apparatus of the present invention is used for freeze drying has been described. However, since the present invention only measures the capacitance between the drying shelf and the heating plate, It is also possible to apply to a ventilation drying apparatus. In addition, when used for freeze-drying, the object to be dried can be stored in a drying chamber before freezing and self-freezing can be performed by subtracting the moisture content by reducing the pressure in the drying chamber. It is also possible to grasp the frozen state of the object to be dried by measuring the capacitance described above.
[0038]
【The invention's effect】
Since the present invention is configured and operates as described above, the following effects can be obtained.
[0039]
(1) Since only the capacitance between the drying shelf and the heating plate is measured, the measuring device is not brought into contact with the object to be dried and differs from the conventional technique for measuring the product temperature by measurement. There is no risk of defective products.
[0040]
(2) Since the electrostatic capacity is measured including all the objects to be dried arranged between the drying shelf and the heating plate, the electrostatic capacity is decreased along with the decrease in moisture until these objects reach the equilibrium moisture content. The capacity measurement value decreases. For this reason, it is possible to accurately grasp the dry state etc. due to fluctuations in the measured capacitance value, and to accurately grasp the drying end point by making the measured value constant, so that the object to be dried can be reliably dried, and extra There is no need to spend drying time or energy for drying, and the object to be dried can be efficiently dried.
[0041]
(3) The upper and lower multi-stage drying shelves or heating plates are configured so that each stage can be switched between an electrically conductive state and an insulated state with respect to the other stages. Can easily grasp the drying state of the entire body to be dried for a plurality of drying shelves, and there is a difference in the drying speed of the body to be dried depending on the position of the drying shelf at the end of the drying process. In addition, it is possible to accurately grasp the end point of drying by individually measuring the capacitance between a specific drying shelf and a heating plate in the vicinity thereof.
[0042]
(4) The heating plate and the drying shelf are generally formed of a metal material having good heat transfer. However, these are usually conductive materials. It is only necessary to add a measuring device and wiring for electrically connecting the measuring device and a heating plate or a drying shelf, and since the power for measurement is small, it can be implemented at low cost. Moreover, since the object to be dried is housed in a container formed of an insulating material, it is not necessary to cover the drying shelf or heating plate that functions as an electrode plate for measuring capacitance with an insulating material, and the heat transfer efficiency of both Can be kept high.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a freeze-drying apparatus showing an embodiment of the present invention.
FIG. 2 is an enlarged cross-sectional view of a main part of the freeze-drying apparatus.
FIG. 3 is a schematic plan view showing a modified example of the drying shelf.
FIG. 4 is a schematic configuration diagram of an experimental apparatus.
FIG. 5 is a graph showing measurement results of the experimental apparatus.
[Explanation of symbols]
1. Drying device (freeze drying device)
2 ... Drying room 7 ... Drying shelf
10 ... Capacitance measuring device
11… Substance to be dried
12 ... Container (synthetic resin tray)
15 ... Heat plate

Claims (8)

A drying shelf (7) housed in the drying chamber (2) and configured to allow the object (11) to be dried to be placed thereon, and a heating plate (15) disposed above the drying shelf (7) ,
The drying shelf (7) and the heating plate (15) are made of a conductive material, and the object to be dried (11) is housed in a container (12) formed of an insulating material.
The capacitance between the drying shelf (7) and the heating plate (15) by electrically connecting the drying shelf (7) and the heating plate (15) to the capacitance measuring device (10). Configured to be measurable ,
The drying shelf ( 7 ) and the heating plate (15) are each configured in multiple upper and lower stages, and the heating plate (15) is disposed above each drying shelf ( 7 ) .
The above stages in the drying cabinet (7), switchably configured into a state of being insulated drying rack (7) and electrically connected state of the other stages, it is in an insulated state with each drying cabinet (7) measurably constituting the electrostatic capacity between the heating plate in the vicinity (15), measurably constituting the capacitance between the plurality of drying cabinet (7) and the heating plate (15) is in the conducting state A drying apparatus characterized by that. The drying apparatus according to claim 1 , wherein in the insulated state, the drying shelf (7) of the other stage is grounded and configured as a guard electrode. Housed in the drying chamber (2) inside, comprising a drying cabinet configured to be dried body (11) to be mounted (7), the heating plate disposed above the drying cabinet (7) and (15) ,
The drying shelf ( 7 ) and the heating plate (15) are made of a conductive material, and the object to be dried (11) is housed in a container (12) formed of an insulating material ,
The drying shelf ( 7 ) and the heating plate (15) are electrically connected to the capacitance measuring device (10) , and the capacitance between the drying shelf ( 7 ) and the heating plate (15). Configured to be measurable,
The drying shelf (7) and the heating plate (15) are respectively configured in upper and lower stages, and the heating plate (15) is disposed above each drying shelf (7).
Each stage of the heating plate (15) is configured to be switchable between an electrically conductive state and an insulated state with the other stage heating plate (15), and in an insulated state, each heating plate (15) It is configured to be able to measure the capacitance between it and the nearby drying shelf (7),
A drying apparatus characterized in that the capacitance between the plurality of heating plates (15) and the drying shelf (7) can be measured in the conductive state . The drying apparatus according to claim 3 , wherein in the insulating state, the heating plate (15) at the other stage is grounded to form a guard electrode. The drying shelf (7) is electrically divided into a plurality of shelf portions (19), and the capacitance between each shelf portion (19) and the heating plate (15) in the vicinity thereof can be measured. The drying apparatus according to any one of claims 1 to 4 . The above heating plate (15) electrically divided into a plurality of leaf portions, was measurably constituting the capacitance between the drying cabinet (7) of each plate portion and the vicinity thereof, of claims 1 The drying apparatus according to any one of 4 . The drying apparatus according to any one of claims 1 to 6 , wherein the peripheral wall (3) of the drying chamber (2) is grounded, and the peripheral wall (3) is configured as a guard electrode. The drying apparatus according to any one of claims 1 to 7 , wherein the inside of the drying chamber (2) is configured to be adjustable to a reduced pressure or a vacuum state.

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