JPS635068B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vacuum freeze-drying method in which water vapor in a drying chamber is sent to a low-temperature trap and frozen by a vacuum pump, and an apparatus used in the method, which can greatly shorten the time required for drying. Another object of the present invention is to easily and reliably uniformly heat an object to be processed, and in particular to efficiently dry foods while maintaining nutrients and aromas.

Next, embodiments of the present invention will be described with reference to illustrative figures.

As shown in FIG. 1, a vacuum pump 3 is communicated with a tank 1a forming a drying chamber 1 that can be closed and opened via a low temperature trap 2, and the vacuum pump 3 is connected to a tank 1a forming a drying chamber 1 that can be opened and closed. Heating plates 5 capable of radiant heating and high-frequency heating are installed in parallel in the drying chamber 1, and a cooling pipe is installed in the low-temperature trap 2 to freeze and capture water vapor from the drying chamber 1. Pump 2 on one end side of 2a.
A refrigerant storage tank 2f is connected to the refrigerant storage tank 2f by a supply pipe 2d equipped with a cooling device b and a cooler 2c, and a return pipe 2e at the other end.
After cooling the refrigerant such as Freon 12 and Freon 22 with low-temperature liquefied gas such as liquefied natural gas, liquid nitrogen, and liquid carbonate supplied from the tank 6 in the cooler 2c, it is circulated through the cooling pipe 2a. It is configured to supply.

To construct the heating plate 5, as shown in FIG. 2, a large number of metal heating tube portions 5c, which are formed so as to span the first and second metal conduit portions 5a and 5b, are arranged in a planar shape and with gaps. They are arranged side by side without any heat pipes, one end of each heating tube section 5c is connected to the first conduit section 5a or the second conduit section 5b every other time through an opening 5d that allows high frequency to pass through, and the other end side is It is connected to the second conduit section 5b or the first conduit section 5a through an opening covered with a wire mesh 5e that blocks the passage of high frequency waves, and each of the heating tube sections 5c is made of Teflon, etc. in order to irradiate the object to be treated with high frequency waves. An opening 5f covered with a heat-resistant airtight material that allows high-frequency waves to pass through, such as glass, is provided in such a way that the width increases toward the side where the wire mesh is installed so as to enable uniform high-frequency irradiation. Another high-frequency irradiation device 7 is connected, and a device 8 for generating a heated fluid such as steam or hot air is connected to the first conduit section 5a by a supply pipe 9 and to the second conduit section 5 by a return pipe 10.
It is connected to b.

The heated fluid generating device 8 and the high frequency irradiation device 7
As shown in FIG. 1, a program type automatic controller 11 is attached to the vacuum pump 3.
A device 14 for detecting the pressure inside the drying chamber 1, and a controller 15 for automatically adjusting the displacement of the vacuum pump 3 in order to maintain the detected value by the detection device 14 within a set range are attached. At the same time, for the low temperature trap 2, there is a device 16 for detecting the temperature of the refrigerant from the cooler 2c, and a low temperature liquefied gas is supplied to the cooler 2c in order to maintain the detected value by the detection device 16 within a set range. Supply amount control valve 1
A controller 18 for automatically adjusting the controller 7 is attached, and these controllers 15 and 18 are linked to the programmable automatic controller 11. In order to automatically adjust the displacement of the vacuum pump 3, a mechanical booster and an oil rotary vacuum pump are connected in series so that the on/off control of the mechanical booster is automatically performed.

Next, a vacuum freeze-drying method using the above apparatus will be explained.

The frozen object to be processed is placed on the tray 4 and placed in the drying chamber 1, and the drying chamber 1 is sealed. and,
The low-temperature trap 2 is activated to supply refrigerant at about -40°C to the cooling pipe 2a, and the programmable automatic controller 11 is activated to activate the vacuum pump 3 to reduce the pressure inside the drying chamber 1 to 0.1. torr to 0.5 torr, operate the heated fluid generator 8 with the high frequency irradiation device 7 stopped, and then sublimate the ice in the frozen object using radiation heating, While trapping water vapor with the low temperature trap 2, and with the programmable automatic controller 11
By appropriately adjusting the output of the heated fluid generating device 8, drying is performed with a large amount of heat input by radiation while suppressing the temperature increase of the object to be treated so as not to change its quality. When the set time has elapsed, the programmable automatic controller 11 activates the high-frequency irradiation device 7, and almost simultaneously lowers the refrigerant temperature in the low-temperature trap 2 to approximately -60°C, and generates heated fluid. The ice inside the object to be treated is sublimated by high-frequency irradiation while the output of the device 8 is appropriately lowered to prevent deterioration due to temperature rise of the object to be treated, and when a set time sufficient to complete drying has elapsed. Then, the entire apparatus is stopped by the programmable automatic controller 11 to complete the drying process.

As mentioned above, with high frequency irradiation, the cooling temperature of the low-temperature trap 2 is lowered, and the water vapor and air in the drying chamber 1 are quickly discharged, resulting in ionization of the water vapor and air. This suppresses glow discharge caused by high-frequency irradiation from becoming noticeable and prevents partial deterioration of the object to be processed due to uneven heating associated with glow discharge.

Although the present invention mainly targets various foods, it can also target various other products, such as pharmaceuticals.

To lower the cooling temperature of the low temperature trap 2,
As shown in FIG. 3, there is a device 12 that detects glow discharge in the drying chamber due to high-frequency irradiation, and the opening degree of the control valve 17 is controlled based on information from the detection device 12 to suppress glow discharge. In drying by high frequency irradiation, the glow discharge detection device 12 is provided with an automatic controller 13 that increases the
When it is detected that about 10% or more of the high frequency irradiation energy is glow discharge, the automatic controller 1
3, the cooling temperature of the low-temperature trap 2 may be gradually lowered stepwise or continuously. Alternatively, the cooling temperature of the low-temperature trap 2 may be lowered stepwise or continuously, or it may be adjusted artificially with the start of high-frequency irradiation or by using the glow discharge detection device 12. Good too. Further, the specific configuration of the low temperature trap 2, the specific means for lowering its cooling temperature, its control configuration, etc. can be changed as desired.

Various types of radiant heating means can be used in place of the heated fluid generating device 8, and these are collectively referred to as the radiant heating device 8, and the specific configuration of the high frequency irradiation device 7 can also be modified in various ways. Further, an operation or a control mechanism may be configured so that the radiant heating is stopped when the high-frequency irradiation is started.

To suppress glow discharge, one or both of a means for reducing the high frequency irradiation output based on information from the detection device 12 and a means for increasing the displacement of the vacuum pump 3 may be used in combination.

In summary, the first invention provides the method described above, in which the object to be processed in the drying chamber 1 is subjected to only radiant heating at the initial stage of drying and then irradiated with high frequency. At the same time, or alternatively, glow discharge accompanying high frequency irradiation is detected by a detection device 12 provided in the drying chamber 1, and the cooling temperature in the low temperature trap 2 is lowered so as to suppress glow discharge.

In other words, in the early stages of drying, we use radiation heating, which can easily apply a large amount of heat, and when the surface of the object to be treated dries and its thermal conductivity decreases, we use high-frequency irradiation, which can efficiently apply heat to the frozen parts inside. By doing so, the time required for drying can be significantly reduced, for example by 30 to 50% compared to using only radiant heating.
The drying time can now be shortened and drying can be carried out extremely efficiently.

In addition, simply irradiating high frequency waves will cause uneven heating, which tends to cause local deterioration and discoloration, which is especially fatal when drying food to prevent loss of nutrients and aroma. Although it is a drawback,
In this way, we investigated the causes of uneven heating and found that gases such as water vapor and air are ionized in the drying chamber 1 and glow discharge occurs, and when about 10% or more of the high-frequency irradiation energy is used for glow discharge. It was discovered that actual damage occurs due to deterioration and discoloration of dried materials.Based on this knowledge, as mentioned above, the cooling temperature of low temperature trap 2 is lowered to quickly discharge water vapor and air from drying chamber 1. By doing so, it has become possible to easily and reliably perform good drying that sufficiently suppresses deterioration and discoloration.

By the way, it is possible to set the cooling temperature of the low-temperature trap 2 low from the beginning of drying, but if you do that, the pressure inside the drying chamber 1 will drop below 0.1 Torr, and the thermal conductivity of the material to be processed will decrease. However, as mentioned above, lowering the cooling temperature of the low-temperature trap 2 at approximately the same time as the start of high-frequency irradiation or thereafter as needed will improve the drying speed. Glow discharge can be suppressed with virtually no adverse effects, and overall good drying can be performed easily, reliably, and quickly, and in particular, food can be dried efficiently without loss of nutrition and flavor. It became.

Further, the vacuum freeze-drying apparatus according to the second invention includes:
The drying chamber 1 is provided with a radiation heating device 8 and a high frequency irradiation device 7 for the object to be processed, and a low-temperature trap 2 that freezes the water vapor sent from the drying chamber 1 by a vacuum pump 3 is provided so that the cooling temperature can be freely changed. , the radiant heating device 8 is activated in the early stage of drying, and when a set time has elapsed after the start of drying,
The apparatus is characterized in that an automatic controller 11 configured to operate the high-frequency irradiation device 7 and lower the cooling temperature of the low-temperature trap 2 is provided.

That is, the automatic controller 11 allows the excellent method according to the first invention to be carried out reliably, and furthermore, a configuration is adopted in which the cooling temperature of the low-temperature trap 2 is lowered almost simultaneously with the high-frequency irradiation. As a result, the control structure can be made relatively simple, and a device that is advantageous in terms of function and structure can be provided.

Moreover, the vacuum freeze-drying apparatus according to the third invention includes:
The drying chamber 1 is provided with a radiant heating device 8 and a high frequency irradiation device 7 for the workpiece, as well as a device 12 for detecting glow discharge accompanying the high frequency irradiation, and the water vapor sent from the drying chamber 1 by a vacuum pump 3 is installed. An automatic controller is provided with a low-temperature trap 2 for freezing, the cooling temperature of which can be freely changed, and is configured to operate the radiant heating device 8 at the initial stage of drying, and to operate the high-frequency irradiation device 7 when a set time has elapsed after the start of drying. 11, and an automatic controller 13 for lowering the cooling temperature of the low temperature trap 2 to suppress glow discharge based on information from the detection device 12.

That is, as in the second aspect of the present invention, the automatic controllers 11 and 13 can reliably perform the excellent method according to the first aspect of the present invention, and moreover, glow discharge exceeding the setting actually occurs. Since the cooling temperature of the low-temperature trap 2 is lowered when the temperature rises, even if radiation heating and high-frequency irradiation are performed simultaneously, the thermal conductivity of the object to be processed will decrease due to the pressure drop as detailed in the first invention. We have now been able to provide a device that is highly functional and can perform drying efficiently while minimizing the amount of drying.

[Brief explanation of the drawing]

The drawings illustrate embodiments of the vacuum freeze-drying method and the apparatus used in the method according to the present invention, FIG. 1 is a flow sheet, FIG. 2 is a schematic explanatory diagram showing a heating plate, and FIG. 3 is a schematic explanatory diagram showing a heating plate. 3 is a flow sheet showing another embodiment. 1...Drying room, 2...Low temperature trap, 3...Vacuum pump, 7...High frequency irradiation device, 8...Radiation heating device, 11...Automatic controller, 12...Glow discharge detection device, 13... Automatic controller.

Claims (1)

[Claims] 1. A vacuum freeze-drying method in which water vapor in a drying chamber 1 is sent to a low-temperature trap 2 by a vacuum pump 3 to freeze it, which Perform only radiant heating and then high-frequency irradiation, and suppress glow discharge by detecting glow discharge accompanying the high-frequency irradiation almost simultaneously with the start of the high-frequency irradiation, or by using a detection device provided in the drying chamber 1. A vacuum freeze-drying method characterized in that the cooling temperature in the low-temperature trap 2 is lowered so as to. 2. The drying chamber 1 is equipped with a radiant heating device 8 and a high-frequency irradiation device 7 for the workpiece, and a low-temperature trap 2 that freezes water vapor sent from the drying chamber 1 by a vacuum pump 3 can be freely set to a cooling temperature. an automatic controller configured to operate the radiant heating device 8 in the early stage of drying, and to operate the high frequency irradiation device 7 and lower the cooling temperature of the low temperature trap 2 when a set time has elapsed after the start of drying; A vacuum freeze-drying device characterized by being equipped with 11. 3 The drying chamber 1 is provided with a radiant heating device 8 and a high frequency irradiation device 7 for the object to be processed, as well as a device 12 for detecting glow discharge accompanying the high frequency irradiation, and the water vapor sent from the drying chamber 1 by the vacuum pump 3 is installed. A low-temperature trap 2 for freezing the water is provided, the cooling temperature of which can be freely changed and set, and automatic control is configured to operate the radiant heating device 8 at the initial stage of drying, and to operate the high-frequency irradiation device 7 when a set time has elapsed after the start of drying. 11, and an automatic controller 13 for lowering the cooling temperature of the low-temperature trap 2 to suppress glow discharge based on information from the detection device 12.