Drying system

Abstract

To provide a drying system capable of grasping a drying state.SOLUTION: A drying system 1 includes: a vessel body 21 for storing a frozen object F obtained by freezing a treated material; a heating medium temperature adjustment unit 3 and stirring means 22 for drying the frozen object F by sublimating a solidified liquid component contained in the frozen object F stored in the vessel body 21 into steam; a vacuum pump 4 for reducing a pressure in the vessel container 21; and an upstream side exhaust passage 511, a cold trap 5, and a downstream side exhaust passage 512 connecting the vessel body 21 and the vacuum pump 4; and an oximeter 44 for measuring an oxygen concentration in the downstream side exhaust passage 512.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a drying system that dries a frozen object by freezing an object to be processed and sublimating a solidified liquid component contained in the frozen object. [Background technology]

[0002] Vacuum freeze-drying technology is known, which freezes materials (hereinafter referred to as the object to be processed) used in foods, cosmetics, medical products, raw materials for electronic components, chemical products, paints, etc., to produce a frozen product, and then sublimates the solidified liquid components contained in the frozen product to obtain a dried product. A typical system using this vacuum freeze-drying technology is a shelf-type drying system. In a shelf-type drying system, shelves are provided in a drying container for placing frozen products, and the temperature of the shelves is adjusted to an appropriate temperature under reduced pressure to dry the frozen product while it is still frozen to obtain a dried product. In the shelf-type drying system, a cold trap is provided in the exhaust path between the drying container and the vacuum pump to prevent the liquid components that have become vaporized by sublimation from reaching the vacuum pump. The inside of this cold trap is cooled by circulating a refrigerant cooled by a refrigerator. The liquid components that have become vaporized in the drying container freeze to solidify as they pass through the cold trap, and are collected by the cold trap.

[0003] In a shelf-type drying system, a tray containing the object to be processed is placed on a shelf and frozen to obtain a frozen product. After that, the pressure inside the drying container is reduced to sublimate the solidified liquid components contained in the frozen product. At that time, the shelf on which the tray is placed is heated to supply heat to the frozen product to promote drying. However, if the product is heated too much, the solidified liquid components contained in the frozen product melt and lumps (aggregations of the object to be processed) form in the dried product, which reduces the quality, so the amount of heat supplied to the frozen product by heating is set to a level that compensates for the heat taken away by sublimation. In addition, the dried product is required to have good restorability (water reconstitution) so that it can be returned to the same state as before drying when dispersed in liquid, but if lumps form, the restorability (water reconstitution) is impaired. In a shelf-type drying system, the frozen product in the tray basically receives heat only from the bottom side where the shelf is located, so the part of the frozen product that receives heat is always the same part, and that part is prone to melting. Even if only the bottom side of the frozen product melts, a small amount of lumps will be mixed into the dried product, which reduces the quality of the dried product. For this reason, in a shelf-type drying system, it is necessary to heat the material while significantly suppressing the amount of heat supplied (heating temperature) to prevent lumps from forming, so it takes a long time to dry the material. The shelf-type drying system described here can be said to be a static drying system in which the frozen material does not move.

[0004] On the other hand, a drying system has been proposed in which the material to be processed is frozen to obtain a frozen material consisting of a large number of blocks of material, and the frozen material is dried while being moved (see, for example, Patent Document 1). The drying in this drying system can be said to be dynamic drying. In the drying system of Patent Document 1, the frozen material stored in a drying container is dried while being moved in the drying container, so that heat can be applied uniformly to the surface of the frozen material, and therefore a larger amount of heat can be supplied to the frozen material (higher heating temperature) compared to a shelf-type drying system, and the drying time is shortened. In addition, frictional heat is generated between the frozen materials by moving the frozen material, so that the frozen material is heated in areas other than those where heat from the outside is transmitted, and the drying time is further shortened. Even in a dynamic drying system such as Patent Document 1, liquid components that have become vapor are collected by a cold trap installed in the exhaust path between the drying container and the vacuum pump. In addition, whether the drying system is static or dynamic, it is confirmed that the drying is completed and the frozen material has become the desired dried material by the disappearance of pressure fluctuations in the drying container and the exhaust path and temperature fluctuations of the frozen material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2022-72411 Summary of the Invention [Problem to be solved by the invention]

[0006] As the drying process nears the end, the amount of liquid components that turn into vapor decreases, and so does the amount of vapor captured by the cold trap. As the refrigerant circulating between the refrigerator and the cold trap is no longer heated by the cold trap, the refrigerator that cools the cold trap may enter a low-pressure cut state and the cooling function of the refrigerant may stop. After the low-pressure cut state is entered, the pressure of the refrigerant increases over time, and when the refrigerant pressure increases, the refrigerator operation is restarted, so the refrigerator repeatedly stops and restarts its function. This causes the temperature and pressure of the cold trap to fluctuate, and the pressure and temperature in the exhaust path and drying container connected to the cold trap also fluctuate, so in conventional drying systems it was difficult to determine whether the drying was complete.

[0007] In addition, at the end of the drying process, the liquid content of the frozen material is reduced, so the risk of the frozen material melting is reduced. For this reason, in dynamic drying systems, there is a demand to shorten the drying time by increasing the speed and frequency at which the frozen material is moved. However, as described above, the pressure and temperature in the drying container and the exhaust path fluctuate depending on the operation of the refrigerator, so in conventional drying systems, it is difficult to determine whether the drying process is at the end from the pressure and temperature measurement results.

[0008] In view of the above circumstances, an object of the present invention is to provide a drying system that makes it possible to grasp the drying status. [Means for solving the problem]

[0009] The drying system of the present invention which solves the above problems includes: A container body for storing a frozen object obtained by freezing the object to be processed; A drying means for drying the frozen object by sublimating a solidified liquid component contained in the frozen object stored in the container body into vapor; A pressure reducing device for reducing the pressure inside the container body; an exhaust path connecting the container body and the pressure reducing device; and an oxygen concentration meter for measuring the oxygen concentration in the exhaust path.

[0010] According to this drying system, by measuring the oxygen concentration, which increases as the liquid component contained in the frozen material decreases, it is possible to grasp the drying status of the frozen material.

[0011] Here, the drying system may include a cold trap that receives the vapor and collects the vapor by freezing it. The cold trap may be provided in the exhaust path. In other words, the exhaust path may exhaust the gas in the container body via the cold trap. The drying system may include an exhaust path pressure gauge that measures the pressure of the exhaust path, and a control means that adjusts the amount of outside air that is allowed to flow into the exhaust path according to the pressure of the exhaust path. It may be determined that the drying process is nearing the end based on the oxygen concentration measured by the oxygen concentration meter. It may also be determined that the drying process is completed based on the oxygen concentration measured by the oxygen concentration meter.

[0012] In this drying system, 2. The drying system according to claim 1, further comprising a control unit that adjusts a drying speed of the drying unit in response to the oxygen concentration measured by the oxygen concentration meter.

[0013] The control means can appropriately adjust the drying speed to shorten the drying time.

[0014] In addition, in this drying system, a frozen object operating unit that moves the frozen object stored in the container body within the container body, The control means may adjust at least one of a speed at which the frozen object is moved by the frozen object operating unit and a frequency at which the frozen object is moved, depending on the oxygen concentration measured by the oxygen concentration meter.

[0015] The control means controls the movement of the frozen material at a speed and frequency suited to the drying state of the frozen material in response to the oxygen concentration, thereby making it possible to shorten the drying time. Effect of the Invention

[0016] According to the present invention, it is possible to provide a drying system that makes it possible to grasp the drying status. [Brief description of the drawings]

[0017] [Figure 1] 1 is a system diagram of a drying system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing a control configuration of the drying system shown in FIG. [Diagram 3] 2 is a flowchart showing control in a drying process of the drying system shown in FIG. 1. [Figure 4] 2 is a graph showing the pressure and oxygen concentration in the exhaust path during a drying process using the drying system shown in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A drying system according to an embodiment of the present invention will now be described in detail with reference to the drawings. The drying system described below is a system for freezing a processing object and drying the frozen object.

[0019] FIG. 1 is a system diagram of a drying system 1 according to one embodiment of the present invention. In the upper right part of FIG. 1, a table is shown showing the correspondence between symbols of the elements constituting the drying system 1, such as valves and instruments, and the names of the components indicated by the symbols. Since the components indicated by these symbols and their functions are well known, some of them will not be described in the description of this embodiment. Furthermore, the measurement results of the components indicated by these symbols that belong to the instruments are appropriately transmitted to control means 10 (see FIG. 2). In addition, the opening and closing and the opening degree of the motor-operated valves, among the components indicated by these symbols, are controlled by control means 10.

[0020] 1 includes a drying container 2, a heat medium temperature adjusting section 3, a vacuum pump 4, a cold trap 5, a common refrigerator 6, and a heat exchanger 7. An example of the heat exchanger 7 is a cooling tower.

[0021] The drying container 2 has a container body 21, a stirring means 22, and a jacket 23. In Fig. 1, the container body 21 is shown in a schematic vertical cross section so that the inside can be seen. In Fig. 1, the frozen material F in the container body 21 is shown by a dot pattern.

[0022] The container body 21 is supported by a support pillar (not shown). The container body 21 is composed of a cylindrical upper portion, an inverted cone-shaped portion that gradually reduces in diameter as it moves away from the upper portion, and an upper lid that covers the upper end. The container body 21 is also provided with a container thermometer 211 that measures the temperature of the stored items such as the brine liquid and frozen items F stored inside, and a brine liquid outlet 212. The container thermometer 211 constantly measures the temperature of the stored items. The lower end of the container body 21 is provided with an outlet 213 for discharging the stored items. The outlet 213 is closed by an outlet lid 214 that can be opened and closed except when discharging the stored items.

[0023] The upper lid of the container body 21 is provided with an inlet 215, an exhaust port 216, and a vortex breaker 217. For example, a dispersion liquid in which the material to be treated is dispersed in a liquid is introduced into the container body 21 through the inlet 215. Then, the dispersion liquid is frozen while being stirred in the container body 21, and a frozen material F consisting of a number of processed material chunks is generated. Note that a brine liquid is stored in the container body 21 before the dispersion liquid is introduced, and the dispersion liquid is frozen in the brine liquid, and then only the brine liquid is drained from the brine liquid outlet 212, so that the frozen processed material chunks remain in the container body 21. However, the frozen material F may be prepared using a dispersion liquid in another device, and the frozen material F may be directly introduced into the empty container body 21 through the inlet 215 and stored in the container body 21. Also, the material to be treated containing a liquid component may be directly frozen in the container body 21 without using a dispersion liquid to produce the frozen material F. Furthermore, the object to be processed containing a liquid component may be directly frozen in another device without using a dispersion liquid to prepare a frozen object F, which may then be introduced into the empty container body 21 through the introduction port 215 and stored in the container body 21. In this embodiment, ethanol is used as the brine liquid, but instead of ethanol, organic compounds such as paraffins, alicyclic hydrocarbons, alcohols, and ethers having a melting point of −30° C. or lower and a boiling point of less than 100° C. may be used.

[0024] The exhaust port 216 is for discharging gases such as air in the container body 21 and steam generated in the container body 21 to the outside of the container body 21. The exhaust port 216 is connected to an upstream exhaust path 511 via an exhaust filter (not shown). Gas that has passed through the exhaust filter enters the upstream exhaust path 511. A cold trap 5 is connected downstream of the upstream exhaust path 511. A vacuum pump 4 is installed downstream of the cold trap 5 via a downstream exhaust path 512. The upstream exhaust path 511, the cold trap 5, and the downstream exhaust path 512 form an exhaust path. That is, the container body 21 and the vacuum pump 4 are connected by the exhaust path. The upstream exhaust path 511 is provided with an exhaust path pressure gauge 513, which is a vacuum gauge that measures the pressure in the upstream exhaust path 511. The pressure in the upstream exhaust path 511 measured by the exhaust path pressure gauge 513 is constantly transmitted to the control means 10 (see FIG. 2). Note that instead of or in addition to the exhaust line pressure gauge 513, a pressure gauge may be installed to measure the pressure inside the vessel body 21, the pressure inside the cold trap 5, or the pressure of the downstream exhaust line 512. Note that the pressure inside the vessel body 21, the pressure inside the upstream exhaust line 511, the pressure inside the cold trap 5, and the pressure inside the downstream exhaust line 512 are all gas pressures.

[0025] The vortex current breaker 217 is attached to the lower end of a shaft hanging down from the upper lid of the container body 21. The vortex current breaker 217 is disposed at a position facing the cylindrical upper part of the container body 21 with a gap therebetween, and is composed of an arc-shaped plate that follows the cylindrical shape of the upper part. The vortex current breaker 217 guides the frozen material F that has reached the top of the container body 21 downward.

[0026] The stirring means 22 has a rotating spiral ribbon 221, a stirring drive shaft 222, and a stirring drive device 223. This stirring means 22 corresponds to an example of a frozen material operating unit. The spiral ribbon 221 is made entirely of metal, is supported by a plurality of rod-shaped support members protruding radially from the stirring drive shaft 222, and travels around the inner surface of the container body 21 in the vicinity of the inner surface of the container body 21. The spiral ribbon 221 may be made of a resin such as engineering plastic or fiber-reinforced plastic. The spiral ribbon 221 has a spiral shape that tapers downward. This spiral ribbon 221 rotates as the stirring drive shaft 222 rotates around its axis. The stirring drive shaft 222 penetrates the upper lid of the container body 21, and the penetration portion is sealed. The stirring drive device 223 is a motor that rotates the stirring drive shaft 222. The agitation drive shaft 222 rotates around its axis by driving the agitation drive device 223, thereby rotating the spiral ribbon 221. The rotation of the spiral ribbon 221 generates a circulatory flow of the frozen material F stored in the container body 21. That is, the rotation of the spiral ribbon 221 causes the frozen material F located near the inner surface of the container body 21 to be lifted upward, and the frozen material F located in the center part in a plan view of the container body 21 to move downward. This causes the frozen material F stored in the container body 21 to be agitated. By increasing the rotation speed of the spiral ribbon 221, that is, the agitation rotation speed of the frozen material F, the frozen material F is lifted further upward, and the flow speed in the circulatory flow of the frozen material F increases, so that the frozen material F is moved more at a faster speed.

[0027] The jacket 23 covers the outer periphery of the container body 21. A heat medium supply path 231 and a heat medium recovery path 232 are connected to the jacket 23. The heat medium supply path 231 has a leading end connected to the lower part of the jacket 23 and a rear end connected to the heat medium temperature adjustment unit 3. On the other hand, the heat medium recovery path 232 has a leading end connected to the heat medium temperature adjustment unit 3 and a rear end connected to the upper part of the jacket 23. The heat medium supplied to the jacket 23 through the heat medium supply path 231 flows inside the jacket 23 and is discharged to the heat medium recovery path 232. The outside of the jacket 23 is covered with a heat insulating member (not shown) so that the temperature of the heat medium in the jacket 23 does not change depending on the installation environment of the drying container 2.

[0028] The heat medium temperature adjustment unit 3 includes a heat medium pump 31, a cooling flow rate adjustment valve 33, a constant flow rate valve 34, a heat medium cooler 35, a heat medium heater 36, a heat medium tank 37, and a heat exchanger 38. In FIG. 1, the heat medium temperature adjustment unit 3 is surrounded by a two-dot chain line. This heat medium temperature adjustment unit 3 corresponds to an example of a supply heat amount adjustment unit. In addition, in FIG. 1, the heat medium cooler 35 and the heat medium heater 36 are shown in a schematic cross section cut vertically so that the inside can be seen. The heat medium pump 31 delivers the liquid heat medium at an arbitrary flow rate. The heat medium is ethanol, which is the same as the above-mentioned brine liquid. Of course, the heat medium may be other than ethanol, and may be different from the brine liquid. The delivered heat medium is divided into the heat medium cooler 35 and the heat medium heater 36 at the divided flow rates set by the cooling flow rate adjustment valve 33 and the constant flow rate valve 34, respectively. The constant flow valve 34 is a valve that allows the heat medium to flow at a set flow rate.

[0029] The cooling flow rate control valve 33 is an electric valve that changes the flow rate of the heat medium passing therethrough under the control of the control means 10 (see FIG. 2), which will be described later. The cooling flow rate control valve 33 can be closed to set the flow rate to zero, and by setting it to zero, the heat medium flows only to the heat medium heater 36. The control means 10 adjusts the flow rate sent out by the heat medium pump 31 according to the opening degree of the cooling flow rate control valve 33 so that the flow rate of the heat medium toward the heat medium heater 36 is always constant. Under the control of the control means 10, a constant amount of the heat medium always flows to the heat medium heater 36, and a flow rate according to the opening degree of the cooling flow rate control valve 33 flows to the heat medium cooler 35. The heat medium that has passed through the heat medium heater 36 is supplied to the jacket 23 through the heat medium supply path 231, so that a constant amount of the heat medium always circulates between the jacket 23 and the heat medium temperature adjustment unit 3. The flow rate toward the heat medium heater 36 may be changed by adjusting the flow rate sent out by the heat medium pump 31 and the opening degree of the cooling flow rate control valve 33. Alternatively, instead of or in addition to the constant flow valve 34, an electric valve may be disposed in the flow path toward the heat medium heater 36, thereby making it possible to form a flow of the heat medium toward only the heat medium cooler 35.

[0030] The heat medium cooler 35 cools the heat medium passing through it. The heat medium cooled by passing through this heat medium cooler 35 passes through the heat exchanger 38 and flows toward the heat medium tank 37. A refrigerant circulates between the heat medium cooler 35 and the common refrigerator 6. The refrigerant cooled by the common refrigerator 6 is sent to the heat medium cooler 35, where it is heated by the heat medium and returned to the common refrigerator 6. That is, in the heat medium cooler 35, the heat medium is cooled and the refrigerant is heated. A cooler expansion valve 351 is provided immediately before the heat medium cooler 35 in the refrigerant flow. The high-pressure refrigerant cooled by the common refrigerator 6 is decompressed by this cooler expansion valve 351 to a state where it is easy to evaporate, and the amount set by the cooler expansion valve 351 flows to the heat medium cooler 35. The flow of this refrigerant will be described later. The outside of the heat medium cooler 35 is covered with a heat-insulating member. In FIG. 1, the heat retaining member is shown by cross-hatching.

[0031] The heat medium heater 36 heats the heat medium passing through it. However, the heat medium heater 36 can also pass the heat medium as it is without heating it. The heat medium that has passed through the heat medium heater 36 flows toward the jacket 23 through the heat medium supply path 231. The heat medium heater 36 is provided with a heating thermometer 361 that measures the heating temperature at which the heat medium is heated. In addition, a heat medium thermometer 362 that measures the temperature of the heat medium that has passed through the heat medium heater 36 is provided downstream of the heat medium heater 36 in the flow of the heat medium. The measured values ​​of these thermometers are constantly transmitted to the control means 10 (see FIG. 2). The control means 10 controls the heating temperature of the heat medium by the heat medium heater 36 based on these measured values ​​so that the heat medium flowing from the heat medium heater 36 toward the jacket 23 has a desired temperature. The heat medium heater 36 is covered on the outside with a heat retaining member. In FIG. 1, the heat retaining member is indicated by cross-hatching.

[0032] The heat medium tank 37 stores the heat medium returned from the jacket 23 through the heat medium recovery path 232 and the heat medium that has passed through the heat medium cooler 35. The heat medium stored in the heat medium tank 37 is extracted at a desired flow rate by the heat medium pump 31 and sent out from the heat medium pump 31. The heat medium sent out from the heat medium pump 31 flows toward the branch section 32 that branches into the heat medium cooler 35 and the heat medium heater 36.

[0033] The heat exchanger 38 exchanges heat between the cooling water flowing from the common refrigerator 6 toward the heat exchanger 7 and the heat medium flowing from the heat medium cooler 35 toward the heat medium tank 37. A waste heat supply valve 381, which is an electric valve that adjusts the flow rate of the cooling water toward the heat exchanger 38, is provided in the front stage (upstream side) of the heat exchanger 38 in the flow of the cooling water. The opening degree of the waste heat supply valve 381 is controlled by the control means 10 (see FIG. 2). In addition, a bypass path that connects the front stage (upstream side) and the rear stage (downstream side) of the heat exchanger 38 in the flow of the cooling water is formed in the vicinity of the heat exchanger 38. The bypass path is provided with a waste heat bypass valve 382, ​​which is an electric valve. The opening degree of the waste heat bypass valve 382 is also controlled by the control means 10. When heat exchange is not required, the waste heat supply valve 381 is closed and the waste heat bypass valve 382 is opened, so that the cooling water flows toward the heat exchanger 7 without passing through the heat exchanger 38. Conversely, when heat exchange is required, the waste heat supply valve 381 is opened and the waste heat bypass valve 382 is closed, so that the cooling water flows toward the heat exchanger 7 after passing through the heat exchanger 38. When only a portion of the cooling water is to be heat exchanged, the ratio of the flow rate of the cooling water that is heat exchanged in the heat exchanger 38 to the flow rate of the cooling water that is not heat exchanged can be set arbitrarily by adjusting the opening degree of each of the waste heat supply valve 381 and the waste heat bypass valve 382.

[0034] The heat medium temperature adjustment unit 3 circulates the heat medium, the temperature of which is adjusted to a set temperature mainly by the heat medium cooler 35 and the heat medium heater 36, between the jacket 23 and the heat medium temperature adjustment unit 3. That is, the temperature-adjusted heat medium is repeatedly circulated, such as being supplied to the jacket 23 through the heat medium supply path 231, and then being returned from the jacket 23 to the heat medium temperature adjustment unit 3 through the heat medium recovery path 232. By circulating and supplying the heat medium to the jacket 23, the temperature of the container body 21 can be adjusted from the outside, and the temperature inside the container body 21 can be adjusted to a desired temperature. That is, the heat medium temperature adjustment unit 3 adjusts the amount of heat supplied to the frozen object F from the heat medium flowing between the jacket 23 and the heat medium temperature adjustment unit 3. The heat medium temperature adjustment unit 3 can adjust both the temperature and flow rate of the heat medium, and can adjust the amount of heat supplied to the frozen object F in the container body 21 by either of these. However, in this embodiment, an example will be described in which the flow rate of the heat medium supplied to the jacket 23 is controlled to be constant, and the amount of heat supplied to the frozen object F in the container body 21 is adjusted by adjusting the temperature of the heat medium. Although the heat medium temperature adjusting unit 3 mainly supplies heat to the frozen object F, it can also be used to cool the brine liquid in the container body 21, which will be described later in detail.

[0035] The vacuum pump 4 reduces the pressure in the container body 21, the upstream exhaust path 511, the cold trap 5, and the downstream exhaust path 512. Hereinafter, the container body 21, the upstream exhaust path 511, the cold trap 5, and the downstream exhaust path 512 may be collectively referred to as the container body 21. The vacuum pump 4 is provided at the downstream end of the flow of gas that has passed through the exhaust port 216 of the container body 21. This vacuum pump 4 corresponds to an example of a pressure reducing device. In addition, the vacuum pump 4, the heat medium temperature adjusting unit 3, and the stirring means 22 correspond to an example of a drying means. By driving the vacuum pump 4, the solidified liquid component contained in the frozen material F in the container body 21 sublimes and becomes vapor. In addition, the solidified liquid component contained in the frozen material F sublimes and becomes vapor when the frozen material F is warmed by the heat medium whose temperature is adjusted by the heat medium temperature adjusting unit 3, or when the frozen material F is warmed by frictional heat generated by the rotation of the spiral ribbon 221. The steam generated in the container body 21 and gases such as air that were in the container body 21 are drawn toward the vacuum pump 4. Then, the gases that reach the vacuum pump 4 are exhausted to the outside of the vacuum pump 4. However, liquid components contained in the gases are collected by the cold trap 5 before they reach the vacuum pump 4.

[0036] By driving the vacuum pump 4, the pressure inside the container body 21 and the like is reduced to about 13 Pa or more and 120 Pa or less. In order to prevent this pressure from dropping too much, the downstream exhaust path 512 is connected to the intake path 41, which draws in outside air. The intake path 41 is provided with a pressure regulating valve 42, which is an electric valve. If the pressure inside the upstream exhaust path 511 measured by the exhaust path pressure gauge 513 is too low, the control means 10 (see FIG. 2) adjusts the opening of the pressure regulating valve 42 according to the pressure. As a result, outside air according to the opening of the pressure regulating valve 42 passes through the intake path 41 and enters the downstream exhaust path 512, and the pressure inside the container body 21 and the like is maintained at a predetermined pressure of 13 Pa or more and 120 Pa or less. An intake filter 43 for reducing intake noise and foreign matter contamination is attached to the end of the intake path 41 opposite to the end connected to the downstream exhaust path 512.

[0037] The downstream exhaust passage 512 is provided with an oxygen concentration meter 44 for measuring the oxygen concentration in the downstream exhaust passage 512. This oxygen concentration meter 44 measures the oxygen concentration downstream of the connection point between the downstream exhaust passage 512 and the intake passage 41 in the gas flow, that is, on the vacuum pump 4 side of the connection point. Since the steam generated in the container body 21 is almost oxygen-free, the oxygen concentration in the downstream exhaust passage 512 changes mainly depending on the amount of outside air sucked in through the intake passage 41. Since the amount of steam generated from the frozen object F is large in the early and middle stages of the drying process, the pressure inside the container body 21 and the like is increased by the pressure increase action of the steam generated in the container body 21 and the decompression action of the vacuum pump 4, and the amount of outside air sucked in through the intake passage 41 becomes zero or very small. On the other hand, at the end of the drying process, the liquid component contained in the frozen object F is reduced, so the steam generated in the container body 21 is greatly reduced. As a result, the amount of outside air sucked in through the intake passage 41 increases at the end of the drying process, and the oxygen concentration in the downstream exhaust passage 512 increases. Alternatively, the intake passage 41 may be connected to the upstream exhaust passage 511, and an oxygen concentration meter 44 may be provided in the upstream exhaust passage 511 to measure the oxygen concentration in the upstream exhaust passage 511. However, in this configuration, moisture contained in the outside air in addition to the steam generated in the container body 21 is collected by the cold trap 5, so it is preferable to connect the intake passage 41 to the downstream exhaust passage 512 to measure the oxygen concentration.

[0038] The cold trap 5 is for freezing and collecting the received vapor. In FIG. 1, the cold trap 5 is shown in a vertical cross section so that the inside can be seen. Basically, vapor freezes by sublimation (solidification) in the cold trap 5, but a very small amount of vapor may condense (liquefy) and then solidify (freeze) to become a solid. A refrigerant circulates between the cold trap 5 and the common refrigerator 6. This refrigerant is a refrigerant that is used in common with the refrigerant circulating between the heat medium cooler 35 and the common refrigerator 6. A part of the refrigerant cooled in the common refrigerator 6 is sent to the cold trap 5, passes through the cooling pipe 51 that is folded back multiple times in the cold trap 5, and then returns to the common refrigerator 6. A trap expansion valve 55 is provided immediately before the cold trap 5 in the refrigerant flow. The high-pressure refrigerant cooled in the common refrigerator 6 is decompressed by the trap expansion valve 55 to a state that is easy to evaporate, and the amount of the refrigerant set by the trap expansion valve 55 flows into the cooling pipe 51. The steam passing through the cold trap 5 is cooled and frozen in the cooling tube 51, and adheres to the surface of the cooling tube 51, and the thickness of the adhesion gradually increases from the surface of the cooling tube 51. The outside of the cold trap 5 is covered with a heat-insulating material. In Fig. 1, the heat-insulating material is indicated by cross-hatching.

[0039] The cold trap 5 is provided with a trap thermometer 53 for measuring the temperature inside the cold trap 5. The cold trap 5 is also provided with a load cell 56 for measuring the mass of the vapor generated by the sublimation of the liquid component of the frozen object F and collected by the cold trap 5. In order to measure the mass with the load cell 56, a flexible hose 54 is installed in the vicinity of the cold trap 5 of each pipe connected to the cold trap 5. The load cell 56 measures the mass of the part located closer to the cold trap 5 than the flexible hose 54, and constantly transmits the measurement result to the control means 10 (FIG. 2). The load cell 56 and the control means 10 correspond to an example of a monitoring means. In this embodiment, the load cell 56 measures the total mass of the part located closer to the cold trap 5 than the flexible hose 54 and the collected vapor, and transmits it to the control means 10, and the control means 10 calculates the mass of the collected vapor. However, the mass of the collected vapor may be directly measured by the cold trap 5 and transmitted to the control means 10 by setting the mass of the vapor before collection to zero in the load cell 56 .

[0040] The common refrigerator 6 supplies refrigerant to both the heat medium cooler 35 and the cold trap 5. The common refrigerator 6 has a refrigerant compression cooling section 61 and a refrigerant pressure gauge 62. The refrigerant returning from the heat medium cooler 35 and the refrigerant returning from the cold trap 5 join in a refrigerant recovery passage 64 to become a mixed refrigerant. The refrigerant compression cooling section 61 compresses the mixed refrigerant to a high pressure, and cools the refrigerant that has become hot by compression with cooling water to condense it and send it to the refrigerant supply passage 63. The refrigerant supply passage 63 branches into a cooler refrigerant supply passage 631 leading to the heat medium cooler 35 and a trap refrigerant supply passage 632 leading to the cold trap 5. The cooler refrigerant supply passage 631 is provided with a cooling refrigerant supply valve 633. The cooling refrigerant supply valve 633 is operated under the control of the control means 10 (see FIG. 2), and is a valve that opens when the supply of refrigerant to the heat medium cooler 35 starts and closes when the supply is stopped. The cooler expansion valve 351 described above is disposed between the cooling refrigerant supply valve 633 and the heat medium cooler 35. The refrigerant, which has expanded in the cooler expansion valve 351 to become a low-pressure liquid, evaporates into gas by cooling the heat medium in the heat medium cooler 35, and is then returned to the common refrigerator 6 through the refrigerant recovery path 64. Note that if the heat medium does not pass through the heat medium cooler 35, if the amount of heat medium passing through the heat medium cooler 35 is small, or if the heat medium passing through the heat medium cooler 35 is sufficiently cooled, some or all of the refrigerant may return to the common refrigerator 6 from the heat medium cooler 35 in liquid form.

[0041] Further, the trap refrigerant supply passage 632 is provided with a trap refrigerant supply valve 634. This trap refrigerant supply valve 634 is operated under the control of the control means 10 (see FIG. 2), and is a valve that opens when the supply of refrigerant to the cold trap 5 is started and closed when the supply is stopped. The above-mentioned trap expansion valve 55 is disposed between the trap refrigerant supply valve 634 and the cold trap 5. The refrigerant that has expanded to a low-pressure liquid by the trap expansion valve 55 flows into the cooling pipe 51 in the cold trap 5, freezes the vapor, and evaporates to a gas, and is then returned to the common refrigerator 6 through the refrigerant recovery passage 64. Note that when the amount of vapor received by the cold trap 5 decreases, a part or all of the refrigerant may return from the cold trap 5 to the common refrigerator 6 in a liquid state.

[0042] The refrigerant recovery path 64 is a refrigerant flow path formed by joining a cooler refrigerant recovery path 641 connected to the heat medium cooler 35 and a trap refrigerant recovery path 642 connected to the cold trap 5. The refrigerant that joins in the refrigerant recovery path 64 flows into the refrigerant compression and cooling section 61. The refrigerant pressure gauge 62 measures the pressure of the refrigerant after the refrigerant recovery path 64 joins and before the refrigerant flows into the refrigerant compression and cooling section 61. That is, the refrigerant pressure gauge 62 measures the pressure of the low-pressure side of the refrigerant.

[0043] As the drying process approaches the end, the liquid component contained in the frozen material F decreases, and the vapor generated in the container body 21 also decreases. As a result, the amount of vapor collected in the cold trap 5 decreases, and the refrigerant circulating between the cold trap 5 and the common refrigerator 6 is no longer heated in the cold trap 5. As the drying process progresses further, the temperature of the refrigerant hardly increases in the cold trap 5, and the pressure of the refrigerant measured by the refrigerant pressure gauge 62 decreases. When the pressure of the refrigerant measured by the refrigerant pressure gauge 62 falls below a predetermined pressure, the low pressure cut state is entered and the common refrigerator 6 stops the operations of refrigerant compression, refrigerant cooling, and refrigerant circulation. In contrast, in this embodiment, the refrigerant used in common by the heat medium cooler 35 and the cold trap 5 is controlled to be warmed in the heat medium cooler 35, so that the operation of the common refrigerator 6 is not stopped. The details of this control will be described later.

[0044] The heat exchanger 7 is for cooling the cooling water circulating between the common refrigerator 6 and the heat exchanger 7. The heat exchanger 7 is provided with a chemical injection device 71 that injects a chemical to keep the water in the heat exchanger 7 in an optimal state. As described above, the cooling water selectively passes through the heat exchanger 38 on the way from the common refrigerator 6 to the heat exchanger 7, and flows toward the common refrigerator 6 after being cooled by the heat exchanger 7. This flow is formed by the cooling water pump 72 located on the way from the heat exchanger 7 to the common refrigerator 6.

[0045] FIG. 2 is a block diagram showing a control configuration of the drying system 1 shown in FIG.

[0046] As shown in FIG. 2, the control means 10 includes a control unit 101 and a storage unit 102. The control means 10 is a PLC (Programmable Logic Controller). Note that, instead of or in addition to the PLC, other computers may be used as the control means 10. Measurement results of various instruments, such as an oxygen concentration meter 44, a load cell 56, a refrigerant pressure gauge 62, a container thermometer 211, a heat medium thermometer 362, and an exhaust passage pressure gauge 513, are transmitted to the control means 10. In response to these measurement results, the control means 10 controls each of the controlled components, such as the heat medium pump 31, the cooling flow rate control valve 33, the heat medium heater 36, the pressure control valve 42, and the agitation drive device 223, provided in the drying system 1, by the control unit 101. The control means 10 also performs calculations based on the measurement results of the various instruments as necessary. The storage unit 102 is composed of a volatile memory and a non-volatile memory. This storage unit 102 stores a program in which the control operation of each control target configuration by the control unit 101 is described.

[0047] Next, a description will be given of a drying method for obtaining a dried material by drying the frozen material F using the drying system 1 shown in Fig. 1. The processing in this drying method is executed by the control means 10 controlling each controlled object configuration.

[0048] In this drying system 1, a frozen material F is produced as a preparation step before starting the drying process. In the production of the frozen material F, a brine liquid is supplied from the inlet 215 of the container body 21 to the container body 21, the inside of which is empty. Then, when the container body 21 is sealed, the control means 10 is made to start the preparation step. The control means 10 opens the cooling refrigerant supply valve 633 and operates the common refrigerator 6 and the cooling water pump 72. The control means 10 also controls the heat medium temperature adjustment unit 3 to open the cooling flow rate adjustment valve 33 to start driving the heat medium pump 31, close the waste heat supply valve 381, and open the waste heat bypass valve 382. Thereafter, the heat medium is cooled by the heat medium temperature adjustment unit 3 to a desired cooling temperature (for example, -30°C) that is equal to or lower than the freezing point of the dispersion liquid, while measuring the temperature of the brine liquid by the container thermometer 211. The control means 10 controls the heat medium heater 36 not to heat the heat medium until the cooling temperature is reached.

[0049] When the brine reaches a desired cooling temperature, the dispersion is poured into the container body 21 and rapidly frozen by immersion in the brine, thereby producing a frozen product F in which the dispersion is frozen. In this embodiment, an example is described in which a dispersion using water as a liquid component is used, but a dispersion using a liquid component other than water may be used. In addition, the dispersion is pre-frozen in advance and crushed to a degree that allows it to pass through the inlet 215, and a plurality of processed material chunks may be used as the frozen product F. When cooling the brine, the control means 10 also starts driving the stirring means 22 to rotate the spiral ribbon 221. This stirs the brine and the entire brine is cooled evenly. Then, the dispersion dropped into the brine is divided by the rotation of the spiral ribbon 221 to become a frozen product F consisting of a number of processed material chunks. When the frozen product F is obtained, only the brine is discharged from the brine outlet 212 provided in the container body 21. As a result, the frozen product F remains in the container body 21. Thereafter, the control means 10 opens the trap refrigerant supply valve 634 to circulate the refrigerant between the cold trap 5 and the common refrigerator 6 to lower the temperature of the cold trap 5 to -40°C. In addition, the control means 10 closes the cooling flow rate control valve 33 to start heating by the heat medium heater 36 to adjust the heating temperature and control the temperature of the heat medium to -20°C, which is a temperature below the eutectic point of the frozen object F. Furthermore, the control means 10 controls the spiral ribbon 221 to rotate at 10 rotations per minute. In the case where the basic minimum rotation speed of the spiral ribbon 221 is 10 rotations per minute, it is preferable that the maximum rotation speed that can be adjusted depending on the situation is 15 rotations per minute. The rotation speed set in this preparation process becomes the minimum rotation speed of the spiral ribbon 221 in the drying process. Then, the control means 10 adjusts the rotation of the spiral ribbon 221 to the minimum rotation speed or a higher rotation speed depending on the progress of the drying process. Instead of changing the rotation speed, intermittent stirring may be performed by repeatedly rotating and stopping the spiral ribbon 221. In this case, the control means 10 controls the time allocation between the driving time and the driving stop time of the stirring means 22 instead of the rotation speed.The temperature of the heat medium, the number of revolutions of the spiral ribbon 221, or the intermittent time distribution of the spiral ribbon 221 in the case of intermittent stirring, are set by the operator selecting a value that does not reliably melt the frozen material F according to the type of the object to be processed, the type of liquid component of the dispersion, or the proportions of the container body 21, and inputting it into the control means 10, and can be changed appropriately by the operator. In addition, by using a means that can automatically recognize the input conditions, it is possible to perform the preparation process in an automatic operation. By executing the above preparation process, preparation for starting the drying process is completed. Note that the method of generating the frozen material F using a brine solution is only one example, and there are various other preliminary freezing methods, such as a freezing method in which the dispersion is evacuated and sprayed, and a freezing method in which the jacket 23 is heated to around 0°C to make the inside of the container body 21 less than 600 PaA and self-freeze, and any of these methods may be used to generate the frozen material F.

[0050] Fig. 3 is a flowchart showing control in the drying process of the drying system 1 shown in Fig. 1. Also, Fig. 4 is a graph showing the pressure in the exhaust path and the oxygen concentration in the drying process using the drying system 1 shown in Fig. 1.

[0051] When the drying process is started, the control means 10 drives the vacuum pump 4 while maintaining the temperature of the heat medium, the temperature in the cold trap 5, and the rotation speed of the spiral ribbon 221 at the values ​​set in the preparation process. The pressure in the container body 21 is reduced to about 13 Pa or more and 120 Pa or less by driving the vacuum pump 4. As shown in FIG. 4, in this embodiment, the pressure in the container body 21 and the like is maintained at about 50 Pa by controlling the opening degree of the pressure regulating valve 42 by the control means 10 during the execution of the drying process. When the pressure in the container body 21 is reduced to about 50 Pa, and further, by receiving frictional heat from the spiral ribbon 221 and the container body 21 or heat of the heat medium in the jacket 23, moisture, which is a liquid component of the frozen object F that has been solidified, sublimes and begins to generate steam. Most of the steam generated during this drying process is frozen by the cold trap 5 on the way to the vacuum pump 4 and collected as ice (solid). The process of performing this drying process corresponds to an example of a collection process. In addition, there may be a small amount of brine liquid remaining in the container body 21 that was not completely drained during the preparation process. In such a case, the gas generated in the container body 21 may contain evaporated brine liquid, but this is an extremely small amount and usually does not pose a problem.

[0052] The control means 10 periodically repeats the processing of steps S11 to S26 shown in FIG. 3 at a predetermined time interval (for example, every 10 minutes) until the drying process is completed. Hereinafter, each of these periodically repeated processes may be referred to as a periodic process. As shown in FIG. 3, the control means 10 obtains temperature data of the frozen object F at the start of each periodic process from the container thermometer 211, and determines whether the temperature of the frozen object F is equal to or lower than a reference temperature (step S11). The reference temperature is the temperature (eutectic point) at which the frozen object F begins to melt under the pressure inside the container body 21, or a temperature slightly lower than that temperature. For example, this reference temperature is −15° C. at the beginning of the drying process, and is gradually increased (raised) according to the elapsed time from the start of the drying process to finally reach 20° C.

[0053] If the temperature of the frozen object F is equal to or lower than the reference temperature (YES in step S11), the control means 10 judges whether the mass measured by the load cell 56 has changed from the previous mass stored in the memory unit 102 (step S12). This change in mass is a change caused by the steam collected as ice by freezing in the cold trap 5 during the period from the start of the previous regular processing to the start of the current regular processing, and is an increasing change. Therefore, the changed mass corresponds to the mass of the steam collected in the most recent regular processing, and is calculated by subtracting the previous mass stored in the memory unit 102 from the mass measured this time by the load cell 56. Hereinafter, this changed mass may be referred to as the collected mass. The existence of the collected mass indicates that the moisture contained in the frozen object F has sublimated and the drying process has progressed smoothly. In the first regular processing, the information on the previous mass is not stored in the memory unit 102, so this step S12 is NO.

[0054] If there is a change in the mass of ice collected in the cold trap 5 (YES in step S12), the control means 10 judges whether the temperature of the heat medium supplied to the jacket 23 is less than the maximum temperature (step S13). This maximum temperature is, for example, 20°C. The maximum temperature is set by an operator selecting and inputting into the control means 10 a value according to the type of material to be treated and the type of liquid component of the dispersion, and can be changed as appropriate by the operator. On the other hand, if there is no change in the mass of ice collected in the cold trap 5 (NO in step S12), the process proceeds to step S17.

[0055] If the temperature of the heat medium supplied to the jacket 23 is less than the maximum temperature (YES in step S13), the temperature of the heat medium supplied to the jacket 23 is increased by 3° C. (step S14). That is, when the control means 10 judges in step S12 that the drying of the frozen object F is proceeding smoothly and in step S13 that there is still room for increasing the temperature of the heat medium, the temperature of the heat medium is increased to increase the amount of heat supplied to the frozen object F, thereby increasing the drying speed. The temperature to be increased to in step S14 is set by the operator by selecting and inputting it into the control means 10, and can be changed as appropriate by the operator, but is preferably 3° C. or more and 10° C. or less. Note that if an increase of 3° C. would cause the temperature of the heat medium to exceed the maximum temperature, the temperature of the heat medium is increased only to the maximum temperature.

[0056] When the process of increasing the temperature of the heat medium in step S14 is completed or the temperature of the heat medium supplied to the jacket 23 is equal to or higher than the maximum temperature (NO in step S13), the control means 10 judges whether the rotation speed of the spiral ribbon 221 is less than the maximum rotation speed (step S15). If the rotation speed of the spiral ribbon 221 is less than the maximum rotation speed (YES in step S15), the rotation speed of the spiral ribbon 221 is increased by 4 rotations / min (step S16). That is, when it is judged in step S12 that the drying of the frozen object F is proceeding smoothly and in step S15 that there is still room for increasing the rotation speed of the spiral ribbon 221, the rotation speed of the spiral ribbon 221 is increased to move the frozen object F more, thereby increasing the drying speed. The rotation speed to be increased in step S15 is set by the operator selecting and inputting it into the control means 10, and can be appropriately changed by the operator. Note that, if the maximum rotation speed is exceeded by increasing the rotation speed by 4 rotations / min, the increase in the rotation speed is limited to the maximum rotation speed. This maximum rotation speed is set by the operator to about 4 to 10 times the minimum rotation speed (10 rotations / min). In this embodiment, the maximum rotation speed of the spiral ribbon 221 is set to 86 rotations / min. By increasing the rotation speed of the spiral ribbon 221, the frozen object F is lifted higher.

[0057] If the process of increasing the number of rotations of the spiral ribbon 221 in step S16 is completed, if there is no change in the mass of ice captured in the cold trap 5 (NO in step S12), or if the number of rotations of the spiral ribbon 221 is equal to or higher than the maximum number of rotations (NO in step S15), the control means 10 judges whether the oxygen concentration measured by the oxygen concentration meter 44 is equal to or higher than the first reference concentration (step S17). As described above, in order to maintain the pressure inside the container body 21, etc. at about 50 Pa, the control means 10 controls the opening degree of the pressure regulating valve 42. At the end of the drying process, the moisture content of the frozen object F is low and the steam generated inside the container body 21 is greatly reduced, so the pressure in the exhaust path is likely to decrease. In response to this, the control means 10 increases the opening degree of the pressure regulating valve 42 in order to maintain the pressure, and the amount of outside air flowing into the downstream exhaust path 512 increases. Due to the oxygen contained in this outside air, the oxygen concentration in the downstream exhaust path 512 increases at the end of the drying process, as shown in FIG. 4. As can be seen from Fig. 4, the oxygen concentration is stable and almost constant in the beginning and middle stages of the drying process, but increases rapidly toward the end of the drying process, so the first reference concentration is set to a concentration slightly higher than the oxygen concentration in the beginning and middle stages of the drying process to determine that the drying process is at the end. In this embodiment, the oxygen concentration in the beginning and middle stages of the drying process is about 54 ppm, so the first reference concentration is set to 60 ppm. The first reference concentration is a value selected by the operator based on the amount of dispersion liquid and the amount of frozen material F poured into the container body 21, and set by inputting it into the control means 10.

[0058] If the rotation speed of the spiral ribbon 221 is increased significantly in the beginning or middle of the drying process, the frozen object F is likely to melt due to frictional heat between the spiral ribbon 221 and the frozen object F, frictional heat between the frozen object F and the inner surface of the container body 21, and frictional heat between the frozen objects F themselves. However, at the end of the drying process, the moisture content of the frozen object F is reduced, so that the risk of melting is reduced even if the rotation speed of the spiral ribbon 221 is increased. For this reason, it is preferable to shorten the drying time by increasing the rotation speed of the spiral ribbon 221 at the end of the drying process. By shortening the drying time, not only can the production efficiency be improved, but also the energy required for drying can be reduced. Furthermore, by increasing the rotation speed of the spiral ribbon 221, the frozen object F is raised to a higher position, so that the frozen object F comes into contact with the inner surface of the container body 21 even in the upper part of the container body 21, and the heat of the heat medium can be efficiently transferred to the frozen object F. 3, if the oxygen concentration is equal to or higher than the first reference concentration (YES in step S17), the rotation speed of the spiral ribbon 221 is increased to the maximum rotation speed to increase the drying speed (step S18). On the other hand, if the oxygen concentration is lower than the first reference concentration (NO in step S17), the drying process is still in the early or middle stage, so that the process proceeds to step S24 without executing step S18 and step S19 described later so as not to melt the frozen object F.

[0059] Also, when the oxygen concentration is equal to or higher than the first reference concentration (YES in step S17), the amount of vapor received by the cold trap 5 is extremely small, so the refrigerant passing through the cooling pipe 51 returns to the common refrigerator 6 without being heated. For this reason, the common refrigerator 6 is likely to be in a low-pressure cut state. When the common refrigerator 6 is in a low-pressure cut state, the cooling function of the common refrigerator 6 is temporarily stopped, and the pressure and temperature in the cold trap 5 increase, and when the cooling function of the common refrigerator 6 is resumed, the pressure and temperature in the cold trap 5 decrease. This is repeated. Depending on the pressure and temperature in the cold trap 5, the pressure and temperature in the container body 21, the upstream exhaust path 511, and the downstream exhaust path 512 also fluctuate, so it becomes difficult to judge the drying state and whether or not drying is completed based on these pressures and temperatures. In addition, if the pressure and temperature in the container body 21 fluctuate, there is a risk that the frozen object F will melt, and if it melts, the quality of the dried product will decrease. Furthermore, there is a risk that due to fluctuations in the temperature of the cold trap 5, the vapor cannot be captured by the cold trap 5 and reaches the vacuum pump 4, causing damage to the vacuum pump 4. In response to this, in this embodiment, when the oxygen concentration is equal to or higher than the first reference concentration, step S19 is executed to warm the refrigerant in the heat medium cooler 35, thereby controlling the common refrigerator 6 not to enter a low pressure cut state.

[0060] Specifically, in step S19, the control means 10 controls the heat medium temperature adjustment unit 3 to open the cooling flow rate adjustment valve 33, open the waste heat supply valve 381, and close the waste heat bypass valve 382. As a result, the heat medium that flowed only to the heat medium heater 36 also flows to the heat medium cooler 35, and the heat medium is cooled by the heat medium cooler 35. On the other hand, the refrigerant is heated in the heat medium cooler 35 and expands or evaporates, increasing its pressure and flowing to the common refrigerator 6, so that the pressure of the refrigerant measured by the refrigerant pressure gauge 62 increases, and the low-pressure cut state can be avoided. In other words, by raising the temperature of the refrigerant in the heat medium cooler 35, the load on the common refrigerator 6 is increased, and the low-pressure cut state can be avoided. The control means 10 fully opens the cooling flow rate adjustment valve 33 in step S19, but may also control the cooling flow rate adjustment valve 33 to be opened slightly when the collected mass becomes smaller than a predetermined amount in step S12, and then to increase the opening of the cooling flow rate adjustment valve 33 as the collected mass decreases.

[0061] Furthermore, by opening the waste heat supply valve 381 and closing the waste heat bypass valve 382, ​​the heat medium cooled in the heat medium cooler 35 and the cooling water heated in the common refrigerator 6 are heat exchanged in the heat exchanger 38. As a result, the heat medium is heated, and therefore less energy is required to heat the heat medium to a set temperature in the heat medium heater 36. Furthermore, as the cooling water is cooled in the heat exchanger 38, even colder cooling water can be obtained in the heat exchanger 7. As a result, the energy consumed in the drying system 1 can be reduced. After the above step S19 is completed, proceed to step S24.

[0062] If the temperature of the frozen material F exceeds the reference temperature in step S11 described above (NO in step S11), there is a risk that the frozen material F will melt if left as is. Therefore, the control means 10 sets the temperature of the heat medium supplied to the jacket 23 to a lowering temperature that is equal to or lower than the eutectic point of the frozen material F (step S21). This reduces the drying speed of the frozen material F, and suppresses melting of the frozen material F. This lowering temperature is, for example, -5°C. The lowering temperature is set by the operator selecting it according to the type of the material to be treated and the type of liquid component of the dispersion liquid, and inputting it into the control means 10, and can be changed as appropriate by the operator.

[0063] Following the start of the temperature change of the heat medium in step S21, the control means 10 judges whether the rotation speed of the spiral ribbon 221 exceeds a predetermined rotation speed (step S22). This predetermined rotation speed is set to 10 rotations / min, which is the minimum rotation speed. However, this predetermined rotation speed can be changed appropriately by the operator. If the rotation speed of the spiral ribbon 221 exceeds the predetermined rotation speed (YES in step S22), the control means 10 reduces the rotation speed of the spiral ribbon 221 to the minimum rotation speed (step S23). This reduces the drying speed of the frozen object F, and further suppresses the melting of the frozen object F. When the process of step S23 is completed or the rotation speed of the spiral ribbon 221 does not exceed the predetermined rotation speed (NO in step S22), the process proceeds to step S24.

[0064] In step S24, the mass information obtained from the load cell 56 in the current periodic process is stored in the storage unit 102. Here, when step S24 is executed via steps S21 to S23, there is no mass information in the current periodic process, so the previous mass information is stored in the storage unit 102 as the current mass information. When step S24 is executed via steps S21 to S23, mass information may be obtained from the load cell 56 in step S24 and stored in the storage unit 102. The mass data stored in the storage unit 102 may be overwritten for each drying process, but it is preferable to leave all data during the drying process or data for multiple periodic processes as history data in the storage unit 102 together with data measured by each instrument such as the oxygen concentration meter 44 and the exhaust pressure meter 513. These data can be used when verifying the set values ​​set by the operator in the drying process. After storing the mass information, the control means 10 judges whether a predetermined time has elapsed since the start of the current periodic process (step S25). Then, the process waits until a predetermined time has elapsed (NO in step S25). This predetermined time is 10 minutes, which is the time interval for regular processing. Note that the predetermined time in step S25 can be changed as appropriate by an operator, and by changing this predetermined time, the time interval for regular processing can be changed as desired.

[0065] When a predetermined time has elapsed (YES in step S25), the control means 10 judges whether the oxygen concentration measured by the oxygen concentration meter 44 is equal to or greater than the second reference concentration (step S26). If the oxygen concentration is equal to or greater than the second reference concentration (YES in step S26), the drying process is terminated since the drying process is complete. As shown in FIG. 4, in this embodiment, when the moisture contained in the frozen object F is gone, the oxygen concentration saturates at a level slightly above 80 ppm, so in this embodiment, the second reference concentration is set to 80 ppm, which provides sufficient quality for the drying section. On the other hand, if the oxygen concentration is less than the second reference concentration (NO in step S26), the process returns to step S11 and the next periodic process is started.

[0066] According to the drying system 1 of this embodiment, the oxygen concentration in the exhaust path changes depending on the drying status, and by measuring the oxygen concentration, it is possible to grasp when the drying process is nearing the end and when the drying is complete. The control means 10 increases the speed at which the frozen material F is moved in response to the drying process reaching the end, so that the drying speed of the frozen material F at the end of the drying process increases, the drying time is shortened, and the energy required for drying can be reduced. Furthermore, since it is possible to accurately grasp when the drying process is complete by measuring the oxygen concentration in the exhaust path, it is possible to prevent the drying process from being continued unnecessarily after the drying process is completed, and therefore the energy required for the continuation can also be reduced.

[0067] The present invention is not limited to the above-mentioned embodiment, and various modifications can be made within the scope of the claims. For example, in the above-mentioned embodiment, the spiral ribbon 221 basically rotates all the time, but it may be configured to rotate and stop repeatedly, and the drying speed may be adjusted by changing the frequency of moving the frozen material F by changing the ratio of the driving time and the driving stop time of the stirring means 22 instead of the rotation speed of the spiral ribbon 221, or the drying speed may be adjusted by changing both the rotation speed of the spiral ribbon 221 and the frequency of moving the frozen material F. Furthermore, when it is determined that the oxygen concentration has reached the first reference value or more, the drying speed may be further increased by changing the temperature of the heat medium supplied to the jacket 23 to the maximum temperature in addition to changing the rotation speed of the spiral ribbon 221. Furthermore, instead of the spiral ribbon 221, a stirring blade consisting of a blade-shaped paddle member having a flat surface in the vertical direction at the tip of a metal arm radially protruding from the stirring drive shaft 222 may be provided in the container body 21 to move the frozen material F.

[0068] In addition, instead of the stirring means 22, the entire container body 21 may be supported by a tubular shaft so that it can rotate or swing freely, and the container body 21 may be rotated or swinged by a motor, so that the frozen object F is moved within the container body 21. In such a configuration, the shaft supporting the container body 21, the container body 21, and the motor rotating or swinging the container body 21 correspond to an example of a frozen object operating unit. In that case, instead of adjusting the number of rotations of the spiral ribbon 221, it is preferable to adjust the frequency of rotation or swing of the container body 21. However, the number of rotations or swing of the container body 21 may be adjusted by controlling the container body 21 to always rotate or swing.

[0069] Furthermore, instead of the common refrigerator 6 that cools both the heat medium cooler 35 and the cold trap 5, a dedicated refrigerator may be provided for each of the heat medium cooler 35 and the cold trap 5.

[0070] In addition, even if a constituent element is included only in the description of the embodiment and each modified example described above, that constituent element may be applied to the embodiment and each modified example. [Explanation of symbols]

[0071] 1 Drying System 3 Heat medium temperature adjustment section 4. Vacuum pump 5. Cold Trap 21 Container body 22 Stirring means 44 Oxygen Concentration Meter 511 Upstream exhaust passage 512 Downstream exhaust passage F Frozen material

Claims

1. A container body for storing a frozen object obtained by freezing the object to be processed; A drying means for drying the frozen object by sublimating a solidified liquid component contained in the frozen object stored in the container body into vapor; A pressure reducing device for reducing the pressure inside the container body; an exhaust path connecting the container body and the pressure reducing device; and an oxygen concentration meter for measuring an oxygen concentration in the exhaust path.

2. 2. The drying system according to claim 1, further comprising a control means for adjusting a drying speed of said drying means in response to the oxygen concentration measured by said oxygen concentration meter.

3. a frozen object operating unit that moves the frozen object stored in the container body within the container body, The drying system according to claim 2, characterized in that the control means adjusts at least one of the speed at which the frozen material is moved by the frozen material operating unit and the frequency at which the frozen material is moved in accordance with the oxygen concentration measured by the oxygen concentration meter.

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