JP2016109348A - Terminal point detection method for vacuum drying and vacuum drying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a drying terminal point to be detected as fast as possible even if a pressure within a drying tank is measured by a first vacuum meter such as a barrier membrane pressure gauge and a second vacuum meter such as Pirani vacuum meter and the like when a vacuum frozen drying is carried out, and when a time in which a difference between the measured indicated values at the first vacuum meter and the second vacuum meter is small and converged is judged as a drying terminal point, the drying terminal point can be detected as fast as possible even if a pressure in the drying tank is varied in reference to the type or volume of items to be dried.SOLUTION: A terminal point detection method of vacuum drying in accordance with this invention is carried out in such a way that when a pressure measured by the second vacuum meter 5b is once turned to increase while a pressure in the drying tank is being decreased as an interior of the drying tank 1 is drawn in vacuum, an index value is calculated under application of one inflection point and another inflection point when it is turned to descend and this calculated index value is judged while being converted to the measured indicated value of the second vacuum meter.SELECTED DRAWING: Figure 2

Description

  The present invention evacuates the inside of the drying tank in which the object to be dried is disposed, exhausts the water vapor evaporated from the object to be dried, and dries the object to be dried while adsorbing it to the cold trap. The present invention relates to a vacuum drying end point detection method and a vacuum drying apparatus for detecting a drying end point.

  This type of end point detection method for vacuum drying is known, for example, from Patent Document 1. In this method, during the drying process, the pressure in the drying tank is measured by the gas type and the first vacuum gauge such as a diaphragm pressure gauge that can measure the total pressure without being affected by the measurement instruction value depending on the gas type. A difference occurs in the indicated value, and measurement is performed with a second vacuum gauge such as a Pirani vacuum gauge capable of measuring the total pressure. Then, the point in time when the difference between the measurement instruction values in the first and second vacuum gauges is small and converges is determined as the drying end point. However, it has been found that there are cases where the end point of drying cannot be detected by any time even if an attempt is made to detect the end point of drying using the method of the conventional example.

  Therefore, the inventors of the present invention have conducted extensive research and have evacuated the inside of a drying tank (to be dried in some cases while heating) to be dried such as chemicals and foods. It came to know that depending on the kind and amount of the dried material, the measurement indication value of the second vacuum gauge was caused to repeat rising and falling. This is because when the amount of water vapor evaporated from the material to be dried increases, the amount of water vapor condensing in the condenser tube of the cold trap increases, and the temperature of the refrigerant circulating in the condensing tube rises due to the heat of aggregation at that time, Along with this, the temperature of the condensing tube rises, so that the adsorption capacity of the cold trap once decreases, and the pressure in the drying tank increases. On the other hand, once the adsorption capacity is reduced, the amount of water vapor condensed in the condensing tube is reduced, so that the temperature of the refrigerant is lowered. The pressure drops. Then, by repeating these, the pressure in the drying tank fluctuates, and at this time, the second vacuum gauge, which generates a difference in the measurement instruction value due to the gas type (water vapor), is particularly affected, and the measurement instruction value is greatly increased. This is thought to be due to fluctuations.

  In such a case, if the amount of the object to be dried at once in the drying tank is reduced, or if a high performance thing having sufficient adsorption capacity for water vapor is used as a cold trap, the above conventional example This method can also detect the end point of drying, but this causes a problem that the equipment cost and running cost for drying and cooling become large.

Japanese Patent No. 5094372

  The present invention has been made on the basis of the above knowledge, and it is possible to detect the end point of drying as quickly as possible even when the pressure in the drying tank varies depending on the type and amount of the object to be dried. It is an object of the present invention to provide a drying end point detection method and a vacuum drying apparatus.

  In order to solve the above-mentioned problem, the drying tank in which the object to be dried is evacuated is evacuated, and the water vapor evaporated from the object to be dried is exhausted and dried in the drying process while adsorbed on the cold trap. The vacuum drying end point detection method of the present invention for detecting the drying end point of an object to be dried includes a first vacuum gauge capable of measuring the total pressure of the pressure in the drying tank without being affected by the measurement instruction value by the gas type, Measured with a second vacuum gauge capable of measuring the total pressure, which causes a difference in the measured instruction value depending on the gas type, and the time when the difference between the measured instruction values of both the first and second vacuum gauges converges is the end point of drying. The first inflection point when the pressure measured by the second vacuum gauge temporarily starts to rise while the pressure in the drying tank is decreasing as the vacuum in the drying tank is evacuated, The index value was obtained using other inflection points when turning down to Characterized by determining the target value by replacing the measurement instruction value of the second gauge.

  In the above, for example, when the one inflection point is the minimum value, the other inflection point is the maximum value, and the difference between the maximum value and the minimum value is not more than a predetermined value, the maximum value and the minimum value at that time At least one of the values can be used as the index value. On the other hand, the one inflection point is the minimum value and the other inflection point is the maximum value, and an intermediate value between the maximum value and the minimum value is acquired, and the difference between the acquired intermediate values is predetermined. When the value is less than or equal to the value, at least one intermediate value at that time can be used as the index value.

  According to the above, for example, using one inflection point and another inflection point, such as when the difference between the maximum value and the minimum value or the difference between successive intermediate values is less than or equal to a predetermined value. An index value is obtained, this index value is regarded as a measurement instruction value of the second vacuum gauge, and a point in time when the difference from the measurement instruction value of the first vacuum gauge is small and converges is determined as the drying end point. Therefore, even when the pressure in the drying tank varies depending on the type and amount of the object to be dried, the end point of drying can be detected as quickly as possible. In this case, it is not necessary to reduce the amount of objects to be dried at once in the drying tank, or to use a cold trap having a very high water vapor adsorption capacity, which is advantageous. When the pressure in the drying tank fluctuates, the measurement indication value of the first vacuum gauge may also change independently of the fluctuation of the second vacuum gauge, but the fluctuation amount in the region where the drying end point is detected is Compared with that of the second vacuum gauge, it is extremely small and has little influence on the detection of the drying end point. However, even in the first vacuum gauge, when the pressure measured with the first vacuum gauge once rises while the pressure in the drying tank is decreasing due to the vacuuming in the drying tank, the change occurs. If the inflection point where the inflection point turns to the minimum value and then descends is the maximum value, and the minimum value and the maximum value decrease continuously several times per unit time, the maximum and minimum values at that time If at least one of them or the average value of the minimum and maximum values decreases continuously per unit time, the average value at that time can be used as the measurement indication value of the first gauge. The end point of drying may be detected as quickly and reliably as possible.

  In the present invention, the case where the one inflection point and the other inflection point are continuously decreased per unit time is added to the condition for obtaining the index value, and the second of the index values If the measurement instruction value of the vacuum gauge is replaced, the end point of drying can be detected more reliably.

  In the present invention, a diaphragm pressure gauge is preferably used as the first vacuum gauge, and a Pirani vacuum gauge is preferably used as the second vacuum gauge.

  In order to solve the above problems, the apparatus includes a drying tank in which an object to be dried is arranged, a vacuum pump that evacuates the vacuum tank, and a cold trap that adsorbs water vapor evaporated from the object to be dried. The vacuum drying apparatus of the present invention, which can detect the end point of vacuum drying when the object to be dried is dried while being evacuated and adsorbed to a cold trap, the pressure in the drying tank is affected by the measurement instruction value depending on the gas type. The first vacuum gauge capable of measuring the total pressure that is not received, the second vacuum gauge capable of measuring the total pressure that causes a difference in the measurement instruction value depending on the gas type, and the measurement instructions in both the first and second vacuum gauges A determination unit that determines a point of time when the difference between the values converges to be a drying end point, and the determination unit includes a second unit while the pressure in the drying tank is decreasing due to vacuuming in the drying tank. Once the pressure measured by the vacuum gauge starts to rise An index value is obtained using one inflection point and another inflection point when turning downward, and the obtained index value is replaced with the measurement indication value of the second vacuum gauge. It is characterized by.

The schematic diagram which shows the structure of the vacuum drying apparatus used for implementation of the end point detection method of the vacuum drying of this invention. (A) And (b) is a flowchart for the end point detection of vacuum drying. The graph which shows the pressure fluctuation of both the 1st and 2nd vacuum gauge at the time of vacuum drying.

  Hereinafter, with reference to the drawings, the vacuum drying apparatus of the present invention is a vacuum freeze-drying apparatus, and the vacuum of the present invention is taken as an example when the object to be dried S such as medicines and foods is vacuum-freeze-dried using this vacuum freeze-drying apparatus. An embodiment of a drying end point detection method and a vacuum drying apparatus will be described.

  Referring to FIG. 1, DM is a vacuum freeze-drying apparatus to which the vacuum drying end point detection method of the present invention can be applied. The vacuum freeze-drying apparatus DM heats the object to be dried S, a drying tank 1 having a predetermined volume, a cold trap 2 for adsorbing water vapor evaporated from the object to be dried S, a vacuum pump 3 for evacuating the inside of the drying tank 1, and the like. And the heater 4 to be used. In the drying tank 1 as an airtight container, a plurality of shelves 11 on which the object to be dried S can be placed are installed at intervals in the vertical direction. The cold trap 2 includes a condensing tube 21 built in the drying tank 1 and a refrigerator 22 that supplies a refrigerant to the condensing tube 21. The condensing tube 21 is always cooled to a constant temperature (for example, about −50 ° C.). It has come to be. In addition, since the thing of a well-known structure can be utilized as the refrigerator 22, detailed description is abbreviate | omitted here including the temperature control.

  Further, the vacuum pump 3 includes, for example, a mechanical booster pump 32 and an oil rotary vacuum pump 33 on the back pressure side connected to the drying tank 1 through an exhaust pipe 31, and the drying tank 1 has a predetermined pressure. It can be evacuated. In addition, although this embodiment demonstrates to an example what the condensation pipe | tube 21 is incorporated in the drying tank 1, a sealed container is connected to a drying tank via a connection pipe, and a condensation pipe is built in the said sealed container. In addition, a configuration in which an exhaust pipe from a vacuum pump is connected may be employed. Further, as the heater 4, a resistance heating type or a lamp type may be used as long as it can heat an object to be dried to a predetermined temperature at which moisture is vaporized. In this case, it can be provided inside or outside the drying tank 1 or can be built in the shelf 11, and the heater 4 can be omitted depending on the object to be dried S.

  The drying tank 1 is provided with a first vacuum gauge 5a and a second vacuum gauge 5b having different measurement methods in order to measure the pressure (total pressure) in the tank. As the first vacuum gauge 5a, a capacitance manometer that is a diaphragm pressure gauge that can measure the total pressure in a pressure range of about 1 Pa to 200 Pa during drying and is not affected by the type of gas is used. On the other hand, as the second vacuum gauge 5b, a Pirani vacuum that can measure the total pressure in the pressure range of about 1 Pa to 200 Pa at the time of drying and causes a difference in the measurement instruction value depending on the type of measurement gas using heat conduction. A meter is used.

  The operation of the refrigerator 22, the vacuum pump 3, the first and second vacuum gauges 5a and 5b, etc. of the vacuum freeze-drying apparatus DM is provided with a microcomputer, a sequencer, a memory, etc., and also has a function as a determination means. The end point of the vacuum drying is the time when the difference converges to a small extent based on the measurement instruction values that are controlled by the unit 6 and measured by the first and second vacuum gauges 5a and 5b and input to the control unit 6, respectively. Detected as Hereinafter, the end point detection of the vacuum drying according to the present embodiment will be described in detail with reference to FIGS.

As shown in FIG. 2 (a), when the object to be dried S is set in the drying tank 1 and the drying process is started (STEP 1), the cold trap 2, the vacuum pump 3 and the heater 4 are respectively operated. Then, the inside of the drying tank 1 is evacuated by the vacuum pump 3, the water vapor evaporated from the object to be dried S is exhausted by heating and adsorbed by the cold trap 2, and the object to be dried S is dried. The pressure in 1 gradually decreases. Next, the pressure in the drying tank 1 measured by both the first and second vacuum gauges 5a and 5b is input to the control unit 6 at a constant cycle (STEP 2), and the first vacuum gauge 5a at that time Are set (stored) in the control unit 6 as DG and the measurement instruction values of the second vacuum gauges 5b as PG (STEPs 3 and 4). Then, the difference between DG and PG when comparing DG and PG is lower than the predetermined value (SP) set in advance in the control unit 6, which can determine that the object to be dried S is sufficiently dried. whether it is discriminated (STEP5), the is equal to or less than a predetermined value SP _1, determines that both the first and second gauge 5a, the difference between the measured indicated value of the at 5b has converged small, the time Is detected as the end point of vacuum drying (STEP 6). Incidentally, when the difference between the DG and PG is higher than a predetermined value SP ₁ returns to STEP2, this time, both the first and second gauge 5a, the pressure in the drying chamber 1 are respectively measured by 5b What is input to the control unit 6 and the measurement instruction value at that time is set in the control unit 6 as new DG and PG is updated.

  By the way, depending on the type of the material to be dried S and the amount of the material to be dried S to be processed in the drying tank 1, for example, an amount of water vapor exceeding the capacity of the cold trap 2 is vaporized, as shown in FIG. The measurement indication values of the first and second vacuum gauges 5a and 5b repeatedly rise and fall, and there is a possibility that the end point of vacuum drying cannot be determined as quickly as possible due to this (indicated by a solid line in FIG. 3). The thing measured with the 1st vacuum gauge 5a, and the thing shown with a dotted line is what was measured with the 2nd vacuum gauge 5b). Therefore, in the present embodiment, both the first and second vacuums are performed during the period in which the pressure in the drying tank 1 continues to fall normally as the vacuum in the drying tank 1 is evacuated, and during the period recognized by the control unit 6. An index value is obtained using one inflection point when the pressure measured by the total 5a, 5b once rises and another inflection point when the pressure next falls, and the obtained index value Was replaced with the measurement instruction values of both the first and second vacuum gauges 5a and 5b. For example, when the pressure measured by both the first and second vacuum gauges 5a and 5b once rises, the first inflection point is set to the minimum value (DGmin, PGmin). The inflection point is set to the maximum value (DGmax, PGmax) (see also FIG. 3), and when the difference between the maximum value and the minimum value becomes a predetermined value or less, at least one of the maximum value and the minimum value at that time is used as the index value, This index value is judged by replacing it with the measurement instruction values of both the first and second vacuum gauges 5a and 5b. That is, in the flow of detecting the end point of vacuum drying shown in FIG. 2A, when one inflection point occurs, DG and PG set in STEP 3 and 4 are replaced based on the maximum value or the minimum value. It was decided. In the following, referring to FIG. 2B, an example of setting DG and PG based on the maximum value which is another inflection point (example in which DG and PG in STEP 3 and 4 are replaced with the value in STEP 24) is concretely shown. Explained.

  Measured by both the first and second vacuum gauges 5a and 5b in the state where DG and PG are set in STEPs 3 and 4 in the vacuum drying end point detection flow (STEP 1 to 6) shown in FIG. When the pressure in the drying tank 1 is input to the control unit 6 (STEP 11: same as STEPs 2 to 4), the measurement instruction value at this time is compared with the set DG and PG, and whether or not it is increased Is discriminated (STEP 12). If it has risen, it is assumed that one inflection point has occurred, the measurement instruction value at this time is set to the minimum value, DGmin and PGmin are set in the control unit 6 (STEP 13), and the end point detection flow of vacuum drying ( In STEP 1 to 6), the determination in STEP 5 is performed after STEP 24 ends. Although not specifically illustrated and described, when one inflection point is not found, DG and PG are set according to the vacuum drying end point detection flow (STEPs 1 to 6), and the end point is determined. Further, as described above, the inflection point is determined by comparing the measurement instruction value input to the control unit 6 with the set values (DG, PG), but is not limited thereto. For example, as the measurement instruction value input to the control unit 6, a value obtained by adding an averaging process for removing noise components can be used (in this case, the time range of the sample group to be averaged is the target). Other methods such as a ratio limit and a first-order lag filter can also be applied. That is, a value to which a known noise reduction technique is added can be used for the determination of the inflection point as the measurement instruction value input to the control unit 6 and the set pressure value.

  On the other hand, when the minimum values DGmin and PGmin are set, for example, the amount of water vapor exceeding the capacity of the cold trap 2 is vaporized, so that the measurement instruction values of the first and second vacuum gauges 5a and 5b are increased. When the pressure in the drying tank 1 measured by the first and second vacuum gauges 5a and 5b is input to the control unit 6 (STEP 14), it can be regarded that the lowering is repeated. It is determined whether or not the measurement instruction value has started to decrease after once increasing compared to DGmin and PGmin (STEP 15). If the descent has started, the measurement instruction value at that time is set to the maximum value and set as DGmax, PGmax in the control unit 6 (STEP 16).

  Next, after the maximum values DGmax and PGmax are set, when the pressure in the drying tank 1 measured by the first and second vacuum gauges 5a and 5b is input to the control unit (STEP 17), It is determined whether or not DGmin and PGmin need to be updated because the measurement instruction value at that time has started to rise again and is a measurement instruction value lower than the set minimum value (STEP 18). In such a case, the values set in the control unit 6 as the new DGmin and PGmin are updated (STEP 19). Then, after the minimum value is updated, when the pressure in the drying tank 1 measured by both the first and second vacuum gauges 5a and 5b is input to the control unit 6 (STEP 20), the measurement at this time It is determined whether or not DGmax and PGmax need to be updated because the measured value is higher than the preset maximum value after the command value has once increased and then started to decrease (STEP 21). If this is the case, the measurement instruction values set at that time in the control unit 6 as new DGmax and PGmax are updated (STEP 22).

Next, when the maximum values DGmax and PGmax are updated, the difference between DGmax and DGmin and the difference between PGmax and PGmin for the first and second vacuum gauges 5a and 5b are less than or equal to predetermined values SP ₂ and SP _{3, respectively.} (STEP 23), and when the values are less than or equal to the predetermined values SP ₂ and SP ₃ , respectively, the maximum values DGmax and PGmax at that time are used as index values, and these index values are shown in FIG. DG and PG in the flow for detecting the end point of vacuum drying shown in a) are respectively replaced (DG and PG in STEP 3 and 4 are replaced with values DGmax and PGmax in STEP 24), and then STEP 5 is determined to detect the end point of vacuum drying. If not determined, the process returns to STEP 17 although not shown. If it is higher than the predetermined values SP ₂ and SP ₃ , STEP 5 is not discriminated and the process returns to STEP 17.

According to the above embodiment, even when the amount of water vapor evaporated from the material to be dried S is large and the measurement indication values of both vacuum gauges 5a and 5b vary, the difference between DGmax and DGmin and the difference between PGmax and PGmin are When the values are less than or equal to the predetermined values SP ₂ and SP ₃ , the values DGmax and PGmax at that time are used as index values, and these index values are regarded as measurement instruction values DG and PG. Since the time of convergence is determined as the end point of drying, the end point of drying can be detected as quickly as possible even when the pressure in the drying tank 1 varies depending on the type and amount of the material to be dried S. As another method, although not particularly illustrated, the minimum values DGmin and PGmin as one inflection point and the maximum values DGmax and PGmax as other inflection points respectively decrease continuously per unit time. In this case, the end point of drying can be detected by replacing the measurement rate values of the first and second vacuum gauges 5a and 5b when the reduction rate falls within a preset value range. . Moreover, if it judges by combining a some method, a drying end point can be detected more reliably. As a result, it is not necessary to reduce the amount of objects to be dried at once in the drying tank 1 or to use a cold trap 2 having a very high water vapor adsorption capacity, which is advantageous.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to said thing. In the above embodiment, the index value is obtained from the maximum values DGmax and PGmax, and this is replaced with DG and PG in the vacuum drying end point detection flow shown in FIG. It is not something. For example, the index value may be obtained from the minimum values DGmin and PGmin, or the index value may be obtained from the maximum value DGmax and the minimum value PGmin, or from the minimum value DGmin and the maximum value PGmax. Furthermore, although not shown and described in particular, an intermediate value is acquired for each vacuum gauge 5a, 5b from the maximum value DGmax, PGmax and the minimum value DGmin, PGmin in a certain cycle, and the difference between the intermediate values acquired before and after May be replaced with measurement instruction values DG and PG when the intermediate value continuously decreases per unit time.

  Moreover, in the said embodiment, although it replaces about each measurement instruction | indication value of both the 1st and 2nd vacuum gauges 5a and 5b, it is not limited to this. That is, when the pressure in the drying tank 1 fluctuates, the measurement instruction value of the first vacuum gauge 5a may fluctuate regardless of the fluctuation of the second vacuum gauge 5b, but in the region where the drying end point is detected. The amount of variation may be very small compared to that of the second vacuum gauge 5b. In such a case, the index value obtained according to the above may be replaced with the measurement instruction value of the second vacuum gauge 5b.

  DESCRIPTION OF SYMBOLS 1 ... Vacuum freeze-drying apparatus, 1 ... Drying tank, 2 ... Cold trap, 3 ... Vacuum pump, 4 ... Heater, 5a ... Capacitance manometer (1st vacuum gauge), 5b ... Pirani vacuum gauge (2nd vacuum gauge) , S: To be dried.

Claims (6)

The inside of the drying tank where the object to be dried is placed is evacuated, and the vaporized water vapor from the object to be dried is exhausted, and the drying end point of the object to be dried is detected in the drying process where the object to be dried is adsorbed by the cold trap. An end point detection method for vacuum drying,
The first vacuum gauge capable of measuring the total pressure of the pressure in the drying tank without being affected by the measurement instruction value depending on the gas type, and the second vacuum capable of measuring the total pressure that causes a difference in the measurement instruction value depending on the gas type. In the case where the difference between the measured indication values in both the first and second vacuum gauges is small and converges is determined as the drying end point,
The first inflection point when the pressure measured by the second vacuum gauge once rises while the pressure inside the drying tank is decreasing as the pressure in the drying tank is reduced, and then the pressure decreases. A method for detecting the end point of vacuum drying, wherein an index value is obtained using another inflection point, and the obtained index value is replaced with a measurement instruction value of a second vacuum gauge.   When the one inflection point is the minimum value and the other inflection point is the maximum value, and the difference between the maximum value and the minimum value is less than or equal to a predetermined value, at least one of the maximum value and the minimum value is the index. The end point detection method for vacuum drying according to claim 1, wherein the value is a value.   The one inflection point is the minimum value, the other inflection point is the maximum value, an intermediate value between the maximum value and the minimum value is acquired, and the difference between the acquired intermediate values is less than or equal to a predetermined value. The end point detection method for vacuum drying according to claim 1, wherein at least one intermediate value at that time is used as the index value.   When the one inflection point and the other inflection point continuously decrease per unit time, the index value is replaced with a measurement instruction value of a second vacuum gauge, The end point detection method for vacuum drying according to any one of claims 1 to 3.   The end point detection of the vacuum drying according to any one of claims 1 to 4, wherein a diaphragm pressure gauge is used as the first vacuum gauge, and a Pirani vacuum gauge is used as the second vacuum gauge. Method. A drying tank in which an object to be dried is disposed, a vacuum pump for evacuating the inside of the vacuum tank, and a cold trap that adsorbs water vapor evaporated from the object to be dried are evacuated and exhausted while being adsorbed by the cold trap. A vacuum drying apparatus capable of detecting the end point of vacuum drying when drying a dried product,
The first vacuum gauge capable of measuring the total pressure of the pressure in the drying tank without being affected by the measurement instruction value depending on the gas type, and the second vacuum capable of measuring the total pressure that causes a difference in the measurement instruction value depending on the gas type. And a determination means for determining that the difference between the measurement instruction values in both the first and second vacuum gauges is small and converges as a drying end point,
The determination means includes one inflection point when the pressure measured by the second vacuum gauge once rises while the pressure in the drying tank is decreasing as the vacuum in the drying tank is reduced, A vacuum drying apparatus characterized in that an index value is obtained by using another inflection point when turning downward, and the obtained index value is replaced with a measurement instruction value of a second vacuum gauge.

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