Gas circulation system

Abstract

A gas circulation system (201) comprises: an openable / closable supply path (19) for supplying a gas to a processing space (1) for performing a prescribed process that uses harmful gas; an openable / closable discharge path (20) for discharging the gas in the processing space (1) outside of the processing space (1); a circulation path (31) to which the supply path (19) and the discharge path (20) are connected, and both ends of which are connected to the processing space (1); a circulation unit for circulating the supply of gas in the processing space (1) through the circulation path (31); a first pressure sensor (2) that measures the pressure of gas in the circulation path (31); a storage tank (14) that can at least temporarily store some of the gas from the circulation path (31); and air supply units (12), (13) that supply gas between the storage tank (14) and the circulation path (31).

Description

Gas Circulation System

[0001] The present invention relates to a gas circulation system.

[0002] Japanese Patent Laid-Open Publication No. 2018-84570 (Patent Document 1) is a background art of this technical field. This publication states that "the gas filling unit fills a nuclear reaction vessel with a target gas, and the gas sealing unit seals the nuclear reaction vessel filled with the target gas. The radiation irradiation unit irradiates the nuclear reaction vessel sealed with the target gas with radiation for a predetermined period of time to cause a nuclear reaction in the target gas. After the nuclear reaction vessel is opened, the RI-labeled compound synthesis unit synthesizes an RI-labeled compound by reacting a radioactive isotope contained in the target gas after the nuclear reaction with a liquid compound. The impurity trapping unit removes impurities from the target gas after the reaction and returns the removed target gas to the nuclear reaction vessel" (see Abstract).

[0003] Another example of background art is Japanese Patent Laid-Open Publication No. 2013-15349 (Patent Document 2), which states, "A first radioactive gas leakage amount measuring device includes a flow path formed by connecting a container that is connected to an intake line via a valve and that contains waste, another container that is connected to the container via a valve, another container that is connected to the container via a valve, and a vacuum pump that is connected to the container via a valve and that evacuates the container, a pressure transmitter that measures the pressure within this flow path, a device that obtains measured values ​​by signal processing an output signal from a radioactive gas detector that detects radiation from gas stored in the container, and a computer that processes the measured values ​​obtained by the device to measure the amount of radioactive gas leaking from the waste container" (see Abstract).

[0004] JP 2018-84570 A JP 2013-15349 A

[0005] However, the techniques disclosed in Patent Documents 1 and 2 leave room for improvement in terms of maintaining an appropriate gas pressure within a processing space, etc., when processing a gas in a processing space containing harmful gas while circulating the gas in the processing space through a circulation path in a sealed state. Therefore, an object of the present invention is to provide a gas circulation system that can maintain an appropriate gas pressure within a processing space, etc., when processing a gas in a processing space containing harmful gas while circulating the gas in the processing space through a circulation path in a sealed state.

[0006] In order to solve the above problems, the present invention comprises an openable / closable supply path that supplies a harmful gas to a processing space where a predetermined processing is performed with the gas, an openable / closable exhaust path that exhausts the gas in the processing space to the outside of the processing space, a circulation path to which the supply path and the exhaust path are connected and both ends of which are connected to the processing space, a circulation unit that circulates and supplies the gas in the processing space within the circulation path, a first pressure sensor that measures the pressure of the gas within the circulation path, a storage tank that can at least temporarily store a portion of the gas in the circulation path, and an air supply unit that supplies the gas between the storage tank and the circulation air supply unit.

[0007] According to the present invention, it is possible to provide a gas circulation system that can maintain an appropriate gas pressure in a processing space, etc., when processing a processing space containing harmful gases while circulating the gas in the processing space through a circulation path in a sealed state. Problems, configurations, and effects other than those described above will become clear from the description of the following embodiments.

[0008] FIG. 10 is a system diagram of a gas circulation system according to a first embodiment of the present invention. FIG. 11 is a plan view illustrating a detachable structure of a bypass path. FIG. 12 is a plan view illustrating a detachable structure of a bypass path. FIG. 13 is a block diagram illustrating the electrical connections of a control system of a gas circulation system. FIG. 14 is a flowchart illustrating the content of control of the gas circulation system executed by a control unit. FIG. 15 is a flowchart illustrating the content of control of the gas circulation system executed by a control unit. FIG. 16 is a graph illustrating the control content of FIG. 7. FIG. 17 is a system diagram of a gas circulation system according to a second embodiment of the present invention. FIG. 18 is a system diagram of a gas circulation system according to a third embodiment of the present invention. FIG. 19 is a system diagram of a gas circulation system according to a fourth embodiment of the present invention. FIG. 19 is a system diagram of a gas circulation system serving as a comparative example.

[0009] Hereinafter, several embodiments of the present invention will be described with reference to the drawings. In each drawing, arrows indicate the direction of flow of gas or the like.

[0010] [Comparative Example] First, a comparative example to the present embodiment will be described below. Fig. 11 is a system diagram of a gas circulation system serving as a comparative example. Fig. 11 schematically shows a processing space 101 that handles substances that generate harmful gases, and a pass box 4 that introduces samples, items required for processing, and the like from the outside into the processing space 101. The processing space 101 is a space surrounded by walls or the like where, for example, work such as producing chemicals from radioactive substances is performed. In this case, harmful gases containing radioactive substances will be generated within the processing space 101.

[0011] A pass box 104 connected to the processing space 101 is provided with an outer door 105 and an inner door 103 for transferring samples, articles, etc. between the outside of the processing space 101 and the pass box 104. The pass box 104 is provided with an inlet pipe 107 for introducing clean gas such as air or nitrogen from the outside of the processing space 101, and an on-off valve 106 for opening and closing the inlet pipe 107. The pass box 104 also includes an exhaust pipe 108 and an exhaust pump 109 for exhausting and sending gas from the pass box 104 to the processing space 101.

[0012] First, introduction of samples, objects, etc. from outside the processing space 101 into the processing space 101 using the pass box 104 is performed in the following procedure. First, clean gas is introduced from the outside into the pass box 104 using the inlet pipe 107 and its open / close valve 106. Then, the outer door 105 of the pass box 104 is opened, and the samples, objects, etc. are carried into the pass box 104. Then, after the outer door 105 of the pass box 104 is closed, the inner door 103 of the pass box 104 is opened, and the samples, objects, etc. in the pass box 104 are carried into the processing space 101.

[0013] Next, the operation of using the pass box 104 to unload samples, articles, etc. from the processing space 101 to the outside is performed according to the following procedure. First, the inner door 103 of the pass box 104 is opened, and the samples, articles, etc. are loaded into the pass box 104. Then, after closing the inner door 103 of the pass box 104, the contaminated gas inside the pass box 104 is exhausted into the processing space 101 using the exhaust pipe 108 and the exhaust pump 109. Thereafter, the inside of the pass box 104 is filled with clean gas using the inlet pipe 107 for introducing clean gas and its opening / closing valve 106. Then, the outer door 105 of the pass box 104 is opened, and the samples, articles, etc. are unloaded to the outside.

[0014] By using the pass box 104 to take samples, articles, etc. in and out, it is possible to generally prevent potentially contaminated gas from leaking out of the processing space 101. However, even if the above-described operation is performed, there is still a possibility that a small amount of contaminated gas may leak out when the outer door 105 or inner door 103 of the pass box 104 is opened or closed. Furthermore, even if the airtightness of the processing space 101 is insufficient, there is a risk that contaminated gas may leak out.

[0015] For this reason, it is common practice to maintain the pressure within the processing space 101, where contaminated gas is generated, lower than the pressure outside the processing space 101. However, if the pressure within the pass box 104 or the pressure difference between the pass box 104 and the processing space 101 is large relative to the outside of the processing space 101, the outer door 105 and inner door 103 of the pass box 104 become difficult to open and close due to the influence of the pressure difference. For this reason, the pressure within the processing space 101 is generally controlled to be several hPa lower than the external atmospheric pressure, that is, several thousandths of an atmosphere. With this pressure difference of several hPa, the door of the pass box 104 is subjected to a pressure of approximately several grams per square centimeter. Therefore, if the size of the outer door 105 and inner door 103 is approximately 30 cm square, the door of the pass box 104 is subjected to a pressure of several kilograms. Since a large pressure difference requires a large force to open and close the door, the pressure inside the processing space 101 is generally set to be several hPa lower than the outside air pressure. Also, since a large pressure difference causes gas to leak from the outside rapidly, the pressure difference between the processing space 101 and the outside air cannot be made too large.

[0016] A pressure sensor 102 is provided to measure the pressure difference between the processing space 101 and the outside air pressure in order to maintain the pressure inside the processing space 101 at a level several hPa lower than the outside air. For the same reason, an inlet pipe 119 is provided to introduce clean external gas into the processing space 101, and an outlet pipe 134 is provided to discharge the gas inside the processing space 101 to the outside. The inlet pipe 119 is provided with an inlet pump 132 for introducing the external gas into the processing space 101 and a filter device 133 for removing dust and the like present in the introduced gas. The outlet pipe 134 is also connected to a filter device 135 for removing dust and the like present in the gas, as well as treatment devices 129 and 130 for removing contaminants from the contaminated gas. After the contaminants and the like have been sufficiently removed from the gas, the gas is discharged to the outside via an outlet pipe 120 by an outlet pump 136.

[0017] Two treatment devices 129, 130 are connected to the exhaust system, but typically multiple types of treatment devices 129, 130 are used depending on the type of contaminants in the gas within the processing space 101. In this example, these devices are a moisture removal device (treatment device 129) that removes moisture from the contaminated gas, and a removal device (treatment device 130) that removes contaminants from the gas after the moisture removal. Because moisture in gas often adversely affects the removal of contaminants, a device configuration that combines moisture removal and contaminant removal is often used as a contaminant removal device. Furthermore, contaminants are often dissolved in moisture, and moisture removal can also be considered a means of removing contaminants.

[0018] The processing space 101 is controlled as follows based on the measurement value of a pressure sensor 102 that measures the differential pressure between the atmospheric pressure inside the processing space 101 and the atmospheric pressure inside the processing space 101. That is, based on the measurement value, an introduction pump 132 that introduces gas from the outside and an exhaust pump 136 that exhausts gas inside the processing space 101 to the outside are controlled to maintain the pressure inside the processing space 101 at a state that is several hPa lower than the external atmospheric pressure. As the exhaust pump 109, the introduction pump 132, and the exhaust pump 136, positive displacement pumps such as a diaphragm pump or a piston pump are used to prevent backflow of gas and ensure airtightness of the processing space 101 from the outside.

[0019] In the above-described supply and exhaust system, the pressure inside the processing space 101 is maintained several hPa lower than the external pressure, and contaminated gas exhausted from the processing space 101 can be purified by the processing devices 129 and 130 before being exhausted to the outside.

[0020] [Issues of the Embodiment] The issues of the present embodiment will be described with reference to the comparative example and the patent documents 1 and 2. In the comparative example, contaminated gas is not discharged to the outside of the processing space 101. Therefore, even if gas with the highest anticipated contamination level in the processing space 101 is discharged at the maximum discharge rate required to maintain the pressure in the processing space 101 at a specified value, it is necessary to reliably decontaminate and discharge the gas. Therefore, the processing equipment 129, 130 tends to become complicated and large, and there is a problem that the processing equipment 129, 130 becomes complicated and large, particularly in a processing space 101 where highly contaminated gas is present.

[0021] To prevent these problems, a circulation path is provided, both ends of which are connected to the processing space 101, to prevent contaminated gas from remaining in the processing space 101. The contaminated gas in the processing space 101 is circulated through the circulation path, and while maintaining a sealed state of the system centered around the processing space 101, the gas contamination is gradually removed in the circulation path by a relatively small decontamination device or the like. This allows the gas in the processing space 101 to be brought to a safe level.

[0022] In this case, it is necessary to perform the gas contamination treatment while controlling the gas pressure so that the gas pressure is slightly negative not only within the processing space 101 but also within the circulation path. However, the comparative example and Patent Documents 1 and 2 do not disclose any technical idea of ​​providing such a circulation path. Furthermore, they do not disclose any technical idea of ​​appropriately adjusting the gas pressure in a system centered around the processing space 101, including the circulation path.

[0023] Therefore, in the present embodiment described below, an object is to provide a gas circulation system that can maintain an appropriate gas pressure within a processing space, etc., when processing gas in the processing space containing harmful gases by circulating the gas in the processing space through a circulation path in a sealed state.

[0024] [Embodiment 1] In each embodiment described below, when an expression "XX path" is used, it is preferable that the "XX path" is composed of piping of an appropriate configuration. However, the present invention is not limited to this, and the "XX path" can be implemented in various forms as long as it is a flow path through which gas can flow appropriately.

[0025] FIG. 1 is a system diagram of a gas circulation system according to a first embodiment of the present invention. The processing space 1 and pass box 4 of the gas circulation system 201 have the same configurations as the processing space 101 and pass box 104 of the comparative example. However, the processing space 101 is not limited to the configurations of the comparative example, as long as it is a space in which a predetermined process is performed using a harmful gas. Harmful gas may remain within the processing space 1. Furthermore, the configurations and usage methods of the inlet line 7, exhaust line 8, on-off valve 6, and exhaust pump 9 are also similar to the inlet pipe 107, exhaust pipe 108, on-off valve 106, and exhaust pump 109 of the comparative example. The pass box 4, outer door 5, inner door 3, inlet line 7, on-off valve 6, exhaust line 8, and exhaust pump 9 are also similar to the pass box 104, outer door 105, inner door 103, inlet pipe 107, on-off valve 106, exhaust pipe 108, and exhaust pump 109 of the comparative example.

[0026] The gas circulation system 201 includes a circulation path 31 having both ends connected to the processing space 1. The gas circulation system 201 also includes a supply path 19 that can be opened and closed by a valve 19a and that supplies gas to the processing space 1, and a discharge path 20 that can be opened and closed by a valve 20a and that discharges gas from the processing space 1 to the outside of the processing space 101. The supply path 19 and the discharge path 20 are connected to the circulation path 31, and thus can perform the above-mentioned intake and exhaust of gas to and from the processing space 101.

[0027] In this example, the circulation unit 21 is a pump that circulates gas within the circulation path 31. The pump is a positive displacement pump. As a result, the gas within the processing space 1 circulates through the circulation path 31 from the right end of the processing space 1 and returns to the processing space 1 from the left end of the circulation path 31. The circulation unit 21 within the circulation path 31 constantly circulates and sends the gas within the processing space 1 within the circulation path 31 at a predetermined flow rate.

[0028] The storage tank 14 is connected to the circulation path 31 via two gas sending units 12, 13 (pumps in this example). The two gas sending units 12, 13 are the gas sending unit 13 for introducing a portion of the gas in the circulation path 31 into the storage tank 14, and the gas sending unit 12 for discharging a portion of the gas in the storage tank 14 into the circulation path 31. The storage tank 14 is provided with a second pressure sensor 15 for detecting the pressure of the gas therein.

[0029] The first pressure sensor 2 is provided in the processing space 1 and detects the pressure in the circulation path 31 (directly provided in the processing space 1). The bypass paths 23, 26, and 10a are connected to the circulation path 31 and are flow paths that draw in and return gas from the circulation path 31.

[0030] The bypass paths 23, 26 are each equipped with a treatment section 29, 30 that detoxifies harmful gases. The treatment sections 29, 30 are, for example, devices that decontaminate gases contaminated with radioactive materials. The bypass paths 23, 26 are each equipped with a filter 24, 27 that filters harmful air before processing in the treatment sections 29, 30, and a heating section 22, 28 that heats the gas in the bypass paths 23, 26 after decontamination in the treatment sections 29, 30. The heating section 22, 28 detects the temperature of the gas in the bypass paths 23, 26 and heats the gas in accordance with that temperature.

[0031] The contaminated gas flowing through the circulation path 31 is sent to the bypass path 26 via the branch valve 25 of the bypass path 26. The contaminated gas sent to the bypass path 26 has coarse dust particles removed from the gas by a filter 27, and then the contaminants in the gas are removed in a treatment section 29. One known method for removing contaminants from the gas is to lower the temperature of the gas, liquefy the contaminants, and then adsorb and remove them using molecular sieves, activated carbon, or the like. However, since the temperature of the gas from which the contaminants have been removed by this method has been lowered, the gas is returned to the normal gas temperature in the treatment space 1 and the circulation path 31 by a heating section 28 before being returned to the circulation path 31.

[0032] Therefore, the heating unit 28 is provided with a temperature sensor 28a that measures the temperature of the gas in the bypass path 26 and a heater 28b that heats the gas in the bypass path 26. If necessary, the heating unit 28 may also be provided with a humidity sensor that detects the humidity of the gas in the bypass path 26. The heating unit 28 may be provided with both of these sensors, or only one of them.

[0033] Similarly, the heating unit 22 includes a temperature sensor 22a that measures the temperature of the gas in the bypass path 23 and a heater 22b that heats the gas in the bypass path 23, both of which are provided in the bypass path 23 that branches off from the circulation path 31 via the branch valve 71. If necessary, the heating unit 22 may also include a humidity sensor that detects the humidity of the gas in the bypass path 23. The heating unit 22 may include both of these sensors, or only one of them.

[0034] Additionally, in addition to or instead of the heating units 22, 28, the bypass paths 26, 23 may include at least one of a cooling unit for cooling the gas in the bypass paths 26, 23, a dehumidifying unit for dehumidifying the gas, and a humidifying unit for humidifying the gas. The circulation path 31 is provided with two treatment units 29, 30 via the two bypass paths 23, 26. The reason for using multiple treatment units 29, 30 is to accommodate cases where multiple types of contaminants need to be removed. Another reason is that if the contaminated gas has a high humidity, i.e., a high water content, the first treatment unit 29 can dehumidify the contaminated gas, and the next treatment unit 30 can remove the contaminants themselves. When contaminated gas with a high water content is cooled and removed, moisture adheres to molecular sieves or activated carbon that adsorb the contaminants, reducing the recovery efficiency of the contaminants that should be removed. To prevent this, it is effective to thoroughly dehumidify the contaminated gas before decontaminating it.

[0035] Furthermore, providing multiple treatment units 29, 30 via multiple bypass paths 23, 26 in the circulation path 31 is also important for replacement and maintenance of the treatment units 29, 30. Regardless of the type, the treatment units 29, 30 gradually decrease in contaminant recovery and dehumidification efficiency as they dehumidify and decontaminate contaminated gases. When the contaminant recovery and dehumidification efficiencies decrease, switching between the bypass paths 23, 26 allows for uninterrupted decontamination of the gas in the circulation path 31. In this sense, although only two decontamination bypass paths 23, 26 are shown in the circulation path 31, if the treatment units 29, 30 have different purposes, such as moisture removal and contaminant recovery, it is preferable to provide at least four decontamination bypass paths. Of course, since more decontamination processes may be required, the decontamination bypass paths are not necessarily four. Figure 1 shows only two decontamination bypass paths 23, 26 because showing multiple decontamination bypass paths would make the diagram more complicated.

[0036] As described above, regardless of the type of treatment unit 29, 30, the efficiency of contaminant recovery and dehumidification gradually decreases as the contaminated gas is dehumidified and decontaminated. Furthermore, even a brand new treatment unit has a limit to its decontamination capacity. Therefore, depending on the capacity and condition of the treatment unit 29, 30 and the contamination level of the contaminated gas, contaminants may remain in the gas that has passed through the treatment unit 29, 30. To prevent this, it is necessary to use a treatment unit 29, 30 that can ensure sufficient decontamination capacity for the contamination level of the contaminated gas. However, in reality, achieving this would require the treatment units 29, 30 to be extremely large.

[0037] In the first embodiment, when decontamination of contaminated gas is performed in the bypass paths 26, 23 provided in the circulation path 31, even if the decontamination of the contaminated gas in the treatment units 29, 30 is insufficient, the gas is returned to the circulation path 31 and is never discharged to the outside. Furthermore, gas containing remaining hazardous substances passes through the treatment space 1 and the circulation path 31 and is again guided to the treatment units 29, 30, where it is again decontaminated. This process is repeated. A contamination level detection sensor 10 is provided in the circulation path 31 via another bypass path 10a, enabling measurement of the contamination level of the gas in the circulation path 31. The gas in the circulation path 31 is repeatedly decontaminated by the treatment units 29, 30. The gas in the circulation path 31 is not exhausted to the outside through the exhaust path 20 until sufficient decontamination of the gas is confirmed by the measurement by the contamination level detection sensor 10. This ensures that contaminated gas is not discharged to the outside, even in relatively small treatment units 29, 30.

[0038] In the first embodiment, it is also possible to use the branch valves 25, 25 to send only a portion of the gas circulating in the circulation path 31 to the decontamination bypass paths 23, 26. In cases where the amount of contamination or moisture in the gas to be decontaminated or dehumidified is too high for the capacity of the processing sections 29, 30, sending only a portion of the circulating gas to the decontamination bypass paths 23, 26 makes it possible to promote decontamination or dehumidification of the circulating gas within the decontamination capacity of the processing sections 29, 30. This enables efficient dehumidification or decontamination of harmful air.

[0039] Furthermore, the branch valve 25 is switched so that the gas is guided only to the dehumidification bypass path (for example, the bypass path 26 relatively upstream of the circulation path 31 in FIG. 1 ), and after the circulating gas has been sufficiently dehumidified, the branch valve 25 is switched again. Then, by guiding the gas only to the decontamination bypass path (for example, the bypass path 23 relatively downstream of the circulation path 31 in FIG. 1 ), the decontamination capacity of the treatment unit 30 can be maximized.

[0040] The circulation path 31 is provided with a temperature sensor 17 that detects the temperature of the gas in the circulation path 31. In addition to or instead of the temperature sensor 17, the circulation path 31 may also be provided with a humidity sensor that detects the humidity of the gas in the circulation path 31.

[0041] 2 to 4 are plan views illustrating the detachable structure of each bypass path. As shown in Fig. 2, the bypass paths 23 and 26 are configured to be detachable at the processing sections 29 and 30. This detachable structure can be easily achieved by, for example, a pair of one-touch joints 211 and 212.

[0042] Alternatively, as shown in Fig. 3, the bypass paths 23, 26 may be configured to be detachable at the portion of the circulation path 31. In this case, the detachable structure can be easily achieved by, for example, a pair of one-touch joints 211, 212. Similarly, as shown in Fig. 4, the bypass path 10a can also be configured to be detachable at the portion of the circulation path 31. In this case, the detachable structure can be easily achieved by, for example, a pair of one-touch joints 211, 212.

[0043] The circulation path 31 is provided with a pressure sensor 16 for measuring a known pressure therein, a temperature sensor 17 for detecting the temperature of the gas, and a humidity sensor 18 for measuring the humidity of the gas. Figure 5 is a block diagram showing the electrical connections of the control system of the gas circulation system. This control system is centered around a control unit 221, which is composed of a microcomputer or the like that controls the gas circulation system 201. Although not shown, the control unit 221 also includes a central processing unit (CPU) that performs various calculations and centrally controls each unit of the gas circulation system 201. The control unit 221 also includes a main memory device that serves as a work area for the CPU, and an auxiliary memory device (storage medium) that stores a program 222 that serves as a control program for controlling the gas circulation system 201 and various fixed data. Various sensors and actuators (most of which are not shown) are connected to the control unit 221 via predetermined interfaces.

[0044] In particular, the first pressure sensor 2, the air supply units 12 and 13, the second pressure sensor 15, the temperature sensor 17, the temperature sensor 28a, the heater 28b, the temperature sensor 22a, and the heater 22b are connected to the control unit 221. The control unit 221 executes the functions of a pressure control unit 241, a pump control unit 242, and a temperature control unit 243 by processing based on a program 222.

[0045] 6A and 6B are flowcharts illustrating the control of the gas circulation system executed by the control unit. First, the process of FIG. 6A will be described. When it is necessary to control the pressure in the circulation path 31 and the processing space 101 (circulation pressure control) (Yes in step S1), the pressure control unit 241 detects the pressure using the first pressure sensor (step S2). The pressure control unit 241 then performs a circulation pressure comparison (step S3) and controls the gas pressure in the circulation path 31 to a value within a preset range using the pump control unit 242 (steps S4 to S10). Here, the circulation pressure comparison is a process of comparing the gas pressure in the circulation path 31 with a set value to determine whether it is within a preset range. In this example, the circulation pressure comparison determines whether the pressure in the circulation path 31 and the processing space 101 (circulation pressure) exceeds an upper control limit, falls below a lower control limit, or is within both of these values.

[0046] If the circulation pressure comparison shows that the circulation pressure is less than the control lower limit (step S3), the pump control unit 242 detects the pressure of the gas in the storage tank 14 using the second pressure sensor 15 (step S4).Then, the pump control unit 242 sets the pump rotation speed or the conduit throttling (setting for supply to the circulation path 31) of the gas supply unit 12 (pump) (step S5), and operates the gas supply unit 12 (pump) (storage tank 14 → circulation path 31) (step S6).

[0047] If the circulation pressure comparison shows that the circulation pressure is greater than the control upper limit (step S3), the pump control unit 242 detects the pressure of the gas in the storage tank 14 using the second pressure sensor 15 (step S7).Then, the pump control unit 242 sets the pump rotation speed or pipe line restriction (setting for discharge from the circulation path 31) of the air supply unit 13 (pump) (step S8), and operates the air supply unit 13 (pump) (circulation path 31 → storage tank 14) (step S9).

[0048] If the circulation pressure comparison shows that "lower control limit value ≦ circulation pressure ≦ upper control limit value" (step S3), the pump control unit 242 stops the gas supply units 12 and 13 (pumps) (step S10). When it is not time to control the pressure in the circulation path 31 and the processing space 101 (circulation pressure control) (No in step S1), the pressure control unit 241 stops the process of FIG. 6A.

[0049] The process of FIG. 6B will be described. When performing temperature control of the bypass paths 26, 23 (Yes in step S11), the temperature control unit 243 detects the temperature of the gas inside the bypass paths 26, 23 using the temperature sensors 28a, 22a (step S12). Then, the temperature control unit 243 determines whether the temperature of the bypass paths 26, 23 is less than the set temperature (step S13). The set temperature is a predetermined temperature that has been set in advance. If the temperature of the bypass paths 26, 23 is less than the set temperature (Yes in step S13), the temperature control unit 243 activates the heaters 28b, 23b (performed by PID control or the like) (step S14) to heat the inside of the bypass paths 26, 23. If the temperature of the bypass paths 26, 23 is greater than or equal to the set temperature (No in step S13), the temperature control unit 243 stops the heaters 28b, 23b (step S15) and does not heat the inside of the bypass paths 26, 23. When it is not time to control the temperatures of the bypass paths 26 and 23 (No in step S11), the temperature control unit 243 stops the process of Fig. 6B. Although the bypass paths 26 and 23 are described together above, this is for convenience's sake, and the temperature detection, temperature judgment, heater control, etc. are performed separately for the bypass paths 26 and 23.

[0050] In this case, humidity sensors may be provided in place of or in addition to the temperature sensor 28a and the temperature sensor 22a, and the control unit 221 may function as a humidity control unit that individually humidifies the gas in the bypass paths 26, 23 using a predetermined humidifier according to the detected humidity. As described above, the gas circulation system 201 connects the closable supply path 19 and discharge path 20 to the processing space 1 via the circulation path 31, and circulates contaminated gas generated in the processing space 1 within the circulation path 31, thereby preventing the contaminated gas from leaking to the outside. Furthermore, decontamination bypass paths 23, 26 may be provided in the circulation path 31, and contaminated gas may be drawn in by treatment units 29, 30 within the bypass paths 23, 26 and detoxified.

[0051] 11 , the gas discharged from the processing space 101 passes through the two treatment devices 129 and 130 only once before being discharged to the outside. However, in this embodiment 1, the circulation path 31 is provided, and the gas in the processing space 101 can be treated any number of times in the treatment devices 29 and 30, so that the gas can be detoxified more reliably than in the comparative example. Therefore, the two treatment devices 29 and 30 can be made smaller and simpler than the two treatment devices 129 and 130, and the manufacturing costs and running costs of the gas circulation system 201 can be reduced.

[0052] In this case, the volume of the internal material and therefore the internal pressure are likely to fluctuate within the processing space 1 and the circulation path 31 due to temperature changes and the like. However, in this embodiment 1, the first pressure sensor 2, the storage tank 14 as a gas buffer, and the gas supply units 12 and 13 are provided. Therefore, the first pressure sensor 2 detects pressure fluctuations within the system consisting of the processing space 1, the circulation path 31, and the like, and gas can be introduced into and released from the storage tank 14 by the gas supply units 12 and 13. This allows the pressure within the system consisting of the processing space 1, the circulation path 31, and the like to be adjusted within an appropriate range. In this case, the appropriate range is preferably a pressure slightly negative compared to atmospheric pressure to prevent external leakage of gas from the processing space 1, etc. More specifically, it is preferable to maintain the pressure within the processing space 1 at a level several hPa lower than the external pressure to prevent contaminated gas from leaking to the outside from the processing space 1 where various processing operations are performed.

[0053] Therefore, according to the first embodiment, it is possible to provide a gas circulation system 201 that can maintain an appropriate gas pressure in the processing space 1, etc., when processing the gas in the processing space 1 containing harmful gas while circulating the gas through the circulation path 31 in a sealed state. Furthermore, in the first embodiment, such pressure adjustment is performed by the control of the control unit 221. Therefore, it is easy to respond to both subtle and sudden pressure adjustments, and the pressure adjustment can be performed accurately.

[0054] Furthermore, each of the bypass paths 23, 26, and 10a is detachable from the circulation path 31 (see FIGS. 2 to 4). This allows for safe and easy maintenance of each of the bypass paths 23, 26, and 10a, the processing units 29 and 30, and the contamination level detection sensor 10. The circulation path 31 is provided with the aforementioned exhaust path 20 and supply path 19, which are both closed during system operation, thereby maintaining the processing space 1 and the circulation path 31, including it, in a sealed state that prevents contaminated gas from leaking to the outside. However, in a sealed space, the internal pressure fluctuates due to various factors. The main causes of pressure fluctuations are temperature and humidity changes of the internal gas. The circulation path 31 is equipped with a pressure sensor 16, a temperature sensor 17, and a humidity sensor 18, allowing these physical quantities to be constantly measured. This allows for the temperature and humidity of the gas circulating in the circulation path 31 to be adjusted to maintain a constant temperature and humidity. 1 does not show means for adjusting the temperature and humidity of the circulating gas. However, as described above, in this embodiment 1, the decontamination bypass paths 23, 26 are provided with processing sections 29, 30 that dehumidify the circulating gas by cooling it, and heating sections 22, 28 that reheat the dehumidified and cooled gas to a predetermined temperature. Therefore, by utilizing these, it is possible to control the humidity and temperature of the gas in the circulation pipeline to a certain extent without providing dedicated temperature and humidity adjustment means.

[0055] Next, we will explain why the various functional components in the above-described configuration are not directly installed in the circulation path 31 but are instead located in the bypass path. As described above, the processing units 29 and 30 are located in the bypass paths 26 and 23 to adjust the amount of contaminated gas drawn into the bypass paths 26 and 23 and to make the bypass paths 26 and 23 detachable as described above, facilitating maintenance. The contamination level detection sensor 10 is also located in the bypass path 10a for the same reason. In the case of the contamination level detection sensor 10, this is to guide only the amount and concentration of gas required for the measurement sensitivity level of the sensor to the contamination level detection sensor 10. This is also to facilitate replacement of the contamination level detection sensor 10 when it deteriorates. However, replacement of the contamination level detection sensor 10 is unlikely to be performed while contaminated gas is circulating. Therefore, for contamination level detection sensors 10 whose measurement sensitivity level is not affected even when constantly exposed to a contaminated gas environment, it is not necessarily necessary to install them in the bypass path 10a. In the first embodiment, the filter 11 provided in the circulation path 31 is disposed within the circulation path 31, without an intervening bypass path. This is because it is considered unlikely that the filter 11 would be attached or detached while contaminated gas is circulating. Similarly, the pressure sensor 16, temperature sensor 17, and humidity sensor 18, which are directly connected to the circulation path 31, are also provided directly in the circulation path 31 without an intervening bypass path. Whether or not various functional components are to be installed within the circulation path 31 is preferably determined taking into consideration the effects of contaminated gas, the need for maintenance, and the like.

[0056] Next, the concept behind the arrangement and order of various functional components within the circulation path 31 of this embodiment 1 will be described. The circulation path 31 is configured by connecting a gas supply path 19 and a gas exhaust path 20 for the processing space 1, and a circulation unit 21 for circulating gas is disposed at one location within the circulation path 31 to supply the gas within the circulation path 31. Discharge paths 20, supply path 19, pressure sensor 16, temperature sensor 17, humidity sensor 18, gas supply unit 13, gas supply unit 12, filter 11, and bypass path 10a are disposed downstream of the circulation unit 21. Furthermore, bypass paths 23 and 26 are disposed upstream of the circulation unit 21. This arrangement is based on the fact that the downstream side of the circulation unit 21 is the gas supply path side to the processing space 1, and the upstream side of the circulation unit 21 is the gas exhaust path side for the processing space 1.

[0057] Since the gas sent to the circulation path 31 side of the processing space 1 is first subjected to contamination treatment as a top priority, the processing devices 29 and 30 should be located immediately after the gas is introduced into the circulation path 31. The gas after decontamination treatment is then sent to the circulation part 21. In this embodiment 1, the processing devices 29 and 30 are not necessarily configured to be able to completely decontaminate the gas by a single treatment. However, it is still preferable to locate all of the processing devices 29 and 30 upstream of the circulation part 21 in order to minimize the contamination level of the contaminated gas supplied to the circulation part 21.

[0058] A supply path 19 and a discharge path 20 for the gas in the circulation path 31 are arranged immediately downstream of the circulation unit 21. Because equipment is arranged downstream of the circulation unit 21 as the gas supply path to the processing space 1, it is preferable that the supply path 19 for introducing gas from outside is also arranged immediately downstream of the circulation unit 21. The discharge path 20 for the gas in the circulation path 31 is arranged between the circulation unit 21 and the supply path 19 because, if the discharge path 20 for the gas in the circulation path 31 were arranged upstream of the circulation unit 21, the circulation unit 21 would not be able to discharge the gas in the processing space 1 or the circulation path 31. Discharging the sufficiently decontaminated gas in the processing space 1 and the circulation path 31 to the outside and introducing new gas can be performed by opening the supply path 19 and the discharge path 20 and operating the circulation unit 21. At this time, the gas in the processing space 1 and the circulation path 31 is sucked by the circulation unit 21, resulting in a negative pressure state overall. When the circulation unit 21 is disposed downstream of the supply path 19 and the exhaust path 20 and a similar gas introduction / exchange operation is performed, the circulation unit 21 performs a pressurized gas supply operation, and the gas in the processing space 1 and the circulation path 31 becomes positive pressure. From the viewpoint of preventing unexpected gas leakage to the outside, the circulation unit 21 is preferably disposed upstream of the supply path 19 and the exhaust path 20.

[0059] In this embodiment, a group of sensors including a pressure sensor 16, a temperature sensor 17, and a humidity sensor 18 are disposed immediately downstream of the supply path 19 in the circulation path 31. These sensors are used to monitor the state of the gas supplied to the processing space 1. In particular, since the pressure in the circulation path 31 is highest at the position where the supply path 19 is disposed, it is important to sense the pressure in this position with the pressure sensor 16 in order to prevent gas leakage from the processing space 1 and the circulation path 31.

[0060] The gas supply units 13 and 12 are connected downstream of the group of sensors, pressure sensor 16, temperature sensor 17, and humidity sensor 18, and by using these to supply and discharge gas to and from the storage tank 14 from the circulation path 31 side, the pressure in the processing space 1 and the circulation path 31 can be appropriately controlled as described above.

[0061] The reason why the gas supply unit 13 and the gas supply unit 12 are independently connected to the storage tank 14 is to allow for the discharge of gas from the storage tank 14. That is, a situation may occur in which the gas is not completely decontaminated in the treatment units 29 and 30 arranged in the circulation path 31 by the bypass paths 23 and 26. As a result, contaminated gas also enters the storage tank 14, which feeds gas into and out of the circulation path 31 to control the gas pressure. In order to decontaminate the contaminated gas in the storage tank 14, it is necessary to discharge the gas in the storage tank 14 to the circulation path 31 toward the treatment units 29 and 30. Therefore, the storage tank 14 is connected to the gas supply unit 13 for supplying gas from the circulation path 31 side, and the gas supply unit 12 for exhausting gas from the storage tank 14 to the circulation path 31 side. This allows the amount of gas taken into the storage tank 14 and the amount of gas exhausted from the storage tank 14 to be controlled independently. By constantly operating the air supply units 13 and 12 with respect to the storage tank 14 and providing a difference in the amount of air supplied, it is possible to circulate the gas in the storage tank 14 within the circulation path 31 while controlling the pressure within the circulation path 31. In this case, by connecting the air supply unit 12 downstream of the air supply unit 13, the gas in the storage tank 14 can be efficiently circulated and discharged into the circulation path 31. For this reason, the connection position between the circulation path 31 and the air supply unit 12 is located downstream of the connection position between the circulation path 31 and the air supply unit 13.

[0062] A filter 11 is disposed downstream of the air supply unit 12, and a contamination level detection sensor 10 is disposed downstream of that, with the circulation path 31 connected to the processing space 1. The filter 11 is disposed at a position just before the inflow of gas into the processing space 1 in order to prevent various coarse dust particles from entering the processing space 1. The contamination level detection sensor 10 is disposed downstream of the filter 11 because accurate measurement results cannot be obtained if contaminated coarse dust particles enter the sensor.

[0063] Next, a description will be given of a means for controlling the pressure in the processing space 1 and the circulation path 31 using the storage tank 14. The gas is introduced into and released from the storage tank 14 based on the measurement value of a first pressure sensor 2 provided in the processing space 1. In actual operation, it is important that the pressure in the processing space 1, where samples and articles are introduced and removed and where predetermined processing is performed, is maintained at a pressure several hPa lower than the outside air. Therefore, it is preferable that the pressure on the circulation path 31 side by the storage tank 14 be controlled based on the measurement value of a first pressure sensor 2 provided in the processing space 1 that can detect the differential pressure between the inside of the processing space 1 and the outside.

[0064] The main factors that affect the pressure difference between the pressure inside the processing space 1 and the external pressure, which is the pressure difference to be controlled, are as follows. First, there is the volume of gas that flows in from the outside when samples or objects to be processed in the processing space 1 are transferred into or removed from the processing space 1 from the outside using the pass box 4. As described above, in order to prevent contaminated gas from being released from the processing space 1 to the outside, when samples or objects are transferred into or removed from the pass box 4, gas is introduced into the pass box 4 through the inlet path 7, and the gas inside the pass box 4 is discharged using the exhaust path 8 to the processing space 1 and the exhaust pump 9. Therefore, when samples or objects are transferred into or removed from the processing space 1 from the outside using the pass box 4, at least the volume of outside air inside the pass box 4 is introduced into the sealed space formed by the processing space 1, the circulation path 31, etc.

[0065] Next, when the gas is heated during processing in the processing space 1 or the circulation path 31, the gas volume within the sealed space formed by the processing space 1, the circulation path 31, etc. increases. Conversely, when the gas is cooled, the gas volume within the sealed space formed by the processing space 1, the circulation path 31, etc. decreases. In addition, when the liquid is evaporated during processing in the processing space 1 or the circulation path 31, the gas volume within the sealed space increases, and when the gas is dehumidified to remove moisture, the gas volume decreases. As described above, the processing units 29 and 30 cool the gas to remove moisture and contaminants from the gas. The bypass paths 26 and 23 equipped with the processing units 29 and 30 are provided with heating units 22 and 28 that reheat the decontaminated gas to a specified temperature. This not only serves to restore the gas temperature to its original value, but also plays an important role in restoring the volume of the gas, which has decreased due to the temperature drop associated with the process of removing moisture and contaminants from the gas, to its original state. Since the temperature and moisture content of the gas in the processing space 1 and the circulation path 31 have a significant effect on the gas volume, the circulation path 31 is provided with a temperature sensor 17 and a humidity sensor 18 in addition to the pressure sensor 16 to constantly monitor the state of the gas and control the predetermined pressure value, etc. within a certain range.

[0066] In addition to the intrusion of gas from the outside into the processing space 1 and the circulation path 31 and changes in the temperature and humidity of the internal gas, changes in external air pressure are also a factor that significantly affects the pressure difference between the pressure inside the processing space 1 and the external pressure. Depending on the length of time, changes in external air pressure on the ground can vary by several tens of hPa even within a single day at the same location. Over the course of a year, the pressure can fluctuate by several hundred hPa between periods of low and high pressure. When controlling the pressure inside the processing space 1 to always be several hPa lower than the external air pressure, changes in external air pressure are a major influencing factor.

[0067] Therefore, the expected number of times the pass box 4 is opened and closed during a specific process in the processing space 1, the total amount of outside air entering during each opening and closing, the change in gas volume due to liquid evaporating in the processing vessel during the expected process, and fluctuations in outside air pressure occurring during the expected processing time must be taken into consideration. The gas volume required in the storage tank 14 must be determined based on these considerations. However, since the gas stored in the storage tank 14 is gas, increasing the pressure of the gas stored therein allows a smaller storage tank 14 to hold a larger amount of gas. However, the higher the pressure in the storage tank 14, the greater the risks of external leaks, leaks in the circulation paths from each pump, and the pressure-resistance safety of the storage tank 14 itself. If possible, it is desirable to keep the maximum internal pressure of the storage tank 14 below 2 atmospheres absolute pressure and 1 atmosphere gauge pressure. Therefore, if the storage tank 14 is at a gauge pressure of 1 atmosphere or less and the processing time, i.e., the time for sealing the gas in the processing space 1, is set to one to several days, the following results are obtained. That is, when extreme fluctuations in external air pressure are not expected, the storage tank 14 needs to have a volume of at least 5 to several tens of percent of the volume of the sealed space, such as the processing space 1 and the circulation path 31. However, if unexpected fluctuations in external air pressure occur, or if gas expansion or liquid vaporization occurs during processing in the processing space 1, or if gas inflow from the outside occurs, it may not be possible to maintain the specified negative pressure condition within the processing space 1 (a pressure several hPa lower than the specified atmospheric pressure). Therefore, the storage tank 14 is provided with a second pressure sensor 15 that monitors its internal pressure. If the pressure within the storage tank 14 exceeds a predetermined upper or lower limit during processing of a sample generating contaminated gas, it is necessary to stop the processing in the processing space 1 and immediately decontaminate the internal gas.

[0068] As described above, the pump control unit 242 detects the pressure of the gas in the storage tank 14 using the second pressure sensor 15. Then, the pump control unit 242 variably controls the drive speed of the gas supply units 12 and 13 based on the pressure of the gas in the storage tank 14 detected by the second pressure sensor 15. The pumps of the gas supply units 12 and 13 are positive displacement pumps. These will be described in detail below.

[0069] As described above, in order to control the pressure in the circulation path 31 within a specified range, the gas in the circulation path 31 is supplied to and discharged from the storage tank 14. As a result, the gas pressure in the circulation path 31 is always controlled to a pressure that is several hPa lower than the outside air pressure. Meanwhile, the internal gas pressure of the storage tank 14 varies greatly, from near vacuum to 2 atmospheres or more, depending on the amount of gas supplied or discharged. In order to control the pressure in the circulation path 31 within a specified range, the intake and exhaust between the storage tank 14 and the circulation path 31 must be performed under various differential pressure conditions of ±1 atmosphere or more.

[0070] It is desirable to use a positive displacement pump for intake and exhaust between the circulation path 31 and the storage tank 14, where a large pressure difference occurs. So-called positive displacement pumps, such as diaphragm pumps, piston pumps, and tubing pumps, can supply air even under pressure differences because they supply air while isolating the gas on the intake and exhaust sides. However, when using the storage tank 14, whose internal gas pressure varies from near vacuum to 2 atmospheres or higher, the following control is required to control the pressure inside the circulation path 31 to a pressure several hPa lower than the outside air pressure.

[0071] 7 is a graph showing a schematic diagram of the relationship between the drive speed of the positive displacement pump that sends gas from the storage tank 14 to the circulation line 31 and the amount of gas sent to the circulation line. The volume of gas changes in proportion to the pressure, but the amount of gas sent to the circulation line 31 on the vertical axis is expressed as the amount of gas when sent to the circulation line 31 that is the object of control, that is, the gas volume in the circulation line 31, which is at approximately atmospheric pressure.

[0072] In the graph, the solid line "N" indicates the case where the pressure in the storage tank 14 is approximately atmospheric pressure, the dashed line "H" indicates the case where the pressure in the storage tank 14 is approximately twice atmospheric pressure, and the dashed-dotted line "L" indicates the case where the pressure in the storage tank 14 is approximately half atmospheric pressure. When the pressure in the storage tank 14 is approximately atmospheric pressure, if the volumetric pump (air supply unit 12) is driven at a specified speed, the amount of air sent to the circulation path 31 is as shown on the solid line N. The circle N0 on the solid line N in the figure indicates the driving speed of a certain volumetric pump and the amount of air sent to the circulation line. In this case, if the pressure in the storage tank 14 becomes approximately twice atmospheric pressure under the same driving speed of the volumetric pump, the amount of air sent to the circulation path 31, i.e., the volume of gas H1 supplied to the circulation path 31 per unit time, will approximately double. Furthermore, when the pressure inside the storage tank 14 becomes approximately half of the atmospheric pressure, the amount of air L1 sent to the circulation line becomes approximately half.

[0073] This is because even if the same volume of gas is introduced from the storage tank 14 into the circulation path 31 by the volumetric pump (air supply unit 12), expansion and compression of the gas occurs within the circulation path 31, which is at approximately atmospheric pressure. Because the amount of air supplied to the circulation path 31 varies greatly depending on the pressure in the storage tank 14, it becomes difficult to precisely control the pressure within the circulation path 31 while maintaining a constant drive speed of the volumetric pump. Therefore, in this embodiment 1, the drive speed of the volumetric pump (air supply unit 12) is varied depending on the pressure in the storage tank 14. For example, when the pressure in the storage tank 14 becomes approximately twice the atmospheric pressure, the drive speed of the volumetric pump is reduced by approximately half, thereby making the volume of gas supplied per unit time to the circulation path 31, i.e., the amount of air supplied to the circulation path 31, H2, approximately the same as when the pressure in the storage tank 14 is at atmospheric pressure. Furthermore, when the pressure in the storage tank 14 becomes approximately half of atmospheric pressure, the drive speed of the volumetric pump is approximately doubled so that the amount of air sent to the circulation path 31, L2, becomes approximately the same as when the pressure in the storage tank 14 is at atmospheric pressure. Since the relationship between the drive speed of the volumetric pump (air sending unit 12) and the amount of air sent to the circulation path 31 is affected, strictly speaking, by the pressure difference between the storage tank 14 and the circulation path 31, it is desirable to control this using the pressure difference between the storage tank 14 and the circulation path 31. However, when the pressure in the storage tank 14 changes significantly, such as ±1 atmosphere or more, and the pressure in the circulation path 31 is to be controlled to be close to atmospheric pressure, it is possible to sufficiently perform delicate pressure control in the circulation path 31 by controlling the drive speed of the volumetric pump (air sending unit 12) only with the pressure value of the storage tank 14.

[0074] On the other hand, when gas is discharged from the circulation path 31 to the storage tank 14, the drive speed of the positive displacement pump (gas supply unit 13) and the amount of gas discharged from the circulation path 31 are hardly affected by differences in pressure within the storage tank 14. This is because the pressure within the circulation path 31 on the discharge side is always atmospheric pressure, so there is almost no change in the volume of gas within the volume sent by the positive displacement pump (gas supply unit 13). For this reason, with regard to the pump (gas supply unit 13) on the discharge side of gas from the circulation path 31 to the storage tank 14, it is not really necessary to control the drive speed of the positive displacement pump based on the gas pressure within the storage tank 14, as is the case with the pump (gas supply unit 12) on the supply side of gas from the storage tank 14 to the circulation path 31.

[0075] The control of intake and exhaust of gas between the circulation path 31 and the storage tank 14 described with reference to Figure 7 etc. has been described using an example of an ideal positive displacement pump for ease of explanation. It goes without saying that an actual positive displacement pump will deviate from the characteristics described above with reference to Figure 7 etc. depending on its type and performance.

[0076] For example, in a tubing pump, the pressure of the gas being sent, i.e., the internal pressure of the storage tank 14, causes the tube of the tubing pump to expand or compress. As a result, the influence of the pressure in the storage tank 14 on the pump drive speed and the amount of gas sent to the circulation path 31 becomes greater than previously described, resulting in nonlinear characteristics.

[0077] Furthermore, even in a positive displacement pump that uses a relatively rigid volume body such as a diaphragm or piston pump, the characteristics of the amount of gas sent relative to the pressure inside the storage tank 14 are affected by factors such as gas leakage from valves, etc. In an actual positive displacement pump, controlling the pump drive speed in accordance with the characteristics of the positive displacement pump being used is important in controlling the pressure inside the circulation path 31 with high precision.

[0078] Furthermore, even with a positive displacement pump that can block the pressure difference between the storage tank 14 and the circulation path 31, it may be difficult to completely prevent gas leakage from shutoff mechanisms such as valves when the pressure difference is large. In order to suppress gas leakage when a large pressure difference occurs between the storage tank 14 and the circulation path 31, it is preferable to provide the following in the connecting path between the storage tank 14 and the circulation path 31. That is, a pipe shutoff valve or the like is provided together with the positive displacement pump, and control to shut off the pipe when the positive displacement pump is stopped is also used in conjunction with the control of the positive displacement pump.

[0079] Furthermore, even in the control of the positive displacement pump on the gas discharge side from the circulation path 31, which is hardly affected by pressure differences inside the storage tank 14, the above-mentioned control of the positive displacement pump or flow path shutoff control may be used depending on the type and performance of the positive displacement pump used. The arrangement of the above-mentioned flow path shutoff valve, etc., and the necessity of the positive displacement pump or flow path shutoff control are preferably determined taking into consideration the type and performance of the positive displacement pump used and the pressure controllability inside the circulation path 31, which is the control target.

[0080] Furthermore, when using a positive displacement pump whose drive speed is difficult to control, a controllable throttle valve may be provided upstream of the positive displacement pump to throttle the flow path and thereby control the amount of air sent to the circulation path 31, thereby substituting for controlling the drive speed of the pump. The purpose of controlling the pressure in the circulation path 31 is to control the pressure in the circulation path 31 as well as in the processing space 1 connected to it, and it goes without saying that the processing space 1 can be a part of or the processing device itself that handles substances that generate harmful gases.

[0081] Next, a means for more efficiently using the storage tank 14 connected to the circulation path 31 will be described. As described above, the storage tank 14 is used to exhaust gas from the circulation path 31 and introduce gas into the circulation path 31 in order to maintain the pressure in the processing space 1 and the circulation path 31 at a pressure lower than atmospheric pressure by several hPa. Factors that significantly affect the pressure difference between the pressure in the processing space 1 and the circulation path 31 and the external pressure include the intrusion of gas from the outside, changes in the temperature and humidity of the internal gas, and changes in external air pressure. Changes in the temperature and humidity of the internal gas, changes in external air pressure, etc., do not change the total amount of gas and substances present in the processing space 1 and the circulation path 31. Therefore, if the storage tank 14 has a sufficient volume, pressure control in the processing space 1, etc. is possible simply by transferring gas between the storage tank 14 and the circulation path 31. However, depending on the handling of substances that generate harmful gases, samples, objects, etc. are transferred between the processing space 1 and the outside. At this time, gas will infiltrate into the processing space 1 and the circulation path 31 from the outside, increasing the amount of contaminated gas. Furthermore, since the processing space 1 and the circulation path 31 are maintained at a pressure lower than the outside, there is a possibility of infiltration of minute leaks of gas from the outside. In any case, there is a possibility that external gas will gradually infiltrate into the processing space 1 and the circulation path 31, which are maintained at a pressure lower than the outside. As a result, the amount of gas held in the storage tank 14, which controls the pressure inside the processing space 1 and the circulation path 31, gradually increases while fluctuating in accordance with the above-mentioned control.

[0082] The following method is also effective for efficiently using the capacity of the storage tank 14. Before handling a substance that generates harmful gas in the processing space 1, the amount of gas in the storage tank 14 is reduced, i.e., the storage tank 14 is depressurized, until the amount of gas required for subsequent processing (such as a reduction in the external air pressure or cooling and dehumidifying the gas in the processing space 1 and the circulation path 31) is reached. Thereafter, the amount of gas held in the storage tank 14 increases due to gas flowing in from the outside, and the internal pressure of the storage tank 14 gradually increases while fluctuating in accordance with the above-described control. By reducing the amount of gas in the storage tank at the initial stage, it becomes possible to handle substances that generate harmful gas in the processing space 1 for a longer period of time, even with a storage tank 14 of the same capacity.

[0083] Furthermore, as a means for efficiently using the capacity of the storage tank 14, it is possible to evacuate the storage tank 14 before handling a substance that generates harmful gas in the processing space 1. In this case, if the pressure in the processing space 1 and the circulation path 31 becomes lower than a specified value due to a drop in the external air pressure, cooling of the gas, dehumidification, or the like during the initial stage of a predetermined process in the processing space 1, a means for introducing the gas into the processing space 1, etc., using an external gas introduction means such as a cylinder 37 and an introduction electromagnetic valve 38, etc., can be applied, as in the second embodiment. Then, after a controllable amount of gas is secured in the storage tank 14, the pressure in the processing space 1 and the circulation path 31 can be controlled by introducing and discharging the gas from the storage tank 14. This means that a substance that generates harmful gas can be handled in the processing space 1 for an even longer period of time using the storage tank 14 of the same capacity.

[0084] By using these means, it is possible to efficiently use the capacity of the storage tank 14 and minimize the final total amount of contaminated gas, i.e., the total amount of gas in the processing space 1, the circulation path 31, and inside the storage tank 14.

[0085] [Embodiment 2] In each of the following embodiments, the same reference numerals are used for components and the like that are the same as those in the previous embodiments, and detailed descriptions thereof will be omitted (see the descriptions of the embodiment and comparative example).

[0086] 8 is a system diagram of a gas circulation system according to a second embodiment of the present invention. In this gas circulation system 202, a circulation path 31 and a storage tank 14 are connected via an exhaust electromagnetic valve 40. The gas circulation system 202 also includes a cylinder 37 whose internal pressure is higher than that of the circulation path 31, and the cylinder 37 and the circulation path 31 are connected via an introduction electromagnetic valve 38. Gas is discharged from the circulation path 31 to the storage tank 14 via the exhaust electromagnetic valve 40. Gas is introduced from the cylinder 37 into the circulation path 31 via the introduction electromagnetic valve 38. A decompression pump 39 is connected to the storage tank 14 to previously discharge the gas from the storage tank 14 and reduce the pressure. Before processing the contaminated gas in the processing space 1, the gas in the storage tank 14 is discharged using the pressure reducing pump 39, and the interior is kept at a negative pressure lower than the outside air pressure (atmospheric pressure).By opening the exhaust electromagnetic valve 40 connected to the circulation path 31, the gas in the circulation path 31 can be drawn into the storage tank 14.

[0087] In this configuration, the storage tank 14 and the cylinder 37 are connected to the circulation path 31 by electromagnetic valves, and the gas supply mechanism can be simpler than the configuration in which the storage tank 14 and the circulation path 31 are connected via a pump as in embodiment 1. Furthermore, in this configuration, the pressure in the storage tank 14 must always be lower than the outside air pressure during pressure control in the circulation path 31, and there is almost no possibility that contaminated gas in the storage tank 14 will leak to the outside during pressure control of the system centered on the processing space 1 and the circulation path 31.

[0088] However, only a maximum amount of gas corresponding to the volume of the storage tank 14 at atmospheric pressure can be collected in the storage tank 14. In contrast, if the air supply mechanism that collects gas from the circulation path 31 to the storage tank 14 is a pump instead of a valve, as in the first embodiment, a larger amount of gas can be collected from the circulation path 31 to the storage tank 14.

[0089] In the second embodiment, the system centered on the processing space 1 and the circulation path 31 is controlled to be several hPa lower than the external pressure (atmospheric pressure). When the pressure in the processing space 1 approaches the external pressure, the gas in the circulation path 31 is discharged to the storage tank 14, and the pressure in the circulation path 31 and the processing space 1 connected thereto is controlled to be reduced. Conversely, when the pressure in the processing space 1 is lower than the external pressure and falls below a predetermined pressure difference, gas is replenished from the cylinder 37 to the circulation path 31, thereby controlling the pressure in the circulation path 31 and the processing space 1 connected thereto to be higher. Basically, the pressure control in the processing space 1 and the circulation path 31 similar to the configuration in the first embodiment, in which gas stored in one storage tank 14 is introduced into and released from the circulation path 31, is also possible in the second embodiment.

[0090] However, the configuration of embodiment 1 is more suitable when the pressure in the processing space 1 is prone to fluctuations and is unstable due to a predetermined processing process or the like performed in the processing space 1. In the configuration of embodiment 1, gas stored in one storage tank 14 is introduced into and discharged from the circulation path 31, but in the configuration of embodiment 2, the storage tank 14 is used only to discharge gas from the circulation path 31 side, and gas is replenished to the circulation path 31 side from a gas cylinder 37.

[0091] As described above, factors that have a significant effect on the pressure difference between the pressure inside the processing space 1 and the external pressure include the intrusion of gas from outside the processing space 1, changes in the temperature and humidity of the gas inside, changes in the external air pressure, etc. The intrusion of gas from outside into the processing space 1 etc. increases the amount of gas present in the processing space 1 and the circulation path 31, but other changes in the temperature and humidity of the internal gas, changes in the external air pressure, etc. do not change the total amount of gas and material present in the processing space 1 and the circulation path 31. These changes are caused by the specific process performed in the processing space 1 and the circulation path 31 and changes in the external air pressure, and the pressure can increase or decrease over time.

[0092] In the configuration of embodiment 2, when the pressure in the processing space 1 drops, gas is replenished from the outside. Therefore, as the frequency of pressure fluctuations in the processing space 1 increases, the frequency of gas supply from the outside also increases. The gas supplied into the processing space 1 from the outside becomes contaminated gas in the processing space 1, resulting in an increase in the amount of contaminated gas. Furthermore, as the frequency of pressure fluctuations in the processing space 1 increases, the frequency of gas being discharged from the circulation path 31 to the storage tank 14 also increases, resulting in a rapid increase in the amount of contaminated gas accumulated in the storage tank 14. For this reason, the configuration of embodiment 1 is advantageous when the pressure in the processing space 1 fluctuates and is unstable.

[0093] Pressure gradients can also occur, causing pressure fluctuations, when large objects are moved or objects are moved at high speeds during a predetermined process performed in the processing space 1. When the pressure difference to be controlled is small, on the order of a few hPa, even small pressure fluctuations can have an effect. The configuration of embodiment 1 is also advantageous when a process that causes a pressure gradient occurs in the processing space 1.

[0094] In the configuration of the first embodiment, the gas stored in one storage tank 14 is introduced into and released from the circulation path 31, so unless gas enters from the outside, the total amount of gas and material in the storage tank 14 in the processing space 1 and the circulation path 31 does not change. Therefore, even in an environment where pressure fluctuations occur in the processing space 1, it is possible to effectively utilize the volume of the storage tank 14 and control the pressure difference between the processing space 1 and the outside air of the system centered on the circulation path 31 so that it remains within an appropriate range for a long period of time.

[0095] [Embodiment 3] Figure 9 is a system diagram of a gas circulation system according to Embodiment 3 of the present invention. This gas circulation system 203 differs from Embodiment 1 in that it uses two storage tanks 45, 41. Each of these storage tanks 45, 41 has a configuration similar to that of the storage tank 14 described above. Furthermore, each storage tank 45, 41 transfers gas to and from the circulation path 31 via gas supply units 47, 43, respectively. Each storage tank 45, 41 is provided with a pressure sensor 46, 42 that measures the pressure of the gas in that storage tank 45, 41. These pressure sensors 46, 42 are similar to the second pressure sensor 15 described above. Furthermore, a decompression pump 44 is connected to the storage tank 45, which can discharge gas from the storage tank 45 to the outside. This decompression pump 44 is similar to the decompression pump 39 described above.

[0096] A bidirectional positive displacement pump can be used for the gas supply units 47 and 43. This allows for a single connection path between the storage tanks 45 and 41 and the circulation path 31, unlike the storage tank 14 in the first embodiment. A rotary pump, such as a vane pump or a tubing pump, can be used as the bidirectional positive displacement pump. In this case, in addition to the gas supply speed, a head capable of transferring gas between the storage tanks 45 and 41 and the circulation path 31, which are at different pressures, and maintaining airtightness between the storage tanks 45 and 41 and the circulation path 31 when gas supply is stopped are required. It is difficult to ensure these performance characteristics with current general bidirectional positive displacement pumps. Therefore, in the first embodiment, separate pipelines are used for discharging gas from the circulation path 31 to the storage tank 14 and for replenishing gas from the storage tank 14 to the circulation path 31, and two positive displacement pumps (gas supply units 13 and 12) are used. As in the third embodiment, by using an appropriate bidirectional positive displacement pump, the number of connection paths between the storage tanks 45, 41 and the circulation path 31 can be reduced to one, thereby reducing the number of gas transport paths and pumps, etc., thereby reducing the manufacturing costs of the gas circulation system 203.

[0097] In the gas circulation system 203 of the third embodiment, the decontamination performance of the processing units 29 and 30 does not need to be set higher than necessary. However, contaminated gas may flow downstream of the circulation path 31, i.e., at the connection point of the circulation path 31 to the storage tanks 45 and 41. During a predetermined processing operation in the processing space 1, the pressure control described above is constantly performed to prevent leakage of contaminated gas to the outside. Therefore, it is possible that contaminated gas may also flow into the storage tanks 45 and 41. Therefore, after handling of a substance that generates harmful gas in the processing space 1 is completed, it is preferable to decontaminate the gas in the storage tanks 45 and 41 as well as the gas in the processing space 1 and the circulation path 31. In the configuration of the first embodiment, the gas in the storage tank 14 is decontaminated by simultaneously operating the gas supply unit 12 from the storage tank 14 to the circulation path 31 and the gas supply unit 13 from the circulation path 31 to the storage tank 14. That is, by simultaneously operating both gas supply units 12, 13 and adjusting and controlling the difference in the gas supply amounts, the pressure in the processing space 1 and the circulation path 31 is adjusted within a specified range. Furthermore, the gas in the storage tank 14 is discharged into the circulation path 31, and is sent to the processing units 29, 30 via the processing space 1 and the circulation path 31 for decontamination.

[0098] In the case where there is a single flow path for introducing gas from the storage tanks 45, 41 into the circulation path 31 and a single flow path for discharging the gas, as in the third embodiment, it may be difficult to efficiently discharge the gas from the storage tanks 45, 41 into the circulation path 31. In such a configuration using a single gas supply unit 47, 43 for each storage tank 45, 41, one possible means for discharging the gas from the storage tanks 45, 41 into the circulation path 31 while maintaining the pressure in the processing space 1 and the circulation path 31 within an appropriate range is the following configuration. That is, this is a method in which the introduction of gas from the storage tanks 45, 41 into the circulation path 31 and the discharge of gas from the circulation path 31 to the storage tanks 45, 41 are alternated at regular intervals. In this case, the allowable pressure range in the processing space 1 and the circulation path 31 is expected to be quite narrow (approximately several hPa), and therefore, it may take a long time to decontaminate the gas in the storage tanks 45, 41.

[0099] Therefore, as a method for significantly improving the efficiency of the decontamination process of the gas in the storage tank 14, in the third embodiment, unlike the storage tank 14 in the first embodiment, two storage tanks 45, 41 are connected to the circulation path 31. However, three or more storage tanks may be used. Below, the decontamination process of the gas in the storage tanks when two storage tanks 45, 41 are used will be described. First, when handling a substance that generates a harmful gas in the processing space 1, only the storage tank 41 is used to control the pressure in the processing space 1 and the circulation path 31. If the harmful gas cannot be completely decontaminated by the processing units 29, 30 connected to the circulation path 31, the harmful gas will flow downstream of the circulation path 31, and contaminated gas will also be mixed into the storage tank 41, which transfers gas to and from the circulation path 31 for pressure control.

[0100] After handling of the substance that generates harmful gas in the processing space 1 has been completed, it is necessary to decontaminate the processing space 1, the circulation path 31, and the contaminated gas in the storage tank 41. The contaminated gas in the processing space 1 and the circulation path 31 is decontaminated by circulating it while passing through the processing units 29 and 30.

[0101] Next, prior to decontamination of the contaminated gas in the storage tank 41, the gas in the storage tank 45 connected to the circulation path 31 is discharged to the outside by the gas supply unit 47. The gas in the storage tank 45, which is not used for pressure control during handling of substances that generate harmful gas in the processing space 1, is uncontaminated and can be discharged to the outside. After the gas in the storage tank 45 is discharged to the outside, the contaminated gas in the storage tank 41 is introduced into the circulation path 31, decontaminated in the processing units 29 and 30 connected to the circulation path 31, and then discharged from the circulation path 31 into the storage tank 45. At this time, the amount of contaminated gas introduced from the storage tank 41 to the circulation path 31 and the amount discharged into the storage tank 45 are controlled so that the first pressure sensor 2, which measures the differential pressure between the inside of the processing space 1 and the outside, is within an appropriate pressure difference range. The contaminated gas in the storage tank 41 is sent to the storage tank 45 through the processing units 29 and 30 connected to the circulation path 31. If sufficient decontamination cannot be achieved in this process, the gas (containing residual contamination) in the storage tank 45 is transferred by airflow to the storage tank 41 via the circulation path 31, and the gas in the storage tank 45 is again discharged. Then, the contaminated gas in the storage tank 41 is introduced into the circulation path 31, decontaminated in the treatment units 29 and 30 connected to the circulation path 31, and then discharged from the circulation path 31 into the storage tank 45. This process is repeated.

[0102] When the gas is sent from the storage tank 45 to the storage tank 41 via the circulation path 31, the gas may be decontaminated by the treatment devices 29, 30 connected to the circulation path 31. However, since the storage tank 45 is installed upstream of the circulation path 31 from the storage tank 41, a portion of the gas introduced from the storage tank 45 to the circulation path 31 is discharged to the storage tank 41 without passing through the treatment devices 29, 30. For this reason, it is preferable to decontaminate the contaminated gas in the storage tank when the gas is sent from the storage tank 41, which is installed downstream of the circulation path 31, to the storage tank 45, which is further upstream.

[0103] The method of using two storage tanks 45, 41 as in the third embodiment enables efficient decontamination because almost all of the contaminated gas in the storage tank 41 can be reliably guided to the treatment units 29, 30 for decontamination. This decontamination process of the gas in the storage tank 41 using two storage tanks 41, 45 is also effective in the configuration shown in the first embodiment in which one storage tank 14 is connected to the circulation path 31 by two gas supply units 12, 13. In the first embodiment, the process of simultaneously operating the gas supply unit 12 and the gas supply unit 13 to the circulation path 31 was described as a means for decontaminating the contaminated gas in the storage tank 14. However, as in the third embodiment, guiding the gas in the storage tank 41 to another storage tank 45 via the circulation path 31 and the treatment units 29, 30 connected thereto enables more efficient decontamination of the contaminated gas in the storage tank 41.

[0104] The second storage tank 45 added to the storage tank 41 for decontamination is intended to efficiently decontaminate the gas in the storage tank 41, and is not necessary if there is almost no contamination of the gas in the storage tank 41. Therefore, the storage tank 45 does not particularly need to be permanently installed, as long as it is configured so that it can be additionally installed in the circulation path 31 as needed.

[0105] [Embodiment 4] Figure 10 is a system diagram of a gas circulation system according to embodiment 4 of the present invention. This gas circulation system 204 relates to an alternative to the decontamination means for decontaminating contaminated gas in the storage tank 14 in embodiment 1. In embodiment 4, gas in the storage tank 14 is discharged at a constant rate by a pump 51, and the gas is decontaminated and discharged to the outside by treatment units 48, 49 (configured similarly to the treatment units 29, 30 described above). By gradually sending gas from the storage tank 14 by the pump 51 in an amount sufficient for the treatment units 48, 49 to decontaminate, the gas in the storage tank 14 can be gradually discharged to the outside within the decontamination capacity of the treatment units 48, 49. By disposing treatment units 48, 49 capable of decontaminating at a rate equal to or greater than the inflow rate of gas flowing from the outside into the processing space 1 or the circulation path 31, hazardous substances that produce hazardous gases in the processing space 1 can be treated. However, even in this case, it is preferable to ensure that the capacity of the storage tank 14 is sufficient so that it can respond to pressure changes due to changes in the temperature and humidity of the internal gas, changes in external air pressure, etc., other than the intrusion of gas from the outside.

[0106] It should be noted that the present invention is not limited to the above-described examples and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0107] Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be partially or entirely implemented in hardware, for example, by designing them as integrated circuits. The above-described configurations, functions, etc. may also be implemented in software, with a processor interpreting and executing a program that implements each function. Information such as the programs, tables, and files that implement each function can be stored in a memory, a recording device such as a hard disk or SSD (Solid State Drive), or a recording medium such as an IC card, SD card, or DVD.

[0108] In addition, the control lines and information lines shown are those that are considered necessary for the explanation, and do not necessarily show all the control lines and information lines in the product. In reality, it can be assumed that almost all components are interconnected.

[0109] REFERENCE SIGNS LIST 1 Processing space 2 First pressure sensor 10 Contamination level detection sensor 10a, 23, 26 Bypass path 12, 13 Gas supply section 14 Storage tank 15 Second pressure sensor 17 Temperature sensor 19 Supply path 20 Discharge path 21 Circulation section (pump, positive displacement pump) 22, 28 Heating section 29, 30 Processing section 31 Circulation path 201 to 204 Gas circulation system 241 Pressure control section 242 Pump control section 243 Temperature control section

Claims

1. A gas circulation system comprising: an openable supply path that supplies a harmful gas to a processing space in which a predetermined process is performed with the gas; an openable exhaust path that exhausts the gas in the processing space to the outside of the processing space; a circulation path to which the supply path and the exhaust path are connected, the two ends of which are connected to the processing space; a circulation unit that circulates and supplies the gas in the processing space within the circulation path; a first pressure sensor that measures the pressure of the gas within the circulation path; a storage tank that can at least temporarily store a portion of the gas in the circulation path; and an air supply unit that supplies the gas between the storage tank and the circulation path.

2. A gas circulation system as described in claim 1, characterized in that it is provided with a pressure control unit that controls the gas supply unit based on the pressure value measured by the first pressure sensor and supplies the gas between the storage tank and the circulation unit, thereby controlling the pressure of the gas in the circulation path to be within a preset range.

3. A gas circulation system as described in claim 1, characterized in that it is provided with a second pressure sensor that detects the pressure of the gas in the storage tank, the circulation unit is provided with a pump that supplies the gas, and a pump control unit that variably controls the driving speed of the pump or the amount of throttling of the supply pipe to the pump based on the pressure of the gas in the storage tank measured by the second pressure sensor.

4. The gas circulation system according to claim 3, wherein the pump is a positive displacement pump.

5. The gas circulation system according to claim 1, further comprising a processing unit for rendering the gas in the circulation path harmless.

6. The gas circulation system according to claim 1, further comprising at least one of a temperature sensor for detecting the temperature of the gas in the circulation path and a humidity sensor for detecting the humidity of the gas.

7. A gas circulation system as described in claim 6, further comprising a temperature control unit that, when the temperature sensor is provided, controls the temperature of the gas in the circulation path to a value within a predetermined range based on the temperature of the gas detected by the temperature sensor.

8. A gas circulation system as described in claim 6, which, when equipped with the humidity sensor, is provided with a humidity control unit that controls the humidity of the gas in the circulation path to a value within a predetermined range based on the humidity detected by the humidity sensor.

9. The gas circulation system according to claim 1, further comprising a contamination level detection sensor for detecting the contamination level of the gas in the circulation path.

10. A gas circulation system as described in claim 6, characterized in that it is provided with one or more bypass paths connected to the circulation path and which draw in and return the gas in the circulation path, and at least one of a processing unit which detoxifies the gas in the circulation path, the temperature sensor, and the humidity sensor is provided in the bypass path.

11. The gas circulation system according to claim 10, wherein at least one of the bypass paths is detachable in part or in whole from the circulation path.

12. A gas circulation system as described in claim 1, further comprising one or more bypass paths connected to the circulation path for drawing in and returning gas within the circulation path, wherein the bypass paths are provided with at least one of a cooling section for cooling the gas, a heating section for heating the gas, a dehumidifying section for dehumidifying the gas, and a humidifying section for humidifying the gas.

13. The gas circulation system according to claim 1, characterized in that a plurality of the storage tanks are provided.

Images