Gas separation method and gas separation device

Abstract

The present invention provides a gas separation method that separates a target gas from a raw gas containing the target gas by means of a separation cycle that involves repeating an adsorption step of sending the raw gas from a raw gas storage tank to an adsorption unit to cause the target gas to be adsorbed by the adsorption unit and a separation step of desorbing the target gas adsorbed by the adsorption unit in the adsorption step from the adsorption unit and sending the desorbed target gas to a target gas storage tank for storage, wherein, before stopping the separation cycle, the target gas adsorbed in the adsorption step immediately before stopping is desorbed from the adsorption unit.

Description

Gas separation method and gas separation device

[0001] The present invention relates to a gas separation method and a gas separation apparatus.

[0002] In the manufacturing process of semiconductor products such as semiconductor integrated circuits or display devices such as liquid crystal panels, plasma generated by high-frequency discharge in a rare gas atmosphere is used. While argon has traditionally been used as the rare gas in such processes, krypton and xenon have recently attracted attention for more advanced processing. In the field of lamps, argon has traditionally been used as the fill gas in light bulbs, but in recent years, high-value-added products using krypton or xenon have been manufactured to reduce power consumption and improve brightness. Similarly, in the field of glass, argon has traditionally been used as the fill gas in double-glazed glass, but krypton has recently been manufactured to improve thermal insulation performance.

[0003] However, krypton and xenon are extremely rare and expensive gases due to their abundance in the air used as raw materials and the complexity of the separation process, and their use has led to problems such as an imbalance in supply and demand and a significant increase in costs. To make the use of such gases economically viable, it is extremely important to separate and recover used rare gases at a high recovery rate and reuse them.

[0004] A known method for separating and recovering xenon or krypton at a high concentration and with a high recovery rate is one that utilizes pressure swing adsorption (PSA) (see, for example, Patent Document 1).

[0005] Japanese Patent Application Laid-Open No. 2006-61831

[0006] When target gases such as xenon and krypton are separated from a feed gas using a pressure swing adsorption separation method, heat is generated (temperature rise) due to adsorption in the adsorption unit during the adsorption step, and heat is absorbed (temperature drop) due to desorption from the adsorption unit during the separation step. Therefore, the temperature of the adsorption unit periodically changes within a predetermined temperature change range during the separation cycle. Because the upper limit of the predetermined temperature change range is typically higher than ambient temperature, if the separation cycle is stopped, for example, upon completion of the adsorption step, the temperature of the adsorption unit will decrease over time from the temperature at the time of stopping to ambient temperature. If the separation cycle is restarted after the temperature of the adsorption unit has reached ambient temperature, the temperature change will begin from a state where the temperature change range of the adsorption unit has shifted below the predetermined temperature change range, potentially resulting in a decrease in the concentration quality of the separated target gas. Once the temperature change range has shifted, it takes a very long time for it to return to its original state.

[0007] Therefore, an object of the present invention is to provide a gas separation method and gas separation apparatus that can quickly obtain a target gas with good concentration quality after the separation cycle is restarted.

[0008] One aspect of the present invention is as follows.

[0009] [1] A gas separation method for separating a target gas from a raw material gas by a separation cycle that repeats an adsorption step in which raw material gas containing the target gas is sent from a raw material gas storage tank to an adsorption unit, thereby adsorbing the target gas into the adsorption unit, and a separation step in which the target gas adsorbed in the adsorption unit by the adsorption step is desorbed from the adsorption unit and sent to a target gas storage tank for storage, wherein the target gas adsorbed in the adsorption step immediately before the separation cycle is stopped is desorbed from the adsorption unit before the separation cycle is stopped.

[0010] [2] The gas separation method according to [1], wherein the target gas adsorbed in the adsorption step immediately before stopping the separation cycle is desorbed from the adsorption section by reducing the pressure to atmospheric pressure or below.

[0011] [3] The gas separation method according to [1] or [2], wherein the target gas adsorbed in the adsorption step immediately before stopping the separation cycle is desorbed from the adsorption section until the temperature of the adsorption section becomes equivalent to the ambient temperature before stopping the separation cycle.

[0012] [4] The gas separation method according to any one of [1] to [3], wherein the adsorption step includes passing the raw gas from the raw gas storage tank through the adsorption section and the auxiliary adsorption section in this order and sending the raw gas to a post-separation gas storage tank, thereby adsorbing the target gas into the adsorption section and the auxiliary adsorption section; the separation cycle includes a recovery step of desorbing the target gas adsorbed in the auxiliary adsorption section in the adsorption step from the auxiliary adsorption section, sending the target gas through the adsorption section to the raw gas storage tank, and storing it therein; the adsorption step, the separation step, and the recovery step are repeated in this order; and the gas separation method includes desorbing the target gas adsorbed in the adsorption step immediately before stopping the separation cycle from the auxiliary adsorption section before stopping the separation cycle.

[0013] [5] The gas separation method according to [4], wherein the target gas adsorbed in the adsorption step immediately before stopping the separation cycle is desorbed from the auxiliary adsorption section by reducing the pressure to atmospheric pressure or below before stopping the separation cycle.

[0014] [6] The gas separation method according to [4] or [5], wherein the separation cycle includes a rinsing step in which the separated gas stored in the separated gas storage tank by the adsorption step is passed through the auxiliary adsorption section and the adsorption section in this order to desorb the target gas from the auxiliary adsorption section, and the target gas is sent to the raw gas storage tank and stored therein; and the adsorption step, separation step, recovery step, and rinsing step are repeated in this order.

[0015] [7] The gas separation method according to any one of [1] to [6], wherein the separation cycle includes a purging step in which the target gas is sent from the target gas storage tank to the adsorption unit to adsorb the target gas to the adsorption unit, and the adsorption step, the purging step, and the separation step are repeated in this order, and the gas separation method includes desorbing the target gas adsorbed in the purging step immediately before stopping the separation cycle from the adsorption unit before stopping the separation cycle.

[0016] [8] A gas separation apparatus comprising: a raw material gas storage tank for storing raw material gas containing a target gas; an adsorption unit for adsorbing the target gas; a target gas storage tank for storing the target gas desorbed from the adsorption unit; and a control unit for separating the target gas from the raw material gas by controlling a separation cycle that repeats an adsorption step of sending the raw material gas from the raw material gas storage tank to the adsorption unit to adsorb the target gas into the adsorption unit, and a separation step of desorbing the target gas adsorbed in the adsorption step from the adsorption unit and sending it to the target gas storage tank for storage, wherein the control unit desorbs the target gas adsorbed in the adsorption step immediately before stopping the separation cycle from the adsorption unit before stopping the separation cycle.

[0017] [9] The gas separation apparatus according to [8], further comprising a vacuum pump, wherein the control unit desorbs the target gas adsorbed in the adsorption step immediately before stopping the separation cycle from the adsorption unit by reducing the pressure to below atmospheric pressure using the vacuum pump before stopping the separation cycle.

[0018]

[10] The gas separation apparatus according to [8] or [9], further comprising a thermometer for measuring the temperature of the adsorption section, wherein the control section desorbs the target gas adsorbed in the adsorption step immediately before stopping the separation cycle from the adsorption section until the temperature of the adsorption section measured by the thermometer becomes equivalent to the ambient temperature before stopping the separation cycle.

[0019]

[11] The gas separation apparatus according to any one of [8] to

[10] , further comprising: an auxiliary adsorption section that adsorbs the target gas; and a post-separation gas storage tank, wherein the adsorption step involves sending the raw gas from the raw gas storage tank through the adsorption section and the auxiliary adsorption section in this order to the post-separation gas storage tank, thereby adsorbing the target gas into the adsorption section and the auxiliary adsorption section, the separation cycle includes a recovery step in which the target gas adsorbed in the auxiliary adsorption section in the adsorption step is desorbed from the auxiliary adsorption section and sent to the raw gas storage tank through the adsorption section for storage, and the adsorption step, separation step, and recovery step are repeated in this order, and the control section desorbs the target gas adsorbed in the adsorption step immediately before stopping the separation cycle from the auxiliary adsorption section before stopping the separation cycle.

[0020]

[12] The gas separation apparatus according to

[11] , further comprising an auxiliary vacuum pump, wherein the control unit desorbs the target gas adsorbed in the adsorption step immediately before stopping the separation cycle from the auxiliary adsorption unit by reducing the pressure to below atmospheric pressure using the auxiliary vacuum pump before stopping the separation cycle.

[0021] According to the present invention, it is possible to provide a gas separation method and a gas separation apparatus that can quickly obtain a target gas with good concentration quality after the separation cycle is restarted.

[0022] FIG. 1 is an explanatory diagram illustrating a state when the adsorption step (A) and the separation step (B) are performed in the gas separation method according to the first embodiment of the present invention. FIG. 1 is an explanatory diagram illustrating a state when the recovery step (B) is performed while the adsorption step (A) is continued from the state shown in FIG. 2 is an explanatory diagram illustrating a state when the rinsing step (B) is performed while the adsorption step (A) is continued from the state shown in FIG. 3 is an explanatory diagram illustrating a state when the purge step (A) and the equalization step (B) are performed from the state shown in FIG. 4 is an explanatory diagram illustrating a state when the separation step (A) and the adsorption step (B) are performed from the state shown in FIG. 5 is an explanatory diagram illustrating a state when the recovery step (A) is performed while the adsorption step (B) is continued from the state shown in FIG. 6 is an explanatory diagram illustrating a state when the equalization step (A) and the purge step (B) are performed from the state shown in FIG. 7 is an explanatory diagram illustrating a state when the separation cycle is stopped in the gas separation method according to the second embodiment of the present invention. FIG. 1 is an explanatory diagram illustrating a state when the separation cycle is stopped in the gas separation method according to the third embodiment of the present invention.

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0024] As shown in FIGS. 1 to 8, in the first embodiment of the present invention, the gas separation method is a gas separation method in which a target gas is separated from a raw material gas by a separation cycle (A) that repeats an adsorption step (A) in which a raw material gas containing a target gas is sent from a raw material gas storage tank 1 to an adsorption unit (A) 10A to adsorb the target gas to the adsorption unit (A) 10A, as shown by the thick solid lines in FIGS. 1 to 3, and a separation step (A) in which the target gas adsorbed in the adsorption unit (A) 10A by the adsorption step (A) is desorbed from the adsorption unit (A) 10A (for example, by reducing pressure) and sent to a target gas storage tank 2 for storage, as shown by the thick solid lines in FIG. 5. Before stopping the separation cycle (A), the target gas adsorbed in the adsorption step (A) immediately before stopping is desorbed from the adsorption unit (A) 10A. The method of "desorbing the target gas adsorbed in the adsorption step (A) immediately before stopping the separation cycle (A) from the adsorption section (A) 10A before stopping the separation cycle (A)" is not particularly limited, and for example, the separation step (A) may be performed before stopping the separation cycle (A), or the separation step (A) may be performed before stopping the separation cycle (A) and then the recovery step (A) may be performed, or a step may be performed in which the target gas adsorbed in the adsorption section (A) 10A by the adsorption step (A) is desorbed from the adsorption section (A) 10A and sent to the raw gas storage tank 1 for storage before stopping the separation cycle (A), or, although not shown in the figure, a step may be performed in which the target gas is desorbed from the adsorption section (A) 10A and discharged to the outside before stopping the separation cycle (A).

[0025] When the environmental temperature is below the lower limit of the temperature change range, which is the range of the temperature of the adsorption unit (A) 10A that changes periodically during the separation cycle (A), the target gas adsorbed in the adsorption step (A) immediately before the separation cycle (A) is desorbed from the adsorption unit (A) 10A before stopping the separation cycle (A), thereby suppressing a downward shift in the temperature change range in the adsorption unit (A) 10A when the separation cycle (A) is resumed. Furthermore, when the environmental temperature is lower than the upper limit and higher than the lower limit of the temperature change range, the target gas adsorbed in the adsorption step (A) immediately before the separation cycle (A) is stopped is desorbed from the adsorption unit (A) 10A before stopping the separation cycle (A), thereby suppressing a downward shift in the temperature change range in the adsorption unit (A) 10A when the separation cycle (A) is resumed. Therefore, with the above configuration, a gas separation method can be realized that allows target gas of good concentration quality to be obtained promptly after the separation cycle (A) is resumed.

[0026] The gas separation method may be configured such that, before the separation cycle (A) is stopped, the target gas adsorbed in the adsorption step (A) immediately before the stop is desorbed from the adsorption unit (A) 10A by reducing the pressure to below atmospheric pressure. This configuration makes it easy to lower the temperature of the adsorption unit (A) 10A at the time the separation cycle (A) is stopped so that it approaches the ambient temperature. This reduces the temperature change in the adsorption unit (A) 10A over time after the stop, and as a result, reduces a downward shift in the temperature change range in the adsorption unit (A) 10A when the separation cycle (A) is restarted. The method for "desorption by reducing the pressure to below atmospheric pressure" is not particularly limited, and for example, a vacuum pump 6 may be used as in the second embodiment shown in FIG. 9 .

[0027] The gas separation method may be configured such that, before the separation cycle (A) is stopped, the target gas adsorbed in the adsorption step (A) immediately before the stop is desorbed from the adsorption unit (A) 10A until the temperature of the adsorption unit (A) 10A becomes equal to the ambient temperature (for example, by reducing the pressure). This configuration further suppresses temperature changes in the adsorption unit (A) 10A over time after the stop, and as a result, further suppresses a downward shift in the temperature change range in the adsorption unit (A) 10A when the separation cycle (A) is restarted.

[0028] As shown by the thick solid lines in Figures 1 to 3, the adsorption step (A) involves passing the raw material gas from the raw material gas storage tank 1 through the adsorption section (A) 10A and the auxiliary adsorption section (A) 11A in this order and sending it to the post-separation gas storage tank 3, thereby adsorbing the target gas in the adsorption section (A) 10A and the auxiliary adsorption section (A) 11A. As shown by the thick solid lines in Figure 6, the separation cycle (A) has a recovery step (A) in which the target gas adsorbed in the auxiliary adsorption section (A) 11A by the adsorption step (A) is desorbed from the auxiliary adsorption section (A) 11A and sent through the adsorption section (A) 10A to the raw material gas storage tank 1 for storage. The adsorption step (A), separation step (A), and recovery step (A) are repeated in this order, and in this gas separation method, before stopping the separation cycle (A), the target gas adsorbed in the adsorption step (A) immediately before stopping is desorbed from the auxiliary adsorption section (A) 11A. According to the above configuration, by using the auxiliary adsorption unit (A) 11A in combination, it is possible to easily obtain a high-concentration separated gas with a high target gas removal rate from the separated gas storage tank 3. Moreover, by "desorbing the target gas adsorbed in the adsorption step (A) immediately before stopping the separation cycle (A) from the auxiliary adsorption unit (A) 11A before stopping the separation cycle (A)" as described above, it is possible to suppress a downward shift in the temperature change range in the auxiliary adsorption unit (A) 11A when the separation cycle (A) is restarted, and therefore it is possible to obtain a target gas with good concentration quality promptly after the separation cycle (A) is restarted. The method for "desorbing the target gas adsorbed in the adsorption step (A) immediately before stopping the separation cycle (A) from the auxiliary adsorption section (A) 11A before stopping the separation cycle (A)" is not particularly limited, and for example, the recovery step (A) may be performed before stopping the separation cycle (A), or, although not shown, a step may be performed in which the target gas is desorbed from the auxiliary adsorption section (A) 11A and recovered in the raw gas storage tank 1 without passing through the adsorption section (A) 10A before stopping the separation cycle (A), or, although not shown, a step may be performed in which the target gas is desorbed from the auxiliary adsorption section (A) 11A and discharged to the outside before stopping the separation cycle (A).

[0029] In this gas separation method, before the separation cycle (A) is stopped, the target gas adsorbed in the adsorption step (A) immediately before the stop is desorbed from the auxiliary adsorption section (A) 11A by reducing the pressure to below atmospheric pressure. This configuration facilitates lowering the temperature of the auxiliary adsorption section (A) 11A to approach the ambient temperature when the separation cycle (A) is stopped, thereby suppressing temperature changes in the auxiliary adsorption section (A) 11A over time after the stop. As a result, it is possible to suppress a downward shift in the temperature range of the auxiliary adsorption section (A) 11A when the separation cycle (A) is restarted. The method for "desorption by reducing the pressure to below atmospheric pressure" is not particularly limited, and for example, an auxiliary vacuum pump 7 may be used, as in the third embodiment shown in FIG. 10 .

[0030] 7, the separation cycle (A) includes a rinse step (A) in which the separated gas stored in the separated gas storage tank 3 by the adsorption step (A) is passed through the auxiliary adsorption section (A) 11A and the adsorption section (A) 10A in this order, thereby desorbing the target gas from the auxiliary adsorption section (A) 11A and sending it to the raw gas storage tank 1 for storage, and the adsorption step (A), separation step (A), recovery step (A), and rinse step (A) are repeated in this order. The above configuration can increase the recovery rate of the target gas.

[0031] As shown by the thick solid line in Figure 4, the separation cycle (A) includes a purge step (A) in which the target gas is sent from the target gas storage tank 2 to the adsorption unit (A) 10A to adsorb the target gas to the adsorption unit (A) 10A. The adsorption step (A), purge step (A), and separation step (A) are repeated in this order, and the gas separation method involves desorbing the target gas adsorbed in the purge step (A) immediately before stopping the separation cycle (A) from the adsorption unit (A) 10A before stopping it. According to the above configuration, the purge step (A) makes it easy to obtain a high concentration of target gas from the target gas storage tank 2. Furthermore, by "desorbing the target gas adsorbed in the purge step (A) immediately before stopping the separation cycle (A) from the adsorption unit (A) 10A before stopping the separation cycle (A)," a downward shift in the temperature change range in the adsorption unit (A) 10A when the separation cycle (A) is restarted can be suppressed.

[0032] As shown in FIGS. 1 to 8, in this embodiment, the gas separation apparatus includes a raw material gas storage tank 1 that stores raw material gas containing a target gas, an adsorption unit (A) 10A that adsorbs the target gas, and a target gas storage tank 2 that stores the target gas desorbed from the adsorption unit (A) 10A. An adsorption step (A) in which the raw material gas is sent from the raw material gas storage tank 1 to the adsorption unit (A) 10A to adsorb the target gas to the adsorption unit (A) 10A, and a separation step (A) in which the target gas adsorbed in the adsorption unit (A) 10A by the adsorption step (A) is desorbed from the adsorption unit (A) 10A and sent to the target gas storage tank 2 for storage. By controlling this separation cycle (A), the target gas adsorbed in the adsorption unit (A) 10A by the adsorption step (A) is separated from the adsorption unit (A) 10A and sent to the target gas storage tank 2 for storage. This gas separation apparatus has a control unit that separates the target gas from the raw material gas, and the control unit desorbs the target gas adsorbed in the adsorption step (A) immediately before stopping the separation cycle (A) from the adsorption unit (A) 10A. According to the above configuration, a gas separation apparatus can be realized that can quickly obtain target gas with good concentration quality after the separation cycle (A) is restarted.

[0033] 9 , the gas separation apparatus may have a vacuum pump 6, and the control unit may be configured to desorb the target gas adsorbed in the adsorption step (A) immediately before stopping the separation cycle (A) from the adsorption unit (A) 10A by reducing the pressure to below atmospheric pressure using the vacuum pump 6. This configuration can suppress a downward shift in the temperature change range in the adsorption unit (A) 10A when the separation cycle (A) is restarted.

[0034] The gas separation apparatus may have a thermometer (A) TA that measures the temperature of the adsorption unit (A) 10A, and the control unit may desorb the target gas adsorbed in the adsorption step (A) immediately before stopping the separation cycle (A) from the adsorption unit (A) 10A until the temperature of the adsorption unit (A) 10A measured by the thermometer (A) TA becomes equivalent to the ambient temperature before stopping the separation cycle (A). This configuration further suppresses a downward shift in the temperature change range in the adsorption unit (A) 10A when the separation cycle (A) is restarted.

[0035] The gas separation apparatus has an auxiliary adsorption section (A) 11A that adsorbs the target gas, and a post-separation gas storage tank 3. In the adsorption step (A), the raw material gas is sent from the raw material gas storage tank 1 through the adsorption section (A) 10A and the auxiliary adsorption section (A) 11A in this order to the post-separation gas storage tank 3, thereby adsorbing the target gas in the adsorption section (A) 10A and the auxiliary adsorption section (A) 11A. In the separation cycle (A), the target gas adsorbed in the auxiliary adsorption section (A) 11A by the adsorption step (A) is desorbed from the auxiliary adsorption section (A) 11A and sent through the adsorption section (A) 10A to the raw material gas storage tank 1 for storage. The adsorption step (A), separation step (A), and recovery step (A) are repeated in this order. Before stopping the separation cycle (A), the control section desorbs the target gas adsorbed in the adsorption step (A) immediately before stopping from the auxiliary adsorption section (A) 11A. According to the above configuration, by using the auxiliary adsorption section (A) 11A in combination, it is possible to easily obtain high-concentration separated gas with a high target gas removal rate from the separated gas storage tank 3, and further, it is possible to quickly obtain target gas with good concentration quality after the separation cycle (A) is resumed.

[0036] 10 , the gas separation apparatus has an auxiliary vacuum pump 7, and before stopping the separation cycle (A), the control unit desorbs the target gas adsorbed in the adsorption step (A) immediately before stopping from the auxiliary adsorption section (A) 11A by reducing the pressure to below atmospheric pressure using the auxiliary vacuum pump 7. With this configuration, it is possible to suppress a downward shift in the temperature change range in the auxiliary adsorption section (A) 11A when the separation cycle (A) is restarted.

[0037] As shown in FIGS. 1 to 8 , the gas separation apparatus in this embodiment includes a raw material gas storage tank 1 for storing raw material gas containing a target gas, an adsorption unit (A) 10A for adsorbing the target gas, an adsorption unit (B) 10B for adsorbing the target gas, a target gas storage tank 2 for storing the target gas desorbed from each of the adsorption units (A) 10A and (B) 10B, a separation cycle (A) that repeats an adsorption step (A) in which raw material gas is sent from the raw material gas storage tank 1 to the adsorption unit (A) 10A to adsorb the target gas in the adsorption unit (A) 10A, and a separation step (A) in which the target gas adsorbed in the adsorption unit (A) 10A by the adsorption step (A) is desorbed from the adsorption unit (A) 10A and sent to the target gas storage tank 2 for storage; The gas separation device has a control unit that separates the target gas from the raw material gas by controlling a separation cycle (B) that repeats an adsorption step (B) in which a raw material gas is sent to an adsorption unit (B) 10B to adsorb the target gas into the adsorption unit (B) 10B, and a separation step (B) in which the target gas adsorbed in the adsorption unit (B) 10B by the adsorption step (B) is desorbed from the adsorption unit (B) 10B and sent to a target gas storage tank 2 for storage. Before stopping the separation cycle (A) and the separation cycle (B), the control unit desorbs from the adsorption unit (A) 10A the target gas adsorbed in the adsorption step (A) immediately before the stoppage, and / or desorbs from the adsorption unit (B) 10B the target gas adsorbed in the adsorption step (B) immediately before the stoppage. According to the above configuration, by appropriately shifting the separation cycle (A) and the separation cycle (B) from each other, it is possible to realize a gas separation device that can efficiently separate the target gas and can quickly obtain target gas of good concentration quality after the separation cycle (A) and the separation cycle (B) are resumed.

[0038] The gas separation apparatus has an auxiliary adsorption unit (B) 11B that adsorbs the target gas, and the separation cycle (B) has a purge step (B) in which the target gas is sent from the target gas storage tank 2 to the adsorption unit (B) 10B to adsorb the target gas in the adsorption unit (B) 10B, as shown by the thick dashed line in FIG. 8 , and the separation cycle (A) has a purge step (A) in which the target gas is sent from the target gas storage tank 2 to the adsorption unit (A) 10A to adsorb the target gas in the adsorption unit (A) 10A, as shown by the thick solid line in FIG. 4 , and As shown in Fig. 1, the system includes a pressure equalization step (A) in which adsorption unit (A) 10A and auxiliary adsorption unit (A) 11A are pressurized with gas flowing out from adsorption unit (B) 10B and auxiliary adsorption unit (B) 11B in purge step (B), and the adsorption step (A), purge step (A), separation step (A), and pressure equalization step (A) are repeated in this order, and the control unit desorbs the target gas adsorbed in the purge step (A) immediately before stopping the separation cycle (A) from adsorption unit (A) 10A. According to the above configuration, the purge step (A) makes it easier to obtain a high-concentration target gas from the target gas storage tank 2, and also suppresses a downward shift in the temperature change range in adsorption unit (A) 10A when the separation cycle (A) is restarted. Furthermore, the pressure equalization step (A) allows the target gas contained in the gas flowing out from the adsorption section (B) 10B in the purge step (B) to be adsorbed by the adsorption section (A) 10A (and the auxiliary adsorption section (A) 11A), thereby increasing the recovery rate of the target gas.

[0039] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the above-described embodiments can be modified in various ways without departing from the gist of the present invention.

[0040] Comparative Example Using the gas separation apparatus of the first embodiment, separation cycle (A) and separation cycle (B) were carried out under the valve control shown in Table 1. The conditions were as follows.

[0041] Gas introduced from outside the apparatus into raw gas storage tank 1: mixed gas of xenon and argon (xenon concentration 10%) 2.0 L / min (all hereinafter at 0°C and atmospheric pressure) Highly adsorbable component (target gas): xenon 0.2 L / min Weakly adsorbable component: argon 1.8 L / min Adsorption section (A) 10A, adsorption section (B) 10B, auxiliary adsorption section (A) 11A, auxiliary adsorption section (B) 11B: stainless steel pipe 80A (inner diameter 83.1 mm) filled with 1.5 kg of activated carbon as adsorbent to a filling height of 500 mm Compressor 4: diaphragm compressor 20 L / min Compressor 5: diaphragm compressor 2.0 L / min

[0042]

[0043] After 48 hours of continuous operation under the above operating conditions, the argon concentration extracted from the post-separation gas storage tank 3 and the xenon concentration extracted from the target gas storage tank 2 settled almost constant. The results at this time were as follows: Argon concentration in xenon 443 ppm → Product xenon concentration 99.95% Xenon concentration in argon 387 ppm → Xenon recovery rate 99.6% Temperature change of adsorption section (A) 10A and adsorption section (B) 10B: 26°C to 38°C Temperature change of auxiliary adsorption section (A) 11A and auxiliary adsorption section (B) 11B: 22°C to 26°C Ambient temperature: 24°C

[0044] Thereafter, operation was stopped when the adsorption section (A) 10A and the auxiliary adsorption section (A) 11A completed the equalization and pressurization step (A). The temperatures of the adsorption sections at that time were as follows: adsorption section (A) 10A: 26.2°C, adsorption section (B) 10B: 37.5°C, auxiliary adsorption section (A) 11A: 22.8°C, auxiliary adsorption section (B) 11B: 25.8°C.

[0045] After 12 hours of shutdown, the temperature of each adsorption section reached approximately 24°C. After that, the temperature changes in each adsorption section immediately after restarting operation were as follows: Adsorption section (A) 10A: 26-42°C Adsorption section (B) 10B: 7-25°C Auxiliary adsorption section (A) 11A: 22-26°C Auxiliary adsorption section (B) 11B: 18-22°C

[0046] After restarting operation, it took 24 hours for the temperature change in each adsorption section to become equal to the temperature change before shutdown. It also took 27 hours for the argon concentration extracted from the post-separation gas storage tank 3 and the xenon concentration extracted from the target gas storage tank 2 to become equal to the concentrations before shutdown.

[0047] Example 1 The operation described in the comparative example was carried out, and the operation was stopped when the adsorption section (A) 10A and the auxiliary adsorption section (A) 11A completed the equalization and pressurization step (A). Thereafter, valve V11 was opened to release the highly adsorbable component in the adsorption section (B) 10B into the target gas storage tank 2. The temperatures of the adsorption sections after the operation were as follows: adsorption section (A) 10A: 26.1°C, adsorption section (B) 10B: 32.3°C, auxiliary adsorption section (A) 11A: 22.6°C, auxiliary adsorption section (B) 11B: 25.9°C

[0048] After 12 hours of shutdown, the temperature of each adsorption section reached approximately 24°C. After that, the temperature changes in each adsorption section immediately after restarting operation were as follows: Adsorption section (A) 10A: 26-42°C Adsorption section (B) 10B: 13-32°C Auxiliary adsorption section (A) 11A: 22-26°C Auxiliary adsorption section (B) 11B: 18-22°C

[0049] After restarting operation, it took 18 hours for the temperature change in each adsorption section to become equal to the temperature change before shutdown, and 22 hours for the argon concentration extracted from the separated gas storage tank 3 and the xenon concentration extracted from the target gas storage tank 2 to become equal to the concentrations before shutdown.

[0050] Example 2 The operation described in the comparative example was carried out, and the operation was stopped when the adsorption section (A) 10A and the auxiliary adsorption section (A) 11A completed the pressure equalization step (A). Thereafter, valve V11 was opened to release the strongly adsorbed component in adsorption section (B) 10B into target gas storage tank 2. Valve V11 was then closed, and valves V6 and V13 were opened to release the strongly adsorbed component and the weakly adsorbed component in the auxiliary adsorption section (B) 11B into feed gas storage tank 1 via adsorption section (B) 10B. The temperatures of the adsorption sections after the above operation were as follows: adsorption section (A) 10A: 26.2°C; adsorption section (B) 10B: 29.3°C; auxiliary adsorption section (A) 11A: 22.7°C; auxiliary adsorption section (B) 11B: 24.5°C

[0051] After 12 hours of shutdown, the temperature of each adsorption section reached approximately 24°C. After that, the temperature changes of each adsorption section immediately after restarting operation were as follows: Adsorption section (A) 10A: 26-42°C Adsorption section (B) 10B: 15-33°C Auxiliary adsorption section (A) 11A: 22-26°C Auxiliary adsorption section (B) 11B: 20-25°C

[0052] After restarting operation, it took 16 hours for the temperature change in each adsorption section to become equal to the temperature change before shutdown. It also took 21 hours for the argon concentration extracted from the post-separation gas storage tank 3 and the xenon concentration extracted from the target gas storage tank 2 to become equal to the concentrations before shutdown.

[0053] Example 3 The operation described in the comparative example was carried out, and the operation was stopped when the adsorption section (A) 10A and the auxiliary adsorption section (A) 11A completed the pressure equalization step (A). Thereafter, valve V11 was opened to release the adsorbable component in adsorption section (B) 10B into target gas storage tank 2, and the adsorbable component was further released using vacuum pump 6 until the temperature in adsorption section (B) 10B reached approximately 24°C. The temperatures of each adsorption section and the pressure in adsorption column adsorption section (B) 10B after the above operation were as follows: Adsorption section (A) 10A: 26.1°C Adsorption section (B) 10B: 23.8°C Auxiliary adsorption section (A) 11A: 22.7°C Auxiliary adsorption section (B) 11B: 25.9°C Pressure in adsorption section (B) 10B: -40 kPaG

[0054] After that, the temperature changes in each adsorption section immediately after restarting operation were as follows: Adsorption section (A) 10A: 26-42°C Adsorption section (B) 10B: 25-39°C Auxiliary adsorption section (A) 11A: 22-26°C Auxiliary adsorption section (B) 11B: 18-22°C

[0055] After restarting operation, it took three hours for the temperature change in each adsorption section to become equal to the temperature change before shutdown. It also took six hours for the argon concentration extracted from the separated gas storage tank 3 and the xenon concentration extracted from the target gas storage tank 2 to become equal to the concentrations before shutdown.

[0056] REFERENCE SIGNS LIST 1 raw gas storage tank 2 target gas storage tank 3 separated gas storage tank 4-5 compressors 6 vacuum pump 7 auxiliary vacuum pump 10A adsorption section (A) 10B adsorption section (B) 11A auxiliary adsorption section (A) 11B auxiliary adsorption section (B) TA thermometer (A) TB thermometer (B) V1-15 valves

Claims

1. A gas separation method for separating a target gas from a raw gas by a separation cycle that repeats an adsorption step in which raw gas containing a target gas is sent from a raw gas storage tank to an adsorption unit, thereby adsorbing the target gas into the adsorption unit, and a separation step in which the target gas adsorbed into the adsorption unit by the adsorption step is desorbed from the adsorption unit and sent to a target gas storage tank for storage, wherein the target gas adsorbed in the adsorption step immediately before the separation cycle is stopped is desorbed from the adsorption unit before the separation cycle is stopped.

2. A gas separation method as described in claim 1, in which the target gas adsorbed in the adsorption step immediately prior to stopping the separation cycle is desorbed from the adsorption section by reducing pressure to below atmospheric pressure before stopping the separation cycle.

3. A gas separation method as described in claim 1, wherein before the separation cycle is stopped, the target gas adsorbed in the adsorption step immediately before stopping is desorbed from the adsorption section until the temperature of the adsorption section becomes equivalent to the environmental temperature.

4. The gas separation method according to claim 1, wherein the adsorption step comprises passing the raw gas from the raw gas storage tank through the adsorption section and the auxiliary adsorption section in this order and sending it to a post-separation gas storage tank, thereby adsorbing the target gas into the adsorption section and the auxiliary adsorption section; the separation cycle comprises a recovery step in which the target gas adsorbed in the auxiliary adsorption section by the adsorption step is desorbed from the auxiliary adsorption section and sent through the adsorption section to the raw gas storage tank for storage; the adsorption step, separation step and recovery step are repeated in this order; and the gas separation method comprises desorbing the target gas adsorbed in the adsorption step immediately before stopping the separation cycle from the auxiliary adsorption section before stopping the separation cycle.

5. A gas separation method as described in claim 4, wherein the target gas adsorbed in the adsorption step immediately prior to stopping the separation cycle is desorbed from the auxiliary adsorption section by reducing pressure to below atmospheric pressure before stopping the separation cycle.

6. The gas separation method described in claim 4, wherein the separation cycle includes a rinsing step in which the separated gas stored in the separated gas storage tank by the adsorption step is passed through the auxiliary adsorption section and the adsorption section in that order to desorb the target gas from the auxiliary adsorption section and send it to the raw gas storage tank for storage, and the adsorption step, separation step, recovery step and rinsing step are repeated in that order.

7. The gas separation method according to claim 1, wherein the separation cycle includes a purging step of sending the target gas from the target gas storage tank to the adsorption section to adsorb the target gas into the adsorption section, and the adsorption step, the purging step, and the separation step are repeated in this order, and the gas separation method further includes desorbing the target gas adsorbed in the purging step immediately before stopping the separation cycle from the adsorption section before stopping the separation cycle.

8. A gas separation apparatus having: a raw material gas storage tank for storing raw material gas containing a target gas; an adsorption unit for adsorbing the target gas; a target gas storage tank for storing the target gas desorbed from the adsorption unit; and a control unit for separating the target gas from the raw material gas by controlling a separation cycle that repeats an adsorption step in which the raw material gas is sent from the raw material gas storage tank to the adsorption unit to adsorb the target gas into the adsorption unit, and a separation step in which the target gas adsorbed in the adsorption step is desorbed from the adsorption unit and sent to the target gas storage tank for storage, wherein the control unit desorbs the target gas adsorbed in the adsorption step immediately before stopping from the adsorption unit before stopping the separation cycle.

9. A gas separation apparatus as described in claim 8, further comprising a vacuum pump, wherein the control unit desorbs the target gas adsorbed in the adsorption step immediately prior to stopping the separation cycle from the adsorption unit by reducing the pressure to below atmospheric pressure using the vacuum pump before stopping the separation cycle.

10. A gas separation apparatus as described in claim 8, further comprising a thermometer for measuring the temperature of the adsorption section, and the control unit desorbs the target gas adsorbed in the adsorption step immediately before stopping the separation cycle from the adsorption section until the temperature of the adsorption section measured by the thermometer becomes equivalent to the ambient temperature before stopping the separation cycle.

11. A gas separation apparatus as described in claim 8, further comprising: an auxiliary adsorption section for adsorbing the target gas; and a post-separation gas storage tank, wherein the adsorption step comprises sending the raw gas from the raw gas storage tank through the adsorption section and the auxiliary adsorption section in this order to the post-separation gas storage tank, thereby adsorbing the target gas into the adsorption section and the auxiliary adsorption section, the separation cycle comprises a recovery step in which the target gas adsorbed into the auxiliary adsorption section by the adsorption step is desorbed from the auxiliary adsorption section and sent through the adsorption section to the raw gas storage tank for storage, and the adsorption step, separation step and recovery step are repeated in this order, and the control section desorbs the target gas adsorbed in the adsorption step immediately before stopping the separation cycle from the auxiliary adsorption section before stopping the separation cycle.

12. A gas separation apparatus as described in claim 11, further comprising an auxiliary vacuum pump, wherein the control unit desorbs the target gas adsorbed in the adsorption step immediately prior to stopping the separation cycle from the auxiliary adsorption unit by reducing the pressure to below atmospheric pressure using the auxiliary vacuum pump before stopping the separation cycle.

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