Recovery device

Abstract

The present invention provides a recovery device (10) that allows for higher pressure in an adsorption columns (11, 12, 13) at the start of an adsorption operation. The recovery device comprises: a first blower (17) disposed in a duct (16) through which exhaust gas from a combustion device (15) flows; adsorption columns in which an adsorbent (14) is accommodated and to which exhaust gas is supplied by the first blower; a vacuum pump (23) that depressurizes the adsorption columns; and a switching device (31) that switches between a first state in which the first blower supplies exhaust gas to the adsorption columns and the adsorbent adsorbs a target gas and a second state in which the adsorption columns are depressurized by the vacuum pump and the adsorbent desorbs the target gas, wherein before changing over from the second state to the first state, a third state is achieved by introducing atmospheric air into the adsorption columns.

Description

Recovery device

[0001] The present invention relates to a recovery device for recovering a specific gas from the exhaust gas of a combustion device.

[0002] One technique for recovering specific gases from the exhaust gas of a combustion system involves repeatedly performing an adsorption operation, in which the exhaust gas is introduced into an adsorption tower containing an adsorbent using a blower to adsorb and separate the gas, and a desorption operation, in which the adsorption tower is depressurized using a vacuum pump to desorb the adsorbed gas. During the desorption operation, the pressure in the adsorption tower becomes negative, below atmospheric pressure, so the adsorption tower becomes negative pressure immediately after switching from the desorption operation to the adsorption operation. If a blower is installed in the duct of the combustion system, the combustion system and the adsorption tower are connected via the blower, which could reduce the pressure inside the combustion system and cause the fire to go out.

[0003] JP 2017-12978 A

[0004] Patent Document 1 discloses a prior art technique in which a pressure equalization operation is performed between the desorption operation and the adsorption operation to reduce the pressure difference in the adsorption column, but the pressure increase from a negative pressure state is insufficient.

[0005] The present invention has been made to solve this problem, and an object of the present invention is to provide a recovery device which can sufficiently increase the pressure in the adsorption column at the start of the adsorption operation.

[0006] A first aspect for achieving this object includes a first blower arranged in a duct through which exhaust gas from a combustion device flows, an adsorption tower containing an adsorbent and to which exhaust gas is supplied by the first blower, a vacuum pump for depressurizing the adsorption tower, and a switching device for switching between a first state in which the first blower supplies exhaust gas to the adsorption tower and the adsorbent adsorbs the target gas, and a second state in which the adsorption tower is depressurized by the vacuum pump and the adsorbent desorbs the target gas, and the switching device introduces air into the adsorption tower to set it to a third state before changing from the second state to the first state.

[0007] The second embodiment is the same as the first embodiment, except that in the third state, the pressure in the adsorption tower into which the air has been introduced is set to 50 kPa or higher.

[0008] In a third aspect, the pressure in the adsorption tower into which the air has been introduced is increased to atmospheric pressure or higher in the first or second aspect.

[0009] In a fourth aspect, in any one of the first to third aspects, a dehumidifying section is provided for removing water, and the air passes through the dehumidifying section and reaches the adsorbent contained in the adsorption tower.

[0010] In a fifth aspect, in the fourth aspect, the dehumidifying section is provided inside the adsorption tower and contains a dehumidifying agent that adsorbs water.

[0011] A sixth aspect is the adsorption apparatus according to any one of the first to fifth aspects, further comprising a second blower that supplies gas to the adsorption tower.

[0012] A seventh aspect is any of the first to fifth aspects, further comprising a bypass pipe that bypasses the suction side and discharge side of the first blower, a first control valve arranged in the bypass pipe, and a first pressure gauge arranged on the suction side of the first blower, and the switching device adjusts the opening degree of the first control valve based on the pressure detected by the first pressure gauge.

[0013] An eighth aspect is any of the first to fifth aspects, further comprising a second pressure gauge arranged on the suction side of the first blower and a second control valve arranged on the discharge side of the first blower, and the switching device adjusts the opening degree of the second control valve based on the pressure detected by the second pressure gauge.

[0014] A ninth aspect is any of the first to fifth aspects, further comprising a third pressure gauge arranged on the suction side of the first blower, and the switching device adjusts the rotation speed of the first blower based on the pressure detected by the third pressure gauge.

[0015] According to the present invention, before the adsorption tower is depressurized by a vacuum pump and the adsorbent desorbs the target gas in a second state, to the first state, in which the first blower supplies exhaust gas to the adsorption tower and the adsorbent adsorbs the target gas, atmospheric air is introduced into the adsorption tower to create a third state, thereby enabling the pressure in the adsorption tower to be sufficiently increased immediately after the state is changed to the first state (at the start of the adsorption operation).

[0016] Fig. 1 is a piping system diagram of a recovery device in a first embodiment. Fig. 2 is a table showing the passage of time and operations performed in an adsorption tower. Fig. 3 is a piping system diagram of a recovery device in a second embodiment. Fig. 4 is a piping system diagram of a recovery device in a third embodiment. Fig. 5 is a piping system diagram of a recovery device in a fourth embodiment. Fig. 6 is a piping system diagram of a recovery device in a fifth embodiment. Fig. 7 is a piping system diagram of a recovery device in a sixth embodiment.

[0017] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a piping diagram of a recovery system 10 according to a first embodiment. The recovery system 10 recovers a target gas from exhaust gas using pressure swing adsorption. The recovery system 10 includes adsorption towers 11, 12, and 13, and an adsorbent 14 for adsorbing the target gas is accommodated in the adsorption towers 11, 12, and 13 as a fixed bed.

[0018] The adsorbent 14 has a property that its adsorption capacity (the amount of gas adsorbed per unit of adsorbent) varies depending on the partial pressure of the target gas. Therefore, the recovery device 10 can separate target gases that are easily adsorbed by the adsorbent 14 and recover target gases (the same gas as the target gas) by increasing or decreasing the pressure of the adsorption towers 11, 12, and 13, or can separate target gases that are difficult to adsorb by the adsorbent 14 (gases different from the target gas) and recover target gases. Examples of the adsorbent 14 include activated carbon, silica gel, zeolite, molecular sieving carbon, mesoporous silica, metal-organic frameworks (MOFs), and porous coordination polymers (PCPs), and are selected appropriately depending on the target gas.

[0019] The recovery device 10 is connected to a duct 16 through which exhaust gas from a combustion device 15 flows. The combustion device 15 is a device that produces high-temperature gas for heating or simply burns gas, and examples of such a device include a boiler and an incinerator. In this embodiment, the recovery device 10 will be described using carbon dioxide as a target gas as an example. When the combustion device 15 is operating, it supplies a substantially constant flow rate of exhaust gas to the duct 16. The duct 16 is a pipe through which the exhaust gas passes, including a flue.

[0020] A first blower 17 is disposed in the duct 16. The first blower 17 is exemplified by a compressor or a blower. A buffer tank 18 is disposed in the duct 16 between the combustion device 15 and the first blower 17. The buffer tank 18 is a tank for storing exhaust gas from the combustion device 15, and reduces the effect of pressure fluctuations in the recovery device 10 on the combustion device 15.

[0021] The duct 16 downstream of the first blower 17 branches into three supply pipes 19, 20, and 21, which are connected to the adsorption towers 11, 12, and 13, respectively. When the first blower 17 is activated, the exhaust gas flowing through the duct 16 is sent to the adsorption towers 11, 12, and 13 through the supply pipes 19, 20, and 21.

[0022] A desorption tube 22, through which the target gas desorbed from the adsorbent 14 flows, is connected to the adsorption towers 11, 12, and 13. When a vacuum pump 23 arranged in the desorption tube 22 is activated, the pressure in the adsorption towers 11, 12, and 13 is reduced, and the target gas desorbed from the adsorbent 14 is introduced into the desorption tube 22.

[0023] A cleaning pipe 24 is connected to the adsorption towers 11, 12, and 13. A recovery tank 25 is connected to the desorption pipe 22 downstream of the vacuum pump 23 and the cleaning pipe 24. The recovery tank 25 stores the target gas desorbed from the adsorbent 14. A liquefier 26 connected to the recovery tank 25 is a device that liquefies the target gas to reduce its volume.

[0024] Of the exhaust gases sent to the adsorption towers 11, 12, and 13 through the supply pipes 19, 20, and 21, the gases that have not been adsorbed by the adsorbent 14 are exhausted through a first exhaust pipe 27. Of the gases sent to the adsorption towers 11, 12, and 13 through the cleaning pipe 24, the gases that have not been adsorbed by the adsorbent 14 are exhausted through a second exhaust pipe 28.

[0025] The inlet pipes 29 connected to the adsorption towers 11, 12, and 13 are pipes through which gas flows to be introduced into the adsorption towers 11, 12, and 13 to raise the pressure in the adsorption towers 11, 12, and 13 to atmospheric pressure or higher. In this embodiment, the gas flowing through the inlet pipe 29 is atmospheric air. A dehumidifying unit 30 that removes water from the gas is disposed in the inlet pipe 29. The dehumidifying unit 30 removes water vapor contained in the gas that passes through the inlet pipe 29 and reaches the adsorbent 14. Examples of the dehumidifying unit 30 include a dehumidifier filled with an adsorbent (dehumidifying agent) that adsorbs water, a membrane air dryer, and a refrigerated air dryer.

[0026] The switching device 31 includes valves 32-49 and a control device (not shown). The valves 32-49 operate upon receiving electrical signals from the control device. The switching device 31 opens and closes the valves 32-49 to switch the adsorption and desorption states of the adsorption towers 11, 12, and 13. The valves 32, 33, and 34 are disposed in the supply pipes 19, 20, and 21, respectively. The valves 35, 36, and 37 are disposed in the desorption pipe 22. The valves 38, 39, and 40 are disposed in the cleaning pipe 24. The valves 41, 42, and 43 are disposed in the first exhaust pipe 27. The valves 44, 45, and 46 are disposed in the second exhaust pipe 28. The valves 47, 48, and 49 are disposed in the inlet pipe 29.

[0027] The operation of the recovery system 10 will be described with reference to Figures 1 and 2. Figure 2 is a table showing the passage of time and the operations performed in the adsorption towers 11, 12, and 13. The switching device 31 opens and closes valves 32-49 so that the operations of adsorption, cleaning, desorption, and pressure recovery are repeated in each of the adsorption towers 11, 12, and 13 in that order. In Figure 2, the adsorption tower 11 is represented as "adsorption tower 1" or "1," the adsorption tower 12 as "adsorption tower 2" or "2," and the adsorption tower 13 as "adsorption tower 3" or "3," with 1-6 indicating the passage of time. The operations are repeated, with times 1-6 being one cycle. During the adsorption, cleaning, desorption, and pressure recovery operations, the first blower 17 and the vacuum pump 23 are always operating.

[0028] At "Time 1" shown in Figure 2, an adsorption operation is performed in adsorption tower 11, a cleaning operation is performed in adsorption tower 12, and a desorption operation is performed in adsorption tower 13. During the adsorption operation, switching device 31 opens valves 32 and 41 and closes valves 33, 34, 35, 38, 44, and 47. Exhaust gas is supplied to adsorption tower 11 by first blower 17, and the pressure in adsorption tower 11 increases. The target gas (carbon dioxide) is adsorbed by adsorbent 14 contained in adsorption tower 11, and gas not adsorbed by adsorbent 14 is discharged outside adsorption tower 11 through first exhaust pipe 27. A state in which adsorption tower 11 is pressurized during the adsorption operation and the pressure in adsorption tower 11 is higher than atmospheric pressure is referred to as a first state.

[0029] In the cleaning operation, the switching device 31 opens the valves 39 and 45 and closes the valves 36, 40, 42, and 48. A portion of the target gas in the recovery tank 25 is introduced into the adsorption tower 12 through the cleaning pipe 24. The gas that has not been adsorbed by the adsorbent 14 is discharged to the outside of the adsorption tower 12 through the second exhaust pipe 28 by the target gas introduced into the adsorption tower 12.

[0030] During the desorption operation, the switching device 31 opens the valve 37 and closes the valves 43, 46, and 49. The adsorption tower 13 is depressurized by the vacuum pump 23, and the pressure in the adsorption tower 13 decreases. The target gas adsorbed by the adsorbent 14 contained in the adsorption tower 13 is desorbed, and the target gas passes through the desorption tube 22 and is recovered in the recovery tank 25. During the desorption operation, the pressure in the adsorption tower 13 is in a negative pressure state below atmospheric pressure. The state in which the adsorption tower 13 is depressurized during the desorption operation and is in a negative pressure state is referred to as the second state.

[0031] At "Time 2," adsorption operation continues in adsorption tower 11, desorption operation is performed in adsorption tower 12, and pressure recovery operation is performed in adsorption tower 13. During the desorption operation, switching device 31 opens valve 36 and closes valves 42, 45, and 48. The vacuum pump 23 depressurizes adsorption tower 12, and the pressure in adsorption tower 12 decreases. The target gas adsorbed by the adsorbent 14 contained in adsorption tower 12 is desorbed, and the target gas passes through desorption tube 22 and is recovered in recovery tank 25.

[0032] In the prior art (Patent Document 1), an adsorption tower after a desorption operation is connected to an adsorption tower after an adsorption operation, and a pressure equalization operation is performed to reduce the pressure difference between the adsorption towers. However, because the difference between the pressure in the adsorption tower 13 after the desorption operation and atmospheric pressure is large, even if the pressurized adsorption tower after the adsorption operation is connected to the adsorption tower 13, the pressure increase in the adsorption tower 13 after the pressure equalization operation is insufficient.

[0033] In contrast, during the pressure recovery operation, the switching device 31 opens valve 49 and closes valves 37, 39, 40, 43, and 46. Due to the pressure difference between the negative pressure in the adsorption tower 13 and atmospheric pressure, atmospheric air is introduced into the adsorption tower 13, which is in a negative pressure state, through the inlet pipe 29. As a result, the pressure in the adsorption tower 13 becomes 50 kPa (absolute pressure) or higher, nearly equal to atmospheric pressure. The pressure recovery operation allows the pressure in the adsorption tower 13 to be higher than that achieved by the pressure equalization operation of the prior art. The state of the adsorption tower 13 during the pressure recovery operation is referred to as the third state.

[0034] During the pressure recovery operation, moisture in the atmosphere is removed by the dehumidifying unit 30 disposed in the inlet pipe 29, thereby reducing the amount of water in the atmosphere adsorbed onto the adsorbent 14 contained in the adsorption tower 13. Since it is possible to prevent the amount of adsorption of the target gas from decreasing due to the influence of water adsorbed onto the adsorbent 14, it is possible to ensure the amount of adsorption of the target gas by the adsorbent 14.

[0035] At "time 3," an adsorption operation is performed in the adsorption tower 13. During the adsorption operation, the switching device 31 opens valves 34 and 43 and closes valves 32, 33, 37, 40, 46, and 49. The adsorption tower 13 and the combustion device 15 are connected via the first blower 17 disposed in the duct 16. However, since the pressure in the adsorption tower 13, for which the pressure recovery operation has been performed, is approximately equal to atmospheric pressure, the pressure drop inside the combustion device 15 can be reduced.

[0036] Furthermore, since pressure fluctuations in the combustion device 15 can be reduced when the adsorption tower 13 and the combustion device 15 are connected via the first blower 17, it is possible to reduce the size of the buffer tank 18 that alleviates pressure fluctuations in the recovery device 10. It is also possible to omit the buffer tank 18 by setting the pressure and conditions of each part of the recovery device 10.

[0037] At "time 3", a cleaning operation is further performed in the adsorption tower 11, and a desorption operation is subsequently performed in the adsorption tower 12. The operation of the switching device 31 during the cleaning operation and desorption operation at time 3 is similar to the operation of the switching device 31 during the cleaning operation and desorption operation at time 1, and therefore a description thereof will be omitted.

[0038] As described above, the recovery system 10 introduces air into the adsorption tower 13 to enter a third state before transitioning from a second state in which the adsorption tower 13 is depressurized by the vacuum pump 23 and the target gas is desorbed by the adsorbent 14 to a first state in which the first blower 17 supplies exhaust gas to the adsorption tower 13 and the target gas is adsorbed by the adsorbent 14. This ensures that the pressure in the adsorption tower 13 rises sufficiently immediately after transitioning to the first state (at the start of the adsorption operation). Since combustion in the combustion device 15 connected to the recovery system 10 is stabilized, the flame in the combustion device 15 does not become smaller or go out.

[0039] A second embodiment will be described with reference to Figure 3. In the first embodiment, a case where the pressure in the adsorption tower 13 during the pressure recovery operation is increased to approximately atmospheric pressure is described. In contrast, in the second embodiment, a case where the pressure in the adsorption tower 13 during the pressure recovery operation is increased to an even higher pressure is described. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted (the same applies to Figures 4 to 7).

[0040] 3 is a piping diagram of a recovery device 50 according to the second embodiment. The recovery device 50 includes dehumidifying sections 51, 52, and 53 provided inside the adsorption towers 11, 12, and 13, respectively. The dehumidifying sections 51, 52, and 53 are filled with a dehumidifying agent that adsorbs water. Examples of the dehumidifying agent include calcium chloride and silica gel. The dehumidifying agent used has a water adsorption capacity greater than that of the adsorbent 14 at the same partial pressure.

[0041] During the pressure recovery operation, the air flowing from the inlet pipe 29 toward the adsorption towers 11, 12, and 13 passes through the dehumidifying units 51, 52, and 53 and reaches the adsorbent 14, so that moisture in the air is adsorbed by the dehumidifying units 51, 52, and 53. Since the amount of water in the air adsorbed by the adsorbent 14 can be reduced, the amount of adsorption of the target gas by the adsorbent 14 can be ensured. Furthermore, because the dehumidifying units 51, 52, and 53 are provided inside the adsorption towers 11, 12, and 13, the space required for providing the dehumidifying units outside the adsorption towers 11, 12, and 13 can be saved.

[0042] The adsorbent 14 and dehumidifying sections 51, 52, 53 are arranged inside the adsorption towers 11, 12, 13 so that the exhaust gas reaches the dehumidifying sections 51, 52, 53 while the target gas and water vapor are sequentially adsorbed onto the adsorbent 14 during the adsorption operation. Because the water vapor concentration of the exhaust gas is low when it passes through the dehumidifying sections 51, 52, 53, the water adsorbed in the dehumidifying sections 51, 52, 53 during the pressure recovery operation is desorbed during the adsorption operation. Because the dehumidifying agents in the dehumidifying sections 51, 52, 53 are regenerated during the adsorption operation, the amount of water adsorbed by the dehumidifying agents during the pressure recovery operation can be ensured.

[0043] The second blower 54 disposed in the inlet pipe 29 operates only during the pressure recovery operation. When the second blower 54 operates, the adsorption towers 11, 12, and 13 are pressurized by the gas supplied through the inlet pipe 29. As a result, the pressure in the adsorption towers 11, 12, and 13 during the pressure recovery operation becomes equal to or higher than atmospheric pressure. The pressure in the adsorption towers 11, 12, and 13 at this time can be set to approximately the same as the pressure in the adsorption towers 11, 12, and 13 during the adsorption operation, for example.

[0044] If the pressure in the adsorption tower 13, which has undergone a pressure recovery operation at time 2 (see FIG. 2 ), is increased by the second blower 54 to approximately the same pressure as during the adsorption operation, fluctuations in pressure on the discharge side of the first blower 17 can be reduced when the adsorption operation is performed in the adsorption tower 13 at time 3. As a result, even when the first blower 17 is operated at a substantially constant rotation speed, the adsorption operation can be performed in the adsorption tower 13 immediately after time 3. Because the pressure fluctuations are small, the buffer tank 18 (see FIG. 1 ), which reduces pressure fluctuations, can be made smaller or omitted. Therefore, the space occupied by the recovery device 50 can be reduced by the space occupied by the buffer tank 18.

[0045] The concentration of the target gas in the atmosphere introduced into the adsorption tower 13 during the pressure recovery operation is much lower than the concentration of the target gas in the exhaust gas, and the adsorption capacity of the adsorbent 14 for components other than the target gas in the atmosphere is much smaller than the adsorption capacity of the adsorbent 14 for the target gas. Therefore, even if the pressure in the adsorption tower 13 during the pressure recovery operation is approximately the same as the pressure during the adsorption operation, the effect of the atmosphere introduced into the adsorption tower 13 during the pressure recovery operation on the amount of adsorption of the target gas during the adsorption operation can be reduced.

[0046] A third embodiment will be described with reference to Fig. 4. In the first and second embodiments, a dehumidifying unit is provided to remove water from the air introduced during the pressure recovery operation. In contrast, in the third embodiment, a case will be described in which air whose moisture content has been reduced outside the recovery device 60 is introduced during the pressure recovery operation.

[0047] 4 is a piping diagram of a recovery device 60 according to a third embodiment. In the recovery device 60, an inlet pipe 29 is connected to a liquefier 26, and exhaust gas from the liquefier 26 is supplied to the inlet pipe 29. The liquefier 26 is equipped with a dehumidifier for reducing moisture content mixed in the liquefied target gas, and the exhaust gas from the liquefier 26 contains dry air in which atmospheric moisture has been reduced by operating the dehumidifier. The dry air (atmospheric air) discharged from the liquefier 26 is supplied to the adsorption towers 11, 12, and 13 through the inlet pipe 29 during the pressure recovery operation, so that a dehumidification unit for removing atmospheric moisture can be omitted.

[0048] A fourth embodiment will be described with reference to Fig. 5. In the second embodiment, the second blower 54, which sends gas to the adsorption towers 11, 12, and 13 during the pressure recovery operation, reduces pressure fluctuations on the discharge side of the first blower 17 when switching from the pressure recovery operation to the adsorption operation. In contrast, in the fourth embodiment, a bypass pipe 71 is provided that bypasses the suction side and discharge side of the first blower 17, thereby reducing pressure fluctuations on the discharge side of the first blower 17 when switching from the pressure recovery operation to the adsorption operation.

[0049] 5 is a piping diagram of a recovery device 70 according to a fourth embodiment. The recovery device 70 includes a bypass pipe 71 that bypasses the suction side and discharge side of the first blower 17, a first control valve 72 disposed in the bypass pipe 71, and a first pressure gauge 73 disposed on the suction side of the first blower 17. The reason why the pressure on the suction side of the first blower 17 is detected by the first pressure gauge 73 is that the pressure on the suction side of the first blower 17 changes less than the pressure on the discharge side of the first blower 17, which changes significantly as the adsorption operation progresses through the initial, middle, and final stages, even when the first blower 17 is operated at a constant rotation speed.

[0050] The bypass pipe 71 connects the suction side and discharge side of the first blower 17, and since the pressure on the discharge side of the first blower 17 is positive, when the first control valve 72 is open, the pressure (negative pressure) on the suction side of the first blower 17 can be made closer to atmospheric pressure.

[0051] When time 2 (see FIG. 2 ) changes to time 3, when time 4 changes to time 5, and when time 6 changes to time 1, one of the adsorption towers 11, 12, and 13 switches from pressure recovery operation to adsorption operation, causing fluctuations in the pressure on the discharge side of the first blower 17. Along with the fluctuations in the pressure on the discharge side of the first blower 17, the pressure on the suction side of the first blower 17 detected by the first pressure gauge 73 changes.

[0052] Because the switching device 31 adjusts the opening of the first adjustment valve 72 based on the pressure detected by the first pressure gauge 73, even when the first blower 17 is operated at a substantially constant rotation speed, it is possible to adjust the pressure on the suction side of the first blower 17 and reduce fluctuations in pressure on the discharge side of the first blower 17. Since the buffer tank 18 (see FIG. 1) that reduces pressure fluctuations can be made smaller or omitted, the space occupied by the recovery device 70 can be reduced.

[0053] A fifth embodiment will be described with reference to Fig. 6. In the fourth embodiment, a bypass pipe 71 is provided to bypass the suction side and discharge side of the first blower 17, and pressure fluctuations on the discharge side of the first blower 17 are reduced when switching from pressure recovery operation to adsorption operation. In contrast, in the fifth embodiment, a second control valve 82 is provided on the discharge side of the first blower 17, and pressure fluctuations are reduced.

[0054] 6 is a piping diagram of a recovery device 80 according to the fifth embodiment. The recovery device 80 includes a second pressure gauge 81 disposed on the suction side of the first blower 17 and a second control valve 82 disposed on the discharge side of the first blower 17.

[0055] When time 2 (see FIG. 2 ) changes to time 3, when time 4 changes to time 5, and when time 6 changes to time 1, one of the adsorption towers 11, 12, and 13 switches from pressure recovery operation to adsorption operation, causing the pressure on the discharge side of the first blower 17 to fluctuate, and accordingly, the pressure on the suction side of the first blower 17 connected via the first blower 17 to fluctuate.

[0056] Because the switching device 31 adjusts the opening of the second control valve 82 based on the pressure detected by the second pressure gauge 81, it is possible to reduce pressure fluctuations on the discharge side of the first blower 17 even when the first blower 17 is operated at a substantially constant rotation speed. Since the buffer tank 18 (see FIG. 1) that reduces pressure fluctuations can be made smaller or omitted, the space occupied by the recovery device 80 can be reduced.

[0057] A sixth embodiment will be described with reference to Fig. 7. In the first to fifth embodiments, the first blower 17 is operated at a substantially constant rotation speed. In contrast, the sixth embodiment describes a case in which the rotation speed of the first blower 17 is adjusted to reduce fluctuations in pressure on the discharge side of the first blower 17 when switching from pressure recovery operation to adsorption operation.

[0058] 7 is a piping diagram of a recovery device 90 according to the sixth embodiment. The recovery device 90 includes a third pressure gauge 91 disposed on the suction side of the first blower 17. When time 2 (see FIG. 2 ) changes to time 3, when time 4 changes to time 5, or when time 6 changes to time 1, one of the adsorption towers 11, 12, and 13 switches from pressure recovery operation to adsorption operation, causing the pressure on the discharge side of the first blower 17 to fluctuate, and accordingly, the pressure on the suction side of the first blower 17 connected via the first blower 17 to fluctuate.

[0059] The switching device 31 adjusts the rotation speed of the first blower 17 based on the pressure on the suction side of the first blower 17 detected by the third pressure gauge 91. This reduces fluctuations in pressure on the discharge side of the first blower 17, making it possible to reduce the size or eliminate the buffer tank 18 (see FIG. 1) that reduces pressure fluctuations. As a result, the space occupied by the recovery device 90 can be reduced.

[0060] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0061] For example, the piping system of the recovery device 10 is an example and can be set as appropriate. In the embodiment, the recovery device 10 is described as having three adsorption towers 11, 12, and 13, but this is not necessarily limited to this. The number of adsorption towers can be set to one or more as appropriate.

[0062] In the embodiment, the recovery device 10 is described as sequentially performing the adsorption operation, the cleaning operation, the desorption operation, and the pressure recovery operation, but this is not necessarily limited to this. For example, it is of course possible to omit the cleaning operation. By omitting the cleaning operation, it is not necessary to return a portion of the target gas recovered in the recovery tank 25 to the adsorption towers 11, 12, and 13, and therefore the recovery rate of the target gas can be improved.

[0063] In the second embodiment, the second blower 54 is disposed in the inlet pipe 29, but it is possible to omit the second blower 54. In this case, the dehumidifying units 51, 52, and 53 are provided inside the adsorption towers 11, 12, and 13, and therefore the space occupied by the dehumidifying units provided outside the adsorption towers 11, 12, and 13 can be eliminated.

[0064] In the third embodiment, a pipe for introducing atmospheric air may be connected to the introduction pipe 29, or dry gas discharged from another device may be supplied to the introduction pipe 29. It is desirable to provide a dehumidifying unit in the pipe for introducing atmospheric air.

[0065] In the fourth to sixth embodiments, it is of course possible to replace the dehumidifying unit 30 with dehumidifying units 51, 52, and 53 provided inside the adsorption towers 11, 12, and 13. Furthermore, it is of course possible to provide a second blower 54 in the inlet pipe 29 in the fourth to sixth embodiments.

[0066] 10, 50, 60, 70, 80, 90 Recovery device 11, 12, 13 Adsorption tower 14 Adsorbent 15 Combustion device 16 Duct 17 First blower 23 Vacuum pump 30, 51, 52, 53 Dehumidification section 31 Switching device 54 Second blower 71 Bypass pipe 72 First control valve 73 First pressure gauge 81 Second pressure gauge 82 Second control valve 91 Third pressure gauge

Claims

1. A recovery device comprising: a first blower arranged in a duct through which exhaust gas from a combustion device flows; an adsorption tower containing an adsorbent and to which the exhaust gas is supplied by the first blower; a vacuum pump that depressurizes the adsorption tower; and a switching device that switches between a first state in which the first blower supplies the exhaust gas to the adsorption tower and the adsorbent adsorbs the target gas, and a second state in which the adsorption tower is depressurized by the vacuum pump and the adsorbent desorbs the target gas, wherein the switching device introduces air into the adsorption tower to bring it into a third state before changing from the second state to the first state.

2. A recovery system according to claim 1, wherein in the third state, the pressure in the adsorption tower into which the atmosphere is introduced is set to 50 kPa or more.

3. A recovery system according to claim 1, wherein in the third state, the pressure in the adsorption tower into which the atmosphere has been introduced is made equal to or higher than atmospheric pressure.

4. A recovery device according to claim 1, further comprising a dehumidifying section for removing water, wherein the air passes through the dehumidifying section and reaches the adsorbent contained in the adsorption tower.

5. A recovery device according to claim 4, wherein the dehumidifying section is provided inside the adsorption tower and contains a dehumidifying agent that adsorbs water.

6. A recovery system according to any one of claims 1 to 5, further comprising a second blower for supplying the gas to the adsorption tower.

7. A recovery device as described in any one of claims 1 to 5, comprising: a bypass pipe that bypasses the suction side and discharge side of the first blower; a first control valve arranged in the bypass pipe; and a first pressure gauge arranged on the suction side of the first blower, wherein the switching device adjusts the opening degree of the first control valve based on the pressure detected by the first pressure gauge.

8. A recovery device as described in any one of claims 1 to 5, comprising: a second pressure gauge arranged on the suction side of the first blower; and a second control valve arranged on the discharge side of the first blower, wherein the switching device adjusts the opening of the second control valve based on the pressure detected by the second pressure gauge.

9. A recovery device as described in any one of claims 1 to 5, further comprising a third pressure gauge arranged on the suction side of the first blower, and the switching device adjusts the rotation speed of the first blower based on the pressure detected by the third pressure gauge.

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