Gas treatment method

Abstract

The present invention provides a method that enables efficient decomposition of N2O contained in a treatment target gas containing CO2 and N2O.　This method comprises: a step (a) for passing a treatment target gas, which contains CO2 and N2O and in which the CO2 concentration is 3% or more, through a first adsorbent having adsorptivity with respect to CO2 at a level more dominant than that with respect to N2O; a step (b) for accumulating a first gas itself which has passed through the first adsorbent and which contains N2O at a concentration higher than that of the treatment target gas, or accumulating N2O contained in the first gas; and a step (c) for decomposing the gas accumulated in said step (b). Said step (c) is for feeding the gas accumulated in said step (b) into a decomposition space formed of an ultraviolet ray irradiation region and / or a region in which plasma is formed.

Description

Gas Treatment Method

[0001] The present invention relates to a gas treatment method, and more particularly to a method for treating a gas containing a mixture of carbon dioxide (CO2) and nitrous oxide (N2O).

[0002] Since the Industrial Revolution, the average temperature of the Earth has been rising, making global warming a pressing issue. Greenhouse gases known to cause global warming include CO2, methane (CH4), N2O, and chlorofluorocarbons. Of these gases, CO2 is the most abundant, followed by CH4, and then N2O.

[0003] On the other hand, when we look at the global warming potential (GWP), it has been reported that the GWP of CH4 is 25 times that of CO2, and that of N2O is 298 times that of CO2. For these reasons, the impact of N2O emissions on global warming cannot be ignored.

[0004] As a method for reducing NO emissions, for example, Patent Document 1 listed below discloses a technology in which exhaust gas containing NO emitted from an engine is irradiated with ultraviolet laser light from an excimer laser device to decompose the NO.

[0005] Japanese Patent Application Laid-Open No. 2021-088964

[0006] NO is emitted, for example, during the management of farm soil and livestock waste, the incineration of waste, and the treatment of wastewater. When NO is generated by microorganisms, the composition of the emitted gas is mostly atmospheric components, and NO is often present in low concentrations of around several tens of ppm. On the other hand, NO is also found in the exhaust gas when organic matter is incinerated. In this case, the composition of the emitted gas is around several hundred ppm of NO, and also contains high concentrations of CO derived from combustion.

[0007] In consideration of irradiating a gas to be treated with ultraviolet light to decompose NO, it is expected that the energy efficiency of decomposing NO will be extremely low if the concentration of NO contained in the gas to be treated is low. That is, as described in Patent Document 1, when irradiating the gas to be treated with excimer laser light, the irradiation dose of the excimer laser light must be extremely high. This means that the amount of energy required to decompose the NO contained in the gas to be treated, in other words, the amount of power input to the excimer laser light source, will increase, which raises concerns about an increase in CO2 emissions due to the increased power consumption.

[0008] In other words, even though the treatment is carried out with the aim of decomposing the NO contained in the gas to be treated from the viewpoint of curbing global warming, the treatment may induce an increase in emissions of CO, a greenhouse gas. Therefore, for gas to be treated that contains a low concentration of NO, the method of irradiating the gas with ultraviolet light with the aim of decomposing NO from the viewpoint of preventing global warming cannot be said to be effective.

[0009] One method for efficiently decomposing N2O contained in a gas to be treated at low concentrations is to adsorb N2O from the gas to be treated to increase its concentration, and then decompose the N2O.

[0010] One method for concentrating NO involves passing the gas to be treated through an adsorbent to temporarily adsorb NO onto the adsorbent, and then desorbing the NO from the adsorbent with a certain amount of NO adsorbed. This method makes it possible to make the concentration of NO contained in the desorbed gas higher than that of NO contained in the gas to be treated. Therefore, it appears that photodecomposition of NO by irradiating the desorbed gas with, for example, ultraviolet light may improve the efficiency of NO decomposition compared to direct irradiation of ultraviolet light on the gas to be treated.

[0011] However, as described above, when the gas to be treated is passed through an adsorbent to adsorb the NO contained in the gas, the adsorbent may adsorb not only NO but also CO. For example, the CO concentration in exhaust gas from incineration may be as high as more than 10%, and in such cases, much of the adsorbent is used to adsorb CO. Therefore, it is difficult to say that the adsorbent itself is being used effectively.

[0012] Furthermore, when recovering the adsorbed NO, heat is applied to the adsorption material, but more CO is recovered than the amount of NO. In other words, most of the input thermal energy is consumed in recovering CO, which poses a problem in terms of effective energy utilization from the perspective of the original NO recovery.

[0013] As described above, even if a method of concentrating the gas to be treated by passing it through an adsorbent is adopted, it is difficult to efficiently increase the concentration of NO contained in the gas to be treated, and as a result, the effect of improving the decomposition efficiency of NO can be said to be extremely limited.

[0014] In view of the above problems, an object of the present invention is to provide a method that enables efficient decomposition of N2O contained in a gas to be treated that contains CO2 and N2O.

[0015] The gas treatment method according to the present invention comprises the steps of: (a) sending a gas to be treated, which contains CO2 and N2O and has a CO2 concentration of 3% or more, to a first adsorbent, which is an adsorbent having a dominant adsorption property for CO2 compared to N2O; (b) collecting the first gas itself, which has passed through the first adsorbent and contains N2O at a higher concentration than the gas to be treated, or the N2O contained in the first gas; and (c) decomposing the gas collected in the step (b), wherein the step (c) includes a step of sending the gas collected in the step (b) into a decomposition space formed by at least one of an ultraviolet ray irradiation region and a plasma generation region.

[0016] When decomposing a gas to be treated that contains CO2 and N2O, even if the gas is directly decomposed to decompose CO2 and N2O at the same time without pre-treatment, the decomposition will involve a gas that contains a relatively large amount of CO2, resulting in wasted energy.

[0017] Therefore, in the above-described method, an adsorbent (first adsorbent) having a dominant adsorption property for CO compared to NO is disposed at the destination of the gas to be treated, and the gas to be treated is collected after passing through the first adsorbent. Note that the gas that has passed through the first adsorbent is hereinafter referred to as the "first gas."

[0018] In other words, according to the above method, the gas (first gas) after CO2 contained in the gas to be treated has been removed by the first adsorbent is accumulated, so that it is possible to generate a gas containing NO from the gas to be treated from which CO2 has been removed or reduced. That is, the accumulated gas contains a higher concentration of NO than the gas to be treated. In the following description, the term "reducing" may be used to refer to both the complete removal of a substance contained in a gas and the partial removal of the substance.

[0019] The accumulated gas is decomposed in step (c). When performing step (c), for example, at least one of an excimer lamp using a dielectric barrier discharge and an atmospheric pressure plasma generation device can be used.

[0020] The first adsorbent used in the gas treatment method, which is an adsorbent having predominant adsorption properties for CO compared to NO, can typically be an amine-based material. The amine-based material refers to an amine compound having one or more primary, secondary, or tertiary amino groups. There are no particular limitations on the amine compound as long as it has carbon dioxide absorption properties, and it can be used alone or as a mixture.

[0021] Examples of amine compounds that can be contained in the amine material include primary amines such as monoethanolamine, 2-amino-2-methyl-1-propanol, and phenylethylamine; secondary amines such as diethanolamine, 2-methylaminoethanol, and 2-ethylaminoethanol; diamines such as ethylenediamine, N,N-dimethylethylenediamine, ortho-xylylenediamine, meta-xylylenediamine, and para-xylylenediamine; triamines such as diethylenetriamine; and benzylamines such as benzylamine, para-methoxybenzylamine, and para-trifluoromethylbenzylamine.

[0022] The first adsorbent may be installed in any manner. For example, an adsorption tower (first adsorption tower) containing the first adsorbent may be installed between a gas supply source of the gas to be treated and a region where the gas accumulation step (b) is performed (referred to here as the "accumulation region"). In this case, the gas supply source and the first adsorption tower are connected by a pipe, and the first adsorption tower and the accumulation region are connected by a pipe. In another embodiment, the first adsorbent may be filled in a portion of the pipe connecting the gas supply source and the accumulation region. In this case, it is preferable that the pipe filled with the first adsorbent is connected to pipes before and after it with joints so that the desorption step of the first adsorbent can be performed.

[0023] In the gas treatment method according to the present invention, the source of the gas to be treated containing CO2 and NO can be any. For example, in a combustion plant, NO concentrations are as high as several hundred ppm, and CO2 concentrations are also high, exceeding 10%. On the other hand, in a low-concentration emission source, the gas to be treated can be the gas after concentrating NO. In this case, the concentration technology will not be described in detail, but adsorption methods are generally well known. In this method, a material that adsorbs CO2 along with NO is used, and the adsorbed NO and CO2 can be used as the gas to be treated.

[0024] The gas components to be accumulated in step (b) include NO and other gases such as oxygen and nitrogen, with CO2 removed from the gas to be treated by the first adsorbent. A certain amount of this gas may simply be accumulated, and then in step (c) the gas may be sent to an area irradiated with ultraviolet light and an area where plasma is formed, where it is decomposed. Until a certain amount is accumulated, ultraviolet irradiation and plasma formation are not required, which allows power consumption to be limited.

[0025] The step (b) may be a step of supplying the first gas to a second adsorbent containing zeolite as a main component, thereby accumulating N2O contained in the first gas at the center.

[0026] The constituent material of the second adsorbent exhibits the property of adsorbing CO2 as well as NO. However, if CO2 has already been completely removed by performing step (a), only NO gas among the gas components to be accumulated in step (b) can be selectively accumulated. By desorbing the accumulated NO gas from the zeolite, an ultra-high concentration gas containing NO as the main component can be achieved. In this way, an adsorbent material may be used in the accumulation step (b) to provide an auxiliary function to gas accumulation.

[0027] In this way, improving the NO component ratio in the gas by devising a gas collection method means nothing but reducing the amount of gas flowing into the area (decomposition space) where step (c) is performed, which contributes to space savings by reducing the number of ultraviolet and plasma driving devices, extending the device life by reducing driving time, and reducing the size of piping and processing equipment by reducing the amount of gas flowing in.

[0028] The gas treatment method may include a step (d) of desorbing the adsorbed substance adsorbed by the first adsorbent, and when the step (d) is performed, the step (b) may be controlled so as not to be performed on the gas discharged from the first adsorbent.

[0029] Step (d) corresponds to a step of regenerating the first adsorbent. For example, step (d) can be performed using a method including at least one of heating the first adsorbent and creating a negative pressure in the region (adsorption tower) where the first adsorbent is housed. When the first adsorbent is regenerated, the adsorbed CO2 is released. This CO2 is not required for performing steps (b) and (c). Therefore, as described above, it is preferable to control step (b) so that the gas discharged from the first adsorbent in association with the execution of desorption step (d) is not subjected to step (b). Specifically, a method can be employed in which an on-off valve is provided on the path of the piping through which the gas discharged from the first adsorbent flows, and the piping is isolated from the region (accumulation region) where accumulation step (b) is performed by controlling this valve.

[0030] The gas treatment method may include a step (e) of releasing the gas accumulated in the step (b), and the step (c) may be performed only during the time period when the step (e) is being performed.

[0031] When step (b) is a step of accumulating gas in a second adsorbent in a gas accumulation tower constituting an accumulation region, step (e) can be a method including at least one of heating the second adsorbent and creating a negative pressure in the gas accumulation tower. During step (e), the adsorbed NO is released and becomes the target for decomposition in the subsequent step (c). In other words, this method can decompose NO after increasing the concentration of NO in the gas to be treated, significantly reducing the energy required for decomposition and improving decomposition efficiency. This can be expected to improve the operating efficiency of the decomposition device and extend the operating life of the device.

[0032] A plurality of first adsorption towers each containing the first adsorbent may be prepared. In this case, the step (a) may include a step (a1) of switching the first adsorption tower as a destination of the gas to be treated, the step (a1) being a step of switching the destination of the gas to be treated to a first adsorption tower that has adsorption capacity reserve and that was not a destination of the gas to be treated until immediately before the upper limit of adsorption performance of the first adsorbent contained in the first adsorption tower as a destination of the gas to be treated reaches the upper limit, and the step (d) may be performed with the first adsorption tower, from which the introduction of the gas to be treated has been stopped in the step (a1), disconnected from equipment in which the step (b) is performed.

[0033] According to the above method, after the CO adsorption performance of the first adsorbent housed in one first adsorption tower reaches its limit, the CO in the gas to be treated can be adsorbed using the first adsorbent housed in another first adsorption tower. This makes it possible to continuously adsorb the CO contained in the gas to be treated and regenerate the first adsorbent, and also to always use the gas that has passed through the first adsorbent that exhibits high adsorption performance as the gas to be accumulated in step (b).

[0034] A plurality of gas accumulation towers each containing the second adsorbent may be prepared. In this case, the step (b) may include a step (b1) of switching the gas accumulation tower as the destination of the first gas, the step (b1) being a step of switching the destination of the first gas to a gas accumulation tower that has adsorption capacity and that was not a destination of the first gas until immediately before the adsorption performance of the second adsorbent contained in the gas accumulation tower as the destination of the first gas reaches an upper limit, and the step (c) may be performed on the gas accumulated in the gas accumulation tower from which introduction of the first gas has been stopped in the step (b1).

[0035] According to the above method, after the NO adsorption capacity of the second adsorbent housed in one gas collection tower reaches its limit, the NO in the gas (first gas) that has passed through the first adsorbent can be adsorbed using the second adsorbent housed in another gas collection tower. This allows for continuous adsorption of NO contained in the first gas and regeneration of the second adsorbent, and ensures that the gas that has passed through the second adsorbent, which always exhibits high adsorption capacity, is the gas to be decomposed in step (c). In other words, even if NO gas continuously flows in from the first adsorption tower, the gas collection tower can always accept it. Similarly, according to the above method, the rate at which a gas containing a high concentration of NO is produced from the gas to be treated can be increased.

[0036] The present invention may be configured so that a plurality of treatment systems each including the first adsorption tower, the gas accumulation tower disposed downstream of the first adsorption tower, and a decomposition device disposed downstream of the gas accumulation tower are provided. In this case, the steps (a) and (b) may be steps of simultaneously or alternately passing the gas to be treated through the first adsorption towers of the plurality of treatment systems.

[0037] According to the present invention, it is possible to efficiently decompose N2O contained in a gas to be treated that contains CO2 and N2O.

[0038] 12. It is a block diagram showing typically an example of a gas processing system capable of executing an embodiment of a gas processing method according to the present invention. It is a flowchart showing typically an execution procedure of an embodiment of a gas processing method according to the present invention. It is a flowchart showing typically an execution procedure of an embodiment of a gas processing method according to the present invention. It is a cross-sectional view showing typically an example of the configuration of a decomposition tower. It is a schematic side view of an excimer lamp constituting a decomposition device. It is a schematic cross-sectional view of the excimer lamp shown in FIG. 5 taken along line A1-A1. It is a schematic cross-sectional view of an excimer lamp having a different structure constituting a decomposition device. It is a schematic plan view of an excimer lamp having a different structure constituting a decomposition device. It is a schematic cross-sectional view of the excimer lamp shown in FIG. 8 taken along line A2-A2. It is a schematic side view of an atmospheric pressure plasma generation device constituting a decomposition device. It is a schematic cross-sectional view of the excimer lamp shown in FIG. 10 taken along line A3-A3. It is a block diagram showing typically another example of a gas processing system. It is a drawing showing an enlarged schematic view of an installation location of a second adsorbent in the gas processing system shown in FIG. 1 is a diagram schematically showing a state in which a pipe containing a second adsorbent is separated from surrounding pipes. 2 is a block diagram schematically showing another example of a gas processing system. 3 is a block diagram schematically showing another example of a gas processing system.

[0039] The present invention relates to a gas treatment method for increasing the concentration of N2O in a gas to be treated containing CO2 and N2O, and for decomposing the N2O in the gas to be treated. Hereinafter, an embodiment of this method will be described with reference to the drawings as appropriate.

[0040] It should be noted that the following drawings are schematic illustrations, and the dimensional ratios on the drawings do not necessarily match the actual dimensional ratios. Furthermore, the dimensional ratios between the drawings may not match each other.

[0041] FIG. 1 is a block diagram schematically illustrating an example of a system (hereinafter referred to as a "gas processing system 1") capable of implementing an embodiment of a gas processing method according to the present invention. The gas processing system 1 shown in FIG. 1 includes a gas supply source 3, a first adsorption tower 10, a gas accumulation tower 20, and a decomposition tower 30. Hereinafter, a unit including the first adsorption tower 10, which is located between the gas supply source 3 and the gas accumulation tower 20, may be referred to as a "first adsorption unit 18" as appropriate. In addition, a unit including the gas accumulation tower 20 may be referred to as a "gas accumulation unit 28" as appropriate.

[0042] The gas supply source 3 is a supply source of the gas Gt to be treated, which contains CO and NO. As an example, the gas supply source 3 is composed of a cylinder, piping, etc., which collects gas containing high concentrations of CO derived from combustion in addition to NO generated from a waste incineration plant, or gas generated from a wastewater treatment plant or the like after concentration treatment. The gas Gt to be treated has a CO concentration of 3% or more.

[0043] The first adsorption tower 10 contains a first adsorbent 11. The first adsorbent 11 is configured to include a material that has a dominant adsorption property for CO compared to NO, and typically includes an amine-based material. There are various materials that can absorb CO, but amine-based materials selectively adsorb CO through chemical bonds and are virtually unreactive with NO, so they have extremely high selectivity for CO.

[0044] The gas accumulation tower 20 accommodates therein a second adsorbent 21. The second adsorbent 21 is made of a material capable of adsorbing CO and NO, and as an example, the second adsorbent 21 mainly contains relatively inexpensive materials such as zeolite, MOF, and CMS.

[0045] The decomposition tower 30 houses therein a device (referred to as a "decomposition device") capable of generating a decomposition space for decomposing NO, and is disposed downstream of the gas accumulation tower 20. A detailed description of the decomposition device will be given later.

[0046] In the gas processing system 1 shown in Fig. 1, the gas supply source 3 is connected to the first adsorption tower 10 through a pipe 40. The first adsorption tower 10 is connected to the gas accumulation tower 20 through a pipe 41 and a pipe 41a. The gas accumulation tower 20 is connected to the decomposition tower 30 through a pipe 48 and a pipe 48a.

[0047] 1 , a pipe 41a and an exhaust flow path 51 branch off from a pipe 41, and a three-way valve 71 is provided at the branching point. The three-way valve 71 is configured to be able to switch between sending the gas (first gas G1) discharged from the first adsorption tower 10 to the gas accumulation tower 20 or to the exhaust flow path 51.

[0048] 1 , a pipe 48a and an exhaust flow path 58 branch off from the pipe 48, and a three-way valve 78 is provided at the branching point. The three-way valve 78 is configured to be able to switch between sending the gas (second gas G2) discharged from the gas accumulation tower 20 to the decomposition tower 30 or to the exhaust flow path 58.

[0049] However, instead of the three-way valves (71, 78), similar flow rate control may be performed by providing an on-off valve in each pipe. In this case, for example, two pipes (41a, 51) may be connected to the first adsorption tower 10 on the downstream side in the flow direction, one pipe 41a being connected to the gas accumulation tower 20, and the other pipe 51 forming a discharge flow path. The same applies to the pipes downstream of the gas accumulation tower 20.

[0050] 1, each of the pipes (40, 41, 48) is provided with a gas sensor (60, 61, 68) capable of measuring the concentration of a substance contained in the gas flowing therethrough. More details are as follows.

[0051] 1, a gas sensor 60 is provided in the pipe 40 connecting the gas supply source 3 and the first adsorption tower 10. This gas sensor 60 is configured to be able to measure the NO concentration of the gas to be treated Gt sent from the gas supply source 3 to the first adsorption tower 10. However, if the NO concentration of the gas to be treated Gt is known or if a gas sensor capable of measuring the NO concentration is provided on the gas supply source 3 device side, the gas sensor 60 is not necessary.

[0052] 1 , a gas sensor 61 is provided in a pipe 41 connecting the first adsorption tower 10 and a three-way valve 71. The gas sensor 61 is configured to be able to measure the CO concentration or NO concentration of the first gas G1 flowing out from the first adsorption tower 10. The gas sensor 61 may be installed inside the first adsorption tower 10, downstream of the first adsorbent 11 in the first adsorption tower 10.

[0053] 1 , a gas sensor 68 is provided in the pipe 48 connecting the gas accumulation tower 20 and the three-way valve 78. The gas sensor 68 is configured to be able to measure the NO concentration of the second gas G2 flowing out from the gas accumulation tower 20. The gas sensor 68 may be installed inside the gas accumulation tower 20 and downstream of the second adsorbent 21 in the gas accumulation tower 20.

[0054] 2 and 3 are flow charts showing a typical procedure for carrying out the gas processing method of this embodiment. In the following description, step numbers shown in the flow charts of FIGS. 2 and 3 will be referred to as appropriate.

[0055] (Step #1) The gas to be treated Gt is supplied from the gas supply source 3 via the pipe 40 to the first adsorption tower 10. As described above, the gas to be treated Gt is a gas containing CO2 and N2O.

[0056] An on-off valve (not shown) may be provided at the connection between the gas supply source 3 and the piping 40 or in the middle of the piping 40, and by controlling this on-off valve, the gas to be treated Gt from the gas supply source 3 may be supplied to the first adsorption tower 10.

[0057] As described above, the first adsorption tower 10 contains the first adsorbent 11 capable of adsorbing CO. Therefore, when the gas to be treated Gt is supplied to the first adsorption tower 10, the first adsorbent 11 installed in the first adsorption tower 10 starts adsorbing the CO contained in the gas to be treated Gt.

[0058] In the initial stage, the adsorption performance of the first adsorbent 11 in the first adsorption tower 10 is high, and therefore CO contained in the gas Gt to be treated is adsorbed by the first adsorbent 11. As a result, the first gas G1 that has passed through the first adsorption tower 10 becomes a gas from which CO has been substantially removed.

[0059] The first adsorption tower 10 contains a first adsorbent 11 made of a material that has a dominant adsorption property for CO compared to N2O. Therefore, when the gas to be treated Gt is sent to the first adsorption tower 10, the first adsorbent 11 adsorbs CO2 contained in high concentrations in the gas to be treated Gt. The first adsorbent 11 does not substantially adsorb N2O contained in the gas to be treated Gt. In other words, the first gas G1, which is a gas that has passed through the first adsorption tower 10, has a lower CO2 concentration than the gas to be treated Gt.

[0060] For this verification, a mixed gas Q1 obtained by mixing 7.70% CO and 173.2 ppm NO with air as a base gas was used as a gas simulating the gas Gt to be treated, and the mixed gas Q1 was passed through the first adsorbent 11 to obtain a mixed gas Q2, which was then analyzed for its components. The mixed gas Q2 corresponds to a gas simulating the first gas G1. The mixed gas Q1 was supplied to the first adsorbent 11 at a flow rate of 0.5 L / min. The first adsorbent 11 was a diamine solution in which PEG and diamine were mixed at a volume ratio of 1:5, supported on silica as a support.

[0061] Specifically, the first adsorbent 11 was formed into a columnar shape with an inner diameter larger than the flow path cross-sectional area of ​​the piping, and piping was connected to each of one end and the other end of the first adsorbent 11. Mixed gas Q1 was supplied through the piping connected to the upstream end of the first adsorbent 11, and mixed gas Q2 discharged through the piping connected to the downstream end of the first adsorbent 11 was sent to a gas analyzer (manufactured by HORIBA, Ltd., model number: PG-344CN), where the components of the mixed gas Q2 were analyzed. The results are shown in Table 1.

[0062]

[0063] According to Table 1, it is confirmed that when mixed gas Q1 containing CO and NO is supplied to the first adsorbent 11, most of the CO contained in the mixed gas Q1 is adsorbed in the first adsorbent 11, while almost no NO contained in the mixed gas Q1 is adsorbed in the first adsorbent 11. In other words, as described above, the first adsorbent 11 can be said to be an adsorbent made of a material whose adsorption property for CO is dominant compared to that for NO.

[0064] Therefore, in this step #1, the gas to be treated Gt passes through the first adsorption tower 10 containing the first adsorbent 11, thereby obtaining a first gas G1 having a reduced CO concentration compared to the gas to be treated Gt. This is because the first adsorbent 11 does not substantially adsorb NO contained in the gas to be treated Gt. As a result, the first gas G1 obtained after passing through the first adsorption tower 10 has a relatively increased NO concentration compared to the gas to be treated Gt.

[0065] This first gas G1 is sent directly to the gas accumulation tower 20 located downstream. In the case of the gas treatment system 1 shown in FIG. 1 , the three-way valve 71 may be controlled to connect the first adsorption tower 10 and the gas accumulation tower 20 via the pipes 41 and 41 a.

[0066] This step #1 corresponds to process (a).

[0067] (Step #2) In this step #2, the concentration of CO in the first gas G1 is measured. As an example, as shown in FIG. 1 , the concentration of CO in the first gas G1 discharged from the first adsorption tower 10 through the pipe 41 is measured by the gas sensor 61.

[0068] At the initial point when execution of step #1 begins, the CO2 contained in the gas to be treated Gt is adsorbed by the first adsorbent 11 in the first adsorption tower 10, so the CO2 concentration in the first gas G1 is sufficiently low.

[0069] In step #2, the gas sensor 61 monitors the CO2 concentration of the first gas G1 over time.

[0070] (Step #3) Step #3 is a step of detecting, based on the measurement result of the gas sensor 61, whether a predetermined first timing has arrived.

[0071] As time passes, when the adsorption performance of the first adsorbent 11 in the first adsorption tower 10 approaches its limit, the amount of CO contained in the supplied treatment target gas Gt becomes greater than the amount of CO that can be adsorbed per unit time by the first adsorbent 11. As a result, the CO concentration of the first gas G1 that has passed through the first adsorbent 11 begins to show an increasing trend. In other words, the first timing here refers to the timing at which the CO concentration of the first gas G1 begins to show an increasing trend. This timing can also be referred to as the timing at which the NO concentration begins to decrease relatively.

[0072] (Step #4) Until the arrival of the first timing is detected in step #3 (No in step #3), the first gas G1 that has passed through the first adsorption tower 10 continues to be sent to the downstream gas accumulation tower 20. When the arrival of the first timing is detected in step #3 (Yes in step #3), step #8, which will be described later, is executed.

[0073] A second adsorbent 21 is disposed in the gas accumulation tower 20, and NO contained in the first gas G1 is adsorbed by the second adsorbent 21. Even if the second adsorbent 21 has the ability to adsorb both NO and CO, it can selectively adsorb only NO because most of the CO has already been removed in step #1.

[0074] This step #4 corresponds to process (b).

[0075] (Steps #5 and #7) In step #5, the accumulation state of the first gas G1 in the gas accumulation tower 20 or the adsorption state of the second adsorbent 21 is measured. Step #7 is performed for the purpose of detecting whether the timing to start execution of step #8 (hereinafter referred to as "second timing"), which will be described later, has arrived based on the measurement results of step #5.

[0076] The second timing here refers to a timing at which it can be determined that the adsorption performance of the second adsorbent 21 in the gas accumulation tower 20 for NO in the first gas G1 has decreased. Typically, this is a timing at which the second adsorbent 21 indicates a state close to its adsorption limit for NO.

[0077] It is expected that the NO adsorption performance of the second adsorbent 21 in the gas accumulation tower 20 will decrease over time as the first gas G1 continues to be supplied. Therefore, if the second adsorbent 21 reaches its NO adsorption limit, even if the first gas G1 is subsequently supplied to the gas accumulation tower 20, the NO contained in the first gas G1 will not be adsorbed by the second adsorbent 21 and will be discharged from the gas accumulation tower 20 as the second gas G2 containing a large amount of NO.

[0078] Conversely, during a time period when the adsorption performance of the second adsorbent 21 is high, most of the NO contained in the first gas G1 can be adsorbed by the second adsorbent 21. Therefore, during this time period, the second gas G2 that has passed through the second adsorbent 21 can be discharged through the discharge flow path 58. In other words, during the time period until the second timing arrives, the three-way valve 78 may be configured to connect the pipe 48 and the discharge flow path 58.

[0079] Several methods can be employed to execute step #7. One example is a method in which the gas sensor 68 detects the arrival of the second timing when the concentration of NO contained in the gas (second gas G2) that has passed through the second adsorbent 21 in the gas accumulation tower 20 reaches a predetermined value or more. Another example is a method in which the gas accumulation tower 20 is provided with a weight sensor or volume sensor (not shown) capable of measuring the weight of the second adsorbent 21, and the arrival of the second timing is detected when the measured value of the weight or volume of the second adsorbent 21 by this sensor reaches a predetermined value or more. These predetermined values ​​may be set as appropriate based on the concentration of NO contained in the gas to be treated Gt, the initial weight of the second adsorbent 21, etc.

[0080] That is, when it is confirmed by the gas sensor 68 that the concentration of NO contained in the second gas G2 has reached a predetermined value or more, this typically means that the second adsorbent 21 in the gas accumulation tower 20 is close to or has reached its limit for adsorbing NO. Similarly, when it is confirmed by a weight sensor or a volume sensor that the weight or volume of the second adsorbent 21 has reached a predetermined value or more, this typically means that the second adsorbent 21 is close to or has reached its limit for adsorbing NO.

[0081] (Step #8) As described above, when the arrival of the first timing is detected in step #3 (Yes in step #3), the supply of the target gas Gt to the first adsorption tower 10 is stopped. Also, when the arrival of the second timing is detected in step #7 (Yes in step #7), the supply of the target gas Gt to the first adsorption tower 10 is stopped.

[0082] (Step #9) Thereafter, a desorption step is performed on the first adsorbent 11 in the first adsorption tower 10. Specifically, the desorption step is performed by heating the first adsorbent 11, reducing the pressure of the first adsorbent 11, or the like. As an example of the former method, a method can be adopted in which the first adsorbent 11, or the first adsorption tower 10 containing the first adsorbent 11, is heated by performing heat exchange between the first adsorbent 11 and a high-temperature fluid.

[0083] At the time of performing step #9, the pipe 41 and the discharge flow path 51 may be connected by the three-way valve 71. In this case, the first gas G1 obtained by desorption from the first adsorbent 11 is discharged to the outside via the discharge flow path 51. By performing step #9, the adsorption performance of the first adsorbent 11 is restored.

[0084] Step #9 corresponds to step (d). When performing this desorption step, in order to exhaust the substances adsorbed to the first adsorbent 11 in the airflow, for example, a small amount of nitrogen gas may be introduced into the first adsorption tower 10 through a gas inlet (not shown) provided in the first adsorption tower 10. Alternatively, this may be achieved by applying negative pressure (typically a vacuum state) to the first adsorption tower 10 and drawing the substances adsorbed to the first adsorbent 11 to the pipe 41 side.

[0085] In this specification, the gas discharged from the first adsorption tower 10 is referred to as the "first gas G1." However, the first gas G1 discharged from the first adsorption tower 10 in this step #9 has a different meaning from the first gas G1 discharged from the first adsorption tower 10 toward the downstream gas accumulation tower 20 during the execution of steps #1 to #8.

[0086] The latter first gas G1 is a gas obtained by passing the supplied treatment target gas Gt through the first adsorption tower 10. In other words, the first gas G1 here is a gas obtained after the treatment target gas Gt passes through the first adsorbent 11 and CO contained in the treatment target gas Gt is adsorbed during a time period when the first adsorbent 11 exhibits relatively high adsorption performance, and is a gas with a lower CO concentration than the treatment target gas Gt. In contrast, the former first gas G1 is a gas obtained after CO adsorbed by the first adsorbent 11 is desorbed, and is therefore expected to have a higher CO concentration than the treatment target gas Gt.

[0087] By performing step #9, a very high concentration of CO2 can be obtained from the discharge line 51, and this CO2 can also be used for secondary purposes. In recent years, methods for utilizing the separated and captured CO2 have begun to be studied (CCUS [Carbon dioxide Capture, Utilization and Storage]), and progress is being made in, for example, using it as fuel such as methanol, burying it underground, or converting it into carbon credits.

[0088] (Step #13) As described above, after step #8, the supply of the gas to be treated Gt from the gas supply source 3 to the first adsorption tower 10 is stopped. In step #13, a desorption process is performed on the second adsorbent 21 in the gas accumulation tower 20. Specifically, this is performed by heating the second adsorbent 21, depressurizing the second adsorbent 21, or the like. As a result, the NO adsorbed in the second adsorbent 21 is desorbed from the second adsorbent 21, and the adsorption performance of the second adsorbent 21 is restored. As an example of this method, a method can be adopted in which the second adsorbent 21 or the gas accumulation tower 20 in which the second adsorbent 21 is accommodated is heated by performing heat exchange between the second adsorbent 21 and a high-temperature fluid.

[0089] At the time of performing step #13, the pipe 48 and the decomposition tower 30 may be connected by the three-way valve 78. That is, the second gas G2 containing a high concentration of NO obtained by desorption from the second adsorbent 21 is sent to the decomposition tower 30. Then, by performing step #13, the adsorption performance of the second adsorbent 21 is restored.

[0090] When performing this desorption step, in order to exhaust the substances adsorbed to the second adsorbent 21 on the airflow, for example, a small amount of nitrogen gas may be introduced into the gas accumulation tower 20 through a gas inlet (not shown) provided in the gas accumulation tower 20. Alternatively, this may be achieved by applying negative pressure (typically a vacuum state) to the gas accumulation tower 20 and drawing the substances adsorbed to the second adsorbent 21 to the pipe 48 side.

[0091] In this specification, the gas discharged from the gas accumulation tower 20 is referred to as the "second gas G2," but the second gas G2 discharged from the gas accumulation tower 20 in step #13 has a different meaning from the second gas G2 discharged from the gas accumulation tower 20 in an earlier time period.

[0092] The latter second gas G2 is a gas obtained by passing the first gas G1 supplied to the gas accumulation tower 20 through the gas accumulation tower 20, and is a gas after NO has been adsorbed by the second adsorbent 21 in the gas accumulation tower 20. Therefore, as described above, this second gas G2 has a low NO concentration and can be discharged to the outside via the discharge flow path 58.

[0093] In contrast, the former second gas G2 is a gas obtained after desorbing the N2O adsorbed by the second adsorbent 21 in the gas accumulation tower 20, and therefore is a gas with an extremely increased concentration of N2O compared to the gas to be treated Gt.

[0094] In the gas treatment method according to the present invention, step #13 may be performed to desorb NO adsorbed in the second adsorbent 21 before the adsorption performance of the second adsorbent 21 in the gas accumulation tower 20 reaches its limit, in other words, even when the second adsorbent 21 still has a margin of adsorption capacity. The second gas G2 containing a high concentration of NO, which is exhausted from the gas accumulation tower 20 by performing the desorption process according to step #13, is sent to the decomposition tower 30.

[0095] (Step #14) As described above, the second gas G2 from which the substances adsorbed on the second adsorbent 21 in the gas accumulation tower 20 have been desorbed is sent to the decomposition tower 30 via the pipes 48 and 48a. In this step #14, NO contained in the second gas G2 is decomposed in the decomposition tower 30.

[0096] This step #14 corresponds to process (c).

[0097] As described above, the second gas G2 sent from the gas accumulation tower 20 to the decomposition tower 30 after step #13 contains NO at a higher concentration than the gas to be treated Gt. Therefore, by decomposing the NO contained in this second gas G2 in the decomposition tower 30, NO with a high GWP can be efficiently decomposed.

[0098] Fig. 4 is a cross-sectional view schematically illustrating an example of the configuration of the decomposition tower 30. In the example shown in Fig. 4, the decomposition tower 30 is equipped with a decomposition device 80 consisting of an excimer lamp. Fig. 5 corresponds to a schematic side view of the excimer lamp constituting the decomposition device 80 in this example, and Fig. 6 corresponds to a cross-sectional view taken along line A1-A1 in Fig. 5.

[0099] This excimer lamp includes a tube 81 and a pair of electrodes (82a, 82b). In this example, the tube 81 has a double-tube structure. More specifically, as shown in Fig. 6, the tube 81 has a cylindrical outer tube 81a located on the outside, and a cylindrical inner tube 81b located inside the outer tube 81a and coaxially with the outer tube 81a, with an outer diameter smaller than the inner diameter of the outer tube 81a.

[0100] 5 and 6 show an example of an excimer lamp (decomposition device 80) in which the tube axis direction of the tube body 81 is arranged along the flow direction d1 of the second gas G2. However, the tube axis direction of the tube body 81 does not necessarily need to be parallel to the flow direction d1 of the second gas G2, and these drawings are merely an example. Hereinafter, for convenience, the flow direction d1 of the second gas G2 and the tube axis direction of the tube body 81 are assumed to be parallel, and in order to avoid an increase in the number of symbols, the same symbol "d1" as the flow direction is used for the tube axis direction.

[0101] The outer tube 81a and the inner tube 81b are both sealed at their ends in the tube axis direction d1 (not shown), and a light-emitting space having a ring shape (here, a circular ring shape) when viewed from the tube axis direction d1 is formed between them. A light-emitting gas 83G that forms excimer molecules by discharge is sealed in this light-emitting space.

[0102] An electrode 82a is disposed on the outer wall of the outer tube 81a. In this embodiment, the electrode 82a has a mesh or linear shape. A rod-shaped electrode 82b extends along the axial direction of the tube body 81 and is inserted into the inner tube 81b.

[0103] The outer tube 81a and the inner tube 81b are made of a dielectric material such as synthetic quartz glass that is transparent to the ultraviolet light L1. The electrodes (82a, 82b) are made of a metal material such as stainless steel, aluminum, copper, tungsten, titanium, or nickel.

[0104] When a high-frequency AC voltage of, for example, about 1 kHz to 5 MHz is applied between the electrodes (82a, 82b) via a power supply (not shown), the voltage is applied to the light-emitting gas 83G via the tube body 81. At this time, a discharge plasma is generated in the discharge space in which the light-emitting gas 83G is sealed, and the atoms of the light-emitting gas 83G are excited to an excimer state, and excimer light emission occurs when these atoms transition to the ground state. In other words, ultraviolet light L1 derived from excimer light is generated due to the dielectric barrier discharge.

[0105] The material of the light emitting gas 83G determines the wavelength of the ultraviolet light L1 emitted from the tube 81. When a gas containing xenon (Xe) is used as the light emitting gas 83G, the excimer light emission becomes ultraviolet light L1 having a main peak wavelength in the vicinity of 172 nm.

[0106] The wavelength of the ultraviolet light L1 can be changed by changing the substance used as the luminous gas 83G. For example, ArBr (main peak wavelength near 165 nm), ArCl (main peak wavelength near 175 nm), F (main peak wavelength near 153 nm), etc. can be used as the luminous gas 83G. Here, a case where the luminous gas 83G is a gas containing Xe will be described.

[0107] As described above, in the excimer lamp of this embodiment, the electrode 82a disposed on the outer wall of the outer tube 81a has a mesh shape. Therefore, gaps exist in the electrode 82a, and the ultraviolet light L1 is extracted toward the outside of the outer tube 81a through these gaps. This ultraviolet light L1 is irradiated onto the second gas G2 flowing through the decomposition tower 30.

[0108] When the ultraviolet light L1 is irradiated onto the N2O contained in the second gas G2, the reaction of the following formula (1) occurs. 1 D) is excited atomic oxygen. The left side of equation (1) conveniently expresses that ultraviolet light with a wavelength λ (frequency ν) is absorbed by N2O. The same applies to the following equations. N2O + hν → N2 + O( 1 D) ...(1)

[0109] Theoretically, the decomposition reaction of the above formula (1) occurs when ultraviolet light L1 with a wavelength λ of 340 nm or less is used. However, since the absorption cross section of NO for light with a wavelength of 200 nm or more is small, it is preferable to use light with a wavelength of less than 200 nm, which has a relatively large absorption cross section, in order to promote the decomposition reaction of the formula (1).

[0110] As described above, when the gas to be treated Gt is derived from gas generated from a waste incineration plant, a wastewater treatment plant, or the like, the gas to be treated Gt contains N2, O2, and CO2 derived from air. In other words, it is expected that the second gas G2 sent out from the gas accumulation tower 20 also contains a fair amount of O2 due to the gas to be treated Gt being supplied to the first adsorption tower 10. The O2 contained in the second gas G2 absorbs the ultraviolet light L1. When the wavelength λ of the ultraviolet light L1 is less than 242 nm, the reaction represented by the following formula (2) proceeds. When the wavelength λ is less than 175 nm, the reaction represented by the following formula (3) proceeds. In formula (2), O( 3 P) is atomic oxygen in the ground state. O2 + hν → O( 3 P) + O( 3 P) ‥‥(2) O2 + hν → O( 1 D) + O( 3 P) ... (3)

[0111] Some of the O atoms generated in the formulas (2) and (3) react with O2 contained in the second gas G2 to generate ozone (O3) according to the following formula (4). In formula (4), M represents a third body (the same applies below). In formula (4), O( 1 D) and O( 3 O + O2 + M → O3 + M (4)

[0112] When ultraviolet light L1 is absorbed by O3 obtained by the above formula (4), the reaction of the following formula (5) proceeds: O3 + hν → O( 1 D) + O2 (5)

[0113] Excited state atomic oxygen O( 1 Since NO) is a highly reactive substance, when it comes into contact with NO contained in the second gas G2, the reaction of formula (6) or (7) occurs. NO + O ( 1 D) → O2 + N2 ‥‥(6) N2O + O( 1 D) → NO + NO (7)

[0114] According to the above, when the second gas G2 is supplied to the decomposition tower 30, NO in the second gas G2 is decomposed by the reactions of the above formulas (1), (6), and (7), etc. As a result, the treated gas Gd (see FIG. 4) that has passed through the decomposition tower 30 contains substances with low GWP, and can be discharged to a subsequent stage (or to the atmosphere) via the pipe 49 (see FIG. 1).

[0115] 4, the decomposition tower 30 includes a decomposition device 80 formed of an excimer lamp, which generates a decomposition space 31 corresponding to the irradiation region of the ultraviolet light L1, and the second gas G2 passes through this decomposition space 31, thereby decomposing NO in the second gas G2. For example, the operation of the decomposition device 80 may be started at the timing when execution of step #14 is started (corresponding to process (c)). More specifically, if the decomposition device 80 is formed of an excimer lamp, the excimer lamp may be energized at this timing.

[0116] By executing step #13, the substances adsorbed to the second adsorbent 21 in the gas accumulation tower 20 are desorbed and sent to the decomposition tower 30 as a second gas G2 containing the substances, where decomposition processing is performed in the decomposition tower 30. In other words, when the execution of step #13 progresses to a certain extent, the substances adsorbed to the second adsorbent 21 in the gas accumulation tower 20 are sufficiently desorbed.

[0117] When an index value indicating the state of adsorption of substances in the second adsorbent 21 in the gas accumulation tower 20 is measured, the index value shows a gradual downward trend from the start of execution of step #13. For example, when it is detected that the index value has reached a predetermined threshold or less, it may be determined that the substances adsorbed to the second adsorbent 21 have been sufficiently desorbed, and the operation of the decomposition device 80 may be stopped. In particular, when the decomposition device 80 is composed of an excimer lamp, when it is detected that the index value has reached a predetermined threshold or less, the power supply to the excimer lamp may be stopped. This makes it possible to extend the life of the excimer lamp and reduce the amount of energy consumed by the excimer lamp when decomposing NO.

[0118] When the decomposition device 80 is configured with an excimer lamp, the structure of the excimer lamp illustrated in FIGS. 5 and 6 is merely an example.

[0119] For example, as shown in Fig. 7, an excimer lamp may have a single tube 81. Fig. 7 is a schematic cross-sectional view of an excimer lamp illustrated similarly to Fig. 6. The tube 81 is sealed at its end in the longitudinal direction, i.e., in the tube axis direction d1 (not shown), and a light-emitting gas 83G is sealed in the internal space. A mesh-shaped or linear electrode 82a is disposed on the outer wall surface of the tube 81, and a rod-shaped electrode 82b is disposed inside (inside) the tube 81.

[0120] As another example, as shown in Figures 8 to 9, a configuration can be employed in which both electrodes (82a, 82b) are disposed on the outer wall surface of a tube 81 of an excimer lamp. Figures 8 to 9 are drawings that schematically show the structure of an excimer lamp of this alternative configuration example, with Figure 8 corresponding to a plan view and Figure 9 corresponding to a cross-sectional view taken along line A2-A2 in Figure 8. The excimer lamp shown in Figures 8 and 9 has a single tube 81, and both electrodes (82a, 82b) are disposed on the outer wall surface of the tube 81 so as to face each other across the tube 81. The electrodes (82a, 82b) are both mesh-shaped or linear-shaped so as not to interfere with the extraction of ultraviolet light L1 generated within the tube 81 to the outside of the tube 81.

[0121] Furthermore, the decomposition device 80 for generating the decomposition space 31 as described above is not limited to an excimer lamp. As another example, the decomposition device 80 may be configured by an atmospheric pressure plasma generator, as illustrated in Figures 10 and 11 .

[0122] 10 and 11 are drawings showing a structural example of an atmospheric pressure plasma generator as a decomposition device 80, with Fig. 10 corresponding to a side view of the atmospheric pressure plasma generator and Fig. 11 corresponding to a cross-sectional view taken along line A3-A3 in Fig. 10. Unlike an excimer lamp, this atmospheric pressure plasma generator does not have a light-emitting gas 83G sealed inside the tubular body 81. Also, in Fig. 10, a second gas G2 is caused to flow inside the tubular body 81. The rest of the configuration is similar to that of the excimer lamp described above with reference to Figs. 5 and 6.

[0123] When a voltage is applied between the two electrodes (82a, 82b) from a power supply (not shown), a dielectric barrier discharge occurs within the tubular body 81. As a result, a dielectric barrier discharge occurs in the second gas G2 flowing through the decomposition space 31 formed within the tubular body 81, and the second gas G2 is converted into plasma.

[0124] When NO contained in the second gas G2 flows through the atmospheric pressure plasma space, the reaction of the following formula (8) occurs. In formula (8), AP means that energy is added by atmospheric pressure plasma. This also applies to the following formulas. In formulas (8) to (10) below, O( 1 D) and O( 3Both NO and AP are expressed as atomic oxygen O. NO + AP → N + O (8)

[0125] The O2 contained in the second gas G2 undergoes the reaction of the following formula (9) when flowing through the atmospheric pressure plasma space: O2 + AP → O2 + O2 (9)

[0126] Atomic oxygen O produced in the reaction (9) reacts with O2 contained in the second gas G2 to produce O3 according to the reaction (4) described above. The reaction (4) is shown below: O + O2 + M → O3 + M (4)

[0127] When energy from atmospheric pressure plasma is applied to the O3 obtained by the above formula (4), the reaction shown in formula (10) below proceeds: O3 + AP → O + O2 (10)

[0128] That is, when the second gas G2 flows through the decomposition space 31 formed by the atmospheric pressure plasma generator, O3 is introduced into the second gas G2, and O( 1 D) is generated. As a result, O( 1 When D) comes into contact with N2O contained in the second gas G2, N2O is decomposed via the reaction of formula (6) or (7).

[0129] From the above, it can be seen that oxygen contributes to the decomposition of NO in both cases where ultraviolet light and plasma are used in step 14. Therefore, although not shown, a predetermined amount of oxygen may be introduced into the inlet of the decomposition device 80, and a mixed gas of O and the second gas G2 containing a high concentration of NO may be sent to the decomposition device 80, thereby decomposing the second gas G2.

[0130] (Step #10) After step #8, the supply of the target gas Gt from the gas supply source 3 to the first adsorption tower 10 is stopped. Then, by executing step #9 described above, a desorption process is performed on the first adsorbent 11 in the first adsorption tower 10. Furthermore, by executing steps #13 and #14 described above, a desorption process is performed on the second adsorbent 21 in the gas accumulation tower 20, and a decomposition process is performed on the second gas G2 discharged by this desorption. After these processes are completed, if there is any target gas Gt remaining in the gas supply source 3, or if it is necessary to continue processing the target gas Gt (Yes in step #10), the process returns to step #1. On the other hand, if the processing of the target gas Gt is to be terminated or interrupted (No in step #10), the process is terminated.

[0131] Another embodiment of the gas processing system 1 will be described.

[0132] In the above embodiment, the first adsorbent 11, which is predominantly adsorbent for CO, is accommodated in the first adsorption tower 10. However, as shown in Fig. 12, the first adsorbent 11 may be embedded in a pipe. In this case, the gas processing system 1 does not include the first adsorption tower 10.

[0133] 13, a configuration can be adopted in which a pipe 110 having a first adsorbent 11 embedded therein is connected by a joint to a location sandwiched between a pipe 40 and a pipe 41 that connect the gas supply source 3 and the gas accumulation tower 20. In this case, when the adsorbed substance is desorbed from the first adsorbent 11 in step #9, the pipe 110 can be separated from the pipes 40 and 41, and then the desorption step can be performed on the first adsorbent 11, as shown in FIG.

[0134] If a new pipe (not shown) containing the first adsorbent 11 is loaded into the pipe 110 the moment the pipe 110 is separated from the pipes 40 and 41, the first gas G1 can be continuously supplied to the downstream gas accumulation tower 20. Meanwhile, the separated pipes 110 are individually regenerated and loaded at the next opportunity. Therefore, multiple first adsorbents 11 can be used in parallel, sequentially swapped. This eliminates the transition from the detection of the arrival of the first timing in step #3 (Yes in step #3) to step #8, as described in FIG. 2 . This has the advantage of reducing downtime of the gas processing system 1 and enabling continuous acceptance of the gas to be processed Gt.

[0135] The configuration described above with reference to FIG. 13 can also be applied to the following other embodiments.

[0136] As shown in Fig. 15 , first adsorption units 18 each including a first adsorption tower 10 may be arranged in parallel in a plurality of stages, and the first gas G1 may be fed from each of the first adsorption units 18 to the same gas accumulation tower 20. Note that, although Fig. 15 illustrates elements within the first adsorption unit 18 that are similar to those in Fig. 1 , the configuration shown in Fig. 12 may also be used.

[0137] Hereinafter, when it is necessary to distinguish between the first suction units 18, 18, . . . , they will be referred to as "first suction unit 18A" and "first suction unit 18B."

[0138] 15 , for example, the first adsorption unit 18 to which the gas to be treated Gt is supplied from the gas supply source 3 can be switched by controlling the on-off valves (37, 38). This switching step corresponds to step (a1).

[0139] Specifically, in step #1, the on-off valve 37 is opened and the on-off valve 38 is closed, and the gas to be treated Gt is supplied from the gas supply source 3 to the first adsorption unit 18A. Then, steps #2 to #7 are executed. When the arrival of the first timing is detected in step #3, the on-off valve 38 is opened and the on-off valve 37 is closed, and the gas to be treated Gt is supplied from the gas supply source 3 to the first adsorption unit 18B. Then, steps #2 to #7 are executed without interruption.

[0140] The control of the three-way valve 71 is the same as in the embodiment described above. For convenience of explanation, in Fig. 15, the three-way valve 71 arranged on the first adsorption unit 18A side is designated as the three-way valve 71A, and the three-way valve 71 arranged on the first adsorption unit 18B side is designated as the three-way valve 71B. The following description will be given using these designations.

[0141] While the gas to be treated Gt is being supplied from the gas supply source 3 to the first adsorption unit 18A, the three-way valve 71A is controlled to connect the pipe 41 and the pipe 41a until the first timing arrives (No in step #3). In the embodiment shown in FIG. 15 , an on-off valve 39A is provided between the pipe 41a connected to the first adsorption unit 18A and the gas accumulation unit 28. Before the first timing arrives, the on-off valve 39A is also controlled to be open. As a result, the first gas G1 with a reduced CO concentration is sent from the first adsorption unit 18A to the gas accumulation tower 20 via the pipe 41a, and steps #4 to #7 are executed. Thereafter, when the first timing arrives (Yes in step #3), the three-way valve 71A is controlled to connect the pipe 41 and the exhaust flow path 51, and the first gas G1 with a low CO concentration that has passed through the first adsorption unit 18A is exhausted via the exhaust flow path 51.

[0142] Even after the destination of the gas supply source 3 to be treated Gt is switched from the first adsorption unit 18A to the second adsorption unit 18B, the same process is performed in accordance with the state in which the gas supply source 3 to be treated Gt is being supplied to the first adsorption unit 18A. That is, until the first timing arrives (No in step #3), the three-way valve 71B is controlled to connect the pipe 41 to the pipe 41a, and the on-off valve 39B is also controlled to be open. As a result, the first gas G1 with a reduced CO concentration is sent from the first adsorption unit 18B to the gas accumulation tower 20 via the pipe 41a, and steps #4 to #7 are executed. Thereafter, when the first timing arrives (Yes in step #3), the three-way valve 71B is controlled to connect the pipe 41 to the exhaust flow path 51, and the first gas G1 with a low CO concentration that has passed through the first adsorption unit 18B is exhausted via the exhaust flow path 51.

[0143] 15 , the first gas G1 from the plurality of first adsorption units 18 is alternately fed into the gas accumulation tower 20. This makes it possible to efficiently treat the target gas Gt from the gas supply source 3.

[0144] 15 , the target gas Gt from the gas supply source 3 can be fed into the first adsorption tower 10 constituting the first adsorption unit 18B at the same time that desorption is being performed on the first adsorbent 11 in the first adsorption tower 10 constituting the first adsorption unit 18A. In other words, a process for restoring the adsorption performance of the first adsorbent 11 in the first adsorption tower 10 and a process for adsorbing substances contained in the target gas Gt onto the first adsorbent 11 in another first adsorption tower 10 can be performed in parallel. This improves the processing capacity of the target gas Gt from the gas supply source 3 and enables continuous processing.

[0145] 16, a configuration may be adopted in which a plurality of gas accumulation units 28, 28, ... are provided and the first gas G1 is supplied to each of the gas accumulation units 28, 28, .... Hereinafter, when it is necessary to distinguish between the gas accumulation units 28, 28, ..., they will be referred to as "gas accumulation unit 28A" and "gas accumulation unit 28B."

[0146] Specifically, the on-off valve 35 is opened and the on-off valve 36 is closed, and the first gas G1 is supplied to the gas accumulation unit 28A. When the arrival of the second timing is detected in step #7, the on-off valve 36 is opened and the on-off valve 35 is closed, and the first gas G1 is supplied to the gas accumulation unit 28B. Then, steps #8 to #14 are executed.

[0147] 16 , the second gas G2 from the plurality of gas collection units 28, 28, ... is switched and fed into the decomposition tower 30, thereby enabling the first gas G1 to be efficiently treated. This switching step corresponds to step (b1).

[0148] 16 , the first gas G1 from the first adsorption unit 18 can be sent to the gas accumulation tower 20 constituting the gas accumulation unit 28B at the same time that desorption is being performed on the second adsorbent 21 in the gas accumulation tower 20 constituting the gas accumulation unit 28A. That is, a process for restoring the adsorption performance of the second adsorbent 21 in the gas accumulation tower 20 and a process for adsorbing substances contained in the first gas G1 onto the second adsorbent 21 in another gas accumulation tower 20 can be performed in parallel. This improves the processing capacity of the first gas G1 from the first adsorption unit 18 and enables continuous processing.

[0149] Furthermore, a configuration including a plurality of gas accumulation units 28, 28, ... as shown in Fig. 16 may be combined with a configuration including a plurality of first adsorption units 18, 18, ... as shown in Fig. 15. In this configuration, the target gas Gt to be treated from the gas supply source 3 can be completely continuously treated, thereby achieving high treatment efficiency.

[0150] 1 may be provided as a plurality of independent systems. The same applies to other embodiments.

[0151] The configurations of the gas processing system 1 described above with reference to the drawings can be combined as appropriate as necessary.

[0152] As described above, the first gas G1 delivered from the first adsorption tower 10 in step #4 has a higher NO concentration than the target gas Gt. Therefore, the gas accumulation tower 20 may simply be a buffer tank for storing the first gas G1. In this case, in step #7, it can be determined that the second timing has arrived when the volume of the first gas G1 stored in the buffer tank constituting the gas accumulation tower 20 exceeds a predetermined value. In this case, step #13 is omitted.

[0153] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail for a better understanding of the present invention, and are not necessarily limited to those having all of the configurations described. The scope of the present invention is defined by the claims, and it is intended to include all modifications within the meaning and scope of the claims.

[0154] 1: Gas treatment system 3: Gas supply source 10: First adsorption tower 11: First adsorbent 18, 18A, 18B: First adsorption unit 20: Gas accumulation tower 21: Second adsorbent 28, 28A, 28B: Gas accumulation unit 30: Decomposition tower 31: Decomposition space 35, 36, 37, 38, 39A, 39B: On-off valve 40, 41, 41a, 48, 48a, 49: Piping 51, 58: Discharge flow path 60, 61, 68: Gas sensor 71, 71A, 71B, 78: Three-way valve 80: Decomposition device 81: Tube body 81a: Outer tube 81b: Inner tube 82a, 82b: Electrode 83G: Luminous gas 110: Piping G1: First gas G2: Second gas Gd: Processed gas Gt: Gas to be processed L1: Ultraviolet light

Claims

1. A gas treatment method comprising the steps of: (a) sending a gas to be treated, which contains CO2 and N2O and has a CO2 concentration of 3% or more, to a first adsorbent which is an adsorbent having a dominant adsorption property for CO2 compared to N2O; (b) collecting the first gas which has passed through the first adsorbent and contains N2O at a higher concentration than the gas to be treated, or the N2O contained in the first gas; and (c) decomposing the gas collected in step (b), wherein step (c) includes a step of sending the gas collected in step (b) into a decomposition space formed by at least one of an ultraviolet ray irradiation area and an area where plasma is formed.

2. The gas treatment method according to claim 1, wherein the first adsorbent comprises an amine-based material.

3. The gas treatment method according to claim 1, wherein step (b) is a step of collecting N2O contained in the first gas by supplying the first gas to a second adsorbent containing zeolite as a main component.

4. The gas treatment method according to claim 1, further comprising a step (d) of desorbing the adsorbed substance adsorbed in the first adsorbent, wherein control is exercised so that when step (d) is being carried out, step (b) is not carried out on the gas discharged from the first adsorbent.

5. The gas treatment method according to claim 3, further comprising a step (e) of releasing the gas accumulated in the step (b), wherein the step (c) is carried out only during the time period when the step (e) is being carried out.

6. The gas treatment method according to claim 4, wherein a plurality of first adsorption towers each containing the first adsorbent are prepared, and step (a) includes step (a1) of switching the first adsorption tower as the destination of the gas to be treated, wherein step (a1) is a step of switching the destination of the gas to be treated to the first adsorption tower that has adsorption capacity and was not a destination of the gas to be treated until just before the adsorption performance of the first adsorbent contained in the first adsorption tower as the destination of the gas to be treated reaches an upper limit, and step (d) is performed with the first adsorption tower, from which the introduction of the gas to be treated has been stopped by step (a1), disconnected from the equipment in which step (b) is performed.

7. A gas treatment method according to claim 5, characterized in that a plurality of gas accumulation towers containing the second adsorbent are prepared, the step (b) includes a step (b1) of switching the gas accumulation tower to which the first gas is to be sent, wherein, when the adsorption capacity of the second adsorbent contained in the gas accumulation tower to which the first gas is to be sent reaches an upper limit, the destination of the first gas is switched to a gas accumulation tower having adsorption capacity that was not a destination of the first gas until immediately before that point, and the step (c) is performed on gas accumulated in the gas accumulation tower from which the introduction of the first gas has been stopped by the step (b1).

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