Exhaust gas treatment equipment

Abstract

Provided is an exhaust gas processing device (100) for processing an exhaust gas discharged from a combustion device (200) that combusts a fuel containing ammonia, the exhaust gas processing device (100) comprising: an ammonia decomposition part (10) having an ammonia decomposition catalyst with which ammonia contained in the exhaust gas is decomposed; and a nitrogen oxide decomposition part (20) having a second catalyst with which nitrous oxide and NOx contained in the exhaust gas in which ammonia has been decomposed by the ammonia decomposition part (10) are decomposed.

Description

Technical Field

[0001] The present invention relates to an exhaust gas treatment device. Place

Background Art

[0002] In recent years, in order to suppress global warming, the realization of carbon neutrality has been demanded, and the application of ammonia fuel as a fuel that does not emit carbon dioxide during combustion has been studied. When using ammonia fuel, since the exhaust gas contains not only NOx but also ammonia (NH3), nitrous oxide (N2O), etc., it is necessary to remove these from the exhaust gas to reduce the impact on the environment.

[0003] Conventionally, an ammonia treatment device that decomposes ammonia into nitrogen and water by oxidizing ammonia using an ammonia decomposition catalyst is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in Patent Document 1, although ammonia can be decomposed, for example, when the gas to be treated contains nitrous oxide, nitrous oxide cannot be decomposed.

[0006] Also, conventionally, in order to decompose NOx contained in exhaust gas etc. discharged from a combustion device, a selective catalytic reduction method (Selective Catalytic Reduction: SCR) in which ammonia or aqueous urea as a reducing agent is sprayed into the exhaust gas to reduce NOx is known. However, in the selective catalytic reduction method, although NOx can be decomposed, nitrous oxide cannot be decomposed.​

[0007] This disclosure is made in view of the above circumstances and describes an exhaust gas treatment device capable of appropriately decomposing ammonia, nitrous oxide, and NOx contained in exhaust gas emitted from a combustion device that burns ammonia-containing fuel. Place The purpose is to provide it. [Means for solving the problem]

[0008] To address the above issues, this disclosure employs the following measures. The exhaust gas treatment device according to this disclosure is an exhaust gas treatment device for treating exhaust gas discharged from a combustion device that burns a fuel containing ammonia, comprising: a first treatment unit having a first catalyst for decomposing ammonia contained in the exhaust gas; and a second treatment unit having a second catalyst for decomposing nitrous oxide and NOx contained in the exhaust gas from which ammonia has been decomposed in the first treatment unit.

[0009] The exhaust gas treatment device design method according to the present disclosure is a method for designing an exhaust gas treatment device that treats exhaust gas discharged from a combustion device that burns a fuel containing ammonia, wherein when the concentration of ammonia contained in the exhaust gas is higher than the sum of a first concentration obtained by multiplying the concentration of nitrous oxide contained in the exhaust gas by a first coefficient and a second concentration obtained by multiplying the concentration of NOx contained in the exhaust gas by a second coefficient, the exhaust gas treatment device is designed such that a first processing unit having a first catalyst for decomposing ammonia contained in the exhaust gas is placed downstream of the combustion device, and a second processing unit having a second catalyst for decomposing nitrous oxide and NOx contained in the exhaust gas from which ammonia has been decomposed by the first processing unit is placed downstream of the first processing unit, and when the concentration of ammonia contained in the exhaust gas is less than or equal to the sum of the two concentrations, the exhaust gas treatment device is designed such that the second processing unit is placed downstream of the combustion device without placing the first processing unit. [Effects of the Invention]

[0010] According to this disclosure, an exhaust gas treatment device capable of properly decomposing ammonia, nitrous oxide, and NOx contained in exhaust gas emitted from a combustion device that burns fuel containing ammonia. Place It can be provided. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram showing an exhaust gas treatment apparatus according to the first embodiment of this disclosure. [Figure 2] This graph shows the decomposition characteristics of an ammonia decomposition catalyst. [Figure 3] This graph shows the relationship between ammonia concentration and temperature rise in an ammonia decomposition catalyst. [Figure 4] This graph shows the decomposition characteristics of nitrous oxide in relation to exhaust gas temperature. [Figure 5] This graph shows the decomposition characteristics of NO in relation to exhaust gas temperature. [Figure 6] This is a flowchart showing the supply process of a reducing agent in an exhaust gas treatment apparatus according to the first embodiment of this disclosure. [Figure 7] This is a flowchart showing the switching process of a bypass valve in an exhaust gas treatment device according to the first embodiment of this disclosure. [Figure 8] This is a schematic diagram showing an exhaust gas treatment apparatus according to a second embodiment of the present disclosure. [Figure 9] This flowchart shows the switching process of the bypass valve of the exhaust gas treatment device according to the second embodiment of this disclosure. [Figure 10] This is a schematic diagram showing an exhaust gas treatment apparatus according to the third embodiment of this disclosure. [Figure 11] This is a flowchart showing a design method for an exhaust gas treatment apparatus according to the fourth embodiment of this disclosure. [Figure 12] This is a schematic diagram showing an exhaust gas treatment apparatus according to the fifth embodiment of this disclosure. [Figure 13] This graph shows the decomposition rate of nitrous oxide in the nitrogen oxide decomposition section in relation to the exhaust gas temperature, comparing the case where the NO concentration is 0 ppm and the case where it is 450 ppm. [Figure 14] A flowchart showing the supply process of fuel and reducing agent in the exhaust gas treatment apparatus according to the fifth embodiment of the present disclosure. [Figure 15] A flowchart showing the supply process of fuel and reducing agent in the exhaust gas treatment apparatus according to the fifth embodiment of the present disclosure. [Figure 16] A flowchart showing the supply process of fuel and reducing agent in the exhaust gas treatment apparatus according to the fifth embodiment of the present disclosure. [Figure 17] A schematic configuration diagram showing an exhaust gas treatment apparatus according to a modified example of the fifth embodiment of the present disclosure.

Embodiments for Carrying Out the Invention

[0012] 〔First Embodiment〕 Hereinafter, the exhaust gas treatment apparatus 100 according to the first embodiment of the present disclosure will be described with reference to the drawings. The exhaust gas treatment apparatus 100 of the present embodiment is an apparatus that treats exhaust gas discharged from a combustion apparatus 200 that burns fuel containing ammonia, and reduces ammonia, nitrous oxide, and NOx discharged to the outside.

[0013] The combustion apparatus 200 is an apparatus that burns fuel containing ammonia. For example, it is a marine diesel engine that generates the propulsion force of a ship. The combustion apparatus 200 of the present embodiment, for example, co - burns ammonia and other fuels (heavy oil, LNG (liquefied natural gas), LPG (liquefied petroleum gas)). Also, the combustion apparatus 200 may be an apparatus that uses only ammonia as fuel, for example.

[0014] Since ammonia is used as fuel in the combustion apparatus 200, the exhaust gas discharged from the combustion apparatus 200 contains unburned ammonia. Also, the exhaust gas discharged from the combustion apparatus 200 contains NOx (NO, NO₂) and nitrous oxide (N₂O) generated by the combustion of ammonia and other fuels. The exhaust gas treatment apparatus 100 of the present embodiment reduces ammonia, NOx, and nitrous oxide contained in the exhaust gas discharged from the combustion apparatus 200.

[0015] Figure 1 is a schematic diagram showing an exhaust gas treatment apparatus according to the first embodiment of the present disclosure. As shown in Figure 1, the exhaust gas treatment apparatus 100 of this embodiment includes an ammonia decomposition unit (first processing unit) 10, a nitrogen oxide decomposition unit (second processing unit) 20, an ammonia decomposition unit (third processing unit) 30, a detection unit 40, a first supply unit 50 that supplies ammonia or urea water as a reducing agent, a temperature sensor 60, a bypass valve 70, and a control unit 80.

[0016] The exhaust gas discharged from the combustion device 200 is supplied to the ammonia decomposition unit 10 via piping L1. The exhaust gas that has passed through the ammonia decomposition unit 10 is supplied to the nitrogen oxide decomposition unit 20 via piping L2. The exhaust gas that has passed through the nitrogen oxide decomposition unit 20 is supplied to the ammonia decomposition unit 30 via piping L3. The exhaust gas that has passed through the ammonia decomposition unit 30 is discharged to the outside via piping L4. If the bypass valve 70 is open, a portion of the exhaust gas that has passed through the nitrogen oxide decomposition unit 20 is led from piping L3 to piping L5 and then to piping L4 without passing through the ammonia decomposition unit 30.

[0017] In this embodiment, the exhaust gas treatment device 100 is equipped with piping L5 and a bypass valve 70, but a modified version without these may also be used. In this modified version, the entire amount of exhaust gas that has passed through the nitrogen oxide decomposition unit 20 is led to the ammonia decomposition unit 30.

[0018] The ammonia decomposition unit 10 has an ammonia decomposition catalyst (first catalyst) that decomposes ammonia contained in the exhaust gas discharged from the combustion device 200. The ammonia decomposition catalyst is a multi-functional catalyst that not only decomposes ammonia but also decomposes NOx and suppresses the generation of nitrous oxide. The ammonia decomposition catalyst of this embodiment is a catalyst consisting of a first component, which is silica and / or zeolite supported with one or more noble metals selected from platinum (Pt), palladium (Pd), iridium (Ir), and rhodium (Rh), and a second component, which is a composition consisting of oxides of one or more elements selected from titanium (Ti), tungsten (W), and vanadium (V). Examples of the ammonia decomposition catalyst will be described later.

[0019] The ammonia decomposition catalyst in the ammonia decomposition section 10 decomposes NH3 by the following formulas (1) and (2) using the first component. 4NH3 + 3O2 → 2N2 + 6H2O (1) 4NH3 + 5O2 → 4NO + 6H2O (2)

[0020] Furthermore, the ammonia decomposition catalyst in the ammonia decomposition section 10 decomposes NH3 according to the following formula (3) using the second component, and removes at least a portion of the NO by-products in formula (2). 4NH3 + 4NO + O2 → 4N2 + 6H2O (3)

[0021] Furthermore, in the ammonia decomposition catalyst of the ammonia decomposition section 10, it is presumed that nitrous oxide (N2O) is generated from NO2 produced by the oxidation of NH3 according to equation (4) according to equation (5). In the ammonia decomposition catalyst, a small amount of noble metal catalyst is uniformly present on the denitrification catalyst, so there is a high probability that the NO2 produced on the noble metal catalyst will immediately react with the NO produced in equation (2) on the denitrification catalyst as shown in equation (6) to form N2, thereby reducing the byproduct production of N2O. 4NH3 + 7O2 → 4NO2 + 6H2O (4) 4NH3 + 4NO2 + O2 → 4N2O + 6H2O (5) NO + NO2 + 2NH3 → 2N2 + 3H2O (6)

[0022] The nitrogen oxide decomposition unit 20 has a nitrogen oxide decomposition catalyst (second catalyst) that decomposes nitrous oxide and NOx contained in the exhaust gas from which ammonia has been decomposed in the ammonia decomposition unit 10. The nitrogen oxide decomposition catalyst contains a support containing SiO2 and Al2O3, and an iron element supported thereon. In the support, SiO2 and Al2O3 may be included as a mixture or as a composite. An example of a composite of SiO2 and Al2O3 is an aluminosilicate (xM2O·yAl2O3·zSiO2·nH2O). Examples of the nitrogen oxide decomposition catalyst will be described later.

[0023] The nitrogen oxide decomposition catalyst in the nitrogen oxide decomposition section 20 decomposes nitrous oxide by reducing it with NH3 according to the following formula (7). 3N2O + 2NH3 → 4N2 + 3H2O (7)

[0024] The nitrogen oxide decomposition catalyst in the nitrogen oxide decomposition section 20 decomposes NOx by reducing it with NH3 according to the following formulas (8), (9), and (10). 4NO + 4NH3 + O2 → 4N2 + 6H2O (8) NO + NO2 + 2NH3 → 2N2 + 3H2O (9) 6NO2 + 8NH3 → 7N2 + 12H2O (10)

[0025] The ammonia decomposition unit 30 has an ammonia decomposition catalyst (third catalyst) that decomposes ammonia contained in the exhaust gas that has passed through the nitrogen oxide decomposition unit 20. The ammonia decomposition catalyst is a multi-functional catalyst that not only decomposes ammonia but also decomposes NOx and suppresses the generation of nitrous oxide. The ammonia decomposition catalyst is a catalyst consisting of a first component, which is silica and / or zeolite supported with one or more noble metals selected from platinum (Pt), palladium (Pd), iridium (Ir), and rhodium (Rh), and a second component, which is a composition of oxides of one or more elements selected from titanium (Ti), tungsten (W), and vanadium (V). The configuration of the ammonia decomposition unit 30 is the same as that of the ammonia decomposition unit 10, so the following explanation is omitted.

[0026] The detection unit 40 is a device that detects the concentrations of nitrous oxide and NOx contained in the exhaust gas that has passed through the ammonia decomposition unit 10. The detection unit 40 detects the concentrations of nitrous oxide and NOx contained in the exhaust gas that has passed through the piping L3. The concentrations of nitrous oxide and NOx detected by the detection unit 40 are transmitted to the control unit 80.

[0027] The first supply unit 50 is a device that supplies ammonia or urea water, which is a reducing agent, to the exhaust gas supplied from the ammonia decomposition unit 10 to the nitrogen oxide decomposition unit 20. The first supply unit 50 supplies the reducing agent to pipe L2 via pipe L6 and mixes it with the exhaust gas flowing through pipe L2. Pipe L6 mixes the reducing agent with the exhaust gas by, for example, spraying the reducing agent into pipe L2. The first supply unit 50 adjusts the amount of reducing agent supplied to pipe L2 according to a control signal transmitted from the control unit 80.

[0028] When urea solution is supplied as a reducing agent, the urea solution mixed with the exhaust gas in piping L2 undergoes hydrolysis in the exhaust gas to produce ammonia. Then, the nitrogen oxide decomposition catalyst in the nitrogen oxide decomposition unit 20 decomposes NOx by reducing it with ammonia (NH3) according to the aforementioned equations (7), (8), and (9).

[0029] The temperature sensor 60 is a device that detects the temperature of the exhaust gas flowing through the piping L2. The temperature sensor 60 transmits the detected exhaust gas temperature to the control unit 80.

[0030] The bypass valve 70 is an on / off valve located in piping L5. The open / closed state of the bypass valve 70 is controlled by the control unit 80. When the bypass valve 70 is open, exhaust gas is guided from piping L3 to piping L4 via piping L5. When the bypass valve 70 is closed, no exhaust gas is guided to piping L5, and the entire amount of exhaust gas flowing through piping L3 is guided to piping L4 via the ammonia decomposition unit 30.

[0031] The control unit 80 is a device that controls each part of the exhaust gas treatment device 100. The control unit 80 controls each part of the exhaust gas treatment device 100 by reading and executing a control program stored in the memory unit (not shown).

[0032] The control unit 80 controls the amount of reducing agent supplied by the first supply unit 50 to the piping L2 according to the concentrations of nitrous oxide and NOx detected by the detection unit 40 and the temperature of the exhaust gas detected by the temperature sensor 60. The control unit 80 also controls the open / closed state of the bypass valve 70 according to the concentrations of nitrous oxide and NOx detected by the detection unit 40 and the temperature of the exhaust gas detected by the temperature sensor 60.

[0033] Next, with reference to Figure 2, the decomposition characteristics of the ammonia decomposition catalyst in the ammonia decomposition unit 10 of this embodiment will be described. Figure 2 is a graph showing the decomposition characteristics of the ammonia decomposition catalyst. As shown in Figure 2, as the temperature of the exhaust gas containing ammonia rises from 350°C to 450°C, the ammonia decomposition rate [%] by the ammonia decomposition catalyst in the ammonia decomposition unit 10 increases.

[0034] Next, with reference to Figure 3, the relationship between ammonia concentration and temperature rise in the ammonia decomposition catalyst of the ammonia decomposition unit 10 of this embodiment will be explained. Figure 3 is a graph showing the relationship between ammonia concentration and temperature rise in the ammonia decomposition catalyst.

[0035] As shown in Figure 3, the ammonia decomposition catalyst in the ammonia decomposition unit 10 generates heat when decomposing ammonia, causing the temperature of the exhaust gas to rise as the concentration of unburned ammonia in the exhaust gas discharged from the combustion device 200 increases. By burning the unburned ammonia in the ammonia decomposition catalyst of the ammonia decomposition unit 10, the temperature of the ammonia decomposition unit 10 can be increased, thereby increasing the ammonia decomposition rate. In addition, the temperature of the exhaust gas discharged from the ammonia decomposition unit 10 can be increased.

[0036] Next, with reference to Figure 4, the decomposition characteristics of nitrous oxide with respect to exhaust gas temperature will be explained. Figure 4 is a graph showing the decomposition characteristics of nitrous oxide with respect to exhaust gas temperature. The catalyst AF shown in Figure 4 corresponds to the catalyst AF described in the example of nitrogen oxide decomposition catalyst described later. As shown in Figure 4, in all catalyst AFs, the decomposition rate of nitrous oxide increases as the exhaust gas temperature rises. Therefore, when ammonia is decomposed by the ammonia decomposition catalyst in the ammonia decomposition section 10 and the exhaust gas temperature is raised, the decomposition rate of nitrous oxide increases with the rise in exhaust gas temperature.

[0037] Next, with reference to Figure 5, the decomposition characteristics of NO with respect to exhaust gas temperature will be explained. Figure 5 is a graph showing the decomposition characteristics of NO with respect to exhaust gas temperature. The catalyst AF shown in Figure 5 corresponds to the catalyst AF described in the example of nitrogen oxide decomposition catalyst later. As shown in Figure 5, in all catalysts AF, the decomposition rate of NO increases as the exhaust gas temperature rises. Therefore, when ammonia is decomposed by the ammonia decomposition catalyst in the ammonia decomposition section 10 and the exhaust gas temperature is raised, the decomposition rate of NO increases with the rise in exhaust gas temperature.

[0038] In this embodiment, the ammonia decomposition unit 10 is installed upstream of the nitrogen oxide decomposition unit 20 because it is assumed that the amount of unburned ammonia supplied in the exhaust gas discharged from the combustion device 200 exceeds the amount of ammonia required to decompose nitrous oxide and NOx in the nitrogen oxide decomposition unit 20. In this embodiment, the exhaust gas treatment device 100 decomposes excess ammonia in the ammonia decomposition unit 10, and the heat generated when the ammonia is decomposed raises the temperature of the exhaust gas, thereby increasing the decomposition rate of nitrous oxide and NOx in the nitrogen oxide decomposition unit 20.

[0039] The exhaust gas treatment device 100 of this embodiment assumes that the concentrations of ammonia, nitrous oxide, and NOx contained in the exhaust gas discharged from the combustion device 200 satisfy the following equation (11). Ammonia concentration > α × nitrous oxide concentration + β × NOx concentration (11)

[0040] Here, α and β are coefficients, for example, α = 1.0 and β = 1.5. α = 1.0 is obtained by multiplying the molar ratio of ammonia to nitrous oxide in reaction (7) (ammonia / nitrous oxide = 2 / 3) by 1.5. β = 1.5 is obtained by multiplying the molar ratio of ammonia to NO in reaction (8) (ammonia / NO = 1 / 1) by 1.5. Note that the values ​​multiplied by α and β are not limited to 1.5; for example, they may be set to any value between 1.2 and 2.0, depending on the properties of the exhaust gas from the combustion device 200.

[0041] On the other hand, if, for example, the amount of exhaust gas discharged from the exhaust gas treatment device 100 or the amount of ammonia contained in the exhaust gas is less than expected, the entire amount of unburned ammonia will be decomposed in the ammonia decomposition unit 10, resulting in a shortage of ammonia needed as a reducing agent in the nitrogen oxide decomposition unit 20. Therefore, in this embodiment, if there is a shortage of ammonia needed as a reducing agent in the nitrogen oxide decomposition unit 20, the shortage of ammonia in the nitrogen oxide decomposition unit 20 is compensated for by supplying a reducing agent from the first supply unit 50.

[0042] Next, with reference to Figure 6, the reducing agent supply process in the exhaust gas treatment device 100 of this embodiment will be described. Figure 6 is a flowchart showing the reducing agent supply process in the exhaust gas treatment device 100 of this embodiment. Each step in Figure 6 is performed by the control unit 80 controlling each part of the exhaust gas treatment device 100. The process in this flowchart starts when the combustion operation by the combustion device 200 begins.

[0043] In step S101, the control unit 80 determines whether the temperature Ta of the exhaust gas flowing through the pipe L2, as transmitted from the temperature sensor 60, is above the supply temperature (for example, 350°C) at which the reducing agent can be supplied to the nitrogen oxide decomposition unit 20. If YES, the process proceeds to step S102; otherwise, the process proceeds to step S108.

[0044] In step S108, the control unit 80 controls the supply of the reducing agent by the first supply unit 50 to stop because the temperature Ta of the exhaust gas flowing through the piping L2 is lower than the supply temperature at which the reducing agent can be supplied to the nitrogen oxide decomposition unit 20.

[0045] In step S102, the control unit 80 determines whether the NOx concentration detected by the detection unit 40 is less than or equal to a first predetermined concentration (for example, 200 ppm). If the result is YES, the process proceeds to step S103; otherwise, the process proceeds to step S105.

[0046] In step S103, the control unit 80 determines whether the nitrous oxide concentration detected by the detection unit 40 is less than or equal to a second predetermined concentration (for example, 50 ppm). If YES, the process proceeds to step S104; otherwise, the process proceeds to step S105.

[0047] In step S104, the control unit 80 determines that the reduction treatment of NOx and nitrous oxide by ammonia is being carried out appropriately because the NOx concentration is below a first predetermined concentration and the nitrous oxide concentration is below a second predetermined concentration, and controls the first supply unit 50 to reduce the amount of reducing agent supplied.

[0048] In step S105, the control unit 80 determines that the reduction treatment of NOx and nitrous oxide by ammonia is not sufficiently carried out because the NOx concentration is higher than the first predetermined concentration or the nitrous oxide concentration is higher than the second predetermined concentration, and controls the first supply unit 50 to increase the amount of reducing agent supplied, and proceeds to step S101.

[0049] In step S106, the control unit 80 determines whether the combustion device 200 is stopped. If it determines that the result is YES, it proceeds to step S107; otherwise, it repeats step S101. The combustion device 200 transmits its operating state, including the state in which the combustion operation is stopped, to the control unit 80.

[0050] In step S107, the control unit 80 determines that since the combustion device 200 is stopped, the reduction treatment of NOx and nitrous oxide by ammonia is unnecessary, and stops the supply of the reducing agent by the first supply unit 50, thus ending the process in this flowchart. When the combustion device 200 starts combustion operation, the control unit 80 resumes the process in this flowchart.

[0051] Next, with reference to Figure 7, the switching process of the bypass valve 70 in the exhaust gas treatment device 100 of this embodiment will be described. Figure 7 is a flowchart showing the switching process of the bypass valve 70 in the exhaust gas treatment device 100 of this embodiment. Each step in Figure 7 is performed by the control unit 80 controlling each part of the exhaust gas treatment device 100. The process in this flowchart starts when the combustion operation by the combustion device 200 begins.

[0052] The exhaust gas treatment device 100 of this embodiment has an ammonia decomposition unit 30 located downstream of the nitrogen oxide decomposition unit 20. The ammonia decomposition unit 30 is provided, for example, when the ammonia concentration in the exhaust gas discharged from the combustion device 200 is higher than a predetermined concentration and cannot be completely decomposed by the ammonia decomposition unit 10 and the nitrogen oxide decomposition unit 20, in order to reliably decompose excess ammonia and prevent it from being discharged to the outside.

[0053] On the other hand, if the concentration of ammonia in the exhaust gas discharged from the nitrogen oxide decomposition unit 20 is below a predetermined permissible concentration, the ammonia decomposition unit 30 does not need to treat the exhaust gas, and pressure loss occurs when the exhaust gas passes through the ammonia decomposition unit 30. Therefore, in this embodiment, if the concentration of ammonia in the exhaust gas discharged from the nitrogen oxide decomposition unit 20 is below a predetermined permissible concentration, a portion of the exhaust gas discharged from the nitrogen oxide decomposition unit 20 is guided to the piping L5 to prevent pressure loss when the exhaust gas passes through the ammonia decomposition unit 30.

[0054] In step S201, the control unit 80 determines whether the temperature Ta of the exhaust gas flowing through the pipe L2, as transmitted from the temperature sensor 60, is above the supply temperature (for example, 350°C) at which the reducing agent can be supplied to the nitrogen oxide decomposition unit 20. If YES, the process proceeds to step S203; otherwise, the process proceeds to step S202.

[0055] In step S202, the control unit 80 controls the bypass valve 70 to close because the temperature Ta of the exhaust gas flowing through the piping L2 is below the supply temperature at which the reducing agent can be supplied to the nitrogen oxide decomposition unit 20, and the temperature of the exhaust gas discharged from the combustion device 200 has not risen to an appropriate temperature.

[0056] In step S203, the control unit 80 determines whether the load on the combustion device 200 is less than or equal to a predetermined load (for example, 50% load). If it determines that the load is YES, it proceeds to step S204; otherwise, it repeats step S201. The combustion device 200 transmits the load of the combustion operation to the control unit 80.

[0057] In step S204, the control unit 80 controls the bypass valve 70 to open because the load on the combustion device 200 is below a predetermined load. When the load on the combustion device 200 is below a predetermined load, the concentration of ammonia in the exhaust gas discharged from the nitrogen oxide decomposition unit 20 is below a predetermined allowable concentration (for example, 5 ppm), and there is no need to treat the exhaust gas in the ammonia decomposition unit 30. Therefore, in order to reduce the pressure loss that occurs when the exhaust gas passes through the ammonia decomposition unit 30, a portion of the exhaust gas flowing through piping L3 is guided from piping L5 to piping L4.

[0058] In step S205, the control unit 80 determines whether the combustion device 200 is stopped. If it determines that the result is YES, it proceeds to step S206; otherwise, it repeats step S201. The combustion device 200 transmits its operating state, including the state in which the combustion operation is stopped, to the control unit 80.

[0059] In step S206, the control unit 80 closes the bypass valve 70 because the combustion device 200 is stopped, and terminates the processing of this flowchart. When the combustion device 200 starts combustion operation, the control unit 80 resumes the processing of this flowchart.

[0060] In the above description, the detection unit 40 is assumed to detect the concentrations of nitrous oxide and NOx contained in the exhaust gas that has passed through the ammonia decomposition unit 10, but other configurations are also possible. The detection unit 40 may detect the concentration of either nitrous oxide or NOx contained in the exhaust gas that has passed through the ammonia decomposition unit 10. If the detection unit 40 detects the concentration of nitrous oxide, the process in step S102 of Figure 6 is omitted. Also, if the detection unit 40 detects the concentration of NOx, the process in step S103 of Figure 6 is omitted.

[0061] [Examples of ammonia decomposition catalysts] The ammonia decomposition catalyst for the ammonia decomposition unit 10 of this embodiment can be obtained, for example, by any of the following embodiments.

[0062] Example 1 1.33 × 10 -2 To 1 liter of wt% aqueous solution of chloroplatinic acid (H2[PtCl6]·6H2O), 100 g of fine silica powder (manufactured by Tomita Pharmaceutical Co., Ltd., anhydrous silicic acid) was added and evaporated to dryness on a sand bath. The mixture was then calcined in air at 500°C for 2 hours to prepare 0.05 wt% Pt·SiO2, thereby obtaining the catalyst composition powder of the first component.

[0063] On the other hand, 46.7 kg of titanium dioxide powder (manufactured by Ishihara Sangyo Co., Ltd., product name, MCH, SO4 content: 3 wt%) contains ammonium paratungstate ((NH4) 10 ·W 12 O 41 7.43 kg of (5H2O) and 3.0 kg of ammonium metavanadate were added and kneaded using a kneader. The resulting paste was granulated, dried, and calcined at 550°C for 2 hours. The resulting granules were pulverized to obtain the catalyst composition powder, which is the second component. The composition is Ti / W / V = 91 / 5 / 4 (atomic ratio).

[0064] A slurry was prepared by suspending 20 g of the first component and 2.02 kg of the second component in 3.06 kg of water. This slurry was then immersed in a paper honeycomb carrier (manufactured by Nichias Corporation, trade name: Honeycle 3722, 150 mm x 150 mm square, 50 mm long) to impregnate the carrier with the slurry. After impregnation, the slurry was removed by air blowing to obtain the catalyst of this example. This was air-dried in the atmosphere for 12 hours and then calcined at 500°C for 2 hours. The ratio of the first component to the second component in this catalyst is 1 / 99 (by weight, the same applies below), the Pt content in the catalyst components corresponds to 5 ppm, and the amount of catalyst supported per carrier surface area is 150 g / m² for the first and second components combined. 2 The honeycomb catalyst was obtained, and a 50mm long, 5-stage x 8-cell (11 x 14mm) section was cut out to obtain test pieces.

[0065] Example 2 The catalyst of this example was obtained in the same manner as in Example 1, except that the amount of the first component was changed to 10 g, the second component to 2.02 kg, and the amount of water to 3.04 kg. The ratio of the first component to the second component in this catalyst was 0.5 / 99.5, the Pt content in the catalyst components was 2.5 ppm, and the amount of catalyst supported, with the first and second components combined, was 150 g / m² per surface area of ​​the carrier.2 That was the case.

[0066] Examples 3-5 Using the first and second components obtained in Example 1, the amount of water added during slurry preparation was changed to 476 and 816 kg, respectively. The resulting slurry was then supported on a paper honeycomb carrier (manufactured by Nichias Corporation, trade name: Honeycle 3319, 150 mm x 150 mm square, 50 mm long) in the same manner as in Example 1 to obtain the catalyst of this example. The ratio of the first component to the second component in this catalyst is 1 / 99, and the Pt content in the catalyst components corresponds to 5 ppm. The supported amounts of the catalyst in Examples 3-5 were 100, 80, and 50 g / m² of the carrier surface area for the first and second components combined. 2 That was the case.

[0067] Example 6 The catalyst of this example was obtained in the same manner as in Example 1, except that the paper honeycomb support of Example 1 was replaced with metal lath (SUS304, plate thickness 0.2 mmt, 150 mm x 150 mm square). The ratio of the first component to the second component in this catalyst is 1 / 99, and the Pt content in the catalyst components corresponds to 5 ppm. The amount of catalyst supported, including both the first and second components, is 200 g / m² per surface area of ​​the support. 2 That was the case.

[0068] Example 7 The catalyst for this example was prepared in the same manner as in Example 1, except that the water used for slurry preparation was changed to colloidal silica (manufactured by Nissan Chemical Corporation, trade name, OS sol, SiO2 20%) / water = 3 / 7.

[0069] Example 8 20 g of the first component prepared in Example 1 was suspended in 1000 g of a colloidal silica / water = 3 / 7 solution. A paper honeycomb support was immersed in this solution to impregnate the support with the slurry, then the liquid was removed by air blowing, the support was air-dried in the air for 12 hours, and then calcined at 500°C for 2 hours. The resulting catalyst was immersed in a slurry obtained by suspending 2.02 kg of the second component from Example 1 in 3.06 kg of water, then the liquid was removed, the support was air-dried, and then calcined at 500°C for 2 hours to prepare the catalyst of this example.

[0070] [Examples of nitrogen oxide decomposition catalysts] The nitrogen oxide decomposition catalyst in the nitrogen oxide decomposition unit 20 of this embodiment is, for example, one of the following catalyst AEs.

[0071] Catalyst A (Ion loading process (ion exchange)) 60 g of BEA-type zeolite (SiO2 / Al2O3 ratio = 25) was added to 2000 ml of an aqueous solution containing 13.2 g of iron(III) nitrate nonahydrate (Fe2(NO2)2·9H2O) heated to 80°C. The mixture was then stirred for 3 hours while maintaining the temperature at 80°C to obtain a slurry. The slurry was dehydrated using a suction funnel fitted with filter paper (No. 5C). A predetermined amount of pure water was poured onto the cake on the filter paper and washed. The washed cake was dried at 110°C for 12 hours and then calcined at 500°C for 5 hours. The calcined material was pulverized in a planetary ball mill to obtain powdered Fe-supported zeolite catalyst A.

[0072] (Honeycomb coating process) Fe-supported zeolite catalyst A was added to pure water and then stirred to obtain a catalyst slurry. The catalyst slurry was applied to a honeycomb substrate at a coating rate of 70 g / m2. This was dried at 120°C for 2 hours and then calcined at 500°C for 2 hours to obtain honeycomb catalyst A.

[0073] Catalyst B Powdered Fe-supported zeolite catalyst B and honeycomb catalyst B were obtained using the same manufacturing method as catalyst A, except that BEA-type zeolite (SiO2 / Al2O3 ratio = 25) was replaced with BEA-type zeolite (SiO2 / Al2O3 ratio = 28).

[0074] Catalyst C Powdered Fe-supported zeolite catalyst C and honeycomb catalyst C were obtained using the same manufacturing method as catalyst A, except that BEA-type zeolite (SiO2 / Al2O3 ratio = 25) was replaced with BEA-type zeolite (SiO2 / Al2O3 ratio = 7.5).

[0075] Catalyst D 60 g of CHA-type zeolite (SiO2 / Al2O3 ratio = 24) was added to 2000 ml of an aqueous solution containing 13.2 g of iron(III) nitrate nonahydrate (Fe2(NO3)3·9H2O) heated to 80°C. The mixture was then stirred for 3 hours while maintaining the temperature at 80°C to obtain a slurry. The slurry was filtered using a suction funnel fitted with filter paper (No. 5C). A predetermined amount of pure water was poured over the cake on the filter paper and washed. The washed cake was dried at 110°C for 12 hours and then baked at 500°C for 5 hours. The baked material was ground in a planetary ball mill to obtain a powder.

[0076] This powder was added to 2000 ml of an aqueous solution containing 13.2 g of iron(III) nitrate nonahydrate (Fe2(NO3)3·9H2O), and the above procedure was repeated two more times (a total of three ion exchange steps) to obtain powdered Fe-supported zeolite catalyst D. Honeycomb catalyst D was obtained using the same manufacturing method as catalyst A, except that Fe-supported zeolite catalyst A was replaced with Fe-supported zeolite catalyst D.

[0077] Catalyst E Powdered Fe-supported zeolite catalyst E and honeycomb catalyst E were obtained using the same manufacturing method as catalyst A, except that BEA-type zeolite (SiO2 / Al2O3 ratio = 25) was replaced with MFI-type zeolite (SiO2 / Al2O3 ratio = 30).

[0078] Catalyst F Powdered Fe-supported zeolite catalyst F and honeycomb catalyst F were obtained using the same manufacturing method as catalyst A, except that BEA-type zeolite (SiO2 / Al2O3 ratio = 25) was replaced with BEA-type zeolite (SiO2 / Al2O3 ratio = 24).

[0079] The operation and effects of the exhaust gas treatment device 100 of this embodiment, as described above, will now be explained. According to the exhaust gas treatment device 100 of this disclosure, ammonia contained in the exhaust gas discharged from the combustion device 200 is appropriately decomposed by the ammonia decomposition catalyst as it passes through the ammonia decomposition unit 10. In addition, nitrous oxide and NOx generated when ammonia is burned in the combustion device 200 are appropriately decomposed by the nitrogen oxide decomposition catalyst as they pass through the nitrogen oxide decomposition unit 20. Thus, according to the exhaust gas treatment device 100 of this disclosure, ammonia and nitrous oxide contained in the exhaust gas discharged from the combustion device 200 that burns fuel containing ammonia can be appropriately decomposed.

[0080] According to the exhaust gas treatment device 100 of this embodiment, even if ammonia remains in the exhaust gas after passing through the nitrogen oxide decomposition unit 20, the ammonia can be decomposed in the ammonia decomposition unit 30, thereby preventing the ammonia from being discharged to the outside.

[0081] According to the exhaust gas treatment device 100 of this embodiment, if the detection unit 40 detects that the concentration of nitrous oxide contained in the exhaust gas that has passed through the nitrogen oxide decomposition unit 20 is higher than a first predetermined concentration, or that the concentration of NOx contained in the exhaust gas that has passed through the nitrogen oxide decomposition unit 20 is higher than a second predetermined concentration, a reducing agent is supplied from the first supply unit 50 to the exhaust gas supplied to the nitrogen oxide decomposition unit 20 in order to compensate for the shortage of ammonia for reducing nitrous oxide and NOx. As a result, the shortage of ammonia supplied from the ammonia decomposition unit 10 to the nitrogen oxide decomposition unit 20 is compensated, and the concentrations of nitrous oxide and NOx contained in the exhaust gas that has passed through the nitrogen oxide decomposition unit 20 can be reduced.

[0082] [Second Embodiment] Hereinafter, the exhaust gas treatment device 100A of the second embodiment of this disclosure will be described with reference to the drawings. The exhaust gas treatment device 100A of this embodiment is a modified version of the exhaust gas treatment device 100 of the first embodiment, and is the same as the first embodiment unless otherwise specifically described below, so the following description will be omitted.

[0083] The exhaust gas treatment device 100B of this embodiment differs from the exhaust gas treatment device 100 of the first embodiment in that it includes a piping (bypass piping) L7 that guides a portion of the exhaust gas flowing through piping L1 to piping L2, and a bypass valve 90 located in piping L7.

[0084] Figure 8 is a schematic diagram showing an exhaust gas treatment device 100A according to the second embodiment of this disclosure. As shown in Figure 8, the exhaust gas treatment device 100A of this embodiment includes a pipe L7 that guides a portion of the exhaust gas flowing through pipe L1 to pipe L2, and a bypass valve 90 arranged in pipe L7.

[0085] The bypass valve 90 is an on / off valve located in piping L7. The open / closed state of the bypass valve 90 is controlled by the control unit 80. When the bypass valve 90 is open, exhaust gas is guided from piping L1 to piping L2 via piping L7. When the bypass valve 90 is closed, no exhaust gas is guided to piping L7, and the entire amount of exhaust gas flowing through piping L1 is guided to piping L2 via the ammonia decomposition unit 10.

[0086] In this embodiment, the exhaust gas treatment device 100A closes the bypass valve 90 when the amount of unburned ammonia supplied from the exhaust gas discharged from the combustion device 200 exceeds the amount of ammonia required to decompose nitrous oxide and NOx in the nitrogen oxide decomposition unit 20, guiding the entire amount of exhaust gas flowing through the piping L1 to the ammonia decomposition unit 10, where the excess ammonia is decomposed.

[0087] On the other hand, in this embodiment, if the amount of unburned ammonia supplied from the exhaust gas discharged from the combustion device 200 is equal to or less than the amount of ammonia required to decompose nitrous oxide and NOx in the nitrogen oxide decomposition unit 20, the exhaust gas treatment device 100A opens the bypass valve 90 and directs a portion of the exhaust gas flowing through the piping L1 to the piping L2 without passing through the ammonia decomposition unit 10.

[0088] Next, with reference to Figure 9, the switching process of the bypass valve 90 of the exhaust gas treatment device 100A according to this embodiment will be described. Figure 9 is a flowchart showing the switching process of the bypass valve 90 of the exhaust gas treatment device 100A according to this embodiment. Each step in Figure 9 is performed by the control unit 80 controlling each part of the exhaust gas treatment device 100A. The process in this flowchart starts when the combustion operation by the combustion device 200 begins.

[0089] In step S301, the control unit 80 determines whether the temperature Ta of the exhaust gas flowing through the pipe L2, as transmitted from the temperature sensor 60, is above the supply temperature (for example, 350°C) at which the reducing agent can be supplied to the nitrogen oxide decomposition unit 20. If YES, the process proceeds to step S302; otherwise, the process proceeds to step S305.

[0090] In step S302, the control unit 80 calculates the concentrations of ammonia, nitrous oxide, and NOx in the exhaust gas discharged from the combustion device 200 based on the load of the combustion device 200. The combustion device 200 transmits the load of its combustion operation to the control unit 80. The control unit 80 stores in a memory unit (not shown) a map of the concentrations of ammonia, nitrous oxide, and NOx associated with each of the multiple loads of the combustion device 200. The control unit 80 calculates the concentration associated with the load transmitted from the combustion device 200 by referring to the map stored in the memory unit.

[0091] In step S303, the control unit 80 determines whether the ammonia concentration calculated in step S302 is less than or equal to a predetermined concentration. If it is YES, the process proceeds to step S304; otherwise, the process proceeds to step S305. Here, the predetermined concentration is the concentration shown in the following formula (12). α・Nitrous oxide concentration + β・NOx concentration (12) Here, α and β are coefficients, for example, α = 1.0, which is the same as that described in equation (11) of the first embodiment.

[0092] In step S304, the control unit 80 opens the bypass valve 90 because the ammonia concentration is below a predetermined concentration and there is no need to supply the entire amount of exhaust gas to the ammonia decomposition unit 10 in order to decompose the excess ammonia in the ammonia decomposition unit 10.

[0093] In step S305, the control unit 80 closes the bypass valve 90 because the exhaust gas temperature Ta is below the supply temperature at which the reducing agent can be supplied to the nitrogen oxide decomposition unit 20, or the ammonia concentration is higher than a predetermined concentration. This is because the temperature of the exhaust gas discharged from the combustion device 200 is not sufficiently high, or the ammonia concentration in the exhaust gas is higher than a predetermined concentration, so it is necessary to supply the entire amount of exhaust gas to the ammonia decomposition unit 10.

[0094] In step S306, the control unit 80 determines whether the combustion device 200 is stopped. If it determines that the result is YES, it proceeds to step S307. If it determines that the result is NO, it repeats step S301. The combustion device 200 transmits its operating state, including the state in which the combustion operation is stopped, to the control unit 80.

[0095] In step S307, the control unit 80 closes the bypass valve 90 because the combustion device 200 is stopped, and terminates the processing of this flowchart. When the combustion device 200 starts combustion operation, the control unit 80 resumes the processing of this flowchart.

[0096] The operation and effects of the exhaust gas treatment device 100B of this embodiment, as described above, will now be explained. According to the exhaust gas treatment device 100A of this embodiment, if the concentration of ammonia contained in the exhaust gas discharged from the combustion device 200 is higher than the concentration required as a reducing agent when decomposing nitrous oxide and NOx in the nitrogen oxide decomposition unit 20, the bypass valve 90 can be closed to allow the excess ammonia to be decomposed in the ammonia decomposition unit 10. Also, if the concentration of ammonia contained in the exhaust gas discharged from the combustion device 200 is the same as or lower than the concentration required as a reducing agent when decomposing nitrous oxide and NOx in the nitrogen oxide decomposition unit 20, the bypass valve 90 can be opened to allow the ammonia to be introduced to the nitrogen oxide decomposition unit 20 without being decomposed in the ammonia decomposition unit 10.

[0097] [Third Embodiment] Hereinafter, the exhaust gas treatment device 100B of the second embodiment of this disclosure will be described with reference to the drawings. The exhaust gas treatment device 100B of this embodiment is a modified version of the exhaust gas treatment device 100 of the first embodiment, and is the same as the first embodiment unless otherwise specifically described below, so the following description will be omitted.

[0098] In the first embodiment, the exhaust gas treatment device 100 had an ammonia decomposition unit 10 located upstream of the nitrogen oxide decomposition unit 20. In contrast, the exhaust gas treatment device 100B of this embodiment does not have an ammonia decomposition unit 10 located upstream of the nitrogen oxide decomposition unit 20.

[0099] Figure 10 is a schematic diagram showing an exhaust gas treatment device 100B according to a third embodiment of the present disclosure. As shown in Figure 10, in this embodiment, the exhaust gas treatment device 100B does not have an ammonia decomposition unit 10 located upstream of the nitrogen oxide decomposition unit 20, and the exhaust gas discharged from the combustion device 200 is supplied to the nitrogen oxide decomposition unit 20 via piping L1.

[0100] In this embodiment, the ammonia decomposition unit 10 is not installed upstream of the nitrogen oxide decomposition unit 20 because it is assumed that the amount of unburned ammonia supplied from the exhaust gas discharged from the combustion device 200 is the same as or less than the amount of ammonia required to decompose nitrous oxide and NOx in the nitrogen oxide decomposition unit 20. The exhaust gas treatment device 100B of this embodiment compensates for the deficiency of ammonia required as a reducing agent to decompose nitrous oxide and NOx contained in the exhaust gas by supplying it from the first supply unit 50.

[0101] The exhaust gas treatment device 100B of this embodiment assumes that the concentrations of ammonia, nitrous oxide, and NOx contained in the exhaust gas discharged from the combustion device 200 satisfy the following equation (13). Ammonia concentration ≤ α-nitrous oxide concentration + β-NOx concentration (13) Here, α and β are coefficients, similar to those described in equation (11) of the first embodiment.

[0102] The reducing agent supply process in the exhaust gas treatment device 100B of this embodiment is the same as the process shown in Figure 6 of the first embodiment. Also, the switching process of the bypass valve 70 in the exhaust gas treatment device 100A of this embodiment is the same as the process shown in Figure 7 of the first embodiment.

[0103] The operation and effects of the exhaust gas treatment device 100B of this embodiment, as described above, will now be explained. According to the exhaust gas treatment device 100B of this embodiment, ammonia contained in the exhaust gas discharged from the combustion device 200 is decomposed by the nitrogen oxide decomposition catalyst as a reducing agent when it passes through the nitrogen oxide decomposition section 20, reacting with nitrous oxide and NOx. In addition, nitrous oxide and NOx generated when ammonia is burned in the combustion device 200 are appropriately decomposed by the nitrogen oxide decomposition catalyst when they pass through the nitrogen oxide decomposition section 20. Thus, according to the exhaust gas treatment device 100B of this embodiment, ammonia, nitrous oxide, and NOx contained in the exhaust gas discharged from the combustion device 200 that burns fuel containing ammonia can be appropriately decomposed.

[0104] [Fourth Embodiment] The following describes a design method for an exhaust gas treatment device according to the fourth embodiment of this disclosure. The design method of this embodiment is a method for deciding whether to design an exhaust gas treatment device in which the ammonia decomposition unit 10 is located upstream of the nitrogen oxide decomposition unit 20, as in the exhaust gas treatment devices 100 and 100A described in the first and second embodiments, or to design an exhaust gas treatment device in which the ammonia decomposition unit 10 is not located upstream of the nitrogen oxide decomposition unit 20, as in the exhaust gas treatment device 100B described in the third embodiment.

[0105] Figure 11 is a flowchart showing the design method for the exhaust gas treatment apparatus according to this embodiment. In step S401, the concentrations of ammonia, nitrous oxide, and NOx in the exhaust gas emitted from the combustion device 200 are calculated. The concentrations of each component are determined by assuming that the combustion device 200 operates at a predetermined constant load, and the concentrations of ammonia, nitrous oxide, and NOx in the exhaust gas at that load are identified.

[0106] In step S402, it is determined whether the ammonia concentration calculated in step S401 is below a predetermined concentration. If YES, the process proceeds to step S403; otherwise, the process proceeds to step S404. Here, the predetermined concentration is the concentration shown by formula (12) of the second embodiment, which is the α-nitrous oxide concentration + β-NOx concentration.

[0107] In step S403, since the ammonia concentration in the exhaust gas discharged from the combustion device 200 is below a predetermined concentration, the exhaust gas treatment device 100B of the third embodiment is designed without placing the ammonia decomposition unit 10 upstream of the nitrogen oxide decomposition unit 20. This design is adopted because there is no need to place the ammonia decomposition unit 10 upstream of the nitrogen oxide decomposition unit 20 to decompose excess ammonia.

[0108] In step S404, since the ammonia concentration in the exhaust gas discharged from the combustion device 200 is higher than a predetermined concentration, the exhaust gas treatment device 100 of the first embodiment or the exhaust gas treatment device 100A of the second embodiment is designed with the ammonia decomposition unit 10 located upstream of the nitrogen oxide decomposition unit 20. This design is adopted because, since the ammonia concentration in the exhaust gas is higher than a predetermined concentration, it is necessary to supply the entire amount of exhaust gas to the ammonia decomposition unit 10 to decompose the excess ammonia.

[0109] According to the exhaust gas treatment device design method of this embodiment, if the concentration of ammonia contained in the exhaust gas is higher than the sum of the first concentration obtained by multiplying the concentration of nitrous oxide contained in the exhaust gas by α (first coefficient) and the second concentration obtained by multiplying the concentration of NOx contained in the exhaust gas by β (second coefficient), the exhaust gas treatment device is designed so that the ammonia decomposition unit 10 is located downstream of the combustion device 200 and the nitrogen oxide decomposition unit 20 is located downstream of the ammonia decomposition unit 10, in order to prevent the concentration of ammonia supplied from the ammonia decomposition unit 10 to the nitrogen oxide decomposition unit 20.

[0110] On the other hand, if the ammonia concentration in the exhaust gas is less than or equal to the sum of the first concentration (obtained by multiplying the nitrous oxide concentration in the exhaust gas by α (first coefficient)) and the second concentration (obtained by multiplying the NOx concentration in the exhaust gas by β (second coefficient)), the concentration of ammonia supplied from the ammonia decomposition unit 10 to the nitrogen oxide decomposition unit 20 will not be excessive. Therefore, the exhaust gas treatment device is designed so that the nitrogen oxide decomposition unit 20 is placed downstream of the combustion device 200 without placing the ammonia decomposition unit 10. This makes it possible to design an exhaust gas treatment device with an appropriate configuration according to the ammonia concentration in the exhaust gas discharged from the combustion device 200.

[0111] [Fifth Embodiment] Next, the exhaust gas treatment device 100C of the fifth embodiment of this disclosure will be described with reference to the drawings. The exhaust gas treatment device 100C of this embodiment is a modified version of the exhaust gas treatment device 100 of the first embodiment, and is the same as the first embodiment unless otherwise specifically described below, so the following description will be omitted.

[0112] The exhaust gas treatment device 100C of this embodiment differs from the exhaust gas treatment device 100 of the first embodiment in that it includes a second supply unit 55 that supplies ammonia or urea water as fuel for heating the ammonia decomposition catalyst (first processing unit) of the ammonia decomposition unit 10 to the exhaust gas supplied from the combustion device 200 to the ammonia decomposition unit 10. Furthermore, the exhaust gas treatment device 100C of this embodiment differs from the exhaust gas treatment device 100 of the first embodiment in that it does not include an ammonia decomposition unit 30.

[0113] Figure 12 is a schematic diagram showing the exhaust gas treatment device 100C according to this embodiment. As shown in Figure 12, the exhaust gas treatment device 100C of this embodiment includes an ammonia decomposition unit (first processing unit) 10, a nitrogen oxide decomposition unit (second processing unit) 20, a detection unit 40, a first supply unit 50, a second supply unit 55, a temperature sensor 60, and a control unit 80. The other components, except for the second supply unit 55, are the same as in the first embodiment, so their description is omitted below.

[0114] The second supply unit 55 is a device that supplies ammonia or urea water as fuel for heating the ammonia decomposition catalyst to the exhaust gas supplied from the combustion device 200 to the ammonia decomposition unit 10 when the temperature detected by the temperature sensor 60 is below a predetermined temperature. The second supply unit 55 supplies urea water to pipe L1 via pipe L8, and generates ammonia by the hydrolysis reaction of the urea water.

[0115] The ammonia introduced into the ammonia decomposition unit 10 is decomposed by the ammonia decomposition catalyst through the reaction of formulas (1) and (2) in the first embodiment. The exothermic reaction during the decomposition of ammonia heats the exhaust gas passing through the ammonia decomposition unit 10. Alternatively, instead of supplying urea water from the second supply unit 55, ammonia may be supplied from the second supply unit 55 to the piping L2.

[0116] The inventors experimentally confirmed the relationship between the properties of the exhaust gas discharged from the combustion device 200 and the decomposition rate of nitrous oxide, and found that there is a temperature range in which the decomposition rate of nitrous oxide changes depending on the concentration of NO contained in the exhaust gas. If the decomposition rate of nitrous oxide changes depending on the concentration of NO contained in the exhaust gas, the exhaust gas treatment device 100 of the first embodiment may not be able to obtain the desired decomposition rate of nitrous oxide. Therefore, the exhaust gas treatment device 100C of this embodiment operates the nitrogen oxide decomposition unit 20 in a temperature range in which the decomposition rate of nitrous oxide does not change depending on the concentration of NO contained in the exhaust gas.

[0117] Figure 13 is a graph showing the decomposition rate of nitrous oxide in the nitrogen oxide decomposition unit 20 with respect to exhaust gas temperature, comparing the cases where the NO concentration is 0 ppm and 450 ppm. Figure 13 shows an example in which catalyst A is used as the nitrogen oxide decomposition catalyst in the nitrogen oxide decomposition unit 20. The example shown by the solid line and the example shown by the dotted line in Figure 13 differ in that the NO concentration in the exhaust gas is 450 ppm and 0 ppm, respectively. On the other hand, the example shown by the solid line and the example shown by the dotted line in Figure 13 are similar in that the nitrous oxide concentration in the exhaust gas is 180 ppm, the ammonia concentration in the exhaust gas is 570 ppm, the oxygen concentration in the exhaust gas is 13%, the sulfur dioxide concentration in the exhaust gas is 15 ppm, the water concentration in the exhaust gas is 15%, and the remainder is nitrogen.

[0118] As shown in Figure 13, when the exhaust gas temperature is near 450°C, there is almost no difference in the decomposition rate of nitrous oxide even if the NO concentration in the exhaust gas differs between 450 ppm and 0 ppm. On the other hand, as the exhaust gas temperature falls below 450°C, the difference in the decomposition rate of nitrous oxide increases. Specifically, at the same exhaust gas temperature, the decomposition rate of nitrous oxide when the NO concentration in the exhaust gas is 0 ppm is lower than the decomposition rate when the NO concentration in the exhaust gas is 450 ppm.

[0119] The reason Figure 13 shows the above trend is presumed to be that, in the temperature range below 450°C, the oxygen bonded to the nitrogen oxide decomposition catalyst in equation (11) was removed in equation (12) and / or nitrous oxide was reduced in the reaction of equation (13). In other words, it is presumed that the decomposition rate of nitrous oxide is higher when NO is present in the exhaust gas together with nitrous oxide. 2N2O → 2N2 + 3O2 (11) 4NO + 4NH3 + O2 → 4N2 + 6H2O (12) N2O + NO → N2 + NO2 (13)

[0120] Considering the experimental results shown in Figure 13, the inventors set the temperature range so that the temperature of the exhaust gas discharged from the ammonia decomposition unit 10 is 450°C or higher, so that the decomposition rate of nitrous oxide does not change depending on the concentration of NO contained in the exhaust gas. Furthermore, in order to reduce thermal stress on the catalytic reactor and suppress thermal degradation of the catalyst, the inventors set the temperature range so that the temperature of the exhaust gas discharged from the ammonia decomposition unit 10 is 530°C or lower.

[0121] Next, with reference to Figures 14 to 16, the fuel and reducing agent supply process in the exhaust gas treatment device 100C according to this embodiment will be described. Figures 14 to 16 are flowcharts showing the fuel and reducing agent supply process in the exhaust gas treatment device 100C according to this embodiment. Each step in Figures 14 to 16 is performed by the control unit 80 controlling each part of the exhaust gas treatment device 100C. The process in this flowchart starts when the combustion operation by the combustion device 200 begins.

[0122] In step S401, the control unit 80 determines whether the temperature Ta of the exhaust gas flowing through the pipe L2, as transmitted from the temperature sensor 60, is above the fuel supply temperature (for example, 300°C) at which fuel for heating the ammonia decomposition catalyst (first processing unit) can be supplied from the second supply unit 55 to the ammonia decomposition unit 10. If YES, the process proceeds to step S402; otherwise, the process proceeds to step S403.

[0123] In step S402, the control unit 80 controls the second supply unit 55 to increase the amount of fuel supplied from the second supply unit 55 to the piping L1. When step S402 is executed for the first time after step S401, the amount of fuel supplied by the second supply unit 55 is increased from 0 to a predetermined supply amount.

[0124] In step S403, the control unit 80 controls the second supply unit 55 to stop supplying fuel because the temperature Ta of the exhaust gas flowing through the piping L1 is lower than the fuel supply temperature at which fuel can be supplied to the ammonia decomposition unit 10.

[0125] In step S404, the control unit 80 determines whether the exhaust gas temperature Ta is above the reducing agent supply temperature (for example, 450°C) at which the reducing agent can be supplied to the nitrogen oxide decomposition unit 20. If YES, the process proceeds to step S405; otherwise, the process proceeds to step S402 to increase the amount of fuel supplied from the second supply unit 55.

[0126] In step S405, the control unit 80 controls the first supply unit 50 to increase the amount of reducing agent supplied from the first supply unit 50 to the piping L2. When step S405 is executed for the first time after step S404, the amount of reducing agent supplied by the first supply unit 50 is increased from 0 to a predetermined supply amount.

[0127] In step S406, the control unit 80 determines whether the NOx concentration detected by the detection unit 40 is less than or equal to a first predetermined concentration (for example, 200 ppm). If the result is YES, the process proceeds to step S407; otherwise, the process proceeds to step S414.

[0128] In step S407, the control unit 80 determines whether the nitrous oxide concentration detected by the detection unit 40 is less than or equal to a second predetermined concentration (for example, 10 ppm). If YES, the process proceeds to step S408; otherwise, the process proceeds to step S414.

[0129] In step S408, the control unit 80 controls the combustion device 200 to release the load limit on the combustion device 200. Until the load limit is released in this step, the control unit 80 controls the combustion device 200 to keep the load below a predetermined level. This is because if the amount of reducing agent supplied from the first supply unit 50 to the nitrogen oxide decomposition unit 20 to reduce the NOx concentration and nitrous oxide concentration becomes excessive when the combustion device 200 is operated without a load limit, unreacted ammonia may be discharged from the nitrogen oxide decomposition unit 20 to the outside through the piping L3.

[0130] Until the load limit is released in this step, the combustion device 200 is controlled to remain below a predetermined load, thereby preventing unreacted ammonia from being discharged from the nitrogen oxide decomposition unit 20 to the outside via the piping L3, and keeping the NOx and nitrous oxide concentrations below thresholds, thereby reducing the environmental burden.

[0131] In step S409, the control unit 80 determines whether the temperature Ta is below the first upper limit temperature (for example, 480°C). If it is YES, the process proceeds to step S410; otherwise, the process proceeds to step S411.

[0132] In step S410, the control unit 80 reduces the amount of fuel supplied from the second supply unit 55 to the piping L1 so that the temperature Ta falls below the first upper limit temperature. After executing step S410, the control unit 80 proceeds to step S404.

[0133] In step S411, the control unit 80 reduces the amount of reducing agent supplied from the first supply unit 50 to the piping L2 because the temperature Ta is lower than the first upper limit temperature, and proceeds to step S412.

[0134] In step S412, the control unit 80 determines whether the combustion device 200 is stopped. If it determines that the status is YES, it proceeds to step S413; otherwise, it repeats step S404. The combustion device 200 transmits its operating status, including the state in which the combustion operation is stopped, to the control unit 80.

[0135] In step S413, the control unit 80 stops the supply of reducing agent by the first supply unit 50 and the supply of fuel by the second supply unit 55 because the combustion device 200 is stopped, and terminates the processing of this flowchart. When the combustion device 200 starts combustion operation, the control unit 80 resumes the processing of this flowchart.

[0136] In step S414, the control unit 80 calculates the amount of reducing agent required to reduce NOx and nitrous oxide based on the NOx concentration and nitrous oxide concentration calculated in step S302 in Figure 9. It then determines whether the amount of reducing agent supplied is greater than the amount obtained by multiplying the required amount of reducing agent by a predetermined coefficient γ. If YES, the process proceeds to step S415; otherwise, the process proceeds to step S405. Here, the predetermined amount of reducing agent supplied is the amount supplied by multiplying the amount of reducing agent required to reduce NOx and nitrous oxide contained in the total nitrogen oxide concentration by a predetermined coefficient γ. The coefficient γ is set to a value of, for example, 0.8 or more and 1.2 or less.

[0137] In step S415, the control unit 80 determines whether the temperature Ta is below the second upper limit temperature (for example, 530°C). If YES, the process proceeds to step S416; otherwise, the process proceeds to step S417.

[0138] In step S416, the control unit 80 increases the amount of fuel supplied from the second supply unit 55 to the piping L1. After executing step S416, the control unit 80 proceeds to step S419.

[0139] In step S417, the control unit 80 reduces the amount of fuel supplied from the second supply unit 55 to the piping L1 so that the temperature Ta falls below the second upper limit temperature. In step S418, the control unit 80 reduces the output of the combustion device 200 (for example, by reducing the load by 10%) and proceeds to step S404.

[0140] In step S419, the control unit 80 determines whether the combustion device 200 is stopped. If it determines that the answer is YES, it proceeds to step S420; otherwise, it repeats step S405. The combustion device 200 transmits its operating state, including the state in which the combustion operation is stopped, to the control unit 80.

[0141] In step S420, the control unit 80 stops the supply of reducing agent by the first supply unit 50 and the supply of fuel by the second supply unit 55 because the combustion device 200 is stopped, and terminates the processing of this flowchart. When the combustion device 200 starts combustion operation, the control unit 80 resumes the processing of this flowchart.

[0142] In the above description, fuel is supplied from the second supply unit 55 to generate ammonia through an exothermic reaction by the ammonia decomposition catalyst in the ammonia decomposition unit 10, but other configurations are also possible. For example, ammonia or urea water may be supplied to the piping L1 from the first supply unit 50.

[0143] According to the exhaust gas treatment device 100C of this embodiment, by supplying ammonia or urea solution to the exhaust gas supplied from the combustion device 200 to the ammonia decomposition unit 10, the exothermic reaction due to the oxidation of ammonia in the ammonia decomposition unit 10 can be promoted. This appropriately raises the temperature of the exhaust gas led from the ammonia decomposition unit 10 to the nitrogen oxide decomposition unit 20, and allows the nitrogen oxide decomposition unit 20 to operate within a temperature range in which the decomposition rate of nitrous oxide does not change depending on the concentration of NO contained in the exhaust gas.

[0144] Furthermore, according to the exhaust gas treatment device 100C of this embodiment, by setting the predetermined temperature to 450°C or higher and 530°C or lower, the nitrogen oxide decomposition unit 20 can be operated within an appropriate temperature range in which the decomposition rate of nitrous oxide does not change depending on the concentration of NO contained in the exhaust gas.

[0145] In this embodiment, the exhaust gas treatment device 100C discharges the exhaust gas that has passed through the nitrogen oxide decomposition unit 20 to the outside via piping L3, but other configurations are also possible. For example, as shown in the modified exhaust gas treatment device 100D in Figure 17, the exhaust gas that has passed through the nitrogen oxide decomposition unit 20 may be introduced into the ammonia decomposition unit 30, and the exhaust gas that has passed through the ammonia decomposition unit 30 may be discharged to the outside via piping L4.

[0146] Figure 17 is a schematic diagram showing an exhaust gas treatment device 100D according to a modified example of the fifth embodiment of this disclosure. The ammonia decomposition unit 30 shown in Figure 17 has the same configuration as the ammonia decomposition unit 30 of the first embodiment. According to the exhaust gas treatment device 100D shown in Figure 17, even if the exhaust gas that has passed through the nitrogen oxide decomposition unit 20 contains ammonia, the ammonia decomposition unit 30 can appropriately decompose the ammonia so that it is not discharged to the outside.

[0147] Furthermore, in the exhaust gas treatment device 100D shown in Figure 17, ammonia is properly decomposed in the ammonia decomposition unit 30, so that load limiting of the combustion device 200 before step S408 in Figure 15 becomes unnecessary or the frequency of load limiting can be reduced. In order to eliminate the need for load limiting or reduce the frequency of load limiting, in step S414, the amount of reducing agent required to reduce NOx and nitrous oxide is calculated based on the NOx concentration and nitrous oxide concentration calculated in step S302 in Figure 9, and the coefficient γ multiplied by the required amount of reducing agent is set to a larger value than in the fifth embodiment (for example, 1.5).

[0148] The exhaust gas treatment apparatus and the design method for the exhaust gas treatment apparatus described in each embodiment above can be understood, for example, as follows. The exhaust gas treatment device (100) according to this disclosure is an exhaust gas treatment device (100, 100A) for treating exhaust gas discharged from a combustion device (200) that burns a fuel containing ammonia, and comprises a first processing unit (10) having a first catalyst for decomposing ammonia contained in the exhaust gas, and a second processing unit (20) having a second catalyst for decomposing nitrous oxide and NOx contained in the exhaust gas from which ammonia has been decomposed in the first processing unit.

[0149] According to the exhaust gas treatment device described herein, ammonia contained in the exhaust gas emitted from the combustion device is appropriately decomposed by the first catalyst as it passes through the first treatment unit. Furthermore, nitrous oxide and NOx generated when ammonia is burned in the combustion device are appropriately decomposed by the second catalyst as they pass through the second treatment unit. Thus, according to the exhaust gas treatment device described herein, ammonia, nitrous oxide, and NOx contained in the exhaust gas emitted from a combustion device that burns ammonia-containing fuel can be appropriately decomposed.

[0150] In the exhaust gas treatment apparatus according to this disclosure, the first treatment unit may be configured to remove NOx generated when ammonia contained in the exhaust gas is decomposed by the first catalyst. With this exhaust gas treatment system configuration, NOx generated when ammonia is decomposed in the first treatment unit is removed by the first catalyst, thus effectively preventing an increase in NOx contained in the exhaust gas discharged from the combustion unit as it passes through the first treatment unit.

[0151] In the exhaust gas treatment apparatus according to this disclosure, the apparatus may be configured to include a bypass pipe (L7) that guides the exhaust gas discharged from the combustion device to the second treatment apparatus without passing it through the first treatment apparatus, and a bypass valve (90) arranged in the bypass pipe. With this exhaust gas treatment system configuration, if the concentration of ammonia in the exhaust gas discharged from the combustion device is higher than the concentration required as a reducing agent when decomposing nitrous oxide and NOx in the second treatment unit, the bypass valve can be closed to allow the excess ammonia to be decomposed in the first treatment unit. Conversely, if the concentration of ammonia in the exhaust gas discharged from the combustion device is the same as or lower than the concentration required as a reducing agent when decomposing nitrous oxide and NOx in the second treatment unit, the bypass valve can be opened to allow the ammonia to be introduced to the second treatment unit without being decomposed in the first treatment unit.

[0152] The exhaust gas treatment apparatus according to this disclosure may also be configured to include a third treatment unit (30) that decomposes ammonia contained in the exhaust gas that has passed through the second treatment unit. With this exhaust gas treatment system, even if ammonia remains in the exhaust gas after passing through the second treatment unit, the ammonia is decomposed in the third treatment unit, preventing it from being discharged to the outside.

[0153] The exhaust gas treatment apparatus according to the present disclosure includes a detection unit (40) for detecting the concentration of nitrous oxide and / or NOx contained in the exhaust gas that has passed through the second treatment unit, and a first supply unit (50) for supplying ammonia or urea water to the exhaust gas supplied from the first treatment unit to the second treatment unit when the concentration of nitrous oxide contained in the exhaust gas is higher than a first predetermined concentration, or the concentration of NOx contained in the exhaust gas is higher than a second predetermined concentration, wherein the second catalyst may be configured to be a catalyst that reduces and decomposes the nitrous oxide and NOx contained in the exhaust gas with ammonia.

[0154] In this exhaust gas treatment system, if the detection unit detects that the concentration of nitrous oxide in the exhaust gas that has passed through the second treatment unit is higher than the first predetermined concentration, or that the concentration of NOx in the exhaust gas that has passed through the second treatment unit is higher than the second predetermined concentration, the first supply unit supplies ammonia or urea solution as a reducing agent to the exhaust gas supplied to the second treatment unit in order to compensate for the shortage of ammonia needed to reduce nitrous oxide and NOx. As a result, the shortage of ammonia supplied from the first treatment unit to the second treatment unit is compensated for, and the concentrations of nitrous oxide and NOx in the exhaust gas that has passed through the second treatment unit can be reduced.

[0155] The exhaust gas treatment apparatus according to the present disclosure may also be configured to include a temperature detection unit for detecting the temperature of the exhaust gas discharged from the first treatment unit, and a second supply unit (55) for supplying ammonia or urea water to the exhaust gas supplied from the combustion device to the first treatment unit when the temperature detected by the temperature detection unit is below a predetermined temperature. According to this exhaust gas treatment system configuration, by supplying ammonia or urea solution to the exhaust gas supplied from the combustion device to the first treatment unit, the exothermic reaction caused by the decomposition of ammonia in the first treatment unit can be promoted. This appropriately raises the temperature of the exhaust gas led from the first treatment unit to the second treatment unit, allowing the nitrogen oxide decomposition unit to operate within a temperature range where the decomposition rate of nitrous oxide does not change depending on the concentration of NO contained in the exhaust gas.

[0156] The exhaust gas treatment apparatus according to this disclosure may also be configured to include a third treatment unit (30) that decomposes ammonia contained in the exhaust gas that has passed through the second treatment unit. With this exhaust gas treatment system configuration, even if the exhaust gas that has passed through the second treatment unit contains ammonia, the third treatment unit can appropriately decompose the ammonia so that it is not discharged to the outside.

[0157] In the exhaust gas treatment apparatus according to this disclosure, the predetermined temperature may be configured to be a temperature of 450°C or higher and 530°C or lower. With this exhaust gas treatment device configuration, by setting a predetermined temperature between 450°C and 530°C, the nitrogen oxide decomposition unit can be operated within an appropriate temperature range in which the decomposition rate of nitrous oxide does not change depending on the concentration of NO contained in the exhaust gas.

[0158] The exhaust gas treatment device according to this disclosure is an exhaust gas treatment device (100B) for treating exhaust gas discharged from a combustion device that burns a fuel containing ammonia, comprising: a first supply unit (50) that supplies ammonia as a reducing agent to the exhaust gas discharged from the combustion device; a nitrogen oxide decomposition unit (20) having a decomposition catalyst that reduces nitrous oxide and NOx contained in the exhaust gas with ammonia supplied from the ammonia supply unit; and an ammonia decomposition unit (30) that decomposes ammonia contained in the exhaust gas that has passed through the nitrogen oxide decomposition unit.

[0159] According to the exhaust gas treatment device described herein, ammonia contained in the exhaust gas emitted from the combustion device is decomposed by a decomposition catalyst as a reducing agent when it passes through the nitrogen oxide decomposition section, reacting with nitrous oxide and NOx. In addition, nitrous oxide and NOx generated when ammonia is burned in the combustion device are appropriately decomposed by a decomposition catalyst when they pass through the nitrogen oxide decomposition section. Thus, the exhaust gas treatment device described herein can appropriately decompose ammonia, nitrous oxide, and NOx contained in the exhaust gas emitted from a combustion device that burns fuel containing ammonia.

[0160] The exhaust gas treatment device design method according to the present disclosure is a method for designing an exhaust gas treatment device that treats exhaust gas discharged from a combustion device that burns a fuel containing ammonia, wherein when the concentration of ammonia contained in the exhaust gas is higher than the sum of a first concentration obtained by multiplying the concentration of nitrous oxide contained in the exhaust gas by a first coefficient and a second concentration obtained by multiplying the concentration of NOx contained in the exhaust gas by a second coefficient, the exhaust gas treatment device is designed such that a first processing unit having a first catalyst for decomposing ammonia contained in the exhaust gas is placed downstream of the combustion device, and a second processing unit having a second catalyst for decomposing nitrous oxide and NOx contained in the exhaust gas from which ammonia has been decomposed by the first processing unit is placed downstream of the first processing unit, and when the concentration of ammonia contained in the exhaust gas is less than or equal to the sum of the two concentrations, the exhaust gas treatment device is designed such that the second processing unit is placed downstream of the combustion device without placing the first processing unit.

[0161] According to the exhaust gas treatment device design method of this disclosure, if the concentration of ammonia contained in the exhaust gas is higher than the sum of the first concentration obtained by multiplying the concentration of nitrous oxide contained in the exhaust gas by a first coefficient and the second concentration obtained by multiplying the concentration of NOx contained in the exhaust gas by a second coefficient, the exhaust gas treatment device is designed so that the first processing unit is located downstream of the combustion device and the second processing unit is located downstream of the first processing unit, in order to prevent the concentration of ammonia supplied from the first processing unit to the second processing unit from becoming excessive.

[0162] On the other hand, if the ammonia concentration in the exhaust gas is less than or equal to the sum of the first concentration (obtained by multiplying the nitrous oxide concentration in the exhaust gas by a first coefficient) and the second concentration (obtained by multiplying the NOx concentration in the exhaust gas by a second coefficient), the concentration of ammonia supplied from the first treatment unit to the second treatment unit will not be excessive. Therefore, the exhaust gas treatment system is designed so that the second treatment unit is placed downstream of the combustion device, without placing the first treatment unit. This makes it possible to design an exhaust gas treatment system with an appropriate configuration according to the ammonia concentration in the exhaust gas discharged from the combustion device. [Explanation of symbols]

[0163] 10 Ammonia decomposition section (first processing section) 20 Nitrogen oxide decomposition section (second processing section) 30 Ammonia Decomposition Section (Third Processing Section) 40 Detection unit 50. First Supply Department (Reducing Agent Supply Department) 55 2nd supply section (fuel supply section) 60 Temperature Sensors 70 Bypass valve 80 Control Unit 90 Bypass valve 100, 100A, 100B, 100C, 100D Exhaust gas treatment device 200 Combustion device L1,L2,L3,L4,L5,L6,L7,L8 Piping

Claims

1. An exhaust gas treatment device for treating exhaust gas emitted from a combustion device that burns fuel containing ammonia, A first processing unit having a first catalyst for decomposing ammonia contained in the exhaust gas, A second processing unit having a second catalyst for decomposing nitrous oxide and NOx contained in the exhaust gas from which ammonia has been decomposed in the first processing unit, A detection unit for detecting the concentration of nitrous oxide contained in the exhaust gas that has passed through the second processing unit, The system includes a first supply unit that supplies ammonia or urea solution to the exhaust gas supplied from the first processing unit to the second processing unit when the concentration of nitrous oxide contained in the exhaust gas is higher than a first predetermined concentration, The exhaust gas treatment device is an exhaust gas treatment device in which the second catalyst is a catalyst that reduces and decomposes nitrous oxide contained in the exhaust gas with ammonia.

2. The exhaust gas treatment apparatus according to claim 1, wherein the first processing unit removes NOx generated when ammonia contained in the exhaust gas is decomposed by the first catalyst.

3. A bypass pipe that guides the exhaust gas discharged from the combustion device without passing through the first processing unit to the second processing unit, The exhaust gas treatment apparatus according to claim 1 or claim 2, further comprising a bypass valve disposed in the bypass piping.

4. The exhaust gas treatment apparatus according to claim 1 or claim 2, further comprising a third processing unit for decomposing ammonia contained in the exhaust gas that has passed through the second processing unit.

5. The detection unit detects the concentration of NOx contained in the exhaust gas that has passed through the second processing unit, The first supply unit supplies ammonia or urea solution to the exhaust gas supplied from the first processing unit to the second processing unit when the concentration of NOx contained in the exhaust gas is higher than the second predetermined concentration. The exhaust gas treatment apparatus according to claim 1 or claim 2, wherein the second catalyst is a catalyst that reduces and decomposes NOx contained in the exhaust gas with ammonia.

6. A temperature detection unit for detecting the temperature of the exhaust gas discharged from the first processing unit, The exhaust gas treatment apparatus according to claim 5, further comprising: a second supply unit that supplies ammonia or urea water to the exhaust gas supplied from the combustion device to the first processing unit when the temperature detected by the temperature detection unit is below a predetermined temperature.

7. The exhaust gas treatment apparatus according to claim 6, further comprising a third processing unit for decomposing ammonia contained in the exhaust gas that has passed through the second processing unit.

8. The exhaust gas treatment apparatus according to claim 6, wherein the predetermined temperature is a temperature of 450°C or higher and 530°C or lower.

9. An exhaust gas treatment device for treating exhaust gas emitted from a combustion device that burns fuel containing ammonia, An ammonia supply unit that supplies ammonia or urea solution as a reducing agent to the exhaust gas discharged from the combustion device, A nitrogen oxide decomposition unit having a nitrogen oxide decomposition catalyst that reduces nitrous oxide and NOx contained in the exhaust gas with ammonia supplied from the ammonia supply unit, An ammonia decomposition unit that decomposes ammonia contained in the exhaust gas that has passed through the nitrogen oxide decomposition unit, A detection unit for detecting the concentration of nitrous oxide contained in the exhaust gas that has passed through the nitrogen oxide decomposition unit, An exhaust gas treatment apparatus comprising: a control unit that controls the ammonia supply unit to supply ammonia or urea solution to the exhaust gas supplied from the combustion device to the nitrogen oxide decomposition unit when the concentration of nitrous oxide contained in the exhaust gas is higher than a predetermined concentration.

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