Exhaust purification device

Abstract

An exhaust emission control device (1) comprises: a first catalyst (4) having a function of oxidizing / reducing NH3 and NOx contained in exhaust gas flowing through an exhaust flow path (3); a second catalyst (5) which is disposed downstream of the first catalyst (4) in the exhaust flow path (3) and which has a function for adsorbing / decomposing NH3 that has passed through the first catalyst (4) and a function for oxidizing NH3 that has passed through the first catalyst (4); an air pump (7) for supplying air to the second catalyst (5); an initial determination unit (12) for determining whether the amount of NH3 adsorbed by the second catalyst (5) is less than or equal to a predetermined defined amount in a state in which an ammonia engine (2) is stopped; and an air supply control unit (16) for controlling the air pump (7) so as to supply air to the second catalyst (5) when it is determined by the initial determination unit (12) that the amount of NH3 adsorbed by the second catalyst (5) is not less than or equal to the defined amount.

Description

exhaust purification device

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

[0002] Known as an exhaust purification device is a technology described in, for example, Patent Document 1. The exhaust purification device described in Patent Document 1 includes a three-way catalyst that is disposed in an exhaust pipe connected to an ammonia engine and purifies ammonia, NOx, and hydrogen in the exhaust, and an SCR catalyst that is disposed in the exhaust pipe downstream of the three-way catalyst and purifies NOx in the exhaust using ammonia as a reducing agent.

[0003] Japanese Patent Application Laid-Open No. 2019-167823

[0004] In some exhaust gas purification devices, a second catalyst having an ammonia adsorption function and an ammonia decomposition function is disposed downstream of a first catalyst, which is a three-way catalyst. In this case, when the temperature of the second catalyst is low, unburned ammonia that has passed through the first catalyst is adsorbed by the second catalyst. When the temperature of the second catalyst subsequently rises to its decomposition activation temperature, the ammonia adsorbed by the second catalyst is decomposed into hydrogen and nitrogen.

[0005] However, if the ammonia engine is stopped before the ammonia decomposition process in the second catalyst is completed, the next time the ammonia engine is started, ammonia will already be adsorbed on the second catalyst, and the second catalyst may not be able to adsorb all of the unburned ammonia. In this case, the ammonia will flow through the exhaust pipe and be discharged. Therefore, after the ammonia engine has been started, it cannot be stopped until the ammonia decomposition process in the second catalyst is completed.

[0006] An object of the present invention is to provide an exhaust gas purification device that can stop the engine at any timing without waiting for the completion of the ammonia decomposition process.

[0007] (1) One aspect of the present invention is an exhaust purification device that purifies exhaust gas generated by an engine, comprising: a first catalyst that is disposed in an exhaust flow path connected to the engine and has the function of oxidizing and reducing ammonia and NOx contained in the exhaust gas flowing through the exhaust flow path; a second catalyst that is disposed in the exhaust flow path downstream of the first catalyst and has the function of adsorbing and decomposing ammonia that has passed through the first catalyst and the function of oxidizing ammonia that has passed through the first catalyst; an air supply unit that supplies air to the second catalyst; an initial determination unit that determines, when the engine is stopped, whether the amount of ammonia adsorbed on the second catalyst is equal to or less than a predetermined specified amount; and an air supply control unit that controls the air supply unit to supply air to the second catalyst when the initial determination unit determines that the amount of ammonia adsorbed on the second catalyst is not equal to or less than the specified amount.

[0008] In this exhaust gas purification device, during normal engine operation, ammonia that passes through the first catalyst is adsorbed by the second catalyst, and the ammonia adsorbed by the second catalyst is decomposed when the second catalyst is heated. When the engine is stopped, it is determined whether the amount of ammonia adsorbed by the second catalyst is equal to or less than a specified amount. If the amount of ammonia adsorbed by the second catalyst is greater than the specified amount, air is supplied from the air supply unit to the second catalyst. Then, ammonia oxidation processing is performed in the second catalyst. The ammonia oxidation processing is started at a lower temperature than the ammonia decomposition processing. Therefore, the ammonia oxidation processing is performed in the second catalyst before the ammonia decomposition processing is performed. In this way, even if the decomposition processing of ammonia adsorbed by the second catalyst is not completed when the engine is stopped, the ammonia adsorbed by the second catalyst is removed by supplying air to the second catalyst to oxidize the ammonia adsorbed by the second catalyst. This allows the engine to be stopped at any time without waiting for the ammonia decomposition processing to be completed.

[0009] (2) In the above (1), the exhaust purification device may further include a heating unit that heats the second catalyst, a temperature detection unit that detects the temperature of the second catalyst, a temperature determination unit that determines whether the temperature of the second catalyst detected by the temperature detection unit is equal to or higher than an oxidation activation temperature at which ammonia can be oxidized, and a heating control unit that controls the heating unit to heat the second catalyst when the temperature determination unit determines that the temperature of the second catalyst is not equal to or higher than the oxidation activation temperature, and the heating control unit controls the heating unit to stop heating the second catalyst when it is determined that the temperature of the second catalyst is equal to or higher than the oxidation activation temperature after the heating unit starts heating the second catalyst, and the air supply control unit controls the air supply unit to supply air to the second catalyst when it is determined that the amount of ammonia adsorbed on the second catalyst is not equal to or lower than a specified amount and the temperature of the second catalyst is equal to or higher than the oxidation activation temperature.

[0010] In this configuration, when the temperature of the second catalyst is lower than the oxidation activation temperature, the second catalyst is heated by the heating unit, thereby immediately raising the temperature of the second catalyst. Then, when the temperature of the second catalyst reaches the oxidation activation temperature, air is supplied to the second catalyst from the air supply unit, and the ammonia is oxidized in the second catalyst. Therefore, the ammonia adsorbed on the second catalyst is removed in a short time. Furthermore, by supplying air to the second catalyst from the air supply unit after the temperature of the second catalyst reaches the oxidation activation temperature, unnecessary operation of the air supply unit is avoided. This contributes to power savings.

[0011] (3) In the above (1) or (2), the exhaust purification device may further include a process completion determination unit that determines whether the oxidation process of the ammonia adsorbed on the second catalyst has been completed after the air supply unit has started to supply air to the second catalyst, and the air supply control unit may control the air supply unit to stop the supply of air to the second catalyst when the process completion determination unit determines that the oxidation process of the ammonia adsorbed on the second catalyst has been completed.

[0012] In this configuration, when the oxidation process of the ammonia adsorbed on the second catalyst is completed, the supply of air to the second catalyst is stopped, thereby eliminating the needless operation of the air supply unit, thereby achieving further power savings.

[0013] (4) In (3) above, the treatment completion determination unit may determine that the oxidation process of ammonia adsorbed to the second catalyst is completed when a specified time has elapsed since the air supply unit started supplying air to the second catalyst.

[0014] In this configuration, it is possible to determine whether the ammonia oxidation process has been completed by a simple process by determining whether a predetermined specified time has elapsed since the air supply unit started to supply air to the second catalyst.

[0015] (5) In the above (3), the exhaust purification device may further include a NOx detection unit that detects the concentration of NOx present downstream of the second catalyst in the exhaust flow path, and the processing completion determination unit may determine that the oxidation process of ammonia adsorbed on the second catalyst has been completed when the concentration of NOx detected by the NOx detection unit becomes equal to or less than a predetermined specified value.

[0016] In this configuration, when the oxidation process of the ammonia adsorbed on the second catalyst is completed, the amount of NOx present downstream of the second catalyst in the exhaust flow path decreases. Therefore, by determining whether the concentration of NOx present downstream of the second catalyst in the exhaust flow path is equal to or less than a specified value, it is possible to determine with high accuracy whether the oxidation process of the ammonia has been completed.

[0017] According to the present invention, the engine can be stopped at any timing without waiting for the completion of the ammonia decomposition process.

[0018] It is a schematic configuration diagram showing an exhaust purification device according to one embodiment of the present invention. It is a block diagram showing a control system of the exhaust purification device shown in Figure 1. It is a flowchart showing a processing procedure executed by the ECU shown in Figure 2. It is a block diagram showing a control system of an exhaust purification device according to another embodiment of the present invention. It is a flowchart showing a processing procedure executed by the ECU shown in Figure 4.

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0020] Fig. 1 is a schematic diagram showing the configuration of an exhaust gas purification device according to one embodiment of the present invention. In Fig. 1, the exhaust gas purification device 1 of this embodiment is mounted on a vehicle (not shown). The exhaust gas purification device 1 is a device that purifies exhaust gas generated from an ammonia engine 2.

[0021] The ammonia engine 2 is a ３ ) as fuel. At this time, hydrogen (H ２ ) may be mixed with the ammonia. An exhaust flow path 3 is connected to the ammonia engine 2. The exhaust flow path 3 is a flow path through which exhaust gas generated from the ammonia engine 2 flows.

[0022] The exhaust purification device 1 includes a first catalyst 4 , a second catalyst 5 , an electric heater 6 , an air pump 7 , temperature sensors 8 and 9 , a NOx sensor 10 , and an ECU (Electronic Control Unit) 11 .

[0023] The first catalyst 4 is disposed in the exhaust flow path 3. The first catalyst 4 is used to remove NH contained in the exhaust gas. ３ The first catalyst is a catalyst that has a function of oxidizing and reducing NOx (nitrogen oxides). The first catalyst is, for example, a three-way catalyst.

[0024] The second catalyst 5 is disposed downstream of the first catalyst 4 in the exhaust flow path 3. The second catalyst 5 is used to remove NH ３ and the function of adsorbing and decomposing NH that has passed through the first catalyst 4. ３ The second catalyst 5 has the function of oxidizing NH ３ The catalytic species of the second catalyst 5 is, for example, ruthenium (Ru), rhodium (Rh), cobalt (Co), iron (Fe), or nickel (Ni).

[0025] The electric heater 6 is disposed upstream of the second catalyst 5. The electric heater 6 is a heating unit that heats the second catalyst 5.

[0026] The air pump 7 is an air supply unit that supplies air to the second catalyst 5. The air pump 7 introduces air into the portion of the exhaust flow path 3 between the first catalyst 4 and the second catalyst 5. Therefore, the air from the air pump 7 flows through the exhaust flow path 3 and is supplied to the second catalyst 5.

[0027] The temperature sensor 8 is a sensor that detects the temperature of a portion of the exhaust flow path 3 between the first catalyst 4 and the second catalyst 5. Specifically, the temperature sensor 8 detects the temperature of a portion of the exhaust flow path 3 between the intake portion of the air from the air pump 7 and the second catalyst 5. In other words, the temperature sensor 8 is a sensor that detects the temperature on the inlet side of the second catalyst 5.

[0028] The temperature sensor 9 is a sensor that detects the temperature of a portion of the exhaust passage 3 downstream of the second catalyst 5. In other words, the temperature sensor 9 detects the temperature of the outlet side of the second catalyst 5.

[0029] The NOx sensor 10 is a sensor that detects the concentration of NOx contained in the exhaust gas flowing downstream of the second catalyst 5 in the exhaust flow path 3. The NOx sensor 10 is a NOx detection unit that detects the concentration of NOx present downstream of the second catalyst 5 in the exhaust flow path 3.

[0030] The ECU 11 is composed of a CPU, RAM, ROM, an input / output interface, etc. As shown in Fig. 2, the ECU 11 has an initial determination unit 12, a temperature estimation unit 13, a temperature determination unit 14, a heating control unit 15, an air supply control unit 16, and a processing completion determination unit 17.

[0031] The initial determination unit 12 determines the amount of NH adsorbed on the second catalyst 5 while the ammonia engine 2 is stopped. ３ It is determined whether the amount of the liquid is equal to or less than a predetermined amount. The predetermined amount may be, for example, zero or a value close to zero.

[0032] The temperature estimation unit 13 estimates the temperature of the second catalyst 5 based on the detection values ​​of the temperature sensors 8 and 9. The temperature estimation unit 13 cooperates with the temperature sensors 8 and 9 to form a temperature detection unit that detects the temperature of the second catalyst 5.

[0033] The temperature determination unit 14 determines whether the temperature of the second catalyst 5 estimated by the temperature estimation unit 13 is equal to or higher than the oxidation activation temperature. ３ This temperature differs depending on the type of catalyst used in the second catalyst 5 .

[0034] When the temperature determination unit 14 determines that the temperature of the second catalyst 5 is not equal to or higher than the oxidation activation temperature, the heating control unit 15 controls the electric heater 6 to heat the second catalyst 5. After the electric heater 6 starts heating the second catalyst 5, when the temperature determination unit 14 determines that the temperature of the second catalyst 5 is equal to or higher than the oxidation activation temperature, the heating control unit 15 controls the electric heater 6 to stop heating the second catalyst 5.

[0035] When the initial determination unit 12 determines that the amount of ammonia adsorbed on the second catalyst 5 is not equal to or less than a specified amount, the air supply control unit 16 controls the air pump 7 to supply air to the second catalyst 5. Specifically, when it is determined that the amount of ammonia adsorbed on the second catalyst 5 is not equal to or less than a specified amount and the temperature of the second catalyst 5 is determined to be equal to or higher than the oxidation activation temperature, the air supply control unit 16 controls the air pump 7 to supply air to the second catalyst 5.

[0036] In addition, when the treatment completion determination unit 17 described later determines that the oxidation process of the ammonia adsorbed in the second catalyst 5 has been completed, the air supply control unit 16 controls the air pump 7 to stop the supply of air to the second catalyst 5.

[0037] The treatment completion determination unit 17 determines whether or not the NH adsorbed in the second catalyst 5 has been adsorbed after the air pump 7 has started to supply air to the second catalyst 5. ３ Specifically, the treatment completion determination unit 17 determines whether or not the oxidation treatment of NH adsorbed on the second catalyst 5 has been completed when a predetermined time has elapsed since the air pump 7 started to supply air to the second catalyst 5. ３ It is determined that the oxidation process is complete.

[0038] 3 is a flowchart showing the processing procedure executed by the ECU 11. This processing is executed when an engine stop signal is input to the ECU 11, for example, by a user turning off the ignition switch. At the start of this processing, the heater flag is set to 0. The heater flag is a flag for determining whether or not to turn off the electric heater 6.

[0039] In FIG. 3, the ECU 11 first calculates the amount of NH adsorbed on the second catalyst 5. ３ It is determined whether the removal process of NH is completed (step S101). ３ The removal process is carried out by NH ３ This procedure involves the decomposition and oxidation of NH adsorbed on the second catalyst 5. ３ This corresponds to the procedure for determining whether the amount of the substance is equal to or less than the specified amount.

[0040] For example, the amount of NH adsorbed on the second catalyst 5 can be calculated based on the temperature on the inlet side of the second catalyst 5 and the mixture ratio of the exhaust gas obtained separately. ３ The amount of NH ３ From the amount of NH ３ Therefore, the ECU 11 determines whether a certain time has elapsed, thereby estimating the time until the NH adsorbed on the second catalyst 5 is removed. ３ Determine whether the removal process is complete.

[0041] The ECU 11 detects the amount of NH adsorbed on the second catalyst 5. ３ When it is determined that the removal process of NH adsorbed on the second catalyst 5 is completed, the ECU 11 ends this process. ３ If it is determined that the removal process has not been completed, the ECU 11 acquires the detected values ​​of the temperature sensors 8 and 9 (step S102).Then, the ECU 11 estimates the temperature of the second catalyst 5 based on the detected values ​​of the temperature sensors 8 and 9 (step S103).

[0042] Next, the ECU 11 determines whether the temperature of the second catalyst 5 is equal to or higher than the oxidation activation temperature (step S104). ３ The oxidation activation temperature is the temperature at which the oxidation treatment of NH ３The temperature is lower than the decomposition activation temperature, which is the temperature at which the decomposition process of the present invention starts.

[0043] When the ECU 11 determines that the temperature of the second catalyst 5 is not equal to or higher than the oxidation activation temperature, the ECU 11 controls the electric heater 6 to be ON (step S105). Then, the ECU 11 sets the heater flag to 1 (step S106) and executes step S102 again. When the electric heater 6 is turned ON, the second catalyst 5 is heated by the electric heater 6.

[0044] When the ECU 11 determines in step S104 that the temperature of the second catalyst 5 is equal to or higher than the oxidation activation temperature, it determines whether the heater flag is 0 (step S107). When the ECU 11 determines that the heater flag is 0, it controls the air pump 7 to be ON (step S108). When the ECU 11 determines that the heater flag is 1 rather than 0, it controls the electric heater 6 to be OFF (step S109) and controls the air pump 7 to be ON (step S108).

[0045] When the air pump 7 is turned on, air is supplied from the air pump 7 to the second catalyst 5, and the NH ３ Therefore, the oxidation treatment of NH ３ is removed.

[0046] Next, the ECU 11 determines whether a predetermined time has elapsed since the air pump 7 was turned on (step S110). ３ The specified time is the time required for the oxidation treatment to be completed. The specified time is determined in advance through experiments or the like.

[0047] Next, when the ECU 11 determines that a specified time has elapsed since the air pump 7 was turned on, it turns off the air pump 7 (step S111), and ends this process.

[0048] Here, the initial determination unit 12 executes step S101. The temperature estimation unit 13 executes steps S102 and S103. The temperature determination unit 14 executes step S104. The heating control unit 15 executes steps S105 to S107 and S109. The air supply control unit 16 executes steps S108 and S111. The processing completion determination unit 17 executes step S110.

[0049] In the exhaust gas purification device 1 as described above, when the ammonia engine 2 is started, the exhaust gas generated from the ammonia engine 2 flows through the exhaust flow path 3. Immediately after the ammonia engine 2 is started, the first catalyst 4 is not sufficiently heated, and therefore, unburned NH ３ is absorbed by the second catalyst 5. Even during steady operation of the ammonia engine 2, the NH ３ Fluctuations in the air-fuel ratio (A / F) of the gas and air cause unburned NH ３ may pass through the first catalyst 4 and be adsorbed by the second catalyst 5.

[0050] When the temperature of the second catalyst 5 reaches the decomposition activation temperature, the unburned NH adsorbed on the second catalyst 5 ３ The decomposition reaction occurs, and unburned NH ３ is decomposed into hydrogen and nitrogen. Therefore, unburned NH ３ is removed.

[0051] However, after the ammonia engine 2 is started, unburned NH ３ If the ammonia engine 2 is stopped early before the decomposition process of NH is completed, the following problem occurs. That is, when the ammonia engine 2 is started next time, NH is already present in the second catalyst 5. ３ When the second catalyst 5 is adsorbed, the unburned NH ３ The amount of unburned NH that is not adsorbed by the second catalyst 5 decreases. ３ flows through the exhaust flow path 3 and is discharged into the atmosphere.

[0052] Therefore, when the ammonia engine 2 is stopped early, the air pump 7 is turned on to supply air to the second catalyst 5. Specifically, when the temperature of the second catalyst 5 is equal to or higher than the oxidation activation temperature, the air pump 7 is turned on. When the temperature of the second catalyst 5 is lower than the oxidation activation temperature, the electric heater 6 is turned on to heat the second catalyst 5. Thereafter, when the temperature of the second catalyst 5 reaches equal to or higher than the oxidation activation temperature, the air pump 7 is turned on.

[0053] When air is supplied from the air pump 7 to the second catalyst 5, unburned NH ３ The oxidation reaction of the unburned NH adsorbed on the second catalyst 5 occurs. ３ Generally, in the low temperature range, oxidation reactions are more active than decomposition reactions. ３ Even in the low temperature range where the decomposition reaction of NH ３ Therefore, the unburned NH ３ is removed.

[0054] Also, NH ３ When the oxidation reaction of the above occurs, the temperature of the second catalyst 5 rises due to the heat of oxidation. ３ When the temperature of the second catalyst 5 reaches the decomposition activation temperature, unburned NH ３ The decomposition reaction of the unburned NH adsorbed on the second catalyst 5 occurs. ３ Therefore, unburned NH ３ is surely removed.

[0055] When a specified time has passed since the air pump 7 was turned on, ３ When the oxidation reaction of the air pump 7 is completed, the air pump 7 is turned off, and the supply of air from the air pump 7 to the second catalyst 5 is stopped.

[0056] As described above, in this embodiment, during normal operation of the ammonia engine 2, NH ３ is adsorbed on the second catalyst 5, and the NH adsorbed on the second catalyst 5 in a state where the temperature of the second catalyst 5 is raised ３ When the ammonia engine 2 is stopped, the NH adsorbed on the second catalyst 5 is decomposed. ３ It is then determined whether the amount of NH adsorbed on the second catalyst 5 is equal to or less than a specified amount. ３ When the amount of NH is greater than the specified amount, air is supplied from the air pump 7 to the second catalyst 5. Then, NH ３ The oxidation treatment is carried out. ３ The oxidation treatment is carried out by NH ３Therefore, in the second catalyst 5, the decomposition process of NH ３ Before the decomposition treatment of NH ３ In this way, the NH adsorbed on the second catalyst 5 when the ammonia engine 2 is stopped is oxidized. ３ Even if the decomposition process of NH is not completed, air can be supplied to the second catalyst 5 to decompose the NH adsorbed on the second catalyst 5. ３ By oxidizing the NH adsorbed on the second catalyst 5, ３ is removed. This removes NH ３ Therefore, the ammonia engine 2 can be stopped at any timing without waiting for the completion of the decomposition process.

[0057] In this embodiment, when the temperature of the second catalyst 5 is lower than the oxidation activation temperature, the second catalyst 5 is heated by the electric heater 6, and the temperature of the second catalyst 5 is immediately raised. After that, when the temperature of the second catalyst 5 reaches the oxidation activation temperature, air is supplied to the second catalyst 5 from the air pump 7, and NH ３ Therefore, the NH adsorbed on the second catalyst 5 is oxidized. ３ In addition, by supplying air from the air pump 7 to the second catalyst 5 after the temperature of the second catalyst 5 reaches the oxidation activation temperature, the air pump 7 does not need to be operated unnecessarily, thereby achieving further power savings.

[0058] In this embodiment, the NH adsorbed on the second catalyst 5 ３ When the oxidation process is completed, the supply of air to the second catalyst 5 is stopped, thereby eliminating the needless operation of the air pump 7. This contributes to power saving.

[0059] In this embodiment, by determining whether a specified time has elapsed since the air pump 7 started to supply air to the second catalyst 5, NH ３ It is possible to determine whether the oxidation process is complete.

[0060] In addition, in this embodiment, the temperature of the second catalyst 5 can be detected with high accuracy by estimating the temperature of the second catalyst 5 based on the temperature on the inlet side of the second catalyst 5 and the temperature on the outlet side of the second catalyst 5.

[0061] Fig. 4 is a block diagram showing a control system of an exhaust gas purification device according to another embodiment of the present invention, and corresponds to Fig. 2. In Fig. 4, the exhaust gas purification device 1 of this embodiment includes an ECU 11A instead of the above-described ECU 11. The ECU 11A includes an initial determination unit 12, a temperature estimation unit 13, a temperature determination unit 14, a heating control unit 15, an air supply control unit 16, and a process completion determination unit 17A.

[0062] The treatment completion determination unit 17A determines whether or not the NH adsorbed in the second catalyst 5 has been adsorbed after the air pump 7 has started to supply air to the second catalyst 5. ３ Specifically, when the concentration of NOx detected by the NOx sensor 10 becomes equal to or lower than a predetermined value, the treatment completion determination unit 17A determines whether the oxidation treatment of NH 2 adsorbed on the second catalyst 5 is completed. ３ It is determined that the oxidation process is complete.

[0063] Fig. 5 is a flowchart showing a modified example of the processing procedure executed by the ECU 11A, and corresponds to Fig. 3. In Fig. 5, steps S101 to S109 are the same as those in Fig. 3.

[0064] After executing step S108, the ECU 11A acquires the detection value of the NOx sensor 10 (step S121). Then, based on the detection value of the NOx sensor 10, the ECU 11A determines whether the concentration of NOx present downstream of the second catalyst 5 is equal to or less than a specified value (step S122). Steps S121 and S122 are executed by the process completion determination unit 17A.

[0065] In the second catalyst 5, NH ３ When the oxidation reaction of NH occurs, a small amount of NOx is generated, but the NH ３ If the oxidation reaction of NH does not occur, NOx is unlikely to be generated. ３ The value is preset to a value at which it is determined that the oxidation process is completed.

[0066] If the ECU 11A determines that the concentration of NOx present downstream of the second catalyst 5 is not equal to or less than the specified value, the ECU 11A executes the above-described step S121 again. If the ECU 11A determines that the concentration of NOx present downstream of the second catalyst 5 is equal to or less than the specified value, the ECU 11A controls the air pump 7 to be turned off (step S111), and ends this process.

[0067] In this embodiment, the NH adsorbed on the second catalyst 5 ３ When the oxidation process of NH is completed, the amount of NOx present downstream of the second catalyst 5 in the exhaust flow path 3 decreases. Therefore, by determining whether the concentration of NOx present downstream of the second catalyst 5 in the exhaust flow path 3 is equal to or less than a specified value, the amount of NOx present downstream of the second catalyst 5 in the exhaust flow path 3 decreases. ３ It is possible to determine with high accuracy whether the oxidation process is completed.

[0068] The present invention is not limited to the above embodiment. For example, in the above embodiment, when a predetermined time has elapsed since the air pump 7 was turned on, or when the concentration of NOx present downstream of the second catalyst 5 is equal to or less than a predetermined value, NH ３ It is determined that the oxidation treatment of the second catalyst 5 has been completed, and the supply of air from the air pump 7 to the second catalyst 5 is stopped, but the present invention is not limited to this.

[0069] For example, when the temperature on the outlet side of the second catalyst 5 detected by the temperature sensor 9 is equal to or lower than a predetermined temperature, NH ３ Alternatively, when the difference between the temperature on the inlet side of the second catalyst 5 detected by the temperature sensor 8 and the temperature on the outlet side of the second catalyst 5 detected by the temperature sensor 9 is equal to or less than a predetermined threshold, it may be determined that the oxidation process of NH ３ It may be determined that the oxidation process is completed.

[0070] In the above embodiment, when the temperature of the second catalyst 5 is lower than the oxidation activation temperature, the second catalyst 5 is heated by the electric heater 6, but this is not a particular limitation. For example, Ru, Rh, Co, Fe, and the like used in the second catalyst 5 generate oxidation heat when exposed to air supplied from the air pump 7. Therefore, as long as the oxidation heat can be used to heat the second catalyst 5 to the oxidation activation temperature, the electric heater 6 may not be necessary.

[0071] In the above embodiment, the first catalyst 4 is a three-way catalyst. However, the first catalyst 4 is not limited to a three-way catalyst. ３ Any catalyst may be used as long as it has the function of oxidizing and reducing NOx.

[0072] Furthermore, although the exhaust gas purification device 1 in the above embodiment is mounted on a vehicle, the configuration is not particularly limited to this, and it may be mounted on, for example, a ground-based power generation device or the like.

[0073] REFERENCE SIGNS LIST 1 exhaust purification device 2 ammonia engine (engine) 3 exhaust flow path 4 first catalyst 5 second catalyst 6 electric heater (heating section) 7 air pump (air supply section) 8 temperature sensor (temperature detection section) 9 temperature sensor (temperature detection section) 10 NOx sensor (NOx detection section) 12 initial determination section 13 temperature estimation section (temperature detection section) 14 temperature determination section 15 heating control section 16 air supply control section 17 treatment completion determination section

Claims

1. An exhaust purification device that purifies exhaust gas generated from an engine, comprising: a first catalyst that is disposed in an exhaust flow path connected to the engine and has the function of oxidizing and reducing ammonia and NOx contained in exhaust gas flowing through the exhaust flow path; a second catalyst that is disposed in the exhaust flow path downstream of the first catalyst and has the function of adsorbing and decomposing ammonia that has passed through the first catalyst and the function of oxidizing ammonia that has passed through the first catalyst; an air supply unit that supplies air to the second catalyst; an initial determination unit that determines whether the amount of ammonia adsorbed on the second catalyst is equal to or less than a predetermined specified amount when the engine is stopped; and an air supply control unit that controls the air supply unit to supply air to the second catalyst when the initial determination unit determines that the amount of ammonia adsorbed on the second catalyst is not equal to or less than the specified amount.

2. An exhaust purification device as described in claim 1, further comprising: a heating unit that heats the second catalyst; a temperature detection unit that detects the temperature of the second catalyst; a temperature judgment unit that judges whether the temperature of the second catalyst detected by the temperature detection unit is equal to or higher than an oxidation activity temperature at which the ammonia can be oxidized; and a heating control unit that controls the heating unit to heat the second catalyst when the temperature judgment unit judges that the temperature of the second catalyst is not equal to or higher than the oxidation activity temperature, wherein the heating control unit controls the heating unit to stop heating the second catalyst when it is judged that the temperature of the second catalyst is equal to or higher than the oxidation activity temperature after the heating unit has started heating the second catalyst; and the air supply control unit controls the air supply unit to supply air to the second catalyst when it is judged that the amount of ammonia adsorbed on the second catalyst is not equal to or lower than the specified amount and the temperature of the second catalyst is equal to or higher than the oxidation activity temperature.

3. An exhaust purification device as described in claim 1, further comprising a process completion determination unit that determines whether or not the oxidation process of the ammonia adsorbed on the second catalyst has been completed after the air supply unit has started to supply air to the second catalyst, and when the process completion determination unit determines that the oxidation process of the ammonia adsorbed on the second catalyst has been completed, the air supply control unit controls the air supply unit to stop the supply of air to the second catalyst.

4. An exhaust purification device as described in claim 3, wherein the treatment completion determination unit determines that the oxidation process of ammonia adsorbed on the second catalyst has been completed when a predetermined specified time has elapsed since the air supply unit began supplying air to the second catalyst.

5. An exhaust purification device as described in claim 3, further comprising a NOx detection unit that detects the concentration of NOx present downstream of the second catalyst in the exhaust flow path, and wherein the processing completion determination unit determines that the oxidation process of ammonia adsorbed on the second catalyst has been completed when the concentration of NOx detected by the NOx detection unit becomes equal to or less than a predetermined specified value.

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