Marine SCR system and engine system mounted therewith

Abstract

To achieve both a reduction in emissions of unburnt ammonia and suppression of catalyst deterioration.SOLUTION: A marine SCR system 100, configured to be connected to an ammonia-burning engine 1 and to purify exhaust discharged from the engine 1, comprises: a catalyst unit 115 with a plurality of reaction cells 115a which form an exhaust flow passage and promote a reaction of unburnt ammonia, allowing the unburnt ammonia discharged from the engine 1 to flow into the unit along with exhaust containing the unburnt ammonia; variable cell number means 117, which changes the number of reaction cells, among the plurality of reaction cells 115a, through which the unburnt ammonia, flowing into the catalyst unit 115, passes; and a controller 120 which controls the variable cell number means 117. The controller 120 determines a concentration or an amount of the unburnt ammonia in the exhaust and adjusts the number of reaction cells accordingly, increasing or decreasing the number based on the concentration or amount of unburnt ammonia.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to a marine SCR system and an engine system including the same.

Background Art

[0002] Patent Document 1 discloses a diesel engine that burns a mixture of fuel oil and gaseous ammonia. Specifically, this diesel engine includes a combustion chamber and fuel injection means for injecting fuel oil and ammonia into the combustion chamber.

[0003] Further, the diesel engine according to Patent Document 1 is, for example, a marine diesel engine. This marine diesel engine is configured to uniformly distribute the stratification degree of ammonia in the combustion chamber over the entire circumference in order to increase the combustion rate of ammonia and reduce unburned ammonia.

[0004] On the other hand, Patent Document 2 discloses an exhaust gas treatment device applied to a marine diesel engine as an example of a marine SCR system. Here, the marine diesel engine to which the exhaust gas treatment device is applied is, in particular, an ammonia co-firing engine that is driven by co-firing ammonia fuel and fossil fuel.

[0005] Specifically, the exhaust gas treatment device according to Patent Document 2 includes a mixer and a reactor having a catalyst layer. Here, the mixer mixes exhaust gas with a reducing agent and sends it to the reactor. The reactor selectively advances the reduction reaction between nitrogen oxides and the reducing agent in the exhaust gas received from the mixer by its catalytic action.

[0006] Further, the exhaust gas treatment device according to Patent Document 2 separates an ammonia-containing liquid from ammonia-containing drain and burns the ammonia-containing liquid in an oxidation reactor. The exhaust gas treatment device uses the unburned ammonia component remaining after the combustion as a reducing agent to be mixed with the exhaust gas.

Prior Art Documents

Patent Document

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] In a diesel engine that burns ammonia fuel as in Patent Document 1, it is required to reduce the emission amount of unburned ammonia so that the emission amount is within a predetermined standard value.

[0009] As a measure to meet such demands, for example, it is conceivable to react unburned ammonia with nitrogen oxides in the exhaust gas by using a marine SCR system such as Patent Document 2.

[0010] However, generally, a marine SCR system has to process a large amount of exhaust gas. Therefore, a marine SCR system has to use a huge catalyst as compared with other applications (for example, automobiles). When using a huge catalyst, not only is it troublesome to replace the catalyst, but the cost required for the replacement also becomes extremely large.

[0011] In order to reduce the labor and cost as described above, it is conceivable to suppress the deterioration of the catalyst and extend its service life. However, a mechanism that can be compatible with the suppression of unburned ammonia emissions has not been known so far.

[0012] The present disclosure has been made in view of such a point, and the object thereof is to achieve both reduction of the emission amount of unburned ammonia and suppression of catalyst deterioration.

Means for Solving the Problems

[0013] The first aspect of the present disclosure relates to a marine SCR system connected to a combustion-capable diesel engine and configured to remove unburned ammonia discharged from the diesel engine. This marine SCR system has a plurality of reaction cells that form an exhaust gas flow path and promote the reaction of unburned ammonia, and includes a catalyst unit that allows unburned ammonia discharged from the diesel engine to flow in together with the exhaust gas containing the unburned ammonia, a cell number variable means for changing the number of reaction cells through which the unburned ammonia flowing into the catalyst unit passes, and a controller for controlling the cell number variable means. The controller determines the number of reaction cells so as to increase or decrease according to the concentration or amount of unburned ammonia contained in the exhaust gas.

[0014] According to the first aspect, the cell number variable means adjusts the number of reaction cells (reaction cell number) through which the unburned ammonia passes according to the concentration or amount of unburned ammonia contained in the exhaust gas. By setting the number of reaction cells corresponding to the concentration or amount of unburned ammonia, it becomes possible to remove unburned ammonia without necessarily using all the reaction cells. Thereby, it is possible to suppress the deterioration of the reaction cells and thus the catalyst.

[0015] Thus, according to the first aspect, it is possible to achieve both a reduction in the discharge amount of unburned ammonia and suppression of catalyst deterioration.

[0016] Further, according to the second aspect of the present disclosure, the controller may increase the number of reaction cells as the concentration or amount of the unburned ammonia increases.

[0017] According to the second aspect, it is possible to suppress the deterioration of the catalyst while reducing the discharge amount of unburned ammonia by keeping the number of reaction cells at an appropriate number corresponding to the concentration or amount of unburned ammonia without excessive reaction cells.

[0018] Further, according to a third aspect of the present disclosure, the catalyst unit has a plurality of catalysts connected in parallel or in series with respect to the exhaust gas flow, the cell number variable means is configured to change the number of catalysts through which the unburned ammonia passes among the plurality of catalysts, and the controller may increase the number of catalysts as the concentration or amount of the unburned ammonia increases.

[0019] According to the third aspect, the controller changes the number of reaction cells by changing the number of catalysts (catalyst number) through which the unburned ammonia passes. As a result, it is only necessary to change the flow path leading to each catalyst without providing a complicated mechanism for a specific catalyst, so that the number of reaction cells can be easily changed.

[0020] In addition, when the number of reaction cells is configured to be changed via the number of catalysts, generally, the degree of deterioration will differ for each catalyst. In this case, the reaction cells may be replaced on a catalyst-by-catalyst basis, which can improve the maintainability of the marine SCR system.

[0021] Further, according to a fourth aspect of the present disclosure, the controller controls the cell number variable means based on the number of catalysts set to correspond to the concentration or amount of the unburned ammonia and the combination of catalysts set to correspond to the number of catalysts, and the controller may update the correspondence relationship between the number of catalysts and the combination of catalysts when a predetermined condition occurs.

[0022] According to the fourth aspect, by setting the combination of catalysts through which the unburned ammonia passes for each number of catalysts and configuring the setting to be updated under a predetermined condition, the degree of deterioration of each catalyst can be made uniform. This is advantageous in suppressing the deterioration of the catalyst.

[0023] Further, according to a fifth aspect of the present disclosure, the marine SCR system is disposed in a first exhaust pipe connecting the diesel engine to the catalyst unit, and includes a first concentration sensor that detects an ammonia concentration in the first exhaust pipe. The controller may start the inflow of unburned ammonia into the catalyst unit when the ammonia concentration in the first exhaust pipe exceeds a predetermined reference value based on the detection signal of the first concentration sensor.

[0024] According to the fifth aspect, the first concentration sensor detects the ammonia concentration immediately before being introduced into the catalyst unit. Then, the controller starts the inflow of unburned ammonia into the catalyst unit based on the detection signal of the first concentration sensor. By configuring in this way, it is possible to start the inflow of unburned ammonia without delay as soon as the concentration of unburned ammonia increases. Leakage of unburned ammonia to the outside of the ship (especially leakage at a concentration exceeding a predetermined reference value) can be more reliably suppressed.

[0025] Further, according to a sixth aspect of the present disclosure, the marine SCR system is disposed in a second exhaust pipe connecting the catalyst unit to the outside of the ship, and includes a second concentration sensor that detects an ammonia concentration in the second exhaust pipe. The controller may determine the number of reaction cells through which unburned ammonia passes in the catalyst unit based on the detection signal of the second concentration sensor.

[0026] According to the sixth aspect, the second concentration sensor detects the ammonia concentration immediately after being discharged from the catalyst unit. Then, the controller adjusts the number of reaction cells based on the detection signal of the second concentration sensor. By configuring in this way, it is possible to set the number of reaction cells to the minimum number capable of suppressing the leakage of unburned ammonia without excessively setting the number of reaction cells. Thus, deterioration of the catalyst can be suppressed without hindering the reduction of the discharge amount of unburned ammonia.

[0027] Further, according to a seventh aspect of the present disclosure, the controller may terminate the inflow of unburned ammonia into the catalyst unit when the ammonia concentration in the second exhaust pipe falls below the reference value.

[0028] According to the seventh aspect, the controller terminates the inflow of unburned ammonia into the catalyst unit based on the ammonia concentration immediately after being discharged from the catalyst unit. By configuring in this way, it is possible to more reliably determine that the ammonia concentration in the exhaust gas discharged from the catalyst unit is below the reference value. As a result, the inflow of unburned ammonia into the catalyst unit can be terminated at a more appropriate timing, and the leakage of unburned ammonia to the outside of the ship (especially the leakage at a concentration exceeding a predetermined reference value) can be more reliably suppressed.

[0029] Further, according to an eighth aspect of the present disclosure, the marine SCR system includes a bypass pipe that connects the diesel engine to the outside of the ship so as to bypass the catalyst unit, and a bypass valve that is electrically connected to the controller and opens and closes the bypass pipe. The controller opens the bypass valve when the ammonia concentration in the first exhaust pipe that connects the diesel engine to the catalyst unit is equal to or lower than a predetermined reference value, thereby bypassing the catalyst unit for unburned ammonia through the bypass pipe, and closes the bypass valve when the ammonia concentration in the first exhaust pipe exceeds the reference value, thereby allowing unburned ammonia to flow into the catalyst unit.

[0030] According to a ninth aspect of the present disclosure, the marine SCR system may include a bypass pipe connecting the diesel engine to the outside of the ship so as to bypass the catalytic unit, and a bypass valve electrically connected to the controller and configured to open and close the bypass pipe, wherein when the ammonia concentration in the first exhaust pipe is equal to or lower than the reference value, the controller opens the bypass valve to allow unburned ammonia to bypass the catalytic unit via the bypass pipe, and when the ammonia concentration in the first exhaust pipe exceeds the reference value, the controller closes the bypass valve to allow unburned ammonia to flow into the catalytic unit.

[0031] The term "opening the valve" as used herein includes not only the operation of fully opening the bypass valve but also the general operation of adjusting the opening in the opening direction. Similarly, the term "closing the valve" as used herein includes not only the operation of fully closing the bypass valve but also the general operation of adjusting the opening in the closing direction.

[0032] According to the eighth and ninth aspects, by appropriately opening and closing the bypass valve or adjusting the opening degree based on the ammonia concentration, it is possible to realize more precise control commensurate with the ammonia concentration.

[0033] A tenth aspect of the present disclosure relates to an engine system, which may include the marine SCR system and a diesel engine capable of combusting at least the ammonia, the diesel engine being connected to the marine SCR system.

[0034] According to the tenth aspect, it is possible to reduce the amount of unburned ammonia discharged and to suppress catalyst deterioration at the same time. [Effects of the Invention]

[0035] As described above, according to the present disclosure, it is possible to achieve both a reduction in the amount of unburned ammonia emissions and suppression of catalyst deterioration. [Brief explanation of the drawings]

[0036]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 5B

Figure 5C

Figure 5D

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Figure 7

Figure 8

Figure 9

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Figure 11

MODE FOR CARRYING OUT THE INVENTION

[0037] Hereinafter, a first embodiment of the present disclosure (hereinafter simply referred to as "embodiment") will be described with reference to the drawings. Note that the following description is an example. FIG. 1 is a system diagram illustrating an engine system S, a diesel engine 1, and a marine SCR system 100 that constitute the engine system S.

[0038] <Overall Configuration> As shown in FIG. 1, the engine system S includes a diesel engine (hereinafter also simply referred to as "engine") 1 and a marine SCR system (hereinafter also simply referred to as "SCR system") 100 connected to the engine 1. This engine system S is mounted on large ships such as tankers, container ships, and car carriers.

[0039] The engine 1 can burn at least ammonia. The engine 1 is configured as a uniflow scavenging two-stroke one-cycle engine and is used as a main engine that generates propulsion force for operating the ship. The output shaft of the engine 1 is connected to a propeller (not shown) of the ship via a propeller shaft (not shown). When the engine 1 operates, its output is transmitted to the propeller, and the ship is propelled.

[0040] Specifically, the engine 1 can operate in each of a first mode in which oil fuel containing sulfur is burned alone in the cylinder 21, and a second mode in which at least ammonia among ammonia and oil fuel is burned in the same cylinder 21. The engine 1 can operate in the first mode or the second mode by switching from the first mode to the second mode or from the second mode to the first mode. In the present embodiment, fossil fuels such as heavy oil are used as the oil fuel. Any fuel that can be refined from crude oil may be used as the fossil fuel.

[0041] More specifically, when operating in the second mode, the engine 1 is configured to be capable of performing at least one of co-combustion of ammonia and oil fuel and single combustion of ammonia.

[0042] For example, the engine 1 described in detail below is configured to burn oil fuel alone in the first mode, while burning ammonia and oil fuel in a mixed manner in the second mode. Note that the first mode is not essential. The engine 1 only needs to be operable at least in the second mode.

[0043] Here, when configured to burn ammonia, it is assumed that the exhaust gas discharged from the cylinder 21 (especially the exhaust gas before being discharged outside the ship) may contain unburned ammonia in addition to so-called nitrogen oxides.

[0044] In order to remove the contents in the exhaust gas, the SCR system 100 according to the present embodiment is configured to remove unburned ammonia discharged from the diesel engine 1. This SCR system 100 includes an SCR device 110, and by reacting the unburned ammonia with nitrogen oxides by the device 110, the unburned ammonia can be removed from the exhaust gas.

[0045] Hereinafter, each element constituting the engine system S will be described in order.

[0046] <Details of Engine 1> As shown in FIG. 1, the engine 1 includes an engine body 2 having the aforementioned cylinder 21, an intake and exhaust system 3, and a fuel supply system 4. The intake and exhaust system 3 and the fuel supply system 4 are each connected to the engine body 2.

[0047] (1) Engine Body 2 As shown in FIG. 1, the engine body 2 has a plurality (only three are illustrated in FIG. 1) of cylinders 21. The engine body 2 is a two-stroke engine and is installed in the engine room of a ship. This engine body 2 is configured as a so-called crosshead type internal combustion engine in order to achieve its long stroke.

[0048] FIG. 2 is a diagram illustrating the upper structure of the engine body 2. As shown in FIG. 2, each cylinder 21 houses a piston 22. Each cylinder 21 is composed of a cylinder liner 23 and a cylinder cover 24. Here, the cylinder liner 23 functions as an inner cylinder extending in the vertical direction (corresponding to the vertical direction of the paper surface in FIG. 2). The cylinder cover 24 is fixed to the upper end of the cylinder liner 23 and closes the opening formed at the upper end thereof.

[0049] The engine body 2 further has an exhaust relay pipe 25 and an exhaust valve 26 for each cylinder 21. Here, the exhaust relay pipe 25 connects the central portion of each cylinder cover 24 and an exhaust manifold 2b described later. The exhaust valve 26 opens and closes the central portion of each cylinder cover 24.

[0050] And a combustion chamber 27 is partitioned for each cylinder 21 by the inner wall of each cylinder 21 and the top surface of the piston 22. One or a plurality of first fuel injection valves 28 and one or a plurality of second fuel injection valves 29 are provided in the cylinder cover 24 corresponding to each combustion chamber 27.

[0051] One or a plurality of (two in the illustrated example) first fuel injection valves 28 are provided for each cylinder 21, and each is connected to the first supply system 41. Each first fuel injection valve 28 is arranged in a posture facing the interior of the combustion chamber 27 and is configured to inject oil fuel from its injection port.

[0052] One or a plurality of second fuel injection valves 29 are also provided for each cylinder 21, preferably the same number as the first fuel injection valves 28 (two in the illustrated example), and each is connected to the second supply system 42. Each second fuel injection valve 29 is arranged in a posture facing the interior of the combustion chamber 27 and is configured to inject ammonia from its injection port.

[0053] When the engine 1 is operating in the first mode, among the first and second fuel injection valves 28 and 29, only the first fuel injection valve 28 supplies oil fuel into the combustion chamber 27. The oil fuel supplied from the first fuel injection valve 28 burns alone in the combustion chamber 27.

[0054] On the other hand, when the engine 1 is operating in the second mode, oil fuel is supplied from the first fuel injection valve 28 into the combustion chamber 27, and ammonia is supplied from the second fuel injection valve 29 into the same combustion chamber 27. The thus-supplied oil fuel and ammonia burn in a mixed manner (mixed combustion) in the combustion chamber 27.

[0055] The reciprocating motion of the piston 22 is caused by the combustion corresponding to each mode. At this time, when the exhaust valve 26 operates to release the combustion chamber 27, the exhaust generated by the combustion is pushed out into the exhaust relay pipe 25, and air is introduced into the combustion chamber 27 from a scavenging port (not shown).

[0056] Also, when the piston 22 reciprocates due to combustion, a crank motion occurs via a piston rod, a crosshead, etc., and the crankshaft rotates according to the crank motion. The rotation of the crankshaft rotates the propeller of the ship via a propeller shaft. When the propeller of the ship rotates, the ship is propelled.

[0057] Returning to FIG. 1, the engine body 2 further has a scavenging trunk 2a and an exhaust manifold 2b. The scavenging trunk 2a communicates with each combustion chamber 27 and temporarily stores air. The exhaust manifold 2b communicates with the combustion chamber 27 via the exhaust relay pipe 25, receives the exhaust discharged from the combustion chamber 27, temporarily stores the received exhaust, and changes the dynamic pressure of the exhaust to static pressure.

[0058] (2) Intake and Exhaust System 3 As shown in FIG. 1, the intake and exhaust system 3 has an intake pipe 31 connected to the engine body 2 via the scavenging trunk 2a and an exhaust pipe 32 connected to the engine body 2 via the exhaust manifold 2b.

[0059] The intake pipe 31 communicates with the combustion chamber 27 via the scavenging trunk 2a and is configured to guide air into the combustion chamber 27. The exhaust pipe 32 communicates with the combustion chamber 27 via the exhaust manifold 2b and is configured to guide the exhaust discharged from the combustion chamber 27.

[0060] Specifically, the exhaust pipe 32 has a first exhaust pipe 32a that connects the engine 1 to the SCR device 110 and a second exhaust pipe 32b that connects the SCR device 110 to the outside of the ship.

[0061] The first exhaust pipe 32a is a tubular member having one end (upstream end) connected to the engine 1 and the other end (downstream end) connected to the SCR device 110. The first exhaust pipe 32a forms a passage for guiding exhaust from the engine 1 to the SCR device 110.

[0062] A first concentration sensor 131 that constitutes the SCR system 100 together with the SCR device 110 is disposed in the first exhaust pipe 32a. The first concentration sensor 131 detects the ammonia concentration in the first exhaust pipe 32a.

[0063] The second exhaust pipe 32b is a tubular member having one end (upstream end) connected to the SCR device 110 and the other end (downstream end) connected to the outside of the ship. The second exhaust pipe 32b forms a passage for guiding exhaust from the SCR device 110 to the outside of the ship.

[0064] A second concentration sensor 132 that constitutes the SCR system 100 together with the SCR device 110 is disposed in the second exhaust pipe 32b. The second concentration sensor 132 detects the ammonia concentration in the second exhaust pipe 32b.

[0065] (3) Fuel supply system 4 As shown in FIG. 1, the fuel supply system 4 has a first supply system 41 and a second supply system 42. The first supply system 41 supplies oil fuel to each first fuel injection valve 28. The second supply system 42 supplies ammonia to each second fuel injection valve 29.

[0066] Specifically, the first supply system 41 includes a first fuel tank 41a, a first fuel supply pipe 41b, and a first fuel pump 41c. The first fuel tank 41a stores oil fuel. The first fuel supply pipe 41b connects the first fuel tank 41a to each first fuel injection valve 28. The first fuel pump 41c is disposed in the first fuel supply pipe 41b. The first fuel pump 41c pumps the oil fuel stored in the first fuel tank 41a and supplies it to the first fuel injection valve 28.

[0067] For example, when the engine 1 is operating in the first mode or the second mode, the first fuel pump 41c operates. As a result, the oil fuel stored in the first fuel tank 41a is supplied to each first fuel injection valve 28 via the first fuel supply pipe 41b and is injected from each first fuel injection valve 28 into the corresponding cylinder 21.

[0068] On the other hand, the second supply system 42 includes a second fuel tank 42a, a second fuel supply pipe 42b, and a second fuel pump 42c. The second fuel tank 42a stores ammonia. The second fuel supply pipe 42b connects the second fuel tank 42a to each second fuel injection valve 29. The second fuel pump 42c is disposed in the second fuel supply pipe 42b. The second fuel pump 42c pumps the ammonia stored in the second fuel tank 42a and supplies it to the second fuel injection valve 29.

[0069] For example, when the engine 1 is operating in the second mode, in addition to the first fuel pump 41c, the second fuel pump 42c operates. As a result, the ammonia stored in the second fuel tank 42a is supplied to each second fuel injection valve 29 via the second fuel supply pipe 42b and is injected from each second fuel injection valve 29 into the corresponding cylinder 21.

[0070] <Details of the SCR system 100> FIG. 3 is a block diagram illustrating the schematic configuration of the SCR system 100, and FIG. 4 is a system diagram illustrating the configuration of the SCR system 100. As shown in FIG. 3, the SCR system 100 includes the aforementioned SCR device 110, a controller 120, and first and second concentration sensors 131 and 132.

[0071] Here, the SCR device 110 reacts unburned ammonia (NH3) in the exhaust gas with nitrogen oxides (NO x ) in the same exhaust gas to remove unburned NH3 from the exhaust gas. The controller 120 controls the SCR device 110, particularly the cell number variable means 117 described later. The first and second concentration sensors 131 and 132 respectively output detection signals for controlling the cell number variable means 117 to the controller 120.

[0072] (1) SCR device 110 As shown in FIG. 4, the SCR device 110 includes an exhaust gas flow pipe 111, a mixer 113, the aforementioned catalyst unit 115, a cell number variable means 117, and a backflow prevention means 119.

[0073] Here, the catalyst unit 115 functions as a reactor in selective catalytic reduction (SCR). The catalyst unit 115 has a plurality of reaction cells 115a that form the flow path of the exhaust gas and promote the reaction of unburned NH3. The catalyst unit 115 is configured to allow unburned NH3 discharged from the engine 1 to flow in together with the exhaust gas containing the unburned NH3.

[0074] In addition, the catalyst unit 115 has a plurality of catalysts 116 each having a plurality of reaction cells 115a. The plurality of catalysts 116 are connected in parallel or in series with respect to the flow of the exhaust gas. Each catalyst 116 is composed of a so-called SCR catalyst, a slip catalyst, or the like.

[0075] Particularly in this embodiment, three catalysts 116 are connected in parallel with respect to the exhaust flow. Hereinafter, these multiple catalysts 116 may be referred to as the first catalyst 116a, the second catalyst 116b, and the third catalyst 116c.

[0076] Also, the cell number variable means 117 has a plurality of control valves. Hereinafter, these multiple control valves may be referred to as the first inlet valve 117a, the second inlet valve 117b, the third inlet valve 117c, and the bypass valve 117d.

[0077] Also, the backflow prevention means 119 has a plurality of control valves. Hereinafter, these multiple control valves may be referred to as the first outlet valve 119a, the second outlet valve 119b, and the third outlet valve 119c.

[0078] (1-1) Exhaust flow pipe 111 The exhaust flow pipe 111 extends so as to relay the first exhaust pipe 32a and the second exhaust pipe 32b, and is configured to guide the exhaust flowing in from the first exhaust pipe 32a to the catalyst unit 115 and to guide the exhaust discharged from the catalyst unit 115 to the second exhaust pipe 32b.

[0079] That is, the first exhaust pipe 32a can be regarded as being connected to the engine 1 to the catalyst unit 115 via the exhaust flow pipe 111. Similarly, the second exhaust pipe 32b can be regarded as being connected to the outside of the ship with the catalyst unit 115 via the exhaust flow pipe 111.

[0080] Specifically, the exhaust flow pipe 111 has a first flow pipe 111a, a second flow pipe 111b, a third flow pipe 111c, and a bypass pipe 111d.

[0081] The first flow pipe 111a is a tubular member having one end (upstream end) connected to the downstream end of the first exhaust pipe 32a and the other end (downstream end) connected to the upstream end of the second exhaust pipe 32b.

[0082] In the first flow pipe 111a, a mixer 113, a first inlet valve 117a, a first catalyst 116a, and a first outlet valve 119a are arranged in order from the upstream side.

[0083] The bypass pipe 111d connects the engine 1 to the outside of the ship so as to bypass the catalyst unit 115. In particular, the bypass pipe 111d according to the present embodiment is configured to connect the engine 1 to the outside of the ship through the first exhaust pipe 32a and the second exhaust pipe 32b.

[0084] Specifically, the bypass pipe 111d has one end (upstream end) connected to a first connection portion P1 located in the middle of the first flow pipe 111a, and the other end (downstream end) connected to a second connection portion P2 located in the middle of the first flow pipe 111a and downstream of the first connection portion P1.

[0085] Here, the first connection portion P1 is located downstream of the mixer 113 and upstream of the first inlet valve 117a in the first flow pipe 111a. The second connection portion P2 is located downstream of the first outlet valve 119a in the first flow pipe 111a.

[0086] Also, a bypass valve 117d described later is arranged in the bypass pipe 111d.

[0087] The second flow pipe 111b is connected in parallel to the first flow pipe 111a and the bypass pipe 111d in the exhaust flow direction.

[0088] Specifically, the second flow pipe 111b has one end (upstream end) connected to a third connection portion P3 located in the middle of the bypass pipe 111d, and the other end (downstream end) connected to a fourth connection portion P4 located in the middle of the bypass pipe 111d and downstream of the third connection portion P3.

[0089] Here, the third connection portion P3 is located upstream of the bypass valve 117d in the bypass pipe 111d. The fourth connection portion P4 is located downstream of the bypass valve 117d in the bypass pipe 111d.

[0090] In the second flow pipe 111b, a second inlet valve 117b, a second catalyst 116b, and a second outlet valve 119b are arranged in order from the upstream side.

[0091] The third flow pipe 111c is connected in parallel to the first flow pipe 111a, the second flow pipe 111b, and the bypass pipe 111d in the exhaust flow direction.

[0092] Specifically, the third flow pipe 111c has one end (upstream end) connected to a fifth connection part P5 located in the middle of the bypass pipe 111d, and the other end (downstream end) connected to a sixth connection part P6 located in the middle of the bypass pipe 111d and downstream of the fifth connection part P5.

[0093] Here, the fifth connection part P5 is located downstream of the third connection part P3 and upstream of the bypass valve 117d in the bypass pipe 111d. The sixth connection part P6 is located downstream of the bypass valve 117d and upstream of the fourth connection part P4 in the bypass pipe 111d.

[0094] In the third flow pipe 111c, a third inlet valve 117c, a third catalyst 116c, and a third outlet valve 119c are arranged in order from the upstream side.

[0095] (1-2) Mixer 113 The mixer 113 is configured as an exhaust pipe that injects a reducing agent into the exhaust and mixes them, and vaporizes the reducing agent mixed with the exhaust. In the present embodiment, urea water is used as the reducing agent injected into the exhaust.

[0096] Specifically, as shown in FIG. 4, the mixer 113 according to the present embodiment has a mixing pipe 113a through which the exhaust flows, and an injection nozzle 113b disposed inside the mixing pipe 113a and injecting urea water into the exhaust. The injection nozzle 113b is electrically connected to the controller 120 and injects urea water based on a control signal from the controller 120. The urea water injected into the exhaust becomes NH3 by vaporizing.

[0097] Also, as described later, the NH3 used in this embodiment includes, in addition to the NH3 derived from the aqueous urea solution in the first mode, unburned NH3 derived from the ammonia fuel in the second mode. The aqueous urea solution injected from the injection nozzle 113b as described above is related to the former NH3.

[0098] (1-3) Catalyst unit 115 The catalyst unit 115 promotes a chemical reaction on the reaction cell 115a by bringing the exhaust gas containing NH3 into contact with the reaction cell 115a. As a result, at least NH3 is removed from the exhaust gas. Each catalyst 116 constituting the catalyst unit 115 functions as a so-called reactor in the SCR device 110.

[0099] The reaction cell 115a constituting each catalyst 116 is constituted by a honeycomb structure through which the exhaust gas flows. On each cell wall constituting this honeycomb structure, for example, zeolite that traps NH3 and a metal that reacts with NH3 (for example, a metal that reduces NO x using NH3 as a reducing agent) are supported.

[0100] Also, the first catalyst 116a, the second catalyst 116b, and the third catalyst 116c are connected in parallel with respect to the flow of the exhaust gas as described above. In this embodiment, these catalysts 116 are each configured as an SCR catalyst that reduces NO x using NH3 as a reducing agent.

[0101] (1-4) Cell number variable means 117 The cell number variable means 117 is configured to change the number of reaction cells 115a (hereinafter, also referred to as "the number of reaction cells") through which the NH3 flowing into the catalyst unit 115 passes among the plurality of reaction cells 115a. Here, the "NH3" refers to the NH3 contained in the exhaust gas. Particularly in the second mode, the "NH3" here corresponds to the unburned NH3 that may be contained in the exhaust gas.

[0102] In particular, the cell number variable means 117 according to the present embodiment is configured to change the number of catalysts 116 through which the unburned ammonia passes (hereinafter, also referred to as "the number of catalysts").

[0103] Specifically, the cell number variable means 117 has a plurality of control valves as described above. The plurality of control valves include a first inlet valve 117a, a second inlet valve 117b, a third inlet valve 117c, and a bypass valve 117d.

[0104] The first inlet valve 117a, the second inlet valve 117b, the third inlet valve 117c, and the bypass valve 117d are each constituted by, for example, an electromagnetic valve. The first inlet valve 117a, the second inlet valve 117b, the third inlet valve 117c, and the bypass valve 117d are each electrically connected to the controller 120.

[0105] The first inlet valve 117a operates based on a control signal from the controller 120 to open and close the first flow pipe 111a. When the first inlet valve 117a opens the first flow pipe 111a, the inflow of exhaust gas to the first catalyst 116a is allowed. When the first inlet valve 117a closes the first flow pipe 111a, the inflow of exhaust gas to the first catalyst 116a is restricted.

[0106] The second inlet valve 117b operates based on a control signal from the controller 120 to open and close the second flow pipe 111b. When the second inlet valve 117b opens the second flow pipe 111b, the inflow of exhaust gas to the second catalyst 116b is allowed. When the second inlet valve 117b closes the second flow pipe 111b, the inflow of exhaust gas to the second catalyst 116b is restricted.

[0107] The third inlet valve 117c operates based on a control signal from the controller 120 to open and close the third flow pipe 111c. When the third inlet valve 117c opens the third flow pipe 111c, the inflow of exhaust gas to the third catalyst 116c is allowed. When the third inlet valve 117c closes the third flow pipe 111c, the inflow of exhaust gas to the third catalyst 116c is restricted.

[0108] The bypass valve 117d operates based on a control signal from the controller 120 to open and close the bypass pipe 111d. When the bypass valve 117d opens the bypass pipe 111d, the exhaust can bypass the catalyst unit 115. When the bypass valve 117d closes the bypass pipe 111d, the flow of exhaust through the bypass pipe 111d is restricted.

[0109] For example, when all of the first inlet valve 117a, the second inlet valve 117b, and the third inlet valve 117c are opened with the bypass valve 117d closed, the exhaust will pass through all of the first catalyst 116a, the second catalyst 116b, and the third catalyst 116c. The number of reaction cells through which the exhaust (specifically, unburned NH3 contained in the exhaust) passes becomes the maximum value N3. This maximum value N3 is as illustrated in FIG. 6 described later. At this time, the number of catalysts defined as described above becomes the maximum value = 3.

[0110] Also, when all of the first inlet valve 117a, the second inlet valve 117b, and the third inlet valve 117c are closed with the bypass valve 117d open, the number of reaction cells through which the exhaust passes becomes the minimum value (= zero) as illustrated in FIG. 6. The number of catalysts at this time becomes the minimum value = 0.

[0111] Also, when one of the first inlet valve 117a, the second inlet valve 117b, and the third inlet valve 117c is opened with the bypass valve 117d closed, the exhaust will pass through any one of the first catalyst 116a, the second catalyst 116b, and the third catalyst 116c. The number of reaction cells through which the exhaust passes becomes the first intermediate value N1 closer to the minimum value than the maximum value as illustrated in FIG. 6. The number of catalysts at this time is 1.

[0112] Also, when two of the first inlet valve 117a, the second inlet valve 117b, and the third inlet valve 117c are opened with the bypass valve 117d closed, the exhaust will pass through any two of the first catalyst 116a, the second catalyst 116b, and the third catalyst 116c. The number of reaction cells through which the exhaust passes becomes the second intermediate value N2 closer to the maximum value than the minimum value as illustrated in FIG. 6. The number of catalysts at this time is 2.

[0113] Also, when at least one of the first inlet valve 117a, the second inlet valve 117b, and the third inlet valve 117c is opened with the bypass valve 117d open, the exhaust flow will be split into the catalyst unit 115 and the bypass pipe 111d respectively.

[0114] (1-5) Backflow prevention means 119 The backflow prevention means 119 is configured to prevent the backflow of the exhaust gas that has passed through the catalyst unit 115 or the bypass pipe 111d.

[0115] As described above, the backflow prevention means 119 has a plurality of control valves. The plurality of control valves include a first outlet valve 119a, a second outlet valve 119b, and a third outlet valve 119c.

[0116] The first outlet valve 119a, the second outlet valve 119b, and the third outlet valve 119c are each constituted by, for example, an electromagnetic valve. The first outlet valve 119a, the second outlet valve 119b, and the third outlet valve 119c are each electrically connected to the controller 120.

[0117] The first outlet valve 119a operates based on a control signal from the controller 120 to open and close the first flow pipe 111a. When the first outlet valve 119a opens the first flow pipe 111a, the outflow of the exhaust gas from the first catalyst 116a is allowed. When the first outlet valve 119a closes the first flow pipe 111a, the outflow of the exhaust gas from the first catalyst 116a and the backflow of the exhaust gas into the first catalyst 116a are restricted.

[0118] The second outlet valve 119b operates based on a control signal from the controller 120 to open and close the second flow pipe 111b. When the second outlet valve 119b opens the second flow pipe 111b, the outflow of the exhaust gas from the second catalyst 116b is allowed. When the second outlet valve 119b closes the second flow pipe 111b, the outflow of the exhaust gas from the second catalyst 116b and the backflow of the exhaust gas into the second catalyst 116b are restricted.

[0119] The third outlet valve 119c operates based on a control signal from the controller 120 to open and close the third flow pipe 111c. When the third outlet valve 119c opens the third flow pipe 111c, the inflow of exhaust gas to the third catalyst 116c is permitted. When the third outlet valve 119c closes the third flow pipe 111c, the outflow of exhaust gas from the third catalyst 116c and the backflow of exhaust gas to the third catalyst 116c are restricted.

[0120] (2) Controller 120 (2-1) Schematic configuration The controller 120 has a processor, a volatile memory, a non-volatile memory, and an input / output device. The aforementioned first concentration sensor 131 and second concentration sensor 132 are electrically connected to this controller 120.

[0121] Based on the detection signals input from those sensors, the controller 120 generates a control signal and inputs that control signal, for example, to the mixer 113, the cell number variable means 117, and the backflow prevention means 119. Thereby, the controller 120 controls each part including the cell number variable means 117. The controller 120 inputs a control signal to each part of the SCR system 100 to cause the SCR device 110 to purify the exhaust gas.

[0122] The SCR device 110 illustrated in FIG. 1 is configured to purify the exhaust gas generated in each of the first mode and the second mode. For example, in the first mode in which the oil fuel is combusted alone, the SCR device 110 according to the present embodiment reacts NO x resulting from the oil fuel with NH3 derived from the aqueous urea solution to purify it.

[0123] Specifically, in the first mode, the controller 120 fully opens the first inlet valve 117a, the second inlet valve 117b, and the third inlet valve 117c with the bypass valve 117d closed. Then, the controller 120 appropriately injects the aqueous urea solution from the injection nozzle 113b of the mixer 113.

[0124] In addition, in the second mode in which at least ammonia is to be combusted, the SCR device 110 according to the present embodiment purifies unburned NH3 that may be contained in the exhaust gas by reacting it with NO x derived from the exhaust gas. At this time, the controller 120 according to the present embodiment executes a process that contributes to suppressing the emission of unburned NH3 by appropriately controlling the cell number variable means 117 described above. Hereinafter, this process will be referred to as "unburned NH3 purification process".

[0125] Hereinafter, the process related to the unburned NH3 purification process will be described using specific examples.

[0126] (2-2) Specific Example of Processing in Second Mode FIGS. 5A, 5B, 5C, and 5D are flowcharts illustrating the processing in the second mode.

[0127] First, in step S101 of FIG. 5A, the controller 120 determines whether or not the engine 1 is operating in the second mode. If this determination is YES, the controller 120 advances the control process to step S102. On the other hand, if the determination in step S101 is NO, the controller 120 shifts from the control process shown in FIG. 5A to the control process shown in FIG. 5B and starts the processing suitable for the first mode.

[0128] Specifically, when the determination in step S101 in FIG. 5A is NO, the controller 120 closes the bypass valve 117d in step S201 of FIG. 5B. In the subsequent step S202, the controller 120 controls the cell number variable means 117. Specifically, in step S202, the controller 120 opens all the inlet valves constituting the cell number variable means 117, that is, the first inlet valve 117a, the second inlet valve 117b, and the third inlet valve 117c.

[0129] Furthermore, in step S203 following step S202, the controller 120 controls the backflow prevention means 119. Specifically, in step S203, the controller 120 opens all the outlet valves constituting the backflow prevention means 119, that is, the first outlet valve 119a, the second outlet valve 119b, and the third outlet valve 119c.

[0130] When step S203 ends, the controller 120 ends the control process that continued from FIG. 5A to FIG. 5B. Note that the steps in FIG. 5B may be rearranged or two or more steps may be performed simultaneously.

[0131] On the other hand, when the determination in step S101 in FIG. 5A is YES, the controller 120 acquires the detection value of the first concentration sensor 131 in step S102 of the same figure. The detection value acquired in this step S102 indicates the ammonia concentration (particularly, the concentration of unburned ammonia) in the first exhaust pipe 32a. Since this ammonia concentration corresponds to the ammonia concentration on the exhaust inlet side as seen from the catalyst unit 115, in the following description, this may be referred to as the "inlet concentration" in some cases.

[0132] Note that in step S102, instead of or in addition to the detection value of the first concentration sensor 131, the determination may be made based on the detection value of the second concentration sensor 132.

[0133] In the subsequent step S103, the controller 120 determines whether the inlet concentration acquired in step S103 exceeds a predetermined reference value. This reference value is, for example, a regulatory value defined by laws and regulations and is stored in advance in the controller 120. The controller 120 is configured to appropriately read this reference value as needed. An example of the reference value is as shown by T1 in FIG. 6 described later.

[0134] If the determination in step S103 is YES, the controller 120 advances the control process to step S104 and determines that the unburned NH3 purification process should be started. For example, the controller 120 changes the signal value of a signal indicating the execution flag of the unburned NH3 purification process. The unburned NH3 purification process is a process involving the inflow of unburned NH3 into the catalyst unit 115, as will be described later.

[0135] That is, based on the detection signal of the first concentration sensor 131, when the inlet concentration corresponding to the detection signal exceeds a predetermined reference value (T1), the controller 120 according to the present embodiment starts the inflow of unburned NH3 into the catalyst unit 115.

[0136] On the other hand, if the determination in step S103 is NO, the controller 120 shifts the control process to step S301 in FIG. 5C. In this case, in step S301 of FIG. 5C, the controller 120 opens the bypass valve 117d. In the subsequent step S302, the controller 120 controls the cell number variable means 117. Specifically, in step S302, the controller 120 closes all the inlet valves constituting the cell number variable means 117, that is, the first inlet valve 117a, the second inlet valve 117b, and the third inlet valve 117c.

[0137] Furthermore, in step S303 following step S302, the controller 120 controls the backflow prevention means 119. Specifically, in step S303, the controller 120 closes all the outlet valves constituting the backflow prevention means 119, that is, the first outlet valve 119a, the second outlet valve 119b, and the third outlet valve 119c.

[0138] When step S303 ends, the controller 120 ends the control process that continued from FIG. 5A to FIG. 5C. Note that the steps in FIG. 5C may be rearranged, or two or more steps may be performed simultaneously.

[0139] Also, when returning to step S104, in step S105 that follows from this step, the controller 120 executes an unburned NH3 purification process. The details of the unburned NH3 purification process are as shown in FIG. 5D. When the control process proceeds to step S105, the controller 120 executes each process shown in the figure in order from step S401 in FIG. 5D.

[0140] First, in step S401, the controller 120 acquires the detection value of the second concentration sensor 132. The detection value acquired in this step S401 indicates the ammonia concentration (particularly, the concentration of unburned NH3) in the second exhaust pipe 32b. Since this ammonia concentration corresponds to the ammonia concentration on the exhaust outlet side as seen from the catalyst unit 115, in the following description, this may be referred to as the "outlet concentration" in some cases.

[0141] In step S401, instead of or in addition to the detection value of the second concentration sensor 132, the detection value of the first concentration sensor 131 may be acquired.

[0142] In the subsequent step S402, the controller 120 determines the concentration of unburned NH3 contained in the exhaust gas. Specifically, the controller 120 according to the present embodiment determines the value of the outlet concentration based on the detection signal of the second concentration sensor 132.

[0143] The outlet concentration determined in step S402 is used to determine the number of reaction cells, and thus the number of catalysts, in the subsequent step S403. That is, the controller 120 according to the present embodiment is configured to determine the number of reaction cells in the catalyst unit 115 based on the detection signal of the second concentration sensor 132.

[0144] Further, in step S402, the controller 120 may determine the amount (e.g., flow rate) of unburned NH3 contained in the exhaust gas instead of the concentration of unburned NH3 contained in the exhaust gas. This determination can be executed, for example, by combining the detection signal from at least one of the first concentration sensor 131 and the second concentration sensor 132 with the detection signal of a flow rate sensor capable of detecting the flow rate of the entire exhaust gas.

[0145] In the subsequent step S403, the controller 120 determines the number of reaction cells so as to increase or decrease according to the concentration of unburned NH3. As described above, the controller 120 according to the present embodiment regards the detection value of the second concentration sensor 132 as the concentration of unburned NH3. Further, the number of reaction cells according to the present embodiment is configured to be changed through the number of catalysts described above.

[0146] That is, the number of reaction cells according to the present embodiment is adjusted through the number of catalysts 116 (= the number of catalysts) that allow unburned NH3 to pass through among the first catalyst 116a, the second catalyst 116b, and the third catalyst 116c, and increases or decreases discretely according to the number of catalysts.

[0147] Here, FIG. 6 is a graph showing the relationship between the concentration of unburned NH3 and the number of reaction cells in the second mode. The vertical axis of FIG. 6 can also be read as the number of catalysts proportional to the number of reaction cells as shown on the right side of the paper surface of the graph. When read in that way, the vertical axis becomes one of the values 0, 1, 2, and 3 in order from the minimum value.

[0148] The solid line L2 in FIG. 6 shows the number of reaction cells (the number of catalysts) in the second mode in association with the level of the concentration of unburned NH3. As shown by the arrow A1 in FIG. 6, the controller 120 is configured to increase the number of reaction cells as the concentration of unburned NH3 increases in the second mode. When the number of reaction cells is increased, the number of catalysts also increases accordingly. Therefore, it can also be said that the controller 120 is configured to increase the number of catalysts as the concentration of unburned NH3 increases.

[0149] The dashed line L1 in FIG. 6 indicates the number of reaction cells (number of catalysts) in the first mode. In the first mode, although the emission amount of unburned NH3 is zero in the first place, the dashed line L1 is shown as a straight line parallel to the horizontal axis of FIG. 6 in order to clarify the magnitude relationship with the solid line L2. As shown by the dashed line L1, the controller 120 sets the number of reaction cells and the number of catalysts to the maximum value in the first mode.

[0150] In addition, when configured to determine the amount instead of the concentration of unburned NH3, the controller 120 may determine the number of reaction cells and the number of catalysts so as to increase or decrease according to the amount of unburned NH3. In that case, in the second mode, the controller 120 may be configured to increase the number of reaction cells and the number of catalysts as the amount of unburned NH3 increases.

[0151] In the subsequent step S404, the controller 120 reads a first control map M1 (see FIG. 7) that defines the relationship between the number of reaction cells or the number of catalysts corresponding to the concentration of unburned NH3 and the combination of the catalysts 116 set to correspond to the number of catalysts. The "combination of the catalysts 116" referred to here means the combination of the catalysts 116 through which unburned NH3 should pass among the plurality of catalysts 116.

[0152] The first control map M1 according to the present embodiment is a map that defines the association between the current number of catalysts and the control parameters of the cell number variable means 117. The control parameters defined in the first control map M1 are a list of parameters that determine whether to open or close each control valve constituting the cell number variable means 117.

[0153] FIG. 7 shows an example of the first control map M1. For example, when the number of catalysts = 3, the controller 120 reads the control parameters defined to open (Open) all of the first inlet valve 117a, the second inlet valve 117b, and the third inlet valve 117c and close (Close) the bypass valve 117d.

[0154] In step S405, the controller 120 collates the number of catalysts determined in step S403 with the first control map M1 read in step S404. The controller 120 determines the control parameter of the cell number variable means 117 corresponding to the number of catalysts at that time point.

[0155] In step S406, the controller 120 inputs a control signal to the bypass valve 117d and closes it. The process of step S406 may be performed in conjunction with step S407 that follows, or may be immediately performed before and after step S104 as soon as the determination in step S103 of FIG. 5A becomes YES.

[0156] In step S407, the controller 120 controls the cell number variable means 117 based on the control parameter determined in step S405. Specifically, the controller 120 opens or closes the first inlet valve 117a, the second inlet valve 117b, and the third inlet valve 117c according to the first control map M1.

[0157] Note that the first outlet valve 119a is opened when the first inlet valve 117a is opened, and is closed when the first inlet valve 117a is closed. Similarly, the second outlet valve 119b is opened when the second inlet valve 117b is opened, and is closed when the second inlet valve 117b is closed. The third outlet valve 119c is opened when the third inlet valve 117c is opened, and is closed when the third inlet valve 117c is closed.

[0158] For example, as shown in FIG. 6, when the concentration of unburned NH3 is 0 or more and below the first reference value T1, both the number of reaction cells and the number of catalysts become zero as the minimum value. In this case, the determination in step S103 becomes NO, and the process described with reference to FIG. 5C is executed. The first reference value T1 mentioned here is an example of the "reference value" in the present embodiment.

[0159] Also, as shown in FIG. 6, when the concentration of unburned NH3 exceeds the first reference value T1 and is equal to or less than the second reference value T2, the number of reaction cells becomes the first intermediate value N1, and the corresponding number of catalysts becomes 1. In this case, the controller 120 opens only the first inlet valve 117a and the first outlet valve 119a, and introduces unburned NH3 only into the first catalyst 116a.

[0160] Also, as shown in FIG. 6, when the concentration of unburned NH3 exceeds the second reference value T2 and is equal to or less than the third reference value T3, the number of reaction cells becomes the second intermediate value N2, and the corresponding number of catalysts becomes 2. In this case, the controller 120 opens the first inlet valve 117a and the first outlet valve 119a, and the second inlet valve 117b and the second outlet valve 119b, and introduces unburned NH3 into the first catalyst 116a and the second catalyst 116b.

[0161] Also, as shown in FIG. 6, when the concentration of unburned NH3 exceeds the third reference value T3, the number of reaction cells becomes N3, and the corresponding number of catalysts becomes the maximum value 3. In this case, the controller 120 opens the first inlet valve 117a and the first outlet valve 119a, the second inlet valve 117b and the second outlet valve 119b, and the third inlet valve 117c and the third outlet valve 119c, and introduces unburned NH3 into the first catalyst 116a, the second catalyst 116b, and the third catalyst 116c.

[0162] When the process of step S407 is completed, the controller 120 completes the process of step S105 in FIG. 5A, and advances the control process to step S106.

[0163] In step S106, the controller 120 acquires the outlet concentration again, and determines whether the outlet concentration is below a predetermined reference value. This reference value may be the same as the reference value (T1) referred to in step S103, for example.

[0164] If the determination in step S106 is YES, the controller 120 advances the control process to step S107, and determines that the unburned NH3 purification process should be terminated. For example, the controller 120 changes the signal value of the signal indicating the execution flag of the unburned NH3 purification process.

[0165] That is, when the outlet concentration corresponding to the detection signal of the second concentration sensor 132 falls below a predetermined reference value (T1) based on the detection signal, the controller 120 according to the present embodiment terminates the inflow of unburned NH3 into the catalyst unit 115.

[0166] On the other hand, when the determination in step S106 is NO, the controller 120 returns the control process to step S105. The controller 120 continues the unburned NH3 purification process until the determination in step S106 becomes YES. During the unburned NH3 purification process, the controller 120 changes the number of reaction cells, and thus the number of catalysts, in real time through the processes of steps S402 and S403 in FIG. 5D.

[0167] As described above with reference to FIG. 5D, the controller 120 is configured to control the cell number variable means 117 based on the number of catalysts set to correspond to the concentration or amount of unburned NH3 and the combination of catalysts set to correspond to the number of catalysts.

[0168] Here, the controller 120 updates the correspondence relationship between the number of catalysts and the combination of catalysts on the occasion of a predetermined condition. This update is performed by changing the first control map M1 illustrated in FIG. 7. For example, the controller 120 according to the present embodiment automatically updates the first control map M1 periodically. This automatic update is performed by the controller 120, for example, every time the operation in the second mode is performed for a predetermined period. The predetermined condition may be an operation input by a crew member.

[0169] FIG. 8 is a diagram for explaining the update of the first control map M1. As shown in FIG. 8, each time the operation in the second mode is performed for a predetermined period, the controller 120 updates the first control map M1 to the second control map M2. Each time the operation in the second mode is performed for a predetermined period, the controller 120 updates the second control map M2 to the third control map M3. Each time the operation in the second mode is performed for a predetermined period, the controller 120 updates the third control map M3 to the first control map M1.

[0170] The update targets in the first control map M1 are limited to the control parameters related to the opening and closing of the first inlet valve 117a, the second inlet valve 117b, and the third inlet valve 117c related to the catalyst unit 115, and the first outlet valve 119a, the second outlet valve 119b, and the third outlet valve 119c corresponding to each inlet valve. As illustrated in FIG. 8, the control parameters related to the opening and closing of the bypass valve 117d are excluded from the update targets in the first control map M1.

[0171] <Regarding suppression of unburned NH3 emissions> In a diesel engine configured to burn ammonia, it is required to reduce the emission amount of unburned ammonia so that the emission amount is within a predetermined reference value or less.

[0172] As a measure to meet such a demand, for example, by using a so-called SCR device, unburned NH3 can be made to react with NO in the exhaust gas. x It is conceivable to make it react.

[0173] However, the marine SCR device 110 as illustrated in FIG. 1 generally has to process a large amount of exhaust gas. Therefore, the marine SCR system 100 has to use a huge catalyst as compared with other applications (for example, automobiles). When using a huge catalyst, not only is it troublesome to replace the catalyst, but also the monetary cost required for the replacement becomes extremely large.

[0174] In order to reduce the labor and costs as described above, it is conceivable to suppress the deterioration of the catalyst and extend its lifespan. However, a mechanism that can be compatible with suppressing the emission of unburned NH3 has not been known until now.

[0175] On the other hand, as exemplified in steps S402 to S407 of FIG. 5D, FIGS. 6 and 7, the variable cell number means 117 according to the embodiment adjusts the number of reaction cells 115a (the number of reaction cells) through which the unburned NH3 passes according to the concentration or amount of the unburned NH3 contained in the exhaust gas. By setting the number of reaction cells corresponding to the concentration or amount of the unburned NH3, it becomes possible to remove the unburned NH3 without necessarily using all the reaction cells 115a. Thereby, it is possible to suppress the deterioration of the reaction cells 115a and thus each catalyst 116.

[0176] As described above, according to the embodiment, it is possible to achieve both a reduction in the emission amount of unburned NH3 and suppression of the deterioration of the catalyst unit 115.

[0177] Also, as exemplified in FIG. 6, by adjusting the number of reaction cells, it is possible to suppress the number to an appropriate number corresponding to the concentration or amount of the unburned NH3 without making the number of reaction cells excessive. Thus, it is possible to suppress the deterioration of the catalyst unit 115 while reducing the emission amount of the unburned NH3.

[0178] Also, as exemplified in FIGS. 6 and 7, the controller 120 changes the number of reaction cells by changing the number of catalysts (the number of catalysts) through which the unburned NH3 passes. Thereby, without providing a complicated mechanism for a specific catalyst 116, it is only necessary to change the flow path leading to each catalyst 116, so that it becomes possible to easily change the number of reaction cells.

[0179] Also, when configured to change the number of reaction cells via the number of catalysts, generally, the degree of deterioration will differ for each catalyst 116. In this case, the reaction cells 115a may be replaced on a catalyst 116 unit basis, which can improve the maintainability of the marine SCR system 100.

[0180] Also, as illustrated in FIGS. 7 and 8, by setting the combination of the catalysts 116 through which the unburned NH3 passes for each number of catalysts and configuring to update the setting under predetermined conditions, the degree of deterioration of each catalyst 116 can be made uniform. This is advantageous in suppressing the deterioration of the catalyst unit 115.

[0181] Also, as illustrated in FIG. 1, the first concentration sensor 131 detects the ammonia concentration immediately before being introduced into the catalyst unit 115. Then, as described from step S102 to step S104 in FIG. 5A, the controller 120 starts the inflow of unburned NH3 into the catalyst unit 115 based on the detection signal of the first concentration sensor 131. By configuring in this way, as soon as the concentration of unburned NH3 increases, the inflow of unburned NH3 can be started without delay. The leakage of unburned NH3 to the outside of the vessel (especially the leakage at a concentration exceeding a predetermined reference value) can be more reliably suppressed.

[0182] Also, as illustrated in FIG. 1, the second concentration sensor 132 detects the ammonia concentration immediately after being discharged from the catalyst unit 115. Then, as described from step S401 to step S403 in FIG. 5D, the controller 120 adjusts the number of reaction cells based on the detection signal of the second concentration sensor 132. By configuring in this way, the number of reaction cells can be set to the minimum number capable of suppressing the leakage of unburned NH3 without setting the number of reaction cells excessively. Thus, the deterioration of the catalyst 116 can be suppressed without hindering the reduction of the discharge amount of unburned NH3.

[0183] Also, as exemplified from step S106 to step S107 in FIG. 5A, the controller 120 terminates the inflow of unburned NH3 into the catalyst unit 115 based on the ammonia concentration immediately after being discharged from the catalyst unit 115. By configuring in this way, it is possible to more reliably determine that the ammonia concentration in the exhaust gas discharged from the catalyst unit 115 is below the reference value. As a result, the inflow of unburned NH3 into the catalyst unit 115 can be terminated at a more appropriate timing, and the leakage of unburned NH3 to the outside of the ship (especially the leakage at a concentration exceeding a predetermined reference value) can be more reliably suppressed.

[0184] Also, as exemplified in FIGS. 6 and 7, by appropriately opening and closing or adjusting the opening degree of the bypass valve 117d based on the ammonia concentration, more precise control corresponding to the ammonia concentration can be realized.

[0185] Note that the term "valve opening" in the present embodiment includes not only the operation of fully opening the opening degree of the bypass valve 117d but also the general operation of adjusting the opening degree in the opening direction. Similarly, the term "valve closing" in the present embodiment includes not only the operation of fully closing the opening degree of the bypass valve 117d but also the general operation of adjusting the opening degree in the closing direction. This also applies to the modified examples and other embodiments described later.

[0186] <Modification Example of the Backflow Prevention Means 119> In the above embodiment (the first embodiment), a control valve such as the first outlet valve 119a was used for the backflow prevention means 119, but the backflow prevention means 119 is not limited to a control valve. Air injection may be used for the backflow prevention means 119.

[0187] FIG. 9 is a diagram corresponding to FIG. 4 showing a modification example of the backflow prevention means 119. In FIG. 9, elements having the same configuration and structure as those in FIG. 4 are given the same reference numerals as in the present embodiment.

[0188] The SCR device 110 illustrated in FIG. 9 is provided with a second backflow prevention means 119' using air injection instead of the first backflow prevention means 119 using a control valve. The second backflow prevention means 119' has a first air supplier 119a', a second air supplier 119b', and a third air supplier 119c'.

[0189] The first air supplier 119a' is located at a position between the first inlet valve 117a and the first catalyst 116a in the first flow pipe 111a. The first air supplier 119a' supplies air to the said position. By supplying air with the first inlet valve 117a closed, the backflow of exhaust gas in the first flow pipe 111a is suppressed. The air supply timing by the first air supplier 119a' may be set in the same way as the closing timing of the first outlet valve 119a.

[0190] The second air supplier 119b' is located at a position between the second inlet valve 117b and the second catalyst 116b in the second flow pipe 111b. The second air supplier 119b' supplies air to the said position. By supplying air with the second inlet valve 117b closed, the backflow of exhaust gas in the second flow pipe 111b is suppressed. The air supply timing by the second air supplier 119b' may be set in the same way as the closing timing of the second outlet valve 119b.

[0191] The third air supplier 119c' is located at a position between the third inlet valve 117c and the third catalyst 116c in the third flow pipe 111c. The third air supplier 119c' supplies air to the said position. By supplying air with the third inlet valve 117c closed, the backflow of exhaust gas in the third flow pipe 111c is suppressed. The air supply timing by the third air supplier 119c' may be set in the same way as the closing timing of the third outlet valve 119c.

[0192] The second backflow prevention means 119' may be used instead of the first backflow prevention means 119 illustrated in FIG. 4, or may be used in combination with the first backflow prevention means 119. By using the first backflow prevention means 119 and the second backflow prevention means 119' in combination, the backflow of exhaust can be more reliably prevented.

[0193] <Second Embodiment> In the above embodiment (the first embodiment), a configuration in which a plurality of catalysts (three catalysts 116 in the first embodiment) are connected in parallel to the exhaust flow is illustrated. However, the present disclosure is not limited to such a configuration. The plurality of catalysts may be connected in series to the exhaust flow.

[0194] FIG. 10 is a diagram corresponding to FIG. 4 illustrating a second embodiment of the SCR system. In FIG. 9, elements having the same configuration and structure as those in FIG. 4 are denoted by the same reference numerals in this embodiment. Also, descriptions overlapping with the first embodiment are appropriately omitted.

[0195] (1) SCR device 110' The SCR system 100' according to the second embodiment has a configuration of the SCR device 110' that is different from the configuration according to the first embodiment. Specifically, the SCR device 110' according to the second embodiment includes an exhaust flow pipe 111', a mixer 113, a catalyst unit 115', and a cell number variable means 117', as shown in FIG. 10. The configuration of the mixer 113 is the same as that of the first embodiment.

[0196] The catalyst unit 115' has a plurality of catalysts 116' each having a plurality of reaction cells 115a. The plurality of catalysts 116' are connected in series to the exhaust flow.

[0197] Particularly in the second embodiment, three catalysts 116' are connected in series to the exhaust flow. Hereinafter, the plurality of catalysts 116' may be referred to as a first catalyst 116a', a second catalyst 116b', and a third catalyst 116c'.

[0198] Further, the cell number variable means 117’ has a plurality of control valves as in the first embodiment. Hereinafter, the plurality of control valves may be referred to as a first inlet valve 117a’, a second inlet valve 117b’, a third inlet valve 117c’ and a bypass valve 117d’ as in the first embodiment.

[0199] (1-1) Exhaust flow pipe 111’ The exhaust flow pipe 111’ extends so as to relay the first exhaust pipe 32a and the second exhaust pipe 32b, guides the exhaust flowing in from the first exhaust pipe 32a to the catalyst unit 115’, and guides the exhaust discharged from the catalyst unit 115’ to the second exhaust pipe 32b.

[0200] That is, the first exhaust pipe 32a can be regarded as being connected to the engine 1 to the catalyst unit 115’ via the exhaust flow pipe 111’. Similarly, the second exhaust pipe 32b can be regarded as being connected to the outside of the ship with the catalyst unit 115’ via the exhaust flow pipe 111’.

[0201] Specifically, the exhaust flow pipe 111’ has a first flow pipe 111a’, a second flow pipe 111b’, a third flow pipe 111c’ and a bypass pipe 111d’ as in the first embodiment.

[0202] The first flow pipe 111a’ is a tubular member having one end (upstream end) connected to the downstream end of the first exhaust pipe 32a and the other end (downstream end) connected to the upstream end of the second exhaust pipe 32b.

[0203] In the first flow pipe 111a’, a mixer 113, a first inlet valve 117a’, a first catalyst 116a’, a second catalyst 116b’ and a third catalyst 116c’ are arranged in order from the upstream side.

[0204] The bypass pipe 111d’ connects the engine 1 to the outside of the ship so as to bypass the catalyst unit 115’. In particular, the bypass pipe 111d’ according to the present embodiment is configured to connect the engine 1 to the outside of the ship by passing through the first exhaust pipe 32a and the second exhaust pipe 32b.

[0205] Specifically, the bypass pipe 111d' has one end (upstream end) connected to the first connection part Q1 located in the middle of the first flow pipe 111a', and the other end (downstream end) connected to the second connection part Q2 located in the middle of the first flow pipe 111a' and downstream of the first connection part Q1.

[0206] Here, the first connection part Q1 is located downstream of the mixer 113 and upstream of the first inlet valve 117a' in the first flow pipe 111a'. The second connection part Q2 is located downstream of the third catalyst 116c' in the first flow pipe 111a'.

[0207] Also, a bypass valve 117d' described later is arranged in the bypass pipe 111d'.

[0208] The second flow pipe 111b' extends so as to connect the first flow pipe 111a' and the bypass pipe 111d'. Specifically, the second flow pipe 111b' has one end (upstream end) connected to the third connection part Q3 located in the middle of the bypass pipe 111d', and the other end (downstream end) connected to the fourth connection part Q4 located in the middle of the first flow pipe 111a' and downstream of the first connection part Q1.

[0209] Here, the third connection part Q3 is located upstream of the bypass valve 117d' in the bypass pipe 111d'. The fourth connection part Q4 is located between the first catalyst 116a' and the second catalyst 116b' in the first flow pipe 111a'.

[0210] A second inlet valve 117b' is arranged in the second flow pipe 111b'.

[0211] The third flow pipe 111c' extends so as to connect the first flow pipe 111a' and the bypass pipe 111d'. Specifically, the third flow pipe 111c' has one end (upstream end) connected to the fifth connection part Q5 located in the middle of the bypass pipe 111d', and the other end (downstream end) connected to the sixth connection part Q6 located downstream of the first flow pipe 111a' and the fourth connection part Q4.

[0212] Here, the fifth connection part Q5 is located downstream of the third connection part Q3 and upstream of the bypass valve 117d’ in the bypass pipe 111d’. The sixth connection part Q6 is located between the second catalyst 116b’ and the third catalyst 116c’ in the first flow pipe 111a’.

[0213] A third inlet valve 117c’ is arranged in the third flow pipe 111c’.

[0214] (1-2) Catalyst unit 115’ The catalyst unit 115’ promotes a chemical reaction on the reaction cell 115a’ by bringing the exhaust gas containing NH3 into contact with the reaction cell 115a’. As a result, at least NH3 is removed from the exhaust gas. Each catalyst 116’ constituting the catalyst unit 115’ functions as a so-called reactor in the SCR device 110. The reaction cell 115a’ constituting each catalyst 116’ is the same as that in the first embodiment.

[0215] Also, the first catalyst 116a’, the second catalyst 116b’ and the third catalyst 116c’ are connected in series with respect to the flow of the exhaust gas as described above. In the second embodiment, these catalysts 116 are each configured as an SCR catalyst that reduces NO x using NH3 as a reducing agent.

[0216] (1-2) Cell number variable means 117’ The cell number variable means 117’ changes the number of reaction cells 115a’ (the number of reaction cells) through which the NH3 flowing into the catalyst unit 115’ passes among the plurality of reaction cells 115a’ in the same manner as in the first embodiment.

[0217] The cell number variable means 117’ according to the second embodiment is configured to change the number of catalysts 116’ (hereinafter also referred to as “the number of catalysts”) through which the unburned ammonia passes among the plurality of catalysts 116’.

[0218] Specifically, the cell number variable means 117’ has a plurality of control valves as described above. The plurality of control valves include a first inlet valve 117a’, a second inlet valve 117b’, a third inlet valve 117c’ and a bypass valve 117d’. The configuration of these control valves is the same as that of the first embodiment.

[0219] The first inlet valve 117a’ operates based on a control signal from the controller 120 to open and close the first flow pipe 111a’. When the first inlet valve 117a’ opens the first flow pipe 111a’, the inflow of exhaust gas into the first catalyst 116a’, the second catalyst 116b’ and the third catalyst 116c’ is allowed. When the first inlet valve 117a’ closes the first flow pipe 111a’, the inflow of exhaust gas into at least the first catalyst 116a’ is restricted.

[0220] The second inlet valve 117b’ operates based on a control signal from the controller 120 to open and close the second flow pipe 111b’. When the second inlet valve 117b’ opens the second flow pipe 111b’, the inflow of exhaust gas into the second catalyst 116b’ and the third catalyst 116c’ is allowed. When the second inlet valve 117b’ closes the second flow pipe 111b’, the inflow of exhaust gas into at least the second catalyst 116b’ is restricted.

[0221] The third inlet valve 117c’ operates based on a control signal from the controller 120 to open and close the third flow pipe 111c’. When the third inlet valve 117c’ opens the third flow pipe 111c’, the inflow of exhaust gas into the third catalyst 116c’ is allowed. When the third inlet valve 117c’ closes the third flow pipe 111c’, the inflow of exhaust gas into the third catalyst 116c’ is restricted.

[0222] The bypass valve 117d’ operates based on a control signal from the controller 120 to open and close the bypass pipe 111d’. When the bypass valve 117d’ opens the bypass pipe 111d’, the exhaust gas can bypass the catalyst unit 115’. When the bypass valve 117d’ closes the bypass pipe 111d’, the flow of exhaust gas through the bypass pipe 111d’ is restricted.

[0223] For example, when only the first inlet valve 117a' is opened with the bypass valve 117d' closed, the exhaust gas will pass through all of the first catalyst 116a', the second catalyst 116b', and the third catalyst 116c'. The number of reaction cells through which the exhaust gas (specifically, unburned NH3 contained in the exhaust gas) passes will be the maximum value N3. This maximum value N3 is as illustrated in FIG. 6 described above. At this time, the number of catalysts will be the maximum value = 3.

[0224] Also, when all of the first inlet valve 117a', the second inlet valve 117b', and the third inlet valve 117c' are closed with the bypass valve 117d' open, the exhaust gas will not pass through any of the first catalyst 116a', the second catalyst 116b', and the third catalyst 116c'. The number of reaction cells through which the exhaust gas passes will be the minimum value (= zero) as illustrated in FIG. 6. At this time, the number of catalysts will be the minimum value = 0.

[0225] Also, when only the second inlet valve 117b' is opened with the bypass valve 117d' closed, the exhaust gas will pass through the second catalyst 116b' and the third catalyst 116c'. The number of reaction cells through which the exhaust gas passes will be the second intermediate value N2 that is closer to the maximum value than the minimum value, as illustrated in FIG. 6. At this time, the number of catalysts will be 2.

[0226] Also, when only the third inlet valve 117c' is opened with the bypass valve 117d' closed, the exhaust gas will pass through only the third catalyst 116c'. The number of reaction cells through which the exhaust gas passes will be the first intermediate value N1 that is closer to the minimum value than the maximum value, as illustrated in FIG. 6. At this time, the number of catalysts will be 1.

[0227] Also, when at least one of the first inlet valve 117a', the second inlet valve 117b', and the third inlet valve 117c' is opened with the bypass valve 117d' open, the exhaust gas flow will be divided into the catalyst unit 115' and the bypass pipe 111d' respectively.

[0228] (2) Controller 120 Similar to the first embodiment, the controller 120 according to the second embodiment performs unburned NH3 purification processing. The outline of the unburned NH3 purification processing is the same as the processing illustrated in FIGS. 5A to 5D, except for the processing related to the backflow prevention means 119.

[0229] That is, the controller 120 determines the number of reaction cells so as to increase or decrease according to the concentration or amount of unburned NH3. The content illustrated in FIG. 6 is also the same as that in the first embodiment.

[0230] Similar to the first embodiment, in the second mode, the controller 120 is configured to increase the number of reaction cells as the concentration of unburned NH3 increases. In other words, the controller 120 is configured to increase the number of catalysts as the concentration of unburned NH3 increases.

[0231] The main difference between the processing according to the second embodiment and the processing according to the first embodiment lies in the details of the control map (first control map M1) read in step S404 of FIG. 5D. FIG. 11 illustrates a first control map M1' according to the second embodiment. As described above, this difference is due to the difference in the relationship between the opening / closing status of the first inlet valve 117a' and the like and the number of catalysts realized thereby.

[0232] According to the second embodiment, similar to the first embodiment, it is possible to achieve both a reduction in the emission amount of unburned NH3 and suppression of deterioration of the catalyst unit 115.

[0233] In addition, various advantages related to the first concentration sensor 131 and the second concentration sensor 132, and various advantages related to the relationship between the concentration or amount of unburned NH3 and the number of reaction cells (number of catalysts) can also be enjoyed in the same manner as in the first embodiment.

[0234] <Other Embodiments> In the above-described embodiment, the SCR system 100 including the first and second concentration sensors 131 and 132 has been illustrated. However, the present disclosure is not limited to such a configuration. It is not essential for the SCR system 100 to include both the first and second concentration sensors 131 and 132.

[0235] If the SCR system 100 includes only the first concentration sensor 131, in step S401 of FIG. 5D, the detected value of the first concentration sensor 131 may be acquired instead of the second concentration sensor 132, and in step S106 of FIG. 5A, the inlet concentration may be referred to instead of the outlet concentration. Even in such a configuration, as in the above-described embodiment, the introduction of unburned NH3 into the catalyst unit 115 can be started without delay.

[0236] Similarly, if the SCR system 100 includes only the second concentration sensor 132, in step S102 of FIG. 5A, the detected value of the second concentration sensor 132 may be acquired instead of the first concentration sensor 131, and in step S103 of FIG. 5A, the outlet concentration may be referred to instead of the inlet concentration. Even in such a configuration, the minimum number of reaction cells capable of suppressing the leakage of unburned NH3 can be set without excessively setting the number of reaction cells. By doing so, the deterioration of the catalyst 116 can be suppressed without hindering the reduction of the emission amount of unburned NH3.

[0237] Moreover, in the first place, when performing the processing based on the ammonia concentration as illustrated in FIGS. 6 and 7, it is not essential to use the detection signals of the first and second concentration sensors 131 and 132. For example, the concentration of unburned NH3 may be estimated from various data, and the bypass valve 117d may be appropriately opened / closed or the opening degree may be adjusted based on the estimation result.

Description of Reference Numerals

[0238] S engine system 1 Diesel engine 2 Engine body 21 Cylinder 3 Intake and exhaust system 32 exhaust pipes 32a First exhaust pipe 32b Second exhaust pipe 100 Marine SCR system 110 SCR device 111 Exhaust flow pipe 111d Bypass pipe 115 Catalyst unit 115a Reaction cell 116 Catalyst 116a First catalyst 116b Second catalyst 116c Third catalyst 117 Cell number variable means 117d Bypass valve 120 Controller 131 First concentration sensor 132 Second concentration sensor M1 First control map T1 First reference value (reference value)

Claims

1. A marine SCR system connected to a diesel engine capable of burning ammonia and configured to remove unburned ammonia discharged from the diesel engine, comprising a catalyst unit having a plurality of reaction cells that form an exhaust gas flow path and promote the reaction of unburned ammonia, and allowing the unburned ammonia discharged from the diesel engine to flow in together with the exhaust gas containing the unburned ammonia, cell number variable means for changing the number of reaction cells through which the unburned ammonia flowing into the catalyst unit passes among the plurality of reaction cells, and a controller for controlling the cell number variable means, wherein the controller determines the concentration or amount of unburned ammonia contained in the exhaust gas, and determines the number of the reaction cells so as to increase or decrease according to the concentration or amount of the unburned ammonia A marine SCR system characterized by the above.

2. In the marine SCR system according to Claim 1, the controller increases the number of the reaction cells as the concentration or amount of the unburned ammonia increases A marine SCR system characterized by the above.

3. In the marine SCR system according to Claim 2, the catalyst unit has a plurality of catalysts connected in parallel or in series with respect to the exhaust gas flow, the cell number variable means is configured to change the number of catalysts through which the unburned ammonia passes among the plurality of catalysts, and the controller increases the number of the catalysts as the concentration or amount of the unburned ammonia increases A marine SCR system characterized by the above.

4. In the marine SCR system according to Claim 3, the controller controls the cell number variable means based on the number of the catalysts set to correspond to the concentration or amount of the unburned ammonia and the combination of catalysts set to correspond to the number of the catalysts, and the controller updates the correspondence relationship between the number of the catalysts and the combination of the catalysts on the occasion of a predetermined condition A marine SCR system characterized by the above.

5. In the marine SCR system according to Claim 1, it is provided with a first concentration sensor disposed in a first exhaust pipe connecting the diesel engine to the catalyst unit and detecting the ammonia concentration in the first exhaust pipe, ​ When the ammonia concentration in the first exhaust pipe exceeds a predetermined reference value based on the detection signal of the first concentration sensor, the controller starts the inflow of unburned ammonia into the catalyst unit. A marine SCR system characterized by the above.

6. In the marine SCR system according to claim 5, A second concentration sensor is provided, which is arranged in a second exhaust pipe connecting the catalyst unit to the outside of the ship and detects the ammonia concentration in the second exhaust pipe. Based on the detection signal of the second concentration sensor, the controller determines the number of reaction cells through which unburned ammonia passes in the catalyst unit. A marine SCR system characterized by the above.

7. In the marine SCR system according to claim 6, When the ammonia concentration in the second exhaust pipe falls below the reference value, the controller ends the inflow of unburned ammonia into the catalyst unit. A marine SCR system characterized by the above.

8. In the marine SCR system according to any one of claims 1 to 4, A bypass pipe connecting the diesel engine to the outside of the ship so as to bypass the catalyst unit, A bypass valve that is electrically connected to the controller and opens and closes the bypass pipe. The controller, When the ammonia concentration in the first exhaust pipe connecting the diesel engine to the catalyst unit is equal to or lower than a predetermined reference value, the controller opens the bypass valve to bypass the catalyst unit through the bypass pipe for unburned ammonia. When the ammonia concentration in the first exhaust pipe exceeds the reference value, the controller closes the bypass valve to allow unburned ammonia to flow into the catalyst unit. A marine SCR system characterized by the above.

9. In the marine SCR system according to any one of claims 5 to 7, A bypass pipe connecting the diesel engine to the outside of the ship so as to bypass the catalyst unit, A bypass valve that is electrically connected to the controller and opens and closes the bypass pipe. The controller, When the ammonia concentration in the first exhaust pipe is equal to or lower than the reference value, the controller opens the bypass valve to bypass the catalyst unit through the bypass pipe for unburned ammonia. When the ammonia concentration in the first exhaust pipe exceeds the reference value, the bypass valve is closed to allow unburned ammonia to flow into the catalyst unit. A marine SCR system characterized by the above.

10. The marine SCR system according to claim 1, and at least a diesel engine connected to the marine SCR system and capable of burning the ammonia. An engine system characterized by the above.

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