TWI656908B - Ship exhaust gas denitration system - Google Patents

Abstract

An exhaust gas denitration system for a ship includes a direct exhaust gas exhaust pipe connected to an exhaust port of an exhaust gas collection tank via a first valve; an exhaust gas denitration pipe connected to an exhaust port of an exhaust gas collection tank via a second valve Connection; a denitration reactor connected to the exhaust gas denitration pipeline, including a urea evaporation chamber, a mixer and a reaction chamber, the urea evaporation chamber is provided with a urea solution spray gun, and the mixer is connected to the urea evaporation chamber and the reaction chamber; The valve is opened, the second valve is closed, and the exhaust gas is discharged through the exhaust gas straight line; the first valve is closed, the second valve is opened, and the exhaust gas enters the urea evaporation chamber of the denitration reactor through the exhaust gas denitration pipeline, and is mixed with urea and passed through The mixer enters the reaction chamber for denitration and is discharged. The urea evaporation chamber, the mixer and the reaction chamber in the ship exhaust gas denitration system of the present invention are combined in a denitration reactor, and the structure is more compact.

Description

   Ship exhaust gas denitration system   

The invention relates to the field of atmospheric environmental protection, in particular to a ship exhaust gas denitration system.

This patent application claims priority from Chinese Patent Application No. 201621344640.5 and Chinese Patent Application No. 201611124811.8, filed on the same day on December 8, 2016. The full text of these patent applications is incorporated herein by reference.

In order to control NOx emissions from marine exhaust gas collection tanks, the International Maritime Organization has adopted the amendment to MARPOL 73/78 Annex VI "Rules for Preventing Air Pollution from Ships", which stipulates that effective January 1, 2016, The Emission Control Area (ECA) implements Tier III emission standards. This standard determines a lower NOx emission value, so the ship's exhaust gas needs to be denitrated. Selective Catalytic Reduction (SCR) is the most widely used technology for denitrification of exhaust gas from the exhaust gas collection tanks of ships.

When the selective catalytic reduction technology is used to denitrate the exhaust gas, the reducing agent is first sprayed into the exhaust gas at a temperature of 170 ~ 550 ° C. The reducing agent can be pure ammonia gas, ammonia water or urea solution. Because urea is convenient for storage and transportation, Generally, as the first choice of reducing agent, urea is atomized by spray gun, pyrolyzed or hydrolyzed to ammonia gas. Subsequently, the mixture of ammonia and exhaust gas is catalyzed by the catalyst together to convert the nitrogen oxides into nitrogen and water vapor and then exhaust, thereby reducing the content of NOx in the exhaust gas.

At present, the denitration equipment that realizes the above-mentioned selective catalytic reduction technology mainly includes urea supply system, catalytic reaction system and compressed air system. The urea supply system mainly includes urea tank, urea metering pump and urea solution spray gun. And evaporative mixer, compressed air system mainly includes soot blowing, ventilation and equipment purging. However, the conventional denitration equipment has a complicated structure and requires a large space, which affects the movement space of ship personnel and the arrangement of other equipment.

An object of the present invention is to provide a ship exhaust gas denitration system with a compact structure.

The ship exhaust gas denitration system provided by the present invention comprises: a direct exhaust gas exhaust pipe, which is connected to an exhaust port of an exhaust gas collection tank through a first valve; and an exhaust gas denitration pipeline, which is used for denitrification of exhaust gas The pipeline is connected to the exhaust port of the exhaust gas collection box through a second valve; a denitration reactor, which is connected to the exhaust gas denitration pipeline, including a urea evaporation chamber, a mixer, and a reaction chamber. The urea evaporation chamber is provided with a urea solution spray gun, and the mixer connects the urea evaporation chamber and the reaction chamber; wherein the first valve is opened, the second valve is closed, and the exhaust gas is discharged through the exhaust gas direct discharge pipe; the first valve is closed 2. The second valve is opened, the exhaust gas enters the urea evaporation chamber of the denitration reactor through the exhaust gas denitration pipeline, is mixed with urea, enters the reactor through the mixer for denitration, and is discharged.

Further, the denitration reactor includes first and second ends opposite to each other, an air inlet and an exhaust port of the denitration reactor are located at the first end, the urea evaporation chamber is connected to the air inlet, and The reaction chamber is connected to the exhaust port, the urea evaporation chamber extends from the first end to the second end of the denitration reactor and is arranged along the side wall of the second end, and the outlet of the urea evaporation chamber is located away from the second end On one side of the side wall, the mixer connects the outlet of the urea evaporation chamber with the inlet of the reaction chamber.

Further, the urea evaporation chamber is provided with a deflector at a side wall near the second end.

Further, the ship exhaust gas denitration system further includes an exhaust gas oxidation branch, the exhaust gas oxidation branch is connected to the exhaust gas denitration pipeline and is located between the denitration reactor and the second valve, and the exhaust gas oxidation branch is in turn Equipped with a third valve and a gas oxidizer.

Further, the urea solution spray gun is connected to a urea supply device. The urea supply device includes a urea pipeline, a urea tank, an air pipeline, and an air compressor. The urea tank is connected to the urea solution spray gun through the urea pipeline. A metering pump and a fourth valve are sequentially arranged on the urea pipeline, and the air compressor is connected to the outlet end of the urea pipeline through a fifth valve.

Further, the ship exhaust gas denitration system further includes a urea cleaning pipeline, and the urea cleaning pipeline includes a hot water pipeline and a cold water pipeline, and the hot water pipeline is disposed on the outer wall of the waste heat boiler. A valve is connected to the urea pipeline, the cold water pipeline is connected to the urea pipeline through a seventh valve, and the connection points of the sixth valve, the seventh valve, and the urea pipeline are located between the metering pump and the urea tank .

Further, the exhaust end of the exhaust gas denitration pipe is connected to the exhaust end of the exhaust gas straight pipe through an eighth valve, and the exhaust end of the exhaust gas straight pipe is connected to the exhaust gas denitration pipe. The gas ends are connected to the waste heat boiler.

Further, a turbocharger is provided between the exhaust end of the exhaust gas straight exhaust pipe and the exhaust end of the exhaust gas denitration pipeline and the air inlet of the waste heat boiler.

Further, the exhaust port of the waste heat boiler is provided with a muffler.

Further, each valve is an automatic control valve.

In the embodiment of the present invention, the urea evaporation chamber, mixer and reaction chamber of a ship exhaust gas denitration system are combined in a denitration reactor, and the urea evaporation chamber, mixer, and reaction chamber are arranged in series along the exhaust gas denitration pipeline. In comparison, the length of the pipeline is shortened, and the arrangement of the connecting pieces is reduced, so that the structure of the ship's exhaust gas denitration system is more compact.

10‧‧‧Exhaust gas exhaust pipe

11‧‧‧The first valve

20‧‧‧Exhaust gas denitration pipeline

21‧‧‧Second valve

22‧‧‧ Eighth Valve

30‧‧‧Denitration reactor

31‧‧‧Urea evaporation chamber

32‧‧‧ mixer

33‧‧‧Reaction Room

34‧‧‧ deflector

35‧‧‧ urea solution spray gun

36‧‧‧ the first end

37‧‧‧ second end

40‧‧‧Exhaust Oxidation Branch

41‧‧‧Third valve

42‧‧‧Gas Oxidizer

50‧‧‧Exhaust gas collecting tank

60‧‧‧Urea supply device

61‧‧‧Urea tank

62‧‧‧Urea line

63‧‧‧Fourth valve

64‧‧‧ metering pump

66‧‧‧air compressor

67‧‧‧air line

68‧‧‧Fifth valve

70‧‧‧ urea cleaning pipeline

71‧‧‧ hot water pipeline

72‧‧‧ cold water pipeline

73‧‧‧ sixth valve

74‧‧‧Seventh valve

80‧‧‧ waste heat boiler

81‧‧‧ Silencer

90‧‧‧ turbocharger

FIG. 1 is a schematic structural diagram of a ship exhaust gas denitration system according to an embodiment of the present invention.

In order to make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

FIG. 1 is a schematic structural diagram of a ship exhaust gas denitration system according to an embodiment of the present invention. As shown in FIG. 1, the ship exhaust gas denitration system according to the embodiment of the present invention includes an exhaust gas collection tank 50, an exhaust gas straight line 10, an exhaust gas denitration line 20, a denitration reactor 30, a turbocharger 90 and A waste heat boiler 80, in which a denitration reactor 30 is connected to the exhaust gas denitration pipeline 20, and the exhaust gas straight discharge pipeline 10 and the exhaust gas denitration pipeline 20 are connected between the exhaust gas collection tank 50 and the waste heat boiler 80. The exhaust pipe 10 is connected to the exhaust port of the exhaust gas collecting tank 50 through a first valve 11, and the exhaust gas denitration pipe 20 is connected to the exhaust port of the exhaust gas collecting tank 50 through a second valve 21. The exhaust end of the circuit 20 is connected to the exhaust end of the exhaust straight line 10 through an eighth valve 22, and the turbocharger 90 is connected to the exhaust end of the exhaust straight line 10 and the exhaust denitration line 20 and A muffler 81 is provided between the waste heat boiler 80 and an exhaust port of the waste heat boiler 80.

According to the emission requirements of the area where the ship is located, the exhaust gas in the exhaust gas collection tank 50 can be controlled to be exhausted through the exhaust gas straight line 10 or the exhaust gas denitration line 20. Specifically, in the non-ECA area, the first valve 11 is opened, the second valve 21 and the eighth valve 22 are closed, and the exhaust gas in the exhaust gas collection tank 50 is discharged into the waste heat boiler 80 through the exhaust gas straight line 10 and discharged. In the ECA zone, the first valve 11 is closed, the second valve 21 and the eighth valve 22 are opened, and the exhaust gas in the exhaust gas collection tank 50 enters the denitration reactor 30 through the exhaust gas denitration pipeline 10 for denitration and is discharged into the waste heat boiler 80 Drain again.

The denitration reactor 30 includes a urea evaporation chamber 31, a mixer 32, and a reaction chamber 33. The urea evaporation chamber 31 is provided with a urea solution spray gun 35 and a deflector 34. The mixer 32 connects the urea evaporation chamber 31 and the reaction chamber 33. Specifically, the denitration reactor 30 includes a first end 36 and a second end 37 located at both ends of the denitration reactor 30. The air inlet and exhaust port of the denitration reactor 30 are located at the first end 36, and urea is evaporated. The chamber 31 is connected to the inlet of the denitration reactor 30, the reaction chamber 33 is connected to the exhaust of the denitration reactor 30, and the urea evaporation chamber 31 extends from the first end 36 to the second end 37 of the denitration reactor 30 It extends along the side wall of the second end 37. The outlet of the urea evaporation chamber 31 is located on the side far from the side wall of the second end 37. The mixer 32 connects the outlet of the urea evaporation chamber 31 and the inlet of the reaction chamber 33. Thus, the urea evaporation chamber 31 is wound along the side wall of the denitration reactor 30 to the inlet of the mixer 32 to form a gas channel with a corner. A deflector 34 is disposed in the urea evaporation chamber 31 at a side wall near the second end 37, that is, in the urea evaporation chamber. At the corner of 31.

In this embodiment, the air inlet and the air outlet of the denitration reactor 30 are arranged at the same end of the denitration reactor 30, so that the urea evaporation chamber 31 can be set as a gas passage with a corner, and A deflector 34 is provided at the corner of the passage. In this way, after the exhaust gas enters the urea evaporation chamber 31, the reaction chamber 33 can be preheated and fully mixed with the ammonia gas generated by the decomposition of urea. The mixed gas enters the mixer 32 again. Rotary mixing to improve mixing uniformity can effectively improve denitration efficiency. Meanwhile, in the embodiment of the present invention, the urea evaporation chamber 31, the mixer 32, and the reaction chamber 33 are combined in the denitration reactor 30, and the urea evaporation chamber 31, the mixer 32, and the reaction chamber 33 are arranged in series along the exhaust gas denitration pipeline 20. Compared with this method, the length of the pipeline is shortened, and the arrangement of the connecting pieces is reduced, so that the structure of the ship exhaust gas denitration system is more compact.

Following the above, the urea solution spray gun 35 is connected to the urea supply device 60. The urea supply device 60 includes a urea line 62, a urea tank 61, an air line 67 and an air compressor 66, and the urea tank 61 is connected to the urea solution through the urea line 62 The spray gun 35 is connected, a metering pump 64 and a fourth valve 63 are sequentially arranged on the urea pipeline 62, and the air compressor 66 is connected to the outlet end of the urea pipeline 62 through a fifth valve 68.

Further, the ship exhaust gas denitration system of this embodiment further includes an exhaust gas oxidation branch 40, which is connected to the exhaust gas denitration pipeline 20 and is located between the denitration reactor 30 and the second valve 21, and the exhaust gas is oxidized The branch 40 is provided with a third valve 41 and a gas oxidizer 42 in this order.

Because the content of NO in diesel exhaust gas accounts for the majority (more than 90%) of NOx, the standard reaction usually occurs in the reaction chamber 33: 4NH3 + 4NO + O2 → 4N2 + 6H2O. However, the presence of NO2 causes a rapid reaction in the reaction chamber 33: 2NH3 + NO + NO2 → 2N2 + 3H2O, and the catalytic reaction rate is faster than the standard reaction. In the embodiment of the present invention, the instability of NO can be oxidized to NO2 under the condition of oxygen, and a certain proportion of exhaust gas is adjusted from the exhaust gas denitration pipeline 20 (adjusting the opening degree of the third valve 41) into the gas oxidizer. Internal oxidation of 42. By continuously injecting air into the gas oxidizer 42, NO is oxidized to NO2 by O2 in the air, and the oxidized gas is reinjected into the exhaust gas denitration pipeline 20, and enters the denitration together with the unoxidized exhaust gas. The reactor 30, thereby increasing the proportion of NO2 in NOx, significantly improves the catalytic conversion efficiency of NOx at low temperatures, and can effectively improve the denitration efficiency, thereby reducing ammonia escape.

Further, the ship exhaust gas denitration system of this embodiment further includes a urea cleaning pipeline 70. The urea cleaning pipeline 70 includes a hot water pipeline 71 and a cold water pipeline 72. The hot water pipeline 71 is disposed on the outer wall of the waste heat boiler 80. The water line 71 is connected to the urea line 62 through a sixth valve 73, the cold water line 72 is connected to the urea line 62 through a seventh valve 74, and the connection points of the sixth valve 73, the seventh valve 74 and the urea line 62 Located between the metering pump 64 and the urea tank 61, the temperature of the flushing water can be adjusted by adjusting the opening degrees of the sixth valve 73 and the seventh valve 74.

When the ship enters the non-ECA area, the first valve 11 is opened, the second valve 21 and the eighth valve 22 are closed, and no urea solution supply is required. At this time, the urea pipeline 62 needs to be flushed to prevent the urea crystal from blocking the pipeline. Specifically, the flushing water is provided by the water tank in the cabin, and the flushing water in the hot water pipeline 71 exchanges heat with the waste heat boiler 80. After the water temperature increases, it is mixed with the flushing water in the cold water pipeline 72 to appropriately increase the temperature of the flushing water. It can effectively improve the flushing effect of the flushing water on the urea solution 62 and the urea solution spray gun 35 in the urea solution 62 or the urea crystal. The waste heat boiler 80 is used to heat the flushing water without the need for a separate heating device. The structure is compact and the flushing effect is effectively improved.

Preferably, each of the valves described above is an automatic control valve.

In summary, the ship exhaust gas denitration system of the present invention includes at least the following advantages: (1) combining the urea evaporation chamber, the mixer and the reaction chamber in the denitration reactor, along with the urea evaporation chamber, the mixer, and the reaction chamber; Compared with the way in which exhaust gas denitration pipelines are arranged in series, the length of the pipeline is shortened, and the arrangement of connectors is reduced, which makes the structure of the ship's exhaust gas denitration system more compact; (2) The port and the exhaust port are arranged at the same end of the denitration reactor, so that the urea evaporation chamber can be set as a gas channel with a corner, and a deflector is set at the corner of the gas channel. In this way, the exhaust gas can be aligned with the urea evaporation chamber. The reaction chamber is preheated and fully mixed with the ammonia gas generated by the decomposition of urea. The mixed gas enters the mixer again to rotate and mix to improve the mixing uniformity, which can effectively improve the denitration efficiency; (3) by setting a gas oxidizer By introducing a certain proportion of exhaust gas in the exhaust gas denitration pipeline into the gas oxidizer, the proportion of NO2 in NOx is increased, and the catalytic conversion efficiency of NOx at low temperature is significantly improved, which can effectively improve the denitrification Nitrogen efficiency, thereby reducing ammonia escape; (4) The waste water boiler is used to heat the flushing water of the urea pipeline, without the need for additional heating devices, the structure is compact, and the flushing effect is effectively improved.

Finally, the present invention uses specific examples to illustrate the effects achieved:

Embodiment one:

Exhaust gas denitration treatment for the diesel engine of type A: the exhaust gas is discharged from the diesel engine to the exhaust gas collection tank, and 1/4 of the exhaust gas from the exhaust gas denitration pipeline is oxidized and discharged into the denitration reactor. At this time, the urea solution Under the action of the metering pump, it enters into the urea evaporation chamber and is decomposed into ammonia gas. The mixed gas is laterally mixed into the mixer under the action of the deflector for rotary mixing. The mixed gas enters the reaction chamber to undergo a catalytic reduction reaction. The reacted gas enters the turbocharger, then enters the waste heat boiler and muffler, and is finally discharged into the atmosphere.

After the denitration process is completed, the flushing water enters the hot water pipeline connected to the waste heat boiler, the water is heated, and the flow of hot water into the cold water pipeline is adjusted by adjusting the sixth valve. After the hot water and cold water are mixed, the whole The water temperature is increased, and the flushing water after the temperature rises enters the urea pipeline, and the flushed water is discharged into the urea evaporation chamber through the urea solution spray gun. The test denitration efficiency was improved by 5% compared to the case without using a gas oxidizer.

Embodiment two:

Exhaust gas denitration treatment for the diesel engine of type A: the exhaust gas is discharged from the diesel engine to the exhaust gas collection tank, and 1/2 of the exhaust gas from the exhaust gas denitration pipeline is oxidized and discharged into the denitration reactor. At this time, the urea solution Under the action of the metering pump, it enters into the urea evaporation chamber and is decomposed into ammonia gas. The mixed gas is laterally mixed into the mixer under the action of the deflector for rotary mixing. The mixed gas enters the reaction chamber to undergo a catalytic reduction reaction. The reacted gas enters the turbocharger, then enters the waste heat boiler and muffler, and is finally discharged into the atmosphere.

After the denitration process is completed, the flushing water enters the hot water pipeline connected to the waste heat boiler, the water is heated, and the flow of hot water into the cold water pipeline is adjusted by adjusting the sixth valve. After the hot water and cold water are mixed, the whole The water temperature is increased. After the temperature is increased, the water enters the urea pipeline, and the flushed water is discharged into the urea evaporation chamber through the urea solution spray gun. The test denitration efficiency is increased by 10% compared to the case without using a gas oxidizer.

Embodiment three:

Exhaust gas denitration treatment for diesel engine of type A: The exhaust gas is discharged from the diesel engine to the exhaust gas collection tank, and 1/8 of the exhaust gas from the exhaust gas denitration pipeline is oxidized and discharged into the denitration reactor. At this time, the urea solution Under the action of the metering pump, it enters into the urea evaporation chamber and is decomposed into ammonia gas. The mixed gas is laterally mixed into the mixer under the action of the deflector for rotary mixing. The mixed gas enters the reaction chamber to undergo a catalytic reduction reaction. The reacted gas enters the turbocharger, then enters the waste heat boiler and muffler, and is finally discharged into the atmosphere.

After the denitration process is completed, the flushing water enters the hot water pipeline connected to the waste heat boiler, the water is heated, and the flow of hot water into the cold water pipeline is adjusted by adjusting the sixth valve. After the hot water and cold water are mixed, the whole The water temperature is increased. After the temperature is increased, the water enters the urea pipeline, and the flushed water is discharged into the urea evaporation chamber through the urea solution spray gun. The test denitration efficiency was improved by 2% compared to the case without using a gas oxidizer.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall be included in the protection of the present invention. Within range.

    Industrial applicability    

The ship exhaust gas denitration system of the present invention includes at least the following advantages: (1) Combine the urea evaporation chamber, mixer, and reaction chamber in a denitration reactor, and the urea evaporation chamber, mixer, and reaction chamber along the exhaust gas denitration pipeline Compared with the tandem installation method, the length of the pipeline is shortened, and the arrangement of the connecting pieces is reduced, which makes the structure of the ship's exhaust gas denitration system more compact; (2) by connecting the inlet and exhaust ports of the denitration reactor It is set at the same end of the denitration reactor, so that the urea evaporation chamber can be set as a gas channel with a corner, and a baffle is set at the corner of the gas channel. In this way, after the exhaust gas enters the urea evaporation chamber, the reaction chamber can be preheated It is fully mixed with the ammonia gas generated by the decomposition of urea, and the mixed gas is re-entered into the mixer to be mixed by rotation to improve the uniformity of the mixture, which can effectively improve the denitration efficiency; (3) The exhaust gas is denitrated by setting a gas oxidizer A certain proportion of exhaust gas in the pipeline is introduced into the gas oxidizer for oxidation, which increases the proportion of NO2 in NOx, which significantly improves the catalytic conversion efficiency of NOx at low temperature, which can effectively improve the denitration efficiency. And reduce ammonia escape; (4) Utilize waste heat boiler to heat the flushing water of the urea pipeline, no additional heating device is needed, the structure is compact, and the flushing effect is effectively improved.

Claims (9)

An exhaust gas denitration system for a ship includes: an exhaust gas straight exhaust pipe (10), the exhaust gas straight exhaust pipe (10) is connected to an exhaust port of an exhaust gas collection tank (50) through a first valve (11); A denitration pipeline (20), the exhaust gas denitration pipeline (20) is connected to an exhaust port of an exhaust gas collection tank (50) through a second valve (21); a denitration reactor (30), the denitration The reactor (30) is connected to the exhaust gas denitration pipeline (20), and includes a urea evaporation chamber (31), a mixer (32) and a reaction chamber (33). The urea evaporation chamber (31) is provided with a urea solution spray gun (35), the mixer (32) connects the urea evaporation chamber (31) and the reaction chamber (33); wherein the exhaust end of the exhaust gas denitration pipeline (20) is connected with an eighth valve (22) and The exhaust end of the exhaust straight line (10) is connected, and the exhaust end of the exhaust straight line (10) and the exhaust end of the exhaust denitration line (20) are both connected to a waste heat boiler (80) Connection; the first valve (11) is opened, the second valve (21) is closed, and the exhaust gas is discharged through the exhaust gas straight line (10); the first valve (11) is closed, the second valve (21) is opened, and the exhaust gas After entering the urea evaporation chamber (31) of the denitration reactor (30) through the exhaust gas denitration pipeline (20) Discharged and mixed with urea denitration through the mixer (32) enters the reaction chamber (33). The ship exhaust gas denitration system according to item 1 of the scope of patent application, wherein the denitration reactor (30) includes a first end (36) and a second end (37) opposite to each other, and the denitration reactor (30) The air inlet and the air outlet are located at the first end (36), the urea evaporation chamber (31) is connected to the air inlet, the reaction chamber (33) is connected to the exhaust port, and the urea evaporation chamber ( 31) extending from the first end (36) to the second end (37) of the denitration reactor (30) and arranged along the side wall of the second end (37), and the outlet of the urea evaporation chamber (31) is located away from One side of the side wall of the second end (37), the mixer (32) connects the outlet of the urea evaporation chamber (31) and the inlet of the reaction chamber (33). The exhaust gas denitration system for a ship as described in item 2 of the patent application scope, wherein the urea evaporation chamber (31) is provided with a deflector (34) near a side wall of the second end (37). The exhaust gas denitration system for a ship as described in item 1 of the patent application scope, wherein the exhaust gas denitration system for a ship further includes an exhaust gas oxidation branch (40), the exhaust gas oxidation branch (40), and the exhaust gas denitration pipeline ( 20) It is connected and located between the denitration reactor (30) and the second valve (21). The exhaust gas oxidation branch (40) is provided with a third valve (41) and a gas oxidizer (42) in this order. The exhaust gas denitration system for a ship as described in item 1 of the patent scope, wherein the urea solution spray gun (35) is connected to a urea supply device (60), and the urea supply device (60) includes a urea pipeline (62), urea Tank (61), air line (67) and air compressor (66), the urea tank (61) is connected to the urea solution spray gun (35) through the urea line (62), and the urea line (62 ) Is provided with a metering pump (64) and a fourth valve (63) in this order. The air compressor (66) is connected to the outlet end of the urea pipeline (62) through a fifth valve (68). The ship exhaust gas denitration system according to item 5 of the scope of patent application, wherein the ship exhaust gas denitration system further includes a urea cleaning pipeline (70), and the urea cleaning pipeline (70) includes a hot water pipeline (71) and Cold water pipe (72), the hot water pipe (71) is arranged on the outer wall of the waste heat boiler (80), the hot water pipe (71) is connected to the urea pipe (62) through a sixth valve (73) The cold water pipeline (72) is connected to the urea pipeline (62) through a seventh valve (74), and the sixth valve (73) and the seventh valve (74) are connected to the urea pipeline (62) The point is between the metering pump (64) and the urea tank (61). The exhaust gas denitration system for a ship as described in item 1 of the scope of patent application, wherein the exhaust end of the exhaust gas straight exhaust pipe (10) and the exhaust end of the exhaust gas denitration pipeline (20) and the waste heat boiler ( A turbocharger (90) is provided between the air inlets of 80). The exhaust gas denitration system for a ship as described in item 1 of the scope of the patent application, wherein the exhaust port of the waste heat boiler (80) is provided with a muffler (81). The ship exhaust gas denitration system according to any one of claims 1-8, wherein each valve is an automatic control valve.