A low-carbon emission carbon dioxide transport ship and its control method

Abstract

This invention relates to the field of ship energy conservation and emission reduction technology, and particularly to a low-carbon emission carbon dioxide transport vessel and its control method. A low-carbon emission carbon dioxide transport vessel includes an LNG supply unit, a water glycol circulation unit, a carbon dioxide capture unit, a carbon dioxide storage unit, and a dual-fuel main engine. The LNG supply unit includes an LNG storage tank, a submersible pump, an LNG heat exchanger, a buffer tank, and a main gas supply valve. The carbon dioxide capture unit includes a spray assembly, an absorption and desorption assembly, and a compression liquefaction assembly. The carbon dioxide storage unit includes a carbon dioxide storage tank and a BOG regulating valve. The water glycol circulation unit serves as a cold energy transfer medium, enabling the coupling of LNG cold energy with the carbon capture system. The advantages of this low-carbon emission carbon dioxide transport vessel and its control method are that it reduces the space occupied on the vessel, lowers the vessel's weight, reduces processing costs, and lowers processing energy consumption.

Description

Technical Field

[0001] This invention relates to the field of ship energy conservation and emission reduction technology, and in particular to a low-carbon emission carbon dioxide transport ship and its control method. Background Technology

[0002] In the shipping industry, as awareness of marine environmental protection gradually increases, the requirements for ship emissions are becoming increasingly stringent. Technologies such as ship carbon capture and storage are constantly developing and maturing, and carbon dioxide carriers, as the main means of transporting carbon dioxide, play an important role in areas such as carbon dioxide utilization and storage.

[0003] However, carbon dioxide carriers still pose a carbon dioxide emission problem during transportation. To address this issue, various carbon dioxide treatment technologies have been developed. For example, Chinese invention patent CN114852305A discloses a ship carbon emission reduction system and a gas carrier. This carbon emission system utilizes a carbon-to-fuel reactor to react all or part of the carbon dioxide in engine exhaust with hydrogen to produce fuel oil. The reaction of carbon dioxide and hydrogen to fuel oil reduces carbon emissions, and the generated fuel oil can be reused, reducing the amount of fuel that needs to be stored on board. This patent's technical solution, to reduce atmospheric carbon dioxide pollution, employs a carbon dioxide-hydrogen reaction to produce fuel oil. This solution requires reaction-related equipment, hydrogen, catalysts, etc., significantly increasing the cost of carbon dioxide treatment. Besides this, other methods exist to reduce carbon dioxide emissions, but regardless of the method, they all involve adding various equipment to treat carbon dioxide, occupying ship space, increasing ship weight, raising treatment costs, and increasing energy consumption. Summary of the Invention

[0004] In view of this, the present invention aims to provide a low-carbon emission carbon dioxide transport vessel and control method, which adopts clean energy LNG as ship fuel, makes full use of the low temperature cold energy of LNG fuel for the absorption and storage of carbon dioxide in exhaust gas, and can cool the BOG gas generated during carbon dioxide transport. This technical solution solves the problems of adding various equipment to handle carbon dioxide, occupying ship space, increasing ship weight, increasing handling costs, and increasing handling energy consumption.

[0005] To address the above problems, the present invention provides a low-carbon emission carbon dioxide transport vessel, comprising:

[0006] LNG supply unit, water glycol circulation unit, carbon dioxide capture unit, carbon dioxide storage unit, and dual-fuel main engine;

[0007] The LNG supply unit includes an LNG storage tank, a submersible pump, an LNG heat exchanger, a buffer tank, and a main gas supply valve.

[0008] The carbon dioxide capture unit includes a spray assembly, an absorption and desorption assembly, and a compression and liquefaction assembly;

[0009] The carbon dioxide storage unit includes a carbon dioxide storage tank and a BOG regulating valve.

[0010] The water-glycol circulation unit serves as a cold energy transfer medium, enabling the coupling of LNG cold energy with the carbon capture system.

[0011] Furthermore, in the LNG supply unit, the liquefied natural gas in the LNG storage tank is pumped out by a submersible pump, vaporized by exchanging heat with water glycol in an LNG heat exchanger, enters a buffer tank for pressure control, and then enters the dual-fuel main engine for combustion through the main gas supply valve.

[0012] Furthermore, the spray assembly consists of a seawater pump, a seawater inlet, a seawater outlet, and a spray tower. The seawater pump delivers seawater to the spray tower to cool the exhaust gas from the main unit. After cooling, the exhaust gas enters the absorption and desorption assembly.

[0013] Furthermore, the absorption and desorption assembly includes an absorption tower, a desorption tower, a rich liquid pump, a lean liquid pump, a lean liquid heat exchanger, a steam heat exchanger, a steam regulating valve, and a blower;

[0014] The lean liquor is cooled by exchanging heat with water and ethylene glycol in a lean liquor heat exchanger and then enters the absorption tower to absorb carbon dioxide from the tail gas to form a rich liquor. The rich liquor is then desorbed in the desorption tower to produce carbon dioxide.

[0015] Furthermore, the compression liquefaction assembly includes a carbon dioxide compressor, a liquefaction regulating valve A, a liquefaction regulating valve B, a liquefaction compressor, and a liquefaction heat exchanger;

[0016] After being desorbed, the carbon dioxide is compressed and then liquefied in the liquefaction heat exchanger by passing through liquefaction regulating valve A. In the other path, it enters the liquefaction compressor for further liquefaction through liquefaction regulating valve B.

[0017] Furthermore, in the carbon dioxide storage unit, the BOG gas generated by the carbon dioxide storage tank is sent to the inlet of the carbon dioxide compressor via the BOG regulating valve, and is recompressed and liquefied to achieve closed-loop processing.

[0018] Furthermore, the water glycol circulation unit includes a water glycol circulation pump, a water glycol expansion tank, a lean liquor heat exchange regulating valve, a liquefaction heat exchange regulating valve, a cylinder liner water system, a cylinder liner water heat exchanger, and a cylinder liner water regulating valve.

[0019] After being pumped out, the water-glycol is split into two streams, which enter the lean liquid heat exchanger and the liquefaction heat exchanger respectively. After heat exchange, they merge and flow through the LNG heat exchanger and the cylinder liner water heat exchanger, and then return to the circulation.

[0020] A low-carbon emission control method applicable to transport ships as described in any of the preceding claims.

[0021] Based on LNG cold energy distribution, the following four operating condition control strategies are included:

[0022] (1) Normal navigation and no need to handle BOG: LNG cold energy meets the requirements for lean liquid cooling and carbon dioxide liquefaction, and the remaining cold energy is consumed by the cylinder liner water regulating valve;

[0023] (2) During normal navigation and when BOG needs to be handled: prioritize lean liquid cooling, use the remaining cooling capacity for carbon dioxide liquefaction, and supplement the insufficient cooling capacity by the liquefaction compressor.

[0024] (3) Low-speed navigation: All the cold energy of LNG is used for lean liquid heat exchange, and carbon dioxide liquefaction is completed by the liquefaction compressor;

[0025] (4) Ship docking and shutdown: Carbon capture is stopped, and BOG treatment is entirely provided with cooling capacity by liquefied compressors.

[0026] Furthermore, during normal navigation when BOG does not require handling, the lean liquor temperature is controlled by adjusting the lean liquor heat exchange regulating valve, and the carbon dioxide temperature is controlled by adjusting the liquefaction heat exchange regulating valve. Excess cooling capacity is consumed by the cylinder liner water system.

[0027] Furthermore, during low-speed navigation and docking, liquefaction regulating valve A is closed, and only liquefaction regulating valve B and liquefaction compressor are turned on to complete the liquefaction of carbon dioxide and BOG.

[0028] Compared with existing technologies, the low-carbon emission carbon dioxide transport ship and control method described in this invention have the following advantages:

[0029] The advantages of this technical solution are that it uses clean energy LNG as ship fuel, making full use of the low-temperature cold energy of LNG fuel for the absorption and storage of carbon dioxide in exhaust gas, and can also cool the BOG gas generated during carbon dioxide transportation. This eliminates the need to add various equipment for carbon dioxide treatment, reduces the space occupied on the ship, reduces the weight of the ship, reduces treatment costs, and reduces energy consumption. Attached Figure Description

[0030] Figure 1 This is a block diagram of the control system structure of a low-carbon emission carbon dioxide transport ship according to an embodiment of this application.

[0031] Explanation of reference numerals in the attached figures:

[0032] 1-Submersible pump, 2-LNG storage tank, 3-LNG heat exchanger, 4-Buffer tank, 5-Main gas supply valve, 6-Main unit, 7-Water glycol pump, 8-Water glycol expansion tank, 9-Lean solution heat exchange regulating valve, 10-Liquefaction heat exchange regulating valve, 11-Seawater pump, 12-Seawater inlet, 13-Seawater outlet, 14-Spray tower, 15-Absorber tower, 16-Fan, 17-Rich solution pump, 18-Lean solution pump, 19-Lean solution 20-Desorption tower, 21-Steam inlet, 22-Steam outlet, 23-Steam regulating valve, 24-Carbon dioxide compressor, 25-Liquefaction regulating valve A, 26-Liquefaction regulating valve B, 27-Liquefaction compressor, 28-Liquefaction heat exchanger, 29-Carbon dioxide storage tank, 30-BOG regulating valve, 31-Cylinder liner water system, 32-Cylinder liner water heat exchanger, 33-Cylinder liner water regulating valve, 34-Steam heat exchanger. Detailed Implementation

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] In this invention, the terms "first," "second," "upper," and "lower," etc., are used for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," "upper," or "lower" may explicitly or implicitly include at least one of those features. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. Where the technical solutions of the embodiments can be combined, they are all within the scope of protection claimed by this invention.

[0035] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] like Figure 1As shown, a low-carbon emission carbon dioxide transport vessel includes: an LNG supply unit, a water glycol circulation unit, a carbon dioxide capture unit, a carbon dioxide storage unit, and a dual-fuel main engine 6. The LNG supply unit includes an LNG storage tank 2, a submersible pump 1, an LNG heat exchanger 3, a buffer tank 4, and a main gas supply valve 5. The carbon dioxide capture unit includes a spray assembly, an absorption / desorption assembly, and a compression / liquefaction assembly. The carbon dioxide storage unit includes a carbon dioxide storage tank 29 and a BOG regulating valve 30. The water glycol circulation unit serves as a cold energy transfer medium, coupling the LNG cold energy with the carbon capture system. Fuel is supplied to the main engine 6 through the LNG supply unit. The exhaust gas generated from natural gas combustion in the main engine 6 is sent to the carbon dioxide capture unit, cooled by the spray assembly, and then enters the absorption / desorption assembly, circulating within the carbon dioxide capture unit. The desorbed carbon dioxide is transferred to the carbon dioxide storage unit.

[0037] Furthermore, in the LNG supply unit, the liquefied natural gas in the LNG storage tank 2 is pumped out by the submersible pump 1, and after being vaporized by exchanging heat with water glycol in the LNG heat exchanger 3, it enters the buffer tank 4 for pressure control, and then enters the dual-fuel main engine 6 for combustion through the main gas supply valve 5.

[0038] Furthermore, the spray assembly consists of a seawater pump 11, a seawater inlet 12, a seawater outlet, and a spray tower 14. The seawater pump 11 sends seawater to the spray tower 14 to cool the exhaust gas from the main unit 6. After cooling, the exhaust gas enters the absorption and desorption assembly.

[0039] Furthermore, the absorption and desorption assembly includes an absorption tower 15, a desorption tower 20, a rich liquid pump 17, a lean liquid pump 18, a lean liquid heat exchanger 19, a steam heat exchanger 34, a steam regulating valve 23, and a blower 16.

[0040] After the lean liquor is cooled by exchanging heat with water and ethylene glycol in the lean liquor heat exchanger 19, it enters the absorption tower 15 to absorb carbon dioxide from the tail gas to form a rich liquor. The rich liquor is then desorbed in the desorption tower 20 to produce carbon dioxide.

[0041] Furthermore, the compression liquefaction assembly includes a carbon dioxide compressor 24, a liquefaction regulating valve A, a liquefaction regulating valve B, a liquefaction compressor 27, and a liquefaction heat exchanger 28;

[0042] After being compressed, the desorbed carbon dioxide is liquefied by exchanging heat with water and ethylene glycol in the liquefaction heat exchanger 28 through the liquefaction regulating valve A, and then enters the liquefaction compressor 27 through the liquefaction regulating valve B for further liquefaction.

[0043] Furthermore, in the carbon dioxide storage unit, the BOG gas generated by the carbon dioxide storage tank 29 is sent to the inlet of the carbon dioxide compressor 24 via the BOG regulating valve for recompression and liquefaction to achieve closed-loop processing.

[0044] Furthermore, the water glycol circulation unit includes a water glycol circulation pump, a water glycol expansion tank 8, a lean liquor heat exchange regulating valve 9, a liquefaction heat exchange regulating valve 10, a cylinder liner water system 31, a cylinder liner water heat exchanger 32, and a cylinder liner water regulating valve 33.

[0045] After being pumped out, the water-glycol is split into two streams, which enter the lean liquid heat exchanger 19 and the liquefaction heat exchanger 28 respectively. After heat exchange, they merge and flow through the LNG heat exchanger and the cylinder liner water heat exchanger 32, and then return to the circulation.

[0046] The transport ship with the above-described structure in this embodiment uses clean energy LNG as ship fuel, making full use of the low-temperature cold energy of LNG fuel for the absorption and storage of carbon dioxide in the exhaust gas, and can also cool the BOG gas generated during carbon dioxide transportation. This technical solution eliminates the need to add various equipment for carbon dioxide treatment, reduces the space occupied on the ship, reduces the weight of the ship, reduces treatment costs, and reduces treatment energy consumption.

[0047] Specifically, LNG storage tank 2 contains liquefied natural gas, which is pumped out by the submersible pump 1, heated and converted into a gaseous state by the LNG heat exchanger 3, and then enters the buffer tank 4 for pressure control before entering the dual-fuel main engine 6 for combustion through the main supply valve 5. The LNG heat exchanger 3 exchanges heat with the water glycol in the water glycol circulation unit, vaporizing the LNG and controlling its temperature within a certain range. During this process, the cold energy of the low-temperature LNG is transferred to the water glycol medium.

[0048] The carbon dioxide capture unit includes a spray unit, an absorption and desorption assembly, and a compression and liquefaction assembly. The spray unit consists of a seawater pump 11, seawater inlet / outlet 12 / 13, and a spray tower 14. The seawater pump 11 pumps seawater from the seawater inlet 12 to the top of the spray tower 14, where it enters along with the exhaust gas from the dual-fuel main engine 6. After the exhaust gas is cooled inside the spray tower 14, the seawater flows out from the seawater outlet 13, and the exhaust gas enters the absorption and desorption assembly.

[0049] The absorption and desorption assembly comprises an absorption tower 15, a desorption tower 20, a rich liquid pump 17, a lean liquid pump 18, a lean liquid heat exchanger 19, a steam heat exchanger 34, steam inlets / outlets 21 / 22, a steam regulating valve 23, and a blower 16. The absorption tower 15 and desorption tower 20 contain carbon dioxide absorbent. After being pumped out by the lean liquid pump 18, the absorbent is cooled by heat exchange with the water-glycol system in the lean liquid heat exchanger 19 before entering the top of the absorption tower 15 for spraying. After thorough contact and mixing with the exhaust gas, a rich liquid is formed. This rich liquid is pumped from the bottom of the absorption tower 15 to the top of the desorption tower 20 by the rich liquid pump 17. The rich liquid desorbs carbon dioxide in the desorption tower 20 and enters the compression-liquefaction assembly. The desorbed absorbent becomes lean liquid and is discharged from the bottom. Part of it enters the steam heat exchanger 34 to be heated to a certain temperature and then returned to the desorption tower 20 to provide heat energy for the desorption tower and promote the desorption of the rich liquid; the other part enters the lean liquid pump 18 for continued circulation. The exhaust gas is absorbed by the absorption tower 15 and then extracted from the top of the absorption tower 15 by the blower 16. The steam heat exchanger 34 is heated by steam from the steam inlet, and after the flow rate is regulated by the steam regulating valve 23, it is discharged from the steam outlet 22.

[0050] The aforementioned compression-liquefaction assembly comprises a carbon dioxide compressor 24, liquefaction regulating valves A25 and B26, a liquefaction compressor 27, and a liquefaction heat exchanger 28. The desorbed carbon dioxide is compressed to a certain pressure by the carbon dioxide compressor 24. One path enters the liquefaction heat exchanger 28 via the liquefaction regulating valve A25, where it exchanges heat with the water-glycol system for cooling and liquefaction. The other path enters the liquefaction compressor 27 via the carbon dioxide regulating valve B26 for further cooling and liquefaction. The two streams of liquefied carbon dioxide are then combined and transported to the carbon dioxide storage unit.

[0051] The carbon dioxide storage unit comprises a carbon dioxide storage tank 29 and a BOG regulating valve 30. The carbon dioxide storage tank 29 is used to store and transport low-temperature liquefied carbon dioxide at a certain pressure. During transportation, a certain amount of carbon dioxide BOG gas is generated, which is transmitted to the inlet of the carbon dioxide compressor via the BOG regulating valve 30 for further compression and liquefaction.

[0052] The water glycol circulation unit includes: a water glycol circulation pump 7, a lean liquid heat exchange regulating valve 9, a liquefaction heat exchange regulating valve 10, a cylinder liner water system 31, a cylinder liner water heat exchanger 32, a cylinder liner water regulating valve 34, and a water glycol expansion tank 8. The water glycol expansion tank 8 contains liquid water glycol, which, after being pumped out by the water glycol pump 7, flows through the lean liquid regulating valve 9 into the lean liquid heat exchanger 19, and through the liquefaction heat exchange regulating valve 10 into the liquefaction heat exchanger 28. The two streams of water glycol, after heat exchange, merge and flow through the LNG heat exchanger 3 and the cylinder liner water heat exchanger 32, before returning to the water glycol pump for circulation. The cylinder liner water system 31 provides cylinder liner water as the heat exchange medium, which enters the cylinder liner water heat exchanger 32 via the cylinder liner water regulating valve 34 for heat exchange.

[0053] A low-carbon emission control method applicable to transport ships as described in any of the preceding claims.

[0054] Based on LNG cold energy distribution, the following four operating condition control strategies are included:

[0055] (1) When the ship is sailing normally, and the carbon dioxide storage tank does not require BOG treatment. Under this condition, the LNG has sufficient cold energy, and the water glycol is cooled to a cryogenic medium. The lean liquid heat exchange regulating valve is adjusted to cool the lean liquid to a certain temperature. Under the premise of ensuring the lean liquid heat exchange temperature, the liquefaction regulating valve is adjusted to cool the carbon dioxide to a certain temperature. The remaining cold energy needs to be consumed by adjusting the cylinder liner water regulating valve. In this process, the LNG cold energy meets the cold energy requirements of the entire carbon capture process.

[0056] (2) When the ship is sailing normally, and the carbon dioxide storage tank needs to undergo BOG treatment. Under this condition, the cold energy of LNG can be fully utilized, and water glycol is cooled into a cryogenic medium. The lean liquid heat exchange regulating valve is adjusted to cool the lean liquid to a certain temperature, and the remaining cold energy is used for carbon dioxide liquefaction heat exchange. Under the premise of ensuring the lean liquid heat exchange temperature, the opening of the liquefaction regulating valve is increased as much as possible. The liquefaction regulating valve A is adjusted to reduce the carbon dioxide intake and ensure that the carbon dioxide in this circuit is cooled to a certain temperature. At this time, the liquefaction compressor and carbon dioxide regulating valve B need to be turned on to cool the remaining carbon dioxide to a certain temperature; the cylinder liner water regulating valve is closed, and there is no need for cylinder liner water to provide heat to the system.

[0057] (3) When the ship is sailing at low speed. Under this condition, the LNG has less cold energy, and the water glycol is cooled to a low temperature medium. The lean liquid heat exchange regulating valve is adjusted to 100% opening, and all the LNG cold energy is used for lean liquid heat exchange. The liquefaction regulating valve A is closed, and the liquefaction regulating valve B and the liquefaction compressor are turned on to carry out carbon dioxide liquefaction. If the carbon dioxide storage tank needs to be treated with BOG at this time, the liquefaction compressor will provide all the cold energy. The cylinder liner water regulating valve is closed, and there is no need for the cylinder liner water to provide heat to the system.

[0058] (4) When the ship is docked, the engine is not running. There is no LNG consumption under this condition, and there is no need for carbon dioxide capture. If the carbon dioxide storage tank needs to be treated with BOG at this time, the liquefaction regulating valve B and the liquefaction compressor are turned on, and the liquefaction compressor provides all the cooling capacity.

[0059] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A low-carbon emission carbon dioxide transport ship, characterized in that, include: LNG supply unit, water glycol circulation unit, carbon dioxide capture unit, carbon dioxide storage unit and dual-fuel main engine (6); The LNG supply unit includes an LNG storage tank (2), a submersible pump (1), an LNG heat exchanger (3), a buffer tank (4), and a main gas supply valve (5). The carbon dioxide capture unit includes a spray assembly, an absorption and desorption assembly, and a compression and liquefaction assembly; The carbon dioxide storage unit includes a carbon dioxide storage tank (29) and a BOG regulating valve (30). The water-glycol circulation unit serves as a cold energy transfer medium, enabling the coupling of LNG cold energy with the carbon capture system. The LNG supply unit provides fuel to the host (6). The exhaust gas generated by the combustion of natural gas in the host (6) is sent to the carbon dioxide capture unit, cooled by the spray assembly, and then enters the absorption and desorption assembly, where it circulates within the carbon dioxide capture unit. The desorbed carbon dioxide is then transferred to the carbon dioxide storage unit.

2. The transport ship according to claim 1, characterized in that, In the LNG supply unit, the liquefied natural gas in the LNG storage tank (2) is pumped out by the submersible pump (1), and after being vaporized by exchanging heat with water glycol in the LNG heat exchanger (3), it enters the buffer tank (4) for pressure control, and then enters the dual-fuel main engine (6) for combustion through the main gas supply valve (5).

3. The transport ship according to claim 1, characterized in that, The spray assembly consists of a seawater pump (11), a seawater inlet (12), a seawater outlet (13), and a spray tower (14). The seawater pump (11) sends seawater to the spray tower (14) to cool the exhaust gas of the main unit (6). After cooling, the exhaust gas enters the absorption and desorption assembly.

4. The transport ship according to claim 1, characterized in that, The absorption and desorption assembly includes an absorption tower (15), a desorption tower (20), a rich liquid pump (17), a lean liquid pump (18), a lean liquid heat exchanger (19), a steam heat exchanger (34), a steam regulating valve (23), and a blower (16). After the lean liquid is cooled by exchanging heat with water and ethylene glycol in the lean liquid heat exchanger (19), it enters the absorption tower (15) to absorb carbon dioxide in the tail gas to form a rich liquid. The rich liquid is desorbed in the desorption tower (20) to produce carbon dioxide.

5. The transport vessel according to claim 1, characterized in that, The compression liquefaction assembly includes a carbon dioxide compressor (24), a liquefaction regulating valve A, a liquefaction regulating valve B, a liquefaction compressor (27), and a liquefaction heat exchanger (28). After being compressed, the desorbed carbon dioxide is liquefied by exchanging heat with water and ethylene glycol in the liquefaction heat exchanger (28) through the liquefaction regulating valve A, and then liquefied by entering the liquefaction compressor (27) through the liquefaction regulating valve B.

6. The transport vessel according to claim 1, characterized in that, In the carbon dioxide storage unit, the BOG gas generated by the carbon dioxide storage tank (29) is sent to the inlet of the carbon dioxide compressor (24) via the BOG regulating valve, and is recompressed and liquefied to achieve closed-loop processing.

7. The transport vessel according to claim 1, characterized in that, The water glycol circulation unit includes a water glycol circulation pump, a water glycol expansion tank (8), a lean liquor heat exchange regulating valve (9), a liquefaction heat exchange regulating valve (10), a cylinder liner water system (31), a cylinder liner water heat exchanger (32), and a cylinder liner water regulating valve (33). After being pumped out, the water-glycol is split into two streams, which enter the lean liquid heat exchanger (19) and the liquefaction heat exchanger (28) respectively. After heat exchange, they merge and flow through the LNG heat exchanger and the cylinder liner water heat exchanger (32), and then return to the circulation.

8. A low-carbon emission control method applicable to the transport vessel according to any one of claims 1-7, characterized in that, Based on LNG cold energy distribution, the following four operating condition control strategies are included: (1) Normal navigation and no need to handle BOG: LNG cold energy meets the requirements of lean liquid cooling and carbon dioxide liquefaction, and the remaining cold energy is consumed by the cylinder liner water regulating valve (33); (2) Normal navigation and BOG handling: Priority is given to lean liquid cooling, the remaining cooling capacity is used for carbon dioxide liquefaction, and the insufficient cooling capacity is supplemented by liquefaction compressor (27); (3) Low-speed navigation: All the cold energy of LNG is used for lean liquid heat exchange, and carbon dioxide liquefaction is completed by the liquefaction compressor (27); (4) Ship docking and shutdown: Carbon capture is stopped, and BOG processing is entirely cooled by the liquefied compressor (27).

9. The control method according to claim 8, characterized in that, When there is no need to handle BOG during normal navigation, the lean liquid temperature is controlled by adjusting the lean liquid heat exchange regulating valve (9), and the carbon dioxide temperature is controlled by adjusting the liquefaction heat exchange regulating valve (10). Excess cooling capacity is consumed by the cylinder liner water system (31).

10. The control method according to claim 8, characterized in that, When sailing at low speed or docking, the liquefaction regulating valve A (25) is closed, and only the liquefaction regulating valve B (26) and the liquefaction compressor (27) are opened to complete the liquefaction of carbon dioxide and BOG.

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